Resource Control for Elastic Traffic in CDMA Networks

Transcription

1 Resource Control for Elastc Traffc n CDMA Networks Vaslos A. Srs Insttute of Computer Scence, FORTH Crete, Greece vsrs@cs.forth.gr ACM MobCom 2002 Sep , 2002, Atlanta, U.S.A. Funded n part by BTexact (Brtsh Telecommuncatons), UK V.Srs, ICS-FORTH

2 Our approach CDMA technology: resource constrants, user control varables that affect resource usage + Economc modelng: utlty functons, congeston prces, socal welfare maxmzaton Framework for effcent resource control n CDMA networks V.Srs, ICS-FORTH

3 Roadmap! Objectve: Effcent resource control for elastc traffc n CDMA networks! Overvew of contrbutons! Wreless resource constrants n uplnk & downlnk! Economc modelng: Socal welfare maxmzaton! Applcaton ssues & numercal nvestgatons! Related work & conclusons V.Srs, ICS-FORTH

4 Contrbutons! Formulate and analyze framework for effcent resource control of elastc traffc n CDMA based on socal welfare maxmzaton! Consder wreless resource constrants n both uplnk and downlnk! Jont optmzaton over sgnal qualty and transmsson rate! For elastc traffc, user net utlty optmzaton can be decomposed nto two sub-problems: " Sgnal qualty adaptaton: do at CDMA layer " Rate control: do at transport layer V.Srs, ICS-FORTH

5 Contrbutons (cont)! Unform framework for seamless congeston control n wred/wreless networks " Also account for moble battery consumpton! Use of ECN (Explct Congeston Notfcaton) as common sgnallng framework " Routers marks packets based on congeston n wred network " RNC (Rado Network Controller) marks packets based on congeston n wreless network V.Srs, ICS-FORTH

6 Why economc modelng?! Successfully appled to fxed networks " Kelly, Gbbens et al, Key et al, Low et al, Kunnyur et al, etc " Generalzaton of congeston control algorthms " Use of Explct Congeston Notfcaton (ECN)! Effcent and robust resource utlzaton! Dstrbuted and decentralzed soluton! Other work has also consdered applcaton of economc deas to wreless networks " Utltes and prces V.Srs, ICS-FORTH

7 Congeston control and resource usage! Closed-loop control loop demand (e.g. rate, class) end-system network feedback (e.g. losses, explct)! Feedback depends on level of congeston and resource usage! Shared resources n CDMA: rado spectrum (uplnk) and base staton power (downlnk)! End-system reacton to feedback modeled wth utlty functons V.Srs, ICS-FORTH

8 CDMA (Code Dvson Multple Access)! Wdeband CDMA (WCDMA) most wdely adopted 3G ar nterface " Based on Drect Sequence CDMA (DS-CDMA)! Sgnals from dfferent mobles separated based on unque codes! Transmsson rate can change between frames frequency receved power dfferent codes rate can be dfferent n dfferent frames 5 MHz 10 msec tme V.Srs, ICS-FORTH

9 Resource usage n CDMA: Uplnk p r g p BS RNC RNC: Rado Network Controller target bt energy to nose densty rato E b /N 0 (determnes bt error rate) spreadng bandwdth = W r rate j receved power g g j p p j + η nterference + nose assumng perfect power control uplnk s nterference-lmted 1 resource constrant < 1 W n uplnk resource usage W n uplnk + 1 r r approxmatons for large # of moble users r < r W V.Srs, ICS-FORTH

10 Utlty for elastc traffc! Utlty: user s value for specfc level of servce! Elastc traffc: level of servce=average throughput throughput no mnmum rate throughput wth mnmum rate V.Srs, ICS-FORTH

11 Congeston prcng for elastc traffc: Uplnk! Utlty for elastc traffc r " average throughput: " utlty: ( r ( )) P s P s ( ) U pkt success rate! Charges proportonal to resource usage r! User objectve s to maxmze net utlty maxmze over prce per unt resource ( r P ( )) U s λ r r, resource usage V.Srs, ICS-FORTH

12 Socal welfare maxmzaton: Uplnk! Socal Welfare maxmzaton problem: maxmze over such that { 0, N = 1 = 1,... N},{ r N U = 1 ( r P( )) r W 0, = 1,... N}! Lagrangan for S.W. maxmzaton problem: L = U ( ) + λ W r shadow prce for constrant V.Srs, ICS-FORTH

13 Propertes of the optmal soluton! Net utlty maxmzaton done over two varables: transmsson rate r and sgnal qualty! Proposton: For elastc traffc, optmal * s ndependent of prce λ & utlty, depends only on P s () P s ( )= P s ( )! Above allows decouplng of selecton of (target E b /N 0 ) and of rate adaptaton " selecton of * done at CDMA layer " rate adaptaton done at hgher layer (e.g. transport) V.Srs, ICS-FORTH

14 P s for DPSK modulaton, no FEC ( * ) ' ( * ) * P s P = s P s ( ) < * * (target > E b /N 0 ) * ' P s > P s ( * ) '( * ) * P < ( ) ( * ) * s P s * V.Srs, ICS-FORTH

15 P s for dfferent modulaton and FEC P s ( ) P s ( )! Wth FEC => lower! P s () typcally hgher than 80% V.Srs, ICS-FORTH

16 Power control n WCDMA fast closed-loop power control outer-loop power control (uplnk) BS RNC! Fast closed-loop power control: between MS and BS " Adjusts transmsson power to acheve target sgnal qualty (Sgnal-to-Interference Rato, SIR) " Both uplnk & downlnk, frequency: 1500 Hz! Uplnk outer-loop power control: between BS and RNC " Adjusts target SIR to acheve gven frame error rate (data: 10-20%, voce: 1%) " Frequency < 100 Hz! Our approach affects only outer-loop power control V.Srs, ICS-FORTH

17 Resource usage n CDMA: Downlnk g p r p BS RNC target bt energy to nose densty rato E b /N 0 (determnes bt error rate) = spreadng bandwdth W r θ g rate g j receved power p p j + η nterference + nose downlnk s power-lmted resource constrant n downlnk p < p resource usage n downlnk p V.Srs, ICS-FORTH

18 Congeston prcng for elastc traffc: Downlnk! User optmzaton problem maxmze over prce per unt resource ( r P ( )) U s λ r, resource usage p! Downlnk: for gven rate and qualty, charge depends on path gan, hence moble poston = W r θ g j not the case for the uplnk g p p j + η V.Srs, ICS-FORTH

19 Extenson: Basc addng model cost for of uplnk battery power max r, ( r PU( ( ) r) P ν( p) ) λ r Umax r, s s BS RNC wreless network V.Srs, ICS-FORTH

20 Extenson: Basc addng Extenson: addng model congeston cost for of uplnk charge battery power of fxed network max max U r, r, ( ru max ( Pr ( P ) U) ( ( ) r) λ Pr ν( p) ) µ λ r P ( ) s r, s s s BS BS Router Router RNC wreless network RNC wreless network fxed network V.Srs, ICS-FORTH

21 Seamless wred/wreless congeston control! Congeston control performed at transport layer! Use ECN markng for congeston feedback! RNC performs markng for wreless hop wreless hop wred hop BS Router Router RNC wreless network fxed/wred network End-system ECN marks Transport IP CDMA IP CDMA congeston control loop Transport IP V.Srs, ICS-FORTH

22 Seamless wred/wreless congeston ctrl (2)! RNC performs markng for wreless hop " RNC (IP layer) needs nformaton from BS " markng depends on congeston and resource usage " no shared buffer n uplnk wreless hop wred hop BS Router Router RNC Transport IP CDMA IP CDMA congeston control loop Transport IP V.Srs, ICS-FORTH

23 Rate allocaton at the RNC based on users wllngness-to-pay! Prevous models ncluded prce (congeston) feedback and rate adaptaton by moble users BS RNC BS RNC r w feedback (congeston)! Alternatve s to do rate allocaton at the RNC " * selected as before " users declare a wllngness-to-pay w " rates allocated proportonal to w and 1/ * r 1 = * w j w j W Motvated by Kelly 97 V.Srs, ICS-FORTH

24 Numercal nvestgatons! Qualtatve rather than quanttatve! Dependence of rate and power allocaton on " moble dstance from base staton " utlty (concave, sgmod) " load V.Srs, ICS-FORTH

25 Rate allocaton & dstance concave utlty sgmod utlty! Uplnk: rate ndependent of moble poston! Downlnk: rate depends on moble poston! Sgmod utlty, downlnk: rate drops to zero at some dstance V.Srs, ICS-FORTH

26 Rate allocaton and load! Uplnk & Downlnk: rate drops wth load V.Srs, ICS-FORTH

27 Related work! Mandayam, Goodman, et al. IEEE Personal Comm. 00, IEEE Trans. Comm. 02 " Utlty equal to transferred bts per unt power " Pareto mprovements wth ntroducton of prces! Song & Mandayam, IEEE JSAC 01 " Utlty functon of transmsson rate " Constrants on maxmum error rate " Maxmze sum of utltes " Centralzed soluton! Xao, Shroff & Chong, Infocom 01 " Utlty-based power control " Utlty functon of sgnal qualty! Others: Nandagopal et al., Campbell et al., etc V.Srs, ICS-FORTH

28 Dfferences wth our work! Formulate and analyze framework for effcent resource control of elastc traffc n CDMA networks " Based on socal welfare maxmzaton! Consder wreless resource constrants n both uplnk and downlnk! Jont control of sgnal qualty and transmsson rate " For elastc traffc, user net utlty maxmzaton can be decomposed nto two sub-problems! Unform framework for seamless congeston control n wred/wreless networks & account for moble battery consumpton! ECN (Explct Congeston Notfcaton) as common sgnallng framework V.Srs, ICS-FORTH

29 Other and ongong work! Dfferent forms of utlty & multple wreless hops! Hybrd code and tme dvson multplexng! Cell coverage ( cell breathng ) " Lmted power at moble hosts! Seamless congeston control n wreless/wred " Markng algorthms, IP at RNC?! Interacton & modfcaton of exstng mechansms " Servce dfferentaton! Resource control n WLANs based on Jont project wth BTexact (Brtsh Telecom), UK & Athens Unv. of Economcs and Busness (AUEB) V.Srs, ICS-FORTH