Pilot-aided GNSS data demodulation performance in realistic channels and urban live tests

Abstract

This paper presents a novel technique to improve data demodulation performance of global navigation satellite system (GNSS) signals with data and pilot signal components (e.g. suitable for Galileo E1B/C open service (OS) signals [1]). This technique is called Pilot-aided data demodulation because it uses the coherence between residual phase errors on the data and the pilot components of the GNSS signal to perform channel estimation. Differently from standard techniques [2], where the carrier phase of the received signal is tracked by means of a phase locked loop (PLL) on the pilot component and such estimation is used to control the data correlators, the pilot aided technique does not necessarily requires a PLL, but it can work as well with a simple and more robust frequency locked loop (FLL) or just with open loop frequency estimation. This is particularly valuable in challenging environments, such as urban scenarios, where the phase lock is hard to be maintained for long periods. The main advantage of this technique is clearly visible in terms of page error rate under fades and multipath. In open sky scenarios and additive white Gaussian noise (AWGN) assumption, it exploits the data plus pilot combination, doubling de-facto the power of the received signal with respect to the single data-less component, but it also introduces additional noise (similar to squaring losses) due to the non-linear operations between data and pilot prompt correlators. The output of such technique can then be used to feed the proper decoder according to the coding scheme adopted in the GNSS navigation message (e.g. Viterbi decoder for E1B).