On Secondary User Transmission Schemes in Relay-Assisted Cognitive Radio Networks

We consider a cooperative cognitive radio network with one primary user and many secondary users. In each transmission frame, one secondary user is selected to act as a relay for the primary user and also transmits its own data. Three different schemes for the secondary user´s transmission is studied, namely, time-splitting, superposition coding, and a combined scheme that takes advantages of both time- splitting and superposition coding schemes. We time-splittingformulate the relay selection problem for each scheme with the objective of maximizing the secondary user´s data rate while satisfying a pre- defined gain threshold for the primary user. This constraint provides an incentive for the primary user when allowing the secondary user access its licensed band. We obtain the optimal solution for this problem in each scheme, on which the relay selection is based on. Finally, we compare the of different schemes using Monte-Carlo simulations.