Assessment and Handling of CA Code Self-Interference During Weak GPS Signal Acquisition (Preprint)
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH SENSORS DIRECTORATE
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This paper presents an analysis of GPS CA code self-interference, its impact on the acquisition of weak GPS signal when coexisting with strong GPS signals, and means to mitigate the interference to allow successful acquisition of the weak GPS signals using software GPS receivers. Current software GPS receivers are capable of acquiring and tracking satellite signals with CN0 as low as 24 dB, which is the sensitivity limit of a stand-alone GPS receiver. To achieve this level of sensitivity, there cannot be substantial interference from other satellites with strong signal levels. In practicality, however, the weak signals may coexist with much stronger signals from other satellites. This may happen when only a limited area of the sky is exposed to a receiver such as in the case of navigating in city canyon or under forest canopy. The presence of the strong signals may produce higher cross correlations between the strong signals and a weak signal, resulting in complete loss or false acquisition of weak signals which maybe necessary in helping to determine the user position. Software algorithm are developed that can successfully remove the strong satellite signals from the GPS receiver input. The resulting net input signal can then be used to acquire the weak signals. Experiments using both simulation and simulator data show that with the removal of strong satellite signal from the input, it is possible to acquire weak satellite near the sensitivity limit.
- Navigation and Guidance
- Radio Communications