METHOD OF PROCESSING A DIGITAL SIGNAL DERIVED FROM A DIRECT-SEQUENCE SPREAD SPECTRUM SIGNAL AND A RECEIVER
First Claim
1. A method of processing a digital signal derived from a direct-sequence spread spectrum analog signal containing at least one encoded binary sequence consisting of repetitions of a characteristic basic sequence which extends over a basic interval to determine a multiplicity of correlation sums, the method comprising:
- providing a correlation sequence corresponding to the basic sequence which consists of correlation values of +1 and −
1 each pertaining to one of a series of consecutive chip intervals having a constant chip length,deriving from the digital signal a data sequence consisting of data values which follow upon each other separated in each case by a sampling interval, the sampling intervals having a constant sampling length which is not greater than one half of the chip length such that a plurality of consecutive data values is contained in a chip interval in each case, andcorrelating the data sequence with a plurality of copies of the correlation sequence, the copies having different phase positions with respect to the data sequence, and forming a correlation sum comprising products of correlation values and data values over a correlation interval in each case,wherein a sequence of overlapping chip sums is formed by calculating, for every data value, at least one chip sum with the data value as an initial value, where the chip sum is in each case a linear combination of data values in a set consisting of the initial value and immediately subsequent data values, wherein the summation number of data values contained in the set multiplied by the sampling length differs in each case by at most the sampling length from the chip length,a series of subsequences of chip sums is formed, each subsequence selected from the sequence of chip sums, with the position of the initial value of a first chip sum as a starting point, in such a way thatat every end point of an interval beginning at the starting point of a first subsequence and having a length corresponding to a multiple of a resolution length which is not greater than half the chip length, at least where the end point is situated within a chip length from the said starting point, there is a starting point of a further subsequence whose position differs from the position of the said end point by not more than one half of the sampling length, andeach subsequence has, for every end point of an interval beginning at its starting point and having a length corresponding to a multiple of the chip length, an initial value whose position differs from the position of the said end point by not more than one half of the sampling length, andwherein for every subsequence, every chip sum is multiplied with one corresponding correlation value of the correlation sequence and the products summed up over a partial correlation interval to form a partial correlation sum which is then used for the determination of one of the correlation sums.
1 Assignment
0 Petitions
Accused Products
Abstract
Complex digital data values derived from a DSSS signal, in particular, a GNSS signal, are delivered to a general purpose microprocessor at a rate of 8 MHz and chip sums over eight consecutive data values spaced by a sampling length (TS), each beginning with one of the data values as an initial value, formed and stored. For code removal, each of a series of chip sums covering a correlation interval of 1 ms and each essentially coinciding with a chip interval of fixed chip length (TC), where a value of a basic function (bm) reflecting a PRN basic sequence of a satellite assumes a correlation value (Bm), is multiplied by the latter and the products added up over a partial correlation interval to form a partial correlation sum. The partial correlation interval is chosen in such a way that it essentially coincides with a corresponding Doppler interval having a Doppler length (TD) where a frequency function used for tentative Doppler shift compensation and represented by a step function (sine, cosine) is constant. The partial correlation sums are then each multiplied by the value assumed by the frequency function in the corresponding Doppler interval and the products added up to form a correlation sum.
-
Citations
15 Claims
-
1. A method of processing a digital signal derived from a direct-sequence spread spectrum analog signal containing at least one encoded binary sequence consisting of repetitions of a characteristic basic sequence which extends over a basic interval to determine a multiplicity of correlation sums, the method comprising:
-
providing a correlation sequence corresponding to the basic sequence which consists of correlation values of +1 and −
1 each pertaining to one of a series of consecutive chip intervals having a constant chip length,deriving from the digital signal a data sequence consisting of data values which follow upon each other separated in each case by a sampling interval, the sampling intervals having a constant sampling length which is not greater than one half of the chip length such that a plurality of consecutive data values is contained in a chip interval in each case, and correlating the data sequence with a plurality of copies of the correlation sequence, the copies having different phase positions with respect to the data sequence, and forming a correlation sum comprising products of correlation values and data values over a correlation interval in each case, wherein a sequence of overlapping chip sums is formed by calculating, for every data value, at least one chip sum with the data value as an initial value, where the chip sum is in each case a linear combination of data values in a set consisting of the initial value and immediately subsequent data values, wherein the summation number of data values contained in the set multiplied by the sampling length differs in each case by at most the sampling length from the chip length, a series of subsequences of chip sums is formed, each subsequence selected from the sequence of chip sums, with the position of the initial value of a first chip sum as a starting point, in such a way that at every end point of an interval beginning at the starting point of a first subsequence and having a length corresponding to a multiple of a resolution length which is not greater than half the chip length, at least where the end point is situated within a chip length from the said starting point, there is a starting point of a further subsequence whose position differs from the position of the said end point by not more than one half of the sampling length, and each subsequence has, for every end point of an interval beginning at its starting point and having a length corresponding to a multiple of the chip length, an initial value whose position differs from the position of the said end point by not more than one half of the sampling length, and wherein for every subsequence, every chip sum is multiplied with one corresponding correlation value of the correlation sequence and the products summed up over a partial correlation interval to form a partial correlation sum which is then used for the determination of one of the correlation sums. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
-
-
15. A receiver comprising a front-end circuit with mixers and A/D converters for determining, from a direct-sequence spread spectrum analog signal containing at least one encoded binary sequence consisting of repetitions of a characteristic basic sequence which extends over a basic interval, a multiplicity of correlation sums, in deriving, from the said analog signal, a digital signal consisting of data values which follow upon each other separated in each case by a sampling interval, the sampling intervals having a constant sampling length which is not greater than one half of the chip length such that a plurality of consecutive data values is contained in a chip interval in each case, and for providing a correlation sequence corresponding to the basic sequence which consists of correlation values of +1 and −
- 1 each pertaining to one of a series of consecutive chip intervals having a constant chip length,
the front-end unit further comprising FIR filter circuits for forming a sequence of overlapping chip sums by calculating, for every data value, at least one chip sum with the data value as an initial value, where the chip sum is in each case a linear combination of data values in a set consisting of the initial value and immediately subsequent data values, where the summation number of data values contained in the set multiplied by the sampling length differs in each case by at most the sampling length from the chip length, and the receiver further comprising a base-band processor with a microprocessor unit and a memory unit configured for correlating the data sequence with a plurality of copies of the correlation sequence, the copies having different phase positions with respect to the data sequence, and forming, in each case, one of the correlation sums comprising products of correlation values and data values over a correlation interval, in that a series of subsequences of chip sums is formed, each subsequence selected from the sequence of chip sums, with the position of the initial value of a first chip sum as a starting point, in such a way that at every end point of an interval beginning at the starting point of a first subsequence and having a length corresponding to a multiple of a resolution length which is not greater than half the chip length, at least where the end point is situated within a chip length from the said starting point, there is a starting point of a further subsequence whose position differs from the position of the said end point by not more than one half of the sampling length, and each subsequence has, for every end point of an interval beginning at its starting point and having a length corresponding to a multiple of the chip length, an initial value whose position differs from the position of the said end point by not more than one half of the sampling length, and where for every subsequence, every chip sum is multiplied with one corresponding correlation value of the correlation sequence and the products summed up over a partial correlation interval to form a partial correlation sum which is then used for the determination of one of the correlation sums.
- 1 each pertaining to one of a series of consecutive chip intervals having a constant chip length,
Specification