Buffer-aided relaying scheme with energy harvesting in a cognitive wireless sensor network

This article presents a practical relaying scheme that improves the outage performance of a cognitive wireless sensor network. The relays in the proposed system have finite buffers and they are self-powered by harvesting energy from the primary signal. We adopt a buffer-aided relay selection strategy that reduces overhead for exchanging the channel state information between communication nodes. In particular, a combination of the partial relay selection and the conventional max-max relay selection is proposed to obtain the benefits of both those schemes while avoiding the cases where full/empty buffers are selected to receive/forward packets with limited buffer size. The time-switching relaying protocol is exploited to harvest energy at the relays. The use of energy harvesting in the relay selection process not only prolongs the lifetime of the cognitive wireless sensor network but also improves the outage performance. A tool from Markov chain theory is implemented to model the buffer states of the relay system, which are important in determining the state transition probability. The outage probability of the secondary wireless sensor network is derived, and numerical results are provided to verify the analysis. Different relaying schemes are also compared in terms of the outage probability and average packet delay.