Coverage in mmWave Cellular Networks with Base Station Cooperation

Signal outage, due to shadowing and blockage, is expected to be the main bottleneck in millimeter wave (mmWave) networks. Moreover, the anticipated dense deployment of base stations in mmWave networks is expected to increase the interference from strong line-of-sight base stations too, thus further increasing the probability of outage. To address the issue of reducing outage, this paper explores the possibility of base station co-operation in the downlink of mmWave heterogenous networks. The main focus of this work is showing that, in a stochastic geometry framework that incorporates blockage, co-operation from randomly located base stations decreases the probability of outage/increases the coverage probability. Coverage probabilities are derived accounting for: blockage, different fading distributions on the direct links (but always Rayleigh fading on the interference links), antenna directionality, and different tiers. Numerical results suggest that coverage with base station co-operation in dense mmWave systems (i.e., with high average number of base stations per square meter), without small scale fading on the direct communications links, and with any probability of signal blockage, considerably exceeds coverage without co-operation. In contrast, a small increase in coverage is reported when mmWave networks are less dense, have a high probability of signal blockage and the direct communications links are affected by Rayleigh fading.