  Cell discovery is the procedure in which a user equipment (UE) finds a
suitable base station (BS) to establish a communication link. When beamforming
with antenna arrays is done at both transmitter and receiver, cell discovery in
mm wave systems also involves finding the correct angle of arrival - angle of
departure alignment between the UE and the detected BS. First, we consider the
single BS scenario and present the mathematical model for the cell discovery
problem. We present the details of the beam sweeping based techniques and
explain the beam combining scheme to reduce the training overhead. We
analytically characterize the performance of energy detector at the UE for both
beam sweeping and beam combining methods under some channel assumptions.
Further, we consider the multiple BS case where BSs transmit synchronization
signals along with directional beamforming. We analyze the performance of the
energy detector in this case as well. We finally present simulation studies
with channels generated using generic mm wave channel emulators and draw
inferences on the role of various parameters on the cell discovery performance.
