  Beamforming is an essential requirement to combat high pathloss and to
improve signal-to-noise ratio during initial cell discovery in future
millimeter wave cellular networks. The choice of an appropriate beamforming is
directly coupled with its energy consumption. The energy consumption is even of
more concern at a battery limited mobile station (MS). In this work, we provide
an energy consumption based comparison of different beamforming schemes while
considering both a low power and a high power analog-to-digital converter (ADC)
for a millimeter wave based receiver at the MS. We analyze both context
information (CI) (GPS positioning based) and non context information based
schemes, and show that analog beamforming with CI (where mobile station's
positioning information is already available) can result in a lower energy
consumption, while in all other scenarios digital beamforming has a lower
energy consumption than analog and hybrid beamforming. We also show that under
certain scenarios recently proposed phase shifters network architecture can
result in a lower energy consumption than other beamforming schemes. Moreover,
we show that the energy consumption trend among different beamforming schemes
is valid irrespective of the number of ADC bits. Finally, we propose a new
signaling structure which utilizes a relatively higher frequency sub-carrier
for primary synchronization signals compared to other signaling, which allows a
further reduction in initial cell search delay and energy consumption of the
MS.
