Relay selection in massive MIMO wireless energy harvesting cognitive networks

Abstract

In recent years, there has been an explosive growth in bandwidth-hungry wireless devices and applications which has, in turn, caused a strain on the provisions of the present electromagnetic spectrum. Several technologies have been studied and implemented in the quest to try and alleviate this growing scarcity of the spectrum. This work, therefore, tries to address some of these challenges by looking at spectrum utilisation techniques and how optimal they can be implemented to improve the spectral efficiency and overall system performance. This research seeks to investigate the sum-rate and outage performance of an energy harvesting cognitive massive multiple-input multiple-output (MIMO) multi-relay assisted network with underlay spectrum sharing. The secondary network is permitted to opportunistically access the licenced primary network frequency band provided that the intra-cell interference imposed on the primary base station due to concurrent secondary network transmissions does not exceed the pre-set interference temperature and hence maintain the quality-of-service (QoS) requirements of the primary network. The introduction of relays improves the system performance by increasing the network coverage and this research analyses the performance of the cognitive relay networks by looking at (i) the effect of primary user interference on the relay and subsequently relay selection, (ii) the outage probability of the secondary network being assisted by an amplify-and-forward (AF) relay and (iii) the impact of the number of relay antennas and the number of relays. The power-constrained secondary network nodes harvest energy from concurrent transmissions of the energy sufficient primary users. A time switching protocol is implemented in this work for energy harvesting and closed-form expressions for the harvested energy and achievable sum-rate are derived. To that end, this research seeks to quantify the trade-off between the achievable sum-rate of the network and the harvested energy. The primary base station and secondary destination employ zero-forcing detection and performance is investigated over Rayleigh fading