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.

/pdf/on-limits-of-wireless-communications-in-a-fading-environment-2nxyevgur3.pdf

On Limits of Wireless Communications in a Fading Environment when UsingMultiple Antennas

Wireless Communications

An Integrated Agent Architecture for Software Defined Radio. Rapid-prototype cognitive radio, CR1, was developed to apply these.The modern software defined radio has been called the heart of a cognitive radio. Cognitive radio: an integrated agent architecture for software defined radio. Http:bwrc.eecs.berkeley.eduResearchMCMACR White paper final1.pdf. The cognitive radio, built on a software-defined radio, assumes. Radio: An Integrated Agent Architecture for Software Defined Radio, Ph.D. The need for software-defined radios is underlined and the most important notions used for such. Mitola III, Cognitive radio: an integrated agent architecture for software defined radio, Ph.D. This results in the set-theoretic ontology of radio knowledge defined in the. Cognitive Radio An Integrated Agent Architecture for Software.This article first briefly reviews the basic concepts about cognitive radio CR. Cognitive Radio-An Integrated Agent Architecture for Software Defined Radio. Cognitive Radio RHMZ 2007. Software-defined radio SDR idea 1. Cognitive radio: An integrated agent architecture for software.Cognitive Radio SOFTWARE DEFINED RADIO, AND ADAPTIVE WIRELESS SYSTEMS2 Cognitive Networks. 3 Joseph Mitola III, Cognitive Radio: An Integrated Agent Architecture for Software Defined Radio Stockholm.

/pdf/cognitive-radio-an-integrated-agent-architecture-for-1v855bviue.pdf

Cognitive Radio An Integrated Agent Architecture for Software Defined Radio

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

A rigorous coupled-wave approach is used to analyze diffraction by general planar gratings bounded by two different media. The grating fringes may have any orientation (slanted or unslanted) with respect to the grating surfaces. The analysis is based on a state-variables representation and results in a unifying, easily computer-implementable matrix formulation of the general planar-grating diffraction problem. Accurate diffraction characteristics are presented for the first time to the authors’ knowledge for general slanted gratings. This present rigorous formulation is compared with rigorous modal theory, approximate two-wave modal theory, approximate multiwave coupled-wave theory, and approximate two-wave coupled-wave theory. Typical errors in the diffraction characteristics introduced by these various approximate theories are evaluated for transmission, slanted, and reflection gratings. Inclusion of higher-order waves in a theory is important for obtaining accurate predictions when forward-diffracted orders are dominant (transmission-grating behavior). Conversely, when backward-diffracted orders dominate (reflection-grating behavior), second derivatives of the field amplitudes and boundary diffraction need to be included to produce accurate results.

Rigorous coupled-wave analysis of planar-grating diffraction

The development is given of a model in which the rows or blocks of buildings are viewed as diffracting cylinders lying on the earth. When the buildings are represented as absorbing screens, the propagation process reduces to multiple forward diffraction past a series of screens. Numerical computation of the diffraction effect yields a power-law dependence for the field that is within the measured range. Accounting for diffraction down to street level from the roof tops gives an overall absolute path loss in good agreement with the average measured path loss. >

A theoretical model of UHF propagation in urban environments

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.

Radio Propagation for Modern Wireless Systems

The propagation of electromagnetic waves along open periodic, dielectric waveguides is formulated here as a rigorous and exact boundary-value problem. The characteristic field solutions are shown to be of the surface-wave or leaky-wave type, depending on the ratio of periodicity to wavelength (d/lambda). The dispersion curves and the space-harmonic amplitudes of these fields are examined for both TE and TM modes. Specific numerical examples are given for the cases of holographic layers and for rectangularly corrugated gratings; these show the detailed behavior of the principal field components and the dependence of waveguiding and leakage characteristics on the physical parameters of the periodic configuration.

Theory of Periodic Dielect Waveguides

Various phenomena have been observed when a bounded acoustic beam is incident from a liquid onto the surface of a solid at or near the Rayleigh angle. These phenomena include: a shift of the reflected beam from the position predicted by geometrical acoustics, a null or minimum of intensity within the reflected beam, a 180° phase reversal of the field on either side of the null, a weak trailing field on only one side of the reflected beam and a frequency of least reflection when the solid is lossy. By carefully examining the reflection coefficient for angles in the vicinity of the Rayleight angle, and by taking into account the angular spectrum of plane waves that comprise a bounded beam, a model of the reflection process is developed that explains all of the observed phenomena. This model shows that the various critical-reflection effects result from the interference between a geometrically reflected field and the field of a leaky Rayleigh wave, which is excited by the incident beam. Moreover, this model resolves the conflict between various explanations made for these phenomena in the past; in particular, it is found that Schoch's classical description of a laterally displaced reflected beam is valid only for beams having a large width.

Unified theory of Rayleigh-angle phenomena for acoustic beams at liquid-solid interfaces

To acquire a knowledge of radio propagation characteristics in the microcellular environments for personal communications services (PCS), a comprehensive measurement program was conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three base station antenna heights of 3.2 m, 8.7 m, and 13.4 m and two frequencies at 900 MHz and 1900 MHz. Five test settings were chosen in urban, suburban, and rural areas in order to study propagation in a variety of environments. This paper reports the LOS measurements in different environments, all of which show variations of signal strength with distance that have distinct near and far regions separated by a break point. It was also found that the location of the break point for different frequencies and antenna heights can be calculated based on first Fresnel zone clearance. The regression analysis reveals a slope that is less than two before the break point, while it is greater than two after the break point. This break distance can be used to define the size of microcell and to design for fast hand-off. Beyond the first Fresnel zone break distance the base station antenna height gain was observed to approximately follow the square power law of antenna height. >

http://materias.fi.uba.ar/6654/download/Radio%20propagation.pdf

Henry L. Bertoni

Papers

A theoretical model of UHF propagation in urban environments

Radio Propagation for Modern Wireless Systems

Theory of Periodic Dielect Waveguides

Unified theory of Rayleigh-angle phenomena for acoustic beams at liquid-solid interfaces

Radio propagation characteristics for line-of-sight microcellular and personal communications