A. J. Van Dierendonck

Evolution to modernized GNSS ionoshperic scintillation and TEC monitoring

The ionosphere, if not modeled sufficiently well, is the largest contributor of error in single frequency GNSS receivers. Modeling ionospheric effects is a major concern for a number of GNSS applications. Ionospheric disturbances induce rapid fluctuations in the phase and the amplitude of received GNSS signals. These rapid fluctuations or scintillation potentially introduce cycle slips, degrade range measurements, and if severe enough lead to loss of lock in phase and code. GNSS signals, although vulnerable, themselves provide an excellent way to measure the ionospheric effect continuously worldwide. Until now, ionospheric monitoring was performed using receivers such as the GSV4004B receiver, which was largely based on GPS only dual frequency receivers. Semi-codeless tracking of the GPS L2 signal greatly limited the accuracy, robustness and utility of the ionospheric TEC measurements and was useless for scintillation measurements on L2. The GPS modernization program, the restored GLONASS, and the upcoming GNSS constellations (Galileo and Compass) bring forth huge benefits for ionospheric monitoring. This paper introduces the NovAtels next generation GNSS ionospheric scintillation and TEC monitor, the GPStation-6. By incorporating the proven GSV4004B receiver design with the ability to track multi-constellation, multi-frequency, GNSS measurements, the new receiver engine provides robust and less noisy ionospheric measurements.

Design of the signal and data format for wide area augmentation of the Global Positioning System

The wide area augmentation system (WAAS) is being deployed by the Federal Aviation Administration (FAA) to augment the Global Positioning System (GPS) with additional ranging signals and a supporting ground network. The augmented system can be used as the primary position sensor for enroute through precision approach air navigation. Specifically, the WAAS provides the following three services: integrity monitoring to improve safety; a ranging function to improve time availability and continuity of service; and differential GPS corrections to improve accuracy. This paper describes the design of the WAAS signal and data format. It states the design objectives and describes the basic approach. Then, it analyzes the correction update rates, message duration, messaging rates and the use of forward error correction. This paper does not: give a basic description of the WAAS, analyze the non-interference properties of the signal, or give a description of the data fields.

Recommendations on digital distortion requirements for the civil GPS signals

Rise-/fall-time asymmetries of up to 5 ns in the generation of the baseband C/A code signal onboard the GPS satellites have been inferred and noted to be a source of positioning errors, particularly in differential GPS applications. Such asymmetries have been dubbed ldquodigital distortionrdquo in previous literature. Digital distortion, if present, would have different effects for user equipment tracking the new GPS civil signals with their differing modulation characteristics. This paper analyzes the potential effects of digital distortion on user equipment for the new civil GPS signals and provides recommendations on requirements to control this distortion within the civil signal interface specifications.

RTCA SC-159 Wide Area Integrity Broadcast/Wide Area Differential GPS status

The Wide Area Integrity Broadcast (WIB) (formerly the GPS Integrity Channel-GIC) will use a network of ground stations at known locations to determine the status of every GPS satellite in view. It will then broadcast satellite health to GPS users in real time from a geostationary satellite (GS), thus providing system integrity. This broadcast will also include error estimates for the same GPS satellites that are valid over a specified region, which may include one or more countries or continents. These estimates, if accurate enough, can be used as differential corrections. This concept is called Wide Area Differential GPS (WDGPS). In addition, the broadcast signal will be modulated with a pseudo random noise (PRN) code that is synchronized with GPS time. Thus, it can also be used for ranging to augment the GPS system, thus improving system availability and continuity.<<ETX>>