Unbiased code phase discriminator
First Claim
1. A method of determining the phase of a code signal where the code C consists of a known sequence of positive and negative symbols of average width T, where T>
- 0, which method comprises the following steps;
generating a first correlation kernel, by using a correlator system, that corresponds to non-transitions of the code signal and has a first correlation kernel shape;
generating a second correlation kernel, using the correlator system, that corresponds to transitions of the code signal and has a second correlation kernel shape independent of the shape of the first correlation kernel; and
producing a correlative phase discriminator by multiplying at least one of the said correlations by at least one scale factor, and adding together the first and second correlation kernels after at least one is multiplied by the said scale factor.
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Accused Products
Abstract
A feedback control law steers a reference phase that tracks the phase of a received code sequence. The reference phase clocks a track-reference signal consisting of a series of correlation kernels, over which data is extracted and then summed in various combinations. The correlation kernels are designed in such a manner that errors caused by multipath are eliminated or substantially reduced. Furthermore, the areas of the correlation kernels are balanced across level-transitions of a code and non-transitions to eliminate phase biases when tracking specific satellites. Extra care must be taken to balance the correlation kernels in this manner due to a little known aspect of GPS C/A codes. Specifically, not all C/A codes have the same ratio of level-transitions to non-transitions as has been assumed in prior art.
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Citations
12 Claims
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1. A method of determining the phase of a code signal where the code C consists of a known sequence of positive and negative symbols of average width T, where T>
- 0, which method comprises the following steps;
generating a first correlation kernel, by using a correlator system, that corresponds to non-transitions of the code signal and has a first correlation kernel shape;
generating a second correlation kernel, using the correlator system, that corresponds to transitions of the code signal and has a second correlation kernel shape independent of the shape of the first correlation kernel; and
producing a correlative phase discriminator by multiplying at least one of the said correlations by at least one scale factor, and adding together the first and second correlation kernels after at least one is multiplied by the said scale factor.
- 0, which method comprises the following steps;
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2. A method of determining the phase of a code portion of a signal where the code C consists of a known sequence of positive and negative symbols of average width T, where T>
- 0, with the method comprising the following steps;
generating, by using a correlator system, a first track reference signal S1 consisting of both zero and non-zero segments such that when S1 and C are aligned in phase, all non-zero segments of S1 occur within a width T/2 of the symbol boundaries of C that exhibit level transitions, either positive-to-negative or negative-to-positive; and providing the signal S1 with the further properties that; each non-zero segment of the product of C and S1, when phase aligned, has a right-hand portion and a left-hand portion with the right-hand portion occurring later in time than the left-hand portion and the division between right and left coinciding with a symbol boundary of C; the mass-balance sum of all right-hand portions is zero; and the mass balance sum of all left-hand portions exhibits a non-zero value B1, generating, using the correlator system, a second track reference signal S2 consisting of both zero and non-zero segments such that when S2 and C are aligned in phase, all non-zero segments of S2 occur within a width T/2 of the symbol boundaries of C that exhibit no level transitions, with the signal S2 having the further property that; the mass-balance sum of the product of C and S2, when phase aligned, has a non zero value B2; performing, using the correlator system, a first correlation by accumulating of the product of D and S1 to provide a first correlation kernel with a first correlation kernel shape; performing, using the correlator system, a second correlation by accumulating of the product of D and S2 to provide a second correlation kernel with a second correlation kernel shape independent of the shape of the first correlation kernel; determining at least one scale factor based on the values of B1 and B2; multiplying at least one of the said correlations by at least one said scale factor; forming an error discriminator by adding together the first and second correlation after at least one is multiplied by the said scale factor; and using the error signal, control the phase of S1 and S2 so that the error discriminator is driven to zero. - View Dependent Claims (3, 4, 5)
- 0, with the method comprising the following steps;
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6. A method of providing dead-zone compensation to a first correlation kernel in a correlative phase error discriminator system, which method comprises the steps of:
- providing a first correlation kernel, where said first correlation kernel has a zero value at a nominal track point, a non-zero value to the left and right of the nominal track point, and a zero value in a dead-zone that is not located at the nominal track point;
providing a second correlation kernel with a zero value within a zero-band that includes the nominal track point of said first correlation kernel and a non-zero value on one side of the zero-band;
measuring a phase error using said first correlation kernel; and
providing dead-zone compensation to said first correlation kernel using said second correlation kernel by adding a compensation term to the measured phase error of said first correlation kernel whenever said second correlation kernel reads a non-zero correlation value outside of its zero-band with said compensation term proportional to the size of the non-zero correlation value. - View Dependent Claims (7, 8, 9, 10, 11, 12)
- providing a first correlation kernel, where said first correlation kernel has a zero value at a nominal track point, a non-zero value to the left and right of the nominal track point, and a zero value in a dead-zone that is not located at the nominal track point;
Specification