  Cooperation in cellular networks has been recently suggested as a promising
scheme to improve system performance, especially for cell-edge users. In this
work, we use stochastic geometry to analyze cooperation models where the
positions of Base Stations (BSs) follow a Poisson point process distribution
and where Voronoi cells define the planar areas associated with them. For the
service of each user, either one or two BSs are involved. If two, these
cooperate by exchange of user data and channel related information with
conferencing over some backhaul link. Our framework generally allows variable
levels of channel information at the transmitters. In this paper we investigate
the case of limited channel state information for cooperation (channel phase,
second neighbour interference), but not the fully adaptive case which would
require considerable feedback. The total per-user transmission power is further
split between the two transmitters and a common message is encoded. The
decision for a user to choose service with or without cooperation is directed
by a family of geometric policies depending on its relative position to its two
closest base stations. An exact expression of the network coverage probability
is derived. Numerical evaluation allows one to analyze significant coverage
benefits compared to the non-cooperative case. As a conclusion, cooperation
schemes can improve system performance without exploitation of extra network
resources.
