TABLE OF CONTENTS The preceding chapters described the satellite navigation systems and their user equipment. This chapter reviews a number of techniques that enhance the accuracy, robustness, and reliability of GNSS. Section 8.1 discusses how additional infrastructure may be used to improve GNSS positioning accuracy using differential techniques, while Section 8.2 describes how carrier phase techniques may be used to obtain high-precision position and attitude measurements under good conditions.
Sections 8.3 and 8.4 review techniques for improving GNSS robustness under difficult conditions, covering operation in poor signal-to-noise environments and multipath mitigation, respectively. Section 8.5 describes how signal monitoring networks may be used to protect users from the effects of faulty satellite signals. Finally, Section 8.6 describes how SPS GPS users can use semi-codeless tracking to gain the benefit of dual-frequency operation with legacy signals.
The correlated range errors due to ephemeris prediction errors and residual satellite clock, ionosphere, and troposphere errors vary slowly with time and user location. Therefore, by comparing pseudo-range measurements with those made by equipment at a presurveyed location, known as a reference station or base station, the correlated range errors may be calibrated out, improving the navigation-solution accuracy. This is the principle behind DGNSS. Figure 8.1 illustrates the concept.
This section describes some different implementations of DGNSS, covering a local area with a single reference station or a regional or wide area with multiple reference stations. Before this, the spatial and temporal correlation properties of the various GNSS...
