Cognitive Multihop Wireless Powered Relaying Networks Over Nakagami- ${m}$ Fading Channels

In this paper, we study the end-to-end performance of multi-hop wireless powered relaying networks cognitively operating with primary networks over Nakagami-m fading channels. Our analysis considers multi-hop wireless powered relaying systems in which all communication nodes harvest energy from a multiple antennas power beacon (PB) to transmit data to multiple destinations in the presence of a multiple antennas primary receiver (PR). Aiming at improving end-to-end system performance, we propose two relay selection schemes, namely data channel based relay selection (DbRS) and interference channel based relay selection (IbRS), under cognitive radio approach. By taking into account the harvested energy and the interference power constraint, we derive the exact closed-form expression for the outage probability (OP) of the proposed schemes, which is then verified by Monte Carlo simulations over Nakagami-m fading channels. The tractable asymptotic OP of each scheme is also provided unveiling several important insights on system characteristics and performance trends. Moreover, we develop the asymptotic upper bounds for the ergodic capacity and bit error rate (BER) of the considered multi-hop relaying network. Numerical results in terms of system OP, ergodic capacity, and average BER performance are provided to demonstrate that DbRS scheme outperforms IbRS one, which by its turn outperforms random relay selection scheme. Finally, the influences of the number of antennas at PB and PR, number of relays in each cluster, number of hops, the PB and PR placements, and time switching ratio on the overall system performance are examined and discussed comprehensively.