Single Frequency WAAS Augmentation Observations (L1 vs. L5) on a Ground Based GPS L1 C/A Solution

Abstract

This paper presents observations on the WAAS L1 and L5 signals quality and their impact on the robustness of the navigation solution by quantifying the contributions of each broadcasted differential correction. This work is undertaken with the intent of defining performance benefits of L5 by dual frequency WAAS users and is to provide useful material for Minimum Operational Performance Standard (MOPS) development. In this perspective, a study of the WAAS signal characteristics is first carried out. The information gathered is then used to compare various GPS solutions in terms of frequency diversity, satellite diversity, pseudorange noise and different signal corrections and their impacts. These solutions are compared against a reference standalone GPS solution. All statistics are computed with respect to a post-processed Novatel Waypoint Real-Time Kinematics (RTK) GPS L1/L2 semi-codeless static solution, considered as the reference. A discussion on some simplifications with respect to specifications (i.e. MOPS) that could be considered by receiver manufacturers closes the paper. It is confirmed that the current WAAS navigation message definition is the same on both the L1 and L5 frequencies, the latter further being Manchester coded, thus avoiding data ambiguity. The +5 dB SNR on L5 has minor impacts in terms of reliability and continuous availability in the presented scenarios, but would become especially beneficial in hostile environments, despite a greater number of pulsed interferers. Another demonstration is that the WAAS message varies slightly from one WAAS satellite to another, even if corrections are generated centrally. Finally, it is observed that WAAS and GPS signals pseudorange noise are comparable on a "per frequency" basis.

An Analysis of SBAS Signal Reception in Space

“…A previous study assessing the accuracy of the WAAS L1 and L5 signals was published in 2008, which characterized signal noise and biases, and found that the WAAS signals were predictably noisier than GPS (roughly 4 m, as compared to 1 m for GPS), in keeping with the narrower transmitted bandwidth [12]. Similar conclusions were drawn by Wanninger in [11] and Fortin et al in [27]. The most thorough study of WAAS ranging is found in [13], with a discussion of SBAS ranging errors due to receiver design-specific biases, contributions of multipath at the user's station or in the ground infrastructure of the WAAS system, the difficulty in orbit and clock parameter determination for GEO satellites, code carrier divergence, and others based on a thorough understanding of the WAAS infrastructure.…”

Implementation Strategies for a Universal Acquisition and Tracking Channel Applied to Real GNSS Signals

“…This simplification is useful in analyzing signals, as the associated navigation message does not need to be accounted for. Moreover, multi-frequency signals being characterized by different paths, the extra time offset may then be neglected [ 50 ]. Noise is then quantified as the standard deviation of the second derivative of the pseudo-range : where: is the propagation time; is the number of complete code; is a complete code period; is the chip index of the primary code; is the phase of the chipping rate clock; is the chipping rate; is the pseudo-range noise.…”