Distributed beamforming and autonomous participation decision making in cooperative CR systems

In a cognitive radio (CR) network, a group of CR users can act as relays for a given user to improve the quality of communications for this user. To achieve such cooperative transmission, we propose a distributed beamforming technique that reduces the required feedback overhead in terms of sharing the channel state information between the cooperating CR relays. In return for their cooperation, the assisted CR user can lease its own channel, for a certain amount of time, to the cooperating CR relays for their opportunistic access. However, a particular CR relay spends a certain amount of power to forward the data to the assisted CR user. Therefore, we also propose an autonomous decision making strategy that can help each CR user to independently decide whether to participate in the cooperative transmission or not, by quantifying the reward and cost functions of each CR relay. The presented numerical results show an enhancement in the achievable sum rate of the cooperative CR network up to 43% for a primary channel occupancy probability of 0.3, compared to the case of non cooperative transmission.