Modeling and Analysis for HARQ-Aided NOMA Scheme Using Markov-Based Approach

Recently, non-orthogonal multiple access (NOMA) scheme has been conceived as a promising candidate to improve the spectral efficiency in the fifth generation (5G) wireless communication system. In this paper, we consider power-domain NOMA. We investigate the performance of the downlink NOMA system with the Type I hybrid automatic repeat request (HARQ) scheme. We model the downlink HARQ-aided NOMA system as an absorbing discrete-time Markov chain (DTMC). Then, we study the system performance in terms of the outage probability and the expected number of re-transmissions under perfect and imperfect channel estimation. We show that our DTMC-based analysis is simple, tractable, and accurate. Simulations have been conducted to verify the accuracy of our DTMC-based analysis.