Design Article
SDR Basics Part 3: Transmitters
Bruce A. Fette
11/20/2007 3:04 AM EST
As new and more complex communication standards are developed around the globe, the demand for new transceiver architectures will also grow. However, more and more often the available capital, both financial and human, limits the designs that can be tackled. Fortunately, software radio technology is available for a select and growing group of these architectures that allow a single platform to leverage into many diverse designs. As seen here, this has many distinct advantages and is not limited to interoperability, investment retention, and great flexibility.
As with any software project, quite often the potential is only limited by the imagination of the designer. The great advantage is that as in any software project, if there is a design error, it is as simple as backspace, type, and enter to fix the problem. Fortunately, the last decade has seen significant advances in semiconductor technology that have caused impressive gains [17] not only in performance but also in cost. SDR is one area that has greatly benefited from these varied technologies and will continue to do so as the meaning of SDR is developed, just as has been the case in the history of programming languages.
Although SDR is not the solution to all communication problems, it will offer robust solutions to challenging design issues in the coming years. These issues include phased array technology, location services, interoperability, and complex concepts yet to be defined. However, there are still some challenges preventing full acceptance of this technology. The two main issues are cost and power. Interestingly, these two have a first-order positive relationship; solve one problem and the other will only get better. Without low power, user devices will not be able to take full advantage of SDR technology. Clearly, the power issue comes from the need for high-performance components. High performance means ultra-linear devices. High-linearity devices mean low efficiency through high-standing currents.
Therefore, if the issue of how to design high-linearity devices with lower power can be solved, and it will, then costs too will also fall, opening the door for many other applications. So the key to continued SDR development and evolution is continued device improvement down the Moore's law curve and continued interest in flexible radio architectures. Despite these challenges, the current state of performance is more than sufficient for engineers and manufacturers to seriously begin to investigate the possibilities of SDR.
References
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2. J. Mitola, III, "Software Radio"Cognitive Radio," http://ourworld. compuserve.com/homepages/jmitola/.
3. B. Brannon, D. Efstathiou, and T. Gratzek, "A Look at Software Radios: Are They Fact or Fiction?" Electronic Design, (December 1998): pp. 117"122.
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12. B. Brannon, "Overcoming Converter Nonlinearies with Dither," Analog Devices Applications Note AN-410, www.analog.com.
13. W. Kester, "High-Speed Sampling and High-Speed ADCs," Section 4, High-Speed Design Techniques, www.analog.com.
14. W. Kester, "High-Speed DACs and DDS Systems," Section 6, High-Speed Design Techniques, www.analog.com.
15. About CDMA and CDMA University. Available at http:// www.qualcomm.com.
16. Specifications. Available at http://www.3gpp2.org.
17. R. H. Walden, "Analog-to-Digital Converter Survey and Analysis," IEEE Communications Magazine, 17 (April 1999): pp. 539"550.
18. H. Nyquist, "Certain Topics in Telegraph Transmission Theory," AIEE Transactions, 47 (April 1928): pp. 617"644.
19. AD6645 Datasheet. Available at http://www.analog.com.
Copyright: Printed with permission from Newnes, a division of Elsevier. Copyright 2008. "RF & Wireless Technologies" by Bruce A. Fette. For more information about this title and other similar books, please visit www.newnespress.com.
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