  At millimeter wave (mmWave) frequencies, signals are prone to blocking by
objects in the environment, which causes paths to go from line-of-sight (LOS)
to non-LOS (NLOS). We consider macrodiversity as a strategy to improve the
performance of mmWave cellular systems, where the user attempts to connect with
two or more base stations. An accurate analysis of macrodiversity must account
for the possibility of correlated blocking, which occurs when a single blockage
simultaneously blocks the paths to two base stations. In this paper, we analyze
the macrodiverity gain in the presence of correlated random blocking and
interference. To do so, we develop a framework to determine distributions for
the LOS probability, SNR, and SINR by taking into account correlated blocking.
We consider a cellular uplink with both diversity combining and selection
combining schemes. We also study the impact of blockage size and blockage
density. We show that blocking can be both a blessing and a curse. On the one
hand, the signal from the source transmitter could be blocked, and on the other
hand, interfering signals tend to also be blocked, which leads to a completely
different effect on macrodiversity gains. We also show that the assumption of
independent blocking can lead to an incorrect evaluation of macrodiversity
gain, as the correlation tends to decrease macrodiversity gain.
