Utility maximization for layered transmission using the broadcast approach

We investigate the power allocation problem in layered transmission with successive enhancement using the broadcast approach. This problem is particularly important for multimedia streaming applications and multicasting services over slowly fading channels with partial channel information at the transmitter. We consider the practical scenario of limited and pre-specified source layers, and we propose a generic and efficient solution to optimize the transmission power allocated to each layer in order to maximize the average user satisfaction defined by a utility function of the decoded layers. We assume a block-fading Rayleigh distributed channel model. However, our solution can be extended to a number of other channel distributions. Although the direct formulation of the problem is not convex, we propose change of optimization variable, and we use the dual problem and the perturbation analysis in order to obtain the optimal solution. The solution is based on a one-dimensional bisection search irrespective of the total number of layers. Our optimality analysis indicates that in some cases it may not be optimal to transmit all the layers.