CA2233063A1 - Am compatible digital waveform demodulation using a dual fft - Google Patents
Am compatible digital waveform demodulation using a dual fft Download PDFInfo
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- CA2233063A1 CA2233063A1 CA002233063A CA2233063A CA2233063A1 CA 2233063 A1 CA2233063 A1 CA 2233063A1 CA 002233063 A CA002233063 A CA 002233063A CA 2233063 A CA2233063 A CA 2233063A CA 2233063 A1 CA2233063 A1 CA 2233063A1
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- signal
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Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
- H03D1/00—Demodulation of amplitude-modulated oscillations
- H03D1/22—Homodyne or synchrodyne circuits
- H03D1/2245—Homodyne or synchrodyne circuits using two quadrature channels
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2649—Demodulators
- H04L27/26524—Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04H—BROADCAST COMMUNICATION
- H04H2201/00—Aspects of broadcast communication
- H04H2201/10—Aspects of broadcast communication characterised by the type of broadcast system
- H04H2201/18—Aspects of broadcast communication characterised by the type of broadcast system in band on channel [IBOC]
- H04H2201/186—AM digital or hybrid
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2649—Demodulators
- H04L27/265—Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators
- H04L27/26522—Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators using partial FFTs
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Discrete Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Mathematical Physics (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
- Circuits Of Receivers In General (AREA)
Abstract
The invention provides a method and apparatus for demodulating a composite AM DAB waveform which contains digitally modulated carriers and which employ a mixer (180) for converting a received signal (170) into two signals, the first of these signals represents an in-phase component and the second of the signals represents a quadrature component, two analog-to-digital converters (182, 184) for converting the two signals into digital signals, and two fast Fourier transform elements (188, 190) for extracting data separately from the two digital signals. Complementary digital carrier signals are recovered from the quadrature, 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 (186) is prevented from interfering with the demodulation of the complementary carrier signal's use of separated demodulation channels.
Description
W O 97/08877 PCT~US96/13526 AM COMPATIBLE DIGITAL WAVEFORM DEMODULATION USING A DUAL FFT
R~UND OF THE lNV~. lON
This invention relates to waveform demodulation, and more particularly to methods of and apparatus for receiving and demodulating digitally modulated signals and analog amplitude modulated signals within the same frequency ~h~nnel assignment.
Broadcast and reception of digitally-encoded audio signals is expected to provide improved audio fidelity.
Several approaches have been suggested. Out-of--band t~ ni ques provide broadcast of digital radio signals in a specially designated frequency band. In-band techniques provide broadcast within substantially vacant slots between adjacent channels in the existing broadcast band (interstitial approach) or in under-utilized portions within the same frequency channel allocations currently used by ~- ~cial broadcasters (in-band on-channel or IBOC approach). The in-band on-channel approach may be implemented without the need for additional frequency coordination and with relatively minor changes to existing transmitting equipment. It is also a requirement that any digital audio broadcasting (DAB) technique must not degrade analog signal reception by conventional analog receivers.
In-band approaches to digital audio broadcasting have thus far only been proposed in the FM band (88 MHz to 108 MHz), since the bandwidth of AM channels is relatively narrow as compared to the FM band allocation. However, high fidelity digital audio broadcasting in the AM band (530 kHz to 1700 kHz) would provide AM broadcasting stations with a means to compete with high-quality, portable audio sources such as cassette tapes and compact disc players. It would therefore be desirable to promote an in-band on-channel (IBOC) approach in the AM broadcasting band to provide enhanced fidelity through digital signalling without affecting reception by existing analog AM receivers.
An AM compatible digital broadcast waveform which satisfies the requirement of substantial orthogonality between W O 97/08877 PCT~US96/13526 a conventional analog AM signal and a digitally modulated signal set has been developed. The waveform is described in U.S. Patent Application Serial No. 08/206,368 filed March 7, 1994, entitled METHOD AND APPARATUS FOR AM COMPATIBLE DIGITAL
BROADCASTING. The waveform spectrum consists of in-phase and quadrature components. An in-phase radio fre~uency (RF) carrier is ~n~lllated by an analog audio signal and the in-phase component of a digital signal. The quadrature-phase RF carrier is ~AIll ated b~ the quadrature component of the digital signal.
The digital signal has an orthogonal frequency division multiplexed (OFDM) ~ormat. The in-phase signal consists of the conventional analog AM signal and selected digital carriers.
The in-phase digital carriers are placed outside o~ the spectral region occupied by the analog AM signal. The quadrature-phase carriers are situated both within and outside the spectral region occupied by the analog AM signal (although not at the center frequency occupied by the unmodulated analog carrier). The quadrature digital carriers situated within the same spectral region as the analog AM signal are called complementary carriers. The above described arrangement is further described in U.S. Patent Application Serial No.
08/368,061 filed January 3, 1995, entitled METHOD AND APPARATUS
FOR IMP~OVING AM COMPATIBLE DIGITAL BROADCAST ANALOG FIDELITY.
The context of the present invention is a need to demodulate the composite waveform with mini~l crosstalk. The modulated composite waveform is produced by a modulation method in which an analog amplitude modulated (AM) signal and a digital signal which may be a representation of the analog audio signal (or it may be any other digital signal) are encoded together and transmitted simultaneously in the same frequency channel. This approach places some of the digital carriers in quadrature with the analog AM, thereby enabling the AM DAB data to be extracted and decoded with high ~idelity and without crosstalk, assuming the receiver is capable of proper signal separation.
A receiver (which is not necessarily prior art) has been considered which converts the signal to baseband using conventional I and Q mixers, with the I channel signal being W O 97/08877 PCT~US96/13526 passed through a digital high pass filter to separate the digital signal from the analog signal, as hereinafter explained, a problem has been discovered related to crosstalk between the analog signal and the digital signal. In the receiver under consideration, the analog signal interferes with the demodulation of the complementary carriers if the demodulation of the I and Q component samples is carried out in a single common FFT processor. What is needed is a demodulation technique which minimizes the undesired crosstalk between the analog signal and the digital signals.
8UNMARY OF T~E lNV ~:~.,lON
According to the invention, in an AM compatible digital audio broadcasting (AM DAB) system using an orthogonal frequency division multiplexed (OFDM) modulation format, a radio frequency receiving and demodulating method and apparatus employs dual fast Fourier transform processes on separate respective in-phase and quadrature-phase components of a received OFDM digital signal, the output of the quadrature channel being used to recover the complementary data, and the resultant processed component signals being summed to recover the non-complementary data.
The apparatus includes a mixer for converting a received signal into two signals, the first of the two signals representing an in-phase component and the second o~ the two signals representing a quadrature component; two analog-to-digital converters for converting the two signals into digital signals; and two fast Fourier transform processors for extracting data from the two signals.
The present invention provides better and higher resolution data extraction than heretofore known. Moreover, the invention can be useful in providing an in-band, on-channel (IBOC) solution to digital audio broadcasting (DAB) in the AM
frequency band.
- 35 The advantages of the waveform of the present invention are that (1) the existing analog AM broadcast channels can be upgraded to digital without requiring a new FCC
~requency allocation, (2) the AM broadcast stations can be upgraded to a digital broadcast format with only limited capital expenditure, (3) the composite waveform at appropriate digital power levels yields a coverage area that is essentially equivalent to the existing analog AM station, ( 4) the existing AM receivers can recover the analog portion of the composite signal without modification, and (5) interference between the digital signal and the analog signal is ;nim;zed.
A description of the AM DAB waveform involved is presented in U.S. Serial No. 08/206,368, filed on March 7, 1994, which is herein incorporated by reference.
A further underst~n~;ng of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.
BRIEF DE8CRIPTION OF T~E DRAWING8 The invention will be more readily apparent to those skilled in the art by reference to the ac~omr~nying drawings wherein:
Fig. l is a spectral representation of the in-phase component of a composite analog AM and digital broadcasting signal;
Fig. 2 is a spectral representation of the quadrature component of a digital broadcasting signal;
Fig. 3 is a block diagram of a demodulator which has been considered for the subject waveform;
Fig. 4 is a block diagram of a demodulator in accordance with the present invention;
Fig. 5 is a representation of the signal-to-noise ratio (SNR) for carriers of the receiver shown in Fig. 3; and Fig. 6 is a representation of the signal-to-noise ratio (SNR) for carriers of the receiver in Fig. 4.
DE~TT~n DE8CRIPTION OF 8PECIFIC EMBODIMENT8 This invention provides a method o~ simultaneously receiving both an analog amplitude modulated signal and a digital signal on the same channel assiynment as the existing analog AM broadcasting allocation.
W O 97/08877 PCTrUS96/13526 The AM DAB waveform of the present invention has been previously explained. Fig. 1 is a spectral representation of the in-phase component of a composite analog AM and digital broadcasting signal. The in-phase component contains the conventional analog AM signal 100 and non-complementary digital carriers 102. The in-phase component does not have any digital carriers 102 in the spectral region occupied by the analog AM
signal 100.
Fig. 2 is a spectral representation of the quadrature component of a digital broadcasting signal. The quadrature portion of the spectrum as shown in Fig. 2 contains only digital carriers 110 and 112. The digital carriers that lie outside the spectral region of the analog AM signal 100 are non-complementary signals 112, and the digital carriers that lie in the same frequency region as the analog AM signal 100 are complementary signals 110.
Fig. 3 illustrates a demodulator which was considered in connection with the waveform herein described. The demodulation t~h~ique converts the signal 140 to bas~h~n~
using conventional I and Q mixer 150. Mixer 150 separates the in-phase and quadrature components of the received signal. The I and Q channels are then digitized in analog-to-digital (A/D) converters 154 and 156. Following A/D converter 154, the I
channel is passed through high pass filter 152 which is designed to eliminate the analog AM signal. The high pass filter 152 is in the real world less than ideal, which gives rise to some of the problems overcome by the present invention.
The I and Q channels are then input to a fast Fourier transform (FFT) processor 158 in order to recover and obtain the received data.
While the device revealed in Fig. 3 will demodulate the signal involved, there is room for improvement. In ~ particular, the receiver of Fig. 3 has several problems. For example, some of the analog AM signal leaks through highpass filter stopband 152 and interferes with the demodulation of the complementary carriers.
Fig. 4 illustrates how demodulation is performed in the present invention. This new demodulation technique avoids W O 97/08877 PCT~US96/13526 the problem of the demodulation technique illustrated in Fig. 3 by using two FFTs which operate separately on the I and Q
channels. The received signal 170 is converted to baseband by conventional I and Q mixer 180. As with mixer 150, mixer 180 separates the in-phase and quadrature components of the received signal. The I and Q ~hi~nnels are then separately sent to A/D converters 182 and 184 where they are digitized. The I
channel is passed through high pass filter 186 which attempts to eliminate the analog AM signal. The I and Q channels are then processed separately with dual FFT processors 188 and 190.
The output from the Q channel is used to recover the complementary carriers, and the sum of the I and Q channels is used to recover the non-complementary carriers.
The demodulation t~hnique illustrated in Fig. 4 stops leakage of the AM signal through the highpass filter from inter~ering with the demodulation of the complementary carriers. This tPchnique also reduces the effects of noise and compensates for non-ideal operation o~ the I and Q mixer.
The demodulation t~chn;ques illustrated in Fig. 3 and Fig. 4 are implemented using common, commercially-available RF
hardware, such as mixers and general purpose Digital Signal Processors (DSPs) with software to provide the various features of the demodulator (e.g., FFTs).
Fig. 5 shows the SNR for carriers when the receiver 25 shown in Fig. 3 is used. The low SNR in FFT bins +16 to +19 and -19 to -1~ causes the bit error rate to increase. The carriers in these FFT bins are near the edges of the complementary band, and the corresponding SNR is approximately 16 dB.
Fig. 6 is a plot of SNR for carriers when the demodulator illustrated in Fig 4 is used. The SNR for the complementary carriers in Fig. 6 is approximately 33 dB. This is a significant improvement over the SNR for the complementary carriers for the demodulator illustrated in Fig. 3 and a lower bit error rate results. With the improved demodulator of Fig.
4, the signal can be received further away from the system's transmitter.
W O 97/08877 PCT~US96/13526 Although the foregoing invention has been described in some detail by way of illustration and example, for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.
R~UND OF THE lNV~. lON
This invention relates to waveform demodulation, and more particularly to methods of and apparatus for receiving and demodulating digitally modulated signals and analog amplitude modulated signals within the same frequency ~h~nnel assignment.
Broadcast and reception of digitally-encoded audio signals is expected to provide improved audio fidelity.
Several approaches have been suggested. Out-of--band t~ ni ques provide broadcast of digital radio signals in a specially designated frequency band. In-band techniques provide broadcast within substantially vacant slots between adjacent channels in the existing broadcast band (interstitial approach) or in under-utilized portions within the same frequency channel allocations currently used by ~- ~cial broadcasters (in-band on-channel or IBOC approach). The in-band on-channel approach may be implemented without the need for additional frequency coordination and with relatively minor changes to existing transmitting equipment. It is also a requirement that any digital audio broadcasting (DAB) technique must not degrade analog signal reception by conventional analog receivers.
In-band approaches to digital audio broadcasting have thus far only been proposed in the FM band (88 MHz to 108 MHz), since the bandwidth of AM channels is relatively narrow as compared to the FM band allocation. However, high fidelity digital audio broadcasting in the AM band (530 kHz to 1700 kHz) would provide AM broadcasting stations with a means to compete with high-quality, portable audio sources such as cassette tapes and compact disc players. It would therefore be desirable to promote an in-band on-channel (IBOC) approach in the AM broadcasting band to provide enhanced fidelity through digital signalling without affecting reception by existing analog AM receivers.
An AM compatible digital broadcast waveform which satisfies the requirement of substantial orthogonality between W O 97/08877 PCT~US96/13526 a conventional analog AM signal and a digitally modulated signal set has been developed. The waveform is described in U.S. Patent Application Serial No. 08/206,368 filed March 7, 1994, entitled METHOD AND APPARATUS FOR AM COMPATIBLE DIGITAL
BROADCASTING. The waveform spectrum consists of in-phase and quadrature components. An in-phase radio fre~uency (RF) carrier is ~n~lllated by an analog audio signal and the in-phase component of a digital signal. The quadrature-phase RF carrier is ~AIll ated b~ the quadrature component of the digital signal.
The digital signal has an orthogonal frequency division multiplexed (OFDM) ~ormat. The in-phase signal consists of the conventional analog AM signal and selected digital carriers.
The in-phase digital carriers are placed outside o~ the spectral region occupied by the analog AM signal. The quadrature-phase carriers are situated both within and outside the spectral region occupied by the analog AM signal (although not at the center frequency occupied by the unmodulated analog carrier). The quadrature digital carriers situated within the same spectral region as the analog AM signal are called complementary carriers. The above described arrangement is further described in U.S. Patent Application Serial No.
08/368,061 filed January 3, 1995, entitled METHOD AND APPARATUS
FOR IMP~OVING AM COMPATIBLE DIGITAL BROADCAST ANALOG FIDELITY.
The context of the present invention is a need to demodulate the composite waveform with mini~l crosstalk. The modulated composite waveform is produced by a modulation method in which an analog amplitude modulated (AM) signal and a digital signal which may be a representation of the analog audio signal (or it may be any other digital signal) are encoded together and transmitted simultaneously in the same frequency channel. This approach places some of the digital carriers in quadrature with the analog AM, thereby enabling the AM DAB data to be extracted and decoded with high ~idelity and without crosstalk, assuming the receiver is capable of proper signal separation.
A receiver (which is not necessarily prior art) has been considered which converts the signal to baseband using conventional I and Q mixers, with the I channel signal being W O 97/08877 PCT~US96/13526 passed through a digital high pass filter to separate the digital signal from the analog signal, as hereinafter explained, a problem has been discovered related to crosstalk between the analog signal and the digital signal. In the receiver under consideration, the analog signal interferes with the demodulation of the complementary carriers if the demodulation of the I and Q component samples is carried out in a single common FFT processor. What is needed is a demodulation technique which minimizes the undesired crosstalk between the analog signal and the digital signals.
8UNMARY OF T~E lNV ~:~.,lON
According to the invention, in an AM compatible digital audio broadcasting (AM DAB) system using an orthogonal frequency division multiplexed (OFDM) modulation format, a radio frequency receiving and demodulating method and apparatus employs dual fast Fourier transform processes on separate respective in-phase and quadrature-phase components of a received OFDM digital signal, the output of the quadrature channel being used to recover the complementary data, and the resultant processed component signals being summed to recover the non-complementary data.
The apparatus includes a mixer for converting a received signal into two signals, the first of the two signals representing an in-phase component and the second o~ the two signals representing a quadrature component; two analog-to-digital converters for converting the two signals into digital signals; and two fast Fourier transform processors for extracting data from the two signals.
The present invention provides better and higher resolution data extraction than heretofore known. Moreover, the invention can be useful in providing an in-band, on-channel (IBOC) solution to digital audio broadcasting (DAB) in the AM
frequency band.
- 35 The advantages of the waveform of the present invention are that (1) the existing analog AM broadcast channels can be upgraded to digital without requiring a new FCC
~requency allocation, (2) the AM broadcast stations can be upgraded to a digital broadcast format with only limited capital expenditure, (3) the composite waveform at appropriate digital power levels yields a coverage area that is essentially equivalent to the existing analog AM station, ( 4) the existing AM receivers can recover the analog portion of the composite signal without modification, and (5) interference between the digital signal and the analog signal is ;nim;zed.
A description of the AM DAB waveform involved is presented in U.S. Serial No. 08/206,368, filed on March 7, 1994, which is herein incorporated by reference.
A further underst~n~;ng of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.
BRIEF DE8CRIPTION OF T~E DRAWING8 The invention will be more readily apparent to those skilled in the art by reference to the ac~omr~nying drawings wherein:
Fig. l is a spectral representation of the in-phase component of a composite analog AM and digital broadcasting signal;
Fig. 2 is a spectral representation of the quadrature component of a digital broadcasting signal;
Fig. 3 is a block diagram of a demodulator which has been considered for the subject waveform;
Fig. 4 is a block diagram of a demodulator in accordance with the present invention;
Fig. 5 is a representation of the signal-to-noise ratio (SNR) for carriers of the receiver shown in Fig. 3; and Fig. 6 is a representation of the signal-to-noise ratio (SNR) for carriers of the receiver in Fig. 4.
DE~TT~n DE8CRIPTION OF 8PECIFIC EMBODIMENT8 This invention provides a method o~ simultaneously receiving both an analog amplitude modulated signal and a digital signal on the same channel assiynment as the existing analog AM broadcasting allocation.
W O 97/08877 PCTrUS96/13526 The AM DAB waveform of the present invention has been previously explained. Fig. 1 is a spectral representation of the in-phase component of a composite analog AM and digital broadcasting signal. The in-phase component contains the conventional analog AM signal 100 and non-complementary digital carriers 102. The in-phase component does not have any digital carriers 102 in the spectral region occupied by the analog AM
signal 100.
Fig. 2 is a spectral representation of the quadrature component of a digital broadcasting signal. The quadrature portion of the spectrum as shown in Fig. 2 contains only digital carriers 110 and 112. The digital carriers that lie outside the spectral region of the analog AM signal 100 are non-complementary signals 112, and the digital carriers that lie in the same frequency region as the analog AM signal 100 are complementary signals 110.
Fig. 3 illustrates a demodulator which was considered in connection with the waveform herein described. The demodulation t~h~ique converts the signal 140 to bas~h~n~
using conventional I and Q mixer 150. Mixer 150 separates the in-phase and quadrature components of the received signal. The I and Q channels are then digitized in analog-to-digital (A/D) converters 154 and 156. Following A/D converter 154, the I
channel is passed through high pass filter 152 which is designed to eliminate the analog AM signal. The high pass filter 152 is in the real world less than ideal, which gives rise to some of the problems overcome by the present invention.
The I and Q channels are then input to a fast Fourier transform (FFT) processor 158 in order to recover and obtain the received data.
While the device revealed in Fig. 3 will demodulate the signal involved, there is room for improvement. In ~ particular, the receiver of Fig. 3 has several problems. For example, some of the analog AM signal leaks through highpass filter stopband 152 and interferes with the demodulation of the complementary carriers.
Fig. 4 illustrates how demodulation is performed in the present invention. This new demodulation technique avoids W O 97/08877 PCT~US96/13526 the problem of the demodulation technique illustrated in Fig. 3 by using two FFTs which operate separately on the I and Q
channels. The received signal 170 is converted to baseband by conventional I and Q mixer 180. As with mixer 150, mixer 180 separates the in-phase and quadrature components of the received signal. The I and Q ~hi~nnels are then separately sent to A/D converters 182 and 184 where they are digitized. The I
channel is passed through high pass filter 186 which attempts to eliminate the analog AM signal. The I and Q channels are then processed separately with dual FFT processors 188 and 190.
The output from the Q channel is used to recover the complementary carriers, and the sum of the I and Q channels is used to recover the non-complementary carriers.
The demodulation t~hnique illustrated in Fig. 4 stops leakage of the AM signal through the highpass filter from inter~ering with the demodulation of the complementary carriers. This tPchnique also reduces the effects of noise and compensates for non-ideal operation o~ the I and Q mixer.
The demodulation t~chn;ques illustrated in Fig. 3 and Fig. 4 are implemented using common, commercially-available RF
hardware, such as mixers and general purpose Digital Signal Processors (DSPs) with software to provide the various features of the demodulator (e.g., FFTs).
Fig. 5 shows the SNR for carriers when the receiver 25 shown in Fig. 3 is used. The low SNR in FFT bins +16 to +19 and -19 to -1~ causes the bit error rate to increase. The carriers in these FFT bins are near the edges of the complementary band, and the corresponding SNR is approximately 16 dB.
Fig. 6 is a plot of SNR for carriers when the demodulator illustrated in Fig 4 is used. The SNR for the complementary carriers in Fig. 6 is approximately 33 dB. This is a significant improvement over the SNR for the complementary carriers for the demodulator illustrated in Fig. 3 and a lower bit error rate results. With the improved demodulator of Fig.
4, the signal can be received further away from the system's transmitter.
W O 97/08877 PCT~US96/13526 Although the foregoing invention has been described in some detail by way of illustration and example, for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.
Claims (12)
1. 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.
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.
2. The apparatus for demodulating according to claim 1, wherein the quadrature phase component comprises complementary carriers and non-complementary carriers.
3. The apparatus for demodulating according to claim 2, wherein the first carrier signal and the complementary carriers are located in a same frequency region.
4. The apparatus for demodulating according to claim 1, wherein the means for separating is a quadrature mixer.
5. The apparatus for demodulating according to claim 1, wherein the first means and the second means are analog-to-digital converters.
6. 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.
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.
7. The apparatus for demodulating according to claim 1, wherein the in-phase digital signal is phase coherent with the first carrier signal-
8. 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.
9. 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.
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.
10. The method for demodulating a composite signal according to claim 9, wherein the quadrature data modulates complementary quadrature amplitude modulated carriers.
11. 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.
combining the in-phase data and the quadrature data to produce a fifth signal, the fifth signal comprising non-complementary data.
12. 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.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US301895P | 1995-08-31 | 1995-08-31 | |
US08/604,276 US5633896A (en) | 1996-02-21 | 1996-02-21 | AM compatible digital waveform demodulation using a dual FFT |
US60/003,018 | 1996-02-21 | ||
US08/604,276 | 1996-02-21 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA2233063A1 true CA2233063A1 (en) | 1997-03-06 |
Family
ID=26671176
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002233063A Abandoned CA2233063A1 (en) | 1995-08-31 | 1996-08-21 | Am compatible digital waveform demodulation using a dual fft |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP0847642A4 (en) |
JP (1) | JPH11509066A (en) |
AU (1) | AU6853996A (en) |
BR (1) | BR9610614A (en) |
CA (1) | CA2233063A1 (en) |
WO (1) | WO1997008877A1 (en) |
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Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6295317B1 (en) * | 1998-10-02 | 2001-09-25 | Usa Digital Radio Partners, Lp | Method and apparatus for demodulating and equalizing an AM compatible digital audio broadcast signal |
US6556639B1 (en) * | 1999-06-24 | 2003-04-29 | Ibiquity Digital Corporation | Method and apparatus for determining transmission mode and synchronization for a digital audio broadcasting signal |
GB0020624D0 (en) | 2000-08-21 | 2000-10-11 | Element 14 Inc | Multi band DMT receiver |
ES2181550B1 (en) * | 2000-09-06 | 2003-12-16 | Univ Valencia Politecnica | CARRIER SELECTOR IN OFDM MODULATIONS (MULTIPLEXATION BY DIVISION OF ORTOGONAL FREQUENCY). |
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---|---|---|---|---|
US5128964A (en) * | 1990-10-10 | 1992-07-07 | Intelligent Modem Corporation | Modulation method and apparatus for multicarrier data transmission |
SG44771A1 (en) * | 1991-02-28 | 1997-12-19 | Philips Electronics Nv | System for broadcasting and receiving digital data receiver and transmitter for use in such system |
DE4111855C2 (en) * | 1991-04-11 | 1994-10-20 | Inst Rundfunktechnik Gmbh | Method for the radio transmission of a digitally coded data stream |
US5278826A (en) * | 1991-04-11 | 1994-01-11 | Usa Digital Radio | Method and apparatus for digital audio broadcasting and reception |
FR2707064B1 (en) * | 1993-06-21 | 1996-03-08 | France Telecom |
-
1996
- 1996-08-21 WO PCT/US1996/013526 patent/WO1997008877A1/en not_active Application Discontinuation
- 1996-08-21 JP JP9510405A patent/JPH11509066A/en active Pending
- 1996-08-21 EP EP96928969A patent/EP0847642A4/en not_active Withdrawn
- 1996-08-21 AU AU68539/96A patent/AU6853996A/en not_active Abandoned
- 1996-08-21 BR BR9610614-0A patent/BR9610614A/en not_active Application Discontinuation
- 1996-08-21 CA CA002233063A patent/CA2233063A1/en not_active Abandoned
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BR9610614A (en) | 1999-12-21 |
AU6853996A (en) | 1997-03-19 |
WO1997008877A1 (en) | 1997-03-06 |
JPH11509066A (en) | 1999-08-03 |
EP0847642A1 (en) | 1998-06-17 |
EP0847642A4 (en) | 2001-09-12 |
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EEER | Examination request | ||
FZDE | Discontinued |