A space-time Tx scheme for two-cell MISO-BC with delayed CSIT

Perfect channel state information at the transmitter (CSIT) is required to completely characterize the optimal degrees of freedom (DoF) of an interfering network by zero-forcing. However, it is not always realistic to know the CSIT perfectly when the channel is varying rapidly with time. In that case, a delayed CSIT is a more reasonable assumption. In this paper, we study the DoF of interfering multiple input single output (MISO) broadcast channel (BC) when the delayed CSIT is known perfectly. We propose a space-time transmission scheme based on interference alignment for two-cell interfering MISO-BC with M transmit antennas and K users in each cell. Considering the various cases, we suggest that the achievable per cell DoF converges to K/K+1 in the case when M = K and the outdated CSIT is known perfectly. The DoF per cell approaches 1 as the number of users in each cell approach to infinity.