In this paper, we propose a new design criterion and a new class of unitary signal constellations for differential space-time modulation for multiple-antenna systems over Rayleigh flat-fading channels with unknown fading coefficients. Extensive simulations show that the new codes have significantly better performance than existing codes. We have compared the performance of our codes with differential detection schemes using orthogonal design, Cayley differential codes, fixed-point-free group codes, and product of groups and for the same bit-error rate, our codes allow smaller signal-to-noise ratio (SNR) by as much as 10 dB. The design of the new codes is accomplished in a systematic way through the optimization of a performance index that closely describes the bit-error rate as a function of the SNR. The new performance index is computationally simple and we have derived analytical expressions for its gradient with respect to constellation parameters. Decoding of the proposed constellations is reduced to a set of one-dimensional closest point problems that we solve using parallel sphere decoder algorithms. This decoding strategy can also improve efficiency of existing codes.

A nonconventional approach to the analysis of dedicated computing structures in which the number of compute cycles is used as a design parameter to determine families of transformations implementable in the structure is presented. Using this approach, a single architecture can be used to implement a family of transformations with varying degrees of complexity. The transformations generated by a matrix multiplication array are considered in detail. It is shown that, for some real-time applications it becomes possible to incorporate the compute time as a constraint for designs based in optimality criteria. In particular, a least square approximation problem is discussed.>

Linear maps on a 2-D signal space are considered. Using recent results on fast linear transforms, several categories of fast-2-D maps are identified. The connections between fast processing and type of kernel separability are developed. Companion systolic architectures that efficiently realize the fast forms are discussed. The transfer functions of fast 2-D processors are analyzed and illustrated through examples.>

A recursive algorithm is presented for computing the discrete Fourier transform (DFT). The algorithm is developed for a moving-window-type processing. The computational structure is fully concurrent and allows a vectorized updating of the DFT. The total time required for the updating could be as low as that of only one multiplication and two additions, regardless of the number of points. A possible structure for executing the computations is developed, and possible enhancements are analyzed.>

The problem of m-D filtering using sequential scanning is considered. It is shown that the optimal causal filter and the performance measure depend on the scan selected. Examples show that this effect can be significant. Possible techniques to select a suitable scan are analyzed.