Testing Oscillator Stability as a Limiting Factor in Extreme High- Sensitivity GPS Applications

Oscillator instability is one of the most critical error sources impeding the progress of high-sensitivity GPS applications in signal-degraded environments, especially indoors, in urban canyons, and under heavy foliage. Augmentations such as assisted GPS can improve availability somewhat, but receiver sensitivity is still fundamentally limited by oscillator stability and other factors such as user dynamics. In this paper, the impact of oscillator stability is empirically tested by conducting extremely long coherent integrations and determining the degradation in received signal strength caused by each of a set of test oscillators. Over short intervals of a few seconds, oscillator errors are dominated by characteristic random fluctuations, and by external error-inducing sources such as vibrations, temperature shocks, and accelerations. By limiting those externallyinduced errors, the optimum performance of each specific oscillator is found.