Cochannel and adjacent channel interference to GPS use

Abstract

The growing international user base for the Global Positioning System, coupled with the increasing number of critical applications, is fostering the development of ground and satellite based augmentations. There is a concern that those augmentations that share the registered GPS band, especially using code division multiple access in a fashion similar to GPS, may cause harmful interference.In this paper, the impact of both cochannel and adjacent channel interference from these proposed services to the signals in the GPS LI band is analyzed. Laboratory test results are also presented to support the results obtained through analysis. The carrier-to-noise spectral density ratio (C/N 0 ) degradation and excess tracking error due to cochannel interference are used as performance metrics. The analysis and test results indicate that under certain conditions, when the Interference-toSignal Ratio (ISR) is greater than 10 dB, the C/N 0 degradation could be as high as 7 to 9 dB and the excess tracking error as high as 2 to 3 meters rms. The loss of C/N 0 could mean the loss of significant interference margin for safety-of-life applications. The resultant degradation in tracking error will exceed the error budget of the GPS receiver specification for aviation applications. To be certain that this level of degradation is not experienced by the GPS receiver in critical applications, it is suggested that the proposed services not operate in the GPS LI band. For the services in adjacent bands fo LI, it is recommended to use appropriate emission limits obtained on the basis of total interference, from all the proposed services.

Interference Mitigation for the GPS Receiver Utilizing the Cyclic Spectral Analysis and RR-MSWF Algorithm

“…The adjacent channel interference and/or the cochannel interference from these systems and/or from PPDs may cause the GPS receiver serious performance degradation when their strength is much stronger than that of the GPS signal. For the adjacent channel interference, it mainly arises from the communication satellite or from the wireless mobile communication system whose transmitting frequency or harmonics is close to the frequency of GPS signal [4][5][6]. While for the cochannel interference, it mainly arises from the other satellite navigation system such as Galileo or quasi-zenith satellite system (QZSS) which shares the same downlink frequency with the GPS signal [1].…”