Call Admission Control for Real Time Multimedia Services with Variable Bit Rate in WCDMA Systems

Transcription

1 Cll Adissio Cotrol for Rel Tie Multiedi Services with Vrible Bit Rte i WCDMA Systes Che Y. ee d Ki Wo Sug Dept. of Idustril Egieerig, KAIST 7-, Guseog-dog, Dejeo, Kore che@kist.c.kr, kwsug@kist.c.kr Abstrct Cll dissio cotrol for rel tie ultiedi services with vrible bit rte (VBR) is cosidered i this pper. I the WCDMA syste, oe of the ost previlig services will be the rel tie ultiedi of which dt rte chges dyiclly. We propose two cll dissio schees tht effectively reflect fetures of VBR ultiedi services d well stisfy the objective i this pper. The proposed schees re bsed o SIR of the syste. Especilly, they ticipte the fluctutio of SIR due to the dt rte chge of ech ultiedi service d ke dissio decisio bsed o predictio of future SIR rther th curret SIR vlue. The proposed schees re copred with dissio policy whose dissio decisio depeds oly o the curret SIR vlue. I. INTRODUCTION Recetly, the ded for brod rge of ultiedi services hs icresed rpidly. Thus, the third geertio (G) wireless couictio systes re desiged for the ultiedi couictio. The widebd code divisio ultiple ccess (WCDMA) techology is the ost widely dopted G ir iterfce []. Sice the out of resource required for ultiedi trsissio is uch lrger th tht of the legcy voice service, ore precise rdio resource geet (RRM) strtegy is required to gurtee the qulity of service (QoS) of obile users. Cll dissio cotrol (CAC) occupies iportt prt of the RRM i the wireless couictio systes. My CAC schees hve bee proposed for voice service, d recet works hve strted to focus o CAC for ultiedi services [-5]. owever, the dyic chge of dt rtes, which is coo i trsissio of rel tie ultiedi services, is ot extesively ddressed yet. CAC schees for vrious ultiedi services re proposed i [-]. owever, services re ssued to be costt bit rte (CBR) trffics. I [-5], ultiedi services re odeled s vrible bit rte (VBR) sources, but CACs i these works re bsed o xiu dt rte of services rther th exploitig the chge of dt rtes. I the WCDMA syste, oe of the ost previlig services will be the rel tie video service. Becuse of lrge bdwidth requireet for high-qulity service, it is expected tht ost of the services will be ecoded with copressio techiques [6]. I geerl, the copressio lgoriths geerte VBR source, sice the dt rte of ech fre depeds o the istteous chge of the scee or soud [7]. With VBR trsissio, sigl to iterferece rtio (SIR) of cell fluctutes severely eve with the se uber of ogoig services. Whe CAC does ot reflect the VBR spect, the syste y led to wrog dissio decisio. For exple, ew service y be ccepted whe SIR becoes low for oet, with hevy trffic i verge, d vice vers. To prevet such wrog dissio decisio, CAC schee which reflects the fetures of VBR trffics is required. I this pper, two CAC schees for rel tie VBR video service re proposed. The proposed schees re bsed o SIR of the syste. Especilly, they ticipte the fluctutio of SIR due to the dt rte chge of ech video service d ke dissio decisio bsed o the predictio of future SIR rther th curret SIR vlue. The objective of this pper is to iiize the ew cll blockig probbility while keepig the outge probbility below QoS threshold. SIR of cell is odeled s cotiuous tie stochstic process. With the stochstic odel, the blockig probbility of ew service d the outge probbility of existig services re obtied ccordig to specific dissio schee. The reider of this pper is orgized s follows. I Sectio, the syste odel is explied. The behvior of ech video service is odeled s Mrkov chi. The, blockig probbility d outge probbility re obtied with the stochstic odelig. Cll dissio cotrol lgoriths for rel tie VBR video service re proposed i Sectio. The proposed cll dissio lgoriths re evluted by uericl experiets i Sectio. Filly, the coclusio is preseted i Sectio 5 II. SYSTEM MODE Sigle clss rel tie VBR video service such s video telephoy d video coferecig is cosidered i this pper. Accurte odelig of VBR video source is the first step for predictig SIR. Sice oe of the ost widely used odels is the fiite stte Mrkov chi [7], we follow this odelig techique. To siplify further lysis, VBR video source is ssued to be two-stte cotiuous tie Mrkov chi s show i Fig.. Ech video source hs two dt rtes R d R, which respectively refers to the low dt rte d the high dt rte. We deote d s the trsitio rte fro R to R d //$. IEEE 559

2 , µ,,, µ µ µ µ R Figure. Video source odel. R, µ,, R to R, respectively. Ech video service c be strted fro either R or R. We ivestigte the uplik of cell i the WCDMA syste. I the dowlik, bse sttio coordites trsissios of ll users i cell. Thus, the vritio of SIR due to VBR trsissios c be resolved by proper resource lloctio lgorith. O the cotrry, the trsissio of obile is idepedet with ech other i the uplik. Due to the striget dely requireet of rel tie video service, trsissio buffer is ot cosidered i further lysis. A ew video cll i cell is geerted by expoetil distributio with preter. is divided with d, which respectively deotes the geertio rte of clls tht strts fro R d fro R. The cll copletio rte is lso expoetilly distributed with preter µ. et N d N respectively be the uber of high rte d low rte video clls i cell. Syste stte is defied s row vector s such tht s = if N = i d N = j. The stte spce of ll fesible sttes is deoted by S. We defie d s the dissio probbilities of video cll i stte (i, which strts fro R d R, respectively. d deped o specific cll dissio schee. Thus, the proper deteritio of dissio probbilities i ech stte is i issue i this pper. Withi the stte spce S, the followig four kids of stte trsitios re possible: ew cll is ditted i the cell, oe of the ogoig clls leves the cell, cll icreses the trsissio dt rte, cll decreses the trsissio dt rte. Fig. illustrtes siple exple of the stte trsitio digr with the stte spce of S = { s = ( x, y) x + y }. et p be the stedy stte probbility of stte (i. The, flow blce equtios of the syste re give by I i +, j pi+, j ( i + i, i, j + + I ) µ + I p ( )µ i, j pi, ji, j + Ii, j pi, j i, j + I i+, j pi+, j ( i + ) + Ii, pi, ( j + ) = p ( + + i + iµ + jµ + j ). () I (), I is the biry idictor vrible whose vlue is oe if S, d otherwise, zero., µ, µ, Figure. Siple exple of stte trsitio digr The stedy stte probbility p is obtied by equtio () d the followig orliztio coditio p S =. () Recll tht our objective is iiizig the blockig probbility of ew cll request while keepig the syste outge probbility below give threshold. Blockig probbility is defied s the portio of users whose dissio request is deied. Also, outge probbility is defied s the portio of tie tht the syste experieces outge. We deote the blockig probbility d outge probbility by p B d p out, respectively. Suppose the syste is i stte (i,. A ew cll request with iitil dt rte of R (R )is geerted with the rte of ( ). The, it y be ditted with the probbility ( blocked with the probbility - (- by p B = S + p ) or ). Thus, p B is give. () Aother perforce esure to be obtied is the syste outge probbility. Outge is defied s situtio where the rtio of bit eergy to oise desity ( E b / N ) flls below the predefied threshold vlue. Sice E b / N vlue is differet i ech stte, outge y or y ot occur ccordig to the stte of the syste. Thus, we hve biry idictor vrible for //$. IEEE 56

3 ech stte. et ( E b / N ) be the E b / N vlue of stte (i, d γ be the E b / N requireet of the video cll. The, the idictor for syste outge is defied s Ψ, =, E b if < γ N. () otherwise The uplik E b / N of the CDMA syste is ivestigted i [, 8]. Fro (), the syste outge probbility is give by p = out p S Ψ. (5) I this sectio, we first describe the behvior of VBR video source s two stte Mrkov chi. The, SIR of cell is odeled s cotiuous tie Mrkov process, d the stedy stte probbility is obtied. Filly, we derive two perforces esures, blockig probbility d syste outge probbility. It should be oted, however, tht the stedy stte probbility d perforce esures re ot obtied prcticlly util we deterie dissio probbilities i ll sttes. The deteritio of dissio probbilities, d, will be discussed i the ext sectio. III. CA ADMISSION CONTRO SCEMES CAC is defied s the decisio of whether to dit ew cll request or ot. It rejects the ew cll request if its dissio scrifices the QoS of ogoig clls. Two CAC schees for VBR video service re proposed, ely vrible bit rte cll dissio cotrol (VCAC) d VCAC. These dissio cotrol schees re copred with istteous cll dissio cotrol (), which kes dissio decisio bsed o the istteous SIR of the syste. A. VCAC Syste sttes re grouped ito severl super-sttes to siplify the CAC proble. et us itroduce the cocept of level, which is group of sttes with the se uber of ogoig clls. evel is defied s set of sttes such tht stte (i, is i level if i + j =. With the itroductio of level, four kids of syste trsitios re divided ito two ctegories of trsitios: itrlevel trsitio d iter-level trsitio. Icrese or decrese of trsitted dt rte belogs to itr-level trsitio. O the other hd, eterig of ew cll d levig of ogoig cll costitute the iter-level trsitio. It es tht the dissio decisio is oly cocered with the iter-level trsitio. Thus, we c cocetrte o the iter-level trsitio whe we deterie the dissio probbilities. ( ) - ) ( Figure. Birth-deth process withi level The i ide of the proposed VCAC is to pproxite the syste stte trsitio with trsitio og levels. I other words, we covert the uit of dissio decisio fro stte to level. For stte ( i, which belogs to level, π i () is defied s the stedy stte probbility withi level. Note tht j = i. Sice the stte trsitio withi level is oly cocered with d, the stte trsitio digr withi level is expressed by birth-deth process s give i Fig.. Stedy stte probbility of birth-deth process is esily obtied [9]. Thus, π () is s follows: = i π ( ) =, [!/( )! ] +! [!/( )!] π ( ) =! π (,. (6) ) et Φ be the outge probbility of level. The, Φ is give s follows: Φ where = π ( ) Ψ, (7) i is the stte spce of level. Whe cll is ditted i syste, syste stte oves fro level to level +. To esure tht the outge probbility reis below the QoS threshold, the followig coditios should be stisfied. Φ + pqos d pqos Φ +,. (8) p QoS deotes the threshold of outge probbility. While stisfyig coditio (8), ew cll blockig probbility should be iiized. Thus, the propose VCAC deteries the dissio probbilities s follows. pqos = = x,, S (9) Φ + B. VCAC Nuericl results which will be show i Sectio idicte tht the proposed VCAC well bouds the syste //$. IEEE 56

4 outge probbility below p QoS. owever, VCAC teds to give low outge probbility copred to the outge threshold. ow outge probbility is fvorble i the view of bit error rte, but it lso leds to icresed blockig probbility. To settle the proble of low outge probbility, we propose VCAC, which is siple revisio of VCAC. The outge perforce ily depeds o the dissio probbilities. ow outge probbility idictes tht the dissio probbilities should be icresed. Thus, the followig proportiol expressio is pproxitely estblished, though ot exctly. out ( VCAC ) : p = ( VCAC ) : p. () The se expressio lso holds for. VCAC is bsed o the result of VCAC. If outge probbility with VCAC is less th the outge threshold, the dditiol djustet is executed. QoS ( VCAC ) pqos ( VCAC ) = i,. () p out C. is siple dissio cotrol schee which is itroduced for the copriso with VCAC d VCAC. Whe cll requests to eter cell, deteries whether to dit the cll or ot, bsed o istteous SIR. Thus, does ot reflect the VBR ture of rel tie video service. rejects ew cll request if the dissio of the ew cll results i outge right fter the etrce of the cll. Thus, dissio probbilities re give by = +, =, if Ψi j =,, otherwise IV. = + = NUMERICA RESUTS, if Ψi, j =. (), otherwise I this sectio, we exie the perforces of the three cll dissio schees: VCAC, VCAC, d. VBR video service is cosidered with high dt rte of Kbps d low dt rte of 8 Kbps. First, the effect of trffic itesity is exied i Fig. d Fig. 5. While itiig = = µ, trffic itesity is vried fro to.5. Trffic itesity is defied s ( + ) / µ, where d re ssued to be ideticl. As show i the figures, gives the lowest blockig probbility. owever, it is due to the scrifice of outge probbility. Sice cosiders oly the curret SIR, it cot cope with the chge of SIR, which results i drtic icrese of outge probbility. Oppositely, VCAC well eets the outge requireet. owever, low outge probbility kes the blockig probbility too high. VCAC keeps the outge probbility er the QoS requireet, d gives lower blockig probbility th VCAC. I Fig. 6 d Fig. 7, rtio of d is chged throughout the experiets. We fix s µ, d chge the vlue of fro. to. The left hlf of Fig. 6 d 7 illustrtes the situtio where is less th, which es tht ogoig services re likely to be i the high dt rte durig its coectio. SIR is ticipted to be worse th the curret oe i this coditio. is, however, bsed o oly the curret SIR. Cosequetly, the outge probbility of becoes very high. VCAC gives well bouded outge probbility t y coditio. VCAC results i very low outge probbility but reltively high blockig probbility. O the other hd, the right hlf of the grphs depicts tht is lrger th. Thus, video clls will sped ore tie i the low dt rte. It leds to low trffic lod i the future. Therefore, ll CAC schees shows good perforces. The effect of the differece betwee high dt rte d low dt rte is exied i Fig. 8 d Fig. 9. While itiig the su of R d R s 9 Kbps, we vry R fro 5 Kbps to 96 Kbps. I other words, we vry the vlue of R / R fro.8 to. Whe R pproches to 96 Kbps, the differece of R d R decreses to zero. I this CBR like circustce, frequet chges of SIR do ot occur. Thus, the perforces of VCACs d re lost the se. As low dt rte decreses, the erit of VCACs becoes cler sice lrge differece of low rte d high rte cuses the effect of VBR trsissio ore defiitely. V. CONCUSION Cll dissio schees for rel tie video service with VBR trsissio is cosidered i this pper. We use the Mrkov chi odelig techique d propose two cll dissio cotrol schees. Nuericl results show tht the proposed schees well stisfy the outge requireet d iiize the blockig probbility. REFERENCES []. ol d A. Toskl, WCDMA for UMTS, Wiley d Sos,. [] D. Ayygri d A. Ephreides, Optil Adissio Cotrol i Cellulr DS-CDMA Systes With Multiedi Trffic, IEEE Trsctios o Wireless Couictios, Vol., No.,. [] J. Y. ee, J. G. Choi, K. Prk, d S. Bhk, Relistic Cell-Orieted Adptive Adissio Cotrol for QoS Support i Wireless Multiedi Networks, IEEE Trsctios o Vehiculr Techology, Vol. 5, No.,. [] W. S. Jeo d D. G. Jeog, Cll Adissio Cotrol for CDMA Mobile Couictios Systes Supportig Multiedi Services, IEEE Trsctios o Wireless Couictios, Vol., No.,. [5] T. C. Wog, J. W. Mrk, d K. C. Chu, Joit Coectio evel, Pcket evel, d ik yer Resource Alloctio for Vrible Bit Rte Multiclss Services i Cellulr DS-CDMA Networks With QoS Costrits, IEEE Jourl o Selected Ares i Couictios, Vol., No., //$. IEEE 56

5 [6] U. K. Srkr, S. Rkrish, d D. Srkr, Modelig Full-egth Video Usig Mrkov-Modulted G-Bsed Frework, IEEE/ACM Trsctios o Networkig, Vol., No.,. [7] B. Mglris, D. Astssiou, P. Se, G. Krlsso, d J. D. Robbis, Perforce Models of Sttisticl Multiplexig i Pcket Video Couictios, IEEE Trsctios o Couictios, Vol. 6, No. 7,988 [8] K. S. house, I. M. Jcobs, R. Pdovi, A. J. Viterbi,. A. Wever, d C. E. Whetly III, O the Cpcity of Cellulr CDMA Syste, IEEE Trsctios o Vehiculr Techology, Vol., No., 99. [9] S. M. Ross, Itroductio to Probbility Models, Fifth Editio, Acdeic Press, UK,99. 7 x -.6 Outge probbility 6 5 Outge Threshold Blockig probbility Trffic Itesity Figure. Outge probbility ccordig to trffic itesity (Trffic Itesity =.5) Figure 7. Blockig probbility ccordig to.9.5 x - Blockig probbility Outge probbility Outge Threshold Trffic Itesity Figure 5. Blockig probbility ccordig to trffic itesity R (Trffic Itesity =.5) Figure 8. Outge probbility ccordig to R 6 x -.7 Outge probbility 5 Outge Threshold Blockig probbility (Trffic Itesity =.5) Figure 6. Outge probbility ccordig to R (Trffic Itesity =.5) Figure 9. Blockig probbility ccordig to R //$. IEEE 56