  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.
