SBAS & DGPS



Space Based Augmentation System 'SBAS'


A SBAS is a more recent and different type of differential correction. It incorporates a modular architecture, similar to GPS, comprised of a Ground Segment, Space Segment, and User Segment: The Ground Segment includes reference stations, processing centers, a communication network, and Navigation Land Earth Stations (NELS)The Space Segment includes geostationary satellites (For example, EGNOS currently uses Inmarsat transponders).The user segment consists of the user equipment, such as a BlueStar GPS receiver and antenna In a SBAS a separate correction is made available for each error source rather than the sum effect of errors on the user equipment's range measurements. This results in a more consistent system performance regardless of geographic location with respect to reference stations. Specifically, SBAS calculates separate errors for the following:


Local Differential Correction 'DGPS'


Local Differential GPS, the most common form of DGPS, is essentially a differencing process that removes sources of error from the GPS position solution and improves the integrity of the GPS position solution. This type of differential is often called Local Based Augmentation System (LBAS) with corrections computed from a base station (where the antenna is set on a known point) and applied to the rover GPS either in real-time or in a post-processing software. There are a number of methods of local differential measurement corrections. With BlueStarGPS proprietary differential correction and superior performance, the effects of satellite orbit and timing errors are compensated.





Conventional real-time differential:


This is the most common form of correcting GPS errors in real-time with corrections sent from the base station to the rover GPS receiver by some form of communications equipment. Conventional real-time differential uses C/A code range measurements and their associated corrections. Carrier phase corrections are not used with this form of differential technique.


Post Processing:

This method is often used when either higher accuracy than achievable through conventional differential is needed, or a conventional form of real-time corrections is not available in the region where the rover receiver is being operated. Depending on receiver hardware and the methodology used for the post-processing, performance can be from many centimetres to millimetres precision. A variety of 3rd party software packages are available to post process GPS raw measurement data.


Real-Time Kinematics:


This method uses more sophisticated techniques to resolve the number of wavelengths between the satellite and the user, to provide centimetre-level positioning (or better) in real-time. This technique uses high-end receiver hardware, antennas, and internal operating software to compute accurate position solutions.