Adaptive Probabilistic Decision-Based Energy Saving Strategy for the Next Generation Cellular Wireless Systems

Transcription

1 MITSUBISHI ELECTRIC RESEARCH LABORATORIES hp:// Adapive Probabilisic Decision-Based Energy Saving Sraegy for he Nex Generaion Cellular Wireless Sysems Weihuang Fu, Zhifeng Tao, Jinyun Zhang, Dharma Agrawal TR July 2010 Absrac As mobile saions (MSs) in he nex generaion cellular wireless sysems will more frequenly operae on muliple applicaions, such as web browsing, VoIP, online video ec., energy saving becomes more criical and face new challenges from he qualiy of service (QoS) requiremens. A special operaion sae, called sleep mode, is designed for energy saving of MS, in which MS operaes on coninuous sleep cycles, where every sleep cycle is he sum of a lisening window and a sleep window. This paper proposes an energy saving mehod ha adapively deermines sleep cycles and shifs lisening window. When MS is in sleep mode, he sleep cycles are exended by probabilisic decisions relaed o he raffic saisic aribues. We also inroduce he energy saving sraegy for he frames by mixing bes effor and persisen allocaion raffic. The frequency of sleep cycles is used as one of he parameers for QoS purpose. Differen from convenional mehods, lisening window can be shifed for shorer response ime in our mehod. Exensive simulaion resuls validae he advanages of our mehod boh in erms of energy saving and shorer response ime. IEEE ICC 2010 This work may no be copied or reproduced in whole or in par for any commercial purpose. Permission o copy in whole or in par wihou paymen of fee is graned for nonprofi educaional and research purposes provided ha all such whole or parial copies include he following: a noice ha such copying is by permission of Misubishi Elecric Research Laboraories, Inc.; an acknowledgmen of he auhors and individual conribuions o he work; and all applicable porions of he copyrigh noice. Copying, reproducion, or republishing for any oher purpose shall require a license wih paymen of fee o Misubishi Elecric Research Laboraories, Inc. All righs reserved. Copyrigh c Misubishi Elecric Research Laboraories, Inc., Broadway, Cambridge, Massachuses 02139

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3 Adapive Probabilisic Decision-based Energy Saving Sraegy for he Nex Generaion Cellular Wireless Sysems Weihuang Fu 1, Zhifeng Tao 2, Jinyun Zhang 2, and Dharma P. Agrawal 1 1 Cener for Disribued and Mobile Compuing Deparmen of Compuer Science, Universiy of Cincinnai, Cincinnai, OH 45221, USA 2 Misubishi Elecric Research Laboraories (MERL), Cambridge, MA 02139, USA fuwg@cs.uc.edu, ao@merl.com, jzhang@merl.com, and dpa@cs.uc.edu Absrac As mobile saions (MSs) in he nex generaion cellular wireless sysems will more frequenly operae on muliple applicaions, such as web browsing, VoIP, online video ec., energy saving becomes more criical and face new challenges from he qualiy of service (QoS) requiremens. A special operaion sae, called sleep mode, is designed for energy saving of MS, in which MS operaes on coninuous sleep cycles, where every sleep cycle is he sum of a lisening window and a sleep window. This paper proposes an energy saving mehod ha adapively deermines sleep cycles and shifs lisening window. When MS is in sleep mode, he sleep cycles are exended by probabilisic decisions relaed o he raffic saisic aribues. We also inroduce he energy saving sraegy for he frames by mixing bes effor and persisen allocaion raffic. The frequency of sleep cycles is also used as one of he parameers for QoS purpose. Differen from convenional mehods, lisening window can be shifed for shorer response ime in our mehod. Exensive simulaion resuls validae he advanages of our mehod boh in erms of energy saving and shorer response ime. I. INTRODUCTION Various communicaion/nework applicaions, such as Web browsing, VoIP, online video, ec., have been emerging on handheld devices, i.e., mobile saions (MSs), as wider bandwidh suppor is expeced from he nex generaion cellular wireless echnology (e.g., IEEE802.16m [1], IEEE802.16j [2], LTE advanced [3]). Exacerbaed by more frequen usage of handheld devices, power managemen wih consrain energy supply from carry-on baeries, which has limied size and capaciy, becomes a criical issue in developing hese nex generaion cellular sysem sandards. In his paper, we discuss he problem of energy saving in he nex generaion cellular sysems wih consideraions of raffic qualiy of service (QoS). As he opic of energy saving may use alernae names and erms in differen wireless sysems bu wih same funcions, we illusrae our idea by sandards in he IEEE802.16m sysem. However, he idea and mechanism of our mehod can be easily ransferred and adoped in oher wireless sysem. In an IEEE802.16m sysem, sleep mode is one of hree modes ha an MS in conneced sae [1], in which an MS conducs pre-negoiaed periods of absence from is serving Weihuang Fu worked on his sudy while visiing Misubishi Elecric Research Lab, Cambridge, MA. base saion (BS) air inerface. The ransmiing and receiving of frames by an MS consume relaively higher energy. In sleep mode, MS does no have o lisen o he air-inerface all he ime, and he energy should be saved during he nonransmission periods. When an MS is in is sleep mode, i operaes on a series of coninuous sleep cycles. The period of he sleep cycle is measured in frames in he IEEE802.16m. A sleep cycle consiss of a sleep window and a lisening window. During sleep window, he BS does no ransmi frames o he MS and he MS can urn he radio power off for energy saving. During lisening window, he MS is o receive he downlink ransmissions from he BS as he same way in he sae of normal operaions. The defaul lengh of lisening window can be a fixed value se during he iniiaion of sleep mode or during he sleep cycle updae. In previous wireless sysems, binary runcae exponen (BTE) algorihm [4][5][6] and is variaions [7][8] have been widely implemened. Many wireless cellular sysem including IEEE802.16e [9] use BTE o deermine he lengh of sleep cycles. Afer MS eners in sleep mode, BTE algorihm will double he sleep cycles every ime, unil a pre-negoiaed maximum sleep cycle is reached or he sleep mode is erminaed. In he sleep mode operaing wih BTE algorihm, he MS wakes up a he beginning of every sleep cycle for signals from he BS or daa ransmission. The applicaions running on MSs can include bes effor (BE) raffic and/or persisen allocaion () raffic. In IEEE m, MAC link is connecion-based and he daa exchange is performed by scheduling algorihm. BE raffic is scheduled by BS when ransmission is possible. The examples of BE raffic are web browsing, raffic, ec. is used for he raffic wih periodic paern and relaively fixed payload size o reduce he resource map overhead of connecions. The examples of raffic are voice raffic, video raffic, ec. Our invesigaion shows ha here exiss a space for improvemen beween he performance of BTE algorihm and he opimal soluion. And, BTE algorihm is no suiable for BE and mixed raffic due o he absence of energy saving consideraion o raffic. In his paper, we propose an adapive energy saving sraegy in sleep mode o approach he opimal energy saving. Differen from convenional energy saving ha only considers BE raffic,

4 2 our scheme suppors BE raffic, raffic, and heir mixed raffic. The advanages of our mehod lie in he following aspecs: (i) The sleep cycle is exended based on probabilisic decision insead of binary runcaion. (ii) The se of exension facors in our mehod is adapively derived from he cumulaive disribuion funcion (CDF) of he packe arrivals, so ha he probabiliies of packe capure in sleep window are nearly equal. (iii) Sleep mode is able o adapively deal wih mixed raffic paern by shifing or inerpolaing lisening window in a sleep cycle. (vi) Our mehod is able o deal wih mixed raffic, which is no effecively addressed by prior sleep mode. The remainder of his paper is organized as follows: The problem formulaion and modeling of energy saving mechanism is in Secion II. In Secion III, we analyze he raffic aribue and propose he energy saving sraegies for BE and raffic. Secion IV provides he performance evaluaion wih exensive simulaions. Finally, he paper is concluded in Secion V. ABS AMS 1-g Traffic ON OFF ON OFF ON OFF (a) ON-OFF model g b (b) Sae ransi diagram Fig. 1: Traffic sae model ON Power II. PROBLEM FORMULATION AND MODELING In his secion, we model he energy saving mechanism and inroduce he sleep mode in IEEE802.16m o illusrae severiy of he problem. Our developmen of he sleep model operaion scheme is based on he characerisics of hese raffic o obain near-opimal energy saving wih shorer response ime. A. Traffic Model Applicaion raffic beween advanced MS (AMS) and advanced BS (ABS) can be profiled by an ON-OFF model [10]. For example, a ypical phone conversaion can be marked by a series of periods of acive alking inerleaved by silence/lisening period, as shown in Fig. 1(a). ABS schedules he raffic ransmission for cerain duraion, denoed by arrows in he figure. The scheduling of raffic exchange does no always exis. During some ime inervals, raffic does no exis beween ABS and AMS. The period for he presence of raffic beween AMS and ABS is called ON sae and he period ha raffic no here is he OFF sae. So, he power supply of AMS radio module can be emporarily urned off or be reduced o a sleep power level during he OFF periods, and resume he normal power level during he ON periods. The process can be seen as a random process ha ransis beween ON and OFF saes, as he wo sae Markov chain shown in Fig. 1(b). Since he lengh of frame in IEEE802.16m is fixed, he sae ransi happens only a he end of every frame. Mahemaically, he condiional probabiliy ha he AMS ransis from ON sae o OFF sae can be denoed by b and he condiional probabiliy ha he AMS which is in he ON sae will coninue remain in he ON sae is given by 1 b. Similarly, he condiional probabiliy ha he AMS which is in OFF sae changes o he ON sae a nex frame is denoed by g and he condiional probabiliy ha he AMS will remain in he OFF sae is given by 1 g. The values of he parameers highly depend on he raffic aribues. We illusrae some raffic aribues in ON-OFF model as follows, including BE raffic and raffic. Web browsing raffic: The aribues of web browsing raffic, i.e., HTTP raffic, governed by srucure of webpages and human browsing behavior. I can be approximaed by ON-OFF model. In he ON sae, raffic is ransferred from he websie o he AMS; while he user is reading he webpage, i remains on he OFF sae. When he user finish he reading and open anoher webpage, he sae will be swiched back o he ON sae. Voice raffic: A whole phone conversaion are comprised by acive alking and silence. Six sae model has been inroduced in [11]. If we reduce hose saes ha involve any alk, o he ON sae and reduce he muuall silence sae o OFF sae, a simplified wo sae ON-OFF model is obained. FTP raffic: FTP raffic can be well characerized by ON- OFF model, where he files are in he ransfer in ON sae and user is in reading during he ime inerval of OFF sae. raffic: When raffic is modeled by ON-OFF model, we see ha: in he ON sae, he can be sen o he server or received from he server; in he OFF sae, user is wriing or reading he locally. There are many oher ypes of raffic can be modeled by ON-OFF model, which can refer o [10]. B. Sleep Mode Sleep mode is one of he funcions ha AMS uses in power managemen o conduc pre-negoiaed air inerface power-off inervals. The lengh of sleep cycle is measured in frames in recen IEEE802.16m sysem descripion documen. Normally, a sleep cycle is comprised of a lisening window and a sleep window, which may be measured in unis of subframe. The operaion of sleep mode in IEEE802.16m is as follows [1]: The iniiaion of sleep mode can be acivaed or enered eiher by AMS or ABS, and he parameers of sleep cycle are negoiaed beween he AMS and he ABS. The ABS makes he final decision regarding he AMS reques and insrucs

5 3 CDF CDF F x p/n Lisening window sleep window Packe arrival L 0 L 1 L 2 L 3 L 4 L 5 L 6 L 7 L 8 L 9 L 10 L 11 Inacive sae Acive sae Inacive sae Fig. 2: Equal Probabiliy Division he AMS o ener sleep mode. The negoiaion of sleep parameers is performed by using MAC managemen messages MOB SLP-REQ and MOB SLP-RSP. The AMS can iniiae he negoiaion by sending a MOB SLP-REQ message and receives a MOB SLP-RSP message. Alernaively, he ABS can also send an unsolicied MOB SLP-RSP message o he AMS. During he period of sleep mode, AMS may increase is sleep cycle under several condiions: When he AMS does no receive any packes from is downlink during a lisening window, or When he AMS receives a managemen message indicaing ha he raffic will no be scheduled in he following frames. The erminaion of sleep mode can be made eiher by he AMS or he ABS. If he AMS iniiaes he erminaion, i will send a MOB SLP-REQ message wih deacivaion reques, which ends he sleep mode by confirmaion from he ABS wih responding a MOB SLP-RSP message. The ABS can also send an unsolicied MOB SLP-RSP message o deacivae sleep mode direcly. A. Analysis of Traffic Arrival III. ANALYSIS AND SCHEME In acive sae, packes have shor iner-arrival inervals. As a resul, AMS will have higher probabiliy o receive packes during is lisening window of sleep mode. In conras, AMS has lower probabiliy o receive packes during is lisening window during inacive sae of downlink raffic. Since he duraion of inacive sae can be idenified by ON-OFF raffic model, he power saving should be opimized wih inelligen adapaion of sleep cycle lengh. Fig. 2 illusraes our proposed sleep cycle adapion. In acive sae, lisening window appear everyl 0 ime lengh, where L 0 denoes he normal sleep cycle duraion and is iniiaed a he beginning of sleep mode. When raffic eners inacive sae, AMS prolongs he sleep cycle o save more energy. Assume here are N lisening windows when he raffic is in inacive sae. The opimized design is o le each lisening window have he same probabiliy of capuring packes arrival. In oher words, he probabiliies ha packes arrive during each of hese N lisening windows should be he same. Given his assumpion, he lengh of sleep cycle can be deermined by he reverse mapping from cumulaive disribuion funcion (CDF) F x of raffic arrival in inacive sae. As shown in Fig. 2, sleep cycle duraion L 1, L 2, and L 3 have he same corresponding probabiliy of packe arrivals in CDF F x and heir lisening windows have he same probabiliy o capure hese packe arrivals. For example, when packes arrive during he sleep window of L 3, he AMS will receive he packes in he nex lisening window of L 4. The sleep mode will hus ransi from he inacive sae o he acive sae. When he sleep mode ransis from he acive sae o he inacive sae, he same procedures will be repeaed again. While lisening window of L 8 does no receive raffic, he nex sleep cycle L 9 is exended per he described mehod. Given he CDF of he inacive sae duraion,f x, our scheme divides he probabiliy beween 0 and p (p < 1) ino N equal segmens and ses he saring poins of each sleep cycle accordingly. Fig. 2 illusraes he idea ha CDF F x is equally divided ino N non-overlap segmens beween probabiliy 0 and p so ha he probabiliies ha each sleep window can capure packe arrivals are equal. Given CDF F x, he ih sleep cycle lengh T slp (i) can be compued as: T slp (i) = { Fx 1(p i N ) F 1 T slp (i 1), x (pi 1 N ), i = 1,...,N i > N. Since he sleep cycle is expressed in unis of frame, F x () can also be easily changed o discree CDF F k (i). The corresponding sleep cycle L slp (i) in frame is expressed by: L slp (i) = { F 1 k (p i N ) F 1 L slp (i 1), k (pi 1 N ), i = 1,...,N i > N. The relaionship beween he lengh of curren sleep cycle (1) (2)

6 4 BE raffic ABS L P AMS L min 2L min 4L min 8L min Fig. 3: L min < L P BE raffic ABS L P AMS L min I II Fig. 4: L min L P and he lengh of previous sleep cycle can be given by: F 1 k ( p N ), i = 1 F L slp (i) = 1 k (p i N ) F 1 k (pi 1 N ) F 1 k (pi 1 N ) F 1 i 2 k (p )L slp(i 1), i = 2,...,N N L slp (i 1), i > N. (3) When he AMS eners inacive sae of sleep mode, i compues he sleep cycle by: L slp (i) = min(f ex (i) L slp (i 1), Final Sleep Cycle), (4) where f ex (i) = F 1 k (p i N ) F 1 k (pi 1 N ) F 1 k (pi 1 N ) F 1 k (pi 2 N ). (5) The exension facors can be compued by he ABS and sen o he AMS a he iniiaion of sleep mode or during he sleep cycle updae. They can also be compued by ABS and AMS separaely by negoiaing parameers, p, N, and Fx 1. I should be noed ha doubling of sleep cycle mehod, i.e., BTE algorihm, can be a special case of our mehod where f ex (i) = 2, which is given by: L slp (i) = min(2 L slp (i 1), Final Sleep Cycle). (6) B. Energy Saving for Mixed Traffic The lisening window in a sleep cycle can be shifed for mixed raffic. Mixed raffic consiss of periodic raffic and non-periodic raffic, where periodic raffic is scheduled by persisen allocaion. There are wo cases o consider for mixed raffic: L min < L P and L min L P, where L min denoes he iniial sleep cycle of BE raffic and L P denoes he arrival inerval of raffic in unis of frame. 1) L min < L P : raffic and BE raffic are considered as he example shown in Fig. 3. Sleep Cycle Exension: When no BE daa is received during he lisening window, he sleep cycle is exended o save energy. When only daa is received during he lisening window, he sleep cycle will no be exended. Sleep cycle exension follows: L slp (i) = min(f ex (i) L slp (i 1),L P, Final Sleep Cycle). (7) When AMS is receiving raffic via persisen allocaion, he maximum sleep cycle size will be no larger han L P. If BE daa is received during lisening window, he sleep cycle is rese o L min. Lisening Window Shif: AMS should awake for frames. There are wo siuaions based on he relaive locaion of his frame. In he firs siuaion, frame will be in he lisening window of curren sleep cycle, which does no need any adjusmen for he lisening window. The frame can be received during he lisening window. In he oher siuaion, frame falls in he sleeping window of curren sleep cycle. Wihou adjusmen, he frame will be missed. So, he sleep cycle should be able o shif he lisening window o embrace he frame. This offse is in erm of number of frames. As he example shown in Fig. 3, he lisening window is shifed o he frame locaion for boh lisening and frame receiving purposes. 2) L min L P : The operaion should be synchronized o save energy so ha oher raffic can be scheduled a he same frame used by he. When sleep cycle performs exension, i is also consrained by L P, as Eq. (7) shows. In his case, L min is equal o L P. So, sleep cycle should be repeaed wih he same period and is synchronized wih frames. In he example shown in Fig. 4, when BE raffic arrives, he daa will be ransmied ogeher wih daa o AMS during he lisening window. If here is no BE raffic in arriving, as shown by region I of Fig. 4, he sleep cycle performs exension algorihm. However, due o L min = L P, he exended sleep cycle is sill wih lenghl min. When BE raffic keeps arriving, i will be sen during he lisening windows including

7 BTE NEQ Energy Consumpion Delay in inacive sae BTE NEQ Normalized Energy Consumpion Delay λ λ Fig. 5: Energy Consumpion Fig. 6: Delay in Acive Sae frames, he sleep window may be exended o receive high volume BE raffic, as illusraed by region II of Fig. 4. I is noed ha persisen allocaion may occur before or afer he iniiaion of sleep mode. If sleep mode is se before he, he sleep mode should be rese or updaed in he case L min > L P. By reseing or updaing he defaul sleep cycle, L min can be se o be less han or equal o L P, which operaes as he procedures described in he wo cases above. This case also applies for periodic-only raffic. When persisen allocaion is used during he sleep mode, he final sleep cycle should be changed o be equal o L P. In each sleep cycle, i needs o check he expeced locaion of frame. If he persisen allocaion is erminaed during sleep mode, he sleep cycle exension follows he calculaion indicaed in Eq. (4). IV. PERFORMANCE EVALUATION In his secion, We compare he performance of energy consumpion and packe delay in BTE (i.e., sleep window doubling scheme) wih ha of our proposed N-equal probabiliy (NEQ) algorihms by using simulaion. The Figs. 5 and 6 show he performance of boh algorihms during inacive sae. When packe is formed a he sender, i may be scheduled and ransmied o he receiver a he nex available lisening window. The sleep mode will ransi from inacive sae o acive sae. In he simulaion, he frame ime lengh is se o 5ms and he lengh of lisening window is se o one frame lengh. For he simulaion of BTE algorihm, he iniial sleep cycle is se o four imes of frame lengh and he final sleep cycle lengh is se o 512 imes of he iniial sleep cycle. For he NEQ algorihm, we se p = 0.5. N = 8 if he raffic arrival rae is greaer han 0.05, and N = 20 oherwise. The disribuion of iner-arrival duraion of raffic follows exponenial disribuion. For exponenial disribuion, he combinaion sill follows exponenial disribuion bu having new arrival rae which is he sum of he arrival raes of each raffic. So, we invesigae he performance wih raffic arrival rae in a wide region. In our simulaion, energy consumpion is defined as he energy consumed during lisening windows. Delay, i.e., response ime, is defined as he ime inerval ha is from he AMS enering he sleep mode o is erminaion of sleep mode made by packe arrival. The energy consumpions by lisening windows of BTE and NEQ schemes are compared in Fig. 5. The energy consumed by NEQ is less han ha consumed by BTE under differen packe arrival rae. NEQ saves abou 40 o 60 percen more energy for he given range of arrival raes in he figure. For web browsing raffic, he packe iner-arrival rae is λ = We can see from he figure ha he energy consumpion of NEQ is only around 40 percen of BTE. For VoIP raffic, he packe iner-arrival rae is λ = 0.3. From Fig. 5, we see ha he energy consumpion is a half of convenional mehod. For oher raffic ype or mixed raffic, he efficiency of energy saving can be checked by selecing he appropriae poin of mixed arrival rae on he figure. Fig. 6 shows he delay beween he packe arrival and he firs available lisening window afer he packe arrival. The delay of NEQ algorihm is abou 40 o 60 percen of ha of BTE in he figure. Given web browsing raffic (λ = 0.033), he delay caused by sleep cycle exension is reduced by approximae 85 percen. More imporanly, he delay is reduced more han 50 percen for VoIP raffic (λ = 0.3). We also can check he delay decrease of oher ypes of raffic or mixed raffic by he packe iner-arrival rae. V. CONCLUSION Our proposed mehod for energy saving in sleep mode can significanly reduce he energy consumpion and frame delay caused by sleep cycle exension. This is because our mehod is based on he saisical aribues of various raffic which is able o approach he opimal soluion by saisical echnique. We illusrae our idea and mechanism by he sleep mode operaion in IEEE802.16m and show he simulaion resuls in validaing he performance. Such mechanism can be also uilized in oher mobile communicaion sysems o save MS s energy and prolong he baery life.

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