Utility maximization for layered multimedia transmission via orthogonal multiplexing

In this paper we consider multicast systems that use orthogonal layered source coding over a Rayleigh fading environment. The different layers are transmitted over orthogonal frequency bands with pre-specified ratios of the total bandwidth. For this kind of systems, we optimally allocate the transmission power, and hence the decoding threshold of each layer, in order to maximize the expected satisfaction defined by a utility function of the decoded rates of the users. In particular, we use the Lagrangian dual problem in order to efficiently solve the primal non-convex problem for any number of layers. Furthermore, we show that for some channel statistics, it is not optimal to transmit all the layers, rather we should allocate zero power to some of the upper layers in order to maximize the expected user satisfaction. In this particular case, the bandwidth of the untransmitted layers can be allocated to the lower layers for further enhancement of the expected user satisfaction. We discuss how to modify the solution structure to optimize the power allocation in this case.