Spread spectrum receiver with fast signal reacquisition
DCFirst Claim
1. A method of tracking a spread spectrum source, comprising the steps of:
- acquiring the source from a composite of signals received by determining a delay parameter for that source related to time of receipt of a source specific spread spectrum code in the signals from the source;
correlating signals received from the source with a prompt version of a locally generated source specific code based on the delay parameter;
tracking the signals received from the source by updating the delay parameter in response to the signals from the source;
modeling the delay parameter to continue updating the delay parameter when signals from the source are not being tracked; and
continuously correlating the composite of signals received with a plurality of delayed versions of the locally generated source specific code based on the modeled delay parameter to reacquire the signals from the source.
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Abstract
A spread spectrum receiver, such as a GPS car navigation system, uses multiple, parallel correlations of data in a wide capture window, permits seamless tracking and rapid reacquisition of satellite signals at speeds sufficient to permit position information updates during momentary views available of satellites in intersections. The received data is processed in 11 bit samples, for a total of 186 time segments per 1 msec code period, which are each Doppler shifted and multiplexed into 12 channels. The code correlations are performed 22 times per channel by shifting the 11 bit locally generated code by one bit each correlation. The chip rate of the incoming data is 2f0 and the correlations are performed at 48f0 providing a time magnification advantage of 24.
122 Citations
11 Claims
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1. A method of tracking a spread spectrum source, comprising the steps of:
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acquiring the source from a composite of signals received by determining a delay parameter for that source related to time of receipt of a source specific spread spectrum code in the signals from the source; correlating signals received from the source with a prompt version of a locally generated source specific code based on the delay parameter; tracking the signals received from the source by updating the delay parameter in response to the signals from the source; modeling the delay parameter to continue updating the delay parameter when signals from the source are not being tracked; and continuously correlating the composite of signals received with a plurality of delayed versions of the locally generated source specific code based on the modeled delay parameter to reacquire the signals from the source. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A spread spectrum receiver, comprising:
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means for providing a plurality of versions of a locally generated signal related to a spread spectrum signal to be received; means for combining at least two of the versions of the locally generated signal with the spread spectrum signal to produce a product signal related to each of the at least two versions; means for evaluating the at least two product signals to adjust a parameter of a third version of the local signal; means for combining the adjusted third version of the local signal with the spread spectrum signal to produce a data signal; means for determining a predicted value of the parameter when the spread spectrum signal becomes unavailable; means for combining an additional plurality of versions of the locally generated signal related to the predicted value with received signals to produce additional product signals related to each of the additional plurality of versions of the locally generated signal; and means for evaluating the additional product signals to produce a reacquired data signal. - View Dependent Claims (8, 9, 10)
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11. A method of operating a receiver for coded GPS signals from satellites comprising the steps of:
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correlating early, prompt and late versions of a locally generated model of the code with signals received from GPS satellites to adjust a delay of the prompt version to track a selected satellite; maintaining a predicted value of the delay when the selected satellite is unavailable; correlating a plurality of different early versions of the locally generated code, early with respect to the predicted value of the delay, with signals received from satellites to produce correlation products; correlating a plurality of different late versions of the locally generated code, late with respect to the predicted value of the delay, with signals received from satellites to produce correlation products; and reacquiring the previous unavailable selected satellite by selecting the version producing the largest correlation product above a predetermined threshold.
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Specification