Chapter 6: DIFFERENTIAL GNSS

DIFFERENTIAL GNSS

6.1 INTRODUCTION

Differential global navigation satellite system (differential GNSS; abbreviated DGNSS) is a technique for reducing the error in GPS-derived positions by using additional data from a reference GNSS receiver at a known position. The most common form of DGNSS involves determining the combined effects of navigation message ephemeris and satellite clock errors [including the effects of propagation] at a reference station and transmitting delays corrections, in real time, to a user s receiver. The receiver applies the corrections in the process of determining its position [94]. They include:

• Corrections for completed: (1) selective availability (if present) (2) satellite ephemeris and clock errors.
• (3) ionospheric delay error and (4) tropospheric delay error.
• Still other error sources cannot be corrected with DGNSS: (1) multipath errors and (2) user receiver errors.

6.2 DESCRIPTIONS OF LADGPS, WADGPS, AND SBAS

6.2.1 Local-Area Differential GPS (LADGPS)
LADGPS is a form of DGPS in which the user s GPS receiver receives real-time pseudorange and, possibly, carrier phase corrections from a reference receiver generally located within the line of sight. The corrections account for the combined effects of navigation message ephemeris and satellite clock errors (including the effects of SA) and, usually, atmospheric propagation delay errors at the reference station. With the assumption that these errors are also common to the measurements made by the user s receiver, the application of the corrections will result in more accurate coordinates [117].