Multiuser interference cancellation and detection for users with four transmit antennas

We consider J transmitter units each equipped with N transmit antennas over a wireless Rayleigh fading channel. Previously, it was proved that when each transmitter unit has N transmit antennas, using JN receive antennas, the receiver can completely separate the signals of J users. The provided diversity to each user was shown to be N. Here, we consider the case when all units are synchronized and employ quasi-orthogonal space-time block codes with N = 4 transmit antennas. It is proved that in this case a receiver with J receive antennas can separate the transmitted signals of all units and provide each unit with the same diversity order of N = 4.