Performance Improvement of the Cognitive Radio Networks with User Cooperation

The cognitive radio has been considered as a promising paradigm to achieve efficient spectrum usage by allowing the coexistence of the primary and cognitive radio networks. One fundamental challenge is to ensure the quality of service (QoS) of the primary link while maximizing the achievable transmission rate of the cognitive radio user. In this paper, we investigate the cooperation based spectrum access at the cognitive radio networks. If the QoS requirement is stringent, low power is allowed at the cognitive radio transmitter and hence the transmission rate is limited. It is beneficial that the cognitive radio user obtains cooperation from the surrounding cognitive radio users to increase the transmission rate. The best relay which provides the maximal transmission rate is selected for cooperation. The transmission rate performance is investigated under the peak and average interference temperature constraints. The simulation results show that the cognitive radio link transmission rate can be improved by cooperation, especially when the power of the direct link is limited. Under the average interference temperature constraint, the transmission rate is better than that under the peak interference temperature constraint, due to the power adaptation between the transmitter and relay. Higher gain can be obtained as the number of potential relays increases.