  In this paper, we study the energy-efficient user access control (UAC) based
on resource allocation (RA) in heterogeneous cellular networks (HCNs) with the
required downlink data rate under non-ideal power amplifiers (PAs) and circuit
power. It is proved that the energy consumption minimization is achieved when
the typical user accesses only one base station (BS), while the other BSs
remain in idle mode on the transmission resource allocated to this user. For
this purpose, we reformulate the original non-convex optimization problem into
a series of convex optimization problems where, in each case, the transmit
power and duration of the accessed BS are determined. Then, the BS with the
minimal energy consumption is selected for transmission. Considering the
approximate situation, it is showed that the optimal transmit duration of the
accessed BS can be estimated in closed form. The benefits of our proposed UAC
and RA schemes are validated using numerical simulations, which also
characterize the effect that non-ideal PAs have on the total energy consumption
of different transmission schemes.
