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PROC IEEE INFOCOM RIO DE JANEIRO BRAZIL APRIL 2009 1 Delay Limited Cooperative Communication with Reliability Constraints in Wireless Networks Rahul Urgaonkar Michael J Neely University of Southern California Los Angeles CA 90089 http www scf usc edu urgaonka Abstract We investigate optimal resource allocation for delaylimited cooperative communication in time varying wireless networks Motivated by real time applications that have stringent delay constraints we develop dynamic cooperation strategies that make optimal use of network resources to achieve a target outage probability reliability for each user subject to average power constraints Using the technique of Lyapunov optimization we first present a general framework to solve this problem and then derive quasi closed form solutions for several cooperative protocols proposed in the literature a direct transmission 1 h 2d t h md t h sm This material is supported in part by one or more of the following the DARPA IT MANET program grant W911NF 07 0028 the NSF grant OCE 0520324 the NSF Career grant CCF 0747525 m relay m transmits i t I I NTRODUCTION There is growing interest in the idea of utilizing cooperative communication 1 4 to improve the performance of wireless networks with time varying channels The motivation comes from the work on MIMO systems 18 which shows that employing multiple antennas on a wireless node can offer substantial benefits However this may be infeasible in small sized devices due to space limitations Cooperative communication has been proposed as a means to achieve the benefits of traditional MIMO systems using distributed single antenna nodes Much recent work in this area promises significant gains in several metrics of interest such as diversity gains 1 2 capacity 3 6 energy efficiency 8 etc over conventional methods We refer the interested reader to a recent comprehensive survey 7 and its references The main idea behind cooperative communication can be understood by considering a simple 2

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