Interference alignment based on stacked Alamouti code for 2?2 X channels with multiple antennas

We consider 2×2 X channels with 2M antennas at each node where each transmitter has local channel state information at transmitter (CSIT) and each receiver has full channel state information at receiver (CSIR). We propose an interference alignment (IA) scheme that achieves both the optimal degrees of freedom (DoF) of 8M/3 and the diversity order of 2 using stacked Alamouti codes. Particularly, the proposed IA scheme requires the fixed number of channel uses, regardless of the number of antennas, whereas the numbers of channel uses in the existing schemes increase linearly with the number of antennas.