A fast square-root implementation for BLAST

Bell Labs Layered Space-Time (BLAST) is a scheme for transmitting information over a rich-scattering wireless environment using multiple receive and transmit antennas. The main computational bottleneck in the BLAST algorithm is a "nulling and cancellation" step, where the optimal ordering for the sequential estimation and detection of the received signals is determined. To reduce the computational cost of BLAST we develop an efficient square-root algorithm for the nulling and cancellation step. The main features of the algorithm include efficiency: the computational cost is reduced by 0.7M, where M is the number of transmit antennas, and numerical stability; and the algorithm is division-free and uses only orthogonal transformations. In a 14 antenna system designed for transmission of 1 Mbit/sec over a 30 kHz channel, the nulling and cancellation computation is reduced from 190 MFlops/sec to 19 MFlops/sec, with the overall computations being reduced from 220 MFlops/sec to 49 MFlops/sec. The numerical stability of the algorithm also make it attractive for implementation in fixed-point (rather than floating-point) architectures.