Signal Alignment in Cognitive Radio Networks
Cognitive radio (CR) is a promising technique to overcome spectrum scarcity in wireless networks through dynamic spectrum access and coordinated transmissions between different users based on channel conditions. Sharing wireless spectrum at the same time and frequency introduces multiple access interference (MAI), which can be managed through the cooperation of nodes and signal alignment (SA). In this thesis, a novel approach for eliminating interference in CR systems is introduced by adapting the SA concept used in multiple-input multiple-output (MIMO) Y channel, into an overlay CR scheme. In this system, the primary users (PUs) exchange data in a bi-directional way via the relay, and the relay uses its antennas to communicate with the secondary users (SUs). We designed advanced SA strategies to accommodate different requirements for PU and SU transmissions with different antenna configurations and different user setups. Moreover, we employed strategies to optimize bit error rate (BER) performance of systems.