Correction of pseudorange errors in Galileo and GLONASS caused by biases in group delay

Abstract

Both Galileo E1 OS and GLONASS L1 signals require a wider pre-correlation bandwidth than GPS C/A. The GLONASS channels are uniformly spaced on a frequency division grid, and occupy some 8MHz in total, whereas Galileo E1 OS has sidebands that are separated by about 2MHz. Being wideband is an advantage because of sharper correlation peak (Galileo) and better interference rejection; however it also exposes distant spectral components of the signal to larger variations of the front-end transfer function. Group delay differences are mostly caused by the analog components like the SAW filter or the integrated analog front-end whereas magnitude can be affected by signal conditioning done in the digital domain, for example by the insertion of recursive filters aimed at interference cancellation. These impairments must be estimated and compensated. The benefits for the consumer multiconstellation receiver are an improved precision and an enriched set of potential applications, including timing.

Estimation of the GPS to Galileo time offset and its validation on a mass market receiver

“…The broadcast GGTO introduces virtually no estimation error but requires an accurate knowledge of all the other possible pseudorange and velocity biases introduced by the receiver. The Teseo-II chipset convey GPS and Galileo signals through the same RF path, such that the pseudorange biases induced by the total transfer function of analog plus IF filters, at the receiver side, are negligible [14]. Additional analog filters were inserted by the front-end of the sample record & replay device, which was used as signal generator.…”

“…The broadcast GGTO parameters only corrects for timing differences originated at the satellite transmit side. Other inter system biases introduced by the receiver, like group delay differences [14] or delays generated during the baseband or DSP processing, cannot instead be directly recovered. For this reason, an estimator is proposed, as a complement to the broadcast information.…”