Combating Intersymbol Interference and Cochannel Interference in Wireless Communication Systems

Abstract: Over the last decade the world has witnessed explosive growth in the use of wireless mobile communications. Looking around we find users with mobile phones, wireless PDAs, pagers, MP3 players, and wireless headphones to connect to these devices - a small testament of the impact of wireless communications on our daily lives. In addition the burst of new technologies such as Bluetooth and other short-range wireless communications are encouraging the further development of a wide variety of distributed wireless devices. Two major impediments to high-performance digital wireless communication systems are intersymbol interference (ISI) and cochannel interference (CCI). ISI is caused by the frequency selectivity (time dispersion) of the channel due to multipath propagation. Equalizers can be used to compensate for these channel distortions. One may design an equalizer given the received signal, or one may first estimate the channel impulse response and then design an equalizer based on the estimated channel. CCI, on the other hand, arises from cellular frequency reuse and thus limits the quality and capacity (number of users) of wireless networks. CCI can be reduced by the use of adaptive antenna arrays (also known as "smart antennas"). These systems utilize an array of antenna elements that provide directional (spatial) information about the received signals. Since the desired signal and unwanted cochannel interferers generally arrive from different directions, an adaptive beamforming algorithm can adjust the spatial gain to enhance the desired signal and mitigate the cochannel interferers. In this Thesis, we describe receiver architectures and adaptive signal processing algorithms designed to compensate for the ISI and CCI in wireless communication systems.