Testing and Analysis of Reliability Measures for GNSS Receivers in the Marine Environment

Marine navigation has been revolutionized by the deployment of marine radiobeacon DGPS systems. While most of the precision requirements for marine navigation can now be met with marine DGPS, the reliability of the user’s position is often ignored. The reliability of the DGPS corrections is ensured through the use of redundant shore based equipment and real time integrity checks. However, reliable corrections do not guarantee a reliable user’s position since user blunders can still occur. The reliability of the user’s DGPS position is addressed in two parts. First, software simulations are conducted to evaluate the reliability improvement when DGPS is augmented with single point GLONASS, differential GLONASS, differential geostationary satellites, and height and clock constraints in constricted waterways. These simulations demonstrate that DGPS must be augmented with at least one differential satellite system in order to ensure reliable positioning. Second, the reliability performance of four representative marine user receivers is tested using a differential GPS signal simulator. None of the receivers tested employed a reliability algorithm, thereby allowing the multipath blunders to contaminate the user’s position. Although the higher end receivers mitigated the multipath blunders, gross position errors still occurred. Therefore in addition to augmenting DGPS, it is shown that a simple reliability algorithm can dramatically improve user navigation performance.