Multipath Simulator Taking into Account Reflection and Diffraction (MUSTARD) is a computer program that simulates effects of multipath propagation on received Global Positioning System (GPS) signals. MUSTARD is a very efficient means of estimating multipath-induced position and phase errors as functions of time, given the positions and orientations of GPS satellites, the GPS receiver, and any structures near the receiver as functions of time. MUSTARD traces each signal from a GPS satellite to the receiver, accounting for all possible paths the signal can take, including all paths that include reflection and/or diffraction from surfaces of structures near the receiver and on the satellite. Reflection and diffraction are modeled by use of the geometrical theory of diffraction. The multipath signals are added to the direct signal after accounting for the gain of the receiving antenna. Then, in a simulation of a delay-lock tracking loop in the receiver, the multipath-induced range and phase errors as measured by the receiver are estimated. All of these computations are performed for both right circular polarization and left circular polarization of both the L1 (1.57542-GHz) and L2 (1.2276-GHz) GPS signals.
This program was written by Sung Byun, George Hajj, and Lawrence Young of Caltech for NASA's Jet Propulsion Laboratory.
For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Software category. This software is available for commercial licensing. Please contact Don Hart of the California Institute of Technology at (818) 393-3425. Refer to NPO-40463.
This Brief includes a Technical Support Package (TSP).
Estimating Effects of Multipath Propagation on GPS Signals
(reference NPO-40463) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory, focusing on the estimation of multipath propagation effects on Global Positioning System (GPS) signals. It outlines the development and application of a GPS signal multipath simulator, which is crucial for understanding how GPS signals interact with their environment, particularly in terms of reflections and diffractions caused by obstacles.
The introduction emphasizes the importance of GPS, which relies on a constellation of at least 24 satellites positioned in six orbital planes at an altitude of 20,200 km. The document notes that current GPS accuracy can reach 1–2 parts in 10^9, with advanced techniques developed over the years to improve this precision. These techniques address various factors affecting accuracy, including instrumental noise, tropospheric and ionospheric effects, and multipath interference.
The document details the modeling of the International Space Station (ISS) in a circular orbit at an altitude of 407 km, providing a framework for understanding the dynamics of GPS signal propagation in space. It describes the spacecraft's attitude and the integration of its orbit over time, which is essential for accurate signal modeling.
A significant portion of the document discusses the multipath phenomenon, where GPS signals reflect off surfaces before reaching the receiver, leading to potential errors in positioning. The simulator developed allows for the analysis of these multipath effects, taking into account various parameters such as the angle of incidence and the distance to reflecting surfaces. The document includes mathematical formulations to compute multipath delays and their impact on signal accuracy.
Additionally, the document presents data on how antenna height affects multipath error, providing specific measurements for different heights. This information is vital for optimizing GPS receiver placement to minimize errors caused by multipath propagation.
In conclusion, the Technical Support Package serves as a comprehensive resource for understanding the complexities of GPS signal propagation and the impact of environmental factors on accuracy. It highlights the ongoing efforts to enhance GPS technology through advanced modeling and simulation techniques, ultimately contributing to improved navigation and positioning systems in various applications.
