TITLE:
Single Frequency WAAS Augmentation Observations (L1 vs. L5) on a Ground Based GPS L1 C/A Solution
AUTHORS:
Marc-Antoine Fortin, Jean-Christophe Guay, René Jr. Landry
KEYWORDS:
GPS L1, WAAS L1, WAAS L5, MOPS, Pseudorange Noise
JOURNAL NAME:
Positioning,
Vol.5 No.3,
August
15,
2014
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.