Throughput Analysis Model for IEEE e EDCA with Multiple Access Categories

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1 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee Department of Informaton and Communcaton Enneern Doneu Unversty Busan Korea ABSTRACT IEEE 82.11e standard has een specfed to support dfferentated quaty of servce (QoS) one of the crtca ssues on the conventona IEEE wreess oca area networks (WLANs). Enhanced Dstruted Channe Access (EDCA) s the fundamenta and mandatory contenton-ased channe access method of IEEE 82.11e and devers traffc ased on dfferentated Access Cateores (ACs). A enera three dmensona Markov chan mode of IEEE 82.11e EDCA for performance anayss s proposed n ths paper. The anaytca mode consders mutpe statons wth an artrary numer of dfferent ACs. It aso dfferentates the contenton wndow (CW) szes and the artraton nterframe spaces (AIFSs) and consders vrtua coson mechansm. Based on the mode the saturaton throuhput of EDCA s derved and the accuracy of the proposed mode s vadated va smuatons. Keywords: IEEE 82.11e EDCA Markov mode performance anayss quaty of servce. 1. Introducton IEEE wreess oca area networks (WLANs) [1 have een wdey used for hh speed wreess Internet access. However there are many quatyof-servce (QoS) mtatons n the orna IEEE WLAN standard [1 ecause t was ascay deveoped to serve est effort servces. Its fundamenta access mechansm for the medum access contro (MAC) ayer Dstruted Coordnaton Functon (DCF) [1 cannot satsfy the ncreasn demand for rea-tme appcaton support. Thus a new standard amendment IEEE 82.11e [2 has een specfed to support dfferentated QoS requrements over IEEE WLANs. It provdes dfferentated servce casses n the MAC ayer so that t can dever rea-tme mutmeda traffc n addton to tradtona data packets [2. In IEEE 82.11e a new MAC access mechansm named Hyrd Coordnaton Functon (HCF) s defned [2. The HCF conssts of two channe access methods for the support of dfferentated QoS. One of them s a contenton-ased channe access method named Enhanced Dstruted Channe Access (EDCA) and the other one s HCF Controed Channe Access (HCCA). EDCA s the fundamenta and mandatory method of IEEE 82.11e and devers traffc ased on dfferentated Access Cateores (ACs) whe HCCA s optona and requres centrazed pon and schedun aorthms to aocate the resources. Ths paper covers the mandatory EDCA access method ony. Some anaytca modes for IEEE 82.11e EDCA method have een proposed n the terature [ The performance of the EDCA method has een expored y means of the anaytca modes wth the oa en to ether predct anaytcay performance metrcs or to understand the ehavor of the EDCA method. Xao [3 4 enares Banch s Markovan mode [5 to a mode wth dfferentated contenton wndow (CW) szes and anayzes the effects of the dfferentated CW szes on the throuhput. However the artraton nterframe space (AIFS) dfferentaton and the vrtua coson mechansm specfed n the IEEE 82.11e standard [2 are not ncuded. Xao assumes equa AIFS to a ACs and consders ncorrecty that the coson proaty contros the ackoff actvty whch s actuay controed y the channe usy proaty. Zhan et a. [6 aso assume that the coson proaty s the same as the channe usy proaty. 612 Vo. 11 Auust 213

2 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / Ronson and Randhawa [7 and Hu and Devetskots [8 propose a performance mode to anayze the saturaton throuhput of EDCA y dfferentatn oth the CW szes and the AIFSs. However the vrtua coson mechansm s not ncuded n [7 and the retry mt feature s neected n [8. Furthermore t s assumed that each staton has ony one queue for one AC and the possty of ackoff suspenson s not ceary anayzed n ther modes [7 8. Kon et a. [9 anayze the throuhput performnance of dfferentated servce traffc. They consder that durn the AIFS perod f the channe s sensed usy y an AC ts remann AIFS perod s frozen and defrozen aan when the channe s sensed de aan. However the remann AIFS perod cannot e frozen and has to restart from the ennn. Furthermore the contenson zone specfc transmsson proaty caused y usn dfferent AIFSs s not consdered n [9. Tantra et a. [1 present a three-dmensona Markov chan mode where each staton has four queues for four dfferent ACs. The mode consders oth the effect of usn dfferentated AIFSs and the effect of ackoff suspenson. However they assume three hher prorty ACs have the same AIFS vaue. Furthermore they do not consder the possty of ackoff suspenson for the hher prorty ACs. Xon and Mao [11 consder ony two ACs for anaytca smpcty and mt ther study to one AC per staton. In [11 two Markov chan modes are created for two ACs separatey and the transmsson proaty of a staton n a enerc tme sot s assumed to e constant. The proaty that a hher prorty AC staton sees an de tme sot depends whch contenton zone the tme sot eons to. Athouh they otan two dfferent contenson zone specfc proates the Markov chan for the hher prorty AC uses ony the averae proty. The mode proposed n ths paper remove the aove proem. Lee et a. [12 consder the contenton zone specfc proates that a staton sees an de tme sot whch s nored for hher prorty AC n [11. However three hher prorty ACs have the same AIFS vaue n [12. In ths paper the mode n [12 s extended to the mode where each staton carres traffc from an artrary numer of dfferent ACs. Taher et a. [13 deveop a dscrete-tme Markov chan mode that takes nto account most features ncudn the transmsson opportunty mt (TXOP Lmt) of the 82.11e EDCA method under oth the non-saturaton and the saturaton traffc condton. Tursunova and Km [14 propose a mathematca mode for IEEE 82.11e EDCA under non-saturaton condton. However the coson proaty and the channe usy proaty are assumed to e constant n [ Furthermore vrtua coson mechansm s not consdered n [14 and t s assumed that each staton s usn ony one AC. In ths paper we propose a more enera three dmensona Markov chan mode of IEEE 82.11e EDCA. The proposed anaytc mode consders mutpe statons each of whch has an artrary numer of dfferent ACs. The mode dfferentates the CW szes and the AIFS vaues of dfferent ACs and consders vrtua coson mechansm. We assume that traffc oad s saturated and ony one frame s transmtted n each TXOP. Based on the proposed mode we evauate the throuhput performance of the EDCA wth an artrary numer of dfferent ACs. The resuts of our anaytca mode are then verfed usn smuatons.font. 2. Enhanced dstruted channe access The IEEE DCF has no functonaty to support QoS requrements. To overcome ths drawack and enhance the conventona DCF IEEE 82.11e EDCA has een specfed. EDCA provdes dfferentated and dstruted channe access for packets wth dfferent prortes n a staton. EDCA handes appcaton needs y mappn ther traffc nto four dfferent ACs: AC_BK for ackround traffc AC_BE for est effort traffc AC_VI for vdeo traffc and AC_VO for voce. Indvdua AC s dfferentated y a set CW of ts own EDCA parameters namey mn CW max and AIFS [15 where CWmn and CWmax are nta and maxmum CW szes of nary exponenta ackoff respectvey and AIFS s the tme nterva a packet of a ven AC has to wat after the channe ecomes de efore t can start the ackoff process or transmt [16. EDCA CW assns smaer vaues of mn CW max and AIFS to ACs wth hher prortes. Journa of Apped Research and Technooy 613

3 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / After m cosons the ackoff counter s seected unformy from rane [ mn(2 CWmnCWmax) 1 where m s the maxmum numer of aowae retransmssons. When the tota numer of retransmssons equas m no further retransmssons are attempted and the packet s dscarded [16. In EDCA mechansm each staton mpements a queue for each AC. Packets eonn to dfferent ACs wthn a sne staton may code wth each other when ther ackoff counters decrements to zero smutaneousy. Ths phenomenon s caed a vrtua coson n IEEE 82.11e EDCA and s prevented y ettn the hhest prorty nvoved n the coson wn the contenton [ Anayss wthout vrtua coson We mode the ackoff operaton of each staton wth a Markov chan. Our approach s smar to that of [7. In ths secton we assume that each staton mpements ony one of the mutpe ACs n EDCA. Thus we do not consder vrtua coson whch w e handed n Secton 4. Ths paper supports up to L ACs from the owest prorty servce cass AC to the hhest one AC L- 1. We use dfferent Markov chans for dfferent ACs. Thus L dfferent Markov chans are requred. For 1 L 1 the state of a ven taed staton mpementn AC s consdered at the foown emedded pont; the oundary of each sot tme at whch the ackoff counter for AC L- 1 s actve (see Fure 1). Note that n EDCA the ackoff counter s frozen when a transmsson s detected n the channe and reactvated at the ennn of the ast sot of the correspondn AIFS. Let s (t) e the stochastc process representn the numer of retransmssons of the taed staton at the emedded pont t. The vaue of s (t) ranes from (the frst ackoff stae) to (the retransmsson mt) for AC. Let (t) e the stochastc process representn the vaue of the ackoff counter for the taed staton at tme t. After each packet transmsson the vaue of the ackoff counter for the taed staton mpementn AC s assumed to e consdered from the ennn of the ast sot of the AIFS for AC L- 1 nstead of AC and reman frozen unt the ast sot of the AIFS for the taed staton whch s just for computatona convenence and has no effect on the performance of EDCA. When s( t) the vaue of (t) ranes from 1 to W [AC 1 where CWmn[AC CWmax[AC. W [AC s ven y mn( 2 ) Note that n EDCA when the ackoff counter of a staton expres the staton has to wat for an extra de ackoff sot n order to transmt ts packet. The vaue ( t) 1 represents the end of the extra de sot. The stochastc process r (t) represents the remann AIFS perod for AC at tme t. The vaue of r (t) ranes from to A AIFS[AC AIFS[ACL1 1. The process {( s ( t) ( t) r( t))} s a Markov chan under the assumpton that p [AC (the proaty that from the AC staton s pont of vew at east one of the other statons transmt a packet durn a type sot) and q [AC (the proaty that a packet from the taed AC staton encounters a coson when t s transmtted durn a type- sot) are ndependent of the numer of retransmssons where type- sots are the sots etween the end of AIFS[AC and AIFS[AC 1 and type- sots are the sots after the end of AIFS[AC. Fure 2 shows the transton daram of {( s ( t) ( t) r( t))} for the taed staton mpementn AC where a% denotes the remander of the dvson of a y and W m p and q are used nstead of W [AC m [ AC p [AC and q [AC respectvey. In Fure 2 the states t s 1 are ntroduced whch w e emnated when the statonary proates are normazed. Let [ AC and j k[ac e the statonary dstruton. We have [AC q [AC q [AC [AC A1 A h1 1 1 A A 1 h (1) [AC 614 Vo. 11 Auust 213

4 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / Fure1. Emedded ponts. where A AIFS[AC AIFS[AC 1 for L1 1 L-1 (See Fure 1). We aso have the foowns: j k j k 1[AC L 1 k A AL 1 (1 p[ac ) j k 1[AC A A 1 k A A for 2 L 1 (1 p 1[AC ) j k 1[AC L 1 A A k A A 1 j 1 k 1[AC L 1 k A AL 1 [AC (1 p 1[AC ) j1 k 1[AC L 1 k A A (1 p[ac ) j 1 k 1[AC A A 1 k A A for 23 (1 p1[ac ) j1 k 1[AC 1 k A A1 (1 p1[ac ) j 11[AC (1 p[ac ) j1[ac k (2) and j A [AC 1 W [AC p [AC L1 p 1 [AC j [AC [AC A 1 A h1 j A A 1h [AC (3) where [AC for a k and W [AC k [AC for k A A W [AC j 1 j k 1 k ; k 1[AC L-1k A AL 1 (1 p 1[AC ) k 1[AC L-1k A A (1 p[ac ) k 1[AC [AC A A 1 k A A for 2 3 (1 p1[ac ) k 1[AC 1 k A A 1 (1 p1[ac ) 1[AC (1 p[ac ) [AC k (4) for 1. Each of the state statonary proates can e expressed n terms of [AC and otaned y mposn the normazaton condton Journa of Apped Research and Technooy 615

5 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / /W 1/W 1/W A W -2A W -1A A -A L-1 p L-1 W -2A -A L-1 p L-1 W -1A -A L-1 p L-1 1-p L-1 1-p L-1 1-p L A -A G W -2A -A G W -1A -A G A -A G-1+1 A -A G-1-1 W -2A -A G-1-1 W -1A -A G A -A +2 W -2A -A +2 W -1A -A +2 1-p +1 A -A +1 p +1 W -2A -A +1 p +1 1-p +1 W -1A -A +1 p +1 1-q (+1)%(m+1) (+1)%(m+1) (+1)%(m+1) (+1)%(m+1) q 1-q q 1-q q 1-q -1 q -1-1A -A -1A -A -1A -A A -A -1 1-p +1 1-p A -A +1 A -A -1+2 A -A p W -2A -A p (+1)%(m+1) (+1)%(m+1) 1-q 1 q 1 1-q q p 1 1-p 1 p 1 p 1-p Fure 2. State transton daram. 616 Vo. 11 Auust 213

6 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / A A k [AC w [AC A [AC 1. jk j k (5) For 1 L-1 the proates [AC that a staton of AC transmts n a type- sot s ven y L 1 A 1 A 1A A1 h[ac h1 W [AC 1 A 1 A ja A1 h[ac j1 h1 [AC 1. (6) 1 [AC W [AC 1 j [AC j1. The proates p [AC and q [AC are ven y P j j1 W [AC 1 A A W [AC 1 L1 W [AC 1 A jao A j1 k W [AC 1 A A j1 k -1 A L1 j1 k [AC [AC jk jk h[ac [AC 1 (9) -1k 1 L-1. The proaty P S [AC that a sot contans a successfu transmsson of AC under the condton that the sot s a type- sot s ven y n[ AC1 [ AC L1 PS [ AC (1 [ ACx ) 1 [ AC 1 x n[ ACx (1) for 1 L-1. The proaty P C that a sot tme contans a coson s P C where (11) 1 PI PS' p [AC q [AC 1-(1 -τ [AC ) n[ac 1 (1 τ [AC x x ) n[ac x (7) for 1 L-1 where n [AC s the numer of statons mpementn AC. The proaty P I that a sot s de s L 1 1 L S P P P S [ AC. The saturaton throuhput of E[ P S[ AC P P T P T I S S AC s ven y L1 C C P P S [ AC (12) (13) L 1 L1 n[ac P P (1 τ [AC ) (8) I where the proaty P that an artrary sot s a type- sot s ven y where E [P s the averae enth of packet payoad s the enth of a sot tme T S s the averae enth of a successfu transmsson and T C s the averae enth of a coson. The vaues of T S and T C are ven n [7. Journa of Apped Research and Technooy 617

7 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / Anayss wth vrtua coson We consder the case that each staton runs an artrary numer of dfferent queues wth dfferent ACs. [7. Own to vrtua coson when two or more queues of a staton have ackoff counters of zero the hhest prorty queue s favored and s ven the chance to access the medum. The ower prorty ones st see the coson and they w ncrease ther ackoff staes and choose other ackoff counters [7. For the vrtua coson case we use the same approach as n Secton 3 wth the foown dfferences [7. Frsty snce each staton now has mutpe queues a Markov chan s used to mode each queue nstead of each staton. Secondy the vrtua coson chanes the coson proates seen y ndvdua queues ecause the hhest prorty queue w not see the coson wth the ower prorty queues of the same staton [7. The coson proaty q [AC s now ven y n[ AC 1 [AC 1 (1 [ ) x q AC x x (14) n[ AC (1 [ AC ) x x. x Then f we want to see the throuhput of AC n a staton the staton can e vewed as one wth a sne AC and the aove coson proaty q [AC. Accordny a anaytc resuts n Secton 3 can e used even when we consder the vrtua coson. 5. Numerca resuts In order to evauate the throuhput performance of ACs n IEEE 82.11e EDCA we use the vaues of system parameters shown n Tae 1 for oth anaytca and smuaton resuts. Common Parameters payoad sze PHY header MAC header RTS frame CTS frame ACK frame Vaues 8192 ts 192 ts 272 ts PHY header + 16ts PHY header + 112ts PHY header + 112ts tme sot( ) sec SIFS sec data rate ts/sec m [ AC for a 5 nput parameter set Ⅰ for four dfferent ACs CW mn [AC CW max [AC AIFS[AC SIFS SIFS SIFS SIFS 2 nput parameter set Ⅱ for four dfferent ACs CW mn [AC CW max [AC AIFS[AC SIFS SIFS SIFS SIFS 2 Tae 1. Exampes of the System Parameters. 618 Vo. 11 Auust 213

8 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / Fure 3. Saturaton throuhput: nput parameter set I. Fure 4. Saturaton throuhput: nput parameter set II. Journa of Apped Research and Technooy 619

9 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / Fures 3 and 4 show the saturaton throuhput of four ACs n EDCA for asc access and RTS/CTS exchane methods. From the fures we see the dfferentaton n saturaton throuhput of four ACs due to the CW sze the AIFS vaue and the vrtua coson n IEEE 82.11e EDCA. In order to vadate our mode we have conducted smuatons and smuaton resuts are aso potted n Fs. 3 and 4. The fures ndcate that the anaytc resuts of our proposed mode are cosey matched wth the smuaton resuts for oth asc access and RTS/CTS exchane methods. Ths means that our new proposed mode for the anayss of EDCA can show fathfuy the performance of the EDCA mechansm. From Fures 3 and 4 we can aso nvestate the foowns. In Fure 3 we nvestate the mpact of the AIFS parameter and the vrtua coson on the performance dfferentaton amon statons of varous ACs. Fure 3 shows the saturaton throuhput as a functon of the numer of statons wth dfferent AIFS parameters and the same CW sze as n the nput parameter set I. Snce t s reported that the vrtua coson has tte effect on the performance [1 Fure 3 reveas that AIFS has a pronounced effect on servce dfferentaton. Fure 4 shows the saturaton throuhput as a functon of the numer of statons for the nput parameter set II wth the same AIFS parameter set as n Fure 3. In ths case the performance dfferentaton s ntroduced due to dfferent vaues of CW mn [AC and CW max [AC for the varous AC queues as we as the dfferent vaues of AIFS. The numerca resuts ndcate that EDCA can provde rate dfferentaton amon statons of varous ACs. The hher the prorty of AC s the hher the throuhput for the AC due to smaer CW szes and smaer AIFS vaues. In addton as expected the performance of EDCA wth RTS/CTS enaed shows etter throuhput over a ACs than that of EDCA for asc access method ecause the RTS/CTS exchane method reduces a waste of resource due to cosons. 6. Concusons In ths paper a more enera three dmensona Markov chan mode to anayze IEEE 82.11e EDCA protoco under saturated traffc oad was proposed. The proposed anaytc mode consdered mutpe statons wth an artrary numer of dfferent ACs. It aso dfferentated the CW szes and the AIFS vaues of dfferent ACs and consders vrtua cosons. Based on the proposed mode we anayzed the saturaton throuhput of dfferent ACs n EDCA. The resuts of our anaytca mode were then verfed usn smuatons. The anaytca resuts are very accurate compared wth the smuaton resut for varous EDCA parameters. Acknowedements Ths research was supported y Basc Scence Research Proram throuh the Natona Research Foundaton of Korea (NRF) funded y the Mnstry of Educaton (NRF-213R1A1A4A11394). References [1 IEEE Standard WG Wreess LAN Medum Access Contro (MAC) and Physca Layer (PHY) Specfcatons ANSI/IEEE Std Edton (R23) 23. [2 IEEE Standard WG Wreess LAN Medum Access Contro (MAC) and Physca Layer (PHY) Specfcatons: Medum Access Contro (MAC) Quaty of Servce Enhancements ANSI/IEEE Std 82.11e [3 Y. Xao Performance anayss of IEEE 82.11e EDCF under saturaton condton n IEEE Internatona Conference on Communcatons Pars France 24 pp [4 Y. Xao Performance anayss of prorty schemes for IEEE and IEEE 82.11e wreess LANs IEEE T. Wreess Commun. vo. 4 no. 4 pp [5 G. Banch Performance anayss of the IEEE dstruted coordnaton functon IEEE J. Se. Areas Commun. vo. 18 no. 3 pp [6 Y. Zhan et a. Performance anayss and QoEaware enhancement for IEEE 82.11e EDCA under unsaturatons n IEEE 74th Vehcuar Technooy Conference San Francsco CA Unted States 211 pp [7 W. Ronson and T. S. Randhawa Saturaton throuhput anayss of IEEE 82.11e enhanced dstruted coordnaton functon IEEE J. Se. Areas Commun. vo. 22 no. 5 pp Vo. 11 Auust 213

10 Throuhput Anayss Mode for IEEE 82.11e EDCA wth Mutpe Access Cateores Y. Lee / [8 J. Hu and M. Devetskots A unfed mode for the performance anayss of IEEE 82.11e EDCA IEEE T. Commun. vo. 53 no. 9 pp [9 Z. Kon et a. Performance anayss of IEEE 82.11e contenton-ased channe access IEEE J. Se. Areas Commun. vo. 22 no. 1 pp [1 W. Tantra et a. Throuhput and deay anayss of the IEEE EDCA saturaton n IEEE Internatona Conference on Communcatons Seou Korea 25 pp [11 L. Xon and G. Mao Saturated throuhput anayss of IEEE 82.11e EDCA Comput. Netw. vo. 51 no. 11 pp [12 Y. Lee et a. Saturaton throuhput anayss of IEEE 82.11e EDCA n the 3rd Internatona Conference on Inteent Computn: Advanced Inteent Computn Theores and Appcatons. Wth Aspects of Artfca Inteence Qn Dao Chna 27 pp [13 N. C. Taher et a. An accurate anaytca mode for 82.11e EDCA under dfferent traffc condtons wth contenton-free urstn J. Comput. Netw. Commun. vo. 211 pp [14 S. Tursunova and Y.-T. Km Reastc IEEE 82.11e EDCA mode for QoS-aware moe coud servce provsonn IEEE T. Consum. Eectr. vo. 58 no. 1 pp [15 M. I. Au-Tar and G. Mn Performance evauaton of an enhanced dstruted channe access protoco under heteroeneous traffc n the 2th Internatona Conference on Parae and Dstruted Processn Rhodes Isand Greece 26 pp [16 Z. Tao and S. Panwar Throuhput and deay anayss for the IEEE 82.11e enhanced dstruted channe access IEEE T. Commun. vo. 54 no. 4 pp Journa of Apped Research and Technooy 621

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