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The effect of spatially and temporally correlated Ricean fading on the performance of space-time codes (STCs) at finite signal-to-noise ratio (SNR) is examined. A code design criterion is derived leading to robust STCs in a wide variety of propagation conditions.

This paper presents a stochastic geometry-based model of the multiple-input-multiple-output channel, as seen by the user terminal based on the extraction of cluster parameters from wideband data measured at 1.9 GHz in short-range outdoor macrocellular environments. Clusters are first identified through data visual inspection. Then, a statistical characterization is carried out based on a delay-oriented classification of the clusters. Extraction results show that at each location, six to eight clusters are present, with average cluster delay and azimuth root mean square spreads of about 10-15 ns and 10[degrees]-20[degrees], respectively. A cluster-oriented geometry-based model is then developed and validated with measurement results, including spatial correlations for broadside and inline receive antenna configurations. Index Terms--Clustering, multiple-input multiple-output (MIMO) channels, radio propagation, suburban areas, urban areas.

The impact of mutual coupling induced by two closely spaced minimum scattering antennas at the subscriber unit on 2 x 2 multiple-input multiple-output channels and communications is investigated. Both (de)correlation effects and variations of antenna gain resulting from coupling mechanisms are considered. Relationships between coupling and correlations/channel Frobenius norm are discussed, pointing out the role of the interelement spacing, the array orientation, and the richness of scattering. The analysis also yields useful insight into the influence of mutual coupling on capacity and system performance. Index Terms--Antenna array, multiple-input multiple-output (MIMO) systems, mutual coupling.

The wireless channel for nomadic diversity-based wireless networks operating at 1.9 GHz is characterized. Using a 1 x 2 wideband measurement chain, four typical indoor office and industrial environments have been investigated: a corridor, an office room, a laboratory room and a large industrial hall. The measurement equipment is constituted by an 80-MHz transmitter. At the receiver, two omnidirectional antennas are connected to a wideband channel sounder through a switch, in order to measure an estimate of the instantaneous vector channel. Special attention is given to the experimental procedure itself, so as to take into account the specificity of nomadic systems (as opposed to usual mobile systems). The measurement analysis reveals that the shadowing, Rician K-factor and delay-spread are lognormally distributed. A path-loss model is derived, and cross-correlations between K-factor, delay-spread and shadowing are analyzed. The channel correlations at the user terminal or at the access point are also derived, and related to the individual channel characteristics. Index Terms--Diversity, indoor radio communications, radio propagation, Rician channels, wireless LAN.

This paper investigates the mutual information of several 2 x 2 systems using orthogonal polarizations. Analytical approximations of the mutual information in equi-power allocation scenarios are derived and compared in both Rayleigh and Ricean fading conditions. Index Terms--Capacity, multiple-input multiple-output (MIMO), polarization, Ricean fading.

This paper proposes various metrics to characterize space-time focusing resulting from application of time reversal techniques in richly scattering media. The concept and goals of time reversal are presented. Pertinent metrics describing both the time and space focusing effects are outlined. Two examples based on a model of discrete and continuous scattering media are used to illustrate how the proposed metrics vary as a function of various system and channel parameters, such as the bandwidth, delay and angle spreads, number of antennas, etc. Index Terms--Random media, space-time focusing, time reversal.

This paper aims at characterizing the spatial wireless channel at 1.9 GHz, based on a 1 x 2 measurement chain. A typical campus/residential area and an industrial area have been investigated. The measurement equipment is constituted by an 80-MHz transmitter at 1.9 GHz, located at the top of a building. At the receiver, two omnidirectional antennas are connected to a wide-band channel sounder through a switch in order to measure an estimate of the instantaneous vector channel. It is round that the Ricean K-factor and the delay spread are lognormally distributed, while the azimuth spread at the receive side follows a Gaussian distribution. The range dependence of various parameters are pointed out and compared with empirical models. The impacts of antenna spacing and array orientation on the channel correlation are highlighted and compared to theoretical simulation results. Finally, the cross-correlation properties between K-factor, delay spread, azimuth spread, and channel correlation are analyzed. Index Terms--Multipath channels, multiple-input-multiple-output (MIMO) channels, radio propagation, urban areas.

This paper addresses the extension of a stochastic geometry-based scattering model to multipolarized transmissions. The initial approach is based on a geometrical distribution of obstacles derived from known power-delay profiles. Each scattering process is statistically described by a matrix reflection coefficient corresponding to dual-polarization states. Ultimately, the model allows us to simulate the effects of the range on K-factor, delay-spread, Doppler spectrum, channel correlations and capacity, branch power ratio, and cross-polar discrimination. Simulation results are compared with existing measurements at 2.5 GHz. The proposed model is then used to investigate various dual-polarization 2 x 2 multiple-input-multiple-output (MIMO) schemes such as 0[degrees]/90[degrees] or [+ or -] 45[degrees], as well as to optimize the design of multipolarized MIMO schemes. Index Terms--microwave radio propagation, multiple-input-multiple-output (MIMO), polarization, wireless local area network (WLAN).

This paper describes measurements of the outdoor-to-indoor channel conducted in the Seattle, WA, and San Francisco Bay, CA, areas at 2.5 GHz. With broad-band wireless access in mind, an empirical model similar to the COST 231 model is built from the measured data. The impacts of wall material, angle of incidence, and receive height are noted and introduced in the modeling approach. Index Terms--Attenuation, indoor propagation, wireless systems.

To evaluate the performance of future microcellular IMT-2000 modems, simple physical models are required, so that a number of system characteristics, such as the signal bandwidth, the antenna beamwidth, or the base station height can be accounted for at a limited computational cost. This paper describes a deterministic three-dimensional electromagnetic model, which allows simulation of the radiowave propagation for microcellular wide-band communication systems in urban areas. The model is based on a UTD ray-tracing tool and makes use of an improved mirror method. Simulated power-delay profiles are plotted against measured power-delay profiles recorded at 1.87 GHz in a street of Louvain-la-Neuve, Belgium, by means of an 80-MHz channel sounder. Despite several discrepancies, a satisfying matching is found considering three orders of reflection and single diffraction. Predictions of rms delay-spread accounting for the sounder limited bandwidth are presented. Finally, simulated and measured channels are also compared through the resulting performance of a typical IMT-2000 service in the presence of multiple access interference. Index Terms--Communication system performances, ray tracing, wide-band radio channel measurements.

This paper describes a physically based stochastic approach that allows to predict the narrowband fading statistics for macro- and megacellular networks operating in urban areas. On one hand, macrocellular channels have been mainly covered in the literature by means of empirical models. On the other hand, megacells are typical of upcoming communication systems, such as broadband wireless access and high-altitude platform-based networks. Generally, the path gain of a wireless fading channel can be statistically characterized by a Ricean distribution, which includes Rayleigh fading as a particular case. The key parameter of the distribution is the K-factor K, defined as the ratio of the dominant component to the scatter contribution. In this paper, the K-factor is estimated by means of a physical model, conditionally to a set of geometrical parameters, such as the building height, the street width and the base station-to-terminal distance. These parameters are statistically described by analytical distributions. The model is successfully compared with experimental data at 1.6 GHz and typical applications are presented. Finally, because of its physical background, the model performs very well in analyzing polarization (MIMO) multiplexing schemes. Index Terms--Mobile communication, polarization, radio propagation, urban areas.

This paper investigates so-called diagonally correlated multiple input-multiple output (MIMO) channels, which provide higher ergodic capacity than independent and identically distributed (i.i.d.) fading channels. The presented analysis details physical scenarios leading to such channels, some properties of the channel matrix, and an analytical expression for its ergodic capacity. Index Terms--Capacity, correlation, Multiple-Input Multiple-Output (MIMO), polarization.

A shadowing correlation model is proposed in the context of a physical-statistical approach in the view of satellite diversity in built-up areas. The model relies on a model based on the uniform theory of diffraction, applied in a canonical built-up scenario. The correlation model is described and simulation results are presented and analyzed within a physical point of view. The shadowing correlation model is finally applied to several low-earth-orbit constellations. The impact of geometrical parameters' and of the constellation is investigated. Index Terms--Communication system performances, correlation, satellite mobile communications.

Land mobile satellite (LMS) systems require fade countermeasure techniques since they suffer from limited fade margins and severe channel degradations. In the view of complete recent statistical models for LMS systems in urban areas, this paper deals with several specific mobile satellite urban configurations, such as a long straight street lined on both sides by buildings and a crossroad. Propagation effects are modeled as time series of received power by means of a ray-tracing method, which is used in combination with an orbit generator. The time series results are then postprocessed to simulate the impact of propagation mechanisms and satellite motion on fade mitigation techniques, satellite handover, and diversity. This original approach inherently accounts for the correlation between a number of very different but simultaneous effects that influence system performance. Exemplary results are finally discussed to stress the capability of the time-series approach. Index Terms--Communication system performances, satellite mobile communication, urban areas.