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