Transmitter Layering for Multiuser MIMO Systems

A novel structure for multiple antenna transmissions utilizing space-time dispersion is proposed, where the original data stream is divided into K substreams which are modulated onto all available transmit antennas using stream-specific transmit signature sequences. In order to achieve this, the transmit antennas are partitioned into M groups of antennas, called partitions. The signals from the K data streams are independently interleaved by partition over the entire transmission frame. The interleaved partitions are then added over all K substreams prior to transmission over the MIMO channel. At the receiver, a low-complexity iterative detector adapted from recent CDMA multiuser detection research is used. It is shown that with careful substream power assignments this transmission methodology can efficiently utilize the capacity of rank-deficient channels as it can approach the capacity limits of the multiple antenna channel closely over the entire range of available signal-to-noise ratios and system sizes. This transmission methodology and receiver structure are then applied to multiuser MIMO systems where several multiple antenna terminals communicate concurrently to a joint receiver. It is shown that different received power levels from the different MIMO terminals can be beneficial and that higher spectral efficiencies can be achieved than in the single-terminal case.