System and method for fast code phase and carrier frequency acquisition in GPS receiver
First Claim
1. A GPS receiver, comprising an antenna to collect a GPS signal that is a composite signal comprising a contribution from each GPS satellite in view of the receiver;
- a signal conditioning processor to amplify, filter and downconvert the GPS signal to baseband;
an A/D converter to digitize the GPS signal at a predetermined sample rate;
a memory to store a portion of the GPS signal;
an FFT process to convert the portion of the GPS signal stored in the memory to the frequency domain;
a multiplier for multiplying the frequency representation of the stored GPS signal with a frequency representation of a Gold code associated with one of the GPS satellites in view of the GPS receiver and for storing the result in the memory as a product;
an inverse FFT process for converting the product to the time domain as a convolution; and
a peak detector to find a location of a peak in the convolution, the location of the peak being an estimate of the Gold code phase.
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Accused Products
Abstract
A GPS receiver acquires carrier frequency and Gold code phase using short segments of a received GPS signal. In one embodiment, a 1-ms segment of the GPS signal is transformed to the frequency domain. This is multiplied by a frequency representation of the Gold code. The resulting product is converted to the time domain, and a peak is detected. The location of the peak corresponds to the code phase. If no peak is located, the carrier frequency is changed. Full- and half-bin steps in carrier frequency are considered. Processing gain is achieved by using longer segments of the input signal, for example 4 or 16 ms and integrating 1-ms segments. Considerations are provided for compensating for the effects of a transition, should it occur in the short segment of the GPS signal being processed. Integrations can be performed using non-coherent and coherent techniques.
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Citations
20 Claims
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1. A GPS receiver, comprising
an antenna to collect a GPS signal that is a composite signal comprising a contribution from each GPS satellite in view of the receiver; -
a signal conditioning processor to amplify, filter and downconvert the GPS signal to baseband;
an A/D converter to digitize the GPS signal at a predetermined sample rate;
a memory to store a portion of the GPS signal;
an FFT process to convert the portion of the GPS signal stored in the memory to the frequency domain;
a multiplier for multiplying the frequency representation of the stored GPS signal with a frequency representation of a Gold code associated with one of the GPS satellites in view of the GPS receiver and for storing the result in the memory as a product;
an inverse FFT process for converting the product to the time domain as a convolution; and
a peak detector to find a location of a peak in the convolution, the location of the peak being an estimate of the Gold code phase. - View Dependent Claims (2, 3, 4)
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5. The GPS receiver recited in claim 5, wherein the means for adjusting carrier frequency comprise means for performing a half-bin analysis.
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6. A GPS receiver to receiver and detect a composite GPS signal comprising GPS signals from all GPS satellites in view of the GPS receiver, comprising:
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an antenna to receive the composite GPS signal;
a memory to store a portion of the received composite GPS signal;
means for segmenting the stored GPS signal into plurality of segments;
each segment one millisecond in duration;
an FFT process to perform an FFT on each segment;
a plurality of multipliers to multiply each FFT segment by a frequency representation of a GPS Gold code to generate a plurality of product vectors;
an inverse FFT process to convert each product vector to the time domain;
a magnitude calculator to calculate a point-by-point magnitude vector of each of the magnitude vectors;
an adder to calculate a point-by-point sum of each of the magnitude vectors;
a peak detector to determine a peak location as an estimate of the Gold code phase. - View Dependent Claims (7, 8)
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9. A method for detecting Gold code phase and carrier frequency in a GPS signal comprising the steps of:
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collecting the GPS signal;
storing a one millisecond segment of the GPS signal in a memory;
converting the stored GPS signal to the frequency domain;
multiplying the frequency domain representation of the GPS signal by a frequency representation of a Gold code corresponding to a GPS satellite in view of the GPS receiver to obtain a product;
converting the product to the time domain to obtain a correlation signal;
detecting a peak correlation signal as the Gold code phase. - View Dependent Claims (10, 11, 12, 13, 15, 16, 17, 18, 19, 20)
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14. A method for detecting Gold code phase and carrier frequency in a GPS signal comprising the steps of:
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collecting a multiple millisecond portion of a composite GPS signal in a GPS receiver;
storing the portion of the composite GPS signal in a memory in the GPS receiver;
partitioning the collected composite into one millisecond segments;
converting each one millisecond segment to the frequency domain;
multiplying each of the converted millisecond segments by a frequency representation of a Gold code corresponding to a GP S satellite in view of the receiver to generate a product;
converting each product to the time domain to obtain a correlation signal between each millisecond segment and the Gold code; and
determining a peak location corresponding to a Gold code phase using the correlation signals.
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Specification