Wireless Personal Communications: An International Journal
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Cognitive radio has been considered as a promisingparadigm to achieve efficient spectrum usage by allowing the coexistence of the primary and secondary networks. Onefundamental challenge is to ensure the quality of service (QoS) of the primary link while maximizing the transmission rate of the secondary links. In this paper, we investigate cooperation based spectrum access at the secondary networks. If the QoS requirement of primary link is stringent, low power is allowed at the cognitive radio user and the transmission rate is limited. It is beneficial that the cognitive radio user obtains cooperation from the surrounding users to increase the 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 constraints (IC). Thesimulation results show that the transmission rate of cognitive radio link can be improved by cooperation, especially when the power of the direct link is limited. The achieved transmission rate under the average IC is higher than that under the peak IC, due to power adaptation between the transmitter and relay. And higher gain can be obtained as the number of potential relays increases.