  This paper addresses cooperation in a multicell environment where base
stations (BSs) wish to jointly serve multiple users, under a
constrained-capacity backhaul. We point out that for finite backhaul capacity a
trade-off between sharing user data, which allows for full MIMO cooperation,
and not doing so, which reduces the setup to an interference channel but also
requires less overhead, emerges. We optimize this trade-off by formulating a
rate splitting approach in which non-shared data (private to each transmitter)
and shared data are superposed. We derive the corresponding achievable rate
region and obtain the optimal beamforming design for both shared and private
symbols. We show how the capacity of the backhaul can be used to determine how
much of the user data is worth sharing across multiple BSs, particularly
depending on how strong the interference is.
