  We consider the uplink of a multiuser massive MIMO system wherein a base
station (BS) having $M$ antennas communicates coherently with $K$ single
antenna user terminals (UTs). We study the energy efficiency of this system
while taking the transceiver power consumption at the UTs and the BS into
consideration. For a given spectral efficiency $R$ and fixed transceiver power
consumption parameters, we propose and analyze the problem of maximizing the
energy efficiency as a function of $(M,K)$. For the maximum ratio combining
(MRC) detector at the BS we show that with increasing $R$, $(M,K)$ can be
adaptively increased in such a way that the energy efficiency converges to a
positive constant as $R \rightarrow \infty$ ($(M,K)$ is increased in such a way
that a constant per-user spectral efficiency $R/K$ is maintained). This is in
contrast to the fixed $(M,K)$ scenario where the energy efficiency is known to
converge to zero as $R \rightarrow \infty$. We also observe that for large $R$,
the optimal $(M,K)$ maximizing the energy efficiency is such that, the total
power consumed by the power amplifiers (PA) in all the $K$ UTs is a small
fraction of the total system power consumption.
