  This paper takes into consideration the non-ideal efficiency characteristics
of realistic power amplifiers (PAs) along with the daily traffic profile in
order to investigate the impact of PA dimensioning on the energy efficiency
(EE) of load adaptive massive MIMO system. A multicellular system has been
considered where each base station (BS) is equipped with a large number of
antennas to serve many single antenna users. For a given number of users in a
cell, the optimum number of active antennas maximizing EE has been derived
where total BS downlink power is assumed to be fixed. Under the same
assumption, the PAs have been dimensioned in a way that maximizes network EE
not only for a single time snapshot but over twenty four hours of operation
while considering dynamic efficiency characteristics of the PAs. In order to
incorporate this daily load profile, each BS has been modeled as an M/G/m/m
state dependent queue under the assumption that the network is dimensioned to
serve a maximum number of users at a time corresponding to 100% cell traffic
load. This load adaptive system along with the optimized PA dimensioning
achieves 30% higher energy efficiency compared to a base line system where the
BSs always run with a fixed number of active antennas which are most energy
efficient while serving 100% traffic load.
