Fundamental Limits of Spectrum Sharing for NOMA-Based Cooperative Relaying Under a Peak Interference Constraint

TL;DR

This paper analyzes the performance limits of a NOMA-based cooperative relaying system under spectrum sharing constraints, deriving closed-form expressions for key metrics and demonstrating superior spectral efficiency over traditional OMA in high interference scenarios.

Contribution

It provides the first analytical performance analysis of NOMA-based cooperative relaying with spectrum sharing under peak interference constraints, including closed-form rate and outage expressions.

Findings

NOMA-based CRS outperforms OMA at high interference levels.

Interference from the SU-Tx to PU-Rx significantly impacts system performance.

Analytical results closely match numerical simulations.

Abstract

Non-orthogonal multiple access (NOMA) and spectrum sharing (SS) are two emerging multiple access technologies for efficient spectrum utilization in future wireless communications standards. In this paper, we present the performance analysis of a NOMA-based cooperative relaying system (CRS) in an underlay spectrum sharing scenario, considering a peak interference constraint (PIC), where the peak interference inflicted by the secondary (unlicensed) network on the primary-user (licensed) receiver (PU-Rx) should be less than a predetermined threshold. In the proposed system the relay and the secondary-user receiver (SU-Rx) are equipped with multiple receive antennas and apply selection combining (SC), where the antenna with highest instantaneous signal-to-noise ratio (SNR) is selected, and maximal-ratio combining (MRC), for signal reception. Closed-form expressions are derived for the average achievable rate and outage probabilities for SS-based CRS-NOMA. These results show that for large values of peak interference power, the SS-based CRS-NOMA outperforms the CRS with conventional orthogonal multiple access (OMA) in terms of spectral efficiency. The effect of the interference channel on the system performance is also discussed, and in particular, it is shown that the interference channel between the secondary-user transmitter (SU-Tx) and the PU-Rx has a more severe effect on the average achievable rate as compared to that between the relay and the PU-Rx. A close agreement between the analytical and numerical results confirm the correctness of our rate and outage analysis.