Adaptive antenna arrays and equalization techniques for high bit-rate QAM receivers

Adaptive antenna arrays provides wireless communication systems with larger service capacity and higher link quality through frequency reuse and co-channel-interference rejection. In practice, the propagation environment is non-ideal with shadowing, severe stationary and fast multipath fading. An adaptive equalizer (AEQ) is often employed to compensate for the multipath channels. The performance of adaptive antenna arrays controlled by an adaptive beamformer (ABF) in a multipath, multi-interferer environment is examined and the interactions between ABF and AEQ in a QAM receiver are also investigated. Both outdoor and indoor multipath conditions are considered. A simple yet effective adaptive beamformer structure with real-time tracking capability is presented for a portable unit in PCS applications, followed by simulation results. It is concluded that the proposed receiver rejects the interferers as well as the long-delayed multipaths to reduce the interference level by means of adaptive beamforming and executes diversity combining on the short-delayed multipaths to increase the signal level by means of adaptive equalization. As a consequence, the required equalizer tap length is also reduced