MIMO/OFDM with adaptive interleaved beamforming and power allocation for high-capacity wireless access

Spatial diversity at both the transmitter and receiver has been widely regarded as a key technique with which OFDM can be combined to improve further the system performance of wireless networks. Selection diversity is the simplest way to realize spatial diversity, but the performance improvement of this form of diversity is limited. Adaptive antenna arrays can provide significant increases in a system's capacity and performance, but they are characterized by a relatively higher implementation complexity than selection diversity. We combine the benefits of these two spatial diversity methods and propose an adaptive interleaved beamforming approach for broadband MIMO/OFDM systems. By applying eigenvalue decomposition on the set of all available channel correlation matrices, the best beamforming which corresponds to the largest eigenvalue in the set is adaptively selected for each sub-carrier. By doing so, beamforming is adaptively interleaved in the spatial domain. Simulation results show that the proposed system can result in significant performance improvements over conventional adaptive antenna array based OFDM systems in wireless channels. Numerical results also show that the performance of the proposed system can be further greatly improved by employing interleaved-beamforming-dependent power allocation among the sub-carriers.