Researchers Submit Patent Application, "Method and Apparatus for Determining Physical Characteristics of a Receiving Device in a Navigation System", for Approval
The patent's assignee for patent application serial number 761643 is
News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates generally to navigation systems, e.g., Global Navigation Satellite Systems (GNSSs), and in particular, a method and apparatus for improving the accuracy of physical characteristic calculations, e.g., position, velocity, and/or time accuracy, for a user using a navigation system.
"Satellite navigation technology is used in a variety of electronic devices. For example, many mobile telephones have some form of integrated location system that works with one or more GNSS, such as a GLObalnaya NAvigatsionnaya. Sputnikovaya Sistema (GLONASS) or a Global Positioning System (GPS). Additionally, in car navigation systems are used to determine the velocity of a vehicle for tracking and monitoring purposes.
"Taking GPS as an example, which operates with 24 orbiting satellites, for civilian purposes, each satellite outputs a navigation or location signal on a first channel L1 at 1575.42 MHz. The signal carries a Coarse-grained Acquisition (C/A) code. The C/A code is modulated and repeated on the L1 wave every millisecond and contains the time the code was transmitted, based on an atomic clock onboard the satellite.
"A civilian GPS receiver receives the C/A code from a satellite and compares it with a replica signal generated by the receiver using a receiver clock. From this comparison, a time difference between the satellite's atomic clock and the receiver clock is determined. The time difference is then multiplied by a known value for the speed of light to determine a distance between the GPS receiver and the satellite. This distance measurement is referred to as pseudorange measurement because it will contain inherent inaccuracies, e.g., due to timing errors, atmospheric conditions, measurement errors etc.
"Using the pseudorange measurements for a plurality of satellites, together with the calculated positions of these satellites, a location in a number of dimensions can be calculated. For example, by using three satellites, a user's location in two dimensions can be calculated; by using four satellites, a user's location in three dimensions can be calculated. The additional satellite in each case is used to determine a timing correction. The positions of each of these satellites at the time the original C/A code was transmitted can be determined using orbit parameters (sometimes referred to as 'ephemeris') and/or almanac data broadcast by the satellites. From this information, a satellite coordinate (X,Y,Z) can be computed.
"Several solutions have been proposed to increase the accuracy and/or integrity of location information provided by satellite location systems. One of these solutions is referred to as Receiver Autonomous Integrity Monitoring (RAIM). A solution of this form may use a weight in relation to the measurements to prefer satellites that are positioned over a receiving device rather than at an obtuse angle to the receiving device. For example, satellites that are nearer the horizon in relation to a receiving device positioned on the Earth's surface are likely to suffer from greater errors, and therefore, their contribution may be reduced with appropriate weighting factors. This approach is described in a publication by T. Walter and
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