Performance Analysis of IEEE MAC Protocol with Different ACK Polices

Transcription

1 Prformanc Analysis of IEEE MAC Protocol with Diffrnt Polics S. Mhta and K.S. Kwak Wirlss Communications Rsarch Cntr, Inha Univrsity, Kora Abstract. h wirlss prsonal ara ntwork (WPAN is an mrging wirlss tchnology for futur short rang indoor and outdoor communication applications. h IEEE mdium accss control (MAC is proposd, spcially, for short rang high data rats applications, to coordinat th accss to th wirlss mdium among th compting dvics. his papr uss analytical modl to study th prformanc analysis of WPAN (IEEE MAC in trms of throughput, fficint bandwidth utilization, and dlay with various acknowldgmnt schms undr diffrnt paramtrs. Also, som important obsrvations ar obtaind, which can b vry usful to th protocol architcturs. Finally, w com up with som important rsarch issus to furthr invstigat th possibl improvmnts in th WPAN MAC. Kywords: Analytical Modling, Prformanc Analysis, MAC Protocol, IEEE Introduction h IEEE standard MAC layr [1] is basd on a cntralizd, connction orintd topology which divids a larg ntwork into svral smallr ons trmd piconts. A picont consists of a Picont Ntwork Controllr (PNC and DEVs (DEVics. h DEV is dsignd to b low powr and low cost. On DEV is rquird to prform th rol of PNC (Picont Coordinator, which provids th basic timing for th picont as wll as othr picont managmnt functions, such as powr managmnt, Quality of Srvic (QoS schduling, scurity, and so on. h standard also allows for th formation of child piconts and nighbor piconts. h original picont is calld th parnt picont and th child/nighbor piconts ar calld th dpndnt piconts. hs piconts diffr in th way thy associat thmslvs to th parnt picont. IEEE standard supports multipl powr saving mods and multipl acknowldgmnt ( policis (NO, Imm-, and Dly-,. It is vry robust and supports coxistnc with th othr WLAN tchnologis such as IEEE In IEEE MAC protocol, although communications ar connction basd undr th control of th PNC, connctions and data transfr can b mad with pr to pr connctions. In IEEE MAC protocol, th channl tim is dividd into suprframs, which ach suprfram bginning with a bacon. h suprfram is composd of th thr major parts: th bacon, th optional contntion accss J. Wozniak t al. (Eds.: WMNC 9, IFIP AIC 38, pp , 9. IFIP Intrnational Fdration for Information Procssing 9

2 Prformanc Analysis of IEEE MAC Protocol with Diffrnt Polics 141 priod (CAP, and th channl tim allocation priod (P or channl allocation tim (. Wirlss channl is usually vulnrabl to rrors. Error control mchanisms should b dsignd in MAC protocol to provid a crtin lvl of rliability for th highr ntwork layrs. In accordanc with that, IEEE dfins thr typs of acknowldgmnt mchanisms for s: th No-, Imm-, and Dly- mchanisms. For th Imm- and Dly- mchanisms, rtransmission is adoptd to rcovr corruptd frams in prvious transmissions. For th No- mchanism, is not snt aftr a rcption. In th Imm- mchanism, ach fram is individually d following th rcption of th fram. h Dly- mchanism allows th sourc to snd multipl frams without waiting for individual s. Instad, th s of th individual frams ar groupd into a singl rspons fram to b snt to th sourc DEV. In [2] and som othr litratur proposd implid-acknowldgmnt (Imp- for bidirctional communication. Implid acknowldgmnt (Imp- prmits a to b usd bi-dirctionally within a limitd scop. Implid policy is not allowd in th CAP to avoid ambiguitis btwn a fram that is transmittd in rspons to a fram with an implid rqust and a fram that is transmittd indpndntly whn th original fram was missd. o rduc th ovrhad of th IEEE MAC, w combin th fram aggrgation concpt [3] and Dly- mchanism with diffrnt burst sizs, and w dfin this nw mchanism as Dly--AGG. h ida of fram aggrgation is to aggrgat multipl MAC frams into a singl (or approximatly singl transmission. All ths policis hav a larg impact on th throughput, dlay, and channl utilization of th ntwork and rquird a dtaild study to find ovrall prformanc of th ntwork. In this papr, w prsnt th prformanc analysis of IEEE from protocol architctur s point of viw. Furthrmor, w show th ffct of aggrgation with Dly-, i.. Dly--AGG, on th ntwork prformanc. 2 Rlatd Works o th bst of our knowldg, thr is littl work on th prformanc or channl analysis of IEEE MAC with rspct to diffrnt policis, undr diffrnt paramtrs. Howvr, a larg amount of litratur is availabl on IEEE MAC schduling, optimization of suprfram siz, various traffic analyss and so on. Som of th important rlatd works ar as follow. In [4] authors, prsnts th implmntation of IEEE modul in ns-2 and discuss various xprimntal scnario rsults including various schduling tchniqus. Spcially, to invstigat th prformanc of ral-tim and bst-ffort traffic with various supr fram lngths and diffrnt policis. In [5] authors, prsnts a novl sharing protocol, calld VBR-M that nabls th sharing of s blonging to strams with th sam group idntity. his fatur allows th proposd protocol to xploit th statistical charactristics of variabl bit rat (VBR strams by giving unusd tim units to a flow that rquirs pak rat allocation. And thy prsnts two optimizations to VBR-M, namly VBR-Blind and VBR-oknBus, as wll. In [6, 7], th authors proposd an adaptiv Dly- schm for both CP and UDP traffic. h first on is to rqust th Dly- fram adaptivly or chang th

3 142 S. Mhta and K.S. Kwak burst siz of Dly- according to th transmittr quu status. h scond is a rtransmission countr to nabl th dstination DEV to dlivr th MAC data frams to uppr layr timly and ordrly. Whil latr is mor focusd on optimization of channl capacity. Both paprs laid a good foundation in simulation and analytical works of IEEE MAC protocol. Similarly, in [8] authors, formulat a throughput optimization problm undr rror channl condition and driv a closd form solution for th optimal throughput. h work prsntd in [8] is clos to our work but thir analysis scop is limitd only in trms of throughput analysis. Whil our work span covrs th dlay, throughput, and channl utilization with diffrnt policis undr fram aggrgation and rror channl condition. h papr is outlind as follows. In sction 3 w prsnt th prformanc analysis from protocol architctur s point of viw and finally, conclusions and futur work ar drawn in sction 4. 3 Prformanc Analysis of IEEE MAC Protocol In this sction, w prsnt th prformanc analysis of IEEE MAC to answr svral qustions lik optimization of payload, optimization of policis, ffct of aggrgation tc., undr various paramtrs. 3.1 Analytical Modl W us ground works of Bianchis s modl [9] and [8] to prsnt our analysis work. W divid our analysis in two parts; analysis and CAP analysis. abl 1 shows th notations that w usd for th analytical modl. abl 1. Paramtrs notations Short Intr Fram Spac (SIFS tim SIFS Distributd Coordinat Function Intr Fram Spac (DIFS DIFS tim Minimum Intr Fram Spac (MIFS tim MIFS CW Minimum back-off window siz min ransmission tim of th physical prambl pr. ransmission tim of th PHY hadr PHY L MAC ovrhad in byts MAC H L siz in byts L Payload siz in byts Data ransmission tim of MAC ovrhad MAC H transmission tim ransmission tim for th payload Data f h tim for a transmission considrd faild during CAP CAP s h tim for a transmission considrd succssful during CAP CAP f h tim for a transmission considrd faild during CA s h tim for a transmission considrd succssful during CA h tim-out valu waiting for an O h Normalizd throughput during a CAP tim CAP h Normalizd throughput during a tim n Burst siz in packts burst

4 Prformanc Analysis of IEEE MAC Protocol with Diffrnt Polics 143 h throughput is givn by ransmittd Data h = (1 ransmission Cycl Duration W assum a Gaussian wirlss channl modl. h channl bit rror rat (BER, dnotd as p ( < p < 1, can b calculatd via prvious frams or som othr mchanism. How to obtain p is way out of th scop of this papr. From [9], a fram with a lngth L in bits, th probability that th fram is succssfully transmittd can b calculatd as p s = (1 p L (2 Hr, for th simplicity w assum that a data fram is considrd to b succssfully transmittd if both data fram and ar succssfully transmittd in diffrnt mchanism policis. W us Imm_, No_, D_, and D_AGG_ to dnot th immdiat acknowldgmnt, No acknowldgmnt, dlay acknowldgmnt, and dlay acknowldgmnt with aggrgation, rspctivly. hn w can dfin p for diffrnt mchanisms as follows s p, Imm_=(1 p s ( LData + LMAC H + L Imm *8 ( L + L *8 p Data MAC H,No_=(1 p s p,dly_=(1 p s ( L + L + L *8 Data MAC H Dly (3 p,dly_-agg=(1 p s ( L + L + L + L *8 Data MAC H MAC Hs Dly A succssful transmission tim during a is givn by 1 s = ( + MIFS Data MAC H pr PHY ( 2* + 2* SIFS Data MAC H pr PHY MAC PHY Imm ( ( + MIFS Data MAC H pr PHY SIFS MAC PHY Dly pr ( K * + 2* forno forimm K fordly Data for Dly AGG MAC H MAC HS pr PHY SIFS MAC PHY Dly AGG (4 1 Radrs ar advic to hav a look at tabl 1 whil rfrring quations as w couldn t xplain vry paramtr du to spac limitation.

5 144 S. Mhta and K.S. Kwak from (2, (3 and (4 th normalizd throughput during a is givn by h ps, No _ LData*8 for No s ps, Imm_ LData*8 for Imm s = ps, Dly_ KLData*8 for Dly s ps, Dly_ AGGKLData*8 for Dly AGG s o dmonstrat th ffct of n-dly- and n-dly--agg on bandwidth utilization, w dfin a mtric namd maximum ffctiv bandwidth (MEB basd on [1], which is a fraction of tim th channl is usd to succssfully transmit data frams vrsus th total channl tim. h maximum ffctiv bandwidth utilization during a /CAP slot is givn by MEB MEB CAP LData ps, Dly_ nburst. fordly s = LData ps, Dly_ AGG nburst. for Dly AGG s n 1 LData nψ(1 ψ ps,dly_, nburst. fordly scap = n 1 LData nψ(1 ψ ps, Dly_ AGG nburst. fordly AGG scap During th CAP, w us th analytical modl similar with CSMA/CA mchanism of IEEE Also, w study how to optimiz th channl throughput using diffrnt policis undr rror channl condition. Whn th Imm- mchanism is usd in CAP, ach nod adopts CSMA/CA with binary xponntial backoff. Whn NO- mchanism is usd, ach nod will us a fixd backoff window as it has no knowldg whthr or not th transmittd data fram is succssfully rcivd. If th Dly- mchanism is usd, as long as th backoff timr of a nod rachs zro, th nod will first snd a numbr (K of data frams ach sparatd by an MIFS and a dlay-rqust fram sparatd by an MIFS, and wait for th. If a burst transmission (of K data frams is considrd succssful, th sndr will rst th backoff window to th initial valu; othrwis, th backoff window will b doubld. Dly--AGG follows th (5 (6

6 Prformanc Analysis of IEEE MAC Protocol with Diffrnt Polics 145 sam backoff procdur as Dly-. From [9], th failur probability of a transmission during a CAP is givn by 1 (1 p ps, Imm_ forimm_ pf = 1 (1 p ps, Dly_, fordly_ 1 (1 p ps, Dly _ AGG, for Dly _ AGG For n numbr of stations, th probability of a transmittd fram collision is givn by p ψ (7 1 = 1 (1 n (8 ψ, probability of a station to transmit during a gnric slot tim is also dpnds on numbr of rtry limit. hn, th probability of th busy channl is givn by pb = 1 (1 ψ n (9 From (8 and (9, th probability of a succss transmission occurs in a slot tim is givn by n 1 n ψ(1 ψ p s, No _, forno n 1 nψ(1 ψ ps, Imm _, forimm _ ps = n 1 nψ(1 ψ ps, Dly_, fordly_ n 1 nψ(1 ψ ps, Dly_ AGG, fordly_ AGG A succssful transmission tim during a CAP is givn by scap = ( + MIFS Data MAC H pr PHY ( 2* + 2* SIFS Data MAC H pr PHY MAC PHY Imm ( ( + MIFS Data MAC H pr PHY SIFS MAC PHY Dly pr ( * 2* Data MAC H MAC HS pr PHY SIFS MAC PHY Dly AGG CW for No CW for Imm CW+ K fordly AC K CW+ K fordly AGG (1 (11 whr CW rprsnts th avrag back-off tim. h avrag back-off dfins th back-off duration for light loadd ntworks, i.. whn ach station has accss to th channl aftr th first back-off attmpt and is givn by CW. min slot CW = (12 2

7 146 S. Mhta and K.S. Kwak A failur transmission tim during a is givn by f = ( + MIFS Data MAC H pr PHY ( + SIFS Data MAC H pr PHY o ( ( + MIFS Data MAC H pr PHY o SIFS ( * forno forimm K fordly K fordly AGG Data MAC H MAC HS pr PHY o SIFS from (1, (11, and (13, th normalizd throughput during a CAP is givn by h CAP PL S Data*8 (1 p δ + P + ( p P PL S Data*8 (1 p δ + P + ( p P = PKL S Data*8 (1 p δ + P + ( p P PKL S Data*8 (1 p δ + P + ( p P b S s CAP b S f CAP b S s CAP b S f CAP b S s CAP b S f CAP b S s CAP b S f CAP for No for No for Dly for Dly AGG from (1, w can also calculat th avrag accss dlay during a /CAP. (13 ( Prformanc Evaluation For th prformanc valuation, w adopt th following paramtrs from [11] as shown in tabl 2. Paramtrs SIFS MIFS Prambl and PLCP Hadr abl 2. Paramtrs valus Valus 2.5 usc 1 usc 9 usc CW min 8 Payload Siz Policy Data Rat Control Signal Rat 1~5 KB 3 basic +Dly--AGG policis 1~2 Gbps 48 Mbps Analysis Figurs 1 and 2 show th normalizd throughput for diffrnt payload sizs with diffrnt polics with and without aggrgation, rspctivly. W assum an idal channl conditions for ths rsults. Hr, w can obsrv that No- givs th

8 Prformanc Analysis of IEEE MAC Protocol with Diffrnt Polics 147 suprior rsults as most of th tim is utilizd for data transfr. Howvr, No- policy is not suitabl for vry application and channl condition. h Dly-- AGG policy can achiv somwhat clos rsults to No- policy, as it rducs th unncssary intr-fram tim as wll as th hadr siz. Figurs 1 and 2 giv us th normalizd valu of throughput at diffrnt payload sizs but can t answr for optimum payload siz. So, w produc th sam rsults with Gaussian wirlss channl modl with a givn BER rat. Diffrnt schms without aggrgation Mthod Diffrnt schms with aggrgation mthod hroughput (Mbps hroughput (No--1 Gbps hroughput (Imm--1 Gbps hroughput (2-Dly--1 Gbps hroughput (4-Dly--2 Gbps hroughput (No--2 Gbps hroughput (Imm--2 Gbps hroughput (2-Dly--2 Gbps hroughput (4-Dly--2 Gbps Data Packt Payload (KB Fig. 1. hroughput vrsus payload siz with diffrnt policis hroughput (Mbps hroughput ( No- 1 Gbps hroughput ( 2-Dly- 1 Gbps hroughput ( 4-Dly- 1 Gbps hroughput ( No- 2 Gbps hroughput ( 2-Dly- 2 Gbps hroughput ( 4-Dly- 2 Gbps Data Packt Payload (KB Fig. 2. hroughput vrsus payload siz with diffrnt policis hroughput (Mbps Diffrnt Schms without aggrgation Mthod (BER=.2 hroughput (No--1Gbps hroughput (Imm--1Gbps hroughput (2-Dly--1Gbps hroughput (4-Dly--1Gbps hroughput (No--2Gbps hroughput (Imm--2Gbps hroughput (2-Dly--2Gbps hroughput (4-Dly--2Gbps Data Packt Payload (KB Fig. 3. hroughput vrsus payload siz with diffrnt policis hroughput (Mbps Diffrnt Schms with aggrgation Mthod (BER=.2 18 hroughput (No--1Gbps hroughput (2-Dly--1Gbps hroughput (4-Dly--1Gbps hroughput (No--2Gbps hroughput (2-Dly--2Gbps hroughput (4-Dly--2Gbps Data Packt Payload (KB Fig. 4. hroughput vrsus payload siz with diffrnt policis Figurs 3 and 4 show th throughput for diffrnt payload sizs undr a givn BER valu. It can b sn that an optimal payload siz xists for a givn BER valu. As shown in th mntiond figurs th throughput first incrass, and thn dcrass with incrasing payload siz (vn with th aggrgation in rror pron channls. his is bcaus without th protction of FCS in individual payload fram, a singl bit rror may corrupt th whol fram which will wast lots of mdium tim usag and countract th fficincy producd by an incrasd payload siz. Figur 5 shows th normalizd throughput for diffrnt BER valus with diffrnt policis whn payload siz is st to 1KB. As th BER valu incrass th throughput dcrass. h No-

9 148 S. Mhta and K.S. Kwak policy with aggrgation has largr throughput ovr larg rang of BER valus than any othr policis. o find th ffct of n-dly- on bandwidth utilization as wll as to find th optimal valu of burst siz for n-dly- policy, w dfin th MEB mtric in (6. Figurs 6 and 7 show th MEB with diffrnt burst valus undr a givn BER valu. From ths figur w can obsrv that burst siz = 4 givs good rsults in fairly all givn payload valus. Figur 8 shows th accss dlay prformanc for diffrnt burst sizs with th aggrgation mthod. Hr, w only analyzd n-dly-- AGG policy to gt th uppr bound on th dlay prformanc Gbps and Payload=1KB No- ( Without Aggrgation Imm- 2-Dly- ( Without Aggrgation 4-Dly- ( Without Aggrgation No- (With Aggrgation.25.2 Without aggrgation mthod (BER=.2 Payload = 1KB- 1Gbps Payload = 2KB- 1Gbps Payload = 3KB- 1Gbps Payload = 4KB- 1Gbps Payload = 5KB- 1Gbps 2-Dly- ( With Aggrgation hroughput Dly- ( With Aggrgation MEB BER Burst Siz n Fig. 5. hroughput vrsus BER valu with diffrnt policis Fig. 6. MEB vrsus burst siz With aggrgation mthod (BER=.2 Payload = 1KB- 1Gbps Payload = 2KB- 1Gbps Payload = 3KB- 1Gbps Payload = 4KB- 1Gbps Payload = 5KB- 1Gbps (Data Rat=1Gbps, BER=, n-dly- Payload = 1KB Payload = 2KB Payload = 3KB Payload = 4KB Payload = 5KB MEB.2.15 Dlay (usc Burst Siz n Burst Siz n Fig. 7. MEB vrsus burst siz Fig. 8. Accss dlay vrsus burst siz CAP Analysis Figurs 9 and 1 show th normalizd throughput ovr diffrnt payload sizs with diffrnt policis. Hr, w assum no comptition btwn activ nods, as our main focus is to gt maximum normalizd throughput for ach payload siz. Figurs 11 and 12 show th normalizd throughput for diffrnt payload sizs with diffrnt policis undr a givn BER valu. For ach policis, with th incras of th payload siz, th throughput first incrass, thn dcrass aftr th maximal point. his can b xplaind as follows. In CAP, th tim to transmit th payload is only a

10 Prformanc Analysis of IEEE MAC Protocol with Diffrnt Polics 149 small portion of th total tim usd. hrfor, whn th payload siz incrass, th transmission fficincy can b incras, but th rror probability also incrass. h incras of th curvs in figurs 11 and 12 is bcaus th ffct of incrasd transmission fficincy is mor significant than th ffct of incrasd fram rror probability, and th dcras of th curvs is du to dominant ffct of incrasd fram rror probability whn payload siz furthr incrass. From th abov mntiond figurs w can find out th optimum payload siz valu for a givn BER valu. Hr, it is worth to not that normalizd throughput prformanc dpnds on th numbr of activ stations and backoff window siz during a CAP tim. Figur 13 shows th normalizd throughput for diffrnt BER valus whn payload siz is st to 1KB. Diffrnt schms without aggrgation mthod (During CAP tim 1 hroughput (No--1 Gbps 11 hroughput ( Imm--1 Gbps hroughput (2-Dly--1 Gbps 1 hroughput (4-Dly--1 Gbps hroughput (No-- 2 Gbps 9 hroughput (Imm--2 Gbps hroughput (2-Dly--2 Gbps 8 hroughput (4-Dly--2 Gbps hroughput (Mbps Data Packt Payload (KB hroughput (Mbps Diffrnt schms with aggrgation mthod ( During CAP im hroughput (No- 1 Gbps hroughput (2-Dly- Gbps hroughput (4-Dly- 1 Gbps hroughput (No- 2 Gbps hroughput (2-Dly- 2 Gbps hroughput (4-Dly- 2 Gbps Data Packt Payload (KB Fig. 9. hroughput vrsus payload siz Fig. 1. hroughput vrsus payload siz Diffrnt Schms without aggrgation mthod (During CAP tim, BER=.2 7 hroughput (No--1Gbps hroughput (Imm--1Gbps hroughput (2-Dly--1Gbps 6 hroughput (4-Dly--1Gbps hroughput (No--2Gbps hroughput (Imm--2Gbps 5 hroughput (2-Dly--2Gbps hroughput (4-Dly--2Gbps 3 hroughput (Mbps hroughput (Mbps Diffrnt Schms with aggrgation mthod (During CAP tim, BER=.2 hroughput (No--1Gbps 1 hroughput (2-Dly--1Gbps hroughput (4-Dly--1Gbps hroughput (No--2Gbps 1 hroughput (2-Dly--2Gbps hroughput (4-Dly--2Gbps Data Packt Payload (KB Data Packt Payload (KB Fig. 11. hroughput vrsus payload siz Fig. 12. hroughput vrsus payload siz Similar to duration analysis, Figur 14 and 15 shows th MEB for diffrnt burst valus undr a givn BER valu. Figur 16 shows th accss dlay prformanc for diffrnt burst sizs undr a givn BER valu. h accss dlay prformanc with diffrnt policis is vry snsitiv to backoff window siz and numbr of activ nods. In this papr, w focusd only on n-dly--agg policy to gt th uppr bound on th dlay prformanc.

11 15 S. Mhta and K.S. Kwak hroughput Gbps and Payload = 1 KB ( During CAP im No- ( Without Aggrgation Imm- 2-Dly- ( Without Aggrgation 4-Dly- ( Without Aggrgation No- (With Aggrgation 2-Dly- ( With Aggrgation 4-Dly- ( With Aggrgation MEB Without aggrgation mthod (During CAP BER=.2.2 Payload = 1KB- 1Gbps.18 Payload = 2KB- 1Gbps Payload = 3KB- 1Gbps.16 Payload = 4KB- 1Gbps Payload = 5KB- 1Gbps BER Burst Siz n Fig. 13. hroughput vrsus BER valu with diffrnt policis Fig. 14. MEB vrsus burst siz.25.2 With aggrgation mthod (During CAP, BER=.2 Payload = 1KB- 1Gbps Payload = 2KB- 1Gbps Payload = 3KB- 1Gbps Payload = 4KB- 1Gbps Payload = 5KB- 1Gbps (During CAP, Data Rat = 1Gbps, BER=, n-dly- Payload = 1KB Payload = 2KB Payload = 3KB Payload = 4KB Payload = 5KB 3.5 MEB.15.1 Dlay (msc Burst Siz n Burst Siz n Fig. 15. MEB vrsus burst siz Fig. 16. Accss dlay vrsus burst siz 4 Conclusions and Futur Work In this papr, w prsntd a prformanc analysis of WPAN (IEEE MAC for wirlss snsor ntworks. W hav xtnsivly studid th diffrnt policis in and CAP undr a givn BER valu. h optimal payload siz as wll as optimal burst siz can b dtrmind analytically from th prsntd analysis. For futur work, w want to study th impact of backoff window siz on channl utilization and accss dlay. W hop that th rsults of this papr will hlp snsor ntwork dsignrs to asily and corrctly provision systms basd on IEEE MAC tchnology. Rfrncs 1. P /D17: (C/LM Standard for lcommunications and Information Exchang Btwn Systms - LAN/MAN Spcific Rquirmnts - Part 15.3: Wirlss Mdium Accss Control (MAC and Physical Layr (PHY Spcifications for High Rat Wirlss Prsonal Ara Ntworks (Fbruary 3

12 Prformanc Analysis of IEEE MAC Protocol with Diffrnt Polics Part 15.3: Wirlss Mdium Accss Control (MAC and Physical Layr (PHY Spcifications for High Rat Wirlss Prsonal Ara Ntworks. Amndmnt 1: MAC Sub layr, IEEE Std b (Fbruary 5 3. Xiao, Y.: IEEE 82.11n: Enhancmnts for highr throughput in wirlss LANs. IEEE Wirlss Communications, (Dcmbr 5 4. Chin, K.-W., Low, D.: Simulation study of th IEEE MAC. In: Proc., Australian lcommunications and Ntwork Applications Confrnc (ANAC, Sydny, Australia (4 5. Chin, K.W., Low, D.: A Novl IEEE Sharing Protocol for Supporting VBR Strams. In: Proc. of IEEE ICCCN (5 6. Chn, H., Guo, Z., Yao, R., Li, Y.: Improvd Prformanc with Adaptiv Dly- for IEEE WPAN ovr UWB PHY. IEICE rans. Fundamntals E88-A(9 (Sptmbr 5 7. sng, Y.H., Wu, E.H., Chn, G.H.: Maximum raffic Schduling and Capacity Analysis for IEEE High Data Rat MAC Protocol. In: Proc. of IEEE VC (3 8. Xiao, Y., Shn, X., Jiang, H.: Optimal Mchanisms of th IEEE MAC for Ultra-Widband Systms. IEEE JSAC 24(4 (April 6 9. Bianchi, G.: Prformanc analysis of th IEEE distributd coordination function. IEEE JSAC 18(3, ( 1. Chn, H., Guo, Z., Yao, R.Y., Shn, X., Li, Y.: Prfoamnc Analyis of dlyd Acknowldgmnt Schm in UWB-Basd High-Rat WPAN. IEEE transaction on vhicular tchnology 55(2 (March IEEE P82.15 Working Group for Wirlss Prsonal Ara Ntworks (WPANs.: Unifid and flxibl millimtr wav WPAN systms supportd by common mod. DOC: IEEE c (July 9