Cooperation in decentralized cognitive networks: Relaying, spectrum sensing and randomization

Cooperation has been advanced as a key technology for tackling the challenges of a practical implementation of cognitive radio. In this paper, we give a brief overview of the envisioned applications of cooperation in relay channels and investigate the techniques used to deal with the issues related to spectrum sensing and interference avoidance for cognitive radio systems. Then, an extensive analysis on cooperative diversity in decentralized networks, which is achievable with randomized space time coding (RSTC) over dispersive channels, is discussed. With several randomization techniques introduced, we study performance characterizations in terms of symbol error probability, which measures robustness of the transmissions to fading, focusing on the high signal-to-noise (SNR) regime. Numerical results are provided in order to demonstrate the effectiveness of the proposed randomization schemes.