DSP implementation of a cellular base station receiver
First Claim
1. A method of digitally demodulating an FM signal at one of an IF and base band frequency created by frequency modulating a carrier signal with a modulating signal, the FM signal having in-phase and quadrature components, wherein the in-phase component has the carrier signal and the quadrature component has the modulating signal, the method comprising the steps of:
- sampling the FM signal at an appropriate sample rate to produce a digital channel signal;
digitally filtering the digital channel signal to extract the carrier signal using a narrow frequency bandpass algorithm;
digitally multiplying the carrier signal with the digital channel signal to form a mixed signal which comprises the modulating signal and the carrier signal shifted to a different frequency; and
digitally filtering the mixed signal to recover the modulating signal.
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Accused Products
Abstract
Demodulating FM signals using digital signal processing extracts a carrier signal from digitized channel signals, multiplies the digital channel signal with this extracted carrier signal, and further filters out the carrier signal to produce the demodulated signal. The DSP technique first down converts a group of channels to baseband which are then processed through an A/D converter to produce a digitized composite signal. A bank of bandpass filters, typically based on FFT processors, applied to the composite signal produce (a group of) digitized channel signal(s). The digitized channel signal is then demodulated by recovering a carrier signal by digitally filtering, for example, using a Hilbert bandpass filter, the channel signal and digitally filtering the product of the carrier signal and the channel signal to recover the modulating voice signals.
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Citations
15 Claims
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1. A method of digitally demodulating an FM signal at one of an IF and base band frequency created by frequency modulating a carrier signal with a modulating signal, the FM signal having in-phase and quadrature components, wherein the in-phase component has the carrier signal and the quadrature component has the modulating signal, the method comprising the steps of:
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sampling the FM signal at an appropriate sample rate to produce a digital channel signal; digitally filtering the digital channel signal to extract the carrier signal using a narrow frequency bandpass algorithm; digitally multiplying the carrier signal with the digital channel signal to form a mixed signal which comprises the modulating signal and the carrier signal shifted to a different frequency; and digitally filtering the mixed signal to recover the modulating signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 15)
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12. A method of digitally demodulating a composite signal, having a plurality of channels, each channel created by frequency modulating a carrier signal with a modulating signal, the FM signal having in-phase and quadrature components, wherein the in-phase component has the carrier component and the quadrature component has the modulating signal, the method comprising the steps of:
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shifting a plurality of channels of the FM signal to base band; sampling the FM band signal at a rate at least twice the bandwidth of the FM band signal to produce a digital channel signal; digital bandpass filtering to produce a plurality of digital channel signals; then for each digital channel; digitally filtering the digital channel signal to extract the carrier signal using a Hilbert bandpass filter algorithm, wherein the Hilbert bandpass filter algorithm has a pass band centered about 30 KHz; digitally multiplying the carrier component with the digital channel signal to form a mixed signal which comprises the modulating signal and the carrier signal shifted to a different frequency; and digitally filtering the mixed signal to recover the modulating signal.
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13. An FM signal demodulating device using digital signal processing (DSP), the device comprising:
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means for digitally sampling the FM signal to produce a digital channel signal having in-phase and quadrature components, wherein the in-phase component has a carrier component and the quadrature component has a signal component; first means for digitally filtering, using a narrow frequency bandpass algorithm, the digital channel signal to extract the carrier signal; means for digitally multiplying the carrier signal with the digital channel signal to form a mixed signal which comprises a modulating signal and the carrier signal shifted to a different frequency; and second means for digitally filtering the mixed signal to recover the modulating signal. - View Dependent Claims (14)
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Specification