Optimal weight vectors for broadcast channels

In a multi-transmitter broadcast system, the weight vector for each message signal can provide an additional degree-of-freedom for signal enhancement and interference suppression by taking advantage of the spatial diversity among the users. To date, the design of the optimal weight vectors which maximize the overall channel capacity is still an open problem. The main reason is attributed to the fact that under certain power constraints, the channel capacity R is a highly nonlinear function of the M-dimensional weight vectors {w/sub i/}, where M is the number of transmitters. Therefore, the maximization of R over {w/sub i/} does not seem to be tractable to simple mathematic treatment. In this paper, we present our studies on designing optimal weight vectors for a two-user, multi-transmitter broadcast channel. Our primary contribution is to decouple the weight vectors in R which simplifies the optimization problem to a search for the maxima of a smooth two-dimensional function.