Capacity-approaching space-time codes for systems employing four transmitter antennas

The design of space-time codes that are capable of approaching the capacity of multiple-input-single-output (MISO) antenna systems is a challenging problem, yet one of high practical importance. While a remarkably simple scheme of Alamouti (1998) is capable of attaining the channel capacity in the case of two-transmitter and one-receiver antennas (2,1), no such schemes are known for the case of more than two transmitter antennas. We propose a family of space-time codes that are especially designed for the case of four-transmitter antennas and that are shown to allow the attainment of a significant fraction of the open-loop Shannon capacity of the (4,1) channel.