Adaptive loading in the downlink of OFDM/SDMA-based wireless local networks

A combined OFDM/SDMA approach substantially increases the capacity of wireless local networks while maintaining a feasible implementation complexity. We introduce a new precompensating downlink OFDM/SDMA strategy which achieves diversity A-U+1 for all U users, with A the size of the basestation´s antenna array. We compare this scheme with a pre-compensating strategy we have proposed previously. Furthermore, adaptive loading as a means for increasing the performance in the downlink of such OFDM/SDMA networks is studied. We derive an efficient closed-form expression for the optimal bit distribution and show that substantial gains in symbol error rate (SER) can be achieved at low additional complexity. Finally, a simplified loading algorithm is proposed which possesses a lower computational and signaling cost in return for a small performance penalty