  Massive MIMO base stations use multiple spatial diversity branches, which are
often assumed to be uncorrelated in theoretical work. Correlated branches are
considered seldom since they are mathematically less tractable. For correlated
Rician fading, only the first- and second-order moments have been explored. To
describe propagation environments more accurately, full distribution functions
are needed.
  This manuscript provides these functions for the maximum ratio combining
effective channel, a quadratic form of a random complex normal channel vector.
Its mean vector and covariance matrix are based on a plane wave model
incorporating array geometry, antenna element pattern, power angular spectra
and power delay profiles. Closed-form approximations of the distribution
functions are presented, to allow the fast evaluation of many real-world
scenarios.
  The statistical framework is used to show that low-directivity antenna
elements provide better performance in angular constricted Rician fading with
off-axis incidence than high-directivity elements. Moreover, two base station
array layouts are compared, showing that a half-circle array illuminates a cell
more evenly than a uniform linear array. With the full distribution functions
available, performance can be compared over the full range of received powers
and not only based on the average SNR.
