An Analysis of the Power Imbalance on the Uplink of Power-Domain NOMA

TL;DR

This paper investigates the impact of power imbalance in uplink Power-domain NOMA, revealing that balanced user signals minimize error probability and questioning the fundamental approach of NOMA design.

Contribution

It analytically demonstrates that balanced power signals optimize error performance in uplink NOMA, challenging traditional power imbalance strategies.

Findings

Balanced user signals minimize average error probability

Symmetry in error events is exploited for analysis

Simulations confirm the analytical results

Abstract

This paper analyzes the power imbalance factor on the uplink of a 2-user Power-domain NOMA system and reveals that the minimum value of the average error probability is achieved when the user signals are perfectly balanced in terms of power as in Multi-User MIMO with power control. The analytic result is obtained by analyzing the pairwise error probability and exploiting a symmetry property of the error events. This result is supported by computer simulations using the QPSK and 16QAM signal formats and uncorrelated Rayleigh fading channels. This finding leads to the questioning of the basic philosophy of Power-domain NOMA and suggests that the best strategy for uncorrelated channels is to perfectly balance the average signal powers received from the users and to use a maximum likelihood receiver for their detection.