Effect of Beam Broadening in Directional Beamforming-Based Cellular Networks

The use of directional beamforming at a base station equipped with a linear antenna array has the potential to significantly increase the spectrum utilization efficiency of a cellular network by focusing the information-bearing signal only to the direction of a target mobile user. Unfortunately, however, this beamforming gain can be reduced by the beam broadening effect which broadens the beam width and reduces the directivity gain when the beam is steered away from the boresight direction. Hence, in this paper, assuming poisson point process (PPP)-distributed base stations, we analyze the coverage probability of a directional beamforming-based cellular network considering the beam broadening effect. Analyses are done with the general Nakagami-m fading channel, including two special cases: Rayleigh fading (m = 1) and static (m → ∞) channels. Numerical results show that, although the beam broadening effect can lead to some coverage loss, the achieved gain by the directional beamforming is still significant.