Performance Analysis of Cooperative HARQ Strategies in Single-relay WSNs Based on Outage Probability
Fan Wang, Suoping Li, Jaafar Gaber and Daobing Wang
Limited energy and poor anti-fading capability are two major problems faced by wireless sensor networks (WSNs). In order to improve the network performance, besides the throughput and system time delay, it is necessary to study the energy efficiency to make full use of the finite battery power to extend the network lifespan, and an effective error control technology needs to be introduced to enhance the transmission reliability. Cooperative communication and hybrid automatic repeat request (HARQ) have been proved to be the two effective methods to solve these problems. Inspired by this idea, this paper firstly improves the retransmission strategy by minimizing transmission energy per time slot. Six HARQ protocols (i.e., (C-)HARQ-Type I, (C-)HARQ-CC and (C-)HARQ-IR) are proposed according to the different types of HARQ and whether cooperative communication is adopted. After the description of basic principles, the exact expressions of outage probability for each protocol are obtained. Furthermore, the closed-form expressions of multiple system performance, which includes throughput, energy efficiency and the average transmission delay, under arbitrary maximum transmission number is derived by introducing a 2-dimensional discrete-time Markov chain (DTMC). Finally, four study cases are presented to compare the system performance of six proposed protocols, evaluate the influence of network parameters, such as the maximum transmission number and the location of relay, on system performance, and verify the advantage of proposed strategy in saving energy compared with other existing works.
Keywords: WSNs, HARQ, outage probability, throughput, energy efficiency, average delay