Jeffery A. Wepman and J. Randy Hoffman

Abstract:

Software defined radios (SDR’s) represent a departure from traditional radio design. There is some mystique about what SDR’s are, how they are designed, how they operate, and how performance is determined or verified. This report provides insight into some of these SDR aspects by presenting a detailed example SDR receiver design along with a set of performance measurements at various stages of the receiver. For this example, an Advanced Mobile Phone System (AMPS) cellular B-band base station receiver was configured using SDR technology. The architecture consists of a cellular B-band analog downconverter and digitizer, a digital downconverter that operates in a personal computer, a first-in, first-out (FIFO) buffer memory board, and an analog audio processor. The modular architecture permits signals to be observed at several stages of processing: the digitized IF output, the digitally downconverted and filtered baseband output, the digital FM demodulator output, and the analog audio output. A wide variety of measurements under various RF input signal conditions were made at each of the processing stages. Results of particular interest include the effects of aliasing and the ability to detect a low-level desired signal in the presence of a high-level, in-band interfering signal. The SDR AMPS receiver, while possessing the inherent flexibility advantages of SDR’s, easily met the TIA/EIA-712 cellular base station standards for adjacent and alternate channel desensitization, intermodulation spurious response attenuation, and protection against spurious response attenuation.

Keywords: radio frequency; baseband; aliasing; analog-to-digital converter; demodulation; digital downconverter; downconverter; intermediate frequency; intermodulation; software defined radio (SDR); spurious response

Disclaimer: Certain commercial equipment, components, and software may be identified in this report to specify adequately the technical aspects of the reported results. In no case does such identification imply recommendation or endorsement by the National Telecommunications and Information Administration, nor does it imply that the equipment or software identified is necessarily the best available for the particular application or uses.

For questions or information on this or any other NTIA scientific publication, contact the ITS Publications Office at ITSinfo@ntia.gov or 303-497-3572.

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