Journal of Global Positioning Systems (2008) Vol 7. No 1 GPS RTK Performance Characteristics and Analysis Yanming Feng Faculty of Information Technology, Queensland University of Technology, Australia Jinling Wang School of Surveying and Spatial Information Systems, The University of New South Wales, Australia ABSTRACT Global Navigation Satellite Systems (GNSS) provide various types of positioning state solutions, such as single point positioning (SPP), precise point positioning (PPP), differential GPS (DGPS) and real time kinematic (RTK) solutions. These solutions are obtained involving different data types, receivers, samples, serving different classes of users. Previous studies on performance characteristics have mainly focused on SPP solutions for safety-of-life navigation applications. This paper defines various useful performance characteristics for carrier phase Ambiguity Resolution (AR) and Position Estimation (PE) solutions in the RTK context. These parameters, including base-rover distance, time-to-first fix (TTFF), AR availability, AR reliability, RTK accuracy, availability and integrity, etc, effectively represent the performance of a commercial RTK system and can be used to evaluate different systems and algorithms, and processing strategies through extensive experimental results. Statistical results from extensive field experiments were obtained using a commercial RTK system, demonstrating convincing overall system performance in different perspectives. Experimental results from three baselines were also analysed using a version of research-oriented RTK software, showing that AR performance improvement of using Wide-lane (WL) and Narrow-lane (NL) signals with respect to the original L1 and L2 signals when the baselines exceed 20 kilometres. Key words: GNSS, real time kinematic (RTK) positioning, performance characteristics, ambiguity resolution (AR), RTK integrity. 1. INTRODUCTION Global Navigation Satellite Systems (GNSS) positioning may be classified into several different types, depending on (i) the types of measurements used in the positioning estimation, (ii) the data epochs or data arcs required to create a set of solutions, and (iii) the number of receivers involved in the positioning operations. Single Point Positioning (SPP) produces navigation solutions with pseudorange measurements from a single receiver and a single epoch. Precise Point Positioning (PPP) solutions are obtained using both code and phase measurements from a single receiver, but a period of observations, e.g., tens of minutes to hours, regardless of kinematic or static user applications. Differential GPS (DGPS) solutions are based on code measurements from a single epoch as well, but using the differential corrections from a reference station or network. Real Time Kinematic (RTK) positioning makes use of carrier phase measurements in the differential positioning mode, ideally, from a single epoch. Practically, multiple epochs or a short period of observations are often involved to achieve reliable AR, while the RTK solutions are derived from the current epochs. Different characteristics are required to evaluate various GNSS solutions, to address their positioning performance requirements. Code based SPP and DGPS navigation are the simplest and most robust positioning modes, but, evaluation of code based navigation solutions has been a quite involved problem. The parameters of accuracy, availability, continuity and integrity are defined to evaluate the performance of navigation solutions in aviation navigation (Langley, 1999). For instance, availability is an instantaneous performance characteristic defined as a percentage of time during which the service is available at a certain accuracy. Integrity relates to the level of trust that can be placed in the information provided by the navigation system. It includes the ability of the navigation