US5633896A
Expired / Lapsed
US
⏱️ 0.0 years remaining
AM compatible digital waveform demodulation using a dual FFT
Assignee: Ibiquity Digital Corp
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Filing: 1996-02-21
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Granted: 1997-05-27
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Expires: 2016-02-21
Abstract
Abstract The invention provides a method and apparatus for demodulating a composite AM DAB waveform which contains digitally modulated carriers and which employ (1) a mixer for converting a received signal into two signals (the first of these two signals represents an in-phase component and the second of these two signals represents a quadrature component); (2) two analog-to-digital converters for converting the two signals into digital signals; and (3) two fast Fourier transform elements for extracting data separately from the two digital signals. Complementary digital carrier signals are recovered from the quadrature component, and non-complementary digital carriers are derived from a sum of the complementary data and the output of the in-phase component FFT process. Leakage of the AM signal through a highpass filter is prevented from interfering with the demodulation of the complementary carrier signals' use of separated demodulation channels.
Inventors
- 👤 Barry W. Carlin
- 👤 Mark J. Dapper
- 👤 Michael J. Geile
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 01:13
CPC Classifications
H; H03; H03D; H03D1/00; H03D1/22; H03D1/2245; H04; H04L; H04L27/00; H04L27/26; H04L27/2601; H04L27/2647; H04L27/2649; H04L27/26524; H04H; H04H2201/00; H04H2201/10; H04H2201/18; H04H2201/186
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
135 words
An apparatus for demodulating a composite signal, the composite signal including a first carrier signal amplitude modulated by an analog message signal and a second signal comprising a plurality of digitally modulated carriers, comprising: means for separating the second signal into a third signal and a fourth signal, the third signal representing an in-phase component and the fourth signal representing a quadrature phase component of the composite signal; first means coupled to receive the in-phase component for converting the in-phase component to an in-phase digital signal; second means coupled to receive the quadrature component for converting the quadrature component to a quadrature digital signal; a first fast Fourier transform means for extracting in-phase data from the in-phase digital signal; and a second fast Fourier transform means for extracting quadrature data from the quadrature digital signal.
Claim 2
Independent Claim
135 words
An apparatus for demodulating a composite signal, the composite signal including a first carrier signal amplitude modulated by an analog message signal and a second signal comprising a plurality of digitally modulated carriers, comprising: means for separating the second signal into a third signal and a fourth signal, the third signal representing an in-phase component and the fourth signal representing a quadrature phase component of the composite signal; first means coupled to receive the in-phase component for converting the in-phase component to an in-phase digital signal; second means coupled to receive the quadrature component for converting the quadrature component to a quadrature digital signal; a first fast Fourier transform means for extracting in-phase data from the in-phase digital signal; and a second fast Fourier transform means for extracting quadrature data from the quadrature digital signal.
Claim 3
Dependent Claim
19 words
The apparatus for demodulating according to claim 1, wherein the quadrature phase component comprises complementary carriers and non-complementary carriers.
Claim 4
Dependent Claim
24 words
The apparatus for demodulating according to claim 2, wherein the first carrier signal and the complementary carriers are located in a same frequency region.
Claim 5
Dependent Claim
17 words
The apparatus for demodulating according to claim 1, wherein the means for separating is a quadrature mixer.
Claim 6
Dependent Claim
19 words
The apparatus for demodulating according to claim 1, wherein the first means and the second means are analog-to-digital converters.
Claim 7
Dependent Claim
46 words
The apparatus for demodulating according to claim 1, further comprising: means coupled to receive the in-phase data and the quadrature data, and for combining the in-phase data and the quadrature data to produce a fifth digital signal, the fifth digital signal being representative of non-complementary data.
Claim 8
Dependent Claim
21 words
The apparatus for demodulating according to claim 1, wherein the in-phase digital signal is phase coherent with the first carrier signal.
Claim 9
Dependent Claim
39 words
The apparatus for demodulating according to claim 1, wherein the composite signal is a radio frequency (RF) signal, and wherein the second signal comprising a plurality of digitally modulated carriers is modulated in an orthogonal frequency division multiplexed format.
Claim 10
Independent Claim
136 words
A method of demodulating a composite signal, the composite signal including a first carrier signal amplitude modulated by an analog message signal and a second signal comprising a plurality of digitally modulated carriers, the method comprising the steps of: receiving the composite signal; separating the composite signal into a third signal and a fourth signal, the third signal representing an in-phase component and the fourth signal representing a quadrature phase component of the composite signal; converting the in-phase component to an in-phase digital signal, the in-phase digital signal being phase coherent with the first carrier signal; converting the quadrature component to a quadrature digital signal; extracting in-phase data from the third signal by means of a first fast Fourier transform; and extracting quadrature data from the fourth signal by means of a second fast Fourier transform.
Claim 11
Independent Claim
136 words
A method of demodulating a composite signal, the composite signal including a first carrier signal amplitude modulated by an analog message signal and a second signal comprising a plurality of digitally modulated carriers, the method comprising the steps of: receiving the composite signal; separating the composite signal into a third signal and a fourth signal, the third signal representing an in-phase component and the fourth signal representing a quadrature phase component of the composite signal; converting the in-phase component to an in-phase digital signal, the in-phase digital signal being phase coherent with the first carrier signal; converting the quadrature component to a quadrature digital signal; extracting in-phase data from the third signal by means of a first fast Fourier transform; and extracting quadrature data from the fourth signal by means of a second fast Fourier transform.
Claim 12
Dependent Claim
21 words
The method for demodulating a composite signal according to claim 9, wherein the quadrature data modulates complementary quadrature amplitude modulated carriers.
Claim 13
Dependent Claim
32 words
The method for demodulating a composite signal according to claim 9, further comprising: combining the in-phase data and the quadrature data to produce a fifth signal, the fifth signal comprising non-complementary data.
Claim 14
Dependent Claim
27 words
The method for demodulating a composite signal according to claim 9, wherein the first fast Fourier transform and the second fast Fourier transform are performed substantially simultaneously.
References Cited (Backward Citations)
US5278826A
Cited
US5499271A
Cited
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