# On the Performance Gain of NOMA over OMA in Uplink Single-cell Systems

## TL;DR

This paper analyzes the performance advantages of NOMA over OMA in uplink single-cell systems, highlighting near-far gains and the impact of multiple antennas on sum-rate improvements.

## Contribution

It provides a comprehensive analysis of NOMA's performance gain over OMA in various antenna configurations and quantifies near-far gains in different fading environments.

## Key findings

- NOMA outperforms OMA in asymptotic ergodic sum-rate.
- Large-scale near-far gain increases with cell size.
- Adding antennas at the base station amplifies NOMA's performance gain.

## Abstract

In this paper, we investigate the performance gain of non-orthogonal multiple access (NOMA) over orthogonal multiple access (OMA) in uplink single-cell systems. In both single-antenna and multi-antenna scenarios, the performance gain of NOMA over OMA in terms of asymptotic ergodic sum-rate is analyzed for a sufficiently large number of users. In particular, in single-antenna systems, we identify two types of near-far gains brought by NOMA: 1) the large-scale near-far gain via exploiting the large-scale fading increases with the cell size; 2) the small-scale near-far gain via exploiting the small-scale fading is a constant given by $\gamma = 0.57721$ nat/s/Hz in Rayleigh fading channels. Furthermore, we have analyzed that the performance gain achieved by single-antenna NOMA can be amplified via increasing the number of antennas equipped at the base station due to the extra spatial degrees of freedom. The numerical results confirm the accuracy of the derived analyses and unveil the performance gains of NOMA over OMA in different scenarios.