2014 Volume 4 Issue 1 Pages 53-69
This paper investigates the benefits that cooperative communication brings to cognitive radio networks. We focus on cooperative Multiple Input Multiple Output (MIMO) technology, where multiple distributed single-antenna secondary users cooperate on data transmission and reception. Three cooperative MIMO paradigms are proposed to maximize the diversity gain and significantly improve the performance of overlay, underlay and interweave systems. In the paradigm for overlay systems the secondary users can assist (relay) the primary transmissions even when they are far away from the primary users. In the paradigm for underlay systems the secondary users can share the primary users' frequency resources without any knowledge about the primary users' signals. The transmitted spectral density of the secondary users falls below the noise floor at the primary receivers to meet the strict interference constraint in cognitive radio networks. In the paradigm for interweave systems, secondary users can use cooperative beamforming to avoid the interference at the primary users while still achieving high diversity gain for improved system performance. Numerical and experimental results are provided in order to discuss the advantages and limits of the proposed paradigms.
