Dynamic interference‐limited relay sharing in cognitive radio networks by using hierarchical modulation

Abstract

Sharing a relay in cognitive radio (CR) networks in order to enhance the secondary user's (SU's) performance in an interference-limited scheme is investigated. It is assumed, by utilising hierarchical modulation, a shared relay is used simultaneously between both primary user (PU) and SU. The proposed scheme relies on both power adaptation and rate scheduling. Based on channel side information and tolerable interference limitation at the PU, the SU adapts its power and the transmission data rates are regulated by the PU's status and channels condition. Theoretical analyses and simulation results are provided to evaluate the performance of the proposed dynamic spectrum sharing scheme. It is shown that rate adaptation leads to significant improvement of the throughput of the SU, at the cost of negligible degradation in performance of the PU. The results also demonstrate that sharing CR relay with the PU can compensate the side effects of spectrum sharing and interference caused by the SU, which for instance is equivalent to ∼8 dB (low signal-to-noise ratio (low-SNR) regime) and to 15 dB (high-SNR regime) SNR improvement.