Jointly optimized heterogeneous MIMO broadcast systems

A heterogeneous multiple-input-multiple-output (MIMO) broadcast (BC) system is considered, with some of the users having target-rate requirements while other users are working with best-effort data rates. We assume the use of dirty paper coding, and we exploit the duality between the capacity regions of the multiple access and broadcast channels in order to optimally and jointly optimize the rates, powers and decoding order. We use the concept of stream achievable rate region (rather than user achievable rate region) and show that the best-effort users can achieve higher rates when the data streams of any user are not restricted to be decoded consecutively and when timesharing between different decoding orders is allowed. It is shown that the problem can be formulated as a convex optimization problem. We also propose an algorithm to obtain the time-sharing factors and decoding orders (corner points) required to achieve the optimal solution.