Cooperative spectrum sharing in cognitive radio networks with energy accumulation: design and analysis

The authors propose an efficient spectrum sharing scheme in cooperative cognitive radio networks, where an energy-constrained secondary transmitter (ST) first scavenges radio frequency (RF) energy from the received primary signals, and then the ST assists the primary transmission to obtain the opportunity of spectrum access. Specifically, the ST can forward the primary signal with its own signal by adopting both the Alamouti coding technique and superposition scheme only if the harvested energy is sufficient while the primary data is decoded correctly by the ST. Otherwise, the ST will continue to harvest RF energy. The authors use the discrete Markov chain to model the processes of charging and discharging of the battery. Moreover, two different joint decoding and interference cancellation schemes are employed at the receivers to restore the desired data. Closed-form expressions of outage probabilities for both the primary and secondary systems are derived. Aiming to minimise the outage probability of the secondary system with guaranteeing the primary transmission, an optimal power allocation factor for the ST is determined by Monte-Carlo simulation. Numerical results demonstrate that the proposed scheme can effectively improve the transfer performance of the secondary system while realising the transfer requirement of the primary system.