A general framework is presented to study the diversity gains in a wideband directional channel from a physical wave-field perspective. Parameterization of the quantity is based on system-dependent channel characterization, where the propagation channel captured by multipath delays, angles-of-arrival, and angles-of-departure is defined system-dependently. Starting with a simple single-cluster-single-bounce channel and perfect receiving conditions, the theoretical framework is then extended to more general situations such as channels with multiple reradiating processes and scattering clusters. Using this methodology, we show through numerical examples that the conventional diversity estimate for wideband directional systems may lead to systematic prediction error of the achievable diversity gains

This paper presents some corrections on the equations given in a previous paper for the BER performance of a UCA and ULA in a mobile radio.

We present a realistic frequency-dependent channel model for ultrawideband (UWB) communications and develop a generalized broadband Capon estimator for localization of the spatially dispersed UWB signals. The proposed estimator is able to address the three key aspects of practical UWB radio wave propagation: presence of local scattering, wideband array signals, and frequency-dependent dispersive effects. The particle swarm optimization, which is a high-performance optimizer based on the intelligence of swarms, is then implemented to perform a multidimensional parameter search to jointly estimate the source central angles, the polynomial regression coefficients for angle spreads, and the frequency dependence of propagation modes.

When directional antennas are employed in the transmission link, the channel response is often obtained by applying a complex weight (antenna voltage pattern) to the waves distributing into/coming from different directions and is considered as a spatial filtering process. An important question is whether the antenna directivity has a substantial influence on the spatial pattern of scatterer distribution. As a consequence, allowing for a system-independent channel characterization may be implausible if the answer is yes. We present a systematic method to study the effect of antenna patterns on scatterer distribution in the multipath channel. The workhorse is the recently introduced semi-geometrically based statistical model and two heuristic rules, which establish the correspondence between geometric models and physical wave propagation processes. It is shown that the effect of a directional antenna is twofold. First, it alters the spatial distribution of scatterers by providing a different sample space for the random field; second, it distributes the signal components into the angles-of-departure or collects them from the angles-of-arrival by weighted combination.

A novel geometric model is proposed to expound the propagation process for an ultrawideband channel. This model defines scatterer distribution in a hypothetical azimuth-frequency domain (AFD). One advantage of this approach is the availability of analytical expressions relating signal properties in the AFD to channel properties. A further virtue is to exploit the geometric distribution of scatterers for different spectral components from a physical wave-propagation viewpoint. The analysis is based on the recently reported semigeometrically based statistical model and three heuristic rules, which are an extension of the rules presented in a previous work. These rules are aimed at establishing the underlying relationship between any geometric model and its corresponding physical channel. The power azimuthal spectrum and power delay spectrum are then calculated using this model and compared with empirical data from channel measurements.

Orthogonal frequency division multiplexing (OFDM) can be successfully used in mitigating the effect of multipath in a wireless channel. However, its' performance degrade in the presence of Doppler spreading. In this paper, multiple beamforming using uniform linear arrays (ULA) is used for OFDM systems to reduce Doppler spread and exploit the advantage of diversity. Each of the beams receiver signal which equal Doppler spread, which are combined using equal gain combining (EGC). We also present a method of determining the frequency compensating parameters, for beams pointing in different directions. Finally, our simulation results show that angular diversity in OFDM systems can provide significant improvement as compared to using only single beamforming.

A frequency domain geometric model aimed at clarifying the fundamental propagation characteristics for a wideband time-invariant channel is proposed. This modeling approach envisages a direct mapping from the frequency-domain transfer function T(f) in classic random linear systems to the geometric representation of a broadband channel. One of the main advantages of this approach is the availability of analytical expressions relating signal properties in frequency domain to channel output. A further virtue of this method is to exploit the geometric distribution of scatterers for different spectral components from a physical wave-propagation viewpoint. The workhorse is the semi-geometrically based statistical model and three heuristic rules proposed, which are an extension to the rules presented in the previous work. These rules are so proposed as to provide the missing link between any canonical model and the physical channel it represents. The power azimuthal spectrum and poster delay spectrum are calculated using this model. We further study the channel properties for a macrocell.

In this paper, to meet the Ka-band hostile propagation environment and satisfy the need of high quality multimedia communication, a new ARQ based multistep power control scheme for the Ka-band LEO satellite system is proposed. With low complexity, high throughput and small extra delay, the proposed algorithm alleviates the problem of long control delay inherent in LEO satellite systems. It is suitable for the Ka-band LMS (land mobile satellite) channel where the slow fade has high dynamics (frequently experienced shadowing results in more pronounced channel state transition between shadowing and nonshadowing).

The downlink of a LEO satellite communication system employing power controlled DS-CDMA and exploiting satellite diversity is analyzed and its performance compared with more traditional communication system utilizing single satellite reception. Performance computed using a quasi-analytic method has been thoroughly validated by means of extensive Monte-Carlo simulations. The effect of MAI (multiple access interference) on the system performance has been investigated with power control for various practical scenarios. The quantitative results tend to indicate that diversity improves the system performance provided that an optimal power control scheme is employed. Convolutional coding with hard-decision decoding is considered to obtain specific results.

A receiver structure based on maximum likelihood sequence estimation (MLSE) for receiving quaternary phase shift keyed signals over band-limited, nonlinear satellite channels, in the presence of additive downlink Gaussian noise, is derived. This work is an extension of work done by Mesiya et al. [2] for binary PSK transmission. Error performance of the receiver at low to moderate signal-to-noise ratios is estimated using computer simulation. For moderate to high signal-to-noise ratios, an upper bound on the probability of symbol error is obtained. A suboptimum receiver structure is then developed and its performance evaluated using computer simulation. It is shown that the performance of the suboptimum receiver is very close to that of the MLSE receiver.