Precise point positioning method for a static survey in a high multipath environment

Abstract

Precise point positioning (PPP) methods are generally considered to be point solution methods using undifferenced code and carrier phase measurements. Since the measurements are undifferenced, a means of reducing systematic errors in the measurements is generally used. Precise orbit and satellite clock values from IGS or other organizations are most often used to reduce system biases. PPP methods promise decimeter level positioning or better in stand-alone operation. Many PPP methods rely on code phase. These methods are subject to code multipath and hence typically use long smoothing filters and L1/L2 measurements to reduce multipath. As a result, these methods take a long time to converge to decimeter level accuracies. However, once they do converge, they provide the means for kinematic applications. Other PPP methods are carrier phase only methods. Some of these methods are attempting various types of ambiguity resolution. These show some promise and are providing interesting results. At SRI International, we often have need to provide a stationary survey in an environment that may have very high multipath. We are interested in rapidity of convergence of stand-alone carrier phase positioning methods. We use an IGS rapid ephemeris. This paper describes a carrier phase only solution based on a method derived from weighted batch least squares. Preliminary results show reliable sub-decimeter positioning after six hours. We attempt to quantify the error behavior as the settling time is decreased. Results are compared with several alternative precise positioning methods. Also discussed are the numerical stability issues associated with methods of this type. The phase only method we derive is compared with several carrier smoothed code methods. The data used are from SPS receivers as well as from a PPS receiver.