Navigation data prediction for GPS and glonass weak signal tracking
AssigneeTopcon GPS, LLC
InventorsMichael V. Vorobiev, Javad Ashjaee
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Abstract
Prediction methods for navigation message symbols of satellite systems, such as GPS (Global Positioning System) and GLONASS (Global Orbiting Navigation System), that use information repetition in navigation data messages are disclosed. The methods enable one to eliminate the impact of symbol modulation for a received signal on the threshold performance of any navigation receiver, thereby permitting its operation in severe environments when the carrier-to-noise ratio C/N0 of “weak” satellite signals falls to levels below C/N0=20 dB*Hz.
Claims20
A method of predicting navigation symbols for use in a global positioning tracking process, the navigation symbols being transmitted from a global positioning satellite in the form of a carrier signal modulated by a data-stream signal comprising the symbols, the navigation data symbols being conveyed in a sequence of one or more repeating frames, said data-stream signal having a first group of symbols which is repeated within the stream once every number M of frames at predetermined locations in the frames, M being equal to or greater than 1, said method comprising:
- (a) detecting the symbols of the first group within the frames of the information data stream signal;
- (b) storing in a memory a sequence of the detected symbol values of the first group over at least M frames;
- (c) providing the sequence stored in the memory to the global positioning tracking process;
- (d) subsequently monitoring the data-stream signal to detect a change in the symbol values of the first group, said step comprising the steps of detecting the symbols of the first group within subsequently transmit frames, comparing their values with the sequence of previously detected symbol values stored in memory to find differences, and counting the number of differences encountered since the start of a group of frames;
- and
- (e) repeating steps (a) and (b) when the number of differences exceeds a predetermined number.
A computer program product for directing a computer processor to predict navigation symbols for use in a global positioning tracking process, the navigation symbols being transmitted from a global positioning satellite in the form of a carrier signal modulated by a data-stream signal comprising the symbols, the navigation data symbols being conveyed in a sequence of one or more repeating frames, said data-stream signal having a first group of symbols which is repeated within the stream once every number M of frames at predetermined locations in the frames, M being equal to or greater than one, the data processor having a data input port and a data output port, the computer program product comprising:
- a first computer-readable medium;
- a first set of instructions embodied on the first computer-readable medium which directs the data processor to read from the data input port the symbols of the first group at their predetermined locations within the frames of the information data stream signal;
- a second set of instructions embodied on the first computer-readable medium which directs the data processor to store in a second computer-readable medium a sequence of the detected symbol values of the first group over a set of M frames and a representation of the location of each detected symbol within the set of M frames;
- and
- a third set of instructions embodied on the first computer-readable medium which directs the data processor to generate at the data output port two or more repeating sets of M frames of predicted navigation symbols, said third set of instructions directing the data processor to read the symbols of the first group stored in the second computer-readable medium and to output values representative of the stored symbols of the first group to the data output port at the locations within the frames at which the symbols were initially detected.
Dependencies are inferred from the claim text.