Apparatus and methods for obtaining a correlation function in the frequency domain
First Claim
1. Apparatus for calculating a correlation function between a Direct Sequence Spread Spectrum DSSS signal and a spreading code, the apparatus comprising:
- memory arranged to store a plurality of code replica samples, the code replica samples comprising samples of a complex conjugate of a time-to-frequency domain transformed replica of the spreading code obtained at a first sampling rate;
a time-to-frequency domain transformation unit configured to receive a block of samples of the DSSS signal at a second sampling rate higher than the first sampling rate, and transform the samples from the time domain to the frequency domain to obtain a plurality of frequency-domain signal samples;
a multiplication unit configured to obtain a correlation operator by reproducing the stored replica samples, and multiply the frequency-domain signal samples by the reproduced stored replica samples to obtain a plurality of multiplied samples; and
an integrating unit configured to receive the multiplied samples and perform integration over a plurality of blocks of samples of the DSSS signal to calculate the correlation function.
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Abstract
Apparatus and methods are disclosed for obtaining a correlation function between a Direct Sequence Spread Spectrum (DSSS) signal and a spreading code. A plurality of code replica samples are stored in memory at a relatively low sampling rate compared to the sampling rate at which the input DSSS signal is sampled. A correlation operator is obtained by reproducing the stored code replica samples, in order to obtain a correlation operator with the same number of samples as the block of DSSS signal samples currently being processed. For example, when the sampling rate of the DSSS signal is equal to an integer N multiple of the sampling rate used for the code replica samples, the stored replica samples are reproduced N times to obtain the correlation operator. The correlation operator is then multiplied by the block of DSSS signal samples and integrated to obtain a correlation function.
4 Citations
17 Claims
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1. Apparatus for calculating a correlation function between a Direct Sequence Spread Spectrum DSSS signal and a spreading code, the apparatus comprising:
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memory arranged to store a plurality of code replica samples, the code replica samples comprising samples of a complex conjugate of a time-to-frequency domain transformed replica of the spreading code obtained at a first sampling rate; a time-to-frequency domain transformation unit configured to receive a block of samples of the DSSS signal at a second sampling rate higher than the first sampling rate, and transform the samples from the time domain to the frequency domain to obtain a plurality of frequency-domain signal samples; a multiplication unit configured to obtain a correlation operator by reproducing the stored replica samples, and multiply the frequency-domain signal samples by the reproduced stored replica samples to obtain a plurality of multiplied samples; and an integrating unit configured to receive the multiplied samples and perform integration over a plurality of blocks of samples of the DSSS signal to calculate the correlation function. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of calculating a correlation function between a Direct Sequence Spread Spectrum DSSS signal and a spreading code using a plurality of code replica samples, the code replica samples comprising samples of a complex conjugate of a time-to-frequency domain transformed replica of the spreading code obtained at a first sampling rate, the method comprising:
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receiving a block of samples of the DSSS signal at a second sampling rate higher than the first sampling rate; transforming the samples from the time domain to the frequency domain to obtain a plurality of frequency-domain signal samples; obtaining a correlation operator by reproducing the code replica samples; multiplying the frequency-domain signal samples by the reproduced code replica samples to obtain a plurality of multiplied samples; and integrating the multiplied samples over a plurality of blocks of samples of the DSSS signal to calculate the correlation function. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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Specification