5 IEEE 6th Iteratioal Symposium o Persoal Idoor ad Mobile Radio Commuicatios - (PIMRC): Services Eergy-efficiet HTTP Adaptive Streamig for High- Quality Video over HetNets Yumi Go Oh Cha Kwo ad Hwaju Sog Div. of IT Covergece Egieerig POSTECH (Pohag Uiversity of Sciece ad Techology) Pohag Republic of Korea Software R&D Ceter Samsug Electroics Suwo Republic of Korea Dep. of Computer Sciece Egieerig POSTECH (Pohag Uiversity of Sciece ad Techology) Pohag Republic of Korea gfservat@postech.ac.kr ocha.kwo@samsug.com hwagju@postech.ac.kr Abstract I this work we propose a eergy-efficiet HTTP adaptive streamig for high-quality video over heterogeeous etworks (HetNets). To support high-quality video ad overcome the limitatios of a sigle etwork the proposed system dowloads the video mets by cocurretly usig the HetNets. I the proposed system the met bitrate umber of requested mets etwork sleep time ad size of requested data through each wireless etwork are determied adaptively to provide seamless high-quality video streamig i a eergy ad cost efficiet way. The proposed system is fully implemeted i a Adroid-based mobile device ad tested i a actual wireless etwork eviromets. Keywords HTTP adaptive streamig Heterogeeous etworks Multipath Eergy-efficiet Cost costrait I. INTRODUCTION Recetly HTTP adaptive streamig has bee widely deployed i popular video services such as YouTube ad Dailymotio. Moreover MPEG Dyamic Adaptive Streamig over HTTP (DASH) stadard has bee released i April []. I HTTP adaptive streamig the server stores the video data that are ecoded at differet bitrates ad divided ito multiple fixed-legth mets. The server records the met metadata called media presetatio descriptio (MPD) i MPEG-DASH. Whe a cliet requests the streamig service the cliet firstly receives the MPD from the server. Based o the MPD the cliet requests a proper met accordig to the etwork coditios. The etwork coditios such as etwork throughput ad delay are estimated while the cliet receives the mets []. However buffer uderflow ad low quality cotiuatio problem ca still be occurred eve i HTTP adaptive streamig. Especially the limitatios of a sigle wireless etwork e.g. badwidth limitatio ad time-varyig wireless chael ad user mobility ca severely degrade the performace of the HTTP adaptive streamig. To solve this problem may researches have bee performed to improve the etwork throughput ad quality of service (QoS) by simultaeously harmoizig the HetNets []. Noetheless there are several challeges to harmoize HetNets for HTTP adaptive streamig services i mobile devices. First challege is that much more eergy is cosumed whe the multiple etwork iterfaces are eabled. Secod challege is the moetary cost accordig to the etwork usage such as G ad LTE. I geeral a user may prefer to receive a video streamig service withi his/her ow cost pla. Third challege is met schedulig. Whe a video met is received through multiple wireless etworks with differet characteristics buffer uderflow may occur due to the out-of-order packet delivery. So far may previous works are proposed i order to defeat these challeges []-[9]. I this work we propose a eergy-efficiet HTTP adaptive streamig system for the provisio of seamless highquality video streamig services over HetNets. The proposed system dyamically adjusts the met bitrate umber of requested mets etwork sleep time ad size of the requested data through HetNets cosiderig the eergy cosumptio ad moetary cost costraits i mobile device. Accordig to our kowledge there are o research studies o HTTP adaptive streamig over HetNets while cosiderig the eergy cosumptio video quality ad user moetary cost pla. The rest of this paper is orgaized as follows. I sectio II des of the proposed system are preseted. Experimetal results are provided i sectio III ad cocludig remarks are give i sectio IV. II. PROPOSED HTTP ADAPTIVE STREAMING SYSTEM Based o MPEG-DASH stadard the proposed system requests MPD from the web server through the wireless etwork with strogest sigal stregth amog the available HetNets. The the web server seds back the MPD to the cliet ad the cliet aalyzes the received MPD. With the aalyzed MPD buffered video time ( t buf ) RTT ( t rtt ) ad etwork throughput ( r ) the proposed system determies the optimal cotrol parameters such as the met bitrate ( v ) umber of requested mets ( ) met duratio time ( t dur ) (icludig etwork sleep time) ad met schedulig map ( S ) (i.e. the size of requested data through each wireless etwork). Segmets are requested from the web server accordig to the determied cotrol parameters. While the cliet receives the met from the server the RTT ad throughput of each etwork is estimated. The received packets are sequeced accordig to the met i the reorderig buffer ad ordered data are delivered to the video decoder for video playback. I the proposed system the met duratio plays as a basic operatio time uit as show i Fig.. The met duratio composed of three stages icludig the request stage (icludig RTT of request message) met dowload stage 978--467-678-/5/$. 5 IEEE 6
5 IEEE 6th Iteratioal Symposium o Persoal Idoor ad Mobile Radio Commuicatios - (PIMRC): Services ad sleep stage. For a met duratio multiple partitioed mets ca be requested by usig byte-rage request ad HTTP pipeliig ad they have same met quality i order to provide cosistet video quality to the cliet. I the proposed system eergy cosumptio ad cost are cotrolled by joitly adjustig the requested data size through each wireless etwork ad sleep time of each wireless etwork. The sleep time is determied cosiderig the heterogeeous power states of the wireless etworks. v = Mbps = tdur = 4.5sec S = 5 5 Fig.. Example of met duratio whe two wireless etworks are eabled (umbers i parethesis refer to met bitrate). A. Problem Descriptio It is importat to estimate the coditio of each etwork i order to efficietly utilize the HetNets. The proposed system estimates the etwork coditio by usig the observed TCP iformatio such as TCP widow size ad RTT. The estimated throughput of i -th etwork for the ext met duratio r i is calculated by usig a expoetial weighted movig average with the curret TCP throughput ad previous estimated throughput. The met schedulig map S is represeted by T S = ( s s... s ) sj = ( s j s j... s j) where s j is the met schedulig vector of the j -th met s i j is the umber of packets of the j -th met delivered through the i -th etwork ad N et deotes the umber of usable wireless etworks at a mobile device. I fact partitioed met is requested as byte uit but it causes high computatioal complexity to obtai the optimal met schedulig vector. Thus we assume that each packet icludes a fixed amout of bytes ad the umber of packets is employed istead of the umber of bytes i order to reduce the computatioal complexity. g is the umber of packets for j v the j -th met with met bitrate v that is obtaied by jv = j v pkt = i= i j g b B s () where bj v is the amout of bytes of the j -th met whe the selected met bitrate is v ad B pkt is packet size. The receive time of the requested mets through the i -th etwork ca be approximately calculated by ( ) = ( j ) = t S B s r. () i pkt i j i The moetary cost vector c is symbolized by c = ( c c... c N et ) where c i deotes the required moetary cost per packet for the i -th etwork. The moetary cost for the met duratio c( S ) is calculated by ( ) c S = c s j. () Now we ca formulate our problem as follows. Problem Formulatio: Determie v t dur ad S for the ext met duratio to miimize the followig cost fuctio Ψ ( v tdur S ) ω e( tdur S ) + ( ω) d( v ) subject to c( S ) NC ad (4) rtt { ti + ti ( j S )} δ tbuf + T ( j ) for j (5) i where e( tdur S ) deotes the cosumed eergy per met durig the met duratio d( v ) is the average distortio of the requested mets whe the met bitrate is v ad T is the video playback time of a met. ω is a real umber ( ω ) that is a system parameter to pursue a effective trade-off betwee eergy cosumptio ad video quality ( ω ca be selected by the user preferece) NC deotes the imum moetary cost per met duratio ad δ is a guard gai for the cliet receive buffer to cosider the estimatio ucertaity i.e. the iaccurate estimatio of RTT ad the met dowload time over time-varyig HetNets ( δ ). Eq. 4 deotes the moetary cost costrait ad NC is calculated by acc NC = T NCmt 6 + NCres (6) where NC mt is the imum moetary cost for a miute of acc video playback ad NC res is the accumulated residual moetary cost for the ext met duratio (i.e. obtaied by subtractig the actual moetary cost from the imum moetary cost of the curret met duratio). Eq. 5 meas that the requested met should arrive at the cliet before a buffer uderflow occurs. I the proposed system it is assumed that the rate-distortio model [] of each met is embedded i MPD i order to estimate the average distortio at the cliet that is the correspodig average distortio of mets is modeled by ε { } j d( v ) = γ j ( v ) (7) + where γ j ( γ j R ) ad ε j ( ε j [ ] ) are model parameters of the j -th met depedig o the video sequece. B. Eergy Cosumptio Model We assume that the eergy cosumptio patters of all wireless etworks ca be simplified as show i Fig.. I this work we oly cosiders the met dowload stage (receive state) ad sleep stage ( state ad idle state) i a met duratio. The eergy cosumptio of the met request message is igored sice the size of met request message is very small (less tha KB) ad RTT is too short (less tha slp ms). As show i the figure the sleep time t i ca be calculated by slp rtt ti = tdur ti ti ( S ). (8) The time t i is determied accordig to t slp i as follows. slp Ti if ti Ti ti = (9) slp t otherwise i 6
5 IEEE 6th Iteratioal Symposium o Persoal Idoor ad Mobile Radio Commuicatios - (PIMRC): Services where T i is the fixed time of the i -th etwork [9]. t idle i is the time i the idle state after t i deoted by slp slp idle ti - ti if ti Ti ti = () otherwise. The power states of the i -th etwork are represeted by idle receive power p i power p i ad idle power p i respectively. p i is obtaied by liear model [9] of etwork throughput i.e. pi = ηi r i + μi () where η i ad μ i are model parameters that are obtaied from the eergy profile o the correspodig wireless etwork iterface. Therefore the cosumed eergy per met at the mobile device ca be calculated by e( t S dur ) = { pi ti ( ) pi ti + S i= { i N } } mi ( ) + p t + p t t idle idle rtt i i base dur i et where p base is the base power of the mobile device. Fig.. Simplified eergy cosumptio model. () C. Parameter Selectio Algorithm I this sectio we propose the determiig process of optimal cotrol parameters. I the proposed algorithm some cadidates havig o possibility of beig selected as the optimal solutio are removed. The optimal solutio that miimizes the give cost fuctio is searched by performig a full search amog all the remaiig cadidates. The des of the proposed algorithm are preseted below. cur cur cur cur Step ) Iitialize v t dur S ad Ψ ( v tdur S ) =. Step ) Sort the wireless etworks i ascedig order accordig to the receive power stregth. v for Step ) Geerate the combiatio of ( ) v V ad N (where N is the imum umber of requested mets durig the met duratio ad V is the set of available met bitrates provided by the web server). For the geerated combiatios calculate the imum umber of packets for the i -th etwork. { gi ( ) = mi ( tbuf + T δ T ) r i Bpkt NC ci } for i () If g ( ) i i < g = the elimiate the jq correspodig elemet ( v ). Step ) Produce the combiatio of ( ) filtered set ( ) v S for the v by Step. To determie S the possible rage of s i that deotes the umber of packets through the i -th etwork is determied by gi gi ( ) for i. (4) If g i is give s i j i S is attaied by N ( ) et g gi g if ad k i < j < jr k = j si j = gi s i k if i < ad j = k = i g s k j otherwise. (5) jr k = Step 4) Select oe from the combiatio set acquired by Step ad calculate t dur based o ad S as follows. rtt { ( )} if ti + ti S t buf Tbuf t i rd = tbuf + ( δ ) T otherwise (6) t buf = tbuf + T (7) where t buf is the estimated buffered video time after the dowload of mets ad T buf is the imum buffered video time. Now calculate Ψ ( v tdur S ). If Ψ ( v tdur S ) is Ψ v cur cur t cur S cur the replace less tha ( dur ) ( v cur cur cur cur tdur S ) with ( v tdur S ). Step 5) If all possible combiatios of ( ) v S are examied the termiate the process with the optimal v cur cur t cur S cur. If ot the go back to solutio ( dur ) Step 4. I geeral V ad N et are typically a small iteger because the streamig service provider caot support fiegraied bitrates ad state-of-the-art smart mobile devices oly has a Wi-Fi iterface ad a cellular etwork iterface. I this case the required computatioal complexity of the proposed algorithm is O( V ( ( ))) N gi N. It is low to i operate i real-time at mobile device. III. EXPERIMENTAL RESULTS Durig the experimet the proposed system is implemeted to support MPEG-DASH [] at Samsug Galaxy S4 LTE-A. I additio MPD ad mets also are created o the basis of the MPEG-DASH. We use full HD video that are Big Buck Buy Red Bull Playstreets ad The Swiss Accout []. All videos are ecoded by H.64/MPEG-4 AVC at five differet bitrates (Big Buck Buy: 5 ad 8 Mbps ad the others: 5 ad 6 Mbps). Total video playback time is secods ad the iitial video data bufferig time is fixed to 4 secods (i.e. two mets). Des of the experimetal parameters are summarized i Table I. The proposed system is examied through Wi-Fi ad LTE etwork simultaeously. To emulate the time-varyig wireless etwork coditios DummyNet [] is employed at the Wi-Fi 64
5 IEEE 6th Iteratioal Symposium o Persoal Idoor ad Mobile Radio Commuicatios - (PIMRC): Services access poit. Durig the experimet the RTT of Wi-Fi path is fixed to 4 ms ad etwork throughput of Wi-Fi path is set to chage every secods (6 Mbps Mbps 4 Mbps Mbps 6 Mbps). O the other had the coditio of LTE etwork caot be adjusted sice it is maaged by a commercial telecommuicatio compay. The measured edto-ed throughput of LTE etwork is approximately Mbps ad the measured RTT is about 58 ms. To measure the cosumed eergy the Mosoo Power Moitor is used. The parameters of the eergy cosumptio model are empirically measured as show i Table II ad embedded i the MPD. The required moetary cost per packet for Wi-Fi ad LTE are set to Korea Wo (KRW) ad.85 KRW respectively. Table I. Parameter values used i the experimet. Parameter Descriptio Value N et Number of usable wireless etworks at a mobile device V Number of met quality levels for the requested video 5 N Maximum umber of requested mets 4 mt N Maximum cost per miute of video playback (KRW) 75 β Weightig factor for etwork throughput estimatio.5 δ Cliet receive buffer parameter.9 B pkt Packet size (byte) 46 T Maximum buffered video time (secods) buf T Video display time of a met (secods) Table II. Power profile of the Wi-Fi ad LTE. Parameter Wi-Fi LTE Receive power η =.67(mW/Mbps) η =.(mw/mbps) μ =74.9(mW) μ =4.9(mW) Tail power.66 (mw) 657.4 (mw) Idle power 4.9 (mw) 6. (mw) Tail time (fixed). (secods) (secods) Base power = 774.7 (mw) A. Performace Verificatio of Eergy Cosumptio Model We verify the eergy cosumptio model with the measured eergy cosumptio data. Fig. presets the compariso betwee measured ad estimated eergy cosumptio for each met duratio. It is apparetly observed that the estimated eergy fits well with the measured eergy. However the estimatio error betwee the measured eergy ad estimated eergy still exists due to upredictable job processig i the operatig system ad iaccurate estimatio of etwork coditio ad processig power cosumptio. The average estimatio error rate of both Wi-Fi ad LTE are approximately 8.5%. Cosumed eergy (uah) 5 5 Measured Estimated 4 6 8 Fig.. Eergy cosumptio patter whe both Wi-Fi ad LTE are utilized. B. Performace accordig to Cotrol Parameters We examie the performace of the proposed system with regard to the met bitrate ad the umber of requested mets. For the experimet ω is fixed to.5 ad test video is Big Buck Buy. As idicated i Table III v affects eergy cosumptio because the met data size icreases as v icreases ad more eergy is required to receive higher bitrate mets. The throughput icreases as icreases because the larger provides eough time to icrease the TCP widow size. However the eergy cosumptio also icreases because the dowload time for the requested met icreases. Whe v is fixed to 8 Mbps the bitrate of the requested met is so large that the etwork throughput may be sigificatly chaged durig the met dowload which sometimes causes cliet buffer uderflows. Cosequetly the proposed system adjusts v ad dyamically to miimize the cost fuctio ad avoid buffer uderflows. Table III. Performace compariso with fixed v ad. v Eergy Average Throughp Bufferig (Mbps) (μah) PSNR(dB) ut (Kbps) 95 4.58 485 4 4.58 4769 4 654 4.58 54 56 4.8 469 5.7 5 59 4.8 469 8. 4 6 4.8 545. Proposed Alg. 456 4. 4745 C. Performace accordig to ω I this sectio we ivestigate the performace of the proposed system accordig to ω. The imum moetary cost per selected video ( secods) is set to 5 KRW ad test video is Big Buck Buy. Fig. 4 presets the performace of the proposed system whe ω is.9. The proposed system provides relatively low video quality as show i Fig. 4 (a) ad stays i the sleep state for a loger time to save the eergy as show i Fig. 4 (b). I this case the eergy cosumptio plays a more importat role tha the moetary cost ad the proposed system cosumes about 9946 μah ad.6 KRW which is less tha the imum moetary cost. As illustrated i Fig. 5 whe ω is set to. the proposed system fully utilizes the LTE etwork with the imum moetary cost costrait i.e. the expeded moetary cost is 45.7 KRW ad the cosumed eergy is 456 μah. The summarized results are preseted i Table V. Segmet bitrate (Kbps) 8 6 4 5 4 4 6 8 (a) 4 6 8 Networkig cost (KRW) Wi-Fi LTE 5 5 5 5 4 6 8 (b) Cosumed etworkig cost Maximum etworkig cost 4 5 6 Segmet umber (c) (d) Fig. 4. Performace of the proposed system whe ω =. : (a) requested met bitrate (b) etwork state (grey regio is sleep state) (c) umber of requested mets ad (d) cumulative cosumed moetary cost. 65
5 IEEE 6th Iteratioal Symposium o Persoal Idoor ad Mobile Radio Commuicatios - (PIMRC): Services Segmet bitrate (Kbps) 8 6 4 5 4 4 6 8 (a) 4 6 8 D. Performace Compariso with Existig Algorithms I this sectio the performace of the proposed algorithm is compared with existig system that are Dyamic submet approach (SubSeg) [7] ad GreeBag [8] that are modified slightly for our experimet. For a fair compariso GreeBag employs the quality adaptatio algorithm of SubSeg because it has o quality adaptatio algorithm. I additio SubSeg ad GreeBag employ the same moetary cost strategy of the proposed algorithm (see step i Sectio III.C). ω of the proposed algorithm is set to.. The test videos are Big Buck Buy Red Bull Playstreets ad The Swiss Accout. The experimet results are summarized i Table V. It is clearly observed that the proposed system cosumes the lowest eergy sice it determies ot oly the amouts of requested met data but also the sleep time of the etworks i order to save eergy. I additio the proposed system exhibits the highest video quality because it cosiders the ucertaity of RTT ad met dowload time over time-varyig HetNets. Therefore the proposed algorithm shows best performace i terms of eergy cosumptio ad video quality for all the video sequeces. IV. CONCLUSION 4 6 8 I this work we have proposed a eergy-efficiet HTTP adaptive streamig system that provides seamless high-quality video streamig services with cost costraits over HetNets. I the proposed system the cotrol parameters such as met bitrate umber of requested mets met duratio ad met schedulig map are dyamically determied to pursue a effective trade-off amog video quality ad eergy cosumptio. The experimetal results shows that the proposed system ca provide high-quality HTTP adaptive streamig services over HetNets while reducig the eergy cosumptio of mobile device ad satisfyig the user moetary cost pla. Networkig cost (KRW) Wi-Fi LTE 5 5 5 5 (b) Cosumed etworkig cost Maximum etworkig cost 4 5 6 Segmet umber (c) (d) Fig. 5. Performace of the proposed system whe ω =.9 : (a) requested met bitrate (b) etwork state (grey regio is sleep state) (c) umber of requested mets ad (d) cumulative cosumed moetary cost. Table V. Performace of the proposed system accordig to ω. ω Eergy Average PSNR Networkig cost (μah) (db) (KRW).9 9946.7 4.48.64.5 7. 4.9 4.89. 456. 4. 45.7 Table IV. Performace compariso with existig algorithms. Video Algorithm Eergy (μah) Average PSNR (db) SubSeg 9.4 4.56 Big Buck GreeBag 544. 4.89 Buy Proposed 6.5 4.4 Red Bull Playstreets The Swiss Accout SubSeg 599.7 4.5 GreeBag 55.6 4.48 Proposed 97.6 4.56 SubSeg 8.85 4.57 GreeBag 9854.95 4.78 Proposed 9657.6 4.6 ACKNOWLEDGMENT This work was partly supported by the ICT R&D program of MSIP/IITP [-9-4-5 Research ad Developmet of 5G Mobile Commuicatios Techologies usig CCN-based Multi-dimesioal Scalability] ad Basic Sciece Research Program through the Natioal Research Foudatio of Korea(NRF) fuded by the Miistry of Educatio (NRF- RAA67). REFERENCES [] ISO/IEC 9- Iformatio techology Dyamic adaptive streamig over HTTP (DASH) Part : Media presetatio descriptio ad met formats Apr.. [] T. Stockhammer Dyamic adaptive streamig over HTTP: stadards ad desig priciples i Proceedigs of the ACM coferece o Multimedia Systems (MMSys) pp. -44 Feb.. [] A. L. Ramaboli O. E. Falowo ad A. H. 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