Software-Defined Radios (SDRS) eliminate incompatibilities between the command and control radio systems of different armed-services branches. They also link the communications systems of allied and coalition forces, thereby helping these different forces operate as one cohesive unit. For test engineers, however, SDRs pose a number of challenges. To help these engineers, Anritsu Co. (Morgan Hill, CA) has released a six-page application note titled, "Understanding SDRs and Their RF Test Requirements."
The paper opens by defining SDR and describing current SDRs, which span 2 MHz to 2 GHz and beyond. Currently, the military relies on high-frequency (HF), very-high-frequency (VHF), and ultra-high-frequency (UHF) radios for different applications. SDR encompasses all three radio types while covering higher frequencies. Although the hardware may vary, the radio's software portion is defined by the Software Communications Architecture (SCA). Right now, the SCA specification has two methods for communications between SDR modules: using the middleware Common Object Request Broker Architecture (CORBA) and the Hardware Abstraction Layer (HAL) for high-demand communications between embedded hardware.
To illustrate the test challenges involved in SDRs, the note profiles some example radios. It then explains the test challenges involved with a leading development platform—the SDR-3000 from Spectrum Signal Processing (Burnaby, BC, Canada). This platform's receiver spans almost3 GHz with modulation bandwidths as wide as 30 MHz. Ideally, a test solution would perform measurements on every possible SDR hardware/software combination or waveform. Yet such solutions would demand that the test-equipment manufacturer program instrumentation for up to 30 or more SDR waveforms.
The MG3700A Vector Signal Generator and Signature High Performance Signal Analyzer are one example of a testing solution for SDR front-end performance. The MG3700A spans 250 kHz to 3 GHz (and 6 GHz as an option) with 0.01 Hz frequency resolution. This generator can be programmed to emulate any form of waveform or pair of waveforms. The test tools for SDR RF measurements must emulate the behavior of both the radio's receiver and transmitter sections with adequate frequency range, wide modulation and demodulation bandwidths, wide dynamic range, and excellent level accuracy. Only then can they handle existing and emerging SDR designs.
Anritsu Co., 490 Jarvis Dr., Morgan Hill, CA 950372809; (408) 778-2000, FAX: (408) 776-1744, Internet: www.anritsu.com
