An Optimal Relay Selection and Precoder Designing in MIMO Multi-Relay Cognitive Networks

In this article, we propose a best relay selection scheme along with the impact of precoder designing for multi-input multi-output (MIMO) multi-relay cognitive networks (MCNs). Joint relay selection and precoder designing problem is studied to maximize the energy efficiency of the secondary network
$({\it SN})$
subject to a quality-of-service (QoS), power, and interference constraints at the relays and/or source. In this, amplify-and-forward inspired multiple relays are deployed randomly to facilitate the transmission between source and destination in the
$SN$
. These relays
$(S_{R_{i}})$
help to reduce the power consumption requirements at the secondary transmitter
$(S_{\it TX})$
while meeting the need for quality-of-service (QoS) for both networks, i.e., primary network
$(PN)$
and
$SN$
. This study introduces four different schemes for joint relay selection and precoder designing for
$SN$
. Simulation results show that the opportunistic relay selection scheme outperforms other schemes in terms of maximum end-to-end energy efficiency of the
$SN$
.