Survey of Channel and Radio Propagation Models for Wireless MIMO Systems
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paper_title: Wireless Communications

paper_content:

"Professor Andreas F. Molisch, renowned researcher and educator, has put together the comprehensive book, Wireless Communications. The second edition, which includes a wealth of new material on important topics, ensures the role of the text as the key resource for every student, researcher, and practitioner in the field."Professor Moe Win, MIT, USAWireless communications has grown rapidly over the past decade from a niche market into one of the most important, fast moving industries. Fully updated to incorporate the latest research and developments, Wireless Communications, Second Edition provides an authoritative overview of the principles and applications of mobile communication technology.The author provides an in-depth analysis of current treatment of the area, addressing both the traditional elements, such as Rayleigh fading, BER in flat fading channels, and equalisation, and more recently emerging topics such as multi-user detection in CDMA systems, MIMO systems, and cognitive radio. The dominant wireless standards; including cellular, cordless and wireless LANs; are discussed.Topics featured include: wireless propagation channels, transceivers and signal processing, multiple access and advanced transceiver schemes, and standardised wireless systems.Combines mathematical descriptions with intuitive explanations of the physical facts, enabling readers to acquire a deep understanding of the subject.Includes new chapters on cognitive radio, cooperative communications and relaying, video coding, 3GPP Long Term Evolution, and WiMax; plus significant new sections on multi-user MIMO, 802.11n, and information theory.Companion website featuring: supplementary material on 'DECT', solutions manual and presentation slides for instructors, appendices, list of abbreviations and other useful resources.
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paper_title: On limits of wireless communications in a fading environment when using multiple antennas

paper_content:

This paper is motivated by the need for fundamental understanding of ultimate limits of bandwidth efficient delivery of higher bit-rates in digital wireless communications and to also begin to look into how these limits might be approached. We examine exploitation of multi-element array (MEA) technology, that is processing the spatial dimension (not just the time dimension) to improve wireless capacities in certain applications. Specifically, we present some basic information theory results that promise great advantages of using MEAs in wireless LANs and building to building wireless communication links. We explore the important case when the channel characteristic is not available at the transmitter but the receiver knows (tracks) the characteristic which is subject to Rayleigh fading. Fixing the overall transmitted power, we express the capacity offered by MEA technology and we see how the capacity scales with increasing SNR for a large but practical number, n, of antenna elements at both transmitter and receiver. ::: ::: We investigate the case of independent Rayleigh faded paths between antenna elements and find that with high probability extraordinary capacity is available. Compared to the baseline n = 1 case, which by Shannon‘s classical formula scales as one more bit/cycle for every 3 dB of signal-to-noise ratio (SNR) increase, remarkably with MEAs, the scaling is almost like n more bits/cycle for each 3 dB increase in SNR. To illustrate how great this capacity is, even for small n, take the cases n = 2, 4 and 16 at an average received SNR of 21 dB. For over 99% of the channels the capacity is about 7, 19 and 88 bits/cycle respectively, while if n = 1 there is only about 1.2 bit/cycle at the 99% level. For say a symbol rate equal to the channel bandwith, since it is the bits/symbol/dimension that is relevant for signal constellations, these higher capacities are not unreasonable. The 19 bits/cycle for n = 4 amounts to 4.75 bits/symbol/dimension while 88 bits/cycle for n = 16 amounts to 5.5 bits/symbol/dimension. Standard approaches such as selection and optimum combining are seen to be deficient when compared to what will ultimately be possible. New codecs need to be invented to realize a hefty portion of the great capacity promised.
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paper_title: Wireless Communications

paper_content:

"Professor Andreas F. Molisch, renowned researcher and educator, has put together the comprehensive book, Wireless Communications. The second edition, which includes a wealth of new material on important topics, ensures the role of the text as the key resource for every student, researcher, and practitioner in the field."Professor Moe Win, MIT, USAWireless communications has grown rapidly over the past decade from a niche market into one of the most important, fast moving industries. Fully updated to incorporate the latest research and developments, Wireless Communications, Second Edition provides an authoritative overview of the principles and applications of mobile communication technology.The author provides an in-depth analysis of current treatment of the area, addressing both the traditional elements, such as Rayleigh fading, BER in flat fading channels, and equalisation, and more recently emerging topics such as multi-user detection in CDMA systems, MIMO systems, and cognitive radio. The dominant wireless standards; including cellular, cordless and wireless LANs; are discussed.Topics featured include: wireless propagation channels, transceivers and signal processing, multiple access and advanced transceiver schemes, and standardised wireless systems.Combines mathematical descriptions with intuitive explanations of the physical facts, enabling readers to acquire a deep understanding of the subject.Includes new chapters on cognitive radio, cooperative communications and relaying, video coding, 3GPP Long Term Evolution, and WiMax; plus significant new sections on multi-user MIMO, 802.11n, and information theory.Companion website featuring: supplementary material on 'DECT', solutions manual and presentation slides for instructors, appendices, list of abbreviations and other useful resources.
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paper_title: Generalised array manifold model for wireless communication channels with local scattering

paper_content:

The authors propose the use of a generalised array manifold for parameterised spatial signature estimation in wireless communication channels with local scattering. The array manifold commonly used for point sources is generalised to include linear combinations of the nominal array response vectors and their derivatives. The motivation behind this idea is to obtain better estimates of the spatial signatures for direction of arrival (DOA) based signal waveform estimation. The estimators proposed exploit the orthogonality between the so-called noise and signal subspaces, leading to a separable solution for the derivative coefficients. As a result, a search is required for the DOAs only. For uniform linear arrays, the spatial signatures are shown to be approximately Vandermonde vectors with damped modes, and a closed-form estimator such as ESPRIT may be used in this case. Simulation examples are included to compare the signal estimation performance obtained using the proposed generalised manifold and the conventional array manifold.
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paper_title: On limits of wireless communications in a fading environment when using multiple antennas

paper_content:

This paper is motivated by the need for fundamental understanding of ultimate limits of bandwidth efficient delivery of higher bit-rates in digital wireless communications and to also begin to look into how these limits might be approached. We examine exploitation of multi-element array (MEA) technology, that is processing the spatial dimension (not just the time dimension) to improve wireless capacities in certain applications. Specifically, we present some basic information theory results that promise great advantages of using MEAs in wireless LANs and building to building wireless communication links. We explore the important case when the channel characteristic is not available at the transmitter but the receiver knows (tracks) the characteristic which is subject to Rayleigh fading. Fixing the overall transmitted power, we express the capacity offered by MEA technology and we see how the capacity scales with increasing SNR for a large but practical number, n, of antenna elements at both transmitter and receiver. ::: ::: We investigate the case of independent Rayleigh faded paths between antenna elements and find that with high probability extraordinary capacity is available. Compared to the baseline n = 1 case, which by Shannon‘s classical formula scales as one more bit/cycle for every 3 dB of signal-to-noise ratio (SNR) increase, remarkably with MEAs, the scaling is almost like n more bits/cycle for each 3 dB increase in SNR. To illustrate how great this capacity is, even for small n, take the cases n = 2, 4 and 16 at an average received SNR of 21 dB. For over 99% of the channels the capacity is about 7, 19 and 88 bits/cycle respectively, while if n = 1 there is only about 1.2 bit/cycle at the 99% level. For say a symbol rate equal to the channel bandwith, since it is the bits/symbol/dimension that is relevant for signal constellations, these higher capacities are not unreasonable. The 19 bits/cycle for n = 4 amounts to 4.75 bits/symbol/dimension while 88 bits/cycle for n = 16 amounts to 5.5 bits/symbol/dimension. Standard approaches such as selection and optimum combining are seen to be deficient when compared to what will ultimately be possible. New codecs need to be invented to realize a hefty portion of the great capacity promised.
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paper_title: Array measurement of the double-directional mobile radio channel

paper_content:

We describe a novel technique to measure the double-directional mobile radio channel. The channel is called double-directional since it includes directional spreading at both link ends, namely the base station and the mobile station. We use a double-array multiplexing technique consisting of a switched linear array at the receiver and a virtual array at the transmitter site. The measured microcellular scenarios are an open and a closed courtyard with different transmitter positions. The data are evaluated with an alternating estimation and beamforming technique that relies on (Unitary) ESPRIT estimation of positional parameters and subsequent beamforming for complex weight extraction. Usage of a two-axis crossed array at the transmitter site avoids forward-backward ambiguity. The presented exemplary results show a good agreement of the extracted directional information with the physical environment and give an indication of its scattering properties.
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paper_title: Effect of antenna separation on the capacity of BLAST in correlated channels

paper_content:

As the base station is usually placed above local clutter, the angular spectrum incident on the base is narrow, inducing correlation among base antenna signals, which reduces the capacity of a multiple transmit and receive antenna systems. In this work the general expression for link capacity is derived, when there is correlation among receive antennas and among transmit antennas. It is found that an antenna separation of 4 wavelengths between nearest neighbors in a linear base array of dually polarized antennas allows one to achieve 80% of the capacity attainable in the uncorrelated antenna case.
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paper_title: Fading correlation and its effect on the capacity of multielement antenna systems

paper_content:

We investigate the effects of fading correlations in multielement antenna (MEA) communication systems. Pioneering studies showed that if the fades connecting pairs of transmit and receive antenna elements are independently, identically distributed, MEAs offer a large increase in capacity compared to single-antenna systems. An MEA system can be described in terms of spatial eigenmodes, which are single-input single-output subchannels. The channel capacity of an MEA is the sum of capacities of these subchannels. We show that the fading correlation affects the MEA capacity by modifying the distributions of the gains of these subchannels. The fading correlation depends on the physical parameters of MEA and the scatterer characteristics. In this paper, to characterize the fading correlation, we employ an abstract model, which is appropriate for modeling narrow-band Rayleigh fading in fixed wireless systems.
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paper_title: Statistical characteristics of measured MIMO wireless channel data and comparison to conventional models

paper_content:

This paper presents measured data from a narrowband multiple-input multiple-output (MIMO) channel probe in an indoor office/laboratory environment. The system employs ten transmit and ten receive antennas and computes the 10 /spl times/ 10 narrowband channel matrix at 2.45 GHz every 80 milliseconds. We use the data to study the statistical behavior of the channel coefficients and the resulting channel capacity. We also demonstrate the ability of a simple statistically based physical model to accurately represent the channel behavior. The results of this model are compared to more conventional models that assume complex normal distributions of the channel matrix elements.
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paper_title: MIMO channel modeling and the principle of maximum entropy

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We devise theoretical grounds for constructing channel models for multiple-input multiple-output (MIMO) systems based on information-theoretic tools. The paper provides a general method to derive a channel model which is consistent with one's state of knowledge. The framework we give here has already been fruitfully explored with success in the context of Bayesian spectrum analysis and parameter estimation. For each channel model, we conduct an asymptotic analysis (in the number of antennas) of the achievable transmission rate using tools from random matrix theory. A central limit theorem is provided on the asymptotic behavior of the mutual information and validated in the finite case by simulations. The results are useful both in terms of designing a system based on criteria such as quality of service and in optimizing transmissions in multiuser networks.
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paper_title: A stochastic MIMO channel model with joint correlation of both link ends

paper_content:

Abstract-This paper presents a novel stochastic channel model for multiple-input multiple-output (MIMO) wireless radio channels. In contrast to state-of-the-art stochastic MIMO channel models, the spatial correlation properties of the channel are not divided into separate contributions from transmitter and receiver. Instead, the joint correlation properties are modeled by describing the average coupling between the eigenmodes of the two link ends. The necessary and sufficient condition for the proposed model to hold is that the eigenbasis at the receiver is independent of the transmit weights, and vice versa. The authors discuss the mathematical elements of the model, which can be easily extracted from measurements, from a radio propagation point of view and explain the underlying assumption of the model in physical terms. The validation of the proposed model by means of measured data obtained from two completely different measurement campaigns reveals its ability to better predict capacity and spatial channel structure than other popular stochastic channel models.
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paper_title: Capacity of multi-antenna array systems in indoor wireless environment

paper_content:

Previous studies have shown that a wireless system using n transmitting and n receiving antennas can achieve a capacity n times higher than a single-antenna system in an independent Rayleigh fading environment. We explore the capacities of multiple-element antenna arrays (MEAs) in a more realistic propagation environment simulated via the WiSE ray-tracing tool. We impose an average power constraint and collect statistics of the capacity with optimal power allocation, C/sub wf/, and the mutual information with an equal power allocation, I/sub eq/. In addition, we present expressions for the asymptotic growth rates C/sub wf//n and I/sub eq//n as n/spl rarr//spl infin/ for two cases: (a) independent fadings and (b) correlated fadings at different antennas. We find that C/sub wf//n and I/sub eq//n converge to constants C/sub wf/* and I/sub eq/*, respectively in case (a), and to C/sub wf//sup 0/and I/sub eq//sup 0/ in case (b). We observe that C/sub wf//sup 0/ and I/sub eq//sup 0/ predict very closely the slopes observed for simulated channels, even for moderate n (i.e., 16).
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paper_title: Modeling the indoor MIMO wireless channel

paper_content:

This paper demonstrates the ability of a physically based statistical multipath propagation model to match capacity statistics and pairwise magnitude and phase distributions of measured 4 /spl times/ 4 and 10 /spl times/ 10 narrow-band multiple-input multiple-output data (MIMO) at 2.4 GHz. The model is compared to simpler statistical models based on the multivariate complex normal distribution with either complex envelope or power correlation. The comparison is facilitated by computing channel element covariance matrices for fixed sets of multipath statistics. Multipolarization data is used to demonstrate a simple method for modeling dual-polarization arrays.
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paper_title: Estimation and equalization of fading channels with random coefficients

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Abstract The time-varying tap coefficients of frequency-selective fading channels are typically modeled as random processes with low-pass power spectra. However, traditional adaptive techniques usually make no assumption on the channel's time variations and hence do not exploit this information. In this paper, Kalman filtering methods are derived to track the channel by employing a multichannel autoregressive description of the time-varying taps in a decision-feedback equalization framework. Fitting a model to the variations of the channel's taps is a challenging task because the tap coefficients are not observed directly. Higher-order statistics are employed in this paper in order to estimate the model parameters from input/output data. Consistency of the proposed method is shown, and some illustrative simulations are presented.
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paper_title: Statistical analysis of measured impulse response functions of 2.0 GHz indoor radio channels

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The measurements of the impulse response of a 2.0 GHz indoor radio channel are reported. A statistical analysis of the characteristics of the amplitude of multipath components is presented. In particular, the spatial correlation of the single multipath components and the cross-correlation between the amplitudes of adjacent multipath components have been determined. Conclusions are drawn with regard to the adequacy of the wide sense uncorrelated scattering model as a consistent model for the indoor radio channel.
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paper_title: Validity of spatial covariance matrices over time and frequency

paper_content:

A MIMO channel measurement campaign with a moving mobile has been conducted in Vienna. The measured data will be used to investigate covariance matrices with respect to their dependence on time and frequency. This document focuses on the description of the evaluation techniques which will be applied to the measurement data in the future. The F-eigen-ratio is defined expressing the degradation due to out-dated covariance matrices. Illustrating the derived methods, first results based on the measured data are shown for a simple line-of-sight scenario.
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paper_title: Fading Channels: Information-Theoretic and Communications Aspects

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In this paper we review the most peculiar and interesting information-theoretic and communications features of fading channels. We first describe the statistical models of fading channels which are frequently used in the analysis and design of communication systems. Next, we focus on the information theory of fading channels, by emphasizing capacity as the most important performance measure. Both single-user and multiuser transmission are examined. Further, we describe how the structure of fading channels impacts code design, and finally overview equalization of fading multipath channels.
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paper_title: Joint Multipath-Doppler Diversity in Mobile Wireless Communications

paper_content:

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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paper_title: Empirical characterization of wideband indoor radio channel at 5.3 GHz

paper_content:

Characteristics of wideband indoor radio channel at 5.3 GHz were defined based on an extensive measurement campaign using a wideband channel sounder with 19 ns delay resolution. Pathloss exponents were 1.3-1.5 in LOS and 2.9-4.8 in non-line of sight (NLOS). Large difference in NLOS exponents was due to different dominating propagation mechanisms in different types of building structures. The delay dispersion was characterized by cumulative distribution functions (CDF) of the RMS delay spreads, the values for CDF=0.9 varied from 20 to 180 ns in different setups in an office building and large hall environments. The correlation functions of the radio channel in spatial and frequency domains were extracted. Small scale models for five typical indoor scenarios were developed using tapped delay lines.
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paper_title: Channels, Propagation and Antennas for Mobile Communications

paper_content:

This exceptional book introduces the reader to the principles, theory and applications of physical layer wireless/mobile communications. applicators and millimetric antennas. ::: The book emphasises the basic principles needed to establish an understanding of this technology, whilst treating the tools required - such as the mathematics and statistics - in the manner of a practical handbook, thus avoiding detailed derivations.
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paper_title: On non-WSSUS wireless fading channels

paper_content:

We propose a novel framework for the statistical characterization of fading dispersive channels that do not satisfy the assumption of wide-sense stationary uncorrelated scattering (WSSUS). The local scattering function (LSF) and the channel correlation function (CCF) are introduced and shown to characterize, respectively, the mean power and the correlation of non-WSSUS scatterers. Furthermore, the practically important class of doubly underspread (DU) channels is introduced, and it is shown that for DU channels, the LSF has numerous useful properties. The practical relevance of our approach is illustrated via application examples and numerical experiments.
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paper_title: Characterization of Randomly Time-Variant Linear Channels

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This paper is concerned with various aspects of the characterization of randomly time-variant linear channels. At the outset it is demonstrated that time-varying linear channels (or filters) may be characterized in an interesting symmetrical manner in time and frequency variables by arranging system functions in (timefrequency) dual pairs. Following this a statistical characterization of randomly time-variant linear channels is carried out in terms of correlation functions for the various system functions. These results are specialized by considering three classes of practically interesting channels. These are the wide-sense stationary (WSS) channel, the uncorrelated scattering (US) channel, and the wide-sense stationary uncorrelated scattering (WSSUS) channel. The WSS and US channels are shown to be (time-frequency) duals. Previous discussions of channel correlation functions and their relationships have dealt exclusively with the WSSUS channel. The point of view presented here of dealing with the dually related system functions and starting with the unrestricted linear channels is considerably more general and places in proper perspective previous results on the WSSUS channel. Some attention is given to the problem of characterizing radio channels. A model called the Quasi-WSSUS channel is presented to model the behavior of such channels. All real-life channels and signals have an essentially finite number of degrees of freedom due to restrictions on time duration and bandwidth. This fact may be used to derive useful canonical channel models with the aid of sampling theorems and power series expansions. Several new canonical channel models are derived in this paper, some of which are dual to those of Kailath.
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paper_title: Advanced engineering electromagnetics

paper_content:

Time--Varying and Time--Harmonic Electromagnetic Fields. Electrical Properties of Matter. Wave Equation and Its Solutions. Wave Propagation and Polarization. Reflection and Transmission. Auxiliary Vector Potentials, Contruction of Solutions, and Radiation and Scattering Equations. Electromagnetic Theorems and Principles. Rectangular Cross--Section Waveguides and Cavities. Circular Cross--Section Waveguides and Cavities. Spherical Transmission Lines and Cavities. Scattering. Integral Equations and the Moment Method. Geometrical Theory of Diffraction. Greena s Functions. Appendices. Index.
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paper_title: A uniform geometrical theory of diffraction for an edge in a perfectly conducting surface

paper_content:

A compact dyadic diffraction coefficient for electromagnetic waves obliquely incident on a curved edse formed by perfectly conducting curved ot plane surfaces is obtained. This diffraction coefficient remains valid in the transition regions adjacent to shadow and reflection boundaries, where the diffraction coefficients of Keller's original theory fail. Our method is based on Keller's method of the canonical problem, which in this case is the perfectly conducting wedge illuminated by plane, cylindrical, conical, and spherical waves. When the proper ray-fixed coordinate system is introduced, the dyadic diffraction coefficient for the wedge is found to be the sum of only two dyads, and it is shown that this is also true for the dyadic diffraction coefficients of higher order edges. One dyad contains the acoustic soft diffraction coefficient; the other dyad contains the acoustic hard diffraction coefficient. The expressions for the acoustic wedge diffraction coefficients contain Fresenel integrals, which ensure that the total field is continuous at shadow and reflection boundaries. The diffraction coefficients have the same form for the different types of edge illumination; only the arguments of the Fresnel integrals are different. Since diffraction is a local phenomenon, and locally the curved edge structure is wedge shaped, this result is readily extended to the curved wedge. It is interesting that even though the polarizations and the wavefront curvatures of the incident, reflected, and diffracted waves are markedly different, the total field calculated from this high-frequency solution for the curved wedge is continuous at shadow and reflection boundaries.
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paper_title: Advanced engineering electromagnetics

paper_content:

Time--Varying and Time--Harmonic Electromagnetic Fields. Electrical Properties of Matter. Wave Equation and Its Solutions. Wave Propagation and Polarization. Reflection and Transmission. Auxiliary Vector Potentials, Contruction of Solutions, and Radiation and Scattering Equations. Electromagnetic Theorems and Principles. Rectangular Cross--Section Waveguides and Cavities. Circular Cross--Section Waveguides and Cavities. Spherical Transmission Lines and Cavities. Scattering. Integral Equations and the Moment Method. Geometrical Theory of Diffraction. Greena s Functions. Appendices. Index.
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paper_title: Finite conductivity uniform GTD versus knife edge diffraction in prediction of propagation path loss

paper_content:

Diffraction propagation over hills and ridges at VHF and UHF is commonly estimated using Fresnel knife edge diffraction. This approach has the advantage of simplicity, and for many geometries yields accurate results. However, since it neglects the shape and composition of the diffracting surface, it can in some cases yield results which are in serious disagreement with measurements. To remedy this, attempts have been made to approximate the diffracting hill or ridge by other shapes, most notably cylinders. These approaches have not been widely adopted, due in large part to their greater numerical complexity. In this paper it is proposed to apply wedge diffraction in the format of the geometrical theory of diffraction (GTD), modified to include finite conductivity and local surface roughness effects. It is shown that, for geometries with grazing incidence and/or diffraction angles, significant improvement in accuracy is obtained. Further, the GTD wedge diffraction form used is based on the Fresnel integral, so that it is only slightly more complex numerically than knife edge diffraction. Finally, the GTD includes reflections from the sides of the ridge (wedge faces), and can be extended to multiple ridge diffraction and three-dimensional terrain variations.
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paper_title: Simulating radio channel statistics for different building environments

paper_content:

The design of advanced radio systems requires knowledge of higher order channel statistics, such as the time delay spread and the angle of arrival spread. Time delay has been measured in a number of cities, while angle of arrival has been measured in only a few. Since the link geometry is not the same for all measurements, it is not clear how to compare the measured values, or if they are applicable to other building environments, antenna height, etc. To clarify these issues, we have used a three-dimensional ray tracing code, called the vertical plane launch (VPL) method, to simulate time delay spread and angle of arrival spread in different building environments. Results for elevated base station antennas show that the distribution of root mean square (RMS) delay spreads is not sensitive to the statistical properties of the buildings but increases with distance to the mobiles and increases as the base antenna is lowered below the rooftops. In contrast, the distribution of RMS angle spread is sensitive to the distribution of building heights and to the height of the base station antenna but not to the distance to the mobile. The influence of street geometry on delay and angle spread for low base station antennas is also discussed.
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paper_title: Radio Propagation for Modern Wireless Systems

paper_content:

From the Book: ::: PREFACE: Preface ::: The commercial success of cellular mobile radio since its initial implementation in the early 1980s has led to an intense interest among wireless engineers in understanding and predicting radio propagation characteristics within cities, and even within buildings. In this book we discuss radio propagation with two goals in mind. The first is to provide practicing engineers having limited knowledge of propagation with an overview of the observed characteristics of the radio channel and an understanding of the process and factors that influence these characteristics. The second goal is to serve as text for a master's-level course for students intending to work in the wireless industry. Books on modern wireless applications typically survey the issues involved, devoting only one or two chapters to radio channel characteristics, or focus on how the characteristics influence system performance. Now that the wireless field has grown in scope and size, it is appropriate that books such as this one examine in greater depth the various underlying topics that govern the design and operation of wireless systems. The material for this book has grown out of tutorials given by the author to engineering professionals and a course on wireless propagation given by the author at Polytechnic University as part of a program in wireless networks. It also draws upon the 15 years of experience the author and his students have had in understanding and predicting propagation effects. ::: Cellular telephones gave the public an active role in the use of the radio spectrum as opposed to the previous role of passive listener. This social revolution in the use of theradiospectrum ultimately changed governmental views of its regulation. Driven by the requirement to allow many users to operate in the same band, cellular telephones also created a technical revolution through the concept of spectral reuse. Systems that do not employ spectral reuse avoid interference by operating in different frequency bands and are limited in performance primarily by noise. In these systems, lack of knowledge of the propagation conditions can be compensated for by increasing the transmitted power, up to regulatory limits. In contrast, the concept of spectral reuse acknowledges that in commercially successful systems, interference from other users will be the primary factor limiting performance. In designing these systems, it is necessary to balance the desired signal for each user against interference from signals intended for other users. Finding the balance requires knowledge of the radio channel characteristics. Chapter 1 is intended to introduce the student reader to the concept of spectrum reuse and in the process to give examples of how the propagation characteristics influence the balance between desired signal and interference, and thereby influence system design. As in all chapters, examples are discussed to illustrate the concepts, and problems are included at the end of the chapter to give the students experience in applying the concepts. ::: In modern systems, the radio links are about 20 kilometers or less, the antennas that create the links lie near to or among the buildings or even inside the buildings, and the wavelength is small compared to the building dimensions. As a result, the channel characteristics are strongly influenced by the buildings as well as by vegetation and terrain. In this environment, signals propagate from one antenna to the other over multiple paths that involve the processes of reflection and transmission at walls and by the ground and the process of diffraction at building edges and terrain obstacles. The multipath nature of the propagation makes itself felt in a variety of ways that have challenged the inventiveness of communication engineers. Although initially a strong limitation on channel capacity, engineers have begun to find ways to harness the multipath signals so as to achieve capacities that approach the theoretical limit. However, each new concept for dealing with multipath calls for an even deeper understanding of the statistical characteristics of the radio channel. In Chapter 2 we describe many of the propagation effects that have been observed in various types of measurements, ranging from path loss for narrowband signals, to angle of arrival and delay spread for wideband transmission. As in other chapters, an extensive list of references is cited to aid the professional seeking a detailed understanding of particular topics. For the student reader, this chapter serves as an introduction to the types of measurements that are made, the methods used to process the data, and some of the statistical approaches used to represent the results. Understanding the measurements, their processing, and their representation also serves to guide the theoretical modeling described in subsequent chapters. ::: The level of presentation assumes that the reader has had an undergraduate course in electromagnetics with exposure to wave concepts. The presentation does not attempt to derive the propagation characteristics from Maxwell's equations rigorously; rather, the goal is to avoid vector calculus. The reader's background is relied on for acceptance of some wave properties; other properties are motivated through heuristic arguments and from basic ideas, such as conservation of power. For example, in Chapter 3 we start with the fundamental properties of plane waves and call on the reader's background in transmission lines when discussing reflection and transmission at the ground and walls. Wherever possible in this and following chapters, the theoretical results are compared to measurements. Thus plane waves are used to model observed interference effects, which are referred to as fast fading, and to model Doppler spreading. Plane wave properties and conservation of power are used in Chapter 4 to justify the properties of spherical waves radiated by antennas and to motivate the ray description of reflection at material surfaces. By accounting for these reflections, propagation on line-of-sight paths in urban canyons is modeled. Circuit concepts are used to obtain the reciprocity of propagation between antennas, and to derive expressions for path gain or loss. ::: Diffraction at building edges is an important process in wireless communications. It allows signals to reach subscribers who would otherwise be shadowed by the buildings. Because the reader is not expected to be familiar with this process, Chapter 5 explores diffraction in some detail. For simplicity, the scalar form of the Huygens-Kirchhoff integral is use as a starting point. We first use it to give physical meaning to the Fresnel ellipsoid about a ray, which is widely employed in propagation studies to scale physical dimensions. The geometrical and uniform forms of the fields diffracted by an absorbing half screen are derived. In these expressions we identify a universal component that applies to diffraction by any straight building edge or corner and a diffraction coefficient whose specific form is dependent on the nature of the edge. Diffraction coefficients for several types of edges and corners are given without derivation. Using heuristic ray arguments, the results obtained for plane waves are generalized to spherical waves radiated by antennas and to multiple edges. These results are cast in terms of path gain or loss, which is convenient for wireless applications. ::: Chapter 6 formulates the problem of average path loss in residential environments in terms of multiple diffraction past rows of buildings. Relying on the Huygens-Kirchhoff formulation, the diffraction problem is solved for various ranges of base station and subscriber antenna height. These results show how the frequency, average building height, and row separation influence the range dependence and height gain of the signal. This approach to diffraction is used in Chapter 7 to investigate the effects of randomness in building construction on shadow fading. Chapter 7 also makes use of diffraction to examine the effects of terrain and vegetation on the average path loss. ::: Propagation predictions that make use of a geometrical description of individual buildings are discussed in Chapter 8. Various ray-based models that incorporated the processes of reflection and diffraction at buildings have been developed to make such site-specific predictions. Their accuracy has been evaluated primarily by comparing predictions against measurements of the small area average received signal. However, the ray models have started to be used to predict higher-order channel statistics, such as time delay and angle spread, through Monte Carlo simulations. This approach can generate values for the statistical descriptors of the radio channel that are employed in advanced communication systems and show how these values depend on the distribution of building size and shape in different cities.
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paper_title: An advanced field prediction model including diffuse scattering

paper_content:

Ray tracing (RT) models are now widely adopted for field prediction in urban environment. Nevertheless, conventional RT tools still suffer for excessive central processing unit (CPU) time and inaccuracy in wide-band prediction. By increasing the maximum number of successive interactions (reflections, diffractions) little improvement in wide-band results can be usually achieved while CPU time increases exponentially. In the present paper, it is shown that by integrating reflection/diffraction with diffuse scattering, good narrow-band and wide-band results can be obtained with a low number of interactions. The adopted scattering model is a simple ray-based model, which has been embedded in a three-dimensional (3-D) RT program. The impact of diffuse scattering on narrowband and wide-band parameters is analyzed in the paper and the complete model is compared with measurements in a variety of cases, showing the validity of the approach.
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paper_title: Predicting multi-element receive & transmit array capacity outdoors with ray tracing

paper_content:

We construct a few canonical cases consisting of diffracting wedges and simple linear arrays, as steps towards predicting capacity for an entire cell, highlighting important propagation mechanisms. We show that a diffracting wedge can collapse capacity of multi-element arrays. If more that one wedge is present, the capacity increases. These effects are demonstrated theoretically and numerically through ray-tracing.
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paper_title: Effects on correlation between two mobile radio base-station antennas

paper_content:

The correlation between signals received by two mobile radio base-station antennas is investigated to determine spacing requirements for space diversity. Measurements of the fading of UHF signals received by two base-station horn antennas oriented at different angles with respect to the incoming mobile radio signal were made for different antenna spacings. The experimental results are compared with an analytical expression derived in this paper; they agree fairly well. A further experiment was made after removing the possible local scatterers surrounding the base station. Comparing these two experimental results, we find that the following are true. 1) Propagation in the direction of a line connecting the two base-station antennas is the critical case and requires a large separation of 70 wavelengths. As soon as the incoming wave is 10° away from the in-line axis, the spacing requirement drops to 30 wavelengths. 2) Local scatterers at the base station tend to decrease the correlation between signals received at the two antennas. We conclude that an upper limit to the spacing of antennas used for diversity can be obtained and that it is within the achievable range.
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paper_title: A physical scattering model for MIMO macrocellular broadband wireless channels

paper_content:

This paper presents a physical scattering model that predicts multiple-input multiple-output (MIMO) channel characteristics conforming well to experimental observations in macrocells. Our approach is to start with a given single-input single-output power-delay profile (defined for specific range, bandwidth and antenna parameters) and fit a scattering model that characterizes the MIMO channel. From the derived scattering model and antenna array configurations, the MIMO channel is computed using a ray-based method. Simulations of several MIMO channels are shown to exhibit experimentally observed channel correlations, antenna beamwidth effect, range dependency, and frequency selectivity.
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paper_title: Diffuse channel model and experimental results for array antennas in mobile environments

paper_content:

A wide-band spatial model of the mobile channel has been developed. The model allows the inclusion of array antennas at the base station. The diffuse scattering is modeled using dense discrete scatterers. An algebraic power decay is used for the path loss to the scatterers of the environment and to the mobile. Results from the model are compared with experimental results obtained at 1800 MHz. The parameters that are used are delay spread, power window, and angular spread of incident power. The model elucidates the general diffuse background scattering in a rural and an urban environment. It can be extended with inclusion of spatial specular scatterers where appropriate.
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paper_title: Unified channel model for mobile radio systems with smart antennas

paper_content:

The definition of flat fading and frequency-selective fading channels is extended to low-rank and high-rank channels to include the angular domain. By physical reasoning a generic channel model is introduced incorporating directions of arrival and a set of parameters is given for its configuration. The time evolution of the scattering processes and directions of arrival is taken into account. Analytical expressions are derived for space-correlation coefficients and frequency-correlation coefficients. Spatial correlation decreases with increasing angular spread and decreasing angle of incidence, measured from array broadside.
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paper_title: Influence of the scatterer distribution on power delay profiles and azimuthal power spectra of mobile radio channels

paper_content:

We consider the distribution of scatterers that are responsible for the temporal and angular dispersion of mobile radio channel models. In a first step, we concentrate on the local scatterers around the mobile station. Various approximations for this distribution are analyzed, and their effect on the PDP (power delay profile) and APS (azimuthal power spectrum) are derived. We find that a one-sided Gaussian distribution gives the best agreement with measurements. Measured PDPs are usually exponential and APSs are usually Laplacian. We analyze the difference between single and multiple scattering. Finally, we consider the influence of scatterers that, are situated far away from the mobile station.
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paper_title: A geometrically based model for line-of-sight multipath radio channels

paper_content:

This paper provides a geometrically based model for single bounce multipath components in line-of-sight (LOS) microcell radiowave propagation channels. The model characterizes the excess delay, direction-of-arrival, and received power of multipath components and is particular useful for microcell and PCS systems with low transmitter and receiver antenna heights. The model includes analytical expressions for the probability density functions for all critical channel parameters and is thus useful for analytical purposes. The model is also useful for simulating both wideband and narrowband systems and in particular the model has been used extensively in a study of code division multiple access (CDMA) cellular radio systems employing adaptive antennas and switched beam systems at the base station.
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paper_title: Geometry-based directional model for mobile radio channels -principles and implementation

paper_content:

Adaptive antennas are used in mobile radio systems for improving coverage and increasing capacity. For realistic system design and simulation, channel models are required in order to assess the performance of such systems. We propose the so-called ‘geometry-based stochastic channel model’ (GSCM), which is easy to implement and has a low complexity even when the directional dimension of the channel is taken into account. In this model, we prescribe the probability density function (PDF) of the location of the scatterers. From this, the angularly resolved impulse response can be computed by a simple ray tracing. We then present various extensions of the model in urban environments, namely for diffraction losses and wave guiding by street canyons. We also discuss methods for efficiently implementing GSCM. Copyright © 2003 AEI.
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paper_title: Geometrical-based statistical macrocell channel model for mobile environments

paper_content:

We develop a statistical geometric propagation model for a macrocell mobile environment that provides the statistics of angle-of-arrival (AOA) of the multipath components, which are required to test adaptive array algorithms for cellular applications. This channel model assumes that each multipath component of the propagating signal undergoes only one bounce traveling from the transmitter to the receiver and that scattering objects are located uniformly within a circle around the mobile. This geometrically based single bounce macrocell (GBSBM) channel model provides three important parameters that characterize a channel: the power of the multipath components, the time-of-arrival (TOA) of the components, and the AOA of the components. Using the GBSBM model, we analyze the effect of directional antennas at the base station on the fading envelopes. The level crossing rate of the fading envelope is reduced and the envelope correlation increases significantly if a directional antenna is employed at the base station.
---
paper_title: A flexibly configurable spatial model for mobile radio channels

paper_content:

The application of multiple directive antennas, i.e., directional diversity, may lead to significant capacity benefits in cellular mobile radio systems. A flexibly configurable statistical channel model for mobile radio systems using directional diversity is presented. The parameters of this model, which is available as a FORTRAN77 program, can be easily adjusted to various propagation areas such as, for example, rural, urban, microcellular, and picocellular environments. Therefore, the model is well suited to perform simulations, evaluations, and comparisons of mobile radio systems. Simulation results concerning a code-division multiple-access (CDMA) mobile radio system which uses multiple directive base station (BS) antennas in combination with joint detection illustrate the application of the presented channel model.
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paper_title: Propagation characteristics for indoor broadband radio access networks in the 5 GHz band

paper_content:

This article presents results from wideband propagation measurements at 5.8 GHz in an office environment. Path loss and delay spread values have been estimated for transmitter-receiver separations in the range of 10-30 m. The average basic transmission loss in OLOS is close to 90 dB, while exceeding 105 dB at 30 m separation in NLOS. The typical delay spread is close to 30 ns; it increases up to 60 ns at some locations due to obstructions and larger room size. The relation between the coherence bandwidth and the time-delay spread is also shown.
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paper_title: Directional macro-cell channel characterization from urban measurements

paper_content:

We measured the angular power distribution at the mobile station in downtown Paris at 890 MHz. The transmit antenna was omnidirectional and placed high above rooftops. The receiver antenna, a 21/spl times/41 element rectangular synthetic array, was located on the roof of a van. The refined high-resolution evaluation method, particularly robust against nonstationary signal components, allows an angular resolution of better than 1/spl deg/ in both azimuth and elevation and a delay resolution of 33 ns. Combined angular/temporal domain measurements are crucial for the understanding of the propagation mechanisms. The evaluated sites showed strongly street-dominated propagation. We found a combined circular and rectangular distribution of scatterers around the mobile station in street-dominated environments. Propagation over the roofs was significant; typically 65% of energy was incident with elevation larger than 100. Our results corroborate the hypothesis on the importance of multiple reflections/diffractions in urban macro cells. We explain this behavior by two reasons: narrow streets favoring a canyon effect and strong scatterers without line-of-sight (LOS) to the mobile station.
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paper_title: A generic model for MIMO wireless propagation channels in macro- and microcells

paper_content:

This paper derives a generic model for the multiple-input multiple-output (MIMO) wireless channel. The model incorporates important effects, including i) interdependency of directions-of-arrival and directions-of-departure, ii) large delay and angle dispersion by propagation via far clusters, and iii) rank reduction of the transfer function matrix. We propose a geometry-based model that includes the propagation effects that are critical for MIMO performance: i) single scattering around the BS and MS, ii) scattering by far clusters, iii) double-scattering, iv) waveguiding, and v) diffraction by roof edges. The required parameters for the complete definition of the model are enumerated, and typical parameter values in macro and microcellular environments are discussed.
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paper_title: Statistical characterization of urban spatial radio channels

paper_content:

We present a statistical analysis of wideband three-dimensional channel measurements at base station locations in an urban environment. Plots of the received energy over azimuth, elevation, and delay planes suggest that the incident waves group to clusters in most measured transmitter positions. A super-resolution algorithm (Unitary ESPRIT) allows one to resolve individual multipath components in such clusters and hence enables a detailed statistical analysis of the propagation properties. The origins of clusters-sometimes even individual multipath components-such as street apertures, large buildings, roof edges, or building corners can be localized on the city map. Street guided propagation dominates most of the scenarios (78%-97% of the total received power), while quasi-line-of-sight over-the-rooftop components are weak(3%-13% of the total received power). For this measurement campaign, in 90% of the cases, 75% of the total received power is concentrated in the two strongest clusters, but only 55% in the strongest one. Our analysis yields an exponential decay of power with 8.9 dB//spl mu/s, and a standard deviation of the log-normally distributed deviations from the exponential of 9.0 dB. The power of cross-polarized components is 8 dB below copolarized ones on average (vertical transmission).
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paper_title: A Statistical Model for Indoor Multipath Propagation

paper_content:

The results of indoor multipath propagation measurements using 10 ns, 1.5 GHz, radarlike pulses are presented for a medium-size office building. The observed channel was very slowly time varying, with the delay spread extending over a range up to about 200 ns and rms values of up to about 50 ns. The attenuation varied over a 60 dB dynamic range. A simple statistical multipath model of the indoor radio channel is also presented, which fits our measurements well, and more importantly, appears to be extendable to other buildings. With this model, the received signal rays arrive in clusters. The rays have independent uniform phases, and independent Rayleigh amplitudes with variances that decay exponentially with cluster and ray delays. The clusters, and the rays within the cluster, form Poisson arrival processes with different, but fixed, rates. The clusters are formed by the building superstructure, while the individual rays are formed by objects in the vicinities of the transmitter and the receiver.
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paper_title: Modeling the statistical time and angle of arrival characteristics of an indoor multipath channel

paper_content:

Most previously proposed statistical models for the indoor multipath channel include only time of arrival characteristics. However, in order to use statistical models in simulating or analyzing the performance of systems employing spatial diversity combining, information about angle of arrival statistics is also required. Ideally, it would be desirable to characterize the full spare-time nature of the channel. In this paper, a system is described that was used to collect simultaneous time and angle of arrival data at 7 GHz. Data processing methods are outlined, and results obtained from data taken in two different buildings are presented. Based on the results, a model is proposed that employs the clustered "double Poisson" time-of-arrival model proposed by Saleh and Valenzuela (1987). The observed angular distribution is also clustered with uniformly distributed clusters and arrivals within clusters that have a Laplacian distribution.
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paper_title: Channels, Propagation and Antennas for Mobile Communications

paper_content:

This exceptional book introduces the reader to the principles, theory and applications of physical layer wireless/mobile communications. applicators and millimetric antennas. ::: The book emphasises the basic principles needed to establish an understanding of this technology, whilst treating the tools required - such as the mathematics and statistics - in the manner of a practical handbook, thus avoiding detailed derivations.
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paper_title: A new statistical wideband spatio-temporal channel model for 5-GHz band WLAN systems

paper_content:

In this paper, a new statistical wideband indoor channel model which incorporates both the clustering of multipath components (MPCs) and the correlation between the spatial and temporal domains is proposed. The model is derived based on measurement data collected at a carrier frequency of 5.2 GHz in three different indoor scenarios and is suitable for performance analysis of HIPERLAN/2 and IEEE 802.11a systems that employ smart antenna architectures. MPC parameters are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization (FD-SAGE) algorithm and clusters are identified in the spatio-temporal domain by a nonparametric density estimation procedure. The description of the clustering observed within the channel relies on two classes of parameters, namely, intercluster and intracluster parameters which characterize the cluster and MPC, respectively. All parameters are described by a set of empirical probability density functions (pdfs) derived from the measured data. The correlation properties are incorporated in two joint pdfs for cluster and MPC positions, respectively. The clustering effect also gives rise to two classes of channel power density spectra (PDS)-intercluster and intracluster PDS-which are shown to exhibit exponential and Laplacian functions in the delay and angular domains, respectively. Finally, the model validity is confirmed by comparison with two existing models reported in the literature.
---
paper_title: A Statistical Model for Indoor Multipath Propagation

paper_content:

The results of indoor multipath propagation measurements using 10 ns, 1.5 GHz, radarlike pulses are presented for a medium-size office building. The observed channel was very slowly time varying, with the delay spread extending over a range up to about 200 ns and rms values of up to about 50 ns. The attenuation varied over a 60 dB dynamic range. A simple statistical multipath model of the indoor radio channel is also presented, which fits our measurements well, and more importantly, appears to be extendable to other buildings. With this model, the received signal rays arrive in clusters. The rays have independent uniform phases, and independent Rayleigh amplitudes with variances that decay exponentially with cluster and ray delays. The clusters, and the rays within the cluster, form Poisson arrival processes with different, but fixed, rates. The clusters are formed by the building superstructure, while the individual rays are formed by objects in the vicinities of the transmitter and the receiver.
---
paper_title: Modeling the indoor MIMO wireless channel

paper_content:

This paper demonstrates the ability of a physically based statistical multipath propagation model to match capacity statistics and pairwise magnitude and phase distributions of measured 4 /spl times/ 4 and 10 /spl times/ 10 narrow-band multiple-input multiple-output data (MIMO) at 2.4 GHz. The model is compared to simpler statistical models based on the multivariate complex normal distribution with either complex envelope or power correlation. The comparison is facilitated by computing channel element covariance matrices for fixed sets of multipath statistics. Multipolarization data is used to demonstrate a simple method for modeling dual-polarization arrays.
---
paper_title: A stochastic multipath channel model including path directions for indoor environments

paper_content:

A novel stochastic channel model for the indoor propagation channel is presented. It is especially for, but not limited to future communication systems with multiple antennas like space division multiple access (SDMA), spatial filtering for interference reduction (SFIR), or multiple-input/multiple-output (MIMO). The model is designed for indoor scenarios, straight forward extendable to urban environments. It is based on physical wave propagation. The new approach describes the channel by multipath components, each characterized by its transfer matrix (including loss), delay, direction of arrival, and departure. The appearance and disappearance of multipath components over time is modeled as a birth and death process, a marked Poisson process. This enables first-time the correct modeling of spatial and temporal correlations. In each modeling step, path properties change according to the motion of transmitter and receiver. The changing delay times of propagation paths yield a realistic Doppler behavior of the channel. Deterministic ray tracing results are used to produce the huge data sets required for the statistical evaluation of the parameters of the proposed model. This method enables an automated parameter extraction for new environments or frequencies. The ray tracing tool has been verified by narrowband, wideband, and directional channel measurements. The novel stochastic spatial channel model allows the simulation of third-generation broadband radio systems including arbitrary antenna configurations and patterns. System simulations for the bit-error rate of radio links can be performed including intelligent antenna configurations like SDMA, SFIR, or MIMO. Furthermore, the capacity of complete systems can be investigated.
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paper_title: Fading correlation and its effect on the capacity of multielement antenna systems

paper_content:

We investigate the effects of fading correlations in multielement antenna (MEA) communication systems. Pioneering studies showed that if the fades connecting pairs of transmit and receive antenna elements are independently, identically distributed, MEAs offer a large increase in capacity compared to single-antenna systems. An MEA system can be described in terms of spatial eigenmodes, which are single-input single-output subchannels. The channel capacity of an MEA is the sum of capacities of these subchannels. We show that the fading correlation affects the MEA capacity by modifying the distributions of the gains of these subchannels. The fading correlation depends on the physical parameters of MEA and the scatterer characteristics. In this paper, to characterize the fading correlation, we employ an abstract model, which is appropriate for modeling narrow-band Rayleigh fading in fixed wireless systems.
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paper_title: Analysis and modeling of multiple-input multiple-output (MIMO) radio channel based on outdoor measurements conducted at 2.5 GHz for fixed BWA applications

paper_content:

This paper summarizes our 2/spl times/2 multiple-input multiple-output (MIMO) fixed wireless outdoor propagation measurements at 2.48 GHz conducted in the suburban residential areas of San Jose, California. We report on various channel characteristics such as path loss, Ricean K-factor, cross-polarization-discrimination (XPD) and channel capacity. We present simple models for these characteristics, focusing on excess loss dependency and, derived from that, the variation with distance. Also, we introduce an idea for a generalized MIMO channel model based on these modeled channel characteristics and the correlation properties between them. Path loss results show that blockage due to buildings or foliage causes an excess loss of 35.45 dB compared to free space propagation at a distance of 1 km. The narrowband K-factor distribution matches previously reported results. The XPD of the total received signal varies from -10 to 15 dB at various locations. The K-factor and XPD were found to be very much dependent on excess loss due to blockage conditions at various distances.
---
paper_title: Modeling the indoor MIMO wireless channel

paper_content:

This paper demonstrates the ability of a physically based statistical multipath propagation model to match capacity statistics and pairwise magnitude and phase distributions of measured 4 /spl times/ 4 and 10 /spl times/ 10 narrow-band multiple-input multiple-output data (MIMO) at 2.4 GHz. The model is compared to simpler statistical models based on the multivariate complex normal distribution with either complex envelope or power correlation. The comparison is facilitated by computing channel element covariance matrices for fixed sets of multipath statistics. Multipolarization data is used to demonstrate a simple method for modeling dual-polarization arrays.
---
paper_title: Effect of antenna separation on the capacity of BLAST in correlated channels

paper_content:

As the base station is usually placed above local clutter, the angular spectrum incident on the base is narrow, inducing correlation among base antenna signals, which reduces the capacity of a multiple transmit and receive antenna systems. In this work the general expression for link capacity is derived, when there is correlation among receive antennas and among transmit antennas. It is found that an antenna separation of 4 wavelengths between nearest neighbors in a linear base array of dually polarized antennas allows one to achieve 80% of the capacity attainable in the uncorrelated antenna case.
---
paper_title: Fading correlation and its effect on the capacity of multielement antenna systems

paper_content:

We investigate the effects of fading correlations in multielement antenna (MEA) communication systems. Pioneering studies showed that if the fades connecting pairs of transmit and receive antenna elements are independently, identically distributed, MEAs offer a large increase in capacity compared to single-antenna systems. An MEA system can be described in terms of spatial eigenmodes, which are single-input single-output subchannels. The channel capacity of an MEA is the sum of capacities of these subchannels. We show that the fading correlation affects the MEA capacity by modifying the distributions of the gains of these subchannels. The fading correlation depends on the physical parameters of MEA and the scatterer characteristics. In this paper, to characterize the fading correlation, we employ an abstract model, which is appropriate for modeling narrow-band Rayleigh fading in fixed wireless systems.
---
paper_title: Statistical characteristics of measured MIMO wireless channel data and comparison to conventional models

paper_content:

This paper presents measured data from a narrowband multiple-input multiple-output (MIMO) channel probe in an indoor office/laboratory environment. The system employs ten transmit and ten receive antennas and computes the 10 /spl times/ 10 narrowband channel matrix at 2.45 GHz every 80 milliseconds. We use the data to study the statistical behavior of the channel coefficients and the resulting channel capacity. We also demonstrate the ability of a simple statistically based physical model to accurately represent the channel behavior. The results of this model are compared to more conventional models that assume complex normal distributions of the channel matrix elements.
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paper_title: Capacity of multi-antenna array systems in indoor wireless environment

paper_content:

Previous studies have shown that a wireless system using n transmitting and n receiving antennas can achieve a capacity n times higher than a single-antenna system in an independent Rayleigh fading environment. We explore the capacities of multiple-element antenna arrays (MEAs) in a more realistic propagation environment simulated via the WiSE ray-tracing tool. We impose an average power constraint and collect statistics of the capacity with optimal power allocation, C/sub wf/, and the mutual information with an equal power allocation, I/sub eq/. In addition, we present expressions for the asymptotic growth rates C/sub wf//n and I/sub eq//n as n/spl rarr//spl infin/ for two cases: (a) independent fadings and (b) correlated fadings at different antennas. We find that C/sub wf//n and I/sub eq//n converge to constants C/sub wf/* and I/sub eq/*, respectively in case (a), and to C/sub wf//sup 0/and I/sub eq//sup 0/ in case (b). We observe that C/sub wf//sup 0/ and I/sub eq//sup 0/ predict very closely the slopes observed for simulated channels, even for moderate n (i.e., 16).
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paper_title: Initial investigation of multiple-input multiple-output (MIMO) channels in indoor environments

paper_content:

Theoretical investigation of multiple-input multiple-output (MIMO) channels has shown the potentially huge increases in spectral efficiency that this architecture can offer. The performance of such MIMO systems is dependent on the propagation environment exhibiting sufficient multipath scattering. This paper presents some initial analysis of MIMO channel measurements taken in indoor environments at 5.2 GHz. Outage capacities are calculated and compared between different locations and for different antenna array configurations. Surprisingly, it is shown that the highest channel capacities were actually calculated from data measured in an empty room.
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paper_title: A stochastic MIMO channel model with joint correlation of both link ends

paper_content:

Abstract-This paper presents a novel stochastic channel model for multiple-input multiple-output (MIMO) wireless radio channels. In contrast to state-of-the-art stochastic MIMO channel models, the spatial correlation properties of the channel are not divided into separate contributions from transmitter and receiver. Instead, the joint correlation properties are modeled by describing the average coupling between the eigenmodes of the two link ends. The necessary and sufficient condition for the proposed model to hold is that the eigenbasis at the receiver is independent of the transmit weights, and vice versa. The authors discuss the mathematical elements of the model, which can be easily extracted from measurements, from a radio propagation point of view and explain the underlying assumption of the model in physical terms. The validation of the proposed model by means of measured data obtained from two completely different measurement campaigns reveals its ability to better predict capacity and spatial channel structure than other popular stochastic channel models.
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paper_title: Wideband outdoor MIMO channel model derived from directional channel measurements at 2 GHz

paper_content:

This paper describes the use of directional channel measurements to derive a MIMO channel model. The measurements were obtained using a wideband channel sounder and eight element circular array in a metropolitan area in central Bristol, U.K. The raw measurements were processed using SAGE to extract the parameters of multipath components. The analysis of these parameters revealed several interesting features, notably that their amplitude distribution was well modelled as log-normal, and that there was little evidence of clustering in the angles of arrival. Hence a MIMO channel based on the assumption of finite scattering was derived, using the distributions obtained. The model allows the channel matrix H to be derived in the narrow-band case, and a tapped delay line model is also obtained for wideband systems. While the model derived is based on only a small set of measurements, it provides a case study for MIMO modelling based on measurements.
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paper_title: Microwave Mobile Communications

paper_content:

From the Publisher: ::: IEEE Press is pleased to bring back into print this definitive text and reference covering all aspects of microwave mobile systems design. Encompassing ten years of advanced research in the field, this invaluable resource reviews basic microwave theory, explains how cellular systems work, and presents useful techniques for effective systems development. The return of this classic volume should be welcomed by all those seeking the original authoritative and complete source of information on this emerging technology. An in-depth and practical guide, Microwave Mobile Communications will provide you with a solid understanding of the microwave propagation techniques essential to the design of effective cellular systems.
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paper_title: MIMO channel modeling and the principle of maximum entropy

paper_content:

We devise theoretical grounds for constructing channel models for multiple-input multiple-output (MIMO) systems based on information-theoretic tools. The paper provides a general method to derive a channel model which is consistent with one's state of knowledge. The framework we give here has already been fruitfully explored with success in the context of Bayesian spectrum analysis and parameter estimation. For each channel model, we conduct an asymptotic analysis (in the number of antennas) of the achievable transmission rate using tools from random matrix theory. A central limit theorem is provided on the asymptotic behavior of the mutual information and validated in the finite case by simulations. The results are useful both in terms of designing a system based on criteria such as quality of service and in optimizing transmissions in multiuser networks.
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paper_title: Capacity complying MIMO channel models

paper_content:

In (M. Debbah, et al., 2003) a unified framework for constructing MIMO models based on the principle of maximum entropy was provided. Several MIMO directional and double directional models were derived and in each case, the mutual information was shown to have asymptotically a Gaussian behavior. Interestingly, the results were shown to be accurate, through simulations, in the finite regime with an astonishing small number of antennas. In this paper, the models are analyzed and validated based on a wideband outdoor measurement campaign carried out in Oslo during summer 2002. The measurements were performed at a center frequency of 2.1 GHz with a bandwidth of 100 MHz in three different urban scenarios: a regular street grid scenario, an open city place and an indoor cell site.
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paper_title: Capacity Scaling and Spectral Efficiency in Wideband Correlated MIMO Channels

paper_content:

The dramatic linear increase in ergodic capacity with the number of antennas promised by multiple-input multiple-output (MIMO) wireless communication systems is based on idealized channel models representing a rich scattering environment. Is such scaling sustainable in realistic scattering scenarios? Existing physical models, although realistic, are intractable for addressing this problem analytically due to their complicated nonlinear dependence on propagation path parameters, such as the angles of arrival and delays. In this paper, we leverage a recently introduced virtual representation of physical models that is essentially a Fourier series representation of wide-band MIMO channels in terms of fixed virtual angles and delays. Motivated by physical considerations, we propose a D-connected model for correlated channels defined by a virtual spatial channel matrix consisting of D nonvanishing diagonals with independent and identically distributed (i.i.d.) Gaussian entries. The parameter D provides a meaningful and tractable measure of the richness of scattering. We derive general bounds for the coherent ergodic capacity and investigate capacity scaling with the number of antennas and bandwidth. In the large antenna regime, we show that linear capacity scaling is possible if D scales linearly with the number of antennas. This, in turn, is possible if the number of resolvable paths grows quadratically with the number of antennas. The capacity saturates for linear growth in the number of paths (fixed D). The ergodic capacity does not depend on frequency selectivity of the channel in the wide-band case. Increasing bandwidth tightens the bounds and hastens the convergence of scaling behavior. For large bandwidth, the capacity scales linearly with the signal-to-noise ratio (SNR) as well. We also provide an explicit characterization of the wide-band slope recently proposed by Verdu. Numerical results are presented to illustrate the key theoretical results.
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paper_title: An interim channel model for beyond-3G systems: extending the 3GPP spatial channel model (SCM)

paper_content:

This paper reports on the interim beyond-3G (B3G) channel model developed by and used within the European WINNER project. The model is a comprehensive spatial channel model for 2 and 5 GHz frequency bands and supports bandwidths up to 100 MHz in three different outdoor environments. It further features time-evolution of system-level parameters for challenging advanced communication algorithms, as well as a reduced-variability tapped delay-line model for improved usability in calibration and comparison simulations.
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paper_title: Wideband Spatial Channel Model for MIMO Systems at 5 GHz in Indoor and Outdoor Environments

paper_content:

This work presents a spatial channel model developed within the EC WINNER1project. The channel model is mainly based on double-directional measurement campaigns carried out in the 5 GHz ISM2band with bandwidths of up to 120 MHz. The model is based on a unified structure for indoor and outdoor environment. It covers 6 different propagation scenarios, namely indoor small office, indoor hall, urban microcell, urban macrocell, suburban macrocell, and rural environment. Both line-of-sight (LOS) and non-line-of-sight (NLOS) propagation conditions are modeled.
---
paper_title: A Statistical Model for Indoor Multipath Propagation

paper_content:

The results of indoor multipath propagation measurements using 10 ns, 1.5 GHz, radarlike pulses are presented for a medium-size office building. The observed channel was very slowly time varying, with the delay spread extending over a range up to about 200 ns and rms values of up to about 50 ns. The attenuation varied over a 60 dB dynamic range. A simple statistical multipath model of the indoor radio channel is also presented, which fits our measurements well, and more importantly, appears to be extendable to other buildings. With this model, the received signal rays arrive in clusters. The rays have independent uniform phases, and independent Rayleigh amplitudes with variances that decay exponentially with cluster and ray delays. The clusters, and the rays within the cluster, form Poisson arrival processes with different, but fixed, rates. The clusters are formed by the building superstructure, while the individual rays are formed by objects in the vicinities of the transmitter and the receiver.
---
paper_title: A physical scattering model for MIMO macrocellular broadband wireless channels

paper_content:

This paper presents a physical scattering model that predicts multiple-input multiple-output (MIMO) channel characteristics conforming well to experimental observations in macrocells. Our approach is to start with a given single-input single-output power-delay profile (defined for specific range, bandwidth and antenna parameters) and fit a scattering model that characterizes the MIMO channel. From the derived scattering model and antenna array configurations, the MIMO channel is computed using a ray-based method. Simulations of several MIMO channels are shown to exhibit experimentally observed channel correlations, antenna beamwidth effect, range dependency, and frequency selectivity.
---
paper_title: Outdoor MIMO Wireless Channels: Models and Performance Prediction

paper_content:

We present a new model for multiple-input-multiple-output (MIMO) outdoor wireless fading channels and their capacity performance. The proposed model is more general and realistic than the usual independent and identically distributed (i.i.d.) model, and allows us to investigate the behavior of channel capacity as a function of the scattering radii at transmitter and receiver, distance between the transmit and receive arrays, and antenna beamwidths and spacing. We show how the MIMO capacity is governed by spatial fading correlation and the condition number of the channel matrix through specific sets of propagation parameters. The proposed model explains the existence of "pinhole" channels which exhibit low spatial fading correlation at both ends of the link but still have poor rank properties, and hence, low ergodic capacity. In fact, the model suggests the existence of a more general family of channels spanning continuously from full rank i.i.d. to low-rank pinhole cases. We suggest guidelines for predicting high rank (and hence, high ergodic capacity) in MIMO channels, and show that even at long ranges, high channel rank can easily be sustained under mild scattering conditions. Finally, we validate our results by simulations using ray tracing techniques. Connections with basic antenna theory are made.
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paper_title: Measurement of keyhole effect in a wireless multiple-input multiple-output (MIMO) channel

paper_content:

It has been predicted theoretically that for some environments, the capacity of wireless multiple-input multiple-output systems can become very low even for uncorrelated signals; this effect has been termed "keyhole" or "pinhole." In this letter, we present the (to our knowledge) first measurement of this effect. The measurements are done in a controlled indoor environment, with transmitter and receiver in two adjacent rooms. One of the rooms is shielded, and propagation to the other room can occur only through a hole or a waveguide in the wall. We find that only the waveguide leads to an unambiguous keyhole, while a hole of the same size still allows multimodal propagation. Measurement of amplitude statistics also confirm theoretical predictions.
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paper_title: Keyholes, correlations, and capacities of multielement transmit and receive antennas

paper_content:

Multielement system capacities are usually thought of as limited only by correlations between elements. It is shown here that degenerate channel phenomena called "keyholes" may arise under realistic assumptions which have zero correlation between the entries of the channel matrix H and yet only a single degree of freedom. Canonical physical examples of keyholes are presented. For outdoor environments, it is shown that roof edge diffraction is perceived as a "keyhole" by a vertical base array that may be avoided by employing instead a horizontal base array.
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paper_title: Outdoor MIMO Wireless Channels: Models and Performance Prediction

paper_content:

We present a new model for multiple-input-multiple-output (MIMO) outdoor wireless fading channels and their capacity performance. The proposed model is more general and realistic than the usual independent and identically distributed (i.i.d.) model, and allows us to investigate the behavior of channel capacity as a function of the scattering radii at transmitter and receiver, distance between the transmit and receive arrays, and antenna beamwidths and spacing. We show how the MIMO capacity is governed by spatial fading correlation and the condition number of the channel matrix through specific sets of propagation parameters. The proposed model explains the existence of "pinhole" channels which exhibit low spatial fading correlation at both ends of the link but still have poor rank properties, and hence, low ergodic capacity. In fact, the model suggests the existence of a more general family of channels spanning continuously from full rank i.i.d. to low-rank pinhole cases. We suggest guidelines for predicting high rank (and hence, high ergodic capacity) in MIMO channels, and show that even at long ranges, high channel rank can easily be sustained under mild scattering conditions. Finally, we validate our results by simulations using ray tracing techniques. Connections with basic antenna theory are made.
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paper_title: A generic model for MIMO wireless propagation channels in macro- and microcells

paper_content:

This paper derives a generic model for the multiple-input multiple-output (MIMO) wireless channel. The model incorporates important effects, including i) interdependency of directions-of-arrival and directions-of-departure, ii) large delay and angle dispersion by propagation via far clusters, and iii) rank reduction of the transfer function matrix. We propose a geometry-based model that includes the propagation effects that are critical for MIMO performance: i) single scattering around the BS and MS, ii) scattering by far clusters, iii) double-scattering, iv) waveguiding, and v) diffraction by roof edges. The required parameters for the complete definition of the model are enumerated, and typical parameter values in macro and microcellular environments are discussed.
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Title: Survey of Channel and Radio Propagation Models for Wireless MIMO Systems

Section 1: INTRODUCTION AND OVERVIEW
Description 1: Provide an introduction and overview of the evolution of MIMO technology and the importance of realistic propagation models.

Section 2: Notation
Description 2: Summarize the notation used throughout the paper for matrices, vectors, and other mathematical entities.

Section 3: Previous work
Description 3: Review existing literature on wireless communications and channel modeling, particularly focusing on works that discuss multi-antenna systems.

Section 4: MIMO system model
Description 4: Discuss the characterization of wireless MIMO channels from the perspective of propagation and system-level modeling.

Section 5: Double-directional radio propagation
Description 5: Explain the mechanics of radio propagation described by the double-directional channel impulse response.

Section 6: MIMO channel
Description 6: Describe how MIMO channels are represented and modelled, including the channel matrix and its characteristics.

Section 7: Relationship
Description 7: Provide the linkage between double-directional impulse response and MIMO channel matrix approaches.

Section 8: Model classification
Description 8: Classify various MIMO channel models based on their characteristics and modeling approaches.

Section 9: Stationarity aspects
Description 9: Discuss the concept of channel stationarity and its implications for MIMO systems, including methods to assess stationarity.

Section 10: Deterministic physical models
Description 10: Describe deterministic physical models, such as ray tracing, used to simulate radio propagation in specific environments.

Section 11: Ray-tracing algorithm
Description 11: Detail the methodology of ray-tracing algorithms used for MIMO channel characterization and its computational aspects.

Section 12: Application to MIMO channel characterization
Description 12: Explain the application of ray tracing to the characterization of MIMO channels and performance evaluation.

Section 13: Geometry-based stochastic physical models
Description 13: Discuss geometry-based stochastic physical models that use randomly placed scatterers and simplified ray-tracing procedures.

Section 14: Single-bounce scattering
Description 14: Elaborate on single-bounce scattering models and their advantages in MIMO channel simulations.

Section 15: Multiple-bounce scattering
Description 15: Describe the concept of multiple-bounce scattering and its impact on angle and delay statistics in MIMO systems.

Section 16: Nongeometrical stochastic physical models
Description 16: Introduce nongeometrical stochastic models that describe paths statistically without reference to physical geometry.

Section 17: Extended Saleh-Valenzuela model
Description 17: Explain the extended Saleh-Valenzuela model used for clustering multipath components in delay and angular domains.

Section 18: Zwick model
Description 18: Discuss the Zwick model for indoor channels that generates multipath components independently.

Section 19: Correlation-based analytical models
Description 19: Describe analytical models that use statistical characterizations, such as the i.i.d. model, Kronecker model, and Weichselberger model.

Section 20: Finite scatterer model
Description 20: Discuss the finite scatterer model, which uses a finite number of multipath components for channel modeling.

Section 21: Maximum entropy model
Description 21: Introduce the maximum entropy model, which is based on statistical inference and prior information about the propagation environment.

Section 22: Virtual channel representation
Description 22: Explain the virtual channel representation model that uses DFT matrices and i.i.d. Gaussian matrices for MIMO channel modeling.

Section 23: STANDARDIZED MODELS
Description 23: Provide an overview of standardized MIMO channel models used in various wireless communication standards.

Section 24: COST 259/273
Description 24: Describe the COST 259 and 273 models developed for flexible and personalized wireless communications.

Section 25: COST 259 directional channel model
Description 25: Present the approach and methodology of the COST 259 directional channel model.

Section 26: COST 273
Description 26: Summarize updates and enhancements of the COST 273 channel model compared to COST 259.

Section 27: 3GPP SCM
Description 27: Detail the 3GPP spatial channel model used for evaluating outdoor MIMO concepts.

Section 28: Calibration model
Description 28: Introduce the simplified calibration model used to ensure simulation consistency across different implementations.

Section 29: Simulation model
Description 29: Explain the simulation model intended for performance evaluation, including various model environments and features.

Section 30: WINNER channel models
Description 30: Discuss the WINNER project channel models related to both COST 259 and 3GPP SCM models.

Section 31: IEEE 802.11n
Description 31: Present the IEEE 802.11n channel model developed for indoor environments and MIMO WLANs.

Section 32: SUI models and IEEE 802.16a
Description 32: Introduce the SUI and IEEE 802.16a models developed for macrocellular fixed wireless access networks.

Section 33: SUI channel models
Description 33: Describe the key features and structure of the SUI channel models.

Section 34: IEEE 802.16a channel models
Description 34: Summarize the modifications and additional features of the IEEE 802.16a models based on SUI models.

Section 35: 802.16a-based directional channel models
Description 35: Explain the spatial channel model and its extensions for fixed macrocellular scenarios developed from IEEE 802.16a.

Section 36: KEY FEATURES NOT INCLUDED IN PRESENT MODELS
Description 36: Discuss important aspects not yet sufficiently addressed in current MIMO channel models, such as single vs. double scattering and the keyhole effect.

Section 37: Single versus double scattering
Description 37: Elaborate on the importance of accounting for both single and double scattering in MIMO models.

Section 38: Keyhole effect
Description 38: Discuss the keyhole effect and its implications for MIMO system performance.

Section 39: Diffuse multipath components
Description 39: Introduce the concept of dense or diffuse multipath components and their impact on channel modeling accuracy.

Section 40: Polarization
Description 40: Highlight the role of polarization in MIMO channels and challenges in incorporating it into models.

Section 41: Time variation
Description 41: Discuss the significance of channel time variation and the need for realistic temporal correlations in MIMO models.

Section 42: SUMMARY
Description 42: Provide a comprehensive summary of the survey, highlighting key concepts, model types, standardized models, and open problems in MIMO channel modeling.