Power Efficient Transmission of Layered Video Through Wireless Relay Nodes

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1 MERL A MITSUBISHI ELECTRIC RESEARCH LABORATORY Power Effiient Transmission of Layered Video Through Wireless lay Nodes Zafer Sahinoglu and Phil Orlik TR July 2003 Abstrat Effiay of using a wireless relay node (WRN to minimize total power dissipation in transmission of a layered video between two devies is presented. It is analytially shown that there is a feasible relay region that would have lower power onsumption than diret transmission depending on both the enoding rate of eah layer and reeived signal power level for provisioning required bit error rate. This work may not be opied or reprodued in whole or in part for any ommerial purpose. Permission to opy in whole or in part without payment of fee is granted for nonprofit eduational and researh purposes provided that all suh whole or partial opies inlude the following: a notie that suh opying is by permission of Mitsubishi Eletri searh Laboratories, In.; an aknowledgment of the authors and individual ontributions to the work; and all appliable portions of the opyright notie. Copying, reprodution, or republishing for any other purpose shall require a liense with payment of fee to Mitsubishi Eletri searh Laboratories, In. All rights reserved. Copyright Mitsubishi Eletri searh Laboratories, In., Broadway, Cambridge, Massahusetts 02139

2 Publiation History: 1. First printing, TR , July 2003

3 Power Effiient Transmission of Layered Video Through Wireless lay Nodes Zafer Sahinoglu, Phil Orlik Mitsubishi Eletri searh Labs, In. Murray Hill, New Jersey, Abstrat Effiay of using a wireless relay node (WRN to minimize total power dissipation in transmission of a layered video between two devies is presented. It is analytially shown that there is a feasible relay region that would have lower power onsumption than diret transmission depending on both the enoding rate of eah layer and reeived signal power level for provisioning required bit error rate. EDICS# CL Corresponding Author Zafer Sahinoglu Mitsubishi Eletri searh Labs, In. 558 Central Ave, Murray Hill, NJ Tel: ( Fax: ( zafer@merl.om 1

4 Power Effiient Transmission of Layered Video Through Wireless lay Nodes Zafer Sahinoglu, Phil Orlik Abstrat Effiay of using a wireless relay node (WRN to minimize total power dissipation in transmission of a layered video between two devies is presented. It is analytially shown that there is a feasible relay region that would have lower power onsumption than the diret transmission depending on both the enoding rate of eah layer and reeived signal power level for provisioning required bit error rate (BER. I. INTRODUCTION One major tehnologial trend in wireless appliations is multiasting video on demand (VoD to portable devies. A VoD system usually onsists of servers and several proxyservers distributed over an entire network. To deal with heterogeneous aess rates eah video stream is enoded into a onstant bit rate base layer (BL and multiple variable bit rate enhanement layers (EL [1]. The BL is enoded at a muh lower rate than the ELs. Therefore, if one layer is to be relayed through the proxy, it is more power effiient to relay the EL. Both layers may be relayed of ourse, if the proxy is not to be overloaded. This paper is onerned with seleting proper loations for proxy servers in the network to minimize total power dissipation. II. RADIO MODEL AND ASSUMPTIONS We assume that a video is enoded into a BL and a single EL at average rates of Rb and bps respetively. We denote by, the required reeived signal power level for the EL, and = R / R for the BL to provision ertain BER. To model wireless transmission, we use a simple radio model analogous to the ones in [2,3]. We assume that the total power onsumption of a ommuniations node P t in watts onsists of power onsumed by the transmitter/reeiver radio iruitry,, the transmit amplifier, P amp (R, whih is ontrollable to ahieve a desired BER at transmit rate of R, and additional power to proess reeived bits P re (R. Also, different levels of lutter on the propagation paths are modeled as lognormal shadowing [4]. The shadowing effet between nodes i and j, in db, is given as 10 in watts. R b P amp (R d ij R ( e b e P ir x ij an be expanded as is the distane between i and j, and ij xij / 10 Pamp( R = R 10 dij exponent. Antenna gain is assumed to be unity. III. POWER ANALYSIS xij /10, where is the path loss Assume node A is a server, node B is a ustomer premises equipment (e.g., Aess Point, and node C a proxy server. When both layers are diretly transmitted from A to B, the total power expended in the system, ' P t, is ' a ab ab Pt = Pir + Pamp + Pamp (1 b + Pir + Pre Without loss of generality, we an assume a b P. Let '' ir = P ir = Pir = P P t denote the power dissipated in the ABC triplet when A transmits only the EL to B over C. '' a ab a Pt = Pir + Pamp( Rb + Pamp( + Pir (2 b b + Pamp( + Pir + 2( Pre + Pre The relative power saving with respet to the diret transmission is then " ' P1 = Pt Pt provided that P 1 <0. x P 10 ab / 10 x d 10 a / 10 1 = R ( ab + d e a (3 x b / + d b + P + Pre < 0 III.1. Trigonometri Analysis (Exluding Shadowing Effet The Cartesian oordinates of A, B and C are denoted by, ( 0, 0, ( X b, 0 and ( X, Y respetively. After rearranging (3, and substituting orresponding inter-node distanes in terms of the oordinates, the test ondition in (4 is obtained to find feasible power saving positions (FPSP for the proxy devie C. 2 2 / / 2 P ( X + Y + [( X Xb + Y ] < Xb (4 The term Xb ( P / X b is a threshold to ahieve power savings. If is less than( P + P ( R /, there is no FPSP. Therefore, the diret transmission is always ost effetive and preferred. On the other hand, any relay node at the oordinates, when entered into (4, resulting in a greater value than the threshold is not an FPSP. Figure 1 is a ontour A Figure 1 Feasible power saving positions and orresponding power saving values (no shadowing loss. Note: ( P + P ( R / = 1 3, =3, d ab =100m. re re e / e B 2

5 plot of (4 normalized by Xb ( P / (in db. Negative values show power savings for orresponding positions of the proxy node, while positive values indiate exess power onsumption aused by relaying. When the proxy is loated outside the 0 db boundary, no power saving is ahieved by relaying, but more power is dissipated in the network. The midpoint between A and B is the optimum relay loation to have the maximum power saving (approximately 5dB under given parameter settings in Fig.1. For higher values of path loss exponent, the area under 0db boundary would expand. The ratio P / is ritial in a sense that when it inreases for a fixed, the 0db boundary would shrink. CONCLUSION In this letter, we show that, for wireless streaming of layered video, a proxy server an be exploited as a relay for one or more layers to derease total transmit power dissipated in the network. Future work and simulations would analyze error propagation through the relay node and power effiieny omparison of relaying and regenerating at the proxy under orrelated lognormal shadowing. A senario with more than three ooperative proxy servers will also be studied. REFERENCES [1] D. Saparilla, K. W. Ross, Optimal Streaming of Layered Video, In the pro. of IEEE INFOCOM 2000, pp , Marh, 2000, Tel Aviv, Israel. [2] W. R. Heinzelman, A. Chandrakasan, H. Balakrishnan, Energy-effiient Communiation Protool for Wireless Mirosensor Networks, in the pro. of the IEEE Hawaii Int. Conf. on System Sienes, pp , January, 2000, Maui, Hawaii. [3] P. Chen, B. O Dea, E. Callaway, Energy Effiient System Design with Optimum Transmission Range for Wireless Ad-ho Networks, in the pro of IEEE Int. Conf. on Communiations, ICC 02, pp , May, 2002, New York City, New York. [4] T. S. Rappaport, Wireless Communiations: Priniples and Pratie, Prentie Hall, In., 2 nd edition, pp ,