Signal processing techniques for increasing channel capacity in wireless communications

Adaptive arrays are found to have potential to increase channel capacity. This dissertation addresses the major obstacles encountered in applying the two most applicable adaptive array algorithms to time division multiple access (TDMA) wireless communication systems.; We investigated the reference signal based adaptive diversity combining algorithm, which conventionally relies on feedback symbols in the absence of reference signals. Our simulation revealed that on a fast time varying fading channel, error propagation in the decision directed tracking mode severely degrades performance. We developed a simultaneous diversity combining and decoding technique which incorporates QR decomposition-based recursive least-square parallel weights tracking and M-D decoding algorithms. The M-D algorithm was first developed for the binary convolutional codes and then extended to Trellis-coded modulation. This technique significantly reduces error propagation. Simulation results showed that about 8-10dB improvement in total interference suppression at low ISR and about 5dB improvement at high ISR can be achieved with moderate increase in complexity.; We proposed and studied the use of constrained adaptive array algorithm for extracting signals from interferences at separable directions. This algorithm requires direction-of-arrival (DOA) information and does not need reference signals. However, most of the high resolution DOAs estimation methods are only effective for noncoherent signals, while in mobile radio channels, coherent signals are inevitable. We developed a general spatial smoothing (SS) and a forward backward SS technique for two dimensional arrays to decorrelate coherent signals from arbitrary directions. We found and proved the necessary and sufficient conditions on an array configuration for applying SS.; We investigated the applications of adaptive array technique in DS/CDMA systems. We applied reference-signal-based simultaneous diversity combining and decoding to reduce fading and suppress interference caused by poor synchronization and power control.