Adaptive loading for OFDM/SDMA-based wireless local networks

The combination of orthogonal frequency division multiplexing (OFDM) with linear processing-based spatial diversity multiple access (SDMA) enables high-capacity wireless local networks at reasonable implementation complexity. We investigate adaptive loading of the carriers as a means for lowering the relatively high symbol error rate (SER) of such linear OFDM/SDMA networks and propose efficient closed-form expressions for the optimal bit distributions. We analyze the performance and complexity of the proposed algorithms and show that substantial gains in SER can be achieved. Furthermore, simplified algorithms are proposed which have a small performance penalty but which possess a lower computational and signaling cost