Fuzzy Logic-Based Energy-Optimal Collinear DF Relay Placement in Two-Hop η - μ Fading Channel

The goal of this paper is to investigate the change in energy efficiency of point-to-point (P2P) links in a wireless sensor network (WSN) upon introduction of a third node acting as a relay. In particular, we consider the problem of placing a relay node, either already available in the WSN but was inactive or is inserted after the WSN is formed, on the straight line joining the pair of nodes which terminates the P2P link at both ends. The optimal location is found by devising a fuzzy logic-based scheme whose rules are framed to minimize energy consumption and enhance the lifetime of the WSN. Two variants of the basic two-hop topology have been analysed, first, a non-cooperative variant, where the receiver accepts only the signal from the relay, and second, a more sophisticated variant, where the receiver is able to combine the relayed signal with the original signal from the source. Further, two different combining techniques, maximum ratio combining and selection combining (SC), are considered for the later variant. For our analysis we assumed an adaptive decode and forward (DF) relay for superior outage performance and M-ary quadrature amplitude modulation (MQAM) for better bandwidth efficiency. The eta - mu fading model is general in nature and it combines different popular fading models such as Rayleigh, Nakagami-q (Hoyt) and Nakagami-m etc. We were able to show that combining may not always lead to higher energy efficiency, especially for shorter P2P links. We have also investigated how different design parameters such as spectral efficiency, path loss exponent and fading parameters (eta, mu) affect the optimal relay placement location.