A Performance Study of Uplink Scheduling Algorithms in Point to Multipoint WiMAX Networks

A Performance Study of Uplnk Schedulng Algorthms n Pont to Multpont WMAX Networks by Pratk Dhrona A thess submtted to the School of Computng n conformty wth the requrements for the degree of Master of Scence Queen s Unversty Kngston, Ontaro, Canada December, 2007 Copyrght Pratk Dhrona, 2007

Abstract Applcatons such as vdeo and audo streamng, onlne gamng, vdeo conferencng, Voce over IP (VoIP) and Fle Transfer Protocol (FTP) demand a wde range of QoS requrements such as bandwdth and delay. Exstng wreless technologes that can satsfy the requrements of heterogeneous traffc are very costly to deploy n rural areas and last mle access. Worldwde Interoperablty for Mcrowave Access (WMAX) provdes an affordable alternatve for wreless broadband access supportng a multplcty of applcatons. The IEEE 802.16 standard provdes specfcaton for the Medum Access Control (MAC) and Physcal (PHY) layers for WMAX. A crtcal part of the MAC layer specfcaton s schedulng, whch resolves contenton for bandwdth and determnes the transmsson order of users. It s mperatve for a schedulng algorthm to have a mult-dmensonal objectve of satsfyng QoS requrements of the users, maxmzng system utlzaton and ensurng farness among the users. In ths thess, we categorze and study varous schedulng algorthms for the uplnk traffc n WMAX n vew of these objectves. The algorthms are studed under dfferent mxes of traffc and for varous characterstcs of the IEEE 802.16 MAC layer such as uplnk burst preamble, frame length, bandwdth request mechansms etc. Smulaton results ndcate that legacy algorthms are not sutable for the mult-class traffc n WMAX as they do not explctly ncorporate the WMAX QoS parameters. We provde recommendatons for enhancng exstng schedulng schemes n WMAX, and shed lght on some of the open ssues that need to be addressed.

Acknowledgements Ths work would never have been possble wthout support from people too many to name. However, I would lke to thank the followng. I would lke to thank Queen s Unversty and the School of Computng for gvng me the opportunty and fnancal assstance to pursue the Masters program. I am very thankful to my supervsor Dr.Hossam Hassanen for gvng me the opportunty to be part of the Telecommuncatons Research Lab (TRL) and work under hs gudance. Hs nvaluable techncal assstance, moral support and motvaton are the man reasons for tmely completon of such a challengng project. Hs wonderful personalty and most of all encouragement durng dffcult tmes n my research kept me gong. I am also very grateful to my co-supervsor Dr.Najah Abu Al of the UAE Unversty for her techncal assstance and moral support throughout the course of ths work. Her assstance rght from the topc selecton to the analyss of the results was nvaluable n successful completon of the work. Her deep-rooted knowledge of the system and experence n ths feld enabled me to produce a hgh qualty work and gan valuable knowledge n conductng research. It has been an honor to have worked wth a talented group of students and collaborators at TRL. I would lke to thank Kashf Al for hs assstance wth NS-2 and Lnux. I am also grateful for the valuable feedback of my thess from Kashf and Afzal Mawj that helped me to mprove t by a great deal. I am thankful for all the gudance and frendshp of my colleagues at the TRL group. Thanks to everyone at the School of

Computng and all those who asked how s your thess gong? These memores at the School of Computng wll always be chershed. I am grateful for the emotonal, fnancal and nutrtonal support of my famly. Wthout ther contnuous support and prayers, ths work would not have been accomplshed. Mom and Dad, thank you for drectng me n my academc and professonal lfe. I am thankful to my sster for the support durng dffcult tmes and sharng my success when thngs were gong well. I express my deepest grattude to my uncle, aunt and brother for provdng me wth gudance and supportng all my decsons. I am grateful for all the lfe lessons learned from my grandmother and late grandfather, whch are the cornerstones of my success. I know hs blessngs wll always be wth me n all my endeavors and I dedcate ths success to hm.

TABLE OF CONTENTS Abstract... Acknowledgements... Lst of Tables... v Lst of Fgures... v Lst of Acronyms... x Chapter 1. Introducton... 1 1.1 Thess Contrbuton... 5 1.2 Thess Organzaton... 6 Chapter 2. Background... 8 2.1 Worldwde Interoperablty of Mcrowave Access (WMAX)... 8 2.1.1 The Evoluton of IEEE 802.16 standard... 9 2.1.2 IEEE 802.16 PHY Layer... 11 2.1.3 IEEE 802.16 MAC Layer... 14 2.1.4 IEEE 802.16 Servce Classes... 19 2.2 Packet schedulng for uplnk traffc n WMAX... 21 2.2.1 Homogeneous schedulng algorthms... 23 2.2.2 Hybrd schedulng algorthms... 26 2.2.3 Opportunstc schedulng algorthms... 29 2.3 Summary... 32 Chapter 3. Representatve WMAX uplnk schedulng algorthms... 33 3.1 Homogeneous Algorthms... 36 3.1.1 Weghted Round Robn (WRR)... 37 3.1.2 Earlest Deadlne Frst (EDF)... 38 3.1.3 Weghted Far Queung (WFQ)... 39 3.2 Hybrd Algorthms... 42 3.2.1 Hybrd (EDF+WFQ+FIFO)... 42 3.2.2 Hybrd (EDF+WFQ)... 44 3.3 Opportunstc Algorthms... 46 3.3.1 Cross-Layer schedulng algorthm... 46 3.3.2 Queung Theoretc schedulng algorthm... 49 3.4 Complexty Analyss... 54 3.5 Summary... 56 Chapter 4. Performance Analyss... 57 4.1 NS-2 and WMAX... 57 4.2 Smulaton Model... 59 4.2.1 Transmsson Modes... 59 4.2.2 Traffc Model... 60 4.2.3 Smulaton Parameters... 62 4.2.4 Performance Metrcs... 63 4.3 Smulaton Results... 66 4.3.1 The effect of SS rato... 67 4.3.2 The effect of uplnk burst preamble... 79 4.3.3 The effect of frame length... 95 4.3.4 Bandwdth Request Analyss... 103 v

4.4 Summary... 110 Chapter 5. Conclusons and Future Work... 114 Bblography... 122 Appendx A Intra-class farness (Jan s ndex)... 127 v

Lst of Tables Table 2-1: Traffc classes n 802.16 and ther QoS requrements... 20 Table 3-1: Complexty of representatve uplnk schedulng algorthms... 55 Table 4-1: IEEE 802.16-2004 Transmsson Modes... 60 Table 4-2: VoIP traffc parameters... 61 Table 4-3: Vdeo Streamng parameters... 61 Table 4-4: Fxed Smulaton parameters... 63 Table 4-5: Varable Smulaton parameters... 63 Table 4-6: The effect of SS Rato Parameters... 67 Table 4-7: The effect of uplnk burst preamble Parameters (frame utlzaton)... 80 Table 4-8: The effect of uplnk burst preamble Parameters... 83 Table 4-9: The effect of frame length Parameters (frame utlzaton)... 96 Table 4-10: The effect of frame length Parameters... 99 Table 4-11: Bandwdth request analyss - Parameters... 104 Table 4-12: Comparson of uplnk schedulng algorthms n WMAX... 111 v

Lst of Fgures Fgure 1-1: Sngle-hop cellular network f ths s not yours you need to reference t... 2 Fgure 1-2: Mult-hop cellular network... 2 Fgure 2-1: TDD Frame Structure... 18 Fgure 2-2: Taxonomy of uplnk schedulng algorthms n WMAX... 23 Fgure 3-1: Pseudo-code of WRR algorthm... 38 Fgure 3-2: Pseudo-code of EDF algorthm... 39 Fgure 3-3: Acton upon arrval of packet k of SS arrve(,k)... 41 Fgure 3-4: Acton upon selecton of packet k of SS select (,k)... 41 Fgure 3-5: Pseudo-code of WFQ algorthm... 41 Fgure 3-6: Pseudo-code of hybrd (EDF+WFQ+FIFO) algorthm... 43 Fgure 3-7: Pseudo-code of hybrd (EDF+WFQ) algorthm... 45 Fgure 3-8: Pseudo-code of Cross Layer algorthm... 49 Fgure 3-9: Pseudo-code of Queung Theoretc schedulng algorthm... 54 Fgure 4-1: The effect of SS Rato Average Throughput... 69 Fgure 4-2: The effect of SS Rato Average delay... 72 Fgure 4-3: The effect of SS Rato - Packet loss... 73 Fgure 4-4: The effect of SS Rato: Intra-class Farness Mn-max Index... 76 Fgure 4-5: The effect of SS Rato: Inter-class Farness Jan s Index... 76 Fgure 4-6: The effect of uplnk burst preamble Frame Utlzaton... 81 Fgure 4-7: The effect of uplnk burst preamble Average throughput (Lght load)... 84 Fgure 4-8: The effect of uplnk burst preamble Average delay (lght load)... 85 Fgure 4-9: The effect of uplnk burst preamble Packet loss (lght load)... 85 v

Fgure 4-10: The effect of uplnk burst preamble: Intra-class farness (Lght load)... 87 Fgure 4-11: The effect of uplnk burst preamble: Average throughput (Heavy load)... 88 Fgure 4-12: The effect of uplnk burst preamble: Average delay (Heavy load)... 89 Fgure 4-13: The effect of uplnk burst preamble: Packet loss (Heavy load)... 89 Fgure 4-14: The effect of uplnk burst preamble: Intra-class farness (Heavy load)... 91 Fgure 4-15: The Effect of Frame Length Frame utlzaton... 97 Fgure 4-16: The effect of frame length: Average delay (Lght load)... 99 Fgure 4-17: The effect of frame length: Packet loss (Lght load)... 100 Fgure 4-18: The effect of frame length: Average delay (Heavy load)... 101 Fgure 4-19: The effect of frame length: Packet loss (Heavy load)... 101 Fgure 4-20: Uplnk sub-frame structure: Contenton Request Mechansm... 104 Fgure 4-21: Bandwdth request analyss Lght load... 106 Fgure 4-22: Bandwdth request analyss Heavy load... 107 Fgure A-1: The effect of SS rato: Intra-class farness...127 Fgure A-2: The effect of uplnk burst preamble: Intra-class farness (Lght load).127 Fgure A-3: The effect of uplnk burst preamble: Intra-class farness (Heavy load)...128 v

Lst of Acronyms AAS AMC AMR ARQ ATDD ATM BE BER BPSK BS CBR DCD DHCP DRR DSL EDF ertps ETSI FBWA FDD FEC Adaptve Antenna System Adaptve Modulaton and Codng Adaptve Mult-Rate Automatc Repeat Request Adaptve Tme Dvson Duplex Asynchronous Transfer Mode Best Effort Bt Error Rate Bnary Phase Shft Keyng Base Staton Constant Bt Rate Downlnk Channel Descrptor Dynamc Host Confguraton Protocol Defct Round Robn Dgtal Subscrber Lne Earlest Deadlne Frst extended real-tme Pollng Servce European Telecommuncaton Standards Insttute Fxed Broadband Wreless Access Frequency Dvson Duplex Forward Error Correcton x

GPC GPS GPSS HperMAN HRR HOL IE IEEE LOS MAC MAN MIB MRTR MSTR MUFSS MWFQ MWRR NLOS nrtps OFDM PDU PFS PHY Grant Per Connecton Generalzed Processor Sharng Grant Per Subscrber Staton Hgh performance rado Metropoltan Area Network Herarchcal Round Robn Head Of Lne Informaton Element Insttute of Electrcal and Electronc Engneers Lne-of-Sght Medum Access Control Metropoltan Area Network Management Informaton Base Mnmum Reserved Traffc Rate Maxmum Sustaned Traffc Rate Mult-class Uplnk Far Schedulng Structure Modfed Weghted Far Queung Modfed Weghted Round Robn Non-Lne-of-Sght non real-tme Pollng Servce Orthogonal Frequency Dvson Multplex Protocol Data Unt Proportonal Far Scheduler Physcal Layer x

PMP QAM QoS QPSK RLC RR rtps SC SCa SDMA SDU SINR SLA SNMP SS STC TDD TFTP UCD UGS UNNI VoIP VWRR Pont to MultPont Quadrature Ampltude Modulaton Qualty of Servce Quadrature Phase Shft Keyng Rado Lnk Control Round Robn real-tme Pollng Servce Sngle Carrer Sngle Carrer access Spatal Dvson Multple Access Servce Data Unt Sgnal to Interference Nose Rato Servce Level Agreement Smple Network Management Protocol Subscrber Staton Space Tme Codng Tme Dvson Duplex Trval Fle Transfer Protocol Uplnk Channel Descrptor Unsolcted Grant Servce Unlcensed Natonal Informaton Infrastructure Voce over Internet Protocol Varably Weghted Round Robn x

WFQ WF 2 Q WBRO WMAX Weghted Far Queung Worst-case Far Weghted Far Queung Wreless Broadband Worldwde Interoperablty Mcrowave Access WrelessHUMAN Wreless Hgh Speed Unlcensed Metro Area Network WrelessMAN WRR Wreless Metropoltan Area Network Weghted Round Robn x

Chapter 1. Introducton WMAX (Worldwde Interoperablty for Mcrowave Access), s a cell-based technology amed at provdng last-mle wreless broadband access at a cheaper cost. The last mle s the fnal leg of delverng connectvty from the servce provder to the customer. Ths leg s typcally seen as an expensve undertakng because of the consderable costs of wres and cables. The core of WMAX technology s specfed by the IEEE 802.16 standard that provdes specfcatons for the Medum Access Control (MAC) and Physcal (PHY) layers. The term WMAX was created by the WMAX forum that promotes conformance and nteroperablty of the standard. Wreless Broadband (WBRO) s a technology developed by the Korean telecommuncatons ndustry that mrrors the specfcatons of the IEEE 802.16 standard. Efforts are already underway to defne nteroperablty of WMAX and WBRO equpment. Broadband wreless networks (ncludng WMAX) can be categorzed nto a snglehop, Fgure 1-1 or a mult-hop network Fgure 1-2. A sngle-hop network contans a central entty such as a Base Staton (BS) that makes and delvers decsons to all the nodes such as Subscrber Statons (SSs) n ts cell. A cell s a basc geographc unt of a cellular system. On the other hand, n a cellular mult-hop network, some SSs are not n drect contact wth the BS For example, an object such as a buldng could be blockng the path from the BS to the SS. In such a network, a relay mechansm s requred at ntermedate SSs that wll relay nformaton to other SSs that are not n drect contact wth the BS. 1

Fgure 1-1: Sngle-hop cellular network Fgure 1-2: Mult-hop cellular network In a cellular network such as WMAX, traffc from the BS to the SSs s classfed as downlnk traffc whle that from the SSs to the BS s classfed as uplnk traffc. A schedulng algorthm mplemented at the BS has to deal wth both uplnk and downlnk traffc. In some cases, separate schedulng algorthms are mplemented for the uplnk and downlnk traffc. Typcally, a Call Admsson Control (CAC) procedure s also mplemented at the BS that ensures the load suppled by the SSs can be handled by the network. A CAC algorthm wll admt a SS nto the network f t can ensure that the mnmum Qualty of Servce (QoS) requrements of the SS can be satsfed and the QoS 2

of exstng SSs wll not deterorate. The performance of the schedulng algorthm for the uplnk traffc strongly depends on the CAC algorthm. Packet schedulng s the process of resolvng contenton for shared resources n a network. The process nvolves allocatng bandwdth among the users and determnng ther transmsson order. Schedulng algorthms for a partcular network need to be selected based on the type of users n the network and ther QoS requrements. QoS requrements vary dependng on the type of applcaton/user. For real-tme applcatons such as vdeo conferencng, voce chat and audo/vdeo streamng, delay and delay jtter are the most mportant QoS requrements. Delay jtter s the nter-packet arrval tme at the recever and s requred to be reasonably stable by the real-tme applcatons. On the other hand, for non-real tme applcatons such as fle transfer (FTP), throughput s the most mportant QoS requrement. Some applcatons, such as web-browsng and emal do not have any QoS requrements. In a network, dfferent types of applcatons, wth dverse QoS requrements, can co-exst. A schedulng algorthm s task n a mult-class network s to categorze the users nto one of the pre-defned classes. Each user s assgned a prorty, takng nto account ts QoS requrements. Subsequently, bandwdth s allocated accordng to the prorty of the users as well as ensurng that farness between the users s mantaned. Besdes havng a very close couplng wth the QoS requrements of the users, the desgn of a schedulng algorthm also depends on the type of network t s ntended for. Packet schedulng algorthms can usually be dstngushed based on ther characterstcs. Some of the desrable qualtes a schedulng algorthm must possess and the ssues that need to be addressed by the algorthms nclude [1],[2]: 3

Flexblty: A schedulng algorthm should be able to accommodate users wth dverse QoS requrements and also meet the mnmum requrements of users. Ideally, the desgn of a schedulng algorthm should be flexble enough so that t requres mnmal changes to be deployed n a dfferent network or even a dfferent technology. Smplcty: A schedulng algorthm should be smple, both conceptually and mechancally. Conceptual smplcty allows manageable analyss of the algorthm such that dstrbuton or worst case analyss bound for parameters such as delay and throughput can be derved. Mechancal smplcty allows effcent mplementaton of the algorthm on a large scale. Protecton: A schedulng algorthm needs to be able to protect well-behavng users from sources of varablty such as best effort traffc, msbehavng users and fluctuatons n the network load. Upon admsson nto the network, users enter nto a servce level agreement (SLA) that they wll adhere to (e.g., a user wll specfy peak and mean traffc rates). Sometmes a user wll not abde by the SLA, causng unpredcted traffc fluctuatons n the network. A schedulng algorthm needs to ensure that such fluctuatons do not affect well-behavng users n the network. Farness: Besdes satsfyng the QoS requrements of users, a schedulng algorthm needs to ensure that a reasonable level of farness s mantaned among the users. Farness measures the dfference between users wth respect to the resources allocated to them. In a wreless network, due to the presence of varatons n channel qualty, users experencng poor channel qualty mght be dened servce by the schedulng algorthm. Ths s because bandwdth allocated to users wth nferor channel qualty wll essentally be wasted as the data wll be lost or corrupted pror to reachng the 4

destnaton. A schedulng algorthm needs to have a mechansm to compensate users that have lost servce and mantan farness among all users. Lnk Utlzaton: A schedulng algorthm s requred to assgn bandwdth to the users such that maxmum lnk utlzaton s realzed. Lnk utlzaton s a crtcal property for the servce provders as t s drectly lnked to the revenue generated. A schedulng algorthm needs to ensure that resources are not allocated to users that do not have enough data to transmt, thus resultng n wastage of resources. Power conservaton on the moble devce: Due to lmted power avalable on the moble devce, a schedulng algorthm needs to ensure that lmted processng s done on the devce. Devce moblty: Dfferent cells can have a dfferent noton of tme,.e., the BSs of dfferent cells are not requred to be synchronzed. When a moble devce moves from one cell to another, packets need be tme-stamped based on the noton of tme n the new cell. Schedulng algorthms that allocate bandwdth to the users accordng to the tme-stamp of the packets (e.g. schedule users based on ther packet deadlnes) wll not functon as expected f the packets are not stamped wth the correct noton of tme. 1.1 Thess Contrbuton In ths thess, we focus on evaluatng schedulng algorthms for the uplnk traffc n WMAX. We evaluate a number of WMAX uplnk schedulng algorthms n a snglehop network, whch s referred to as Pont to Multpont (PMP) mode of WMAX. The man contrbutons of our work are: 5

Survey and categorze schedulng algorthms for the uplnk traffc n WMAX. Identfy the strengths and weaknesses of the algorthms based on whch the algorthms wll be selected for evaluaton. Identfy performance metrcs that wll effectvely evaluate the schedulng algorthms. The schedulng algorthms wll be evaluated wth respect to varous characterstcs of WMAX as specfed n the IEEE 802.16 standard. Update the Network Smulator 2 (NS2) extenson of WMAX by ncorporatng the mplementaton of representatve schedulng algorthms. A traffc model based on the WMAX specfcatons s also mplemented. Based on the smulaton results, hghlght the effects of the characterstcs of WMAX on the performance of the schedulng algorthms. We also dentfy open ssues and provde suggestons to mprove the performance of the evaluated algorthms. 1.2 Thess Organzaton The rest of the thess s organzed as follows. In chapter 2, we provde a descrpton of the IEEE 802.16 standards wth a focus on the IEEE 802.16-2004[3] standard. The IEEE 802.16-2004 standard provdes specfcaton for the PMP mode of operaton of WMAX. We also categorze and dscuss schedulng algorthms for uplnk traffc n WMAX. In chapter 3, we provde detaled nformaton about the schedulng algorthms selected for evaluaton. Such nformaton ncludes the pseudo-code of the algorthms and any assumptons made. In chapter 4, we descrbe the smulaton envronment, ncludng the traffc model and values of the MAC and PHY layer parameters, and defne the performance metrcs to be used n evaluatng the algorthms. We then dscuss the results 6

of the experments. In chapter 5, we hghlght the shortcomngs of the algorthms and propose enhancements. We also dscuss some of the open ssues and suggest future research drectons n the area. 7

Chapter 2. Background In ths chapter we wll dscuss the characterstcs of the MAC and PHY layers as specfed n the IEEE 802.16 standard. More specfcally, we wll descrbe the varous schedulng servces, bandwdth request mechansms and the transmsson modes n the IEEE 802.16 standard. We wll then dscuss packet schedulng algorthms for the uplnk traffc n WMAX Pont to Multpont (PMP) mode. We categorze the algorthms nto three classes and dscuss the strengths and weaknesses of each algorthm. 2.1 Worldwde Interoperablty of Mcrowave Access (WMAX) Pror to the ntroducton of the IEEE 802.16 standard, the most effectve ways to obtan access to broadband nternet servce were manly through T1, Dgtal Subscrber Lne (DSL), or cable modem based connectons. However, these wred nfrastructures are consderably more expensve, especally for deployment n rural areas and developng countres. Ths lmtaton propelled the ndustry to devse an alternatve means of obtanng broadband nternet access and the approach taken was va the wreless medum. The IEEE 802.16 standard provdes specfcaton for the MAC and PHY layers for the ar nterface. The standard ncludes detals about the varous flavors of PHY layers supported and characterstcs of the MAC layer such as bandwdth request mechansms and the schedulng servces supported. The WMAX forum, a consortum of about 420 members ncludng major corporatons lke AT&T, Fujtsu, Intel and Semens, was set up n June 2001 to support 8

the WMAX technology and promote ts commercal use. The forum s responsble for preparng profles for systems that comply wth the IEEE 802.16 standard and create nteroperablty tests to ensure dfferent vendors mplementaton can work together. The frst verson of the IEEE 802.16 standard was completed n October 2001 and snce then several verson have emerged addressng ssues such as Non-Lne Of Sght (NLOS) operaton, moblty, multple traffc classes for QoS, operaton n the lcensed and unlcensed frequency bands. 2.1.1 The Evoluton of IEEE 802.16 standard The IEEE 802.16 Workng Group s the body responsble for developng the IEEE 802.16 standard and ts extensons. In ths secton, we provde an overvew of some of functonaltes specfed n the IEEE 802.16 standard and ts extensons. The followng s a chronologcal orderng of the standards and ther respectve content: IEEE 802.16a [4]: Ths was the frst extenson of the IEEE 802.16 standard that allowed the use of lcensed and lcense-free frequences from 2GHz to 11GHz. Most of the ndustral nterest s n the unlcensed frequences. The lower frequences allow sgnals to penetrate obstacles and thus do not requre a Lne-Of-Sght (LOS) between the Subscrber Staton (SS) and the Base Staton (BS). Ths extenson also allows mesh deployment, whereby the subscrbers can act as relay ponts by transferrng nformaton from the BS to other SSs not n drect path of the BS. IEEE 802.16c [5]: Ths extenson contans specfcatons to allow the technology to nter-operate n the lcensed frequency band of 10GHz to 66GHz. The extenson clearly dentfes the mandatory and optonal features of the technology so that mplementaton and nteroperablty are clearer. The extenson also addresses ssues such as performance 9

evaluaton, testng and detaled system proflng along wth addng support for Multple Input Multple Output (MIMO) antennas. IEEE 802.16-2004 [1]: Ths extenson of the standard, popularly known as Fxed WMAX, s the combnaton of 802.16a and 802.16c extensons wth some modfcatons. The standard supports both Tme Dvson Duplex (TDD) and Frequency Dvson Duplex (FDD) servces. The product profle, as specfed by the standard, utlzes the OFDM 256-FFT (Fast Fourer Transform) system profle. One of the enhancements n ths extenson s the concatenaton of Protocol Data Unt (PDU) and Servce Data Unt (SDU) whch reduces the MAC overhead. Ths extenson provdes a substantal mprovement for the pollng mechansm. It allows the SS to be polled ndvdually or n groups. It also allows pggybackng bandwdth requests over data packets thus reducng collsons and system overhead. IEEE 802.16e-2005 [6]: Ths extenson, known as Moble WMAX, adds moblty support for the technology. The extenson preserves the techncal aspects of Fxed WMAX whle addng support for moble broadband wreless access. The standard specfes the use of OFDMA technology wth support for 2000-FFT, 1000-FFT, 512-FFT and 128-FFT system profles. The OFDMA technology allows sgnals to be dvded nto many sub-channels to ncrease resstance to mult-path nterference. The specfcaton n the standard supports moble devce speeds up to 100 km/h. IEEE 802.16f [7]: The extenson s currently an actve amendment wth the ntenton to support Management Informaton Base (MIB). A MIB s a database of nformaton used for managng all the devces n the network. The extenson ams to provde a detaled 10

descrpton of the protocol for managng nformaton between the Subscrber Statons (SSs) and the Base Staton (BS). IEEE 802.16g [8]: Ths extenson s currently under development and t ams to mprove the co-exstence mechansms for lcense exempt operatons. More specfcally, the extenson s attemptng to fnd approaches to allow coexstence between fxed wreless access networks operatng n the lcense exempt bands, prmarly the 5GHz frequency band. Our work s based on the 802.16-2004 standard [1], popularly known as Fxed WMAX, that provdes bandwdth up to 75Mbps, wthout moblty. Ths extenson of the IEEE 802.16 standard s geared to provdng broadband nternet access to resdental and commercal buldngs where moblty s not a requrement. In the next few sectons, we hghlght some of the man features of the PHY and MAC layer as specfed n the 802.16-2004 standard. 2.1.2 IEEE 802.16 PHY Layer The purpose of the PHY layer s the physcal transport of data. In the IEEE 802.16-2004 standard, the PHY layer s defned for frequences rangng from 2 to 66 GHz wth the sub-range 10-66 GHz requrng Lne Of Sght (LOS) propagaton and possblty of Non Lne Of Sght (NLOS) propagaton n the 2-11 GHz frequency range. The prncple technologes behnd the PHY layer of WMAX are Orthogonal Frequency Dvson Multplexng (OFDM) and Orthogonal Frequency Dvson Multple Access (OFDMA). OFDM s a mult-carrer transmsson technque that has recently ganed popularty for hgh-speed bdrectonal wreless data communcaton [9]. OFDM 11

bascally squeezes multple modulated carrers together reducng the requred bandwdth and at the same tme keepng the modulated sgnals orthogonal to each other so they do not nterfere wth each other. OFDM s based on a technology called Frequency Dvson Multplexng (FDM) that uses many frequences to transmt sgnals n parallel. OFDM s more effcent than FDM as t allows sub-channels to be spaced much close to each other by fndng orthogonal frequences. On the other hand, OFDMA allows certan subcarrers to be assgned to dfferent users. A group of sub-carrers consttutes a subchannel wth each sub-channel belongng to a partcular SS. Both Tme Dvson Duplex (TDD) and Frequency Dvson Duplex (FDD) are specfed n the IEEE 802.16-2004 standard. TDD s a technque n whch the system receves and transmts wthn the same frequency channel, assgnng tme slces for transmt and receve modes. In FDD, two separate frequences are requred to transmt and receve, usually separated by 50 to 100 MHz wthn the operatng band. The downlnk and uplnk frame structures n FDD are smlar except they are transmtted n separate channels. When half duplex FDD (H-FDD) s used at the SSs, the BS must make sure that t does not schedule the SSs to transmt and receve at the same tme. Adaptve Antenna System (AAS) s used n WMAX to specfy the beam-formng technques whereby a set of antennas s used at the BS to ncrease the gan to the SSs, at the same tme reducng nterference to and from other SSs. AAS can be used to enable Spatal Dvson Multple Access (SDMA) so that multple SSs that are n dfferent space can receve and transmt on the same sub-channel smultaneously. 12

The IEEE 802.16-2004 standard [1] specfes 5 varants of the PHY layer dstngushed by whether the PHY layer s Sngle Carrer (SC) or uses OFDM technology. The varants wth a bref descrpton follow: Wreless Metropoltan Area Network Orthogonal Frequency Dvson Multplexng (WrelessMAN-OFDM): The WrelessMAN-OFDM PHY s based on OFDM technology desgned manly for fxed SSs, where the SSs are deployed n resdental areas and busnesses. The OFDM PHY supports sub-channelzaton n the uplnk wth 16 sub-channels. It also supports TDD and FDD frame structures wth both FDD and H-FDD optons. The modulaton schemes supported are BPSK, QPSK, 16- QAM and 64-QAM. Wreless Metropoltan Area Network Orthogonal Frequency Dvson Multple Access (WrelessMAN-OFDMA): Ths varant s based on OFDMA technology and offers sub-channelzaton n both uplnk and downlnk. The OFDMA PHY supports both TDD and FDD frame structures, wth both FDD and H-FDD optons. The varant s dfferent from WrelessMAN-OFDM n that t supports sub-channelzaton n both the uplnk and downlnk drectons resultng n broadcast messages beng transmtted at the same tme as data. Wreless Hgh Speed Unlcensed Metro Area Network (WrelessHUMAN): Ths specfcaton of the PHY layer s smlar to the OFDM based layer except t s focused on Unlcensed Natonal Informaton Infrastructure (UNII) devces and other unlcensed bands. Wreless Metropoltan Area Network Sngle Carrer (WrelessMAN-SC): Ths varant specfes the use of the technology n the frequency range 10-66GHz. The PHY 13

Layer desgn supports Pont to Mult-Pont (PMP) archtecture whereby the BS acts as the coordnator for all the SSs n ts cell. In ths desgn, the BS transmts a Tme Dvson Multplexng (TDM) sgnal n whch the SSs are allocated tme slots serally. Ths varant provdes support for both TDD and FDD frame structures. Both TDD and FDD support adaptve burst profles whereby the modulaton and codng optons can be dynamcally assgned on a burst by burst bass. Wreless Metropoltan Area Network - Sngle Carrer Access (WrelessMAN-SCa): Ths varant of the PHY layer uses sngle carrer modulaton n the 2-11GHz frequency range and t s ntended for Non Lne-Of-Sght (NLOS) operatons. It supports both FDD and TDD frame structures wth TDMA n the uplnk and TDM or TDMA n the downlnk. The PHY specfcaton ncludes Forward Error Correcton (FEC) codng for both uplnk and downlnk and framng structures that allow mproved channel estmaton performance over NLOS operatons. 2.1.3 IEEE 802.16 MAC Layer The MAC layer n WMAX bascally provdes ntellgence to the PHY layer. It contans 2 sub layers: servce-specfc convergence sub-layer and the MAC common part sub-layer. The servce-specfc convergence sub-layer s responsble for nterfacng wth upper layers whle the MAC common part sub layer carrers out the key MAC functons [10]. Servce specfc convergence sub-layer: The IEEE 802.16-2004 standard specfes 2 types of servce specfc convergence sub-layers for mappng servce to and from the MAC layer; the ATM sub-layer for mappng ATM servces and the packet sub-layer for 14

mappng packet servces such as IPv4, IPv6 and Ethernet. The man task of the sub-layer s to map Servce Data Unts (SDUs) to MAC connectons, and to enable QoS and bandwdth allocaton based on the parameters receved from the upper layers. The convergence sub-layer also has the ablty to perform more complcated tasks such as payload header compresson. MAC common part sub-layer: The MAC protocol, accordng to the IEEE 802.16-2004 standard, s manly desgned for Pont to Mult-Pont (PMP) operaton. The MAC layer s connecton-orented ncludng connecton-less servces mapped to a connecton whch allows a way of requestng bandwdth and mappng the QoS parameters of the connecton. Connectons contan a 16-bt Connecton Identfers (CIDs) whch act as the prmary addresses used for all operatons. Each SS has a 48-bt MAC address whch s manly used as an equpment dentfer. Upon enterng the network, an SS s assgned 3 management connectons n each of the uplnk and downlnk drectons. These connectons are: Basc Connecton: Ths connecton s responsble for transferrng crtcal MAC and Rado Lnk Control (RLC) messages. Prmary Management Connecton: Ths connecton s responsble for transferrng longer and more delay-tolerant control messages such as those used for authentcaton and connecton setup. Secondary Management Connecton: Ths connecton s used for transfer of standard based management messages such as Dynamc Host Confguraton Protocol (DHCP), 15

Trval Fle Transfer Protocol (TFTP) and Smple Network Management Protocol (SNMP). The functonaltes supported by the Common Part Sub-layer are: Channel Acquston: The MAC protocol ncludes an ntalzaton procedure that allows an SS, upon nstallaton, to scan ts frequency lst to fnd an operatng channel. Once the SS s synchronzed, t wll perodcally search for Downlnk Channel Descrptor (DCD) and Uplnk Channel Descrptor (UCD) messages that nform the SS about the modulaton scheme used on the channel. Rangng and Negotaton: After determnng the parameters to use for rangng, the SS wll search for rangng opportuntes by scannng the UL MAP messages n every frame. The rangng response from the SS allows the BS to fnd out the dstance between tself and the SS. SS authentcaton and Regstraton: Each SS contans a manufacturer ssued dgtal certfcate that establshes a lnk between the 48-bt MAC address of the SS and ts publc RSA key. After verfyng the dentty of the SS, f the SS s admtted nto the network, the BS wll respond to the request wth an Authorzaton Reply contanng an Authorzaton Key (AK), encrypted wth the SS s publc key. Bandwdth Grant and Request: The MAC layer dstngushes between 2 classes of SS, one that accepts bandwdth for a connecton and the other one that accepts bandwdth for the SS. For the Grant per Connecton (GPC) class, bandwdth s granted explctly to the connecton of the SS. Wth the Grant per SS (GPSS) class, bandwdth s granted to the SS and then t s up to the SS on how to dstrbute the bandwdth among ts connectons. The SS can use the bandwdth for the connecton that requested t or for another connecton. 16

The IEEE 802.16-2004 standard allows SSs to request bandwdth va contenton or pggyback mechansms. In contenton mechansm, the SSs wll contend for a slot to send the bandwdth request whle n the pggyback mechansm the SSs wll attach ther bandwdth request onto data packets. A bandwdth request can also be ether ncremental or aggregate. When the BS receves an ncremental bandwdth request, t wll add the quantty of the bandwdth requested to ts current percepton of the bandwdth needs of the SS. When the BS receves an aggregate bandwdth request, t wll replace ts percepton of the bandwdth needs of the SS wth the quantty of bandwdth requested. Pggyback bandwdth requests are always ncremental. Frame structure and MAP messages: IEEE 802.16 MAC supports both TDD and FDD frame structures. The MAC starts buldng the downlnk sub-frame wth DL-MAP (Downlnk MAP) and UL-MAP (Uplnk MAP) messages. The DL-MAP ndcates the PHY transtons on the downlnk whle the UL-MAP ndcates bandwdth allocaton and burst profles n the uplnk. In a TDD frame structure, the frame s dvded nto uplnk and downlnk sub-frames along the tme axs (see Fgure 2-1). The frame starts wth the downlnk sub-frame followed by a short gap called transmt/receve transton gap (TTG). The downlnk sub-frame contans a preamble followed by a header and one or more downlnk bursts. Followng TTG, the uplnk sub-frame contans one or more uplnk bursts. Each uplnk burst contans a preamble that allows the BS to synchronze wth each SS. The uplnk sub-frame s then followed by a short gap called the receve/transmt transton gap (RTG) before the BS can start transmttng agan. 17

Preamble Header DLMAP ULMAP DL Burst1 DL Burst2 DL Burst3 DL Burst4 DL Burst5 UL Burst1 UL Burst2 UL Burst3 UL Burst4 Downlnk sub-frame Uplnk sub-frame TTG RTG Fgure 2-1: TDD Frame Structure Packng and Fragmentaton of MAC SDUs: Ths functonalty s executed n tandem wth the bandwdth allocaton process to maxmze effcency, flexblty and effectveness. Fragmentaton s the process by whch a MAC SDU s dvded nto one or more SDU fragments. Packng s the process n whch multple MAC SDUs are packed nto a sngle MAC PDU payload. Ether functonalty can be ntated by the BS n the downlnk or by the SS n the uplnk. Schedulng Servces: The Common Part Sub-layer maps each connecton to a schedulng servce, where a schedulng servce s assocated wth pre-determned QoS parameters. The IEEE 802.16-2004 standard specfes four schedulng servces: Unsolcted Grant Servce (UGS), real-tme Pollng Servce (rtps), non-real tme Pollng Servce (nrtps) and Best Effort (BE). The bandwdth allocaton mechansm for the UGS servce as specfed n the IEEE 802.16-2004 standard [1] requres the BS to send fxed sze grants to the SSs perodcally. 18

2.1.4 IEEE 802.16 Servce Classes The IEEE 802.16-2004 standard [1] specfes the provson of four schedulng servces: Unsolcted Grant Servce (UGS): Ths schedulng servce s desgned to support applcatons that generate fxed-sze data packets perodcally such as T1/E1 and VoIP wthout slence suppresson. To support the real-tme needs of such applcatons and reduce overhead by the bandwdth request-grant process, the BS allocates fxed sze data grants wthout recevng explct requests from the SS. The sze of the grants s based on the maxmum rate that can be sustaned by the applcaton and s negotated at connecton setup. real-tme Pollng Servce (rtps): Ths schedulng servce s desgned to support realtme applcatons that generate varable sze packets on a perodc bass such as MPEG vdeo or VoIP wth slence suppresson. The BS allows the SSs to make perodc uncast requests and allows them to specfy the sze of the desred grant. Snce a dedcated grant request s contenton-free, the bandwdth request s guaranteed to be receved by the SS n tme. SSs belongng to ths class are prohbted from usng contenton request opportuntes. non real-tme Pollng Servce (nrtps): nrtps s desgned to support non-real tme applcatons that requre varable sze data grant bursts on a regular bass. Ths schedulng servce supports applcatons that are delay tolerant but may need hgh throughput such as Fle Transfer Protocol (FTP) applcatons. The BS allows the SS to make perodc uncast grant requests, just lke the rtps schedulng servce, but the requests are ssued at longer ntervals. Ths wll ensure that the SSs receve request 19

opportuntes even durng network congeston. SSs of ths class are also allowed to use contenton request opportuntes. Best Effort (BE): Ths traffc class contans applcatons such as telnet or World Wde Web (WWW) access that do not requre any QoS guarantee. The bandwdth request by such applcatons s granted on space-avalable bass. The SS s allowed to use both contenton-free and contenton based bandwdth requests, although contenton-free s not granted when the system load s hgh. In Table 2-1, we lst some of the applcatons belongng to each class, ncludng suggested delay guarantees that they requre under both premum and basc servce [11]. Table 2-1: Traffc classes n 802.16 and ther QoS requrements Class of QoS Requrements Knds of servces Servce QoS Factors Premum Basc UGS Packet Delay < 150ms < 250ms VoIP Delay Jtter < 30ms < 50ms Packet Loss < 0.3% < 0.5% Guarantee > 99.9% > 99.5% rtps Packet Delay < 300ms < 600ms Vdeo Telephony, Delay Jtter < 50ms < 100ms Vdeo game, Packet Loss < 1% < 5% VOD, AOD, Guarantee > 99% > 95% Internet shoppng, bank and stock nrtps BE Packet Delay N/A N/A Delay Jtter N/A N/A Packet Loss 0-2% 0-5% Guarantee > 98% > 82% Packet Delay/ Delay Jtter/ Packet Loss/ Guarantee transacton Hgh-speed fle transfer, Multmeda messagng, E-commerce N/A N/A Web-browsng, SMS 20

2.2 Packet schedulng for uplnk traffc n WMAX Packet schedulng algorthms are mplemented at both the BS and SSs. A schedulng algorthm at the SS s requred to dstrbute the bandwdth allocaton from the BS among ts connectons. A schedulng algorthm at the SS s not needed f the BS grants bandwdth to each connecton of the SS separately.e. the Grant Per Connecton (GPC) procedure s followed. If the Grant Per Subscrber Staton (GPSS) procedure s followed, the schedulng algorthm at the SS needs to decde on the allocaton of bandwdth among ts connectons. The schedulng algorthm mplemented at the SS can be dfferent than that at the BS. The focus of our work s on schedulng algorthms executed at the BS for the uplnk traffc n WMAX.e. traffc from the SSs to the BS. A schedulng algorthm for the uplnk traffc s faced wth challenges not faced by an algorthm for the downlnk traffc. An uplnk schedulng algorthm does not have all the nformaton about the SSs such as the queue sze. An uplnk algorthm at the BS has to coordnate ts decson wth all the SSs where as a downlnk algorthm s only concerned n communcatng the decson locally to the BS. Based on our comprehensve survey, we have classfed schedulng algorthms for the uplnk traffc n WMAX nto three categores (see Fgure 2-2): Homogeneous schedulng algorthms: These are legacy schedulng algorthms that attempt to address ssues such as provdng QoS, flow solaton and farness. The algorthms were orgnally proposed for wred networks but are used n WMAX prncpally to satsfy QoS requrements of the four traffc schedulng servces. Algorthms n ths category do not address the ssue of lnk channel qualty. 21

Hybrd schedulng algorthms: Ths category contans algorthms that use a combnaton of legacy schedulng algorthms n an attempt to satsfy QoS requrements of the four schedulng servces. Some of the algorthms n ths category also address the ssue of varable channel condtons n WMAX. An mportant aspect of algorthms n ths category s the overall allocaton of bandwdth among the schedulng servces. Once bandwdth has been assgned to each class, a legacy algorthm s executed for SSs of the class to determne the bandwdth allocaton n that class. Opportunstc schedulng algorthms: Schedulng algorthms n ths category are prmarly focused on explotng the varablty n channel condtons n WMAX. The algorthms also attempt to satsfy QoS requrements of the four schedulng servces and mantan farness between the SSs. 22

Uplnk schedulng algorthms n WMAX Homogeneous algorthms Heterogeneous algorthms Opportunstc algorthms WRR [12] EDF+WFQ+FIFO [23] Cross-Layer [27] DRR [12] EDF+WFQ [24] O-DRR [28] EDF [15], [17] WRR+RR [25] Queung-Theoretc [29] WFQ [15] MWFQ+MWRR+FIFO [26] OFDMA scheduler [30] WF 2 Q [19] TCP-traffc scheduler[31] Modfed EDF [22] Fgure 2-2: Taxonomy of uplnk schedulng algorthms n WMAX 2.2.1 Homogeneous schedulng algorthms Most of the legacy schedulng algorthms can be classfed nto ths category. We wll only dscuss those that have been proposed and evaluated n WMAX. Weghted Round Robn (WRR) and Defct Round Robn (DRR) algorthms are evaluated on a WMAX system n [12]. WRR s evaluated for the uplnk traffc whle DRR s evaluated for the downlnk traffc. WRR s an extenson of the Round Robn (RR) algorthm. It s a work-conservng algorthm n that t wll contnue allocatng bandwdth to the SSs as long as they have backlogged packets. The WRR algorthm assgns weght to each SS and the bandwdth s then allocated accordng to the weghts. The algorthm was orgnally proposed for ATM networks that have fxed sze packets [13]. Snce the 23

bandwdth s assgned accordng to the weghts only, the algorthm wll not provde good performance n the presence of varable sze packets. It has been dscussed n [12] that weght to a SS can be assgned to reflect ts relatve prorty.e. a hgher weght assgned to SSs of the rtps class compared to the weght assgned to SSs of the nrtps and BE classes. DRR, a varaton of RR, s also a work-conservng algorthm wth a constant processng tme [14]. DRR s smlar to the RR algorthm n that a quantum of servce s assgned to each SS. The dfference between the two algorthms s that when a SS s not able to send a packet, the remander quantum s stored n a defct counter. The value of the defct counter s added to the quantum n the followng round. The algorthm s flexble enough as t allows provson of quanta of dfferent szes dependng on the QoS requrements of the SSs. DRR s mostly suted for datagram networks where packet szes vary. Snce the DRR algorthm requres accurate knowledge of packet sze, t s not sutable for the uplnk traffc. N. Ruangchajatupon et al. [15] evaluate the performance of the Earlest Deadlne Frst (EDF) algorthm. EDF s a work conservng algorthm orgnally proposed for realtme applcatons n wde area networks [16]. The algorthm assgns deadlne to each packet and allocates bandwdth to the SS that has the packet wth the earlest deadlne. Deadlnes can be assgned to packets of a SS based on the SS s maxmum delay requrement. The EDF algorthm s sutable for SSs belongng to the UGS and rtps schedulng servces, snce SSs n ths class have strngent delay requrements. Snce SSs belongng to the nrtps servce do not have a delay requrement, the EDF algorthm wll schedule packets from these SSs only f there are no packets from SSs of UGS or rtps 24

class. Wth a large number of SSs from the UGS or rtps class, SSs from the nrtps or BE class can potentally starve. T. Tsa et al. [17] propose an uplnk schedulng algorthm and a token bucket based Call Admsson Control (CAC) algorthm. The CAC algorthm assgns thresholds to each class to avod starvaton of lower prorty classes. The EDF schedulng algorthm s used for the rtps class. The schedulng algorthm frst grants bandwdth to SSs of the UGS class. The algorthm wll then allocate bandwdth to SSs of the rtps class usng the EDF algorthm and restrctng the allocaton to the maxmum grant sze. Fnally, the algorthm wll allocate mnmum requred bandwdth to SSs of the nrtps and BE classes n order. Each SS s controlled by a token rate and bucket sze. A mathematcal model s proposed that estmates the approprate token rate based on the queung delay and the packet loss requrements, for both fnte and nfnte queue length. N. Ruangchajatupon et al. [15] also evaluate Weghted Far Queung (WFQ) for the uplnk traffc n WMAX. WFQ s a packet-based approxmaton of the Generalzed Processor Sharng (GPS) algorthm [18]. GPS s an dealzed algorthm that assumes a packet can be dvded nto bts and each bt can be scheduled separately. Ths s an mpractcal assumpton snce a packet needs to be scheduled n ts entrety. WFQ s a practcal mplementaton of GPS as t assgns fnsh tmes to packets and selects packets n ncreasng order of ther fnsh tmes. The fnsh tmes of packets of a SS are calculated based on the weght assgned to the SS and the sze of the packets. The WFQ algorthm results n superor performance compared to the WRR algorthm n the presence of varable sze packets. The fnsh tme of a packet s essentally the tme the packet would have fnshed servce under the GPS algorthm. The dsadvantage of the WFQ algorthm 25

s that t wll servce packets even f they wouldn t have started servce under the GPS algorthm. Ths s because the WFQ algorthm does not consder the start tme of a packet. Y. Shang and S. Cheng n [19] propose a herarchcal model for packet schedulng based on the proposal of J. Bennet and H. Zhang n [20]. The model s comprsed of three schedulng servers: a hard-qos schedulng server, a soft-qos schedulng server and a best effort schedulng server. The UGS traffc s mapped to the hard-qos server and the rtps traffc s mapped to the soft-qos server. The nrtps traffc can be mapped to ether the soft-qos server or the best effort server. All the servers mplement the Worst-case Far Weghted Far Queung (WF 2 Q) schedulng algorthm [21]. WF 2 Q s another extenson of GPS that addresses the ssue of the WFQ algorthm servcng packets even f they wouldn t have started servce under the GPS scheme. O. Yang and J. Lu n [22] propose a jont CAC and schedulng algorthm based on the concept of EDF to satsfy the QoS requrements of real-tme vdeo applcatons n IEEE 802.16 networks. The algorthm clams to cover throughput requrement, delay constrant and mantan farness among the SSs smultaneously. 2.2.2 Hybrd schedulng algorthms The hybrd class of schedulng algorthms uses a combnaton of legacy schedulng algorthms to satsfy QoS requrements of the mult-class traffc as specfed n the IEEE 802.16-2004 standard [1]. The most crtcal part of hybrd algorthms s the dstrbuton of uplnk bandwdth among dfferent traffc classes. K. Wongthavarawat and A. Ganz propose a hybrd schedulng algorthm n [23] that combnes EDF, WFQ and FIFO schedulng algorthms. The overall allocaton of 26

bandwdth s done n a strct prorty manner.e. all the hgher prorty SSs are allocated bandwdth untl they do not have any packets to send. The EDF schedulng algorthm s used for SSs of the rtps class, WFQ s used for SSs of the nrtps class and FIFO for SSs of the BE class. Besdes the schedulng algorthm, an admsson control procedure and a traffc polcng mechansm are also proposed. All these components together consttute the proposed QoS archtecture. A drawback of ths algorthm s that lower prorty SSs wll essentally starve n the presence of a large number of hgher prorty SSs due to the strct prorty overall bandwdth allocaton. K. Vnay et al. [24] propose a hybrd scheme that uses EDF for SSs of the rtps class and WFQ for SSs of the nrtps and BE classes. Ths algorthm dffers from the one n [23] n a couple of ways. Frst, the WFQ algorthm s used for SSs of both nrtps and BE classes. Secondly, the overall bandwdth allocaton s not done n a strct prorty manner. Although the detals of overall bandwdth allocaton are not specfed, t s brefly mentoned that the bandwdth s allocated among the classes n a far manner. Snce SSs of the BE class do not have any QoS requrements, usng a computatonally complex algorthm such as WFQ for them s not needed. M.Settembre et al. [25] propose a hybrd schedulng algorthm that uses WRR and RR algorthms wth a strct prorty mechansm for overall bandwdth allocaton. In the ntal porton of the algorthm, bandwdth s allocated on a strct prorty bass to SSs of the rtps and nrtps classes only. After that the WRR algorthm s used to allocate bandwdth among SSs of rtps and nrtps classes untl they are satsfed. If any bandwdth remans, t s dstrbuted among the SSs of the BE class usng the RR algorthm. The hybrd algorthm s opportunstc n nature as the WRR and RR algorthms select the SSs 27

wth the most robust burst profles. Ths algorthm wll starve lower prorty SSs n the presence of a large number of hgher prorty SSs. The algorthm can also result n low farness among SSs as t selects SSs wth the most robust burst profles frst. J. Ln and H. Srsena [26] propose an archtecture called Mult-class Uplnk Far Schedulng Structure (MUFSS) to satsfy throughput and delay requrements of the multclass traffc n WMAX. The proposed schedulng dscplne at the BS s Modfed Weghted Round Robn (MWRR), although detals of the modfcatons to the WRR dscplne are not provded by the authors. The model s based on Grant Per Subscrber Staton (GPSS) bandwdth grant mode and thus schedulers are mplemented at the SSs to dstrbute the bandwdth granted among ther connectons. At the SS, Modfed WFQ (MWFQ) s used for UGS and rtps connectons, MWRR s used for nrtps connectons and FIFO s used for BE connectons. Normally, mplementng the schedulng algorthms to cater to all the servce classes and on a per connecton bass s not a trval task. The IEEE 802.16 standard supports changng a connecton s QoS parameters durng ts lfetme. Thus, the schedulng algorthms are requred to adapt to these changes by reassgnng the slots. For nstance, n the case of the WFQ algorthm, dynamc weghts may be the soluton, whch consderably ncreases the algorthm s complexty and renders ts mplementaton challengng. The standard also requres the frame sze to be constant. Ths would result n some of the tme slots not beng utlzed, whch makes the performance of the algorthms closer to that of non work-conservng schedulers, whereas the proposed homogeneous and hybrd algorthms are work-conservng. Therefore, most of the proposals make sgnfcant assumptons that smplfy the mplementaton of the algorthms. In [12], the 28

authors mplement DRR as the downlnk scheduler, wthout consderng the WMAX QoS parameters, and WRR as the uplnk scheduler wth constant weghts, wthout clarfyng how the weghts are chosen, or provdng justfcaton for adoptng constant weghts. 2.2.3 Opportunstc schedulng algorthms Opportunstc schedulng algorthms proposed for WMAX explot varatons n channel qualty gvng prorty to users wth better channel qualty, whle attemptng to satsfy the QoS requrements of the mult-class traffc. A cross-layer schedulng algorthm s proposed n [27] whereby each SS s assgned a prorty based on ts channel qualty and servce status. The SS wth the hghest prorty s scheduled each tme. SSs of the UGS class are assgned a fxed number of tme slots based on ther requred rate. The prorty functon for the rtps class takes the deadlne and watng tme of the HOL packet as nput whle the prorty functon for the nrtps class takes the average throughput and the mnmum requred throughput as nputs. The prorty functon for the BE class only takes the channel qualty of the SS as nput. A coeffcent s ncluded n the prorty functons to reflect the relatve prorty of the classes,.e., a hgher coeffcent s used for the rtps class compared to the coeffcents of nrtps and BE classes. One of the drawbacks of ths algorthm s that t results n poor channel utlzaton snce t schedules only one SS every frame. Ths wll also result n low average throughput and hgher average delay as SSs wll have to wat for longer perod of tme before they are scheduled. H. Rath et al. [28] propose to use an opportunstc extenson of the Defct Round Robn (DRR) algorthm wth the purpose of satsfyng delay requrements of mult-class 29

traffc n WMAX. The proposed algorthm uses a defct counter and a quantum sze just lke the DRR algorthm. A crtcal part of the algorthm s the pollng nterval. At the begnnng of a pollng nterval, a set of schedulable SSs are selected that forms a schedulable set. Untl the next pollng nterval, SSs are selected only from the schedulable set. SSs that are not selected wll have ther quantum accumulated n the defct counter. A major lmtaton of ths algorthm s selectng an approprate pollng nterval. If a large pollng nterval s selected, t wll result n some of the SSs beng dened servce for a long perod of tme. Even f a SS becomes elgble to be added to the schedulable set, t wll not be consdered untl the next pollng nterval. D. Nyato and E. Hossan [29] propose a jont bandwdth allocaton and connecton admsson control algorthm based on queung theory. In order to lmt the amount of bandwdth allocated per class, a bandwdth threshold s assgned to each class. Each SS s assgned a utlty and bandwdth s allocated to the SS wth the least utlty. Utlty for SSs of the rtps and nrtps classes s calculated usng a sgmod functon that takes the average delay and maxmum latency for the rtps class and average throughput and mnmum requred throughput for the nrtps class as nputs. SSs of the BE class are assgned the hghest utlty as long as 1 unt of bandwdth s assgned to them. The unt of bandwdth used n the algorthm s a fxed sze packet called a Protocol Data Unt (PDU). In the ntal stages of the algorthm, mnmum bandwdth s allocated to the SSs n a strct prorty order. Afterwards, the algorthm assgns the resdual bandwdth n PDU unts to the SSs. SSs are sorted n ascendng order based on ther utlty and they are allocated the PDUs based on a water fllng mechansm untl the bandwdth of each class exceeds the class threshold. The thresholds for the classes are calculated such that QoS 30

requrements of the SSs are met and the system revenue s maxmzed. If a packet s too large and the mnmum bandwdth allocated to the SS s not enough to transmt the large packet, the allocaton wll essentally be wasted. Another drawback of the algorthm s that t wll result n maxmum MAC and PHY layer overhead snce t selects all the SSs n the network based on the frst phase of the algorthm as aforementoned. V. Sngh and V. Sharma [30] propose schedulng algorthms for the OFDMA system wth a TDD frame structure for both uplnk and downlnk traffc n WMAX. An optmzaton problem s frst formulated for the allocaton of resources to the SSs. The formulaton consders the channel qualty n terms of bytes/slot a SS can send on a channel, the number of slots allotted to the SS and the total bandwdth demanded by the SS. A lnear programmng soluton to the optmzaton problem s devsed that wll maxmze the throughput of the SSs. Due to the hgh complexty of the lnear programmng soluton, a heurstc algorthm s consdered that provdes close to optmal performance. The heurstc algorthm wll maxmze the throughput of the SSs but s not far whch leads to the desgn of far versons of the algorthm. A defnton of farness s also proposed that requres assgnng bandwdth to a SS proportonal to ts throughput requrement. The bandwdth allocaton among the schedulng servces s done on a prorty bass, smlar to that of the hybrd algorthm proposed n [23]. More specfcally, the BS frst attempts to satsfy the requrements of UGS connectons followed by the requrements of rtps and nrtps connectons. Fnally, any resdual bandwdth s dstrbuted among the BE connectons. Ths mechansm of allocatng bandwdth mght lead to farness among the connectons but can result n starvaton of lower prorty connectons n the presence of a large number of hgh prorty connectons. 31

S.Km and I.Yeom propose an uplnk schedulng algorthm for TCP traffc for the BE class [31]. The proposed algorthm does not requre explct bandwdth request from a SS. It estmates the amount of bandwdth requred by the SS based on the current sendng rate of the connecton at the SS. The purpose of the algorthm s to provde reasonable farness among the SSs based on the max-mn farness crtera whle provdng hgh frame utlzaton. To provde farness, the algorthm requres knowng the demand of each SS. The demand s defned as the amount of bandwdth requested for achevng the maxmum throughput so as not to be lmted by the channel bandwdth. It s shown va smulaton that the algorthm provdes reasonable farness among SSs of the BE class. 2.3 Summary In ths chapter we provde detals of the MAC and PHY layer characterstcs accordng to the specfcatons n the IEEE 802.16-2004 standard [1]. We then categorze and dscuss varous proposals of uplnk schedulng algorthms for WMAX. The homogeneous class of algorthms contans legacy algorthms that were orgnally proposed for wred networks. The algorthms proposed n ths category attempt to satsfy the QoS requrements of the mult-class traffc by assgnng deadlnes to packets or weghts to the SSs. The hybrd class of algorthms contans schemes that bascally combne two or more legacy algorthms. An mportant aspect of hybrd algorthms s the allocaton of bandwdth among the traffc classes, whch can sgnfcantly affect the QoS receved by the SSs. The opportunstc category of algorthm explots varatons n channel qualty as well as attempts to satsfy QoS requrements of the mult-class traffc. 32

Chapter 3. Representatve WMAX uplnk schedulng algorthms In ths chapter, we provde detaled nformaton of the representatve uplnk schedulng algorthms n WMAX. As part of the mplementaton detals, we hghlght any assumptons and mplementaton decsons made n the process. The IEEE 802.16-2004 [1] standard specfes provson of four traffc classes, Unsolcted Grant Servce (UGS), real tme Pollng Servce (rtps), non real tme Pollng Servce (nrtps) and Best Effort (BE). Accordng to the standard, the BS wll provde Data Grant Burst IEs to the SSs at perodc ntervals based upon the Maxmum Sustaned Traffc Rate (MSTR) of the SS. The sze of the grants wll be suffcent enough to hold the fxed length data assocated wth the SS. The IEEE 802.16-2005 standard [6] specfes an addtonal schedulng servce called extended real-tme Pollng Servce (ertps). The ertps s a schedulng servce that bulds on the effcency of both UGS and rtps servces. For SSs belongng to the ertps class, the BS can provde uncast grants n an unsolcted manner lke n UGS, thus savng the latency of a bandwdth request. The SS can also change the sze of the uplnk allocaton by usng the pggyback mechansm or explctly requestng bandwdth. The ertps schedulng servce s desgned to support realtme applcatons that generate varable sze data packets on a perodc bass, such as VoIP wth slence suppresson. Snce the bandwdth allocaton mechansm s specfed for UGS connectons, the mplementaton detals n ths chapter focus on ertps, rtps, nrtps and BE traffc classes only. The standard requres each SS to be assocated wth certan 33

QoS parameters, whose values are specfed by the SS upon admsson nto the network. These parameters are: Mnmum Reserved Traffc Rate (MRTR): Ths parameter specfes the mnmum rate reserved for the SS. The rate s usually expressed n bts per second and specfes the mnmum amount of data to be transported on behalf of the SS when averaged over tme. The MRTR rate wll only be honored when suffcent data s avalable for schedulng. When nsuffcent data exsts, the requrement of ths parameter wll be satsfed by transmttng the avalable data as soon as possble. Maxmum Sustaned Traffc Rate (MSTR): Ths parameter specfes the peak nformaton rate of the SS. The value, expressed n bts per second, does not lmt the nstantaneous rate of the SS but t s used to polce the SS to ensure that t conforms to the value specfed, on average, over tme. Maxmum Latency ( d req ): Ths parameter specfes the maxmum latency between the recepton of a packet by the SS on ts network nterface and the forwardng of the packet to ts RF nterface. Packet Loss (L): Ths parameter, expressed as a percentage, ndcates the percentage of packets dropped from the queue as a result of exceedng the maxmum latency. Packet droppng s performed only for SSs wth real-tme needs as for such SSs delayed packets are useless. The SSs specfy values for all four parameters except the maxmum latency and packet loss, whch are specfed by SSs of ertps and rtps classes only. Followng are varables/functons used n the pseudo-code for the schedulng algorthms: C: the uplnk channel capacty. 34

Ω Total : the set of all admtted SSs Ω ertps : set of all SSs belongng to the ertps class. Ω rtps : set of all SSs belongng to the rtps class Ω nrtps : set of all SSs belongng to the nrtps class. Ω BE : set of all SSs belongng to the BE class. alloc b : bandwdth allocated to SS. deque (P): remove packet P from the queue of SS. enque (P): nsert packet P n the queue of SS. sze (P, γ ): retreve the sze of packet P from the queue of SS. Convert the sze of the packet to number of symbols based on the Sgnal to Interference Nose Rato (SINR ( γ )), of SS. HOL P :Head Of Lne (HOL) packet of SS. CreateIE (sze (P, γ ), ): create an Informaton Element (IE) for SS wth sze (P, γ ) number of symbols. After creaton, the Informaton Element (IE) s added to the ULMAP message. Next (P): Retreve the next packet from the queue of SS. drop (ertps, rtps): drop packets from the queue of all SSs of ertps and rtps class. Due to the open-ended nature of the standard and ambguty of some of the proposals, we have made some mplementaton decsons. To ensure that the number of SSs and ther mnmum requred bandwdth do not exceed the channel capacty, we perform an admsson control calculaton as follows: 35

n = 1 (MRTR n symbols) total uplnk data symbols (3.1) The number of uplnk symbols avalable for data s calculated by subtractng overhead symbols (preamble, bandwdth request symbols and symbols for contenton request opportunty) from the total uplnk capacty. Each SS can have multple connectons, all of them of the same traffc class. The number of connectons per SS wll be vared n the experments so that the load per SS can be changed. Even though a SS can have multple connectons, bandwdth requests wll be granted to a SS and not to each connecton separately.e. Grant Per SS (GPSS) s mplemented. One slot per SS s reserved for bandwdth request and contenton request opportunty. A Tme Dvson Duplex (TDD) frame structure s adopted, where the BS and SS each transmt on the same frequency separated n tme. The IEEE 802.16-2004 standard [1] specfes the use of Informaton Elements n the Uplnk MAP (ULMAP) message. For our purpose, the most mportant components of an IE are the Connecton ID (CID) and the number of symbols allocated to the SS. The lst of IEs consttutes the ULMAP message that s broadcast to all the SSs. In the pseudo-codes that follow, the functon that creates the ULMAP message wll be referred to as CreateIE(). 3.1 Homogeneous Algorthms Ths category contans schedulng algorthms orgnally proposed for wred networks, but have also been wdely adopted by cellular technologes such as GSM, UMTS and WMAX. We have chosen to mplement Weghted Round Robn (WRR), Earlest Deadlne Frst (EDF) and Weghted Far Queung (WFQ) schemes. The three 36

schemes selected satsfy QoS requrements of ther users n dverse ways. The EDF algorthm allocates bandwdth accordng to the delay requrements of the SSs whereas the WRR and WFQ algorthms allocate bandwdth accordng to the weght assgned to the SSs. It s mportant to study schemes wth such dverse behavors so that we can determne whch ones or a combnaton of them are sutable for the mult-class traffc n WMAX. 3.1.1 Weghted Round Robn (WRR) The WRR schedulng algorthm orgnally proposed for ATM traffc n [13] has been mplemented n [12] to evaluate the IEEE 802.16 MAC layer on how effectvely t supports QoS requrements of the mult-class traffc (see Fgure 3-1). The algorthm s executed at the begnnng of every frame at the Base Staton (BS). At the start of a frame, the WRR algorthm determnes the allocaton of bandwdth among the SSs based on ther weghts. A crtcal porton of the WRR scheme s assgnng weghts to each SS. The weghts are assgned to reflect the relatve prorty and QoS requrements of the SSs. Snce MRTR s one of the parameters specfed by a SS that reflect ts QoS requrements, we assgn weght to each SS wth respect to ts MRTR as follows: n W = MRTR MRTR (3.2) j= 1 where, W = weght of SS. n = number of SSs. j 37

1. //Drop packets of ertps and rtps SSs that have mssed ther deadlne 2. drop(ertps, rtps) 3. Assgn weghts to SSs usng (3.2) 4. //Allocate bandwdth accordng to the weght of SSs 5. for Ω Total alloc alloc 6. b = b +W *C 7. end for Stll here you need to check for the capacty 8. //Select packets for transmsson based on bandwdth allocated 9. for Conn do 10. CreateIE() //create IEs based on allocated bandwdth 11. end for Fgure 3-1: Pseudo-code of WRR algorthm 3.1.2 Earlest Deadlne Frst (EDF) Earlest Deadlne Frst (EDF) s one the most wdely used schedulng algorthms for real-tme applcatons as t selects SSs based on ther delay requrements. The algorthm assgns deadlne to arrvng packets of a SS (see Fgure 3-2). Snce each SS specfes a value for the maxmum latency parameter, the arrval tme of a packet s added to the latency to form the tag of the packet. The value of maxmum latency for SSs of the nrtps and BE classes s set to nfnty. In the followng pseudo-code, mn deadlne (P) refers to the packet wth the earlest deadlne. The algorthm below s executed upon arrval of every packet. 38

1. //Drop packets of ertps and rtps SSs that have mssed ther deadlne 2. drop(ertps, rtps) 3. Assgn deadlne upon arrval of a packet. 4. //Assgn bandwdth to the SS wth the packet wth earlest deadlne 5. whle(c>0) alloc alloc 6. b = b + sze (mn deadlne (P), γ ) 7. CreateIE() 8. C = C - sze (mn deadlne (P), γ ) 9. end whle Fgure 3-2: Pseudo-code of EDF algorthm 3.1.3 Weghted Far Queung (WFQ) Both WFQ and WRR schedulng algorthms assgn weghts to SSs. Unlke the WRR algorthm, the WFQ algorthm also consders the packet sze and the channel capacty when allocatng bandwdth to the SSs (see Fgure 3-5). An arrvng packet s tagged wth fnsh tme that s calculated based on the weght of the SS, the packet sze and the uplnk channel capacty. In WFQ, the weght of a SS s calculated n the same way as t s n WRR. Once the weght s assgned, arrvng packets of the SS are stamped wth vrtual fnsh tme as follows: S k k 1 k = max{f, V(a )} (3.3) F k Sk + L k / = Φ (3.4) where, S s the Start tme of k th k packet of SS ; k 1 F s the Fnsh tme of (k-1) th packet of SS ; V ( a k ) s the Vrtual tme of the k th packet of SS ; k a arrval tme of k th packet of SS ; k F s the Fnsh tme of k th packet of SS ; 39

L k s the Length of k th packet of SS ; Φ s the reserved rate of SS, where Φ = C* W ; W s the weght assgned to SS. The complexty of WFQ s hgh due to two man reasons: selecton of the next queue to serve and computaton of the vrtual tme. The complexty of the former s fxed to O (log N) whereas the complexty of the latter s O (N), where N s the number of SSs. We use an approach descrbed n [32] that provdes a practcal mplementaton of WFQ for packet schedulng n IP networks. The transmsson of a packet wll trgger an update to the vrtual tme of ts SS. Snce the schedulng algorthm s mplemented at the BS, the vrtual tme wll be updated once a packet has been selected for transmsson. For a tme nterval τ, the vrtual tme V (t) s updated as follows: where, τ t, j 2,3,... t j j 1 = B j s the set of busy SSs. τ V (t j 1 + τ) = V(t j 1 ) + (3.5) Φ B j Fgures 3-3 and 3-4 descrbe the pseudo-code of the actons that need to be performed upon arrval and selecton of a packet, respectvely. In the followng pseudo code, mn fnshtme (P) refers to the packet wth the smallest fnsh tme. 40

1. //Reset the vrtual and fnsh tme 2. If system dle 3. V(t) = 0 k 1 4. F = 0 5. end f k 6. Calculate Sk and F usng (3.3) and (3.4) 7. f B then 8. B = B + //Add SS to the busy set 9. end f k 10. assgn F to packet k Fgure 3-3: Acton upon arrval of packet k of SS arrve(,k) 1. Update V(t) usng (3.5) 2. CreateIE() 3. f connecton not backlogged 4. B = B //Remove from the busy set 5. end f Fgure 3-4: Acton upon selecton of packet k of SS select (,k) 1. //Drop packets of ertps and rtps SSs that have mssed ther deadlne 2. drop(ertps, rtps) 3. Upon arrval of packet k of SS, 4. arrve(,k) 5. enque (k) 6. //Assgn bandwdth to the SS wth the packet wth earlest fnsh tme 7. whle(c>0) 8. //Allocate bandwdth to SS.e. SS wth the packet wth earlest fnsh tme alloc alloc 9. b = b + sze(mn fnshtme (P), γ ) 10. C = C - sze(mn fnshtme (P), γ ) 11. select(,k) 12. end whle Fgure 3-5: Pseudo-code of WFQ algorthm 41

3.2 Hybrd Algorthms The two hybrd algorthms selected for evaluaton use a dfferent mechansm of overall bandwdth allocaton. An mportant aspect of hybrd algorthms s allocaton of bandwdth among the traffc classes of WMAX. The two algorthms we have selected perform ths task n dfferent ways. The hybrd (EDF+WFQ+FIFO) algorthm uses a strct prorty mechansm for nter-class bandwdth allocaton, whereas the hybrd (EDF+WFQ) algorthm allocates bandwdth among traffc classes based on the number of SSs and ther MRTR n each class. 3.2.1 Hybrd (EDF+WFQ+FIFO) The hybrd algorthm proposed n [23] uses strct prorty mechansm for overall bandwdth allocaton (see Fgure 3-6). The EDF schedulng algorthm s used for SSs of ertps and rtps classes, the WFQ algorthm s used for SSs of nrtps class and FIFO s used for SSs of BE class. The EDF and WFQ algorthms are mplemented as descrbed n sectons 3.1.2 and 3.1.3 respectvely. FIFO s used for BE class as SSs of ths class do not have any QoS requrements. In the followng pseudo-code, queue(conn ertps ), queue(conn rtps ), queue(conn nrtps ) and queue(conn BE ) refer to packet queues of SSs from ertps, rtps, nrtps and BE classes, respectvely. The bandwdth dstrbuton among the traffc classes s executed at the begnnng of every frame whereas the EDF, WFQ and FIFO algorthms are executed at the arrval of every packet. 42

1. //Drop packets of ertps and rtps SSs that have mssed ther deadlne 2. drop(ertps,rtps) 3. Upon arrval of packet k of connecton 4. f( Ω ertps, Ω rtps ) 5. Assgn deadlne to packet k 6. end f 7. f( Ω nrtps ) 8. arrve(,k) 9. end f 10. enque (k) 11. 12. //Execute the EDF algorthm for ertps and rtps SSs 13. for Ω ertps, ΩrtPS 14. whle(c>0 and (queue( Ω ) or queue( ))!= NULL ) ertps Ω rtps 15. b alloc = b alloc + sze (mn deadlne (P), γ ) 16. CreateIE() 17. C = C - sze (mn deadlne (P), γ ) 18. end whle 19. end for 20. 21. //Execute the WFQ algorthm for nrtps SSs 22. for ΩnrtPS 23. whle(c>0 and queue( Ω nrtps )!=NULL) alloc alloc 24. b = b + sze (mn fnshtme (P), γ ) 25. C = C - sze (mn fnshtme (P), γ ) 26. select(,k) 27. end whle 28. end for 29. 30. //Execute the FIFO algorthm for BE SSs 31. whle(c>0 and queue( Ω BE )!=NULL) alloc alloc 32. b = b + deque(p) 33. CreateIE() 34. C = C - sze(p, γ ) 35. end whle Fgure 3-6: Pseudo-code of hybrd (EDF+WFQ+FIFO) algorthm 43

3.2.2 Hybrd (EDF+WFQ) K.Vnay et al. [24] propose a hybrd algorthm that uses the EDF schedulng algorthm for SSs of ertps and rtps classes and WFQ algorthm for SSs of nrtps and BE classes (see Fgure 3-7). Although the mechansm of overall bandwdth dstrbuton s not specfed, t s mentoned n [24] that bandwdth s allocated n a far manner. Just as the hybrd (EDF+WFQ+FIFO) algorthm, the overall bandwdth dstrbuton s executed at the begnnng of every frame whle the EDF and WFQ algorthms are executed at the arrval of every packet. The followng s the overall bandwdth allocaton scheme adopted n our mplementaton: BW BW ertps,rtps nrtps,be n = C * ( MRTR ) /( MRTR ) (3.6) ertps,rtps j= 1 n = C *( MRTR ) /( MRTR ) (3.7) nrtps,be j= 1 j j 44

1. //Drop packets of ertps and rtps SSs that have mssed ther deadlne 2. drop(ertps,rtps) 3. Assgn overall bandwdth usng (3.6) and (3.7) 4. Upon arrval of packet k of SS 5. f( Ω ertps, Ω rtps ) 6. Assgn deadlne to packet k 7. end f 8. f( Ω nrtps, Ω BE ) 9. arrve(,k) 10. end f 11. enque (k) 12. 13. //Execute the EDF algorthm for ertps and rtps SSs 14. for Ω, Ω ertps rtps 15. whle ( BWertPS, rtps >0 and (queue( Ω ertps ) or queue( Ω rtps ))!= NULL) alloc alloc 16. b = b + sze (mn deadlne (P), γ ) 17. CreateIE() 18. BWertPS, rtps = BWertPS, rtps - sze (mn deadlne (P), γ ) 19. end whle 20. end for 21. 22. //Carry-over any bandwdth remanng from executon of EDF (lne 13-19) 23. f( BW ertps, rtps > 0 ) 24. BWnrtPS, BE = BWnrtPS, BE + BWertPS, rtps 25. end f 26. 27. //Execute WFQ algorthm for nrtps and BE SSs 28. for Ω nrtps, Ω BE 29. whle ( BWnrtPS, BE >0 and (queue( Ω nrtps ) or queue( Ω BE ))!= NULL) alloc alloc 30. b = b + sze (mn fnshtme (P), γ ) 31. CreateIE() 32. BWnrtPS, BE = BWnrtPS, BE - sze (mn fnshtme (P), γ ) 33. select(,k) 34. end whle 35. end for Fgure 3-7: Pseudo-code of hybrd (EDF+WFQ) algorthm 45

3.3 Opportunstc Algorthms The two opportunstc algorthms selected for evaluaton use prorty and utlty functons n calculatng the relatve prorty of the SSs. The Queung Theoretc algorthm uses queung theory and sgmod functon n assgnng utlty to the SSs whereas the cross layer algorthm uses delay of HOL packet and average throughput. Both these algorthms use dstngushng mechansms n satsfyng the QoS requrements of the SSs and therefore provde a good representaton of the algorthms n ths category. 3.3.1 Cross-Layer schedulng algorthm The algorthm proposed n [27] uses a prorty functon that ncorporates delay of HOL packet and the mnmum requred throughput of the SSs n ts formulaton. The SS wth the hghest prorty s selected to transmt n the frame (see Fgure 3-8). The prorty of a SS s calculated based on the traffc class t belongs to. Although the prorty functon for SSs of ertps class s not defned n [27], we use the same functon specfed for SSs of rtps class. We have chosen to evaluate ths algorthm as t ncorporates all the requred QoS parameters n the prorty functons. More specfcally, the MRTR and maxmum latency s used n the prorty functon for ertps and rtps SSs and only the MRTR s used n the prorty functon for nrtps SSs. The prorty of BE SSs depends only on the channel qualty of the SS as the BE schedulng servce does not have any QoS requrements. The algorthm s executed at the Base Staton (BS) at the begnnng of every frame whereby prorty s assgned to each SS. Subsequently, the SS wth the hghest prorty s selected for transmsson n the frame. The scheme uses a coeffcent for each class n the prorty functons as shown n the followng equatons: 46

Prorty functon for SSs of ertps/rtps class: R (t) 1 ( βertps, βrtps ) * * f F (t) 1, R (t) 0 R N F (t) φ (t) = ( βertps, βrtps ) f F (t) < 1, R (t) 0 (3.8) 0 f R (t) = 0 req F (t) = d Δd W (t) 1 (3.9) + Prorty functon for SSs of nrtps class: R (t) 1 β nrtps * * f F (t) 1, R (t) 0 R N F (t) φ (t) = β nrtps f F (t) < 1, R (t) 0 (3.10) 0 f R (t) = 0 F (t) = η (t) / η (3.11) Prorty functon for SSs of BE class: R (t) φ ( t) = βbe * (3.12) R N where, ertps φ (t) s the prorty of SS at tme t. β, β, β, β are coeffcents for SSs of ertps, rtps, nrtps and BE classes rtps nrtps BE respectvely such that β ertps, βrtpsβnrtps, βbe [ 0,1] R (t) refers to the amount of data that can be carred by one tme slot based on the channel qualty of the SS. 47

R N refers to the amount of data that can be carred by one tme slot based on the hghest modulaton and codng scheme. F (t) refers to the delay satsfacton ndcator for SSs of ertps and rtps classes and throughput satsfacton ndcator for SSs of nrtps class. req d refers to the delay requrement of SS Δ refers to the guard tme ahead of. d T Δ T [ 0, ] T η (t) refers to the average throughput of SS at tme t. η refers to the Mnmum Reserved Traffc Rate (MRTR) of SS. (t) W W (t) refers to the delay of the Head Of Lne (HOL) packet of SS at tme t, such that [0, T ]. The class coeffcents ( βertps, β rtps, β nrtps, β BE ) can be set to reflect the prorty of the traffc classes. We adopt the same coeffcents as n [27] and normalze them to reflect the relatve prorty of the SSs. Although, coeffcent for SSs of ertps class s not defned n [27], we use a hgher value than coeffcents for the other 3 classes to reflect ther relatve prorty. 48

1. //Drop packets of ertps and rtps SSs that have mssed ther deadlne 2. drop(ertps,rtps) 3. 4. //Assgn prorty to ertps and rtps SSs 5. for Ω ertps, Ω rtps 6. assgn φ(t) accordng to (3.8),(3.9) 7. end for 8. 9. //Assgn prorty to nrtps SSs 10. for Ω nrtps 11. assgn φ(t) accordng to (3.10),(3.11) 12. end for 13. 14. //Assgn prorty to BE SSs 15. for Ω BE 16. assgn φ(t) accordng to (3.12) 17. end for 18. 19. //Select the SS wth the hghest prorty 20. max = max ( φ (t)) 21. 22. //Allocate bandwdth to the SS wth hghest prorty as long as t has backlogged packets 23. whle (C>0 and Next (P)!= φ ) alloc b = alloc b + sze(next (P), γ ) 24. 25. CreateIE() 26. C = C - sze(next (P), γ ) 27. end whle Fgure 3-8: Pseudo-code of Cross Layer algorthm 3.3.2 Queung Theoretc schedulng algorthm Ths uplnk schedulng algorthm [29] uses a queung model to satsfy the QoS requrements of the mult-class traffc. The algorthm uses sgmod functons to assgn utlty to each SS (see Fgure 3-9). The nput to the sgmod functon depends on the traffc class the SS belongs to. The SS wth lowest utlty s gven the hghest transmsson prorty. 49

The proposed resource management model contans a closely coupled schedulng algorthm and a CAC scheme. The focus of our study s to evaluate the performance of the schedulng algorthm only, and therefore the CAC s not mplemented. We have chosen to evaluate ths algorthm as t uses queung theory to satsfy the QoS requrements of the schedulng servces. It also uses thresholds to lmt the bandwdth allocated to SSs of each class. Ths s a unque way of lmtng bandwdth allocaton and ensurng that lower prorty SSs do not starve. The algorthm s executed at the Base Staton (BS) at the begnnng of every frame. The utlty of each SS s calculated at the start of a frame and the bandwdth s allocated accordngly. The utlty functon of a SS s defned as follows: 1 f b 0 U BE (b ) = (3.13) 0 Otherwse U ertps,rtps 1 (b ) = 1 (3.14) req 1+ exp( g (d( γ, λ,b ) d h )) rt rt U nrtps = 1 1+ exp( g ( τ( γ, λ,b ) MRTR h )) (3.15) nrt nrt where, UBE refers to utlty for SSs of BE class. UertPS,rtPS refers to utlty for SSs of ertps and rtps classes respectvely. UnrtPS refers to utlty for SSs of nrtps class. g rt,g nrt are parameters of sgmod functon that determne the steepness(senstvty of the utlty functon to delay or throughput requrement). h rt, h nrt are parameters of the sgmod functon that represent the centre of the utlty functon. 50

d( γ, λ, b ) s the average delay as a functon of SINR( γ ), PDU arrval rate ( λ ) and bandwdth allocated (b). τ γ, λ, b ) s the average throughput as a functon of SINR( γ ), PDU arrval rate ( λ ) and ( bandwdth allocated (b). MRTR s the Mnmum Reserved Traffc Rate of SS. The goal of the scheme s to maxmze the utlty of all the SSs n the network. For ths purpose, an optmzaton problem s formulated. Due to the exponental tme complexty of the optmal approach, the authors mplement the water-fllng algorthm [29]. An mportant part of the algorthm s determnng bandwdth thresholds of each traffc class. An optmzaton approach s dscussed that wll calculate thresholds to maxmze the average system revenue under connecton level QoS constrants such as call blockng probablty. Snce we do not mplement a CAC scheme and therefore call blockng probablty s not a parameter n our system, to be able to compare all the algorthms under the same constrants, we calculate the thresholds as follows: T ertps n ertps MRTR = 1 = *C (3.16) n MRTR j= 1 j T rtps n rtps MRTR = 1 = *C (3.17) n MRTR j= 1 j T nrtps n nrtps MRTR = 1 = *C (3.18) n MRTR j= 1 j 51

T BE n BE MRTR = 1 = *C (3.19) n MRTR j= 1 j where, n j= 1 n ertps = 1 MRTR refers to the sum of MRTR of all the SSs n the network. j n rtps MRTR, MRTR, MRTR, MRTR refers to the sum of MRTR of SSs from = 1 n nrtps = 1 = 1 ertps, rtps, nrtps and BE traffc class, respectvely. n BE 52

1. //Drop packets of ertps and rtps SSs that have mssed ther deadlne 2. drop(ertps,rtps) 3. 4. //Allocate bandwdth to ertps SSs equvalent to ther MRTR 5. for Ω ertps 6. f (C > 0) alloc alloc 7. b = b + MRTR 8. CreateIE() 9. C = C - MRTR 10. end f 11. end for 12. 13. //Allocate bandwdth to rtps SSs equvalent to ther MRTR 14. for Ω rtps 15. f (C > 0) alloc alloc 16. b = b + MRTR 17. CreateIE() 18. C = C - MRTR 19. end f 20. end for 21. 22. //Allocate bandwdth to nrtps SSs equvalent to ther MRTR 23. for Ω nrtps 24. f (C > 0) alloc alloc 25. b = b + MRTR 26. CreateIE() 27. C = C - MRTR 28. end f 29. end for 30. 31. //Allocate bandwdth to BE SSs equvalent to sze of one packet 32. for Ω BE 33. f (C > 0) alloc 34. b = sze (Next (P), γ ) 35. CreateIE() 36. C = C - sze (Next (P), γ ) 37. end f 38. end for 53

40. //Assgn resdual bandwdth accordng to the utlty of the SSs 41. whle(c>0 and Ω Total Empty) 42. Calculate utlty usng (3.13), (3.14), (3.15) 43. = mn(u(b )) //Select connecton wth mnmum utlty alloc alloc 44. b = b + sze (Next (P), γ ) 45. f( b MSTR ) 46. Ω Total = Ω Total 47. end f 48. f( b = TertPS ) Conn 49. Ω Total = Ω Total Ω ertps 50. end f 51. f( b = TrtPS ) Conn 52. Ω Total = Ω Total Ω rtps 53. end f 54. f( b = TnrtPS ) Conn ertps rtps nrtps 55. Ω Total = Ω Total Ω nrtps 56. end f 57. f( b = TBE ) Conn BE 58. Ω Total = Ω Total Ω BE 59. end f 60. end whle Fgure 3-9: Pseudo-code of Queung Theoretc schedulng algorthm 3.4 Complexty Analyss The complexty of legacy algorthms s well known based on comprehensve analyss done n the lterature. The complexty of the WRR algorthm s known to be constant wth respect to the number of SSs.e. O(1) [33]. It has been dscussed n [34] that the complexty of the WFQ algorthm s O(N), where N s the number of SSs. The 54

complexty of the EDF algorthm s also O(N) [35]. The hybrd (EDF+WFQ+FIFO) and hybrd (EDF+WFQ) have a complexty of O(N), just as ther legacy components. The computatonal complexty of the opportunstc algorthms has not been dscussed by ther authors. Based on our analyss of the algorthms, the complexty of the Cross Layer algorthm s O(N). The complexty of the Cross Layer algorthm s domnated by the porton of the code that assgns prorty to the SSs (lnes 1-10 n Fgure 3-8) that loops through all the SSs. The complexty of the Queung Theoretc algorthm s O(N 2 ). Its complexty s domnated by the porton of the algorthm that assgns one unt of bandwdth to the SS wth the mnmum utlty, untl there are no backlogged packets or all the avalable bandwdth has been assgned (lnes 30-50 n Fgure 3-9). Snce the number of teratons of the whle loop (startng at lne 30) at the most can be equvalent to the number of SSs and wthn each teraton utlty s assgned to all the SSs, t results nto a complexty of O(N 2 ). Table 3-1 lsts the schedulng algorthms n ncreasng order of ther complexty, where N s the number of SSs. Table 3-1: Complexty of representatve uplnk schedulng algorthms Algorthm Complexty WRR EDF WFQ Cross Layer Hybrd (EDF+WFQ) Hybrd (EDF+WFQ+FIFO) O(1) O(N) O(N) O(N) O(N) O(N) Queung Theoretc O(N 2 ) 55

3.5 Summary In ths chapter we descrbed mplementaton detals of the schedulng algorthms consdered for evaluaton. The algorthms n each category have been chosen based on how effectvely they demonstrate characterstcs of the respectve category. We also made some mplementaton decsons n the process. These nclude a common CAC algorthm, allowng multple connectons per SS and adopton of TDD frame structure. In chapter 4, we wll analyze the performance of the schedulng algorthms wth respect to the characterstcs of the IEEE 802.16 MAC layer. 56

Chapter 4. Performance Analyss In ths chapter we study the performance of the schedulng algorthms dscussed n Chapter 3 under dfferent condtons. These condtons nclude studyng the performance of the algorthms under varous concentratons of traffc and under the characterstcs of the IEEE 802.16 MAC layer such as uplnk burst preamble, frame length and bandwdth request mechansms. The smulaton tool chosen for the experments s Berkeley s Network Smulator 2 (NS-2) [36] wth an add-on developed by members of Network and Dstrbuted Systems Laboratory at Chang Gung Unversty n Tawan [37]. Numerous modfcatons to the NS-2 extenson for WMAX were made. We wll provde a detaled descrpton of the changes made to the tool, ncludng the traffc model, transmsson modes and choce of MAC layer parameters such as length of uplnk preamble and allocaton start tme. We wll also dscuss the metrcs used to evaluate the schemes. The experments are run on a Lnux PC wth a 2 GHz Intel Core Duo processor and Random Access Memory (RAM) of 2 Gga bytes. The verson of Lnux nstalled on ths PC s Ubuntu. Each experment takes approxmately 10 mnutes to complete executon.e. a smulaton tme of 50 seconds corresponds to 10 mnutes n real-tme. The executon tme vares dependng on the number of SSs and the traffc load used n the experment. 4.1 NS-2 and WMAX The NS-2 extenson for WMAX PMP mode [37], verson 1.06, mplements the Convergence Sub layer (CS), the MAC Common Part Sub layer (CPS) and the PHY layer. The module mplements functonaltes such as rangng, MAC Management, 57

Scheduler, IP-SFID mappng and SFID-TCID mappng. MAC management contans messages such as Uplnk Channel Descrptor (UCD), Downlnk Channel Descrptor (DCD), Bandwdth Request (BW-Req) message and Uplnk MAP (UL-MAP) message and Downlnk MAP (DL-MAP) message. IP-Servce Flow ID (IP-SFID) mappng s used to record the characterstcs of the packets comng from the upper layers whle Servce Flow ID-Transport Connecton ID (SFID-TCID) mappng s used to map the QoS characterstcs of the SSs to one of the four traffc classes (ertps, rtps, nrtps and BE). Our modfcatons to the extenson nclude changes to the uplnk scheduler, support for OFDM, addtonal parameters assocated wth a SS such as maxmum latency, packet loss, MRTR and MSTR. MAC layer parameters such as allocaton start tme and uplnk burst preamble were added to the tool and ther values set accordng to the IEEE 802.16-2004 standard [1]. Our major contrbuton to the NS-2 extenson for WMAX s the addton of seven representatve uplnk schedulng algorthms from the three categores dscussed n chapter 3. An mportant modfcaton to the extenson was to change the bandwdth management functon so that the lst of Informaton Elements (IEs) n the ULMAP message s created accordng to the transmsson order determned by the schedulng algorthm. A traffc model was also added to the extenson. Ths model mplements VoIP traffc for the ertps class, vdeo streamng traffc for the rtps class, FTP traffc for the nrtps class and HTTP traffc for the BE class. Ths traffc model s representatve of the traffc characterstcs of the schedulng classes as specfed n the IEEE 802.16-2004 standard [3]. Detals of the traffc model are dscussed later n the chapter. 58

The wreless channel s modeled usng a block-fadng model, whch s sutable for slow varyng channel condtons as n WMAX PMP mode. The channel qualty of each SS remans constant per frame, but s allowed to vary from frame to frame based on the transmsson modes defned n Table 4-1. Therefore, Adaptve modulaton and Codng (AMC) s mplemented based on sx transmsson modes as descrbed n the IEEE 802.16-2004 standard [1]. The channel qualty s captured usng a sngle parameter, the nstantaneous Sgnal to Nose Rato (SNR), whch remans constant for the duraton of the frame. Each packet, upon arrval, s tagged wth a key and a deadlne. Packets are nserted n the queue of the SS n ncreasng order of the key. To enable ths, a prorty queue class was mplemented that would allow us to nsert packets n order of the key. Addtonally to collect statstcs for analyss, we store the average throughput, average delay and packet loss for each SS. 4.2 Smulaton Model 4.2.1 Transmsson Modes We use sx transmsson modes n our mplementaton whose values are defned n Table 4-1. The raw bt rate vares dependng on the modulaton technque and codng rate used. These values are n conformance wth the IEEE 802.16-2004 standard for channel bandwdth of 20MHz. 59

Table 4-1: IEEE 802.16-2004 Transmsson Modes Mode 1 2 3 4 5 6 Modulaton QPSK QPSK 16QAM 16QAM 64QAM 64QAM Codng rate 1/2 3/4 1/2 ¾ 2/3 3/4 Raw Bt Rate (Mbts/sec) 15.36 23.04 30.72 46.08 61.44 69.12 4.2.2 Traffc Model We have mplemented four dfferent traffc sources, one for each of the traffc classes. VoIP traffc s modeled for SSs of ertps class, vdeo streamng for SSs of rtps class, FTP for SSs of nrtps class and HTTP for SSs of BE class. The values of all the traffc parameters are based on one connecton per SS. VoIP Traffc ertps class (Class 2) An mportant characterstc of VoIP traffc s the presence of talk spurt and slence spurt. The length of the talk spurt and slence spurt depends on the encodng scheme used. There are numerous encodng schemes such as G.711, G.722, and Adaptve Mult-Rate (AMR) that result n dfferent bandwdth requrements. We have used the model descrbed n [38] that assumes the AMR codec and a packet sze of 23 bytes. To sut our smulaton needs, we have modfed the model and added some parameters assocated wth a connecton as specfed n the IEEE 802.16-2004 standard. 60

Parameter Table 4-2: VoIP traffc parameters Value (1 connecton per SS) Mnmum Reserved Traffc Rate (MRTR) Average Traffc rate Maxmum Sustaned Traffc Rate (MSTR) Maxmum Latency 25 Kbps 44 Kbps 64 Kbps 100ms Tolerated packet loss 10% Talk spurt length Slence length Exponental random wth μ =147ms Exponental random wth μ =167ms Vdeo Streamng rtps class (Class 3) The values of a traffc source modeled for vdeo streamng hghly depend on the vdeo trace. Based on the dscussons n [38] and [39], vdeo streamng has been dvded nto two broad categores, low qualty (64-500Kbps) and hgh qualty (1.5-10Mbps). We mplement the low qualty vdeo streamng model wth packet sze unformly dstrbuted between 150 bytes and 300 bytes. Parameter Table 4-3: Vdeo Streamng parameters Value (1 connecton per SS) Mnmum Reserved Traffc Rate (MRTR) Average traffc rate Maxmum Sustaned Traffc Rate (MSTR) Maxmum Latency 64 Kbps 282 Kbps 500 Kbps 150ms Tolerated packet loss 5% 61

FTP nrtps class (Class 4) and HTTP BE class (Class5) We have mplemented an FTP traffc generator wth a constant packet sze of 150 bytes. A value of 45 Kbps for Mnmum Reserved Traffc Rate (MRTR) and 500Kbps for Maxmum Sustaned Traffc Rate s used for each FTP source. An HTTP traffc model s used for the BE class. A value of 64 Kbps for MSTR and a packet sze of 100 bytes are adopted n the mode. Although SSs of the BE class do not have MRTR parameter assocated wth them, snce mplementaton of schemes such as WRR and WFQ requre a weght to be assgned to the SSs based on the MRTR, a value of 1 Kbps s used for MRTR. 4.2.3 Smulaton Parameters Table 4-4 lsts parameters that are constant throughout the smulaton study whereas table 4-5 lsts parameters whose values are vared n the experments to study the performance of the schedulng algorthms. Accordng to the IEEE 802.16-2004 standard [1], the allocaton start tme for WrelessMAN-OFDM PHY layer can ether be the start of the uplnk sub-frame n the current frame or start of the uplnk sub-frame n the next frame. The allocaton start tme s the reference pont for the nformaton n the UL-MAP message. In our experments, the value for allocaton start tme s set such that all the allocaton n the UL-MAP wll start n the current frame after the last specfed allocaton n the DL-MAP. Ths pont n the frame s referred to as Adaptve Tme Dvson Duplexng (ATDD) splt. The default values as specfed n NS-2 are used for PHY layer parameters such as rado propagaton model and antenna type. 62

Parameter Physcal Layer Uplnk burst preamble Allocaton Start Tme Frame structure Bandwdth Table 4-4: Fxed Smulaton parameters Value WrelessMAN-OFDM 16 symbols ATDD splt TDD DL:UL frame rato 1:1 OFDM symbol duraton 20MHz 12.5μ s Node placement Smulaton grd sze Smulaton tme Random 1000mx1000m 50 seconds Table 4-5: Varable Smulaton parameters Parameter Value Number of SSs 1-36 Rato of SS (ertps:rtps:nrtps:be) 1:1:1:3, 1:1:2:2, 1:1:3:1, 1:2:2:1, 1:3:1:1, 2:2:1:1, 3:1:1:1 Frame Length 2.5ms,4ms,5ms,8ms,10ms,12ms,20ms 4.2.4 Performance Metrcs The followng statstcs are collected for each smulaton run: ^ Average Throughput ( τ ): The amount of data selected for transmsson by a user per unt tme. The value s expressed n Kbps and calculated usng an exponental movng average as follows: ^ ^ t = α * ( τ t ) + (1 α) τ t 1 τ 63

^ where, τ and τt 1 are the average throughput at frame t and t-1 respectvely. t ^ τt s the attanable rate at frame t. Ths value corresponds to the raw bt rate based on the channel qualty and thus the modulaton and codng scheme as descrbed n Table 4-1. A value of 0.001 for α as used n [27] s adopted for all our experments wth a wndow sze of 1000ms. Ths metrc wll allow us to understand the effect of preamble overhead and the relatve prorty gven to the SSs. Average Queung delay ( d): The tme between the arrval of a packet n the queue to the departure of the packet from the queue. The value s reported n mllseconds (ms) and s calculated for each SS as follows: ^ ^ d = N = 1 (f N a ) where, ^ d s the average queung delay. f s the tme packet leaves the queue. s the arrval tme of packet n the queue. a N s the number of packets. Packet Loss ( ρ ): The percentage of packets dropped from the queue out of all the packets that arrved n the queue. The metrc ndcates the percentage of packets that mssed ther deadlnes and s calculated as follows: ρ = m = 1 n j= 1 ω κ j 64

where, m = 1 n j= 1 ω κ j s the sum of packets dropped. s the sum of packets arrved n the queue. Both average delay and packet loss wll allow us to determne how effectvely a schedulng algorthm satsfes the QoS requrements of real-tme SSs. Frame Utlzaton: The number of symbols utlzed for data out all the symbols n the uplnk sub-frame. The metrc reported as a percentage s calculated as follows: where, F n = 1 utl = C ϖ 100% s the number of data symbols allocated to a SS ϖ C s the total number of symbols n the uplnk sub-frame. n s the number of connectons. Ths metrc wll allow us to determne how effectvely the schedulng algorthm utlzes the frame. Farness Index: Farness s measured between users of the same traffc class (ntra-class farness) and as an overall measure, between all the users (nter-class farness). We wll use Jan s farness ndex [39] to calculate nter-class farness and Mn-Max farness ndex to calculate ntra-class farness. Due to the hgh smlarty of legacy schedulng algorthms wth respect to ntra-class farness, we use Mn-Max ndex as t s more senstve to servce degradaton and servce unfarness [40]. The farness ndces are defned as follows: 65

Jan s farness ndex = n * n = 1 n = 1 x (x 2 ) 2 Mn-Max farness ndex = x x mn max To calculate nter-class farness usng Jan s ndex, we use normalzed average throughput for x. The average throughput of a SS s normalzed wth respect to the MRTR of the SS.e. ^ τ x =. Mn-Max farness calculates farness between the SS MRTR wth the maxmum average throughput ( average throughput ( x mn ) n the class. x max ) n the class and the SS wth the mnmum Honoured Requests: To evaluate the schedulng algorthms wth respect to varous bandwdth request mechansms, we calculate the percentage of successful requests out of all the requests made by the SS. Ths metrc wll be referred to as percentage of honoured requests n the dscusson. 4.3 Smulaton Results In ths secton, we study the performance of the schedulng algorthms under the context of IEEE 802.16-2004 MAC layer. More specfcally, the effect of preamble symbols, frame length and bandwdth request mechansms on the schedulng algorthms s studed. The experments are executed under dfferent network condtons such as lght/heavy load and number of SSs n the network. Except for the bandwdth request analyss experment, one slot per SS s reserved for bandwdth request and contenton 66

request opportuntes. In all the experments 95% confdence levels are mantaned wth 5% confdence ntervals based on 10 ndependent runs [41]. 4.3.1 The effect of SS rato The objectve of ths experment s to study the performance of the schedulng algorthms under dfferent mxes of traffc. The experment s conducted wth a total traffc arrval rate of 4850 Kbps, of whch 350Kbps s suppled by the ertps class, 2200 Kbps s suppled by the rtps class, 2200 Kbps s suppled by the nrtps class and 100 Kbps s suppled by the BE class. We use a value of 15Kbps for the MRTR of ertps SSs for ths experment. The traffc arrval rate s calculated based on the number of symbols avalable n the uplnk sub-frame after subtractng the preamble symbols, bandwdth request and contenton request symbols. Each SS conssts of one connecton. Ths s determned based on the smple CAC algorthm as descrbed n chapter 3. Table 4-6: The effect of SS Rato Parameters Parameter Value Number of SSs 36 Rato of SS (ertps:rtps:nrtps:be) 1:1:1:3, 1:1:2:2, 1:1:3:1, 1:2:2:1, 1:3:1:1, 2:2:1:1, 3:1:1:1 Frame Length 20 ms 67

Average Throughput per SS (ertps) Average Throughput - Kbps 70 60 50 40 30 20 10 0 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Rato of SS (a) Average Throughput - ertps Average Throughput per SS (rtps) Average Throughput - Kbps 450 400 350 300 250 200 150 100 50 0 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (b) Average Throughput - rtps Average Throughput per SS (nrtps) Average Throughput - Kbps 450 400 350 300 250 200 150 100 50 0 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (c) Average Throughput - nrtps 68

Average Throughput per SS (BE) Average Throughput - Kbps 25 20 15 10 5 0 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (d) Average Throughput - BE Fgure 4-1: The effect of SS Rato Average Throughput In general, the average throughput of SSs of a class decreases wth ncreased concentraton of SSs of that class (see Fgure 4-1). Ths s due to the total provsonng per class beng constant and wth more SSs, the load per SS decreases. The cross layer algorthm results n low average throughput of all the SSs. Ths behavour s due to the algorthm selectng only one SS n a frame. The algorthm results n a hgher average throughput of ertps SSs than SSs of other classes. Due to the tght delay bound of ertps SSs, they tend to get selected by the algorthm most of the tme. Ths s an expected behavour of the cross layer algorthm whereby the lower prorty SSs wll starve n the presence of large number of hgher prorty SSs [27]. The WRR algorthm ndcates lower average throughput of SSs of the ertps class compared to other legacy algorthms when the concentraton of the SSs n the class s low. Ths s due to lower weght assgned to the SSs. The WFQ algorthm also assgns weghts to the SSs, but snce t allocates bandwdth accordng to the requrements, t results n hgher average throughput. When the ratos of SSs are 1:1:3:1, 1:2:2:1 and 1:3:1:1, the resdual capacty shared by actve SSs s based on ther weght, whch s low. Ths results n both WRR and WFQ 69

algorthms ndcatng low average throughput of ertps SSs, snce the dfference between MRTR and MSTR s also large. The WRR algorthm also ndcates poor performance when the packet sze of the traffc s large. Ths behavour s ndcated by the low average throughput of rtps and nrtps SSs, even under hgh concentraton of rtps and nrtps SSs. When the concentraton of SSs of the nrtps class s the hghest (1:1:3:1), the hybrd (EDF+WFQ) algorthm ndcates lower average throughput for SSs of the ertps class. Due to hgh concentraton of nrtps SSs, the overall bandwdth allocaton mechansm wll allocate a small amount of resdual bandwdth to ertps and rtps classes. Both ertps and rtps SSs wll compete for the small amount of bandwdth. Snce the EDF algorthm schedules SSs based on ther delay requrements only, the average throughput wll be low. Ths wll also reflect a low average throughput of rtps SSs when the rato s 1:1:3:1. As well, due to the hgh MSTR of nrtps SSs, they wll consume more bandwdth before reachng the lmt (MSTR). When the concentraton of nrtps SSs s hgh (1:1:3:1, 1:2:2:1), the Queung Theoretc algorthm ndcates lower average throughput for the ertps and rtps classes. Ths behavour s due to a lower resdual bandwdth assgned to the ertps and rtps classes. The average throughput of nrtps SSs under the Queung Theoretc algorthm s low when the rato s 1:1:3:1 because of lower load per nrtps SSs and hgher average delay of ertps and rtps SSs that results n a lower utlty assgned to them. The Queung Theoretc algorthm also ndcates a hgher average throughput for the rtps class when the concentraton of BE and ertps SSs s the hghest (1:1:1:3 and 3:1:1:1). Ths behavour s due to the lower MRTR of BE and ertps SSs that results n a hgher threshold assgned to the rtps class. The EDF algorthm ndcates a lower average throughput for the nrtps 70

class when the concentraton of ertps or rtps SSs s the hghest snce the algorthm provdes strct prorty to SSs wth delay requrements (ertps and rtps SSs). Although the hybrd (EDF+WFQ+FIFO) algorthm also provdes strct prorty to ertps and rtps SSs, t results n a hgher average throughput for the nrtps class than the EDF algorthm. Ths behavour s due to the hybrd (EDF+WFQ+FIFO) algorthm provdng strct prorty to nrtps SSs over BE SSs. On the other hand, under the EDF algorthm, both nrtps and BE SSs wll compete for bandwdth once ertps and rtps SSs don t have any data to send. All the schedulng algorthms, except for hybrd (EDF+WFQ+FIFO), WRR and cross layer algorthms, satsfy the MRTR (1Kbps) of SSs of the BE class. The WRR schedulng algorthm starves the SSs of the BE class due to the large number of SSs of the other three classes (ertps, rtps and nrtps) and the large packet sze of BE traffc (100 bytes). The small amount of bandwdth that s allocated to the SSs of the BE class s not enough to transmt one packet and t s therefore wasted. The hybrd (EDF+WFQ+FIFO) algorthm also results n starvaton of SSs of the BE class due to the strct prorty nature of the algorthm. The Queung Theoretc algorthm ndcates the hghest average throughput for BE SSs snce the mnmum bandwdth allocated to BE SSs s equvalent to one packet sze (100 bytes). Due to the large packet sze of BE traffc, ther average throughput s hgher than that provded by the other algorthms. 71

Average Delay per SS (ertps) 120 Average Delay (ms) 100 80 60 40 20 0 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Rato of SS (a) Average Delay - ertps Average Delay per SS (rtps) 160 Average Delay (ms) 140 120 100 80 60 40 20 0 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Rato of SS (b) Average Delay - rtps Fgure 4-2: The effect of SS Rato Average delay Packet Loss per SS (ertps) Packet Loss (%) 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (a) Packet Loss - ertps 72

Packet Loss per SS (rtps) Packet Loss (%) 120% 100% 80% 60% 40% 20% 0% 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (b) Packet Loss - rtps Fgure 4-3: The effect of SS Rato - Packet loss The WRR algorthm ndcates very hgh average delay for the ertps class except when the concentraton of ertps SSs s the hghest (see Fgure 4-2). Wth a hgh concentraton of ertps SSs, the weght assgned to them s hgh resultng n more bandwdth allocated to the SSs. The Queung Theoretc algorthm ndcates a hgh average delay for the ertps SSs when ther concentraton s low. Ths behavour s due to a low threshold assgned for the ertps class. The EDF and WFQ algorthms ndcate smlar average delay for ertps SSs except when the concentraton of nrtps SSs s hgh. WFQ schedules SSs by ensurng they receve at least bandwdth equvalent to ther MRTR. Due to the large number of nrtps SSs, the bandwdth allocated to ertps SSs wll only be enough to satsfy ts MRTR, but not enough to keep the average delay low. The hybrd (EDF+WFQ) algorthm ndcates a hgh average delay for the ertps class when the ratos are 1:1:2:2, 1:1:3:1 and 1:2:2:1. Ths behavour s due to the overall bandwdth allocaton mechansm of the algorthm that allocates a small amount of bandwdth for the ertps and rtps classes. The algorthm ndcates a hgh average delay for ertps SSs even when ther concentraton s hgh as a result of a larger number of ertps SSs sharng the 73

bandwdth wth the rtps SSs. Due to the hgh load of rtps SSs, a large number of vdeo packets wll arrve before a VoIP packet arrves. Ths wll result, n numerous cases, n a lower deadlne assgned to vdeo packets, even though they have a hgher maxmum latency. The average delay of rtps SSs, n most cases, under the EDF, WFQ and hybrd (EDF+WFQ+FIFO) algorthms, s approxmately 10ms. The value of 10ms corresponds to the allocaton start tme, whch s the tme the allocaton accordng to the UL-MAP message wll start. Snce the EDF and hybrd (EDF+WFQ+FIFO) algorthms provde hgh prorty to rtps SSs, all the data of rtps SSs wll be flushed out n a frame. Due to the hgh MRTR of rtps SSs (64 Kbps), the weght assgned to them by the WFQ algorthm wll also be hgh. The WRR algorthm ndcates a very hgh average delay of rtps SSs manly due to the large packet sze of vdeo traffc (150-300 bytes). If the symbols assgned to the rtps SSs are not enough to transmt a packet due to ts large sze, the packet wll spend a longer tme n the queue that wll ncrease the average delay and even packet loss. The Queung Theoretc algorthm results n a hgh average delay of the rtps class when the ratos are 1:1:3:1, 1:2:2:1, 1:3:1:1 and 2:2:1:1. In the algorthm, all the SSs are allocated ther MRTR ntally. The resdual bandwdth s allocated by usng a water fllng mechansm by allocatng bandwdth equvalent to a PDU sze to the SS wth the lowest utlty. Therefore, some of the ertps and rtps SSs wll not be allocated bandwdth more than ther MRTR due to competton from other ertps and rtps SSs. Ths wll result n packets spendng a longer tme n the queue, thus ncreasng the average delay. The ncrease n average delay of SSs results n an ncrease n packet loss, although the relatonshp between average delay and packet loss s not as explct.e. 74

when a large number of packets are dropped from the queue t may result n a decrease n the average delay (see Fgure 4-3). Ths s because the average delay does not nclude the delay of dropped packets. For nstance, when the rato s 1:3:1:1, the WFQ algorthm has smlar average delay as the EDF algorthm, but results n hgher packet loss. Intra-class Farness (ertps) - Mn-Max Index 1.20 Farness Index 1.00 0.80 0.60 0.40 0.20 0.00 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (a) Intra-class farness - ertps Intra-class Farness (rtps) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (b) Intra-class farness - rtps 75

Intra-class Farness (nrtps) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (c) Intra-class farness - nrtps Intra-class Farness (BE) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc (d) Intra-class farness - BE Fgure 4-4: The effect of SS Rato: Intra-class Farness Mn-max Index Inter-class Farness - Jan's Index 1.20 Farness Index 1.00 0.80 0.60 0.40 0.20 0.00 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 Rato of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Fgure 4-5: The effect of SS Rato: Inter-class Farness Jan s Index 76

The Mn-max ndex wll be used to calculate ntra-class farness due to ts hgh senstvty towards servce unfarness and degradaton, snce we assume that SSs from the same class should be treated equally. Thus, fndng the rato of the mnmum average throughput to the maxmum average throughput s an nformatve ndcator of unfarness. Results of ntra-class farness based on Jan s ndex are provded n Appendx A. When the concentraton of SSs of the nrtps class s hgh (1:1:3:1 and 1:2:2:1), the farness among SSs of the ertps class under the WFQ algorthm s the lowest (see Fgure 4-4). WFQ allocates bandwdth to the SSs based on ther MRTR. However, any addtonal avalable bandwdth s shared among actve SSs based on ther weghts. The weght of the ertps SSs s low due to ther low concentraton and low MRTR. Thus, based on the actve SSs, packet fnsh tmes and resdual bandwdth, some SSs may be allocated bandwdth close to ther MSTR whle others wll be allocated bandwdth close to ther MRTR. A smlar behavour s notced among SSs under the Queung Theoretc algorthm. However, the dfference between the mnmum and maxmum average throughput s smaller due to the fact that the algorthm allocates the resdual capacty on a unt of PDU n a round robn fashon. The low farness can also be attrbuted to large fnsh tmes assgned to the VoIP packets due to the nature of VoIP traffc. Ths defcency of the WFQ algorthm has also been dscussed n [42] and s further emphaszed when studyng the effect of uplnk burst preamble. The cross layer algorthm ndcates relatvely low ntra-class farness for all the SSs (except BE SSs). Ths behavour s due to the algorthm allocatng bandwdth to only one SS n a frame, resultng n a large dfference between the mnmum and maxmum average throughput n the class. The ntra-class farness of the BE class s hgh snce all 77

the BE SSs get allocated very lttle bandwdth. Ths wll result n a small dfference between the mnmum and maxmum average throughput n the class. The Queung Theoretc algorthm ndcates low ntra-class farness among SSs of all the classes (except the BE class) when the concentraton of nrtps SSs s hgh (ratos 1:1:3:1 and 1:2:2:1). The ntra-class farness of ertps and rtps classes s low because of the low resdual bandwdth and the allocaton mechansm as dscussed prevously. The ntra-class farness of the nrtps class s low due to the hgh average delay of ertps and rtps SSs. The hgh average delay of ertps and rtps SSs results n a lower utlty assgned to them compared to the utlty assgned to nrtps SSs. When the ratos are 2:2:1:1 and 3:1:1:1, the ntra-class farness for the ertps class s low. Ths behavour s due to the large number of ertps SSs competng for bandwdth, resultng n a larger dfference n mnmum and maxmum average throughput. When the concentraton of BE SSs s low, the ntra-class farness of the nrtps class s low under the hybrd (EDF+WFQ+FIFO) algorthm. Ths behavour s due to the strct prorty of ertps and rtps SSs and that a larger number of nrtps SSs compete for a small amount of resdual bandwdth. The hybrd (EDF+WFQ) algorthm ndcates a low ntra-class farness for the BE class when the concentraton of nrtps or BE class s low. Ths behavor s due to the competton of BE and nrtps SS for the small amount of bandwdth allocated to them as a result of the overall bandwdth allocaton mechansm of the algorthm. The EDF algorthm shows a hgher nter-class farness when the concentraton of SSs of the BE class s hgh but the farness decreases wth ncreased concentraton of SSs of the ertps, rtps and nrtps classes (see Fgure 4-5). Wth large number of SSs of the 78

nrtps class, the ertps and rtps SSs wll be allocated large amount of bandwdth whereas the nrtps SSs wll compete wth BE SSs for bandwdth. Ths wll result n large dfference n bandwdth allocated between the dfferent classes. When the ratos are 1:3:1:1, 2:2:1:1 and 3:1:1:1, the EDF algorthm shows low nter-class farness because of the large number of ertps and rtps SSs recevng majorty of the bandwdth. The hybrd (EDF+WFQ+FIFO) algorthm ndcates a hgh nter-class farness even when the concentraton of ertps and rtps SSs s hgh. Ths behavour of the algorthm s because t provdes strct prorty to nrtps SSs over BE SSs. Snce the nter-class farness s calculated usng average throughput normalzed wth respect to MRTR of the SSs, the WRR algorthm wll ndcate hgh nter-class farness. Ths s because the WRR algorthm assgns weght to the SSs accordng to ther MRTR and serves all the classes n rounds. The Queung Theoretc algorthm ndcates low nter-class farness except when the concentraton of BE SSs s hgh. Ths s because the utlty functon of the Queung Theoretc algorthm s based on the average delay for rtps and ertps SSs and the average throughput for nrtps SSs. We calculate the nter-class farness based on the average throughput. However, the utlty functon for rtps SSs does not take the average throughput nto consderaton whch s an mportant QoS parameter for the rtps class, but not so mportant for the ertps class. Therefore, the unfarness of rtps SSs due to the average throughput s not detected by the utlty functon, although the purpose of the utlty functon s to provde farness. 4.3.2 The effect of uplnk burst preamble Accordng to the IEEE 802.16-2004 standard [1], each uplnk burst s assocated wth a preamble whose length s defned n the Uplnk Channel Descrptor (UCD) 79

message. The length of the preamble can be ether 16 symbols or 32 symbols. In our experments, we use 16 symbols for uplnk preamble. The purpose of the uplnk burst preamble s to allow the BS to synchronze to each SS as to when they wll begn to transmt a burst of data. Ths can represent a sgnfcant overhead when the number of SS s large, as we wll observe from the results of ths experment. We wll study the effect of the preamble by ncreasng the number of SSs. 4.3.2.1 Effect of uplnk burst preamble on frame utlzaton In ths experment, we wll study the behavor of the algorthms wth respect to frame utlzaton when the number of SSs s ncreased. To be able to dstngush between the algorthms, a large amount of traffc was generated. Snce VoIP and BE traffc have relatvely low rates, we used Vdeo (rtps) and FTP (nrtps) traffc only. The experment was conducted under lght load of 4Mbps and a heavy load of 8Mbps. Table 4-7 lsts the parameters used for the experment. Table 4-7: The effect of uplnk burst preamble Parameters (frame utlzaton) Parameter Value Number of SSs 4-20 Rato of SS (rtps:nrtps) 1:1 Frame Length 10 ms 80

Frame Utlzaton Frame Utlzaton 40.00% 35.00% 30.00% 25.00% 20.00% 15.00% 10.00% 5.00% 0.00% 4 8 12 16 20 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Frame utlzaton under lght load Frame Utlzaton Frame Utlzaton 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% 4 8 12 16 20 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Frame utlzaton under heavy load Fgure 4-6: The effect of uplnk burst preamble Frame Utlzaton Under lght load, as the number of SSs ncreases, ncrease n frame utlzaton s ndcated by all the algorthms except the cross layer algorthm (see Fgure 4-6). Ths behavor s observed untl the number of SSs s eght. Wth more than twelve SSs, the frame utlzaton starts to decrease due to the ncreased overhead of the uplnk burst preamble. The declne n the frame utlzaton s more severe for the Queung Theoretc and WRR algorthms as these algorthms tend to select the maxmum number of SSs n a frame, thus resultng n maxmum overhead. 81

The cross layer algorthm results n the lowest frame utlzaton regardless of the load. Ths s because the algorthm selects only one SS per frame. Under heavy load, the cross layer algorthm stll provdes a stable, although hgher (~28%) frame utlzaton, compared to that under lght load (~14%). As the number of SSs ncrease, the frame utlzaton decreases due to the ncreased overhead of uplnk burst preamble. When the number of SSs s large (greater than 16), the cross layer algorthm ndcates a hgher frame utlzaton than WRR and Queung Theoretc algorthms. Due to the heavy load, the sngle user selected by the cross layer algorthm occupes a sgnfcant porton of the frame whereas n the WRR and Queung Theoretc algorthms a large porton of the frame s wasted by uplnk burst preambles. The hybrd (EDF+WFQ) algorthm ndcates lower frame utlzaton than other legacy algorthms for a large number of SSs. Ths s because the algorthm allocates bandwdth to each traffc class accordng to the MRTR of the SSs n that class. The bandwdth assgned to a class can reman unused f SSs of that class don t have any data to send, resultng n lower frame utlzaton. 4.3.2.2 The effect of uplnk burst preamble on user performance and farness In ths experment, we wll study the effect of uplnk burst preamble on the schedulng algorthms wth respect to average throughput, average delay, packet loss and farness. We wll study the performance of the algorthms both under lght and a heavy load. We use MRTR of 10Kbps for ertps SSs as t allows us to choose approprate values for the parameters. A lght load of 3400 Kbps s suppled wth 500 Kbps reserved for ertps class, 1500 Kbps reserved for rtps class, 1250 Kbps reserved for nrtps class and 150 Kbps reserved for BE class. A heavy load of 6800 Kbps s suppled wth 1000 Kbps 82

reserved for ertps class, 3000 Kbps reserved for rtps class, 2500 Kbps reserved for nrtps class and 300 Kbps reserved for BE class. The remanng parameters for the experment are lsted n Table 4-8. Table 4-8: The effect of uplnk burst preamble Parameters Parameter Value Number of SSs 6-36 Rato of SS (ertps:rtps:nrtps:be) 3:1:1:1 Frame Length 20 ms Lght load: Average Throughput per SS (ertps) Average Throughput - Kbps 350 300 250 200 150 100 50 0 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc Num be r of SS (a) Average Throughput - ertps Average Throughput per SS (rtps) Average Throughput - Kbps 1800 1600 1400 1200 1000 800 600 400 200 0 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Average Throughput - rtps 83

Average Throughput per SS (nrtps) Average Throughput - Kbps 1600 1400 1200 1000 800 600 400 200 0 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (c) Average Throughput - nrtps Average Throughput per SS (BE) Average Throughput - Kbps 200 180 160 140 120 100 80 60 40 20 0 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc Num ber of SS (d) Average Throughput - BE Fgure 4-7: The effect of uplnk burst preamble Average throughput (Lght load) Average Delay per SS (ertps) Average Delay (ms) 100 90 80 70 60 50 40 30 20 10 0 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Average Delay - ertps 84

Average Delay per SS (rtps) Average Delay (ms) 160 140 120 100 80 60 40 20 0 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Average Delay - rtps Fgure 4-8: The effect of uplnk burst preamble Average delay (lght load) Packet Loss per SS (ertps) Packets Dropped (%) 80% 70% 60% 50% 40% 30% 20% 10% 0% 6 12 18 24 30 36 Numbe r of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Packet Loss - ertps Packet Loss per SS (rtps) Packets Dropped (%) 120% 100% 80% 60% 40% 20% 0% 6 12 18 24 30 36 Num ber of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Packet Loss - rtps Fgure 4-9: The effect of uplnk burst preamble Packet loss (lght load) 85

Intra-class farness (ertps) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 6 12 18 24 30 36 Num ber of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Intra-class farness - ertps Intra-class farness (rtps) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 6 12 18 24 30 36 Numbe r of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Intra-class farness - rtps Intra-class farness (nrtps) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 6 12 18 24 30 36 Numbe r of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (c) Intra-class farness - nrtps 86

Intra-class farness (BE) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (d) Intra-class farness - BE Fgure 4-10: The effect of uplnk burst preamble: Intra-class farness (Lght load) Heavy load: Average Throughput per SS (ertps) Average Throughput - Kbps 450 400 350 300 250 200 150 100 50 0 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Average Throughput - ertps Average Throughput per SS (rtps) 3500 Average Throughput - Kbps 3000 2500 2000 1500 1000 500 0 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc Number of SS (b) Average Throughput - rtps 87

Average Throughput per SS (nrtps) Average Throughput - Kbps 3000 2500 2000 1500 1000 500 0 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (c) Average Throughput - nrtps Average Throughput per SS (BE) Average Throughput - Kbps 400 350 300 250 200 150 100 50 0 6 12 18 24 30 36 Num ber of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (d) Average Throughput - BE Fgure 4-11: The effect of uplnk burst preamble: Average throughput (Heavy load) Average Delay per SS (ertps) Average Delay (ms) 120 100 80 60 40 20 0 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Average Delay - ertps 88

Average Delay per SS (rtps) Average Delay (ms) 160 140 120 100 80 60 40 20 0 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Average Delay rtps Fgure 4-12: The effect of uplnk burst preamble: Average delay (Heavy load) Packet Loss per SS (ertps) Packets Dropped (%) 80% 70% 60% 50% 40% 30% 20% 10% 0% 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Packet Loss - ertps Packet Loss per SS (rtps) Packets Dropped (%) 120% 100% 80% 60% 40% 20% 0% 6 12 18 24 30 36 Num ber of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Packet Loss - rtps Fgure 4-13: The effect of uplnk burst preamble: Packet loss (Heavy load) 89

Intra-class farness (ertps) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 6 12 18 24 30 36 Num ber of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Intra-class farness - ertps Intra-class farness (rtps) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 6 12 18 24 30 36 Numbe r of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Intra-class farness - rtps Intra-class farness (nrtps) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 6 12 18 24 30 36 Numbe r of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (c) Intra-class farness - nrtps 90

Intra-class farness (BE) - Mn-Max Index Farness Index 1.20 1.00 0.80 0.60 0.40 0.20 0.00 6 12 18 24 30 36 Number of SS EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (d) Intra-class farness - BE Fgure 4-14: The effect of uplnk burst preamble: Intra-class farness (Heavy load) The average throughput, under both lght and heavy loads, decreases wth an ncreasng number of SSs due to decreasng load per SS and ncrease n bandwdth wasted by uplnk burst preambles. The Queung Theoretc algorthm, for fewer SSs, shows a hgher average throughput for SSs of all traffc classes snce t allocates at least the MRTR n every frame for them (see Fgure 4-7, Fgure 4-11). The algorthm ndcates the hghest average throughput for the ertps class. However, under the heavy load and wth a large number of SSs (greater than 24), the Queung Theoretc algorthm ndcates lower average throughput than the hybrd (EDF+WFQ+FIFO) algorthm. Ths behavour s due to the large overhead ncurred by the Queung Theoretc algorthm as t selects the maxmum number of SSs n a frame. SSs of the BE class get assgned bandwdth equvalent to the sze of one packet (100 bytes). Therefore, due to the large packet sze, the average throughput of BE SSs, under the heavy load and large number of SSs (greater than eghteen), stays at 50 Kbps. The average throughput of SSs of the nrtps class s low wth a large number of SSs and under heaver load (see Fgure 4-11). Ths s because the mnmum allocated bandwdth per frame by the Queung Theoretc algorthm s smaller 91

than the packet sze of FTP traffc. Wth a packet sze of 150 bytes and MRTR of 45 Kbps, at least 112.5 bytes every frame s allocated for each nrtps SS. Ths mnmum allocaton s nsuffcent to transmt one packet and s thus wasted. Wth large number of SSs, the ertps and rtps SSs wll be assgned hgher prorty by the Queung Theoretc algorthm due to ther hgh average delay. Ths wll result n very few transmsson opportuntes for the nrtps SSs and therefore ther MRTR wll not be satsfed. Under lghter load, SSs of the nrtps class get allocated more bandwdth that s large enough to transmt at least one packet (see Fgure 4-7). Due to the lght load, the nrtps SSs wll get more transmsson opportuntes resultng n ther average throughput beng hgher than the MRTR. The cross layer algorthm ndcates the lowest average throughput for the SSs out of all the algorthms as t selects only one SS n a frame. When the number of SSs s hgh, the lower prorty SSs (nrtps and BE classes) are allocated very lttle bandwdth, ndcated by a very low average throughput. Ths s an expected behavour of the cross layer scheme as dscussed n [27]. The dfference n average throughput between the legacy algorthms s more notceable under the heavy load scenaro. The EDF and hybrd (EDF+WFQ+FIFO) algorthms ndcate a hgher average throughput for SSs of ertps and rtps classes due to ther strct prorty nature towards real-tme SSs. The WFQ algorthm ndcates almost dentcal average throughput for SSs of the rtps class when compared wth EDF and hybrd (EDF+WFQ+FIFO) algorthms. Ths behavour s due to the hgh MRTR of SSs of the rtps class, allowng the WFQ algorthm to allocate a large amount of bandwdth for them. The WRR algorthm results n very low average throughput for the BE class due to the low MRTR of SSs of the class and the large packet sze of the BE traffc (100 bytes). 92

The average delay and packet loss ncrease wth ncreasng number of SSs due to ncreasng overhead of uplnk burst preamble and ncreasng number of SSs (see Fgure 4-8, Fgure 4-9, Fgure 4-12 and Fgure 4-13). The cross layer algorthm shows no sgnfcant dfference n average delay under both lght and heavy loads (see Fgure 4-8 and Fgure 4-12). Snce the cross layer algorthm selects only one SS n a frame, t wll result n a large backlog of data. The backlogged packets wll mss ther deadlne and wll therefore be dropped. Ths behavour s reflected by the ncrease n packet loss wth ncreasng number of SSs (see Fgure 4-9 and Fgure 4-13). The WRR and hybrd (EDF+WFQ) algorthms ndcate the hghest average delay wth a large number of SSs (greater than 18 for heavy load and greater than 30 for lght load). Snce these algorthms partton bandwdth accordng to the MRTR and number of SSs, and ther nature of selectng large number of SSs every frame, the amount of bandwdth allocated for SSs of ertps and rtps classes wll be less. Under the hybrd (EDF+WFQ) algorthm, both ertps and rtps SSs wll compete for the bandwdth. Ths wll result n an ncrease n average delay wth ncreasng number of SSs. The lowest average delay under the lght load, as ndcated by the EDF and hybrd (EDF+WFQ+FIFO) algorthms s 10ms, whch s the value of the allocaton start tme. The mnmum amount of tme a packet wll spend n the queue s the start of the uplnk allocaton accordng to the UL-MAP message, whch s the value of allocaton start tme. Under lght load, the Queung Theoretc algorthm results n an ncrease n average delay wth maxmum number of SSs (see Fgure 4-8). Ths behavour s due to more SSs competng for the same amount of bandwdth n a class. The ncreased average delay s also due to the large overhead of the uplnk burst preamble. The ncrease n 93

overhead wll result n a reducton of allocated bandwdth of each class. The ncrease n average delay s more severe under the heavy load (see Fgure 4-12). Although the Queung Theoretc, WRR and hybrd (EDF+WFQ) algorthms ndcate hgher average delay than the cross layer algorthm, they result n a lower packet loss (see Fgures 4-9 and 4-13). The farness among SSs of the ertps class (see Fgure 4-10 and Fgure 4-14) decreases wth an ncreasng number of SSs under the cross layer, WFQ and Queung Theoretc algorthms. Wth an ncreased number of SSs, the cross layer algorthm wll gve the hghest prorty to SSs of the ertps class. Snce only one SS s selected by the cross layer algorthm, the dfference n mnmum and maxmum average throughput n the class wll be hgh. Under the Queung Theoretc algorthm, snce a larger number of SSs compete for the same amount of bandwdth (low provsoned bandwdth per class due to large overhead), some SSs wll receve a large porton of the bandwdth (more than ther MRTR) and some wll not. Ths s the same reason for the decrease n farness among SSs of the rtps class. The WFQ algorthm ndcates a low farness among ertps SSs because of the bursty nature of VoIP traffc. Evaluaton of tme-stamp based schedulers n [42] shows that WFQ ndcates a low farness among users when the traffc s bursty, such as the VoIP traffc used for ertps class n our model. Under the Queung Theoretc algorthm, some SSs wll receve a large porton of bandwdth (more than ther MRTR) and some wll not. Ths s due to the utlty functon of rtps SSs that does not take the average throughput nto account, therefore resultng n fluctuaton of ntra-class farness. The ntra-class farness of the rtps class under the 94

Cross layer algorthm depends on the amount of traffc transmtted by the selected SS e.g. when the number of SSs s 12 and 18. The ntra-class farness for the nrtps class, as ndcated by the cross layer algorthm, dps when the number of SSs s 12. Ths behavour s due to the cross layer algorthm selectng only one SS n a frame and wth only two nrtps SSs t ndcates a large dfference between the mnmum and maxmum average throughput n the class. Under heavy load, the ntra-class farness for the nrtps class fluctuates n the case of the Queung Theoretc algorthm when the number of SSs s greater than eghteen (see Fgure 4-14). For a small number of nrtps SSs, a large amount of resdual bandwdth remans (after allocatng the MRTR to each SS). Consequently, the dfference between the mnmum and maxmum average throughput among the SSs s more perceptble, whch s translated as lower farness. When the number of SSs ncreases to 24, ths dfference n throughput decreases resultng n hgher farness. Although the resdual bandwdth s less, t s enough to satsfy most nrtps SSs, thus resultng n the decrease n dfference between the mnmum and maxmum average throughput. When number of SSs s greater than twenty four, the farness decreases because more nrtps SSs compete for the smaller amount of resdual bandwdth whch s not suffcent to satsfy them all. The ntra-class farness for the BE class s very hgh due to very lttle bandwdth allocated to these SSs, resultng n very lttle dfference between the mnmum and maxmum average throughput n the class. 4.3.3 The effect of frame length Accordng to the IEEE 802.16-2004 standard [1], the supported frame lengths for the WrelessMAN-OFDM PHY layer are 2.5ms, 4ms, 5ms, 8ms, 10ms, 12.5ms and 95

20ms. Wth a larger frame, Subscrber Statons (SSs) can send more data due to more symbols avalable n the frame. For example, wth the largest frame sze of 20ms and symbol duraton of 12.5 μs, the total number of symbols avalable for the uplnk subframe wll be 800. On the other hand, wth the smallest frame sze of 2.5ms, only 100 symbols wll be avalable for the uplnk sub-frame. 4.3.3.1 The effect of frame length on frame utlzaton In ths experment, we wll study the frame utlzaton offered by the varous algorthms under lght load of 4.5Mbps and a heavy load of 9Mbps. We use vdeo (rtps) and FTP (nrtps) traffc only for ths experment. Under the lght load, each rtps SS wll send traffc at a rate of 1000 Kbps and the nrtps SS wll send traffc at a rate of 500 Kbps. Under the heavy load, each rtps SS wll send traffc at a rate of 2000Kbps and the nrtps SS wll send traffc at a rate of 1000 Kbps. Table 4-9 lsts the parameters used for the experment. Table 4-9: The effect of frame length Parameters (frame utlzaton) Parameter Value Number of SSs 5 Rato of SS (rtps:nrtps) 4:1 Frame Length 2.5ms, 4ms, 5ms, 8ms, 10ms, 12.5ms and 20ms 96

Lght load: Frame Utlzaton Frame Utlzaton 45.00% 40.00% 35.00% 30.00% 25.00% 20.00% 15.00% 10.00% 5.00% 0.00% 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc Heavy load: (a) Frame utlzaton under lght load Frame Utlzaton Frame Utlzaton 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Frame utlzaton under heavy load Fgure 4-15: The Effect of Frame Length Frame utlzaton Wth a smaller frame sze and lght load, the cross layer algorthm ndcates hgher frame utlzaton than the WRR and Queung Theoretc algorthms (see Fgure 4-15A). Ths behavor s due to the WRR and Queung Theoretc algorthms selectng the maxmum number of SSs n a frame, thus resultng n the largest overhead. As the frame sze ncreases, the frame utlzaton ncreases sharply under the WRR and Queung Theoretc algorthms, reachng the same level as that of other legacy schedulng 97

algorthms. Ths s because wth larger frames, the effect of the overhead due to preamble symbols for the fve SSs s neglgble. Wth a smaller frame and under heavy load, the cross layer algorthm ndcates the hghest frame utlzaton as the overhead from selectng multple SSs by the other algorthms s sgnfcant (see Fgure 4-15B). As the frame sze ncreases, the frame utlzaton of the legacy and the Queung Theoretc algorthms ncreases whle that of the cross layer algorthm decreases. The amount of data a sngle SS has to send remans the same and wth a larger frame, the cross layer algorthm ndcates lower frame utlzaton. The frame utlzaton ndcated by the WRR algorthm s lower due to the large packet sze of vdeo traffc (150-300 bytes) and FTP traffc (150 bytes). The large packet sze wll result n more symbols wasted under the WRR algorthm. 4.3.3.2 The effect of frame length on average delay and packet loss The frame length mostly affects the average delay and packet loss wth respect to user performance. Snce the traffc load s lmted by the smallest frame sze, wth a large frame length the data to be transmtted wll be nsgnfcant compared to the symbols avalable n the frame. Ths wll result n the schedulng algorthms flushng out all the backlogged data, thus ndcatng very smlar performance between them wth respect to the average throughput. The FTP (nrtps) and HTTP (BE) traffc n ths experment wll essentally be treated as background traffc. A heavy load of 4280 Kbps s suppled wth 180 Kbps reserved for ertps class, 3000 Kbps reserved for rtps class, 1000 Kbps reserved for nrtps class and 100 Kbps reserved for BE class. A lght load of 2140 Kbps s suppled wth 90 Kbps reserved for ertps class, 1500 Kbps reserved for rtps class, 500 98

Kbps reserved for nrtps class and 50 Kbps reserved for BE class. The remanng parameters for the experment are lsted n Table 4-10. Table 4-10: The effect of frame length Parameters Parameter Value Number of SSs 5 Rato of SS (ertps:rtps:nrtps:be) 1:2:1:1 Frame Length 2.5ms, 4ms, 5ms, 8ms, 10ms, 12.5ms and 20ms Lght load: Average Delay per SS (ertps) Average Delay (ms) 35 30 25 20 15 10 5 0 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Average Delay - ertps Average Delay per SS (rtps) Average Delay (ms) 140 120 100 80 60 40 20 0 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Average Delay - rtps Fgure 4-16: The effect of frame length: Average delay (Lght load) 99

Packet Loss per SS (ertps) Packets Dropped (%) 4% 4% 3% 3% 2% 2% 1% 1% 0% 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Packet Loss - ertps Packet Loss per SS (rtps) Packets Dropped (%) 70% 60% 50% 40% 30% 20% 10% 0% 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Packet Loss - rtps Fgure 4-17: The effect of frame length: Packet loss (Lght load) Heavy load: Average Delay per SS (ertps) Average Delay (ms) 90 80 70 60 50 40 30 20 10 0 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Average Delay - ertps 100

Average Delay per SS (rtps) Average Delay (ms) 140 120 100 80 60 40 20 0 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Average Delay - rtps Fgure 4-18: The effect of frame length: Average delay (Heavy load) Packet Loss per SS (ertps) Packets Dropped (%) 12% 10% 8% 6% 4% 2% 0% 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (a) Packet Loss - ertps Packet Loss per SS (rtps) Packets Dropped (%) 70% 60% 50% 40% 30% 20% 10% 0% 2.5 4.0 5.0 8.0 10.0 12.5 20.0 Frame Length (ms) EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO crosslayer QueungTheoretc (b) Packet Loss - rtps Fgure 4-19: The effect of frame length: Packet loss (Heavy load) 101

Under lght load, the average delay of SSs from both the ertps and rtps class ncreases wth ncreasng frame length (see Fgure 4-16). Ths behavour can be attrbuted to the packets spendng a longer tme n the queue wth a larger frame sze. Even though the average delay ncreases, most schedulng algorthms ndcate no packet loss snce abundant bandwdth s avalable for all the data to be flushed out of the queue (see Fgure 4-17). The cross layer algorthm shows an ncrease n packet loss for frame sze greater than 8ms. Snce the algorthm selects only one SS n a frame, wth a larger frame, packets wll spend longer tme n the queue than the maxmum delay bound, resultng n packet loss. Under heavy load, the average delay of SSs from both ertps and rtps classes decrease wth ncreasng frame length (see Fgure 4-18). The decrease n average delay s due to more packets beng flushed out of the queue of the SSs. The cross layer algorthm ndcates an ncrease n average delay for the rtps class as the packets wat a longer tme n the queue due to a larger frame sze. The average delay of SSs of the ertps class under the Queung Theoretc algorthm s hgher than that ndcated by other algorthms. Ths s due to the fact that the Queung Theoretc algorthm tends to satsfy all the SS s MRTR requrements and allocate the resdual bandwdth accordng to the utlty of the SSs. Therefore, dependng on the channel qualty, some SSs wll not be allocated bandwdth any further, thus ther packets spend a longer tme n the queue. The Queung Theoretc algorthm ndcates packet loss for ertps class but not for the rtps class (see Fgure 4-19). The utlty of ertps SSs s calculated usng the same functon as that for the rtps SSs but wth a tghter delay bound. Thus, after satsfyng the MRTR of each SS, f the resdual bandwdth s not enough, packets of ertps SSs wll be dropped frst than those of rtps 102

SSs. The packet loss for the rtps class ncreases under the cross layer algorthm for frame szes greater than 8ms. Ths behavour s manly due to the longer frame length that results n the packets watng a longer perod of tme n the queue. 4.3.4 Bandwdth Request Analyss In ths experment, we compare the pggyback and contenton request mechansms, as specfed n the IEEE 802.16-2004 standard [1]. In the pggyback mechansm, a SS can attach ts bandwdth request onto the data packets whereas n the contenton mechansm a SS wll compete for a slot to send ts bandwdth request. Snce pggyback requests do not have a type feld, they wll always be ncremental requests. When a BS receves an ncremental bandwdth request, t wll add the quantty of the bandwdth requested to ts current percepton of the bandwdth needs of the SS. Due to the possblty of collsons, bandwdth requests under the contenton mechansms wll always be aggregate requests. When a BS receves an aggregate bandwdth request, t wll replace ts percepton of the bandwdth needs of the SS wth the quantty of bandwdth requested. The experment wll be carred out wth SSs of the nrtps and BE classes as contenton for bandwdth s allowed for these classes only. The IEEE 802.16-2004 standard [1] specfes that the block of contenton slots can occur n any order and n any quantty wthn the frame (lmted by the number of avalable symbols n the frame) at the dscreton of the BS uplnk scheduler as ndcated by the UL-MAP message. We compare the pggyback mechansm wth the contenton request mechansm under two dfferent ways of allocatng slots for contenton. In the frst scheme, a fxed number of slots, equal to the number of SSs, wll be reserved for contenton. The second scheme s an enhancement to the frst whereby a fxed number of slots, equal to half the number of 103

SSs, are reserved and the SSs are also allowed to contend n the unused porton of the uplnk sub-frame. The unused porton of the sub-frame s the part of the sub-frame that s not reserved for data symbols. From the UL-MAP message, each SS can determne the unused porton of the uplnk sub-frame. We compare the pggyback and contenton mechansms under heavy load of 6Mbps and a lght load of 1.5Mbps. For the heavy load, the total traffc arrval rate of nrtps SSs s 5Mbps and that of BE SSs s 1Mbps. For the lght load, the total traffc arrval rate of nrtps SSs s 1.2Mbps and that of BE SSs s 0.3Mbps. Fgure 4-20 provdes an overvew of the two contenton request mechansms evaluated and Table 4-11 lsts the parameters of the experment. Fxed number of contenton slots Porton of sub-frame reserved for data Fxed number of contenton slots Porton of subframe reserved for data Flexble porton of the sub-frame for contenton (a) Contenton Mechansm: Fxed number of slots (b) Contenton Mechansm: Varable number of slots Fgure 4-20: Uplnk sub-frame structure: Contenton Request Mechansm Table 4-11: Bandwdth request analyss - Parameters Parameter Value Number of SSs 3-21 Rato of SS (nrtps:be) 2:1 Frame Length 10ms 104

Lght load: Pggyback vs Contenton (Fxed slots) Honoured requests (%) 120.00% 100.00% 80.00% 60.00% 40.00% 20.00% 0.00% 3 6 9 12 15 18 21 Number of SS (a) Pggyback vs Contenton (Fxed slots) EDF - Pggyback WFQ-Pggyback WRR-Pggyback EDF+WFQ-Pggyback EDF+WFQ+FIFO-Pggyback CrossLayer-Pggyback QueungTheoretc-Pggyback Contenton Pggyback vs Contenton (Fxed+Varable slots) 120.00% Honoured requests (%) 100.00% 80.00% 60.00% 40.00% 20.00% EDF - Pggyback EDF - Contenton WFQ-Pggyback WFQ-Contenton WRR-Pggyback WRR-Contenton 0.00% 3 6 9 12 15 18 21 Number of SS (b) Pggyback vs Contenton (Varable slots) Homogenous algorthms 105

Pggyback vs Contenton (Fxed+Varable slots) Honoured requests (%) 1.2 1 0.8 0.6 0.4 0.2 0 3 6 9 12 15 18 21 Number of SS EDF+WFQ - Pggyback EDF+WFQ - Contenton EDF+WFQ+FIFO-Pggyback EDF+WFQ+FIFO-Contenton CrossLayer-Pggyback CrossLayer-Contenton QueungTheoretc-Pggyback QueungTheoretc-Contenton Heavy load: (c) Pggyback vs Contenton (Varable slots) Hybrd and Opportunstc algorthms Fgure 4-21: Bandwdth request analyss Lght load Pggyback vs Contenton (Fxed slots) 120.00% Honoured requests (%) 100.00% 80.00% 60.00% 40.00% 20.00% 0.00% 3 6 9 12 15 18 21 Number of SS (a) Pggyback vs Contenton (Fxed slots) EDF - Pggyback WFQ-Pggyback WRR-Pggyback EDF+WFQ-Pggyback EDF+WFQ+FIFO-Pggyback CrossLayer-Pggyback QueungTheoretc-Pggyback Contenton 106

Pggyback vs Contenton (Fxed+Varable slots) 120.00% Honoured requests (%) 100.00% 80.00% 60.00% 40.00% 20.00% EDF - Pggyback EDF - Contenton WFQ-Pggyback WFQ-Contenton WRR-Pggyback WRR-Contenton 0.00% 3 6 9 12 15 18 21 Number of SS (b) Pggyback vs Contenton (Varable slots) Homogenous algorthms Pggyback vs Contenton (Fxed+Varable slots) Honoured requests (%) 120.00% 100.00% 80.00% 60.00% 40.00% 20.00% 0.00% 3 6 9 12 15 18 21 Number of SS EDF+WFQ - Pggyback EDF+WFQ - Contenton EDF+WFQ+FIFO-Pggyback EDF+WFQ+FIFO-Contenton CrossLayer-Pggyback CrossLayer-Contenton QueungTheoretc-Pggyback QueungTheoretc-Contenton (c) Pggyback vs Contenton (Varable slots) Hybrd and Opportunstc algorthms Fgure 4-22: Bandwdth request analyss Heavy load We can observe that the contenton mechansm s more sutable for the cross layer algorthm than the pggyback mechansm, under both lght and heavy load (see Fgure 4-21 and Fgure 4-22). Ths behavour s due to the cross layer algorthm selectng only one SS n a frame that wll result n only one SS gettng a chance to pggyback ts bandwdth request each frame. The cross layer algorthm ndcates very good 107

performance under the contenton mechansm snce a major porton of the uplnk subframe wll be unused, also ndcated by low frame utlzaton (see Fgure 4-6). The unused porton wll be used for contenton, resultng n a hgh success rate of reservng a slot for bandwdth request. Under lght load, both the contenton mechansms (see Fgure 4-21) ndcate a better chance for the SSs to reserve a slot for bandwdth request than the pggyback mechansm, under the Queung Theoretc and legacy algorthms. Ths s behavour s due to most of the data from the queues of the SSs beng flushed out, resultng n few backlogged packets to pggyback bandwdth requests. Due to the lght load, abundant symbols wll be avalable for the contenton mechansm resultng n very few collsons. Wth fewer SSs, the pggyback mechansm ndcates a slghtly hgher percentage of honoured requests, due to larger load per SS. As the number of SSs ncrease, the load per SS decreases, whch means some SSs wll not have any data backlog to pggyback a bandwdth request, resultng n the contenton mechansm showng superor performance than the pggyback mechansm. Under the pggyback mechansm, the WRR algorthm ndcates a low percentage of honoured requests compared to other algorthms. Intally the percentage of honoured requests decrease snce the bandwdth allocated based on the weght s enough to transmt all the packets from the queues of the SSs. When the number of SSs s 21, the bandwdth allocated to each SS s not enough, thus preventng a SS from sendng ts backlogged packets. Ths s because of the large number of SSs resultng n a large overhead and thus less bandwdth avalable for each SS. Under heavy load, the pggyback mechansm ndcates a hgher percentage of honoured requests than both contenton mechansms (see Fgure 4-22). The EDF 108

algorthm results n the hghest percentage of honoured requests under the pggyback mechansm than all the other algorthms. Ths s due to both nrtps and BE SSs competng for bandwdth that results n a large backlog of data n the frame and allows the SS to pggyback bandwdth request. The hybrd (EDF+WFQ+FIFO) algorthm results n a lower percentage of honoured requests under the pggyback mechansm snce t gves strct prorty to nrtps SSs. Ths wll result n smaller backlog of data for nrtps SSs and due to ther hgh concentraton (2:1 rato) t wll ndcate a lower percentage of honoured requests. The WFQ and hybrd (EDF+WFQ) algorthms also ndcate a lower percentage of honoured requests under the pggyback mechansm. Ths behavour s due to a hgher weght assgned to nrtps SSs that results n smaller backlog of data n ther queues. For fewer SSs (less than 12), the WRR algorthm ndcates a hgher percentage of honoured requests under the contenton mechansm than under the pggyback mechansm. Due to fewer SSs, the bandwdth allocated to each SS s enough to flush out all the data resultng n fewer packets remanng to pggyback the bandwdth request. Wth a large number of SSs (greater than 12), the bandwdth allocated to each SS s not enough to transmt all the packets from the queue resultng n the pggyback mechansm performng better than the contenton mechansm. When the number of SSs s greater than 15, the pggyback mechansm ndcates a decrease n honoured requests. Ths behavour s due to less bandwdth allocated to each SS and the large packet sze of BE and nrtps traffc. The small amount of bandwdth allocated s not enough to transmt one packet, and therefore a large number of SSs don t get selected. Even f a SS has large backlog of data, f the SS s not selected n the current frame, t cannot pggyback on the bandwdth request. 109

The Queung Theoretc algorthm ndcates a hgher percentage of honoured requests under the contenton mechansm (fxed+varable slots) than the legacy algorthms (see Fgure 4-22). Ths behavour s due to the lmtaton on the bandwdth allocaton per class under the Queung Theoretc algorthm. Due to a lower traffc arrval rate of BE SSs, some of the bandwdth allocated to the BE class wll be unused resultng n more symbols avalable for contenton. 4.4 Summary In ths chapter we evaluated the performance of a number of representatve WMAX schedulng schemes. We presented the smulaton envronment, ncludng the traffc model and values for the MAC and PHY layer smulaton parameters. We conducted a seres of experments to observe the performance of schedulng algorthms under the context of IEEE 802.16 MAC layer. Table 4-12 provdes a summary of our fndngs. The experments reveal that the overhead due to the uplnk burst preamble can sgnfcantly affect the bandwdth avalable to the SSs. Schedulng algorthms that select maxmum number of SSs (WRR, Queung Theoretc) result n maxmum overhead compared to algorthms (cross layer) that select the least number of SSs. Even though the cross layer algorthm selects only one SS n a frame, t provdes superor performance than the other algorthms n some select cases. When the load per SS s hgh, wth a smaller frame sze the cross layer algorthm wll result n hgher frame utlzaton. As well, when the number of SSs s hgh, the cross layer algorthm wll result n hgher frame utlzaton. The advantages of the cross layer algorthm are lmted to frame 110

utlzaton only as t ndcates poor performance wth respect to average throughput, average delay and farness under all the scenaros we studed. Table 4-12: Comparson of uplnk schedulng algorthms n WMAX Scheme Farness Sutable Frame Average Average Delay/ bandwdth utlzaton Throughput Packet loss request (ertps/ rtps/ mechansm nrtps/ BE) Intraclass Inter-class (Heavy load/ Lght load) EDF Hgh Low Pggyback / Hgh Hgh/ Hgh/ Low/ Low/ Low Contenton Low WFQ Low Low- Pggyback / Hgh Medum/ Hgh/ Low/ Low Medum Contenton Hgh/ Low- Medum WRR Hgh Hgh Pggyback/ Low, Low/ Medum/ Medum-Hgh/ Contenton Medum 1 Medum/ Low- Medum-Hgh Medum EDF+WFQ Medum Medum Pggyback/ Medum, Hgh/ Medum- Medum-Hgh/ Contenton Hgh 2 Hgh/ Hgh/ Low- Medum-Hgh Medum EDF+WFQ Medum Low- Pggyback/ Hgh Hgh/ Hgh/ Low/ Low +FIFO Medum Contenton Medum/ Low Queung Low- Low- Pggyback/ Medum, Hgh/ Hgh/ Hgh/ Low- Medum/ Low- Theoretc Medum Medum Contenton Low 3 Medum-Hgh Medum Cross layer Low Low Contenton/ Low, Hgh 4 Low/ Low/ Low/ Hgh/ Hgh Contenton Low 1 Low when number of SSs s large or frame sze s small, Medum when number of SSs s small or frame sze s large. 2 Medum when number of SSs s large or frame sze s small, Hgh when number of SSs s small or frame sze s large. 3 Low when number of SSs s large or frame sze s small, Medum when number of SSs s small. 4 Low when number of SSs s small, Hgh when number of SSs s large or frame sze s small. 111

The schedulng algorthms show nterestng results when studed under dfferent mx of traffc. Algorthms such as EDF and hybrd (EDF+WFQ+FIFO) ndcate superor performance for SSs of ertps and rtps classes wth respect to average throughput, average delay and packet loss when the concentraton of real-tme traffc s hgh. These algorthms wll also result n starvaton of SSs of nrtps and BE classes. The dfference between EDF and hybrd (EDF+WFQ+FIFO) algorthms s that under the EDF algorthm SSs of both nrtps and BE classes wll compete for bandwdth whereas n the hybrd (EDF+WFQ+FIFO) algorthm, SSs of nrtps class have strct prorty over SSs of the BE class. The performance of the Queung Theoretc algorthm s lmted by the class thresholds and that of the hybrd (EDF+WFQ) algorthm s lmted by the allocaton of bandwdth among the traffc classes. Under the Queung Theoretc algorthm, f the bandwdth allocated to SSs of a class s equal to the threshold of that class, the SSs of ths class wll not be allocated bandwdth any further n the current frame even f these SSs have a large backlog of data. The WRR algorthm ndcates poor performance under varable packet sze snce bandwdth s allocated to the SSs based solely on ther weght. The frame length also has a sgnfcant mpact on the performance of the schedulng algorthms. The WRR and Queung Theoretc algorthms result n very poor performance wth small frame szes snce most of the avalable resources wll be wasted for the uplnk burst preamble. Ths s because the algorthms tend to select the maxmum number of SSs, resultng n maxmum overhead. Due to the larger frame duraton, the average delay and packet loss experenced by the SSs wll also ncrease. The performance of the schedulng algorthms s also nfluenced by the bandwdth request mechansm adopted by the SSs. The cross layer algorthm wll result n a very 112

hgh success rate for reservng a slot for bandwdth request under the contenton mechansm than under the pggyback mechansm. On the other hand, under the Queung Theoretc and legacy algorthms (homogenous and hybrd), the SSs have a better chance of reservng a bandwdth request slot when usng the contenton mechansm under lght load and the pggyback mechansm under heavy load. The number of slots reserved for contenton has a sgnfcant mpact on the success rate of reservng a bandwdth request slot. 113

Chapter 5. Conclusons and Future Work In recent years, the need for broadband wreless access has ncreased due to applcatons such as vdeo conferencng, VoIP, onlne gamng and streamng audo/vdeo demandng hgh bandwdth and tght delay bounds. The IEEE 802.16 standard specfes a means of broadband nternet access for fxed and moble statons and promses to provde last mle nternet access at an affordable rate. The IEEE 802.16-2004 standard specfes the MAC and PHY layer functonaltes for Fxed WMAX for both PMP and mesh mode operatons. The standard states a QoS framework that specfes four traffc classes, but the schedulng mechansm for these classes s left open for vendor mplementaton. The choce of a schedulng algorthm for the mult-class traffc can have a sgnfcant mpact on the satsfacton of the users. In ths thess, we nvestgated several proposals for uplnk schedulng algorthms amed at satsfyng QoS requrements of the mult-class traffc. We categorzed the uplnk schedulng algorthms nto three classes, namely, homogenous algorthms, hybrd algorthms and opportunstc algorthms. Representatve algorthms from each category were selected for evaluaton. The algorthms were evaluated under dfferent mx of traffc and wth respect to the major characterstcs of IEEE 802.16 MAC layer such as bandwdth request mechansms, frame sze and the uplnk burst preamble. The performance metrcs used to evaluate the schedulng algorthms are average throughput, average delay, packet loss, frame utlzaton and farness. Farness was studed at two levels: ntra-class farness and nter-class farness. Jan s farness ndex s used to measure nter-class farness where Mn-max ndex s used for ntra-class farness. 114

The Mn-max farness ndex s more senstve to servce degradaton and unfarness between users, allowng us to better dstngush between the schedulng algorthms performance wthn the same class. To effectvely study the bandwdth request mechansms, we ntroduced a metrc, honoured requests, whch measures the percentage of successful bandwdth requests. The EDF and hybrd (EDF+WFQ+FIFO) algorthms result n the lowest average delay for ertps and rtps SSs. Both these algorthms provde strct prorty to ertps and rtps SSs. They also do not consder the MRTR of the SSs n decdng the transmsson schedule and result n starvaton of lower prorty SSs. The dfference between the EDF and hybrd (EDF+WFQ+FIFO) algorthm s that n the former, the nrtps and BE SSs wll compete for bandwdth whereas n the latter the nrtps SSs have strct prorty over BE SSs. Therefore, schedulng algorthms that employ a strct prorty mechansm are not a good choce to satsfy the QoS requrements of the mult-class traffc n WMAX. The WRR, WFQ and hybrd (EDF+WFQ) algorthms provde a more far dstrbuton of bandwdth among the SSs. The WFQ and WRR algorthms attempt to satsfy the MRTR of the SSs by assgnng weghts to the SSs based on ther MRTR. The worst case delay bound guaranteed by the WFQ algorthm can be suffcent for the UGS SSs but not for ertps and rtps SSs. The average delay under the WFQ algorthm s greatly affected by the densty of the traffc utlzng the resdual capacty.e. under bursty traffc, such as VoIP, the average delay experenced by the SSs wll be hgh. Therefore, modfcatons to the algorthm are requred to satsfy the delay requrement of the ertps and rtps SSs and ensure the average delay s not consderably affected by the traffc densty. The WRR algorthm does not provde a bound on the delay, even under the worst case, and t does 115

not work well n the presence of varable packet sze. The WRR algorthm also results n the largest overhead snce t selects all the SSs n each frame. The packet sze and the queue length can be ncorporated n the WRR algorthm to provde a delay bound and ensure the algorthm operates well n the presence of varable packet szes. Ths mght requre sacrfcng the smplcty of the algorthm whch s one of ts major advantages. The hybrd (EDF+WFQ) algorthm allocates bandwdth among the traffc classes n a farer manner than the hybrd (EDF+WFQ+FIFO) algorthm. Ths algorthm s also very adaptable to changng concentraton of traffc snce the bandwdth among the traffc classes s dstrbuted accordng to the number of SSs n a traffc class and ther MRTR. The use of a computatonally expensve algorthm such as WFQ for BE SSs s an overwhelmng soluton. Snce BE SSs do not have QoS requrements, smple algorthms such as FIFO or RR would be suffcent. The prorty functons of the cross layer algorthm take nto account all the QoS requrements of the mult-class traffc n WMAX such as the average delay, average throughput and the channel qualty. Even though the algorthm selects only one SS n a frame, t shows superor performance compared to the other algorthms n select cases. One of these cases s when the number of SSs s large and the load per SS s hgh, the cross layer algorthm results n the least overhead due to uplnk burst preamble compared to other algorthms that select multple SSs n a frame. The algorthm results n dssatsfacton of the QoS requrements of the SSs and starvaton of lower prorty SSs, snce t selects only one SS n each frame. The algorthm s also very senstve to the coeffcents assgned to each traffc class, whch s one of the reasons for starvaton of lower prorty SSs n the presence of large number of hgher prorty SSs. 116

The Queung Theoretc algorthm consders the queue sze of the SSs, whch s an mportant factor n the presence of bursty traffc and varable packet sze. The allocaton wthn a traffc class s lmted by the class threshold. Therefore, t s crtcal that an approprate threshold be assgned to each class to ensure the QoS requrements of the SSs n the class are met. The algorthm ensures that BE SSs are not starved even n the presence of large number of ertps, rtps and nrtps SSs. A drawback of the algorthm s that the utlty functon for rtps SSs attempts to satsfy the delay requrement only. MRTR s also an mportant QoS parameter of the rtps class, but s gnored n the utlty functon. The algorthm also results n large overhead due to uplnk burst preamble snce t selects all the SSs n each frame. Legacy schedulng algorthms (homogenous and hybrd) do not explctly consder all the requred QoS parameters of the traffc classes n WMAX. The algorthms consder only some of the parameters whch are not suffcent snce the schedulng classes have multple QoS parameters such as the rtps class that requres delay, packet loss and throughput guarantee. The algorthms mplctly attempt to meet the QoS requrements such as the EDF algorthm satsfyng the delay requrement of ertps and rtps SSs. On the other hand, the Cross Layer and Queung Theoretc algorthms nclude the maxmum latency, MRTR and the channel qualty n the prorty functons. Therefore, the legacy schedulng algorthms are not the most sutable for the mult-class traffc n WMAX, as they do not explot the characterstcs of WMAX and the requrements of the varous traffc classes. Although, the Cross Layer and Queung Theoretc algorthms nclude all the QoS parameters n ther prorty/utlty functons, they have certan drawbacks as well. 117

Snce the WFQ algorthm does not perform well under traffc that s bursty such as VoIP, more sutable algorthms for VoIP traffc would be EDF and Queung Theoretc. Both EDF and Queung Theoretc algorthms would also be sutable for other real-tme applcatons such as vdeo conferencng and streamng meda. If the number of SSs s very hgh, then the Queung Theoretc algorthm would not provde desrable performance as t results n the maxmum preamble overhead. Queung Theoretc algorthm can be used n networks wth hgh traffc densty but few SSs, whereby many hosts are connected to each SS. The WFQ algorthm would be the most sutable f the type of traffc s predomnantly non real-tme such as FTP traffc. Based on the smulaton results, we observed that the WFQ algorthm tends to provde superor performance wth respect to average throughput, whch s the most mportant QoS requrement for delay tolerant applcatons such as FTP. Next, we propose enhancements to the schedulng algorthms to address some of these drawbacks and dscuss some of the open problems: Multple SSs: A major drawback of the cross layer schedulng algorthm s ts nablty to select multple SSs n a frame. To ncorporate multple SSs n the algorthm whle mantanng ts promse of satsfyng the QoS requrements of the mult-class traffc n WMAX, bandwdth n a frame can be allocated accordng to the normalzed prorty of the SSs. The normalzed prorty of a SS s the prorty of the SS relatve to the sum of prorty of all the SSs (equaton 5.1). More specfcally, f the bandwdth avalable n a frame s C and the prorty of connecton s φ, then the bandwdth allocated n one frame to the connecton s: 118

φ b = C * (5.1) n φ j j= 1 where n j= 1 φ j s the sum of prorty of all the SSs. The above formulaton should allow for a more far allocaton of bandwdth among all the SSs. It wll also ensure that the lower prorty SSs (SSs of nrtps and BE classes) do not starve n the presence of large number of SSs of ertps and rtps classes, as n orgnal algorthm. To ensure that the MRTR of the SSs s satsfed, bandwdth equvalent to the MRTR can frst be allocated to all the SSs. Any resdual bandwdth can be allocated accordng to equaton 5.1. Packet sze: Based on the smulaton results, we notced that the WRR schedulng algorthm ndcates poor performance when the traffc contans packets of varable sze or when the packet sze s too large. To resolve ths ssue, the packet sze of the traffc needs to be ncluded n calculatng the weght of the SSs. A varaton of WRR called Varably Weghted Round Robn (VWRR) s proposed n [43] that adaptvely changes the weght of a SS based on the mean packet sze. In ths algorthm, f the average packet length at any nstance n tme s smaller than the maxmum average packet length, then the weght of the connecton at ths nstance ncreases. It has been shown analytcally that the farness of VWRR n the best case equals that of Defct Round Robn (DRR) and n the worst case equals that of WRR. Ths scheme would be more sutable for the heterogeneous traffc n WMAX. Queue length: The queue length has a sgnfcant mpact on the average delay and the packet loss. Therefore, the schedulng algorthm needs to ncorporate the queue 119

sze to mnmze the delay and packet loss. Addtonally, allocatng resource for a SS wth an empty or near empty queue wll waste resources. A queue aware uplnk bandwdth allocaton and rate control mechansm s proposed n [44]. The bandwdth allocaton mechansm adaptvely allocates bandwdth for pollng servce n the presence of hgher prorty UGS servce by explotng the queue status nformaton. Several schedulng algorthms exst that explot the queue sze n wred networks [45], [46], [47]. H.Wang et al. [47] propose a schedulng algorthm to support premum servce n Dfferentated Servces (DffServ) archtecture [48]. Ths algorthm assgns a weght to each connecton based on the average queue sze, mnmum and maxmum thresholds. The mnmum threshold represents the desred queung delay and the maxmum threshold represents the acceptable queung delay. These algorthms or varatons of them can be used to ensure a reasonable delay can be provded for the real-tme traffc whle ensurng the QoS requrements of other types of traffc are satsfed. Bandwdth request mechansm: The choce of bandwdth request mechansm sgnfcantly affects the performance of the schedulng algorthms. We studed the performance of the algorthms under the pggyback and contenton request mechansms. A crtcal part of the contenton request mechansm s the number of slots reserved for contenton. We evaluated two ways of reservng slots for contenton; the frst whereby fxed number of slots are reserved and the second scheme that ntally reserves fxed number of slots and utlzes any further avalable slots. The number of fxed slots to be reserved for contenton, under both contenton slot reservaton schemes, requres further evaluaton under dfferent traffc loads. If 120

large number of slots s reserved, the slots avalable for data wll be less resultng n lower throughput. If fewer slots are reserved, the success of reservng a slot for contenton wll be low but the throughput wll ncrease due to more slots avalable for data. Call Admsson Control (CAC): The performance of an uplnk schedulng algorthm s hghly dependant on the Call Admsson Control (CAC) scheme adopted. Hence, we appled a basc CAC scheme for all the schedulng algorthms. The Queung Theoretc algorthm proposed n [29] employs a CAC algorthm based on class thresholds. The class thresholds are calculated based on the connecton blockng probablty whle maxmzng the average system revenue. The purpose of the thresholds s to lmt the amount of bandwdth allocated to each traffc class. Further nvestgaton of all the algorthms needs to be carred out under varous common CAC algorthms. Based on the results, we can select a CAC algorthm that can provde reasonable performance for all the schedulng algorthms or dentfy the shortcomngs, f any. Inter-class bandwdth allocaton: The most crtcal part of hybrd algorthms s dstrbuton of bandwdth among the traffc classes. We dscussed the merts of hybrd (EDF+WFQ+FIFO) algorthm that uses a strct prorty mechansm and of the hybrd (EDF+WFQ) algorthm that dstrbutes bandwdth accordng to the MRTR and number of SSs wthn the same traffc class. The bandwdth can also be dstrbuted among the traffc classes to maxmze farness or user satsfacton. The ssue of dstrbuton of bandwdth among traffc classes n hybrd algorthms requres further study. 121

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Appendx A Intra-class farness (Jan s ndex) Followng are the results obtaned from measurng ntra-class farness usng Jan s ndex. Our dscusson n chapter 4 uses Mn-max ndex as t s more senstve to unfarness and servce degradaton. Intra-class Farness (ertps) - Jan's Index Intra-class Farness (rtps) - Jan's Index 1.20 1.20 Farness Index 1.00 0.80 0.60 0.40 0.20 0.00 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Farness Index 1.00 0.80 0.60 0.40 0.20 0.00 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Rato of SS Rato of SS Intra-class Farness (nrtps) - Jan's Index Intra-class Farness (BE) - Jan's Index 1.20 1.05 Farness Index 1.00 0.80 0.60 0.40 0.20 0.00 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Farness Index 1.00 0.95 0.90 0.85 0.80 0.75 1:1:1:3 1:1:2:2 1:1:3:1 1:2:2:1 1:3:1:1 2:2:1:1 3:1:1:1 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Rato of SS Rato of SS Fgure A.1: The effect of SS rato: Intra-class farness Intra-class farness (ertps) - Jan's Index Intra-class farness (rtps) - Jan's Index Farness Index 1.200000 1.000000 0.800000 0.600000 0.400000 0.200000 0.000000 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Farness Index 1.010000 1.000000 0.990000 0.980000 0.970000 0.960000 0.950000 0.940000 0.930000 0.920000 0.910000 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Number of SS Number of SS Intra-class farness (nrtps) - Jan's Index Intra-class farness (BE) - Jan's Index Farness Index 1.200000 1.000000 0.800000 0.600000 0.400000 0.200000 0.000000 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Farness Index 1.002000 1.000000 0.998000 0.996000 0.994000 0.992000 0.990000 0.988000 0.986000 0.984000 0.982000 6 12 18 24 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Num ber of SS Number of SS Fgure A.2: The effect of uplnk burst preamble: Intra-class farness (Lght load) 127

Intra-class farness (ertps) - Jan's Index Intra-class farness (rtps) - Jan's Index Farness Index 1.200000 1.000000 0.800000 0.600000 0.400000 0.200000 0.000000 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Farness Index 1.200000 1.000000 0.800000 0.600000 0.400000 0.200000 0.000000 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Number of SS Number of SS Intra-class farness (nrtps) - Jan's Index Intra-class farness (BE) - Jan's Index Farness Index 1.200000 1.000000 0.800000 0.600000 0.400000 0.200000 0.000000 6 12 18 24 30 36 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Farness Index 1.002000 1.000000 0.998000 0.996000 0.994000 0.992000 0.990000 0.988000 0.986000 0.984000 0.982000 6 12 18 24 EDF WFQ WRR EDF+WFQ EDF+WFQ+FIFO CrossLayer QueungTheoretc Num ber of SS Number of SS Fgure A.3: The effect of uplnk burst preamble: Intra-class farness (Heavy load) 128