Software Radio: A Modern Approach to Radio Engineering

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Features

• NEW - The first comprehensive guide to all aspects of engineering software-based radios.

  • Fills a major gap in the literature by bringing together complete and up-to-date information on software radio engineering, and by helping students understand the crucial interactions between analog and digital subsystems.

• Introductory coverage of RF engineering—Includes coverage of RF front-ends and digital processing techniques for overcoming problems in RF design.

  • Helps students get up to speed if they have a background in either digital signal processing or RF engineering, but not both.

• Advanced SDR Forum case studies—Presents new case studies drawn from leading-edge work by the Software Defined Radio Forum, the leading consortium of companies, universities, and research organizations promoting software radio development.

  • Gives students an understanding of the state-of-the-art in software radio development.

• Object-oriented software radio programming—Presents a systematic, object-oriented approach to creating flexible programs for software radios, including coverage of Java and the Common Object Request Broker Architecture (CORBA).

  • Shows students how to build robust, reliable, high-performance programs for software radios.

• Practical guidance on key tradeoffs—Illuminates key engineering tradeoffs among resolution, sample rate, and dynamic range.

  • Gives students deep insight into the real-world challenges of software radio design.

• Guidance on choosing the right underlying platform—Presents the pros, cons, and tradeoffs associated with utilizing DSP microprocessors, FPGAs, and ASICs.

  • Helps students make one of the most important up-front decisions in software radio engineering.

• Techniques for maximizing software radio performance—Includes in-depth coverage of smart antennas and other adaptive array algorithms.

  • Introduces students to today's best techniques for building high-performance software radio systems.

• Multirate digital signal processing—Presents in-depth coverage of multirate signal processing, a technique that is central to both channelization and synchronization in software radio systems.

  • Helps students understand the crucial role of multirate DSP in software radio design, and leverage multirate DSP to the fullest.

Description

The definitive engineer's guide to designing and building software-based radios.

• The first systematic guide to software radio design and implementation
• Multirate DSP, RF front-ends, direct digital synthesis of modulated waveforms, A/D and D/A conversion, and more
• Enhancing performance through smart antennas and other adaptive array algorithms
• Techniques for building more flexible, extensible software

Radios, once implemented purely in hardware, are increasingly built using programmable digital signal processing (DSP) devices that enhance device flexibility, simplify manufacture, and reduce costs. However, many engineers are unfamiliar with the latest techniques for building software radios for wireless systems and devices. This book fills the gap, introduces the key concepts of software radio design, and covers every issue and technique engineers must understand to successfully utilize DSP in their radio systems and subsystems. Coverage includes:

• Central role of multirate DSP in software radio design
• Constructing RF front-ends: utilizing digital processing to overcome key problems in RF design
• Direct digital synthesis of modulated waveforms
• A/D and D/A converters and conversion processes: key tradeoffs among resolution, sample rate, and dynamic range
• Enhancing performance through smart antennas and other adaptive array algorithms
• Practical techniques for choosing among DSP microprocessors, FPGAs, and ASICs
• A systematic, object-oriented approach to creating flexible software

The book concludes with case studies drawn from the advanced work of the SDR Forum, the leading consortium of companies, universities, and research organizations promoting software radio development.

Communications Engineering & Emerging Technologies Series
Theodore S. Rappaport, Series Editor

Sample Content

Online Sample Chapter

Introduction to Software Radio Concepts

Table of Contents

Preface.


Acknowledgments.


 1. Introduction to Software Radio Concepts.

The Need for Software Radios. What Is a Software Radio? Characteristics and Benefits of a Software Radio. Design Principles of a Software Radio. Questions.

The Purpose of the RF Front-End. Dynamic Range: The Principal Challenge of Receiver Design. RF Receiver Front-End Topologies. Enhanced Flexibility of the RF Chain with Software Radios. Importance of the Components to Overall Performance. Transmitter Architectures and Their Issues. Noise and Distortion in the RF Chain. ADC and DAC Distortion.

Introduction. Sample Rate Conversion Principles. Polyshase Filters. Digital Filter Banks. Timing Recovery in Digital Receivers Using Multirate Digital Filters.

Introduction. Comparison of Direct Digital Synthesis with Analog Signal Synthesis. Approaches to Direct Digital Synthesis. Analysis of Spurious Signals. Spurious Components due to Periodic Jitter. Bandpass Signal Generation. Performance of Direct Digital Synthesis Systems. Hybrid DDS-PLL Systems. Applications of direct Digital Synthesis. Generation of Random Sequences. ROM Compression Techniques.

Preface

Preface

Software radios represent a major change in the design paradigm for radios inwhich a large portion of the functionality is implemented throughprogrammable signal processing devices, giving the radio the ability tochange its operating parameters to accommodate new features andcapabilities. A software radio approach reduces the content of radiofrequency (RF) and other analog components of traditional radios andemphasizes digital signal processing to enhance overall receiverflexibility.

This change in the design paradigm for new radios has occurred so rapidlythat it has left a significant void in the educational material availableto train new radio engineers. Traditional radio engineering textbooksemphasize analog component-level design with little mention of theincreasingly important role of digital signal processing in performingthe central functions of the radio transceiver. Individual referencescovering the key analog and digital subsystems tend to be insufficientin that they fail to provide a full understanding of the interaction betweenthese subsystems.

I became acutely aware of this void when conducting research into thedevelopment of novel high-performance radios for the Defense AdvancedResearch Projects Agency (DARPA). While constructing radioprototypes, I found there was no comprehensive resource to which Icould point my students for information on how to build DSP-basedradios. This experience, combined with similar frustrations voiced bymy colleagues from both academia and industry, has led me to write thisbook on modern radio design principles. My goal in developing thisbook was to provide this necessary understanding of the interaction ofkey subsystems.

Software radios are emerging in commercial and military infrastructure.This growth is motivated by the numerous advantages of software radios.

1. Ease of design—Traditional radio design requires years of experience and great care on the part of the designer to understand how the various system components work in conjunction with one another. The time required to develop a marketable product is a key consideration in modern engineering design, and software radio implementations reduce the design cycles for new products, freeing the engineer from much of the iteration associated with analog hardware design. It is possible to design many different radio products using a common RF front-end with the desired frequency and bandwidth in conjunction with different signal processing software.
2. Ease of manufacture—No two analog components have precisely identical performance, necessitating rigorous quality control and testing of radios during the manufacturing process. However, given the same input, two digital processors running the same software will produce identical outputs. Thus, the move to digital hardware reduces the costs associated with manufacturing and testing the radios.
3. Multimode operation—The explosive growth of wireless has led to a proliferation of transmission standards, and in many cases, it is desirable that a radio operates according to more than one standard. For example, wireless carriers throughout the U.S. are deploying systems that make use of the GSM (Global System for Mobile Communications) standard in some markets and the IS-95 Code Division Multiple Access (CDMA) standard in other markets. Furthermore, the advent of third-generation wireless has introduced a number of standards within that framework. Traditionally, multimode operation has required multiple complete sets of hardware, increasing the size and cost of the radio. However, a software radio can change modes by simply loading appropriate software into the memory.
4. Use of advanced signal processing techniques—The availability of high speed signal processing on board the radio allows implementation of new receiver structures and signal processing techniques. Techniques such as adaptive antennas, interference rejection, and strong encryption, previously deemed too complex, are now finding their way into commercial systems as the performance of digital signal processors continues to increase. The impact will be enhanced range and quality of service to the consumer while reducing overall infrastructure cost for the service provider.
5. Fewer discrete components—A single high-speed digital processor may be able to implement many traditional radio functions such as synchronization, demodulation, error detection, and decryption of data, reducing the number of required components and decreasing the size and cost of a radio.
6. Flexibility to incorporate additional functionality—Software radios may be modified in the field to correct unforeseen problems or upgrade the radio. For example, it may even be possible to transmit software upgrades to the radio, such as a new vocoder to handsets, to improve overall system performance. Another important improved functionality is the capability of self-diagnosis of the radio and network operations, which means improved reliability with less human intervention.

Given these clear advantages and the increasing processing power availablein commercial digital signal processing devices, I anticipate thatradio engineers that software radios will become the standard approachfor radio design.

The challenge in creating the software radio is the broad scope of knowledgenecessary, including digital signal processing algorithms, RF circuits, software methodologies,and digital circuits. The approach in this text is to provide anunderstanding of key areas in radio design for the digital signalprocessing engineer. Forexample, a digital signal processing engineer must know the ramifications of the choices in RFparameters and the resulting limitations to be able to understand the appropriatesubsequent signal processing to account for these limitations. This bookreviews critical and interdependent radio subsystems from the perspectiveof the DSP engineer.

Chapter 1 provides a basic introduction to software radioconcepts, discusses the benefits of software radios, and sets thestage for discussing software radio design.

Digital signal processing engineers tendto know very little about RF engineering and, likewise, RF engineerstend to know very little about digital signal processing. However, to take fulladvantage of the software radio approach, these subsystems cannot be treatedseparately. Chapter 2 provides the digital signal processing engineerwith fundamentals in constructing RF front-ends and describesprocessing that can be performed in the digital domain to overcomeproblem areas in RF design.

Multirate digital signal processing usesdifferent sample rates, and this is the topic of Chapter3. This approach to signal processing is particularlyimportant in software radios where bandwidths and sample rates are highinitially and must be reduced for efficient subsequent processing.Multirate digital signal processing is commonly used to channelize theoperating band into distinct communication channels. Multiratedigital signal processing is also the foundation for modernsynchronization techniques.

Much of the flexibility of asoftware radio comes from being able to create arbitrary modulation typesdirectly within the digital domain. In many cases, the direct digitalsynthesis methods used to generate these signals are more than justdigitized realizations of analog techniques and afford the designer greaterfreedom in design signal waveforms. Chapter 4 surveys the topic ofdirect digital synthesis of modulated waveforms.

Analog to digital converters and digital to analogconverters, along with the power amplifier, are themost critical components in software radio design. The demands on thesecomponents can be very high. A rigorous understanding of the conversionprocess and the trade-offs between the resolution, sample rate, and dynamicrange of the resulting system are the focus of Chapter 5.

An important benefit of software radios is the ability to incorporatesophisticated algorithms, such as smart antennas, into the radio toenhance performance. Chapter 6 reviews the wide variety ofadaptive array algorithms and hardware implementation issues.

Thebasics of digital signal processing microprocessors, Field ProgrammableGate Arrays (FPGAs), andApplication Specific Integrated Circuits (ASICs) and how one would chooseone these alternatives for constructing a software radio are discussedin Chapter 7.

A systematic design approach tocreating software is essential to enable expandability of the radiocapability. Furthermore, as new applications are created to run over thesoftware radio, the radio itself must become transparent to the newapplications. Chapter 8 examines object-oriented programmingapproaches, including JAVA and Common Object Request Broker Architecture (CORBA) forcreating software radios.

Chapter 9 examines some examplesof software radios that have been built. The Software-DefinedRadio (SDR) Forum, a consortium of companies, universities, and researchorganizations, has defined guidelines and standards for the creationof software radios. A description of this standardized software radiois provided in this chapter.

If this book is being used for a course, there is much flexibility inselecting chapters to create a customized course. For the onesemester class, I recommend covering Chapters 1-3, Sections 4.1-4.8, 5.1-5.4, 6.1-6.6, 7.1-7.3, and Chapters 8-9.For a class on the quarter system, I recommend Chapters 1, 2, and 5, Sections 6.1-6.5, Chapter 8, and Sections 9.1-9.3. Although there is muchlatitude in mixing and matching sections to customize the course tothe instructor's objectives, I do recommend that Chapters 8and 9 be covered together as a single unit. Students who havean electrical engineering background in basic circuit analysis(typically junior-level), computer architecture (junior- orsenior-level), and communications (senior-level) have a sufficientbackground for all chapters in this book.

URLs included in the text and in citations were correct when the bookwas written. However, due to the dynamic nature of the World WideWeb, URLs may no longer be active. Periodic updates, information forinstructors, and errata to the book can be found athttp://www.softradios.com/book.html.Additional information about software radios can be found athttp://www.mprg.org/publications/pubs.shtml#Book

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