A Cooperation and Access Spectrum Sharing Protocol with Cooperative Interference Management

In cognitive radio network, the spectrum sharing is considered where secondary (unlicensed) users’ communication co-exists with primary (licensed) users’ communication in the presence of an interferer, and the interferer has a significant impact on the primary performance. Hybrid ARQ (automatic-repeat-request) retransmission mechanisms are employed at primary and interfering links. Based on the mechanisms, a cooperate-and-access spectrum sharing protocol is proposed where the secondary system switches between cooperation mode with forwarding interference and access mode with decoding interfering packet. In the cooperation mode, the secondary transmitter forwards information about the interference to the primary receiver for interference mitigation. Thus, the primary performance is improved compared to the traditional non-cooperative communication system and credits are collected by the secondary system. Adequate credits allow the secondary system running on the access mode, i.e. the secondary packet is delivered to the secondary receiver by using the primary spectrum. Then, compared to the traditional system the primary performance is degraded in the access mode. The condition that this degradation can be fully offset by the advantage accrued from interference mitigation is investigated. The primary throughput in cooperation and access modes and the secondary throughput in access mode are derived. Numerical results show that the proposed protocol has the equal or higher average primary throughput than the traditional system in the low primary SNR region. In addition, when the average transmits SNR of the primary is less than that of the interfering user, the proposed protocol is more efficient than the protocol in Li et al. (IEEE Transactions on Communication 60(10):2861–2870, 2012).