MMC05-4: On the Optimality of Threshold Scheduling Policies for Video Transmission in Markovian Fading Wireless Channels with Channel-Aware ARQ

We consider the problem of optimal transmission scheduling for real time multimedia (video) data transmission over wireless communication links. It is assumed that the wireless channel is Rayleigh fading and can be represented by a finite state Markov chain (FSMC) model, and that retransmissions are allowed via the use of an ARQ protocol. Due to a delay constraint, there is a limit on the number of time slots that may be used to transmit some (pre-designed) number of packets. The problem of optimal transmission scheduling is formulated as a finite horizon Markov decision process (MDP) with a cost function that takes into account the transmission cost and a penalty cost on the packet loss rate. Using the concept of supermodularity and convexity on the optimal cost and immediate cost functions, we prove that the optimal transmission scheduling policy is a threshold function of time and buffer size. These threshold policies are applicable for any delay-sensitive real time packet transmission system. Finally, the theoretical results are illustrated via numerical examples.