Interference Effects on the GPS Signal Acquisition
نویسنده
چکیده
Intentional or unintentional interference and jamming is one of the major concerns in using the Global Positioning System (GPS) in various critical applications. In spite of the GPS frequency bands being protected by International and Federal Communication Commission (FCC) frequency assignments, there is always a chance of disruption of the GPS signal availability in critical times and applications. The GPS system has advantages over narrow-band navigation systems as the signals are spreadspectrum and receiver design techniques can eliminate most of the interference signals. The various sources of unintentional jamming are out-of-band interference caused by nearby transmitters, harmonics of ground transmitters, signals from nearby platforms, pulsed interference and accidental transmission of signals in the wrong frequency band. Any signal or its harmonics near the GPS L1 and L2 frequencies are a potential source of interference. The aim of this paper is to analyze the effect of some interference sources on the GPS spectrum during the acquisition process. The acquisition process determines the signal peak after correlation and then compares it with a detection threshold to determine the success of acquisition. Interference signals cause distortion in the GPS signal resulting in an incorrect, or no correlation peak, during acquisition. The interference signals analyzed in this paper are the continuous wave interference, broadband noise and pulsed interference signals. A GPS simulator (GSS 6560) was used along with a signal generator (E 4431B) and an interference combiner (GSS 4766) to generate the interference signals. The signals were collected using a GPS front end (Signal Tap) data logger. The paper discusses the effect of various interference signals on noise power, signal to noise ratio and effect of coherent/non-coherent integration times on the acquisition process.
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