BER Performance Comparison of AF and DF Assisted Relay Selection Schemes in Cooperative NOMA Systems

Abstract

This study investigates the bit error rate (BER) performance analysis for both amplify-and-forward (AF) and decode-and-forward (DF) assisted relay selection algorithms used in cooperative non-orthogonal multiple access (NOMA) systems. For the relay selection schemes, two different approaches are analyzed; Maximum-Minimum (Max-Min) relay selection and Two-Stage relay selection strategies are evaluated. Unlike existing works, the BER performance analysis for the near and far users are investigated with Monte Carlo simulations over the Rayleigh fading channel, considering the number of relays, power allocation coefficient, distance between nodes, and path loss exponent parameters. From the observed results, the AF assisted Max-Min relay selection method performs better for the far user. Moreover, the AF assisted Two-Stage relay selection method performs almost 10 dB gain compared to the DF scenario for the far user. Finally, the BER performance decreases as the far user is apparently moving away from the relay, while AF relaying outperforms compared to DF relaying for both users.