WO1999049635A1 - Procede et montage de reduction de l'ecretage de signaux multiporteuses - Google Patents

Procede et montage de reduction de l'ecretage de signaux multiporteuses Download PDF

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Publication number
WO1999049635A1
WO1999049635A1 PCT/EP1999/001960 EP9901960W WO9949635A1 WO 1999049635 A1 WO1999049635 A1 WO 1999049635A1 EP 9901960 W EP9901960 W EP 9901960W WO 9949635 A1 WO9949635 A1 WO 9949635A1
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WIPO (PCT)
Prior art keywords
carrier
time domain
symbol
carrier symbol
domain multi
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PCT/EP1999/001960
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English (en)
Inventor
Mohammed Zekri
Leo Van Biesen
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Vrije Universiteit Brussel
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.)
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Publication date
Application filed by Vrije Universiteit Brussel filed Critical Vrije Universiteit Brussel
Priority to AU34173/99A priority Critical patent/AU3417399A/en
Publication of WO1999049635A1 publication Critical patent/WO1999049635A1/fr

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Classifications

    • 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
    • H04L27/2614—Peak power aspects
    • 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
    • H04L27/2626—Arrangements specific to the transmitter only
    • 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

Definitions

  • the present invention relates to a method to reduce the clipping probability of a multi- carrier signal as defined in the non-characteristic part of claim 1, an arrangement to be used in a multi-carrier transmitter of a multi -carrier system wherein this method is applied as defined in the non-characteristic part of claim 2, and a corresponding arrangement to be used in a multi-carrier receiver of this multi-carrier system as defined in the non-characteristic part of claim 3.
  • Such a method and arrangements to perform such a method are already known in the art, e.g. from the contribution T1E1.4/97-323 to the ADSL (Asymmetric Digital Subscriber Line) Standards Committee T7 El.4 of ANSI.
  • the sequences are afterwards again combined into a transformed time domain DMT symbol suitable for transmission towards a DMT receiver. Together with the transformed DMT symbol, an indication is transmitted to the DMT receiver of the transformation applied to the DMT symbol so that the DMT receiver can perform the correct 2 inverse transformation.
  • This inverse transformation typically consists of a fast fourier transformation transforming the transformed time domain DMT symbol into a transformed frequency domain DMT symbol, and an inverse transformation applied to the transformed frequency domain DMT symbol to regenerate the original frequency domain DMT symbol.
  • the latter inverse transformation decomposes the transformed frequency domain DMT symbol in two sequences, rotates the carriers of these two sequences over angles that are an integer multiple of ⁇ /2 radians, the integer multiple being proportional to a carrier index of the respective carrier, and complex conjugates the carriers.
  • the sequences are afterwards combined again thereby constituting the original frequency domain DMT symbol.
  • a clip event occurs if none of the transformations produces an allowed transformed time domain multi-carrier symbol.
  • An object of the present invention is to define a method and equipment to reduce the clipping probability of multi-carrier signals as already known, but which enable to reduce the clipping probability significantly compared to the known technique, whilst not increasing the arithmetic complexity significantly.
  • this object is achieved by the method defined in claim 1, the arrangement to be used in a multi-carrier transmitter as defined in claim 2 and the arrangement to be used in a multi-carrier receiver as defined in claim 3. Indeed, by producing a complex time domain multi-carrier symbol of length N and decomposing this complex time domain multi-carrier symbol into four partitions, a fixed rotation of all carriers of a partition over an integer multiple of ⁇ /2 radians can be implemented by switching and/or inverting the real and imaginary parts of samples of this partition.
  • a device A coupled to a device 8 should not be limited to devices or systems wherein an output of device A is directly connected to on input of device B. It means that there exists a pauh between an output of A and an input of B which may be a path including other devices or means .
  • the system drawn in the figure contains a multi-carrier transmitter TX and a multi-carrier receiver RX intercoupled via a communication line.
  • the multi- carrier transmitter TX is equipped with the cascade connection of an inverse fast fourier transformer IFFT, a transformation unit TRANSF, an observation device OBS, a real part selector REAL, a parallel to serial converter P/S and an adder, and further comprises a pilot tone modulator PILOT MOD with an input connected to an output of the transformation unit TRANSF and an output connected to an input of the adder.
  • a control output of the obser- vation device OBS is coupled to a control input of the transformation unit TRANSF.
  • the multi-carrier receiver RX is provided with the cascade connection of a serial to parallel converter S/P, a fast fourier transformer FFT, and an inverse transformation unit INV TRANSF.
  • the receiver RX includes a pilot tone demodulator PILOT DMOD coupled with its input to an output of the fast fourier transformer FFT and having an output connected to a control input of the inverse transformation unit INV TRANSF.
  • the communication line couples the adder of the multi-carrier transmitter TX to the serial to parallel converter S/P of the multi- carrier receiver RX .
  • the transmitter TX in addition to the shown components contains carrier modulation means, a digital to analogue converter and a line driver
  • the receiver RX in addition to the drawn functional blocks comprises an analogue to digital converter and carrier demodulating means
  • the transmitter TX and receiver PX both may further be equipped with digital equalisers operating in time domain or frequency domain, digital or analogue filters, echo cancellers, rotors, and so on. Since the functionality of these components is not affected by implementation of the present invention, and their presence in a multi-carrier system is rather optional and dependant on environmental conditions, they are not considered any further in this document.
  • bits are allocated to the different carriers depending on the transfer quality of these carriers. This transfer quality may be estimated by signal to noise ratio measurements performed during initialisation of the system.
  • the bits allocated to each one of the carriers are modulated thereon according to certain modulation techniques and constellations which may differ from carrier to carrier.
  • the modulated carriers constituting one multi-carrier symbol are transformed from frequency domain to time domain by the inverse fast fourier transformer IFFT.
  • the modulated carriers thereto are applied in the form of following complex sequence Y(n) to the inverse fast fourier transformer IFF7 :
  • X(n) is a complex value representing the n'th modulated carrier of the multi-carrier symbol to be transmitted, N/2 equals the number of carriers, and n is an integer index.
  • the inverse fast fourier transform of the complex sequence Y(n) is another complex sequence y(n) denoted as:
  • a(n) and b(n) are two real sequences of length N and j is the notation for the square root of -1.
  • the 7 output y(n) of the inverse fast fourier transformer IFFT in other words is a complex time domain sequence of length whose real part a(n) will be transmitted. This real part a(n) will be selected for transmission by the real part selector REAL. It is further remarked that:
  • x(n) represents the real inverse fast fourier transform of the multi-carrier symbol X(n), i.e. the inverse fast fourier transform of the sub- carrier complex conjugate vector built up from X(n) .
  • the time domain multicarrier symbol is subjected to a transformation.
  • the threshold condition is verified by the observation device OBS, which thereupon controls the transformation unit TRANSF to apply the transformation on y(n) .
  • the transformation unit TRANSF is able to apply seven different transformations to the complex time domain multi-carrier symbol y(n) . These seven transformations will be discussed in detail below. If none of the seven transformations produces a transformed time domain multi - carrier symbol whose respective real parts t.
  • t 2 (n) , t 3 (n) , t 4 (n), t 5 (n) , t 6 (n) or t 7 (n) consist of samples with an amplitude below the threshold value, a clip event occurs. This may cause out-of-band radiation on the communication line.
  • the transformation unit TRANSF decomposes the time domain multi-carrier symbol y(n) in four partitions each containing information with respect to special subsets of carriers of the multi-carrier symbol Y(n) .
  • the frequency domain multi-carrier symbol Y(n) would be decomposed in two partitions, the first partition Ya carrying the even 8 numbered carriers and the second partition Yb, carrying the odd numbered carriers.
  • the transformation unit TRANSF first decomposes the time domain multi-carrier symbol y(n) in 4 partitions y (n) , y (n),y 2 (n), and y 3 (n) . Afterwards, the real and imaginary parts of these partitions will be used to constitute a transformed time domain multi-carrier symbol whose real part is denoted either by t. (n) , t.(n), t 3 (n), t_.(n), t 5 (n), t. (n) or t_ (n) .
  • the carriers of a partition may be rotated over an angle which is an integer multiple of 27r/N radians, the integer multiple being proportional to the carrier index n, and may be rotated over a fixed angle equal for all carriers of that partition before the partitions are recombined 10 into the transformed time domain multi -carrier symbol with real parts t ⁇ (n) , t 2 (n) , t- (n) , t 4 (n) , t_ (n) , t.(n) or t,(n) .
  • One of the transformed real time domain multi - carrier symbols parts t. (n) , t 2 (n) , t 3 (n) , t 4 (n) , t_(n), t g (n) or t 7 (n) is selected for transmission, is parallel to serial converted by P/S and transferred to the multi- carrier receiver RX .
  • An indication of the applied transformation is modulated on the pilot carrier by the pilot tone modulator PILOT MOD and added to the multi- carrier symbol before transmission towards the receiver RX . Obviously, the applied transformation may be indicated in another way to the multi carrier receiver RX too.
  • the transformed time domain multi-carrier symbol is again parallelised by the serial to parallel converter S/P and converted into a transformed frequency domain multi -carrier symbol, respectively T. (n) , T. (n) , T- (n) , T 4 (n) , T 5 (n) , T 6 (n) or T contemplat(n), by the fast fourier transformer FFT.
  • the pilot carrier is monitored by the pilot tone demodulator PILOT DMOD, and the information demodulated from this pilot carrier is used to control the inverse transformation unit INV TRANSF so that the exact inverse transformation is applied to the transformed frequency domain multi - carrier symbol T.
  • phasor transformations are used for the inverse transformations.
  • Such phasor transformations are defined by a phasor transformation 11 vector Z (n) .
  • this phasor transformation vector may be expressed as:
  • A is a complex constant (for n even or n uneven) and ⁇ n is any multiple of 2 ⁇ /N proportional to the index n, enlarged by a fixed angle ⁇ .
  • ⁇ n can be written as
  • ⁇ n ⁇ n + n(2( ⁇ M/N) :i7)
  • the real and imaginary parts of the four partitions Y 0 (n) , y. (n) , y 2 (n) and y 3 (n) are combined by the transformation unit TRANSF into the following transformed time domain multi- carrier symbol:
  • t. (n) 2 . (a. (n) +a 3 (n) ) + 2 (a 2 (n+N/8) +b.(n+N/8) +a ⁇ (n+3N/8) -b.(n+3N/8) ) (22)
  • the original frequency domain multi-carrier symbol can be recovered from T (n) by the inverse transformation unit INV TRANSF if the following inverse transformation is applied:
  • X(n) ⁇ T.(n)/Z.(n) for n e ⁇ 2 mod4 ⁇ and 2 ⁇ n ⁇ N/2-l T.(n)/Z 2 (n) for n e ⁇ l mod4 ⁇ and l ⁇ n ⁇ N/2-1 k 0 for N/2 ⁇ n ⁇ N (23)
  • ⁇ 0 mod 4 ⁇ stands for the set ⁇ 0, 4, 8, 12, 16, ... ⁇ .
  • t, (n) 2. (a 0 (n)+a. (n) ) + 2 (a, (n+N/8) +b, (n+5N/8) +a, (n+3N/8) +b, (n+7N/8) ) (24; 13
  • the original frequency domain multi-carrier symbol can be recovered from T, (n) by the inverse transformation unit INV TRANSF if the following inverse transformation is applied:
  • X(n) ⁇ T 2 (n)/Z 1 (n) for n e ⁇ 2 mod4 ⁇ and 2 ⁇ n ⁇ N/2-l T 2 (n)/Z 2 (n) for n e ⁇ 3 mod4 ⁇ and 3 ⁇ n ⁇ N/2-l 0 for N/2 ⁇ n ⁇ N (25)
  • the four partitions y o (n), y (n) , y 2 (n) and y (n) are combined into the following transformed time domain muiti-carrier symbol :
  • the original frequency domain multi-carrier symbol can be recovered from T. (n) by the inverse transformation unit INV TRANSF if the following inverse transformation is applied:
  • the four partitions y (n) , y (n) , y (n) and y 3 (n) are combined into the following transformed time domain multi -carrier symbol :
  • t (n) 2. (a o (n)+a 3 (n) ) + 2 (a 2 (n+3N/8) +b 2 (n+7N/8) +a ⁇ (n+N/8) +b ⁇ (n+5N/8) ) (28)
  • the original frequency domain multi-carrier symbol can be recovered from T (n) by the inverse transformation unit INV TRANSF if the following inverse transformation is applied:
  • X(n) T 4 (n)/Z 2 (n) for n e ⁇ 2 mod4 ⁇ and 2 ⁇ n ⁇ N/2-l T 4 (n)/Z.(n) for n e ⁇ l mod4 ⁇ and l ⁇ n ⁇ N/2-1 L0 for N/2 ⁇ n ⁇ N (29)
  • the four partitions y o (n), y.(n), y 2 (n) and y 3 (n) are combined into the following transformed time domain multi-carrier symbol :
  • t 5 (n) 2. (a 0 (n)+a 1 (n) ) + 2 (a, (n+3N/8) +b 2 (n+7N/8) +a 3 (n+N/8) +b 3 (n+5N/8) ) (30)
  • the original frequency domain, multi-carrier symbol can be re-covered from T (n) by the inverse 15 transformation unit INV TRANSF if the following inverse transformation is applied:
  • the four partitions y o (n) , y ⁇ (n) , y 2 (n) and y 3 (n) are combined into the following tranformed time domain multi-carrier symbol :
  • the original frequency domain multi-carrier symbol can be recovered from T g (n) by the inverse transformation unit INV TRANSF if the following inverse transformation is applied:
  • the original frequency domain muiti- carrier symbol can be recovered from T 7 (n) by the inverse transformation unit INV TRANSF if the following inverse transformation is applied:
  • a first remark is that, although the multi- carrier signal in the above described embodiment is transported over a communication line, the applicability of the present invention is not restricted by the transmission medium via which the signal is transported.
  • the present invention is applicable to multi - carrier transmission over any connection between a 17 transmitting modem TX and receiving modem RX, e.g. a cable connection, a satellite connection, a radio link through the air, and so on.
  • the invention also is not only related to ADSL (Asymmetric Digital Subscriber Line) or similar systems wherein DMT (Discrete Multi Tone) modulation is used.
  • ADSL Asymmetric Digital Subscriber Line
  • DMT Discrete Multi Tone modulation
  • a person skilled in the art will be able to adapt the above described embodiment so that it is applicable in any other system wherein a multi-carrier signal is transmitted from a transmitting modem TX to a receiving modem RX .
  • Systems wherein orthogonal frequency division multiplexing (CFDM) or orthoganally multiplexed quadrature amplitude modulation (OMQAM) is applied for instance are multi-carrier systems wherein the present invention is applicable.
  • CFDM orthogonal frequency division multiplexing
  • OQAM orthoganally multiplexed quadrature amplitude modulation

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

Afin de réduire la probabilité d'écrétage d'un signal multiporteuse, des symboles multiporteuses de domaines de fréquences sont transformés en symboles multiporteuses de domaine temporel complexe par un transformateur de Fourier inverse (TFI). Si un dispositif d'observation (OBS) détecte que la partie réelle d'un échantillon d'un symbole multiporteuse de domaine temporel complexe dépasse un certain niveau de seuil, le symbole multiporteuse de domaine temporel complexe est appliqué à une unité de transformation (TRANSF) pour être transformé. Dans cette transformation, le symbole multiporteuse de domaine temporel complexe est décomposé en quatre partitions, des parties réelles et imaginaires de ces partitions sont commutées et/ou inversées, et des échantillons de ces partitions sont décalés sur un nombre entier de périodes d'échantillon. Pour constituer le symbole de domaine temporel transformé qui sera transmis, l'unité de transformation (TRANSF) recombine les partitions à nouveau et la partie réelle du symbole est sélectionnée pour être transmise. Une indication de la transformation appliquée est transmise avec le symbole multiporteuse transformé à un récepteur multiporteuse (RX) qui ainsi devient capable d'exécuter la transformation inverse.
PCT/EP1999/001960 1998-03-23 1999-03-22 Procede et montage de reduction de l'ecretage de signaux multiporteuses WO1999049635A1 (fr)

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AU34173/99A AU3417399A (en) 1998-03-23 1999-03-22 Method and arrangement to reduce clipping of multi-carrier signals

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NL1008678 1998-03-23
NL1008678 1998-03-23

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001095582A1 (fr) * 2000-06-05 2001-12-13 Gds Gesellschaft Für Digitale Signalverarbeitung Mbh Procede de transmission de donnees a porteuses multiples selon lequel les differentes frequences porteuses sont occupees directement dans la bande utile
KR100447388B1 (ko) * 2000-11-28 2004-09-04 엘지전자 주식회사 전송시스템에서의 클리핑 감소 회로 및 그 구현 방법
WO2006125355A1 (fr) * 2005-05-27 2006-11-30 Huawei Technologies Co., Ltd. Dispositif et procede de saturation de signaux multiporteuse

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0725510A1 (fr) * 1995-02-02 1996-08-07 Motorola, Inc. Procédé et dispositif pour la réduction des exigences imposées au rapport puissance de crête/puissance moyenne, dans un système de communication à porteuses multiples
EP0735731A2 (fr) * 1995-03-31 1996-10-02 Victor Company Of Japan, Limited Modulateur et démodulateur multiporteuses, avec arrangement de réduction du pouvoir maximal

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0725510A1 (fr) * 1995-02-02 1996-08-07 Motorola, Inc. Procédé et dispositif pour la réduction des exigences imposées au rapport puissance de crête/puissance moyenne, dans un système de communication à porteuses multiples
EP0735731A2 (fr) * 1995-03-31 1996-10-02 Victor Company Of Japan, Limited Modulateur et démodulateur multiporteuses, avec arrangement de réduction du pouvoir maximal

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DENIS J.G MESTDAGH AND PAUL M.P SPRUYT: "A method to reduce the Probability of Clipping in DMT-Based transceivers", IEEE TRANSACTIONS ON COMMUNICATIONS, vol. 44, no. 10, October 1996 (1996-10-01), pages 1234 - 1238, XP002110096 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001095582A1 (fr) * 2000-06-05 2001-12-13 Gds Gesellschaft Für Digitale Signalverarbeitung Mbh Procede de transmission de donnees a porteuses multiples selon lequel les differentes frequences porteuses sont occupees directement dans la bande utile
KR100447388B1 (ko) * 2000-11-28 2004-09-04 엘지전자 주식회사 전송시스템에서의 클리핑 감소 회로 및 그 구현 방법
WO2006125355A1 (fr) * 2005-05-27 2006-11-30 Huawei Technologies Co., Ltd. Dispositif et procede de saturation de signaux multiporteuse
US7885343B2 (en) 2005-05-27 2011-02-08 Huawei Technologies Co., Ltd. Device and method for clipping multicarrier signal

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