Outage Performance of Two-Way Relay Non-Orthogonal Multiple Access Systems

TL;DR

This paper analyzes the outage performance of a two-way relay NOMA system considering imperfect and perfect SIC, deriving outage probability expressions and comparing its performance to OMA, highlighting the impact of interference and error floors.

Contribution

It provides the first closed-form outage probability expressions for TWR-NOMA with both imperfect and perfect SIC, and evaluates its performance relative to TWR-OMA.

Findings

TWR-NOMA outperforms TWR-OMA in low SNR regimes.

Interference signals cause error floors and throughput ceilings.

Closed-form outage probabilities are derived for different SIC scenarios.

Abstract

This paper investigates a two-way relay nonorthogonal multiple access (TWR-NOMA) system, where two groups of NOMA users exchange messages with the aid of one half-duplex (HD) decode-and-forward (DF) relay. Since the signal-plus-interference-to-noise ratios (SINRs) of NOMA signals mainly depend on effective successive interference cancellation (SIC) schemes, imperfect SIC (ipSIC) and perfect SIC (pSIC) are taken into consideration. To characterize the performance of TWR-NOMA systems, we derive closed-form expressions for both exact and asymptotic outage probabilities of NOMA users' signals with ipSIC/pSIC. Based on the results derived, the diversity order and throughput of the system are examined. Numerical simulations demonstrate that: 1) TWR-NOMA is superior to TWR-OMA in terms of outage probability in low SNR regimes; and 2) Due to the impact of interference signal (IS) at the relay, error floors and throughput ceilings exist in outage probabilities and ergodic rates for TWR-NOMA, respectively.