  The presence of signal outage, due to shadowing and blockage, is expected to
be the main bottleneck in millimeter wave (mmWave) networks. Moreover, with the
anticipated vision that mmWave networks would have a dense deployment of base
stations, interference from strong line-of-sight base stations increases too,
thus further increasing the probability of outage. To address the issue of
reducing outage, this paper explores the possibility of base station
cooperation in the downlink of a mmWave heterogenous network. The main focus of
this work is showing that, in a stochastic geometry framework, cooperation from
randomly located base stations decreases outage probability. With the presumed
vision that less severe fading will be experienced due to highly directional
transmissions, one might expect that cooperation would increase the coverage
probability; our numerical examples suggest that is in fact the case. Coverage
probabilities are derived accounting for: different fading distributions,
antenna directionality and blockage. Numerical results suggest that coverage
with base station cooperation in dense mmWave systems and with no small scale
fading considerably exceeds coverage with no cooperation. In contrast, an
insignificant increase is reported when mmWave networks are less dense with a
high probability of signal blockage and with Rayleigh fading.
