  We consider a user-centric co-operative cellular network, where base stations
(BSs) close to a mobile co-operate to detect its signal using a (joint) linear
minimum-mean-square-error receiver. The BSs are at arbitrary positions and
mobiles are modeled as a planar Poisson Point Process (PPP). Combining
stochastic geometry and infinite-random-matrix theory, we derive a simple
expression for the spectral efficiency of this complex system as the number of
antennas grows large. This framework is applied to BS locations from PPPs and
hexagonal grids, and are validated through Monte Carlo simulations. The results
reveal the influence of tangible system parameters such as mobile and
base-station densities, number of antennas per BS, and number of co-operating
BSs on achievable spectral efficiencies. Among other insights, we find that for
a given BS density and a constraint on the total number of co-operating
antennas, all co-operating antennas should be located at a single BS. On the
other hand, in our asymptotic regime, for the same number of co-operating
antennas, if the network is limited by the area density of antennas, then the
number of co-operating BSs should be increased with fewer antennas per BS.
