Maximizing throughput in MIMO networks with variable rate streams

The problem that we consider is that of maximizing throughput in a MIMO network while accounting for variable rate streams on MIMO links. The stream rates on a link depend on the channel conditions of the link, and the manner in which the diversity-multiplexing tradeoff is handled. In this work, we use the dependence of stream rates on the channel to develop methods of link selection and stream allocation that approximately maximize the aggregate throughput. Maximizing throughput is closely tied to the problem of allocating streams based on the stream rates of the selected links. Doing this optimally is very complex even for networks with 10 or fewer links. We develop a stream allocation heuristic that approximately maximizes the throughput over a given set of links. Simulation results for single collision domain networks show that our stream allocation heuristic is within 7% of optimal in networks with up to 10 links (in a typical case where the maximum concurrency allowed is 15 links). The algorithm also cuts the difference between heuristic and optimal results in half, compared to a simple greedy algorithm. Our research has also identified the feasibility checking problem for general MIMO networks as being a computationally hard problem. However, we also identify several practical special cases, e.g. when interference suppression is done only at the receiver side, for which feasibility checking remains a polynomial-time operation.