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

This paper presents an overview of progress in the area of multiple input multiple output (MIMO) space-time coded wireless systems. After some background on the research leading to the discovery of the enormous potential of MIMO wireless links, we highlight the different classes of techniques and algorithms proposed which attempt to realize the various benefits of MIMO including spatial multiplexing and space-time coding schemes. These algorithms are often derived and analyzed under ideal independent fading conditions. We present the state of the art in channel modeling and measurements, leading to a better understanding of actual MIMO gains. Finally, the paper addresses current questions regarding the integration of MIMO links in practical wireless systems and standards.

/pdf/from-theory-to-practice-an-overview-of-mimo-space-time-coded-431vesj02q.pdf

From theory to practice: an overview of MIMO space-time coded wireless systems

Theoretical and experimental studies of multiple-input/multiple-output (MIMO) radio channels are presented. A simple stochastic MIMO model channel has been developed. This model uses the correlation matrices at the mobile station (MS) and base station (BS) so that results of the numerous single-input/multiple-output studies that have been published in the literature can be used as input parameters. The model is simplified to the narrowband channels. The validation of the model is based upon data collected in both picocell and microcell environments. The stochastic model has also been used to investigate the capacity of MIMO radio channels, considering two different power allocation strategies, water filling and uniform and two different antenna topologies, 4/spl times/4 and 2/spl times/4. Space diversity used at both ends of the MIMO radio link is shown to be an efficient technique in picocell environments, achieving capacities within 14 b/s/Hz and 16 b/s/Hz in 80% of the cases for a 4/spl times/4 antenna configuration implementing water filling at a SNR of 20 dB.

/pdf/a-stochastic-mimo-radio-channel-model-with-experimental-4fgkgc22dj.pdf

A stochastic MIMO radio channel model with experimental validation

The relatively unused millimeter-wave (mmWave) spectrum offers excellent opportunities to increase mobile capacity due to the enormous amount of available raw bandwidth. This paper presents experimental measurements and empirically-based propagation channel models for the 28, 38, 60, and 73 GHz mmWave bands, using a wideband sliding correlator channel sounder with steerable directional horn antennas at both the transmitter and receiver from 2011 to 2013. More than 15,000 power delay profiles were measured across the mmWave bands to yield directional and omnidirectional path loss models, temporal and spatial channel models, and outage probabilities. Models presented here offer side-by-side comparisons of propagation characteristics over a wide range of mmWave bands, and the results and models are useful for the research and standardization process of future mmWave systems. Directional and omnidirectional path loss models with respect to a 1 m close-in free space reference distance over a wide range of mmWave frequencies and scenarios using directional antennas in real-world environments are provided herein, and are shown to simplify mmWave path loss models, while allowing researchers to globally compare and standardize path loss parameters for emerging mmWave wireless networks. A new channel impulse response modeling framework, shown to agree with extensive mmWave measurements over several bands, is presented for use in link-layer simulations, using the observed fact that spatial lobes contain multipath energy that arrives at many different propagation time intervals. The results presented here may assist researchers in analyzing and simulating the performance of next-generation mmWave wireless networks that will rely on adaptive antennas and multiple-input and multiple-output (MIMO) antenna systems.

Wideband Millimeter-Wave Propagation Measurements and Channel Models for Future Wireless Communication System Design

Space-time processing can improve network capacity, coverage, and quality by reducing co-channel interference (CCI) while enhancing diversity and array gain. This article focuses largely on the receive (mobile-to-base station) time-division multiple access (TDMA) (nonspread modulation) application for high-mobility networks. We describe a large (macro) cell propagation channel and discuss different physical effects such as path loss, fading delay spread, angle spread, and Doppler spread. We also develop a signal model incorporating channel effects. Both forward-link (transmit) and reverse-link (receive) channels are considered and the relationship between the two is discussed. Single- and multiuser models are treated for four important space-time processing problems, and the underlying spatial and temporal structure are discussed as are different algorithmic approaches to reverse link space-time professing with blind and nonblind methods for single- and multiple-user cases. We cover forward-link space-time algorithms and we outline methods for estimation of multipath parameters. We also discuss applications of space-time processing to CDMA, applications of space-time techniques to current cellular systems, and industry trends.

Space-time processing for wireless communications

From the Book:
PREFACE: Smart Antennas for Wireless CommunicationsIS-95 and Third Generation CDMA ApplicationsPrefaceThis text has been created to satisfy the growing demand for knowledge in two emerging areas: adaptive antennas (also known as smart antennas) and Code Division Multiple Access CDMA was commercialized in the early 1990s by Qualcomm, Inc, a San Diego, California, company that pioneered the use of a classic military concept for the burgeoning cellular telephone industry Adaptive arrays, first conceptualized in the 1960s with the birth of digital signal processing, only recently have become practical for deployment; the intense growth rates of wireless services around the world are beckoning for their commercial useThis text has been developed through years of research by the authors and their colleagues at the Mobile and Portable Radio Research Group of Virginia Tech and at Bell Communications Research Our goal in creating this text is to provide fundamental and practical information for practicing engineers, students, and researchers in industry as well as in academia To complement the book, the second author was asked by the Institute of Electrical and Electronics Engineers (IEEE) to provide a compendium of selected readings of key journal papers dedicated to the topic of smart antennas The compendium, when used in conjunction with this text, provides a convenient single source of literature for use in classrooms or industry short coursesThe material and organization of this book stemmed from the first author's 1995 PhD dissertation on the subject of CDMA and smart antennas Since then, a great deal of work has transpired in the field, including the adoption oftheIS-95 J-STD-008 CDMA standard, the new 14,400 bps voice coder for Rate Set 2 channels, new methods and models for implementation and modeling of smart antennas in CDMA, and the stringent wireless E-911 position location requirement 125m, 67% of the time imposed by the Federal Communications Commission We have worked diligently to include up-to-the-minute information in this text The text is arranged into 10 chapters Chapter 1 provides an overview of CDMA and smart antennas; it includes a glossary of terms and a fundamental treatment of synchronous and asynchronous CDMA Antenna and propagation fundamentals, as they relate to CDMA systems, are also presented Chapter 2 provides valuable practical information on the IS-95 J-STD-008 standard, and it provides in-depth descriptions of all of the CDMA channels Also included is an actual link budget design for a PCS CDMA system Chapter 3 provides fundamental material on adaptive antenna arrays and array theory The concepts of beamforming, weighting vectors, and fixed-beam vs adaptive beam antennas are covered Chapter 4 applies this material to specific CDMA implementations that may be used for today's IS-95 and future CDMA systems Chapter 5 combines the concepts of CDMA and adaptive antennas to derive analytical expressions that allow wireless system designers to predict the coverage and capacity gains that adaptive antennas provide in a multi-cell CDMA system This chapter derives classic results that have led to system capacity predictions using CDMA with and without adaptive antennasChapter 6 provides an overview of multipath and Direction-Of-Arrival models for wireless channels A host of propagation models which are useful for analysis and simulation of adaptive array algorithms are presented Chapter 7 then describes complete details of one multipath propagation model, the Geometrically Based Single Bounce Elliptical Model, which provides complete characterization of a multipath environment in microcell/picocell applications Chapter 8 describes optimal spatial filtering approaches that use both adaptive arrays and characteristics of the CDMA signals Building on the fundamentals provided in Chapter 3, this chapter presents optimal methods that null interference while maximizing the carrier-to-noise ratio of a desired user Chapter 9 describes the algorithmic techniques for determining the Direction-Of-Arrival (DOA) of a signal in a multi-user interference environment Such capabilities will be required for position location techniques Chapter 10 concludes this text with a thorough treatment of position location algorithms and approaches Appendix A covers the derivation of the Gaussian Approximation and its many derivatives for spread spectrum systems Other appendices provide information that engineers and educators may find usefulThe authors wish to acknowledge the invaluable assistance, skill, and patience of Aurelia Scharnhorst, a research associate with Virginia Tech's Mobile and Portable Radio Research Group (MPRG), in formatting this text The ingenuity and hard work of Zhigang Rong, Rias Muhamed, and George Mizusawa are represented in parts of Chapters 8, 9, and 10 of this book, as portions of their mastersâ theses have been used with their gracious permission Other MPRG researchers who played an important role in building the knowledge base presented in this text are Rich Ertel, Kevin Krizman, Neal Patwari, Paulo Cardieri, and Tom Biedka The authors would also like to thank Prof M Zoltowski of Purdue University, Prof A Paulraj of Stanford University, M Feuerstein of Metawave, C Thompson of Virginia Tech, and Prof W Tranter and Prof B Woerner of Virginia Techâs MPRG for their review of this text and encouragement to pursue this project Kevin Sowerby of the University of Auckland, New Zealand also helped inspire this work during his 1997 sabbatical at MPRGThe authors would also like to thank Joe Wilkes, Paul Zablocky, and Shimon Moshavi of Bellcore, for valuable discussions regarding IS-95 Daniel Devasirvathm, Scott Seidel, and John Koshy provided insight and assistance that allowed the book to become a reality This text is the product of funded research supported at Virginia Tech through the MPRG industrial affiliates program It is our pleasure to bring this book to you, and we hope you find it usefulJ C L, JrT S R

Smart Antennas for Wireless Communications: Is-95 and Third Generation Cdma Applications

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.

http://www.faculty.poly.edu/~tsr/wp-content/uploads/CV/ICP/1996-05-A%20Geometrically%20Based%20Model%20for%20Line-of-Sight%20Multipath%20Radio%20Channels.pdf

A geometrically based model for line-of-sight multipath radio channels

Examines the performance enhancements that can be achieved by employing spatial filtering in code division multiple access (CDMA) cellular radio systems. The goal is to estimate what improvements are possible using narrow-beam adaptive antenna techniques, assuming that adaptive algorithms and the associated hardware to implement these systems can be realized. Simulations and analytical results are presented which demonstrate that steerable direction antennas at the base station can dramatically improve the reverse channel performance of multicell mobile radio systems, and new analytical techniques for characterizing mobile radio systems which employ frequency reuse are described using the wedge-cell geometry of Rappaport and Milstein (1992). The authors also discuss the effects of using directional antennas at the portable unit. Throughout the paper the authors use phased arrays and steerable, fixed pattern antennas to approximate the performance of adaptive antennas in multipath-free environments. >

Analytical results for capacity improvements in CDMA

Methods and systems in a wireless receiver for enabling the reception of input signals at varied power levels in the presence of co-channel interference utilizing combinations of space-time adaptive processing (STAP), interference cancellation multi-user detection (MUD), and combined STAP/MUD techniques. In MUD, code, timing, and possibly channel information of multiple users are jointly used to better detect each individual user. The novel combination of adaptive signal reconstruction techniques with interference cancellation MUD techniques provides accurate temporal cancellation of interference with minimal interference residuals. Additional methods and systems extend adaptive signal reconstruction techniques to take Doppler spread into account. STAP techniques permit a wireless receiver to exploit multiple antenna elements to form beams in the direction of the desired signal and nulls in the direction of the interfering signals. The combined STAP-MUD methods and systems increase the probability of successful user detection by taking advantage of the benefits of each reception method. An additional method and system utilizes STAP techniques in the case where no pilot signal is available. This method compares the outputs of various hypothesized STAP solutions.

Combined adaptive spatio-temporal processing and multi-user detection for cdma wireless systems

A wireless Internet access system and method supports the transmission and reception of multiple types of traffic between mobile subscriber units and existing networks. A frame structure is used that can support the transmission of multiple types of traffic and adapt to changes in the traffic types needed and the amount of data for a particular traffic type. In addition, data transmission is performed using orthogonal frequency division multiplexing and differential phase shift keying to avoid intersymbol interference. Receiving units in the mobile subscriber units and existing networks include antenna arrays to provide a multipath transmission.

Joseph C. Liberti

Papers

Smart Antennas for Wireless Communications: Is-95 and Third Generation Cdma Applications

A geometrically based model for line-of-sight multipath radio channels

Analytical results for capacity improvements in CDMA

Combined adaptive spatio-temporal processing and multi-user detection for cdma wireless systems

Wireless internet access system and method