Communication signal detection and acquisition
First Claim
1. Apparatus for detecting the presence of a received communication signal having a predetermined recognition pattern of symbols that occur at a predetermined rate (1/T), the apparatus comprisingmeans for processing the communication signal to extract in-phase (I) and quadrature-phase (Q) components of the symbols;
- means for processing the extracted components to compute a complex autocorrelation function of the extracted components with a time parameter equal to an integer multiple (nT) of the symbol period (T);
means for integrating the complex autocorrelation function over a substantial portion of the recognition pattern; and
means for comparing the magnitude of the integrated complex autocorrelation function;
with a predetermined threshold value to detect the presence of the recognition pattern.
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Abstract
The presence of a communication signal having a predetermined recognition pattern of symbols that occur at a predetermined rate (1/T) is detected by processing the communication signal to extract in-phase (I) and quadrature-phase (Q) components of the symbols; processing the extracted components to compute a complex autocorrelation function of the extracted components with a time parameter equal to an integer multiple (nT) of the symbol period (T); integrating the complex autocorrelation function over a substantial portion of the recognition pattern; and comparing the magnitude of the integrated complex autocorrelation function with a predetermined threshold value to detect the presence of the recognition pattern. The communication signal is acquired at a given intermediate frequency and at a given phase by adjusting the frequency of a local oscillator signal in response to a frequency error signal provided by processing the real and imaginary components of the integrated complex autocorrelation function and by adjusting the phase of the local oscillator signal in response to a phase error signal provided by processing extracted I and Q components of the communication signal to compute an arctangent of a quotient of a sum of the values of the Q components extracted over an integer multiple (rT) of the symbol period divided by a sum of the values of the I components extracted over the integer multiple (rT) of the symbol period.
52 Citations
15 Claims
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1. Apparatus for detecting the presence of a received communication signal having a predetermined recognition pattern of symbols that occur at a predetermined rate (1/T), the apparatus comprising
means for processing the communication signal to extract in-phase (I) and quadrature-phase (Q) components of the symbols; -
means for processing the extracted components to compute a complex autocorrelation function of the extracted components with a time parameter equal to an integer multiple (nT) of the symbol period (T); means for integrating the complex autocorrelation function over a substantial portion of the recognition pattern; and means for comparing the magnitude of the integrated complex autocorrelation function;
with a predetermined threshold value to detect the presence of the recognition pattern. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Apparatus for acquiring a received communication signal at a given intermediate frequency, wherein the communication signal includes a predetermined pattern of symbols that occur at a predetermined rate (1/T), and was modulated onto a carrier signal, the apparatus comprising
a local oscillator for providing a local oscillator signal at a local oscillator frequency; -
means for mixing the local oscillator signal with the carrier signal to provide the communication signal at a nominal intermediate frequency; means for processing the communication signal to extract baseband in-phase (I) and quadrature-phase (Q) components of the symbols; and means for processing the extracted components to compute an offset in the nominal intermediate frequency of the received communication signal with respect to the given intermediate frequency and for providing a frequency error signal having a value representative of the computed frequency offset; wherein the local oscillator is responsive to the frequency error signal for adjusting the frequency of the local oscillator signal in accordance with the computed frequency offset so that the mixing means provides the received communication signal at the given intermediate frequency; wherein the processing means are adapted for processing the extracted I and Q components to compute a complex autocorrelation function of the extracted components with a time parameter equal to an integer multiple (nT) of the symbol period (T);
for integrating the complex autocorrelation function; and
for computing the frequency offset by processing the real and imaginary components of the integrated complex autocorrelation function. - View Dependent Claims (11, 12, 13, 14)
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15. Apparatus for acquiring a received communication signal at a given intermediate frequency and at a given phase, wherein the communication signal includes a predetermined pattern of symbols that occur at a predetermined rate (1/T), was modulated onto a carrier signal, and has a nonzero average complex value, the apparatus comprising
a local oscillator for providing a local oscillator signal at a local oscillator frequency; -
means for mixing the local oscillator signal with the carrier signal to provide the communication signal at a nomimal intermediate frequency; means for computing an offset in the nominal intermediate frequency of the received communication signal with respect to the given intermediate frequency and for providing a frequency error signal having a value representative of the computed frequency offset; wherein the local oscillator is responsive to the frequency error signal for adjusting the frequency of the local oscillator signal in accordance with the computed frequency offset so that the mixing means provides the received communication signal at the given intermediate frequency; means for processing the communication signal to extract baseband in-phase (I) and quadrature-phase (Q) components of the symbols; and means for processing the extracted I and Q components to compute an offset in the phase of the received communication signal with respect to the given phase and to provide a phase error signal having a value representative of said computed phase offset; wherein the local oscillator is responsive to the phase error signal for adjusting the phase of the local oscillator signal in accordance with said computed phase offset so that the mixing means provides the received communication signal at the given phase; and wherein the means for computing the phase offset is adapted for computing the phase offset by computing an arctangent of a quotient of a sum of the values of the Q components extracted over an integer multiple (rT) of the symbol period (T) divided by a sum of the values of the I components extracted over the integer multiple (rT) of the symbol period.
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Specification