  This paper is on the spectral efficiency (SE) of a dense multi-cell massive
multiple-input multiple-output (MIMO). The channels are spatially correlated
and the multi-slope path loss model is considered. In our framework, the
channel state information is obtained by using pilot sequences and the BSs are
deployed randomly. First, we study the channel estimation accuracy and its
impact on the SE as the BS density increases and the network becomes densified.
Second, we consider the special case of uncorrelated channels for which the
stochastic geometry framework helps us to simplify the SE expressions and
obtain the minimum value of antenna-UE ratio over which the pilot contamination
is dominant rather than the inter- and intra-cell interference. Finally, we
provide some insights into the obtained SE for the spatially correlated
channels, from a multi-cell processing scheme as well as the single-cell ones
in terms of the BS density. Our results show that while all the detectors
result in non-increasing SE in terms of the BS density, their area SE increases
exponentially as the network becomes densified. Moreover, we conclude that in
order to achieve a given SE, the required value of antenna-UE ratio decreases
as the level of channel correlation increases.
