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 Alamouti (1998), Tarokh et al. (1998), and Hochwald et al. (2001)) 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 2×2 matrix operations in conjunction with single-user or 2-user decoding) and it admits single-user encoding in an overlay fashion