On Impact of HPA Nonlinearity in NOMA Enabled Heterogeneous Cellular Network

Abstract

Heterogeneous cellular network (HCN) is structured on a multi-tier architecture comprising of macro-base stations (MBSs) and small-base stations (SBSs). MBS and SBS are deployed to accommodate a large number of users for the purpose of achieving higher data rates, coverage, and improved outage performance. Recognized for its spectrum efficiency, non-orthogonal multiple access (NOMA) emerges as a viable multiple-access technique for sixth-generation (6G) wireless networks. To maximize power efficiency and reduce outage probability, the power amplifier at the base station is operated close to saturation, which results in nonlinear distortions. Thus, it is vital to understand the fundamental performance guarantees of practical NOMA-enabled HCN systems (HCN-NOMA) under nonlinear distortions introduced by high power amplifiers (HPA). In this paper, we employ an analytical performance evaluation of HCN-NOMA using stochastic geometric approach consisting of a multi-tier architecture with nonlinear distortions produced by HPA. We compare and highlight the impact of HPA operating in the linear and nonlinear regions on orthogonal multiple access (OMA) and NOMA in multi-tier HCN. The performance is assessed and compared in terms of outage probability, system throughput, and energy efficiency. It is observed that the performance is improved by up to 96.6% in HCN employing NOMA versus OMA while considering the nonlinear region of operation of HPA.