Beamforming for Underlay Two - Way Relay Networks

Although underlay networks mitigate the dual problems of spectrum congestion and spectrum under-utilization, the bi-directional (primary-to-secondary and secondaryto-primary) interference issues must be addressed to improve their reliability, coverage and capacity. To address these problems, this thesis investigates beamforming and two-way relaying. Specifically, the two underlay configurations considered are (a) multi-antenna terminals and one single-antenna two-way relay and (b) single-antenna terminals and multiple single-antenna two-way relays. First, for Configuration (a), assuming the availability of perfect channel state information, the performance of sub-optimal beamforming algorithms is characterized. Specifically, the exact and asymptotic outage probabilities in high transmit power and interference temperature limit region are derived considering both path loss effect and small-scale fading. Second, also for Configuration (a), efficient transmitter and receiver beamforming strategies are developed, e.g., transmit powers, transmitterside beamforming and receiver-side beamforming vectors at the two multi-antenna terminals. Third, for Configuration (b), assuming the availability of second-order channel statistics, the joint relaying and transmitter designs are developed. Overall, these research findings show the capability of beamforming and relaying in addressing the bi-directional interferences problems in underlay networks and thus improving their reliability.