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

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.