A space-time coding approach for systems employing four transmit antennas

We propose a novel transmit diversity scheme for the downlink of communication systems that employ four transmit antennas. The scheme can be seen as a simplified transmission architecture admitting an entire family of space-time codes. It can be also seen as an extension of previously proposed techniques (such as those presented in [1] [2] [3]) to the case of four transmit antennas with complex input data symbols. Our technique has a number of appealing features, namely, it enables a significant portion of the open-loop channel capacity, it requires simple receiver processing (involving typically 2 x 2 matrix operations in conjunction with single-user or 2-user decoding) and it admits single-user encoding in an overlay fashion.