  Blocking objects (blockages) between a transmitter and receiver cause
wireless communication links to transition from line-of-sight (LOS) to
non-line-of-sight (NLOS) propagation, which can greatly reduce the received
power, particularly at higher frequencies such as millimeter wave (mmWave). We
consider a cellular network in which a mobile user attempts to connect to two
or more base stations (BSs) simultaneously, to increase the probability of at
least one LOS link, which is a form of macrodiversity. We develop a framework
for determining the LOS probability as a function of the number of BSs, when
taking into account the correlation between blockages: for example, a single
blockage close to the device -- including the user's own body -- could block
multiple BSs. We consider the impact of the size of blocking objects on the
system reliability probability and show that macrodiversity gains are higher
when the blocking objects are small. We also show that the BS density must
scale as the square of the blockage density to maintain a given level of
reliability.
