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An accurate propagation channel model is crucial for evaluating the performance of a communication system. A propagation channel can be described by a Markov model with a finite number of states, each of which is considered to be quasi-stationary over a short period. This work proposes a two-layer multistate Markov model. Instead of a large Markov transition matrix used in a conventional single-layer Markov model, two small Markov transition matrices are employed by a two-layer Markov model to reduce the computational complexity of the model without increasing the memory requirements. The proposed approach characterizes the multiplicative processes of a propagation channel as shadowing and fast fading. Each type of fading is considered as several channel states and each of the states corresponds to a specific mixed Rayleigh-lognormal distribution. Numerical results reveal that the statistical properties of the simulated data are quite close to those obtained from the measurements; indeed, the proposed two-layer Markov model is more accurate and less complex, and requires less memory than the single-layer Markov model. Furthermore, the proposed two-layer Markov model enables the fading statistics and error probability performance of a quadrature phase-shift keying modulation scheme in a typical urban Taipei environment to be more accurately predicted. Besides, it can easily be applied to similar environmental scenarios. Index Terms--Markov model, propagation channel modeling.

A spatial signature is the response vector of a base-station antenna array to a mobile unit at a certain location. Mobile subscribers at different locations exhibit different spatial signatures. The exploitation of spatial diversity (or the difference of spatial signatures) is the basic idea behind the so-called space-division multiple-access (SDMA) scheme, which can be used to significantly increase the channel capacity and quality of a wireless communication system. Although SDMA schemes have been studied by a number of researchers [1]-[6], most of these studies are based on theoretical analyses and computer simulations with ideal assumptions. Not much experimental study [7], [8] has been reported on spatial signature variation due to nonideal perturbations in a real wireless communication environment. The purpose of this paper is to present, for the first time, extensive experimental results of spatial signature variation using a smart antenna testbed. The results to be presented include the spatial signature variation with time, frequency, small displacement, multipath angle spread and beamforming performance. The experimental results show the rich spatial diversity and potential benefits of using an antenna array for wireless communication applications. Index Terms - Adaptive arrays, mobile communication.

In wireless communications, smart antenna systems (or antenna arrays) can be used to suppress multipath fading with antenna diversity and to increase system capacity by supporting multiple co-channel users in reception and transmission. This paper presents experimental results of diversity gain, interference cancellation, and mitigation of multipath fading obtained by using a smart antenna system in typical wireless scenarios. Also given are experimental results for the signal-to-interference ratio (SIR) of two moving users, comparing different beamforming algorithms in typical wireless scenarios. All of the experiments were performed using the 900-MHz smart antenna testbed at The University of Texas at Austin. Index Terms - Antenna arrays, mobile antennas, multipath channels.

This paper presents results from simultaneous Land S-band slant-path fade measurements through a pecan, a cottonwood, and a pine tree employing a tower-mounted transmitter and dual-frequency receiver. A single circularly polarized antenna was used at each end of the link. The objective was to provide information for personal communications satellite up-link power control design on the correlation of tree shadowing between frequencies near 1620 and 2500 MHz. Fade time series obtained simultaneously did not exhibit any significant correlation, but their means were weakly correlated ([r.sup.2] from 0.31 to 0.58). Fades were measured along a 10-m lateral distance with 5-cm spacing. Instantaneous fade differences between L- and S-band exhibited a normal distribution with means usually near 0 dB and standard deviations from 5.2 to 7.5 dB. The cottonwood tree was an exception with 5.4 dB higher average fading at S-than at L-band. More than 90% of the spatial variations occurred with periods larger than 1 [similar to] 2 wavelengths. Simultaneous swept measurements over 160-MHz spans showed that the standard deviation of the power levels as function of frequency increased from about 1 dB at locations with mean fades less than 4 dB to near 6 dB at locations with mean fades of 20 dB. For a 5-dB fade, the central 90% of fade slopes were within a band of 0.7 dB/MHz at L- and 1.9 dB/MHz at S-band.