Unitary space-time constellation design is considered for noncoherent multiple-antenna communications, where neither the transmitter nor the receiver knows the fading coefficients of the channel. By employing the Clarke's subdifferential theorem of the sum of the kappa largest singular values of a unitary matrix, we present a numerical optimization procedure for finding unitary space-time signal constellations of any dimension. The Chernoff bound of the pairwise error probability is used directly as a design criterion. The constellations are found by performing gradient descent search on a family ldquosurrogaterdquo functions that converge to the maximum pairwise error probability. The complexity of the search procedure increases with the dimension and the size of the constellation, but it can be considered to be acceptable for an off-line design procedure. Since the designed constellations are unstructured, and, thus, require an exhaustive search over all codewords in decoding, their main practical value is to serve as constellation design performance benchmarks. We compare the performance of the new constellations to that of some other well-known constellations. Computer simulation results illustrate typically about 0.4-3.5 dB performance gains.

Assuming a single bounce scattering geometric channel model with circularly symmetric scatter density we deduce a general integral relation between angle of arrival (AOA) and scatter density function. Then we show that this relation can be expressed in terms of an integral equation that admits an accurate numerical solution provided that AOA is known. Furthermore, we show that similar integral equation relation between time of arrival (TOA) and scatter density function can be efficiently solved numerically for a given TOA. Results indicate that the scatter density can be numerically computed for a given AOA or TOA. Since these marginal distributions can be directly fit in channel measurements, the method provides means to adjust the applied geometrical channel model through field measurements. Hence, we follow the idea of inverse scattering theory where the far field pattern of scattered waves is known and the aim is to define the structure of the scattering medium. We consider two example AOA distributions, Gaussian and Student's t-distribution, found in literature. Our results show that scatter densities as well as the corresponding TOAs greatly vary depending on the assumed AOA

This paper presents a modulation identification (MOD ID) method for digital M-ary phase-shift keying (M-PSK) under additive white Gaussian channel, using the minimum Hellinger distance (MHD). When compared with the maximum likelihood (ML) method, the MHD has two significant advantages, low complexity and robustness against perturbations. In addition, the MHD is implementable for MOD ID by partitioning the I-Q plane. Our contribution is as follows. We obtain theoretical results for the modulation identification error probability of the MHD. Employing the Hellinger distance criteria, we present a sub-optimal partition design. Computer simulation experiments compare the MHD and the ML methods regarding the MOD ID performance and show that difference in performance is around 2dB in ideal channel.

In this paper, we propose a novel method for creating constellations of unitary space-time signals for non-coherent multiple-antenna communication link, where neither the transmitter nor the receiver knows the fading coefficients. By employing a theorem for the Clarke subdifferential of the sum of the k largest singular values of the unitary matrix, we present a numerical optimization procedure for finding good constellations of unitary space-time signals and report the best constellations found by this procedure. These constellations of unitary space-time signal improve the performance significantly upon previously best known constellations.

In the downlink of the wideband code division multiple-access (WCDMA) system users are separated by means of orthogonal variable spreading factor codes. The orthogonality of the users is lost in multipath channels causing multiple access interference which limits the system capacity and the availability of high data rate services. To suppress the interference in the downlink, it has been proposed to utilize linear channel equalization to partially restore the orthogonality of the users' spreading codes. The well-known direct linear minimum mean-square error (LMMSE) solution for the equalizer suffers from high computational complexity mainly due to the required matrix inversion. The problem is especially severe in case of a high channel delay spread and multi antenna receivers. In this paper, we apply the conjugate-gradient algorithm to iteratively solve the linear space-time equalizer. The performance of the proposed LMMSE space time equalizer is evaluated in the UTRA FDD downlink.