The degrees of freedom for MIMO interference broadcast channels with no CSIT

Multiple-input multiple-output (MIMO) interference broadcast channel (IBC) plays an important role in the modern wireless communications. The upper bound of degree of freedom (DoF) and corresponding achievable schemes have been investigated. However, all the achievable schemes require perfect channel state information at transmitters (CSIT). In the absence of CSIT, the DoF value is still unknown. This paper mainly focuses on the G-cell K-user MIMO IBC, where there are M antennas at each transmitter and N antennas at each receiver. The transmitters only know channel coherent time internals rather than the values of channel coefficients. The users in the same cell are assumed to be able to share the channel information. Based on a heterogeneous block fading model, a blind interference alignment (IA) scheme is proposed for this scenario. We show that when R >= 1/G-1 and R = min(M, KN)/max(M, KN), then a total of GKMN/M + KN degrees of freedom (DoF) can be achieved. The inner bound is same with the decomposition DoF upper bound.