Massive MIMO and NOMA Bits-per-Antenna Efficiency under Power Allocation Policies

TL;DR

This paper compares resource allocation strategies in massive MIMO and NOMA systems, showing NOMA's advantages in spectral and energy efficiency at high device loading using different power allocation policies.

Contribution

It introduces a comparative analysis of power allocation strategies in massive MIMO and NOMA, highlighting NOMA's superior efficiency at high device loadings.

Findings

NOMA outperforms massive MIMO in spectral efficiency by 3x.

NOMA achieves twice the energy efficiency of massive MIMO.

NOMA is more effective at higher device loadings ($0.6< ho<2.0$).

Abstract

A comparative resource allocation analysis in terms of received bits-per-antenna spectral efficiency (SE) and energy efficiency (EE) in downlink (DL) single-cell massive multiple-input multiple-output (mMIMO) and non-orthogonal multiple access (NOMA) systems considering a BS equipped with many ($M$) antennas, while $K$ devices {operate} with a single-antenna, and {the loading of devices} $\rho = \frac{K}{M}$ ranging in $0<\rho\leq 2$ is carried out under three different \ac{PA} strategies: the inverse of the channel power allocation (PICPA), a modified water-filling ($\Delta$-WF) allocation method, and the equal power allocation (EPA) reference method. Since the two devices per cluster are overlapped in the power domain in the NOMA system, the channel matrix requires transformation to perform the zero-forcing (ZF) precoding adopted in mMIMO. Hence, NOMA operating under many antennas can favor a group of devices with higher array gain, overcoming the mMIMO and operating conveniently in the higher loading range $0.6<\rho<2.0$. In such a scenario, a more realistic and helpful metric consists of {evaluating} the area under SE and EE curves, by measuring the bit-per-antenna and bit-per-antenna-per-watt efficiency, respectively. Our numerical results confirm a superiority of NOMA w.r.t. mMIMO of an order of 3x for the SE-area and 2x for the EE-area metric.