US5764704A
Expired / Lapsed
US
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DSP implementation of a cellular base station receiver
Assignee: Microsemi Frequency and Time Corp
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Filing: 1996-06-17
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Granted: 1998-06-09
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Expires: 2016-06-17
Abstract
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.
Inventors
- 👤 Kishan Shenoi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 19:04
CPC Classifications
H; H03; H03D; H03D3/00; H03D3/007; H04; H04B; H04B1/00; H04B1/06; H04B1/16; H04B1/30
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
130 words
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.
Claim 2
Independent Claim
130 words
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.
Claim 3
Dependent Claim
17 words
A method according to claim 1, wherein the narrow frequency bandpass algorithm is a Hilbert bandpass algorithm.
Claim 4
Dependent Claim
28 words
A method according to claim 1, wherein the narrow frequency bandpass algorithm has a band pass range of approximately 300 Hz on each side of the carrier signal.
Claim 5
Dependent Claim
33 words
A method according to claim 2, wherein the Hilbert bandpass filter has a pass band centered about 30 KHz, the sampling rate chosen such that the baseband FM carrier is at 30 KHz.
Claim 6
Dependent Claim
18 words
A method according to claim 2, wherein the Hilbert bandpass filter is an odd-length and odd-symmetry, FIR filter.
Claim 7
Dependent Claim
32 words
A method according to claim 2, wherein the Hilbert bandpass algorithm comprises a phase shift of about 90 degrees and a flat delay of (N-1)/2, in which N is an odd integer.
Claim 8
Dependent Claim
28 words
A method according to claim 6, wherein the ratio of FM carrier frequency at the one of the IF and baseband to the sample rate, being an integer.
Claim 9
Dependent Claim
13 words
A method according to claim 6, wherein (N-1)/2 is a multiple of 4.
Claim 10
Dependent Claim
26 words
A method according to claim 1, wherein the filtering of the mixed signal to produce the modulating signal is performed by filtering out high frequency signals.
Claim 11
Dependent Claim
26 words
A method according to claim 1, wherein the sampling rate for sampling the FM signal is about twice the upper limit frequency of the FM signal.
Claim 12
Dependent Claim
27 words
A method according to claim 1, further comprising the implementation of the steps of claim 1 for other digital channel signals in the FM signal in parallel.
Claim 13
Independent Claim
179 words
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: 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.
Claim 14
Independent Claim
179 words
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: 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.
Claim 15
Dependent Claim
112 words
An FM signal demodulating device using digital signal processing (DSP), the device comprising: 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.
Claim 16
Dependent Claim
112 words
An FM signal demodulating device using digital signal processing (DSP), the device comprising: 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.
Claim 17
Dependent Claim
16 words
A device according to claim 13, wherein the first digitally filtering means performs Hilbert bandpass algorithm.
Claim 18
Dependent Claim
24 words
A method according to claim 7 wherein the delay is an integer multiple of the ratio of the FM carrier to the sample rate.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2001-06-08 | 2001-12-08 | 2002-06-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2005-06-08 | 2005-12-08 | 2006-06-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2009-06-08 | 2009-12-08 | 2010-06-09 | $7700.00 | Window Closed / Lapsed |