Performance off cluster-based multi-hop underlay networks with energy harvesting nodes

In this paper, the authors consider an underlay multi-hop cognitive radio network with energy harvesting secondary nodes, where there is a cluster of secondary decode-and-forward relays in each hop. The secondary nodes have no separate energy source available with them, but wake up from idle mode to harvest energy from the primary signal with the time-switching protocol, and use it for transmitting/relaying using the peak interference constraint. In each cluster, a relay with maximum transmit power is selected except in the last one. In the last cluster, a relay which has a maximum signal-to-noise ratio (SNR) at the secondary destination is selected. Though the suggested scheme has low implementation complexity and requires very little channel estimation, its performance is close to that of a scheme in which the link with the best SNR is chosen in each hop (which requires a lot of channel estimation). Analytical expressions are derived for the end-to-end outage probability and throughput assuming Rayleigh faded channels. They show that it is important to optimise the time-switching parameter (fraction of time devoted to energy harvesting) and the number of hops. Simulations confirm the accuracy of the derived expressions.