Cooperative MIMO Paradigms for Cognitive Radio Networks

This paper investigates the benefits that cooperation brings to cognitive radio networks. We focus on the cooperative Multiple Input Multiple Output (MIMO) technology, where multiple distributed secondary users cooperate on data transmission and reception. Energy efficient cooperative MIMO paradigms are proposed to maximize the diversity gain and significantly improve the performance of both overlay and underlay systems. In the proposed overlay system the secondary users can assist (relay) the primary transmissions even when they are far away from the primary users. In the proposed underlay system the secondary users can share the primary users' frequency resources without any knowledge about the primary users' signals while meet the strict interference constraint that the transmitted spectral density of the secondary users falls below the noise floor at the primary receivers. Numerical and experimental results are provided in order to discuss the advantages and limits of the proposed paradigms.