  Millimeter wave (mmWave) signals are much more sensitive to blockage, which
results in a significant increase of the outage probability, especially for the
users at the edge of the cells. In this paper, we exploit the technique of base
station (BS) cooperation to improve the performance of the cell-edge users in
the downlink transmission of mmWave cellular networks. We design two
cooperative schemes, which are referred to as fixed-number BS cooperation (FNC)
scheme and fixed-region BS cooperation (FRC) scheme, respectively. In FNC
scheme, the cooperative BSs consist of the M nearest BSs around the served
cell-edge users, and in FRC scheme, the cooperative BSs include all the BSs
located within a given region. We derive the expressions for the average rate
and outage probability of a typical cell-edge user located at the origin based
on the stochastic geometry framework. To reduce the computational complexity of
our analytical results for the outage probability, we further propose a Gamma
approximation based method to provide approximations with satisfying accuracy.
Our analytical results incorporate the critical characteristics of mmWave
channels, i.e., the blockage effects, the different path loss of LOS and NLOS
links and the highly directional antenna arrays. Simulation results show that
the performance of the cell-edge users is greatly improved when mmWave networks
are combined with the technique of BS cooperation.
