WMAX DBA Algorthm Usng 2-Ter Mx-Mn Fr Shrng Polcy Pe-Chen Tseng 1, J-Yn Ts 2, nd Wen-Shyng Hwng 2,* 1 Deprtment of Informton Engneerng nd Informtcs, Tzu Ch College of Technology, Hulen, Twn pechen@tccn.edu.tw 2 Deprtment of Electrcl Engneerng, tonl Kohsung, Unversty of Appled Scences, Kohsung, Twn 1098304123@kus.edu.tw, wshwng@ml.ee.kus.edu.tw Abstrct. IEEE 802.16 leves mportnt ssues lke uplnk bndwdth llocton to vendors. Ths pper proposes WMAX DBA lgorthm usng 2-ter Mx- Mn Fr Shrng Polcy (2tMMFS-DBA). In the frst prt of the lgorthm, bndwdth reservtons re set frst for, then for n nd BE pplctons. ext, the mx-mn fr shrng polcy sets mxmum connecton demnds for bndwdth requests nd QoS provsonng. In the second prt, the IEEE 802.16 MAC heder s modfed for pggybckng SS queue sttus messges to help bse sttons determne bndwdth llocton. 2tMMFS-DBA prortzes bndwdth provsonng. An opportunty cost functon bounds the cost of lloctng bndwdth to dfferent clsses so s to mntn selected revenue levels to the servce provder. Smulton shows the proposed dynmc provsonng scheme cn stsfy the bndwdth requrements for dfferent clsses of trffc wth overll mproved system throughput. Keywords: WMx, IEEE 802.16e, QoS, DBA. 1 Introducton The ncresng populrty of cellulr phones nd smlr devces s drvng the development of wreless communcton technology for voce, med nd hgh cpcty dt rte servces. Accordngly, IEEE 802.16e [1] s expected to support qulty of servce (QoS) for rel tme pplctons such s voce over IP (VoIP), vdeo stremng nd vdeo conferencng wth dfferent QoS requrements nd trnsmsson gurntee. IEEE 802.16e s Moble Brodbnd Wreless Access (A) s n extenson provdng for moble subscrber sttons (MSSs) nd cn even support MSSs movng t vehculr speeds. IEEE 802.16e lso provdes for combnng fxed nd moble brodbnd wreless ccess. Compred to wred nternet servce provders, A systems re cpble of fster deployment nd lower deployment cost. IEEE 802.16e s currently the most promsng medum ccess control (MAC) protocol for hgh-speed wreless ccess n both the developed nd developng world. At the MAC lyer, ech connecton belongs to sngle servce flow type nd s * Correspondng uthor. R.-S. Chng, T.-h. Km, nd S.-L. Peng (Eds.): SUComS 2011, CCIS 223, pp. 277 286, 2011. Sprnger-Verlg Berln Hedelberg 2011
278 P.-C. Tseng, J.-Y. Ts, nd W.-S. Hwng chrcterzed by set of QoS prmeters. A number of uplnk schedulng mechnsms re defned, ncludng unsolcted bndwdth grnts, pollng nd contenton procedures. For uplnk schedulng servces, t supports fve servce flow types whch dentfy specfc sets of QoS prmeters: UGS (unsolcted grnt servce), e (extended rel-tme pollng servce), (rel-tme pollng servce), n (nonreltme pollng servce), nd BE (best effort). QoS n 802.16e s supported by lloctng ech connecton between the SS nd the BS (clled servce flow) to specfc QoS clss. Among them, UGS, e, re sutble for rel-tme multmed pplctons such s VoIP servces. Bsed on the IEEE 802.16 stndrd [2], WMAX (Worldwde Interoperblty for Mcrowve Access) provdes hgh-speed dt ccess for vrous trnsmsson modes, e.g. pont-to-multpont lnks to portble nd fully moble Internet ccess. Two types of duplex methods seprte uplnk (UL) nd downlnk (DL) communcton sgnls: Tme Dvson Duplex (TDD) nd Frequency Dvson Duplex (FDD). IEEE 802.16 defnes two operton modes: the mesh mode nd the pont-to-multpont (PMP) mode [3], [4]. In the mesh mode, drect communcton between SSs wthout the need of BS s supported. For the PMP mode (Fg. 1), multple SSs nd vrous publc networks re connected by BS. Fg. 1. Topology of WMAX PMP networks Implementton of the bndwdth llocton lgorthm ws not specfed n the 802.16 stndrd [2]. A performnce chllenge n 802.16 TDD systems s the determnton of the rto of downlnk to uplnk cpctes. TDD cn hndle flexbly both symmetrc nd symmetrc brodbnd trffc. Symmetrc trffc usng n equl splt between uplnk nd downlnk chnnels my led to neffcent bndwdth utlzton. Asymmetrc trffc, such s ADSL, more demnd for downlodng nd less for uplodng, mkes the bndwdth rto determnton problem even more complcted when the trnsport lyer ssue s tken nto ccount. The lst mle ccess for resdentl users tends to be symmetrc. Chng [5] proposed n Adptve Bndwdth Allocton Scheme (ABAS) nd Le [6] proposed CQQ scheme, dynmclly djust the Downlnk/Uplnk (DL/UL) bndwdth to mtch current DL/UL trffc n order to get better chnnel qulty, but the method requres more complcted computng, resultng n reduced prctcl pplcblty. Chou [7] proposed the UBAR protocol (uplnk bndwdth llocton nd recovery), whch employs proportonlly fr shrng scheme for effcent
WMAX DBA Algorthm Usng 2-Ter Mx-Mn Fr Shrng Polcy 279 bndwdth utlzton nd further dopts tmeout-bsed UL-MAP retrnsmsson scheme wth uplnk bndwdth rellocton lgorthms to solve smultneously bndwdth wste problems. But UBAR ncreses system complexty by modfyng the TDD ccess mode. Wth regrd to opportunty cost consderton, Bder [8] proposed wht cn be clled the Rev scheme, whch spns multple tme slots/frmes nd optmlly lloctes them to the dfferent clsses of trffc dependng on ther weghts, the rel-tme bndwdth requrements of ther connectons, the chnnel qulty condtons nd the expected obtned revenues, but ths scheme leds to lest prorty trffc BE strvton, therefore flng to cheve optmzed frness. Thus, Ts [9] proposed the MMFS-DBA lgorthm ( WMAX DBA lgorthm usng Mx-Mn Fr Shrng Polcy). Ths system results n rel-tme drop n clls due to nsuffcent rel-tme bndwdth reservton becuse no clssfcton of rel-tme nd non-reltme pplcton trffc s ncluded t the strt. The remnder of ths study wll focus on the ssue of mplementton of n effcent bndwdth llocton lgorthm, such s s not specfed n the IEEE 802.16 stndrd. Ths pper proposes hgh performnce WMAX DBA (Dynmc Bndwdth Allocton) lgorthm usng 2-ter Mx-Mn Fr Shrng Polcy (2tMMFS-DBA). Ths lgorthm dopts bndwdth reservtons nd the mx-mn fr shrng polcy (MMFS) for effcent llocton of bndwdth. The rest of ths pper s structured s follows: secton 2 descrbes the proposed 2tMMFS-DBA lgorthm. Smulton results re found n secton 3. A fnl summry s presented n concludng secton. 2 2tMMFS-DBA Algorthm The presented 2tMMFS-DBA lgorthm s dvded nto two prts. In the frst prt of the lgorthm, trffc clssfcton, bndwdth reservton nd QoS provsonng re performed,.e. the dfferent bndwdth reservtons re set. The mx-mn fr shrng polcy (MMFS) s used for the mxmum connecton demnd for requested bndwdth, wth QoS provsonng for pplctons. The requested bndwdth s llocted frst to pplctons, then to n pplctons nd fnlly to BE pplctons. BE pplctons hve the lest prorty,.e they hve no QoS gurntee. To vod strvton of BE pplctons, ech pplctons hs weghtng fctor to mke sure ech cheves reltve QoS gurntee, wth BE chevng t lest mnmum vlble bndwdth to keep the BE lve n the WMAX network. In the second prt of the lgorthm, the two reserved felds of the IEEE 802.16 generc MAC heder re modfed v montorng of the SS queue sttus for urgent pckets whch need to be trnsmtted before other pckets. It lso montors remnng pckets n the SS queue. SSs re lso llowed to sk for bndwdth v PggyBck messges to the BS. Under the condton no requrng ddtonl overhed, ths llows the BS to mke decsons for effcent llocton of bndwdth. The 2tMMFS-DBA scheme especlly consders QoS prorty for optml llocton of BS bndwdth to the SSs wth regrd to qulty nd system performnce for rel-tme pplcton servces. The 2tMMFS-DBA method of BS llocton of bndwdth to the SSs mproves the current IEEE 802.16 network, provdng better QoS qulty for multmed servces.
280 P.-C. Tseng, J.-Y. Ts, nd W.-S. Hwng 2.1 Bndwdth Reservton for Connecton Ths pper proposes dynmc bndwdth provsonng scheme for future brodbnd wreless systems. The proposed scheme s desgned to ccommodte mult-clss trffc wth multple connectons hvng dfferent bndwdth requrements nd vryng chnnel qulty condtons. The mn objectve of our scheme s to optmlly llocte bndwdth or the correspondng tme frmes for ech clss of trffc n order to stsfy the bndwdth requrements of ther connectons. In ddton, the proposed scheme unquely ncorportes nd bounds the cost (n terms of revenue loss) of bndwdth provsonng through n opportunty cost functon. Ths provdes greter flexblty to servce provders for determnng the levels of bndwdth provsonng to dfferent trffc clsses so s to gurntee certn level of revenue. To gurntee the rel-tme pplcton servces hve hgher QoS prorty, ths pper frstly consders the proporton,.e. the number of connectons occupyng the number of totl connectons, thereby llowng determnton of reserve connecton bndwdth res _ s n equton (1). Ths ensures tht connectons hve hgher QoS gurntee. The notton n ths pper s s follows: W : the number of connectons : the system weghtng vlue for mxmum connectons c : the totl number of system connectons : the totl system bndwdth for the BS res _ : the bndwdth reservton for tot res_ mx : the mxmum bndwdth reservton for res _ = W res _ mx, tot, f f c c > W W (1) Mx-Mn Fr Bndwdth Shrng In order to stsfy the mxmum bndwdth request for the SS connecton, ths pper extends the Mx-Mn Fr Shrng Polcy (MMFS), frst usng equtons (2) nd (3) to obtn the verge bndwdth of the nd (n +BE) connectons, desgnted respectvely vg _ nd vg _ n + BE. Then the Mx-Mn Fr Bndwdth Shrng polcy s executed to stsfy the demnds of the mxmum bndwdth request of the nd (n +BE) connectons. = vg _ res _ ( 2) vg _ n + BE tot = c res _ (3)
WMAX DBA Algorthm Usng 2-Ter Mx-Mn Fr Shrng Polcy 281 It s frst determned whether the reserved bndwdth res _ for the connecton s equl to or greter thn the entre bndwdth request of the connecton ( req, ). If YES, then there s enough bndwdth for the entre bndwdth request of the connecton, so the reservton bndwdth s llocted to the connecton s n equton (4), where s the number of SS nd δ s the bndwdth llocted to SS. Otherwse, when the reserved bndwdth res _ s less thn the entre bndwdth request of the connecton ( ), then the reserved bndwdth s req, nsuffcent for the entre bndwdth request of the connecton. In ths cse,.e. req, > vg, so the MMFS scheme n equton (2) s executed to llocte the _ mnmum necessry bndwdth R to the connecton, otherwse lloctng the mn necessry bndwdth request to the connecton, s n equton (5). req, req,, f req, vg _ δ = (5) Rmn, f req, > vg _ Smlrly, bndwdth s llocted to the n, BE connecton usng the sme wy s n equtons (1) to (5). After llocton, the nformton must be updted s n equton (6). s the remnder of the vlble bndwdth. The 2nd prt wll execute f > 0 n the 1st run of 2tMMFS-DBA scheme. The frst prt of the 2tMMFS-DBA scheme s for pplcton servce wth the gretest QoS gurntee. Thus, the servce s hndled frst, clcultng the verge bndwdth vg for ech servce flow, then executng the MMFS scheme for fr llocton of the bndwdth. After servce trffc llocton s completed, smlr process s performed for non-rel-tme pplcton servce nd fnlly for the BE servce. 2.2 Evluton of SS Queue Sttus δ = req, A request my be corrupted due to collson when SSs perform bndwdth requests. Km [10] proposed modfng the IEEE 802.16 generc MAC heder n order to let n SS pss the messge to the BS by trnsmttng dt, so the BS llows the SS bndwdth request f no collson occurs. Ths de s extended n the second prt of the 2tMMFS-DBA lgorthm, usng two reserved bts n the IEEE 802.16 generc MAC heder, one for the Crtcl Dt bt ( CD), the other for the Bcklogged Dt bt ( BD ) s shown n Fg. 2. As result, wth no ddtonl SS overhed, the BS gets mportnt nformton v n SS Pggybck messge whch montors the pcket sttus of the SS queue, ncludng evluton of crtcl dt nd/or bcklogged dt pckets n the SS queue. The CD bt s for urgent pckets tht need to be trnsmtted n the SS queue. The BD bt s for pckets not yet trnsmtted n the SS queue. The BS cn use ths nformton to llocte bndwdth more effcently. = tot c 1 δ (4) (6)
282 P.-C. Tseng, J.-Y. Ts, nd W.-S. Hwng Fg. 2. IEEE 802.16 generc MAC heder Becuse of rel-tme servce must tke more better cre of pcket dely tme, therefore need hgher QoS prorty to gurntee qulty. Accordngly, the second prt of the 2tMMFS-DBA system, wth reference to [9], [11], clcultes the pcket dely expry tme Dedlne s n equton (7) nd the expected Remn k Tme RemnTme t for pcket send-out s n equton (8). In equton (7), the r pcket dely expry tme Dedlne s the pcket rrvng tme k ArrvlTm e t plus 0 MxLtency. In equton (8), the expected Remn Tme RemnTme t for pcket k r to send out, s Dedlne mnus the system current tme k CurrentTm e t, where k s c the trnsmttng pcket number. The Crtcl Dt CD bt s set to 1 f RemnTme t r s not more thn one Frme Durton tme, s equton (9). Ths mens tht t s urgent tht the pcket be sent out. Dedlne k = ArrvlTme t 0 + MxLtency (7) RemnTmet = Dedlne CurrentTme t r If tr Frme Durton then CD bt = "1" k c (8) (9) After the full run (, n, BE) of the frst prt of the 2tMMFS-DBA lgorthm, the rest of the bndwdth s ssgned vergely to the crtcl servce flow n the SS queue. In equton (10), ns, ndctes the nsuffcent bndwdth request for servce connecton fter runnng of the frst prt of 2tMMFS-DBA. In equton (11), α s the verge proporton to the rest of the bndwdth for the nsuffcent request bndwdth for servce connecton. The gol of equton (12) s to lmt the obtned bndwdth so tht s not greter thn the orgnl request bndwdth for servce connecton. Then equton (13) s used to updte the rest of the bndwdth. Smlr methodology s used to llocte bndwdth to the crtcl n nd BE connectons s n equtons (10), (11) nd (12). α = = δ ns, req, ns, SS CDbt= " 1" ns, δ + α, f (δ + α ) < δ = req,, f (δ + α ) req, req, (10) (11) (12)
WMAX DBA Algorthm Usng 2-Ter Mx-Mn Fr Shrng Polcy 283 = 1 δ (13) After the bove process, the Bcklogged Dt BD bt n the IEEE 802.16 generc MAC heder s chnged to 1 f there s servce stll left n SS queue, s n equton (14). For BSs recevng ths nformton (.e. BD mrked to 1 ), the rest of the bndwdth s ssgned vergely to the servce flow n the SS queue. ns, s the nsuffcent request bndwdth for servce connecton fter full run of the frst prt of 2tMMFS-DBA. In equton (15), β s the verge proporton to the rest of the bndwdth for the ns, for servce connecton. Equton (16) ensures the obtned bndwdth s not greter thn the orgnl request bndwdth for servce connecton. Then equton (17) s used to updte the rest of the bndwdth. Smlr methodology s used to llocte bndwdth to the crtcl n nd BE connectons s n equtons (14), (15) nd (16). If szeof ( SS ) > 0 then BD bt = " 1" (14) β = ns, = BDbt " 1" ns, (15) δ + β, f δ = req,, f (δ + β ) < (δ + β ) req, req, (16) = 1 δ (17) 3 Smulton Results Ths pper focuses on the IEEE 802.16 pont-to-multpont (PMP) mode, whch s the prmry opertng mode of WMAX for resdentl users. Under PMP, the IEEE 802.16e wreless network wth centrl BS serves severl SSs nd ech SS communctes wth the BS drectly (Fg. 1). To evlute performnce, 2tMMFS-DBA functonlty s smulted by the SIMSCRIPT II.5 lnguge for numercl nlyss. The system weghtng vlue s 0.3. The BS bndwdth s 20 Mbps. The entry possblty of UGS,, n, BS s 30%, 50%, 70%, 100%, respectvely. Ths mens for exmple, f the number of the connectons =100, then UGS gets 30 (=100*30%), gets 35 (=(100-30)*50%), n gets 24.5(=(70-35)*70%) nd BE gets 10.5(=(35-24.5)*100%). In order to obtn more detled smulton vlues, the number of SSs s ncresed by 5. Compred wth Bder s Rev scheme [8], Fg. 3 shows tht droppng rte of the proposed lgorthm s 12.44% lower (better) for connectons when the number of SSs s over 35. At the sme tme, t s 2% hgher (worse) for n connectons, 1.17% hgher (worse) for BE connectons. Fg. 5 shows tht the throughput of the proposed lgorthm s 1.2 Mbps hgher (better) when the number of SSs over 10.
284 P.-C. Tseng, J.-Y. Ts, nd W.-S. Hwng Fg. 3. Droppng rte for Rev vs 2tMMFS Fg. 4. Droppng rte for MMFS vs 2tMMFS Fg. 5. Throughput for Rev vs 2tMMFS Compred wth Ts s MMFS scheme [9], Fg. 4 shows tht droppng rte of the proposed lgorthm s 5.35% lower (better) for connectons when the number of SSs over 35. At the sme tme, t s 4.15% hgher (worse) for n connectons nd 10.57% hgher (worse) n BE connectons. Fg. 6 shows tht the throughput of the proposed lgorthm s 0.17 Mbps hgher (better) when the number of SSs over 10. The results show tht the proposed lgorthm delvers better QoS for the prortzed users, wth overll better system throughput.
WMAX DBA Algorthm Usng 2-Ter Mx-Mn Fr Shrng Polcy 285 Fg. 6. Throughput for MMFS vs 2tMMFS 4 Conclusons Future brodbnd wreless systems wll support wde rnge of multmed pplctons for moble users. However, to mxmze user experence, bndwdth provsonng s crtcl. In ths pper, novel bndwdth provsonng scheme for brodbnd wreless network s proposed. The proposed scheme llows for prortzed bndwdth provsonng to dfferent clsses of trffc for support of multple connectons wth dfferent bndwdth requrements. It lso ncorportes unque opportunty cost functon to bound the cost of lloctng bndwdth to dfferent clsses so s to mntn certn revenue levels to the servce provder. Smulton results revel the presented 2tMMFS-DBA lgorthm effcently lloctes bndwdth for mproved urgent multmed requrements nd provdes hgher QoS gurntees n IEEE 802.16e networks, wth overll enhnced system throughput. Fxed clss weghts, however, cnnot cheve optmzed frness snce the performnce of ech clss s not fxed due to the vryng bndwdth requrements nd vryng chnnel qulty condtons. Thus, our future work wll study dynmc weght updte scheme to compute dynmclly the weghts of dfferent clsses of trffc bsed on ther performnce hstory n order to mxmze nter-clss frness. Ths wy, the resultng frness wll be more dptve to the performnce of the clsses snce t s bsed on ther performnce hstory. Acknowledgments. Ths reserch ws supported by tonl Scence Councl of Twn under project number SC 99-2218-E-277-001. References 1. IEEE Std 802.16eTM -2005: IEEE Stndrd for Locl nd Metropoltn Are etworks Prt 16: Ar Interfce for Fxed nd Moble Brodbnd Wreless Access Systems - Amendment 2: Physcl nd Medum Access Control Lyers for Combned Fxed nd Moble Operton n Lcensed Bnds (2006) 2. IEEE 802.16-2004: IEEE stndrd for Locl nd Metropoltn Are etworks -Prt 16: Ar Interfce for Fxed Brodbnd Wreless Access Systems (2004) 3. L, B., Qn, Y., Low, C.P., Gwee, C.L.: A Survey on Moble WMAX. IEEE Communctons Mgzne 45(12), 70 75 (2007)
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