Degrees of freedom for MIMO interference broadcast channels

Multiple-input multiple-output (MIMO) interference broadcast channel (IBC) plays an important role in the modern wireless communications. The upper bound of degrees of freedom (DoF) and its Corresponding achievable schemes was investigated. However, all the achievable schemes require perfect channel state information at transmitters (CSIT). In absence of CSIT, the DoF value is still unknown. This article 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 coherence 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 semi-staggered block fading model, a blind interference alignment (IA) scheme was proposed for this scenario. It is shown that when R≥1/(G-1) and R = min(M,KN)/max(M,KN), a total of GKMN/(M + KN) DoF can be achieved. The inner bound is same with the decomposition DoF upper bound. Since the complexity is an important performance index to evaluate the achievable scheme, the quantitative analysis for the complexity is presented.