An Efficient Square-Root Algorithm for BLAST

Bell Labs Layers 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, in this paper 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: the algorithm is division-free and uses only orthogonal transformations. In a 14 antenna system designed for transmission of 1Mbit/sec over a 30 kHz channel, the nulling and cancellation computation is reduced from 190 MFlops/sec to 19MFlops/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.