Dynamic sub-channel allocation with adaptive beamforming for broadband OFDM wireless systems

Orthogonal frequency division multiplexing (OFDM) has been widely regarded as an effective modulation technique for mitigating the effectso f ISI in a frequency selective fading channel and for providing reliable high data rate transmission over wireless links. Adaptivea ntenna arrays at the basea nd mobile stations can achieve further increases in system's capacity and bandwidth efficiency, as well as in QoS improvement in conventional OFDM systems. The conventional adaptive antenna arraysb ased OFDM systemsa lways use the sub-carriers characterized by the first largest eigenvalues to transmit the OFDM block symbols. In this paper and in contrast to previous work, wep roposed ynamic sub-channel allocation with adaptive beamforming for broadband OFDM wireless transmission systems. The proposed system adaptively selects the eigenvectors associated with the relatively large sub-channel eigenvalues to generate the beamforming weights at the mobile and base stations and then dynamically assigns the corresponding best sub-channilst to transmit the OFDM block symbols. It is shown by simulation that, without adding much complexity, the proposed system can. achieve a better performance than an adaptive antennaa rrays based, OFDM system without dynamic sub-channel allocation over multipath fading channels. Simulation results also revealt hat the proposed system is not too sensitive to channel estimation errors.