Politecnico di Milano Facoltà di Ingegneria dell Informazione

Transcription

1 Politecnico di Milano Facoltà di Ingegneria dell Informazione WI-3 Wireless Metropolitan Area Networks (WMAN) Wireless Internet Prof. Antonio Capone

2 Broadband Wireless Access (BWA) Core Network o Wireless high speed connections for residential users o Low cost network infrastructure Base Station (BS) Subscriber Station (SS)

3 WiMAX o IP based wireless network architecture o Differently for cellular systems (3G, 4G), WiMax has been designed for fixed wireless access. Mobility has been introduced later on o WiMAX is somehow between 3G cellular systems and WiFi in terms of: n n n n Transmission rate coverage QoS mobility o Other technologies similar to WiMax are under standardization like IEEE for high speed mobility (250 kmph) and IEEE for the the unused channels (cognitive networks on white spaces)

4 IEEE BWA Standards o The IEEE working group has been established in 1998 for designing a BWA with: n n n LOS propagation Point-to-multipoint topology 10 GHz - 66 GHz frequencies o The IEEE standard was released in Dec 2001 and makes use of a single carrier with a TDM based MAC, but the standardization steps of have been quite involved o Then an amendment IEEE a has been approved and is at the basis of current technology: n n Extension to NLOS scenarios on the 2 GHz - 11GHz band with OFDM (Orthogonal Frequency Division Multiplexing) based physical layer MAC layer for dynamic access and flexible scheduling

5 IEEE BWA Standards o Finally, two variants to the base standards have been approved: n IEEE (June2004) for fixed BWA applications n IEEE e-2005 (Dec 2005), with advanced PHY/ MAC, mobility, and fast handover o WiMAX (Worldwide Interoperability for Microwave Access) is the commercial name used for devices compliant with the different versions of IEEE standard

6 BWA Working Groups IEEE Standard IEEE d (IEEE ) Bande di frequenza Approvato 2-66 GHz 2004 IEEE GHz 2004 IEEE e (IEEE e-2005) 2-66 GHz 2005 IEEE f GHz 2005 IEEE i 2-66 GHz no IEEE h 2-66 GHz no IEEE j 2-66 GHz no IEEE k 2-66 GHz no IEEE < 3.5 GHz no Descrizione Interfaccia radio per Fixed Broadband Wireless Access System Coesistenza tra Fixed Broadband Wireless Access Systems Estensione dello standard IEEE d (IEEE ) al fine di supportare sia terminali fissi che mobili Estensione dello standard IEEE d (IEEE ) per il management base Estensione dello standard IEEE d (IEEE ) per il mobile management base Meccanismi per facilitare la coesistenza in frequenze senza licenza Estensione dello standard IEEE d (IEEE ) con specifiche per relay multi-hop Estensione dello standard IEEE d (IEEE ) con specifiche di bridging Interfaccia radio per Mobile Wireless Access Systems

7 WiMAX versus 3G and WiFI o o o o o o o o Flexibility in the spectrum usage (from 1,25 to 20 MHz) With WiFI and WiMAX the OFDM modulation allows an higher spectrum efficiency and higher transmission rate wrt CDMA High physical layer efficiency in WiMAX due to multiple antennas Use of MIMO more complex and less efficient in 3G systems than in WiMAX WiMAX is efficient in providing symmetrical links and more flexible in the assignment of resources to uplink and downlink WiMAX is completely based on IP technology and can provide different traffic types and quality of service guarantees through a flexible MAC layer But so far WiMax has not been very successful And LTE (4G cellular systems) is based on a technology quite similar to WiMax

8 Protocols o o o o The Physical layer is CS SAP defined based on the frequency used and the number of carriers The Privacy sub-layer MAC SAP provides authentication and key exchange mechanisms The Common Part sublayer provides the basic MAC functionalities Privacy sub-layer The Service Specific Convergence sub-layer is the logical adaptation PHY SAP interface with upper layers n ATM, IP, etc. Physical layer (PHY) MAC PHY Service Specific Convergence sub-layer (CS) MAC Common Part sub-layer (MAC CPS)

9 Frequency bands o GHz with license n Attenuation due to obstances, rain, etc. n Line-Of-Sight (LOS) o 2-11 GHz with license n Non-Line-Of-Sight (NLOS) n Multi-path effect o 2-11 GHz without license n Non-Line-Of-Sight (NLOS) n Multi-path effect n Interference due to other systems Urban areas

10 Physical layer (PHY) Type WirelessMAN-SC WirelessMAN-SCa WirelessMAN-OFDM WirelessMAN-OFDMA WirelessHUMAN GHz 2-11 GHz Licensed 2-11 GHz Licenced 2-11 GHz Licenced 2-11 GHz Non licensed Applicability o Modulation n Single Carrier (SC) n Multi Carrier o Orthogonal Frequency Division Multiplexing (OFDM)

11 Orthogonal Frequency Division Multiplexing (OFDM) Frequency domain Data Carriers DC Carrier Pilot Carriers Time domain Guard Band CHANNEL Guard Band T g T b OFDMA: Orthogonal Frequency Division Multiple Access sub-channel #1 sub-channel #2 sub-channel #3 o Sub-channel: group of data sub-carriers X

12 Physical layer (PHY) o PHY based on frames (physical layer blocks) o Time Division Multiple Access (TDMA) with dynamic allocation o Duplexing n Frequency Division Duplexing (FDD) n Time Division Duplexing (TDD)

13 Duplexing Frequency Division Duplexing (FDD) Time Division Duplexing (TDD)

14 MAC Common Part sub-layer o Connection oriented protocol SDU MAC Management msg. SDU: Service Data Unit PDU: Protocol Data Unit Generic Header Payload CRC Generic Header Payload CRC Generic Header Payload CRC MAC PDU 1 MAC PDU 2 MAC PDU 3

15 MAC PDU ü ü MAC management messages Data (SDU) Generic MAC PDU MAC Header Payload CRC opzionale 6 byte byte 4 byte Bandwidth Request MAC Header CRC opzionale 6 byte 4 byte

16 MAC Management o Messages transported in the Payload of MAC PDU o They area used for n Network access n scheduling n etc. Management Message Type Management Message Payload

17 Generic MAC Header HT = 0 EC TYPE Rsv CI EKS Rsv LEN LEN CID CID HCS HT: Header Type EC: Encryption Control TYPE: Payload Type CI: CRC indicator EKS: Encrypted Key Sequence LEN: Length CID: Connection Identifier HCS: Header Check Sequence

18 Bandwidth Request MAC Header HT = 1 EC = 0 TYPE BR BR CID CID HCS BR: Bandwidth Request CID: Connection Identifier EC: Encryption Control HCS: Header Check Sequence HT: Header Type TYPE: Bandwidth Request Type

19 MAC sub-header o 5 types n Mesh n Fragmentation n Packing n Fast Feedback Allocation n Grant Management Generic MAC Header Mesh Grant Management Fast Feedback Allocation Packing/ Fragmentation Payload CRC opzionale

20 Sub-header MESH FRAGMENTATION FC Node ID 2 byte FSN/ BSN Rsv FC: Fragment state FSN: Fragment Sequence Number (se disabled-arq) BSN: Block Sequence Number (se enabled-arq) 2 byte PACKING FC FSN/ BSN Length 3 byte PIGGYBACK Request 2 byte

21 MAC Common Part sub-layer o The MAC Common sub-layer manages: n Network access n Multiple access mechanism n Scheduling n Quality of service (QoS) n Power control

22 Service Convergence Specific sub-layer o Data received from upper layers are classified n Applying a list of rules for getting o Service Flow ID o Connection ID (CID) n And then assigning the a set of QoS parameters

23 Network topologies o The standard IEEE specifies two network topologies: n Point-to-MultiPoint (PMP) n MultiPoint-to-MultiPoint (Mesh) PMP BS Mesh BS o In the Mesh topology, multi-hop connections are possible through direct links among SSs, called Mesh SSs PMP SS PMP SS Mesh SS Mesh SS Mesh SS

24 IEEE BWA Systems IEEE GHz IEEE GHz PMP IEEE e GHz PMP IEEE GHz Mesh Modulazione Single Carrier Single Carrier Multi Carrier (OFDM) Single Carrier Multi Carrier (OFDMA) Multi Carrier (OFDM) Duplexing FDD TDD FDD TDD FDD TDD TDD Banda del canale MHz MHz MHz MHz Mobilità Advanced Antenna Systems (AAS) Multi-hop

25 Point-to-MultiPoint (PMP) IEEE Backbone Network IEEE e-2005 wireless / wired

26 IEEE OFDM

27 OFDM PHY parameters Parameter Description Value N FFT # of points in the FFT 256 N SD Number of data carriers 192 N SP Number of pilot carriers 8 N SN Number of null carriers 56 BW Nominal channel bandwidth variable n Sampling factor Depends on BW G Ratio between cyclic prefix and symbol time (T g /T b ) 1/4; 1/8; 1/16; 1/32 T simbolo OFDM symbol duration dipends on N FFT, BW, n, G T FRAME Frame duration variable N simboli Number of OFDM symbols per frame T FRAME /T simbolo

28 bit source Transmitter RANDOMIZER RS CC INTERLEAVING MODULAZIONE OFDM TX o Channel coding includes three steps n Randomizer n Forward Error Correction (FEC) n Interleaving

29 Coding and modulation Modulation Block [byte] Coded block [byte] Code rate R c Reed Solomon RS code Convolutional code CC rate BPSK /2 (12,12,0) 1/2 QPSK /2 (32, 24, 4) 2/3 QPSK /4 (40, 36, 2) 5/6 16-QAM /2 (64, 48, 8) 2/3 16-QAM /4 (80, 72, 4) 5/6 64-QAM /3 (108, 96, 6) 3/4 64-QAM /4 (120, 108, 6) 5/6

30 Downlink sub-frame (FDD) FCH: Frame Control Header DL-MAP: Downlink MAP UL-MAP: Uplink MAP PDU: Protocol Data Unit Porzione TDM Porzione TDMA Long Preamble FCH DL BURST #1 DL BURST #2 DL BURST #m DL-MAP UL-MAP Preamble MAC PDU MAC PDU Padd. MAC PDU MAC PDU Padd.

31 Downlink sub-frame (TDD) FCH: Frame Control Header DL-MAP: Downlink MAP UL-MAP: Uplink MAP PDU: Protocol Data Unit Porzione TDM Long Preamble FCH DL BURST #1 DL BURST #2 DL BURST #m DL-MAP UL-MAP MAC PDU MAC PDU Padd. MAC PDU MAC PDU Padd.

32 Uplink sub-frame (FDD+TDD) Porzione TDMA Initial Ranging (RNG) Bandwidth Request (BW-REQ) UP PHY PDU SS #k UP PHY PDU SS #n Preamble MAC PDU MAC PDU Padd. UL BURST

33 Network access o The network access and SS initialization process requires: 1. Searching of the downlink channel and synchronization with the a BS 2. Acquiring of the parameters used for the downlink and the uplink 3. Initial ranging 4. Bandwidth negotiation 5. Authentication and registration 6. Acquiring of IP connectivity 7. Set up of the connections defined in the user profile

34 Ranging SS BS RNG-REQ: Ranging Request ü DIUC (Burst Profile) RNG-REQ Initial Ranging (RNG) RNG-RSP Uplink sub-frame Bandwidth Request (BW-REQ) UP PHY PDU SS #k RNG-RSP: Ranging Response ü Timing advance ü Power adjustment ü Frequency adjustment ü UIUC (Burst Profile) ü DIUC confirm/reject ü Basic e Primary CID

35 Bandwidth negotiation SS BS SBC-RSP: SS Basic Capability Response ü Physical Parameters supported ü Bandwidth Allocation support SBC-REQ SBC-RSP SBC-REQ: SS Basic Capability Request ü Physical Parameters supported (N FFT, ecc.) ü Bandwidth Allocation support (Half-Duplex o Full- Duplex)

36 Multiple access mechanism Controllo DOWNLINK BS->SS UPLINK SS->BS SS j SS k SS j SS k DW UP Training sequence Data burst

37 Multiple access mechanism Downlink sub-frame Preamble FCH DL BURST #1 DL-MAP UL-MAP RNG BW-REQ Uplink sub-frame

38 Multiple access mechanism o Three access mechanisms for different traffic classes based on the mechanism for transmitting bandwidth requests n Guaranteed bandwidth o Example: Voice over IP (VoIP) n Polling o Example: Video streaming n Contention o Example: Web browsing o That are applied based on the service request from the SS n Bandwidth n Delay

39 Service flow o The QoS is obtained associating a Service Flow to traffic flows o The QoS is described by a set of parameters n Throughput n Delay n Jitter n Packet loss rate o The Service Flow is a unidirectional flow of packets to which a QoS is associated

40 Service Flow Identifier (SFID) o The service flow is identified by a Service Flow Identifier (SFID) of 32 bits o The Convergence sub-layer associates a Service Flow to a Connection Identifier (CID) of 16 bits o Active Service Flows are identified in the MAC layer by a CID

41 Service flow management o Service Flows can be configured a priori or dynamically o MAC management specific messages are used for this purpose o (details omitted)

42 Predefined scheduling in the uplink o There are four predefined scheduling for the uplink n Unsolicited Grant Service (UGS) n Real-time polling service (rtps) n Non-real-time polling service (nrtps) n Best effort (BE)

43 Unsolicited Grant Service (UGS) o Designed to real-time flows that generate constant size packets periodically (like e.g. Voice over IP) o A constant bandwidth is assigned periodically for the uplink transmissions of the SS without using the bandwidth request procedure o This mechanism allows n To avoid the overhead and delay introduced by the bandwidth request procedure n To guarantee a constant bandwidth that satisfies real-time requirements of the application

44 Real-time polling service (rtps) o Designed for real-time traffic that generates variable length packets periodically (like e.g. MPEG video) o It offer opportunities to transmit bandwidth requests periodically o This mechanism allow n To satisfy real-time requirements n The variable SS bandwidth needs

45 Non-real-time polling service (nrtps) o Designed to support non real-time traffic that generates bursts of packets of variable length (like e.g. FTP) o It offers the opportunity to transmit bandwidth requests periodically o The SS can use the contention based procedure for additional requests

46 Best effort (BE) o This is the service for all traffic with no quality constraints o It uses the bandwidth requests transmitted using the contentionbased mechanism

47 Contention based bandwidth requests o The SS can transmit transmit bandwidth requests with n A PiggyBack message for incremental requests n A Bandwidth Request (BR) message for aggregated bandwidth requests o Requests are in bytes since the temporal resource allocation may vary depending on the link adaptation mechanism o The SS requests are always associated to a specific connection o Bandwidth grants generated by the BS assign resource to a SS without differentiation among connections

48 Backoff window o The selection of the slot in with the Bandwidth Request (BR) is transmitted is based on a binary exponential backoff o The base backoff window is 2 o The SS picks a random number within the window o The request transmission is delay by a number of slots corresponding to the random number o If a collision occur the backoff window is doubled o The maximum window size is set by the BS o There is a maximum number of attempts (also set by the BS)

49 Backoff mechanism o Example without collision Frame n Frame n-1 Frame n+1 BW-REQ BW-REQ BW-REQ SS i X i SS j SS k X k X j X min =2 0 =1 X max =2 3 =8 X i = random(x max ;X min ) = 4 X j = random(x max ;X min ) = 6 X k = random(x max ;X min ) = 1

50 Example with collision Frame n-1 Frame n Frame n+1 BW-REQ DL #1 BW-REQ BW-REQ DL #1 X i SS i X i X min =2 0 =1 X max =2 3 =8 X i = random(x max ;X min ) = 4 X min =2 0 =1 X max =2 4 =16 X i = random(x max ;X min ) = 9

51 Polling based requests o The BS allocates in the UL-MAP some slots to the SS for transmitting Bandwidth Requests o The assignment can be also for a specific connection o If the number of slots is not sufficient for all SSs a slot sharing is possible through the multicast polling

52 PHY profile Frequency [MHz] Duplexing Channel [MHz] WiMax Certification: phase (con licenza) TDD FDD (senza licenza) TDD 10 Frequency [MHz] Duplexing Channel [MHz] WiMax Certification: phase (con licenza) TDD FDD

53 Example: 3.5 GHz profile Parametro Banda di frequenza Valore 3.5 GHz Modulazione Rate del codice R C Massimo throughput per simbolo OFDM [Mbps] Banda del canale (BW) Banda totale T FRAME 3.5 MHz 14 MHz 2, 4, 5 ms BPSK 1/2 4.8 QPSK 1/2 9.6 QPSK 3/ FFT size (N FFT ) 256 Data sub-carriers (N SD ) QAM 1/ QAM 3/ QAM 2/ QAM 3/ Θ = N SD log M T symbol R c

54 MultiPoint-to-MultiPoint (Mesh) wireless / wired IEEE d Backbone Network

55 Topologies Distributed R detected = 2 hop R Centralized detected = HR threshold hop R decoded R detected MESH BS

56 Mesh Frame (TDD) Frame n-2 Frame n-1 Frame n Frame n+1 Frame n+2 Control sub-frame Data sub-frame Control sub-frame Data sub-frame Schedule Control sub-frame TDM Portion Network Control sub-frame TDM Portion Central. Sched. Central. Sched. Distr. Sched. Network Entry Network Config. Network Config.

57 Centralized Mesh Mesh BS Request Grant Mesh SS Mesh SS Mesh SS Mesh SS Mesh SS Mesh SS Mesh SS

58 Distributed Mesh Availabilities Requests Grant/Ack Mesh SS Mesh BS Mesh SS three way handshake Mesh SS Mesh SS Mesh SS

59 IEEE e OFDMA

60 Point-to-MultiPoint (PMP) IEEE Backbone Network IEEE e-2005 wireless / wired

61 Basic concepts o Segment: group of OFDMA sub-channels to which a MAC instance is associated o Pemutation Zone: adjacent OFDMA symbols that use the same sub-channel permutation: n Partial Usage of Sub-Channels (PUSC): only part of n the sub-channels are allocated to the transmitter Full Usage of Sub-Channels (FUSC): all sub-channels are allocated to the transmitter o Slot: time-frequency element of the resource map depending on the permutation used o Data Region: time-frequency allocation of a group of contiguous OFDMA symbols and sub-channels

62 Frame structure (TDD+FDD) DL sub-frame UL sub-frame obbligatorio opzionale Preamble PUSC FUSC PUSC Optional FUSC AMC TUSC PUSC Optional FUSC AMC PUSC: Partial Usage of Sub-Channels Optional PUSC FUSC: Full Usage of Sub-Channels Optional FUSC AMC: Advanced Modulation and Coding Optional AMC TUSC: Advanced Modulation and Coding Optional TUSC Zone Switch IEs

63 Slot and Data Region Slot 0 OFDMA Symbol Index K-2 K-1 K K+1 K+2 Subchannel Number Data Region

64 Example: FFT 512 DL PUSC k K+1 K+3 K+5 K+7 K+9 K+11 K+13 K+15 K+18 K+21 t 0 SLOT 1 2 Subchannel Logical Number P R E A M B L E DL sub-frame UL sub-frame

65 Frame structure o o FCH and DL-MAP must be transmitted in all frames The FCH n Is transmitted with modulation QPSK ½ n It indicates also the length of the DL-MAP Preamble FCH DL-MAP DL Burst #1 DL Burst #4 DL Burst #2 DL Burst #3 DL Burst #5 DL Burst #6 UL Burst #1 UL Burst #2 UL Burst #3 UL Burst #4 Ranging sub-channel Preamble FCH DL-MAP FCH: Frame Control Header DL-MAP: Downlink MAP UL-MAP: Uplink MAP Data Region

66 Frame structure DL Burst #1 FCH DL-MAP DL Burst #1 FCH DL-MAP DL Burst #1 FCH DL-MAP DL Burst #2 DL Burst #5 DL Burst #4 DL Burst #6 DL Burst #2 DL Burst #5 DL Burst #4 DL Burst #6 DL Burst #2 DL Burst #5 DL Burst #4 DL Burst #6 UL Burst #1 UL Burst #2 UL Burst #3 UL Burst #4 Ranging sub-channel UL Burst #1 UL Burst #2 UL Burst #3 UL Burst #4 Ranging sub-channel UL Burst #1 UL Burst #2 UL Burst #3 UL Burst #4 Ranging sub-channel FCH DL-MAP FCH DL-MAP FCH DL-MAP Segment 1 Segment 2 Segment 3

67 Architettura di rete R2 R2 NAP Visited NSP Home NSP ASN R1 BS R6 ASN Gateway SSs/MSSs SS: Subscriber Station MSS: Mobile Subscriber Station R: Reference Point NAP: Network Access Provider ASN: Access Service Network NSP: Network Service Provider CSN: Connectivity Service Network ASP: Application Service Provider R8 BS R6 R6 ASN R4 ASN Gateway R3 CSN ASP Network OR Internet R5 CSN ASP Network OR Internet