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A software radio is a radio whose channel modulation waveforms are defined in software. All wireless telephones are controlled by this software. Written by the leader in the field, this book covers the technology that will allow cellular telephones to greatly expand the types of data they can transmit.
This text first introduces the fundamental concepts of the software radio. These include the placement of the ADC near the antenna, the criticality of realtime streams, and the mix of implementation alternatives from baseband DSP through a variety of SDR alternatives. It then establishes the commercial and military drivers for an open-architecture for software-defined radios. Before addressing subsystem architectures, it identifies the aspects of the radio systems architecture that drive complexity. This is essential because SDR projects often fail because of unanticipated software complexity. It then covers the architecture principles by subsystem from antenna and RF conversion through DSP and software. It completes the core technical discussion by showing how to balance software computational demand against hardware processing capacity to produce software radios that meet specifications, on time and within budget. The text concludes with an overview of applications, including smart antennas and a mobile disaster-relief case study.
This first chapter provides an overview of the software radio (r)evolution shaping wireless systems engineering today. It introduces the software radio functional architecture. It also explains in more detail how analog, digital, and software radios form an implementation continuum, the software radio phase space. After completing the program of study represented by this text, a topnotch systems engineer will be able to position each project in implementation space as the technical, risk, and economic needs of the application dictate. The goal is to introduce most of the new concepts presented in this text.
It is worth emphasizing that this book does not try to sell the software radio. On the contrary, a software radio approach sometimes yields an ineffective product. One must fully appreciate how analog, digital, and software-intensive approaches complement each other. One may then understand the advantages and pitfalls of each. Ultimately, the reader should be able to decide when, where, and how to apply software radio technology. Thus empowered, each of the many participants in the software radio architecture (r)evolution will be able to contribute with greater impact.
This section presents a top-down approach to the software radio architecture. The top level components of an ideal software radio handset consist of a power supply, an antenna, a multiband RF converter, and a single chip containing ADC and DAC. The on-chip general-purpose processor and memory that perform the radio functions are illustrated in Figure 1-1...
Introduction and Overview.
The Radio Spectrum and RF Environment.
Systems-Level Architecture Analysis.
Node-Level Architecture Analysis.
Segment Design Tradeoffs.
Antenna Segment Tradeoffs.
RE/IF Conversion Segment Tradeoffs.
ADC and DAC Tradeoffs.
Digital Processing Tradeoffs.
Software Architecture Tradeoffs.
Software Component Characteristics.
This is therefore a systems engineering text. It is not a design text. This book will not help you design a better filter for a specific SDR. It will, however, help you make better decisions about how to partition the end-to-end system filtering requirements. It will help you allocate the critical functions of dynamic range and processing capacity in such a way that the filter's design constraints are well founded and that the hardware platform, firmware, and software support the filtering requirements of the software radio. This book will also give you quantitative criteria for deciding whether to host that filter in an analog package, digitally on an applications-specific integrated circuit (ASIC), or in software on the latest digital signal processing (DSP) chip. In addition, if the filter is to be implemented in software, this book will give you the skills to ensure that the software is well structured and performs robustly--even when many tasks are competing for processing resources. The appropriate host for such a filter changes over time. Commercial filter ASICs may become obsolete as DSP processing capacity increases, changing the systems-level tradeoffs. As needs, technology, and team expertise evolve, the effective choice will also change. The effective choice also changes as a function of the top-down design constraints placed on the radio system by the economics of the marketplace and by the larger systems architecture. And the effective choice may be to not implement the filter per se at all, but to procure it as part of an off-the-shelf subsystem. As we migrate to systems on a chip, this means the filter may entail intellectual property that has to be partitioned and protected, and yet has to be leveraged by the rest of the system. A sound systems-level architecture facilitates this process, while an inferior architecture inhibits it. The reduced time to market and cost efficiency of such buy-versus-make choices also require balancing the capabilities and design constraints given competing technical and economic constraints.
Software-radio is therefore an interdisciplinary technology, so this is an interdisciplinary text. The radio-oriented chapters are written for people with strong software background but little background in radio engineering. Software radio is about wideband radio frequency (RF) hardware that is given its "personality" by software. Therefore, the software people have to understand the RF hardware and air interface standards to the degree set forth in this text in order to function effectively on an interdisciplinary team. Similarly, the software-oriented chapters are written for people with strong background in RF, analog radio, or DSP but little background with large-scale software. And software radio is increasingly about complex, large-scale software. One of the revolutionary aspects of software radio is that knowing how to code a radio algorithm in C on a DSP just doesn't give a software engineer the core skills needed to contribute effectively to software radio architecture. In fact, that experience becomes a liability if it causes one to minimize the importance of the new large-scale software engineering methods like CORBA. In addition, European readers will have to be patient with the tutorial material on SDL, the ITU-standard Specification and Description Language. In teaching the software radios course on which this book is based, I have found that US engineers make little use of formal methods for specifying radio func-tions. ETSI's emphasis on formal methods and the widespread use of SDL in support of European standards-setting process has not reached across the Atlantic yet. As a result, U. S. practitioners of radio engineering often try to do with pencil and paper what their European counterparts do on a computer--define new air interface standards. This text's treatment of UML extends the SDL material.
This text has several companions. The first is the Special Issue of the IEEE Journal on Selected Areas in Communication on Software Radios, published in April 1999 by the IEEE (New York). This JSAC is a surrogate graduate-level text. As such, it addresses related graduate-level research topics including mathematical structure of the software radio, virtual radios, advanced digital filter ASICs, smart antennas, and other advanced techniques. The IEEE Press Compendium Software Radio Technology by Mitola and Zvonar extends the JSAC with both earlier and more recent technical papers. Prof. Friedrich Jondral's course text in German (U. Karlsruhe) relates fundamental digital radio to SDR.
The dedication of this text to the "public interest" envisions the resulting affordable, robust, high-quality radio services as beneficial to the public interest. If coalition partners can cooperate better using software radios in peacekeeping roles, then that serves the public interest. If governments can acquire radio platforms at lower and more predictable cost, then that makes resources available for other public priorities. The focus of this text is the architecture. In this text, architecture is defined as the consistent set of functions, components, and design rules that promote open-architecture evolution of complex radio systems.
The book is organized for ease of access by a variety of readers. Chapters 1- 3 provide the high-level background needed for a general understanding of how software radio fits in the larger telecommunications technology. Systems engineers and program mangers should have a solid grasp of chapters 4 and 5 in order to lead architecture evolution. Program managers and software engineers need to pay particular attention to the discussion of complexity drivers. Like any other software-intensive project, software radios are subject to subtle changes of the scope of the software. These chapters attempt to forewarn and thus forearm the team against factors that can drive software complexity and processing requirements out of the bounds of time, personnel, or processing capacity available on the project. The chapters on subsystems (6-12) focus on the requirements that software radio brings to the hardware and software segments. The software-oriented chapters are designed to be useful to hardware-oriented readers and the hardware-oriented chapters are designed to be useful to software-oriented readers. Sufficient basics on signal processing are included to provide a relatively self-contained treatment. The concluding chapters (13-16) provide examples of how to apply software radio architecture to create robust yet affordable multiband multi-mode communications systems.
I really enjoy interacting with those of you who are out there creating SDR systems and propelling the software radio evolution forward. Since you have purchased this text, you probably would like to use the knowledge you gain. A few spreadsheet design tools can help with some important aspects of that task. These are the software radio spreadsheets. You get access to them via the author's software radios web site. The URL is http://ourworld.compuserve.com/homepages/jmitola. The site is for folks who purchased this text. By follow-ing the instructions on the site, you can get access to the design aids. I also welcome questions from readers about this text, or anything in the area of software radio technology.