Carrier tracking for AM in-band on-channel radio receivers
First Claim
1. A method for carrier tracking in AM in-band on-channel radio receivers, the method comprising the steps of:
- receiving an input signal;
generating a local oscillator signal in response to an oscillator control signal;
mixing the input signal with a local oscillator signal to produce a first signal;
filtering the first signal to produce a filtered first signal at a decimated sample rate;
detecting the phase error and frequency error of the filtered first signal normalized to mitigate effects of signal fades;
using an adaptive loop filter to produce the oscillator control signal in response to the phase error and frequency error of the filtered first signal;
computing a gain control signal in response to the filtered first signal; and
multiplying the first signal by the gain control signal to produce an output signal, wherein the square of the gain control signal is used to maintain a nearly constant damping factor.
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Accused Products
Abstract
A method for carrier tracking in AM in-band on-channel radio receivers comprises the steps of receiving an input signal, generating a local oscillator signal in response to an oscillator control signal, mixing the input signal with a local oscillator signal to produce a first signal, filtering the first signal to produce a filtered first signal at a decimated sample rate, detecting the phase error and frequency error of the filtered first signal normalized to mitigate effects of signal fades, and using an adaptive loop filter to produce the oscillator control signal in response to the phase error and frequency error of the filtered first signal. An apparatus that performs the method is also provided.
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Citations
21 Claims
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1. A method for carrier tracking in AM in-band on-channel radio receivers, the method comprising the steps of:
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receiving an input signal; generating a local oscillator signal in response to an oscillator control signal; mixing the input signal with a local oscillator signal to produce a first signal; filtering the first signal to produce a filtered first signal at a decimated sample rate; detecting the phase error and frequency error of the filtered first signal normalized to mitigate effects of signal fades; using an adaptive loop filter to produce the oscillator control signal in response to the phase error and frequency error of the filtered first signal; computing a gain control signal in response to the filtered first signal; and multiplying the first signal by the gain control signal to produce an output signal, wherein the square of the gain control signal is used to maintain a nearly constant damping factor. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for carrier tracking in AM in-band on-channel radio receivers, the method comprising the steps of:
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receiving an input signal; generating a local oscillator signal in response to an oscillator control signal; mixing the input signal with a local oscillator signal to produce a first signal; filtering the first signal to produce a filtered first signal at a decimated sample rate; detecting the phase error and frequency error of the filtered first signal normalized to mitigate effects of signal fades; using an adaptive loop filter to produce the oscillator control signal in response to the phase error and frequency error of the filtered first signal; computing a gain control signal in response to the filtered first signal; and multiplying the first signal by the gain control signal to produce an output signal, wherein the gain control signal is derived as a function of an estimated phase error bias magnitude.
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9. A method for carrier tracking in AM in-band on-channel radio receivers, the method comprising the steps of:
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receiving an input signal; generating a local oscillator signal in response to an oscillator control signal; mixing the input signal with a local oscillator signal to produce a first signal; filtering the first signal to produce a filtered first signal at a decimated sample rate; detecting the phase error and frequency error of the filtered first signal normalized to mitigate effects of signal fades; using an adaptive loop filter to produce the oscillator control signal in response to the phase error and frequency error of the filtered first signal; wherein the input signal comprises a plurality of samples; and wherein the step of detecting the phase error and frequency error of the filtered first signal estimates a sample phase error, and estimates a phase difference angle between each pair of the filtered samples for the frequency error. - View Dependent Claims (10, 11)
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12. A method for carrier tracking in AM in-band on-channel radio receivers, the method comprising the steps of:
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receiving an input signal; generating a local oscillator signal in response to an oscillator control signal; mixing the input signal with a local oscillator signal to produce a first signal; filtering the first signal to produce a filtered first signal at a decimated sample rate; detecting the phase error and frequency error of the filtered first signal normalized to mitigate effects of signal fades; using an adaptive loop filter to produce the oscillator control signal in response to the phase error and frequency error of the filtered first signal, wherein the loop filter produces a cancellation signal to reduce phase noise in the local oscillator signal due to a proportional component of a proportional plus integral output of the loop filter; and generating a loop stabilization signal to compensate for a reduction in loop stability due to the cancellation signal.
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13. An apparatus for carrier tracking in AM in-band on-channel radio receivers, the apparatus comprising:
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an input for receiving an input signal; a local oscillator for generating a local oscillator signal in response to an oscillator control signal; a mixer for mixing the input signal with a local oscillator signal to produce a first signal; a filter for filtering the first signal to produce a filtered first signal at a decimated sample rate; a detector for detecting the phase error and frequency error of the filtered first signal, wherein the filtered first signal is normalized to mitigate effects of signal fades; an adaptive loop filter for producing the oscillator control signal in response to the phase error and frequency error of the filtered first signal; a processor for computing a gain control signal in response to the filtered first signal; and a second mixer for multiplying the first signal by the gain control signal to produce an output signal, wherein the square of the gain control signal is used to maintain the nearly constant damping factor. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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20. An apparatus for carrier tracking in AM in-band on-channel radio receivers, the apparatus comprising:
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an input for receiving an input signal; a local oscillator for generating a local oscillator signal in response to an oscillator control signal; a mixer for mixing the input signal with a local oscillator signal to produce a first signal; a filter for filtering the first signal to produce a filtered first signal at a decimated sample rate; a detector for detecting the phase error and frequency error of the filtered first signal, wherein the filtered first signal is normalized to mitigate effects of signal fades; an adaptive loop filter for producing the oscillator control signal in response to the phase error and frequency error of the filtered first signal; a processor for computing a gain control signal in response to the filtered first signal; and a second mixer for multiplying the first signal by the gain control signal to produce an output signal, wherein the gain control signal is derived as a function of an estimated phase error bias magnitude.
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21. An apparatus for carrier tracking in AM in-band on-channel radio receivers, the apparatus comprising:
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an input for receiving an input signal; a local oscillator for generating a local oscillator signal in response to an oscillator control signal; a mixer for mixing the input signal with a local oscillator signal to produce a first signal; a filter for filtering the first signal to produce a filtered first signal at a decimated sample rate; a detector for detecting the phase error and frequency error of the filtered first signal, wherein the filtered first signal is normalized to mitigate effects of signal fades; an adaptive loop filter for producing the oscillator control signal in response to the phase error and frequency error of the filtered first signal, wherein the input signal comprises a plurality of samples; and wherein the phase error estimates a sample phase error and the frequency error estimates a phase difference angle between each pair of the filtered samples.
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Specification