On the degrees of freedom of multiantenna interfering broadcast channels

The degrees of freedom (DoF) of multiantenna interfering broadcast channels is studied in which the first base station (BS) with M₁ antennas wishes to send independent messages to its N₁ serving users and the second BS with M₂ antennas wishes to send independent messages to its N₂ serving users. Each user is assumed to be equipped with a single antenna. For max(M₁, M₂) ≤ min(N₁, N₂), the sum DoF is shown to be upper bounded by N₁(M₁N₂ - M₁M₂) + N₂(M₂N₁-M₁M₂)/N₁N₂-M₁M₂ and lower bounded by N₁N₂(M₁+M₂)/max(M₁ N₂, M₂N₁)+N₁N₂. The results characterize the optimal sum DoF if M₁N₂ = M₂N₁ and further characterize the asymptotically optimal sum DoF when both N₁ and N₂ tend to infinity. Specifically, the optimal sum DoF converges to M₁ +M₂ as N₁ and N₂ tend to infinity.