Recommendations on digital distortion requirements for the civil GPS signals

Rise-/fall-time asymmetries of up to 5 ns in the generation of the baseband C/A code signal onboard the GPS satellites have been inferred and noted to be a source of positioning errors, particularly in differential GPS applications. Such asymmetries have been dubbed ldquodigital distortionrdquo in previous literature. Digital distortion, if present, would have different effects for user equipment tracking the new GPS civil signals with their differing modulation characteristics. This paper analyzes the potential effects of digital distortion on user equipment for the new civil GPS signals and provides recommendations on requirements to control this distortion within the civil signal interface specifications.