ENERGY EFFICIENT WIRELESS TRANSMISSION OF MPEG-4 FINE GRANULAR SCALABLE VIDEO

Transcription

1 NGY FFICINT WISS TANSMISSION OF MG-4 FIN GANUA SCAA VIDO Crstna. Costa, Yftach senberg 2, Fan Zha 2, Aggeos K. Katsaggeos 2 DIT, Unversty of Trento -Va Sommarve 4, I-38 Trento (ITAY) - crstna.costa@ng.untn.t 2 Northwestern Unversty, Departement of C, vanston, I 68, USA - {yesenbe, fzha, agg}@ece.northwestern.edu Abstract - Fne granuar scaabty s a codng too, recenty ntroduced n the emergng MG-4 standard, whch enabes the creaton of very fexbe scaabe vdeo btstreams. Ths paper nvestgates the transmsson of fne granuar scaabe (FGS) vdeo over wreess ns, usng power management for unequa error protecton of the btstream. In wreess systems, energy may be a mted resource, and a wse use of t s mportant for system effcency. An agorthm s proposed whch s abe to optmay dstrbute the tota avaabe power for the transmsson of the enhancement ayer, gven a dstorton or energy constrant. xpermenta resuts demonstrate the performance advantage of the proposed agorthm over fxed power schemes and heurstc approaches. INTODUCTION mergng wreess communcaton systems have evoved from a voce based servce to a mutmeda orented one. Ths transton has ncreased the demands and compexty requred from transmttng devces. Wreess networs have unque characterstcs that dstngush them from more tradtona wred networs. These characterstcs must be taen nto account when desgnng mutmeda systems and, when possbe, expoted as an advantage. One of the maor obstaces n wreess ns s the effects of channe osses on the transmtted data. Ths, combned wth the varabty of the channe characterstcs and the mtaton of resources, such as power, motvates the need for further research nto dfferent approaches for data transmsson. When speang about vdeo codng and transmsson, dfferent approaches have been proposed to cope wth these mtatons. Among them, the use of scaabty has been seen as a usefu too and new methods for achevng t have been ncuded n recent standards []. Scaabty s a codng method that produces an encoded sequence easy capabe of accommodatng dfferent btrates. In order to generate a scaabe btstream, the fne granuar scaabty (FGS) encoder produces two btstreams, commony named ase and nhancement ayers. The ase ayer () can be decoded ndependenty from the nhancement ayer (), and produces a ow quaty reconstructon of the vdeo sequence. A hgher quaty reconstructon can then be acheved by decodng both the ase and nhancement ayers together. Currenty, art 2 of the MG-4 standard ncudes FGS as an encodng too [],[2]. The FGS approach dffers from tradtona ayered methods for vdeo scaabty because of ts capabty to acheve a smooth transton between dfferent bt rates. In MG-4 FGS, the ase ayer behaves as a standard basene MG-4 compressed btstream. The dfference between the reconstructed and the orgna vdeo sequence s encoded n the nhancement ayer. rogressve encodng of the s acheved by a bt-pane codng of the DCT of the resdua mage. The DCT transform s performed on a boc bass, as s done for the ase ayer, but the data n the s entropy coded one bt-pane () at tme. The encoded data s then sent startng from the most sgnfcant bt-pane (MS) to the east sgnfcant bt-pane (S) Due to ts structure, the enhancement ayer can be truncated at any pont. In ths way, rate contro can be performed by smpy truncatng the btstream n order to adapt t to varyng channe characterstcs. Due to ts nherent scaabty and fexbty, FGS aso aows compexty scaabty and easy resource adaptaton dependng on the capabtes of vdeo devces. Thus, n addton to vdeo conferencng, FGS s aso sutabe for vdeo mutcast. An nterestng overvew of appcatons enabed by FGS technoogy s gven n [3]. Wth regard to the reated wor, unequa error protecton (U) between and usng dfferent technques, such as AQ (Automatc epeat request) and FC (Forward rror Correcton), have been studed n the past [4]. The appcaton of U wthn the FGS btstream was frst consdered by Schaar et a. n [], where the Fne-Graned oss rotecton (FG) framewor was ntroduced. ased on t, Yang et a. proposed n [6] a degressve protecton agorthm (D) based on FC for optmay assgnng protecton redundancy among bt-panes. In [7], Wang et a. studed the probem of rate-dstorton optmzed U for rogressve FGS (FGS) over wreess channes usng prortzed forward error correcton (FC) for the and. A smar probem was studed n [8] n whch the obectve was to mnmze the processng power for FGS vdeo gven bandwdth and dstorton constrants. In [9], a ont FC and transmsson power aocaton scheme for ayered vdeo transmsson over a mutpe user CDMA networs was proposed. In that wor, scaabty was acheved usng 3D-SIHT (waveet based codng). The obectve was to mnmze the end-to-end dstorton through optma bt aocaton among source ayers and power aocaton among dfferent CDMA channes. The authors n [] consdered onty adaptng the source bt rate and the transmsson power n order to maxmzng the performance of a CDMA system subect to a constrant on the equvaent bandwdth. In that wor, an H.263+ codec was used to generate the ayered bt stream. In ths wor, we consder the transmsson of an MG-4 FGS vdeo sequence over a snge wreess channe for a snge user. We propose an agorthm that aows U of the enhancement ayer pacets through optma transmsson power aocaton. Gven transmsson power and bt rate constrants, our goa s to mnmze the end-to-end dstorton by optmay aocatng transmsson power to the dfferent pacets n the. 2 FGS IN WISS VIDO TANSMISSION When transmttng n an error prone envronment, error protecton technques become of fundamenta mportance. In I Communcatons Socety /4/$. (c) 4 I

2 scaabe codng, the compressed vdeo s coded nto separate btstreams, whch can receve dfferent eves of protecton. Typcay, the ase ayer s heavy protected so that t s receved neary error free, whe a dfferent and ghter protecton scheme s used for the nhancement ayer. Due to the structure of the FGS btstream, t s aso possbe to perform unequa error protecton wthn the, snce the mportance of the data wthn the ayer decreases gong from the MS to the S. Mean t ane Sze (bytes) t ane Number Fg. Average sze of the bt-panes for the Foreman sequence (QCIF). y anayzng the btstream, we can note that typcay the most sgnfcant bt-pane s the smaest n sze (.e., has the smaest number of bts), and bt-pane sze ncreases from the most sgnfcant to the east sgnfcant bt-pane. As an exampe, n Fg. the average sze of the dfferent bt-panes s potted for the Foreman sequence (the was coded wth bt rate set at 4Kbps). Ths behavor s due to severa factors. It s ey that the frst bt pane contans mosty the nformaton reated to those macrobocs that have more error n the base ayer, such as those wth a ot of moton nformaton. Ths means that the frst bt pane contans a greater number of zeros n regons where there are statc macrobocs, such as the bacground or contnuous tone areas. Fewer bts are requred to encode arge regons of zeros. Another reason s due to the fact that the data n the east sgnfcant bt panes s ess correated, and thus more dffcut to compress wth entropy codng. As a consequence, not a the data n the nhancement ayer has the same mportance. Frst, t s not possbe to decode the data of a bt pane wthout decodng the precedng bt panes. Secondy, the data of the MS aso carres more nformaton, wth respect to the S. It s possbe then to expot ths structure for mpementng unequa error protecton (U) of the enhancement ayer data as n []. Another mportant ssue n mobe envronments s power management. nergy s a precous resource, snce batteres have a mted fe, and usng t n a wse way can greaty mprove the overa quaty of the transmsson. Snce the probabty of pacet ost s drecty reated to the power assgned to the transmtted pacet, we can thn of controng the probabty of oss by varyng the transmsson power n order to acheve unequa error protecton of the pacets []. In ths paper, an agorthm s proposed that aows unequa error protecton of the enhancement ayer pacets through optma transmsson power aocaton. 3 OW ASD UNQUA O OTCTION Tang advantage of the structure of FGS codng, t s possbe to mpement a prortzaton of the enhancement ayer pacets: a hgher eve of protecton can be gven to the more sgnfcant bt-panes, mang the protecton smaer as the bt-panes become ess sgnfcant. Assumng that the s aways receved correcty and that a maxmum amount of energy tot for the frame s gven, our goa s to determne how to aocate the avaabe power n such a way that mnmzes the overa dstorton. If we subdvde the btstream nto pacets and transmt these pacets over the channe, then the tota energy used for transmttng the s gven by the foowng formua: tot, () where s the number of bts n the -th pacet, s the power used for transmttng t, and s the channe bt-rate. The mnmzaton probem can be expressed as n the foows: mn { D [ ]}, s. t. tot, s the expected vaue of the dstorton mprovement ntroduced by onty decodng the and a the correcty receved pacets. If we assume that each pacet s successfuy decoded ony f t and a the prevous pacets are where D s the dstorton of the and [ ] correcty receved, we can wrte [ ] [ ] ( ) where as: (2) ρ, (3) ρ s the oss probabty for the -th pacet, and s the dstorton mprovement ntroduced by t. y ntroducng a agrange mutper λ, the souton of the constraned mnmzaton probem can be found by sovng the foowng unconstraned probem: ( ) mn J mn D + ρ λ.(4) The average transmsson power used by a moduaton scheme drecty affects the probabty of pacet oss. We assume that the reatonshp between the probabty of oss for the -th pacet ρ and the power used for transmttng t s nown at the transmtter: ρ g( ). () The functon g can be defned usng an anaytca mode of the wreess channe or determned from emprca measurements. In Secton 4, we use an anaytca mode based on nformaton theoretc resuts. The frst dervatve of the cost functon J wth respect to can be wrtten as: J ρ ( ) ρ + λ. (6) Note that at the optma souton the dervatve n (6) must equa zero. earrangng equaton (6) we can wrte the foowng expressons, for ρ : ( ) λ f (,, ) ρ, (7) from whch we can easy obtan, for,,-2: I Communcatons Socety /4/$. (c) 4 I

3 h ( ) λ f (,, ) ( ρ ) where f ρ, (8) (,, ) h + ρ. The frst dervatve of the cost functon J wth respect to can be wrtten, for ρ, as: J ρ ( ) ( ) ρ ρ + λ.(9) Substtutng the expressons n (8) nto (9), we obtan, after some smpe manpuatons, for <, the foowng reatonshp, for,,-: ρ ( ρ ). () ρ h ( ρ ) ( ) + ρ + h In the fna expresson, the eft sde represents the nformaton reated to the -th pacet whch depends ony on the power of the foowng pacets, (+) to. Ths observaton motvates our recursve power aocaton agorthm descrbed n the foowng sectons. 4 CHANN MOD DFINITION We assume that each transmtted pacet ether arrves error free or s dropped due to a channe fade. If we defne the channe mode as n [2]: e ρ, () we can rearrange () and obtan the foowng expresson: ( ) ( ) e +. (2) + The ast expresson aows us to recursvey cacuate a (,,-) once vaue of {,, } + s nown. In other words, for a gven we can recursvey cacuate n terms of, and therefore use () n order to cacuate the resutng tota energy. The mnmzaton probem can then be soved by fndng the vaue of that satsfes the energy constrant. A cosed form souton to the probem of fndng the optma s dffcut to compute anaytcay. Therefore, a numerca method such as the bsecton method can be used. Fg.2a shows, for a specfc sequence, the pot of tot versus the power of the ast pacet,. As we can see from Fg.2a, for each vaue of tot (.e. for each energy budget) we can fnd two soutons (.e., two ponts n whch the dervatve of the cost functon equas zero): the agorthm must pc the one that gves the mnmum dstorton. Fg.2b shows the pot of the resutng MS versus. Fg. 2 Foreman QCIF sequence, frame, equa sze pacets: tota energy tot and frame dstorton (MS) versus the power of the ast pacet,. In, the dotted ne represents the energy budget. Fg.3 robabty of pacet oss ρ versus for the ast 4 pacets (- 3,..,). If the ne representng the energy constrant does not ntersect wth the energy curve, t means that a souton usng a maxmum number of pacets max does not exst, because a the soutons ead to a tota energy that s arger than the energy constrant. In ths case we have to consder the souton (the ast pacet s not transmtted) and reconsder the probem by cacuatng the curve wth max -. From the obtaned resuts, we can observe that, n the case of equa sze pacets the power assgned to each + pacet decreases wth :. As a proof one can rearrange equaton (2) n order to obtan: ( ) ( ) + ( ) 2 2 e,(3) + from whch we can derve the foowng nequaty: + +. (4) Snce the power assgned to each pacet s reated by () to the probabty of pacet ost, ths means that the probabty of oss ncreases as the pacet number ncreases. The ast pacet (-th) w be the pacet wth the owest power, and maxmum probabty of oss (Fg.3). I Communcatons Socety /4/$. (c) 4 I

4 DUA OM FOMUATION In the dua probem, we want to mnmze the tota energy used for transmttng the enhancement ayer, subect to a dstorton constrant. In ths case, the mnmzaton probem can be expressed n the foowng way: mn, s. t. Dtot D [ ], () where D tot s the maxmum acceptabe dstorton for the frame. The technques used to sove the mnmum dstorton probem (q. (2)) can aso be used to sove the mnmum energy probem (q. ()). Note that for the mnmum energy probem s teratvey adusted unt the dstorton constrant s met. The dua probem presented here s usefu for appcatons n whch a desred eve of vsua quaty must be mantaned usng the east amount of energy. 6 XIMNTA STU AND SUTS In order to verfy the proposed method, experments wth dfferent types of pacetzaton and codng parameters have been performed. The sequences have been coded usng the MG-4 FGS reference software [3]. The ase ayer was coded wth a fxed target btrate, utzng the mpementaton of the TMN rate contro present n the reference software. The motvaton behnd seectng a fxed s that typcay the ase ayer s compressed at a maxmum btrate, such that t can aways be receved wth neggbe probabty of error. The nhancement ayer can then be parttoned n such a way that t can be transmtted whenever the btrate s greater than (and ess than a certan ), fuy utzng the bandwdth avaabe at the tme of transmsson. In ths way, t s possbe to adapt the coded vdeo to the tme-varyng characterstcs of the channe. Once coded, the s pacetzed usng a fxed pacet ength scheme. Tabe summarzes the parameters chosen for these experments. A the experments reported here have been performed for the QCIF format (44x76 pxes) Foreman test sequence. Smar resuts not presented n ths paper due to space mtatons have been obtaned wth other test sequences, such as Carphone, Ayo, and Saesman. Three sets of experments, named A, and C, have been performed for anayzng the behavor of the agorthm, wth dfferent pacet szes and transmsson rates (Tabe 2). Tabe Genera parameter settngs tot for each frame 4 J Frame rate fps Target bt rate for ( ) 4 Kbps Inta Q for I-Frame Inta Q for -Frame 3 Tabe 2 arameter settngs for the three experments acet Sze Target Tota t ate xperment A bytes Kbps xperment bytes 4 Kbps xperment C bytes 4 Kbps In order to compare the resuts obtaned from the proposed agorthm, an equa energy scheme and an emprc mode have been mpemented. The equa energy scheme assgns to each pacet the same amount of energy. The emprca method vares the power per pacet n a heurstc manor, and has been chosen n order to perform near the optma agorthm. In experment A, the emprca method assgns the power per pacet n the foowng way: tot, 2,,,7 > 7 (6) In Fg. 4a and b, we pot, for each frame, respectvey, the power assgned to each pacet by the emprca method and the optma power for experment A. For experment the emprca method assgns the power per pacet as foows: tot, m 9 < m, m m 2 m m 9 (7), > Frame # acet # Frame # 3 4 acet # 2 Frame # acet # Frame # acet # ) Fg.4 xperment A: power per pacet wth the emprca method and optma power per pacet Frame # acet # Fg. xperment : power per pacet wth the emprca method and optma power per pacet Frame # acet # 26 Fg.6 xperment C: power per pacet wth the emprca method and optma power per pacet I Communcatons Socety /4/$. (c) 4 I

5 (c) F.7 SN: experment A, and (c) C In Fg. a and b, we pot for each frame respectvey the power assgned to each pacet by the emprca method and the optma power for experment. Fnay, for experment C, the emprca method assgns power as foows: tot, m 4 < m, m 4 m 2 m m 4 (8), > In Fg. 6a and b, we pot for each frame respectvey the power assgned to each pacet by the emprca method and the optma power for experment C. The SN per frame for the proposed optma power aocaton approach, the equa energy scheme, and the emprca method are shown for experments A,, and C n Fg. 7. As expected, the SN obtaned from the optmzed method s aways hgher than both the equa energy and emprca methods. Fg. 7 demonstrates the potenta of utzng power adaptaton to acheve unequa error protecton n wreess vdeo communcatons usng FGS. As shown n Fg. 7, the optmzed power aocaton approach acheves an average expected SN that s on average.24 d,.24 d, and.9 d hgher than the equa energy approach for experments A,, and C respectvey. The proposed approach s aso abe to acheve sgnfcant gans over the emprca method, whch adapts the energy per pacet n a heurstc manor. For exampe, n Fg. 7c, the emprca method acheves an average expected SN that s on average.48 d ower than the optmzed approach. The performance of the equa power and emprca approaches strongy depends on the parameter settngs as we as on the characterstcs of the vdeo sequence. Therefore, t s dffcut to desgn a generc emprca agorthm that can aways perform near the optma power aocaton. As shown n Fg. 7, an equa power per pacet approach may perform near the optmzed approach for some parameter settng (Fg. 7a), whe the emprca approach may gve a better approxmaton at other operatng ponts (Fg. 7b). The proposed optma power aocaton scheme on the other hand s abe to adaptvey aocate the avaabe energy based on the transmsson parameters and the source characterstcs. 7 CONCUSIONS An agorthm for optmay aocatng the avaabe transmsson energy to the enhancement ayer pacets n an FGS wreess vdeo communcaton system has been presented. Unequa error protecton s acheved through adaptve power aocaton. The agorthm s smpe, and can be used to effcenty cacuate the optma power dstrbuton between the enhancement ayer pacets as we for vadatng faster emprca methods. The methodoogy used s appcabe not ony to FGS vdeo codng but aso other nds of progressve coders, such as waveet based mage or vdeo codng. FNCS [] ISO/IC MG-4, Informaton Technoogy Codng of Audo Vdeo Obect art2: Vsua Amendment 4: Streamng Vdeo rofe, MG /N38, Juy. [2] W., Overvew of fne granuarty scaabty n MG-4 vdeo standard, I Trans. on Crcuts and Systems for Vdeo Technoogy, vo., pp. 3-37, March. [3] M. van der Schaar,. G. oand, and Q., Nove appcatons of fne-granuar-scaabty: Internet & wreess vdeo, scaabe storage, personazed TV, unversa meda codng, roc. of SCI/ISAS - Orando, USA. [4] U. Horn, K. Stuhmüer, M. n, and. Grod, obust Internet vdeo transmsson based on scaabe codng and unequa error protecton, Image Communcaton, vo., no. -2, pp , Sept [] M. van der Schaar and H. adha, Unequa pacet oss resence for Fne-Granuar-Scaabty vdeo, I Trans. on Mutmeda, vo. 3, pp , Dec.. [6] X. K. Yang, C. Zhu, Z. G., G. N. Feng, S. Wu, and N. ng, A degressve error protecton agorthm for MG-4 FGS vdeo streamng, roc. of I ICI, Sept. 2. [7] G. Wang, Q. Zhang, W. Zhu, and Y.-Q. Zhang, Channe-adaptve unequa error protecton for scaabe vdeo transmsson over wreess channe, roc. of SI, Vsua Communcatons and Image rocessng, pp , San Jose, CA, Jan.. [8] Q. Zhang, W. Zhu, and Y.-Q. Zhang, Networ-adaptve scaabe vdeo streamng over 3G wreess networ, roc. I ICI, Thessaon, Greece, Oct.. [9] S. Zhao, Z. Xong, and X. Wang, Jont error contro and power aocaton for vdeo transmsson over CDMA networs wth mutuser detecton, I Trans. Crcuts and Systems for Vdeo Technoogy, vo.2, pp , June 2. [] Y. S. Chan and J. W. Modestno, Transport of scaabe vdeo over CDMA wreess networs: A ont source codng and power contro approach, roc. I ICI, Oct.. [] Y. senberg, C.. una, T.N. appas,. erry, and A.K. Katsaggeos, Jont source codng and transmsson power management for energy effcent wreess vdeo communcatons, I Trans. on Crcuts and Systems for Vdeo Technoogy, vo. 2, pp , June 2. [2]. Ozarow, S. Shama, and A.Wyner, Informaton theoretc consderatons for ceuar mobe rado, I Trans. Vehcuar Tech., vo. 43, Issue 2, pp , May 994. [3] ISO/IC MG-4 FGS eference Software, avaabe va March 3. I Communcatons Socety /4/$. (c) 4 I