Minimum Variance Maximum Mean Relay Selection Scheme for Cooperative NOMA Networks

Abstract

Cooperative communication is a key factor in 5G and beyond standards for increasing the quality of service and aids for dense networks. It works in conjugate with non-orthogonal multiple access (NOMA) to increase the connectivity and spectral efficiency. In this paper, a novel minimum variance maximum mean relay selection scheme with fixed power allocation (MVMM-FPA) is proposed for two-stage cooperative NOMA (C-NOMA) networks using decode-and-forward protocol. The outage probability analytical expressions are derived for the MVMM-FPA over Rayleigh fading channel and its performance is observed with the conventional relay selection (RS) schemes. The impact of outage performance on target rate for users and number of relays have been analyzed for the proposed scheme. Monte Carlo simulations are used to corroborate the analytical expressions of outage probability. Simulation results reveal that the MVMM-FPA RS scheme for C-NOMA offers a minimal outage probability than existing max-min RS and orthogonal multiple access schemes without sacrificing the spectral efficiency. IntroductionThe goals of 5G and beyond wireless communications are high spectral efficacy, high data rates, low latency and seamless connectivity. One of the trustworthy entrant for 5G is non-orthogonal multiple access (NOMA), when compared to alternative technologies like time division multiple access (TDMA), frequency division multiple access (FDMA) and orthogonal frequency division multiple (OFDM) access schemes [1][2][3][4][5][6][7]. NOMA permits multiple users to transmit data simultaneously at same frequency band using power domain, [8][9][10]. NOMA with cooperative communication will further improve the quality of the service (QoS). The state of art cooperative NOMA (C-NOMA) techniques are discussed below.