Differential Bell-Labs Layered Space Time Architectures

Most research on differential MIMO is based on space-time block codes, aiming to achieve maximum transmit diversity and thus make the transmission more robust by the aid of the special orthogonal or quasi-orthogonal code structures. However, a differential scheme based on a spatial multiplexing approach such as the Bell-Labs layered space time (BLAST) wireless architecture would be likely to provide a much greater capacity. To this end, in this paper, we derive a simple differential modulation scheme based on BLAST for any number of transmit antennas and receive antennas. A special symbol mapping method is developed to avoid amplitude variation of the transmitted signals, which can also improve the system performance. This differential scheme can significantly reduce the system complexity, since it avoids the need for channel estimation. Moreover, an improved sub-optimal detection algorithm based on a Gaussian approximation is applied to greatly reduce computational complexity at the receiver, otherwise prohibitive, with only very slight performance loss.