GPS C/N0 estimation in the presence of interference and limited quantization levels

The carrier-to-noise density ratio (C/N₀) is considered an important parameter describing the GPS receiver performance. This paper compares the performance of two popular coarse-acquisition (C/A) C/N₀ algorithms appearing in literature: the variance summing method (VSM) (Psiaki et al., 2003, Psiaki, 2001), and the power ratio method (PRM) (Van Dierendonck, 1996, Sayre, 2003), in terms of their estimates in 1) additive white Gaussian noise (AWGN), 2) narrowband continuous wave interference (CWI), 3) their response to quantization and saturation effects, and their 4) dynamic range. The algorithms were implemented as a part of a software receiver. Two LI GPS data sets are examined; one was obtained from a GPS raw data collection setup, while the other was obtained from a GPS signal simulator. The collected set was stored with almost constant C/N₀ level while the simulated one contained variable C/N₀ levels. The effect of adding AWGN on the C/N₀ estimate was directly proportional with the noise power. The C/N₀ estimates suffered more when the CWI frequency was closer to the IF of the receiver. The PRM suffered from saturation at higher C/N₀ levels. The VSM showed good tracking at high C/N₀ levels and better immunity to limited quantization levels, while its C/N₀ estimate suffered from rapid fluctuations in power levels when sudden power steps occurred