Degrees of freedom of the K-user interference channel with transmitter cooperation

We consider the K-user Gaussian interference channel in the context of the downlink of a cellular system where the base stations can exchange messages through a backhaul network, and the interfering users can be jointly served by multiple base stations. To limit the load on the backhaul network, the number of (base station) transmitters sharing a given message is bounded by a number M, which we call the cooperation order. We provide outer bounds on the sum degrees of freedom of this system, which are shown to be tight in special cases.