September 1976 | NTIA Technical Report OT 76-104

Measurements of Digital Systems in Gaussian Additive Noise and Interference

John R. Juroshek; G. E. Wasson


A series of experimental measurements are described that examine the performance of the five different digital modems in Gaussian noise and additive interference. These experimental results are then compared with theoretical predictions to determine if the performance of digital systems can be accurately predicted. Some of the modems tested are: frequency-shift keying (FSK), phase-shift keying with coherent detection (CPSK), and differentially encoded phase-shift keying with coherent detection (DESPSK). Also tested are two modems that use bandwidth conservation types of modulation. One of the bandwidth conservation modems uses minimum-shift keying (MSK) as its basic modulation format.

Test results are presented showing the results of interference from both unmodulated, continuous wave (CW) interference and modulated interference. For the modulated interference, the interfering signal has the same modulation format as the victim. The bit error rate of each of the modems is described as a function of signal-to-interference ratio and signal-to-noise ratio. The report also describes the effect of frequency offset of the interferer relative to the victim. Experimental results are then compared with theoretical predictions of the modems' performance in the given interference environments. Generally the measurements show that the amount of degradation from interference can be predicted at signal-to-interference ratios of 10 db or greater. However, somewhat larger errors were noted at signal-to-interference ratios of 5 dB.

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.

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