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WO1997008877A1 - Demodulation d'une forme d'onde numerique compatible modulee en amplitude, en utilisant deux processeurs fft - Google Patents

Demodulation d'une forme d'onde numerique compatible modulee en amplitude, en utilisant deux processeurs fft Download PDF

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Publication number
WO1997008877A1
WO1997008877A1 PCT/US1996/013526 US9613526W WO9708877A1 WO 1997008877 A1 WO1997008877 A1 WO 1997008877A1 US 9613526 W US9613526 W US 9613526W WO 9708877 A1 WO9708877 A1 WO 9708877A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
quadrature
phase
digital
data
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1996/013526
Other languages
English (en)
Inventor
Barry W. Carlin
Mark J. Dapper
Michael J. Geile
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
USA Digital Radio Partners LP
Original Assignee
USA Digital Radio Partners LP
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/604,276 external-priority patent/US5633896A/en
Application filed by USA Digital Radio Partners LP filed Critical USA Digital Radio Partners LP
Priority to EP96928969A priority Critical patent/EP0847642A4/fr
Priority to JP9510405A priority patent/JPH11509066A/ja
Priority to AU68539/96A priority patent/AU6853996A/en
Priority to BR9610614-0A priority patent/BR9610614A/pt
Publication of WO1997008877A1 publication Critical patent/WO1997008877A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

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

Definitions

  • 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 channel assignment.
  • Broadcast and reception of digitally-encoded audio signals is expected to provide improved audio fidelity.
  • Out-of-band techniques provide broadcast of digital radio signals in a specially designated frequency band.
  • In-band techniques provide
  • IBOC approach in-band on-channel or IBOC approach.
  • DAB digital audio broadcasting
  • IBOC in-band on-channel
  • An AM compatible digital broadcast waveform which satisfies the requirement of substantial orthogonality between 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 frequency (RF) carrier is modulated by an analog audio signal and the in-phase component of a digital signal.
  • the quadrature-phase RF carrier is modulated by the quadrature component of the digital signal.
  • the digital signal has an orthogonal frequency division
  • the in-phase signal consists of the conventional analog AM signal and selected digital carriers.
  • the in-phase digital carriers are placed outside of 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
  • the context of the present invention is a need to demodulate the composite waveform with minimal 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.
  • AM analog amplitude modulated
  • 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.
  • 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 passed through a digital high pass filter to separate the digital signal from the analog signal, as hereinafter
  • 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 of 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
  • 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.
  • IBOC in-band, on-channel
  • DAB digital audio broadcasting
  • inventions are that (1) the existing analog AM broadcast
  • channels can be upgraded to digital without requiring a new FCC frequency 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 minimized.
  • Fig. 1 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;
  • Fig. 6 is a representation of the signal-to-noise ratio (SNR) for carriers of the receiver in Fig. 4.
  • SNR signal-to-noise ratio
  • 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.
  • demodulation technique converts the signal 140 to baseband 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
  • 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.
  • FFT fast Fourier transform
  • 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 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.
  • mixer 180 separates the in-phase and quadrature components of the
  • the I and Q channels 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
  • the demodulation technique illustrated in Fig. 4 stops leakage of the AM signal through the highpass filter from interfering with the demodulation of the complementary
  • This technique also reduces the effects of noise and compensates for non-ideal operation of the I and Q mixer.
  • the demodulation techniques 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).
  • DSPs Digital Signal Processors
  • Fig. 5 shows the SNR for carriers when the receiver shown in Fig. 3 is used.
  • the low SNR in FFT bins +16 to +19 and -19 to -16 causes the bit error rate to increase.
  • the carriers in these FFT bins are near the edges of the
  • Fig. 6 is a plot of SNR for carriers when the
  • 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.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Discrete Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
  • Circuits Of Receivers In General (AREA)

Abstract

L'invention concerne un procédé et un appareil pour démoduler une forme d'onde composite d'audiodiffusion numérique (DAB) modulée en amplitude qui contient des porteuses modulées numériquement et qui fait appel à un mélangeur (180) pour convertir un signal reçu (170) en deux signaux, le premier de ces signaux représentant un composant en phase et le second un composant en quadrature de phase, deux convertisseurs de type analogique/numérique (182, 184) pour convertir les deux signaux en signaux numériques et deux éléments de transformée de Fourier rapide (FFT) (188, 190) pour extraire les données séparément des deux signaux numériques. Des signaux des porteuses numériques complémentaires sont récupérés du composant en quadrature de phase et des porteuses numériques non complémentaires sont obtenues par l'addition des données complémentaires et de la sortie de l'élément FFT recevant le composant en phase. On évite que les fuites des signaux modulés en amplitude dans un filtre passe-haut (186) n'interfèrent avec la démodulation des signaux complémentaires de la porteuse en utilisant des canaux de démodulation séparés.
PCT/US1996/013526 1995-08-31 1996-08-21 Demodulation d'une forme d'onde numerique compatible modulee en amplitude, en utilisant deux processeurs fft Ceased WO1997008877A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
EP96928969A EP0847642A4 (fr) 1995-08-31 1996-08-21 Demodulation d'une forme d'onde numerique compatible modulee en amplitude, en utilisant deux processeurs fft
JP9510405A JPH11509066A (ja) 1995-08-31 1996-08-21 二重ｆｆｔを使用したａｍ互換ディジタル波形復調
AU68539/96A AU6853996A (en) 1995-08-31 1996-08-21 Am compatible digital waveform demodulation using a dual fft
BR9610614-0A BR9610614A (pt) 1995-08-31 1996-08-21 Aparelho e processo para demodular um sinal compósito

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US301895P 1995-08-31 1995-08-31
US60/003,018 1996-02-21
US08/604,276 US5633896A (en) 1996-02-21 1996-02-21 AM compatible digital waveform demodulation using a dual FFT
US08/604,276 1996-02-21

Publications (1)

Publication Number Publication Date
WO1997008877A1 true WO1997008877A1 (fr) 1997-03-06

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1996/013526 Ceased WO1997008877A1 (fr) 1995-08-31 1996-08-21 Demodulation d'une forme d'onde numerique compatible modulee en amplitude, en utilisant deux processeurs fft

Country Status (6)

Country Link
EP (1) EP0847642A4 (fr)
JP (1) JPH11509066A (fr)
AU (1) AU6853996A (fr)
BR (1) BR9610614A (fr)
CA (1) CA2233063A1 (fr)
WO (1) WO1997008877A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000021261A1 (fr) * 1998-10-02 2000-04-13 Usa Digital Radio, Inc. Procede et appareil de demodulation et d'egalisation d'un signal de radiodiffusion audio numerique compatible am
ES2181550A1 (es) * 2000-09-06 2003-02-16 Univ Valencia Politecnica Selector de portadoras en modulaciones ofdm (multiplexacion por division de frencuencia ortogonal).
US7406141B1 (en) 2000-08-21 2008-07-29 Broadcom Corporation Multi-band DMT receiver

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5278826A (en) * 1991-04-11 1994-01-11 Usa Digital Radio Method and apparatus for digital audio broadcasting and reception
US5499271A (en) * 1991-04-11 1996-03-12 Institut Fur Rundfunktechnik Gmbh Method for broadcasting a digitally coded stream of data using an already occupied frequency spectrum

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
FR2707064B1 (fr) * 1993-06-21 1996-03-08 France Telecom

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5278826A (en) * 1991-04-11 1994-01-11 Usa Digital Radio Method and apparatus for digital audio broadcasting and reception
US5499271A (en) * 1991-04-11 1996-03-12 Institut Fur Rundfunktechnik Gmbh Method for broadcasting a digitally coded stream of data using an already occupied frequency spectrum

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0847642A4 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000021261A1 (fr) * 1998-10-02 2000-04-13 Usa Digital Radio, Inc. Procede et appareil de demodulation et d'egalisation d'un signal de radiodiffusion audio numerique compatible am
AU753955B2 (en) * 1998-10-02 2002-10-31 Ibiquity Digital Corporation Method and apparatus for demodulating and equalizing an AM compatible digital audio broadcast signal
RU2222872C2 (ru) * 1998-10-02 2004-01-27 Айбиквити Диджитал Корпорейшн Способ и устройство для демодуляции и коррекции сигнала вещания цифрового аудиосигнала, совместимого с амплитудно-модулированным сигналом
US7406141B1 (en) 2000-08-21 2008-07-29 Broadcom Corporation Multi-band DMT receiver
US7583742B2 (en) 2000-08-21 2009-09-01 Broadcom Corporation Multi-band DMT receiver
ES2181550A1 (es) * 2000-09-06 2003-02-16 Univ Valencia Politecnica Selector de portadoras en modulaciones ofdm (multiplexacion por division de frencuencia ortogonal).

Also Published As

Publication number Publication date
CA2233063A1 (fr) 1997-03-06
EP0847642A4 (fr) 2001-09-12
AU6853996A (en) 1997-03-19
BR9610614A (pt) 1999-12-21
EP0847642A1 (fr) 1998-06-17
JPH11509066A (ja) 1999-08-03

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