Accurate and tractable channel modeling is critical to realizing the full potential of antenna arrays in wireless communications. Current approaches represent two extremes: idealized statistical models representing a rich scattering environment and parameterized physical models that describe realistic scattering environments via the angles and gains associated with different propagation paths. However, simple rules that capture the effects of scattering characteristics on channel capacity and diversity are difficult to infer from existing models. We propose an intermediate virtual channel representation that captures the essence of physical modeling and provides a simple geometric interpretation of the scattering environment. The virtual representation corresponds to a fixed coordinate transformation via spatial basis functions defined by fixed virtual angles. We show that in an uncorrelated scattering environment, the elements of the channel matrix form a segment of a stationary process and that the virtual channel coefficients are approximately uncorrelated samples of the underlying spectral representation. For any scattering environment, the virtual channel matrix clearly reveals the two key factors affecting capacity: the number of parallel channels and the level of diversity. The concepts of spatial zooming and aliasing are introduced to provide a transparent interpretation of the effect of antenna spacing on channel statistics and capacity. Numerical results are presented to illustrate various aspects of the virtual framework.

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Deconstructing multiantenna fading channels

One of the main assumptions in Clarke's classic channel model is isotropic scattering, i.e., uniform distribution for the angle of arrival (AOA) of multipath components at the mobile station. However, in many mobile radio channels we encounter nonisotropic scattering, which strongly affects the correlation function and power spectrum of the complex envelope at the mobile receiver. We propose the use of the versatile von Mises (1918) angular distribution, which includes and/or closely approximates important distributions like uniform, impulse, cardioid, Gaussian, and wrapped Gaussian, for modeling the nonuniform AOAs at the mobile. Based on this distribution, the associated correlation function and. power spectrum of the complex envelope at the mobile receiver are derived. The utility of the new results is demonstrated by comparison with the correlation function estimates of measured data.

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A parametric model for the distribution of the angle of arrival and the associated correlation function and power spectrum at the mobile station

We introduce a new approach for achieving diversity in spread-spectrum communications over fast-fading multipath channels. The RAKE receiver used in existing systems suffers from significant performance degradation due to the rapid channel variations encountered under fast fading. We show that the Doppler spread induced by temporal channel variations in fact provides another means for diversity that can be further exploited to combat fading. We develop the concept of Doppler diversity and propose a framework that exploits joint multipath-Doppler diversity in an optimal fashion. Performance analysis shows that even the relatively small Doppler spreads encountered in practice can be leveraged into significant diversity gains via our approach. The framework is applicable in several mobile wireless multiple access systems and can provide substantial performance improvement over existing systems.

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Joint multipath-Doppler diversity in mobile wireless communications

The authors detail the results of narrowband propagation measurements performed at five factories. The extensive empirical data indicate that path loss is dependent upon local surroundings and is log-normally distributed, temporal fading is Rician, and small-scale signal fluctuations due to receiver motion are primarily Rayleigh, although Rician and log-normal distributions fit some of the data. Shadowing effects of common factory equipment likely to obstruct indoor radio paths are also examined. >

UHF fading in factories

Estimation of the power spectrum S(f) of a stationary random process can be viewed as a nonparametric statistical estimation problem. We introduce a nonparametric approach based on a wavelet representation for the logarithm of the unknown S(f). This approach offers the ability to capture statistically significant components of ln S(f) at different resolution levels and guarantees nonnegativity of the spectrum estimator. The spectrum estimation problem is set up as a problem of inference on the wavelet coefficients of a signal corrupted by additive non-Gaussian noise. We propose a wavelet thresholding technique to solve this problem under specified noise/resolution tradeoffs and show that the wavelet coefficients of the additive noise may be treated as independent random variables. The thresholds are computed using a saddle-point approximation to the distribution of the noise coefficients. >

Wavelet thresholding techniques for power spectrum estimation

"This is an IEEE classic reissue of the book published by John Wiley & Sons in 1974.This definitive text and reference covers all aspects of microwave mobile systems design. Encompassing ten years of advanced research in the field, it reviews basic microwave theory, explains how cellular systems work and presents useful techniques for effective systems development. Key features include: complete coverage of microwave propagation techniques to design successful cellular systems, extensive chapters covering the broad fundamentals of microwave usage in mobile radio propagation and the functions of mobile radio antennas, comprehensive treatment of modulation methods, interference, noise, layout and control of high-capacity systems, and more! The return of this classic volume should be welcomed by all those seeking an authoritative and complete source of information on this emerging technology."

Mobile Radio Propagation

On August 12, 1960, a 100-foot-diameter spherical balloon was placed in orbit around the earth by the National Aeronautics and Space Administration. The objective was to demonstrate the feasibility of long distance communication by means of reflection of microwaves from a satellite. It was intended that a two-way coast-to-coast voice circuit be established between the Jet Propulsion Laboratories facility at Goldstone, California, and a station provided for this purpose by Bell Telephone Laboratories at Holmdel, New Jersey. Similar tests were also planned with the Naval Research Laboratory and other stations. Construction of the Holmdel station was begun early in 1959. This paper describes the general organization and operation of the station, and discusses the results of the Project Echo experiments that took place between the launching of the balloon March 1, 1961. Successful voice communication wvas achieved a number of times using a variety oj modulation methods, including frequency modulation with feedback, amplitude modulation, single-sideband modulation, and narrow-band phase modulation. Careful measurements were also made of the loss in the transmission path.

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Participation of bell telephone laboratories in project echo and experimental results

This chapter contains sections titled: Synopsis of Chapter This chapter contains sections titled: Mobile Antennas Base Station Antennas Polarization Effects This chapter contains sections titled: References

Antennas and Polarization Effects

Mobile Radio Systems

This chapter contains sections titled: Synopsis of Chapter This chapter contains sections titled: Factors Affecting Transmission Observed Attenuation on Mobile Radio Paths over Smooth Terrain Effects of Irregular Terrain Statistical Distribution of the Local Mean Signal Prediction of Field Strength This chapter contains sections titled: References 
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William C. Jakes

Papers

Mobile Radio Propagation

Participation of bell telephone laboratories in project echo and experimental results

Antennas and Polarization Effects

Mobile Radio Systems

Largescale Variations of the Average Signal