Analysis of Degrees of Freedom of Interfering MISO Broadcast Channels

In this paper, we provide a lower and upper bound for the number of degrees of freedom (DOF) of B multiple-input single-output (MISO) broadcast channels (BC) where each base station (BS) equipped with M antennas supports its corresponding K single antenna users suffering from inter-cell interference. We show that two bounds meet with each other when M = 1 or M ≥ K or B >max(M,K)/min(M,K). From the derived result, we learn that the available DOF of the B-user multiple-input multiple-output (MIMO) interference channels is degraded by disabling receive cooperation if and only if M < K and B ≤ max(M,K)/min(M,K). We observe that even for that case, the multiple BCs where interference mitigation should be fully performed at the transmitters due to the distributed receive antennas can achieve the DOF more than 2/3 of the DOF of the MIMO interference channels. In addition, the exact number of DOF is derived for two mutually interfering and deterministic broadcast channels in the presence of cognitive BSs. Our result shows that in two BCs interfering with each other, whether receive cooperation exists or not, it does not affect the DOF if one of two transmitters is a cognitive BS.