EP1232644A1 - Systeme et procede d'annulation d'echo - Google Patents

Systeme et procede d'annulation d'echo

Info

Publication number
EP1232644A1
EP1232644A1 EP00977136A EP00977136A EP1232644A1 EP 1232644 A1 EP1232644 A1 EP 1232644A1 EP 00977136 A EP00977136 A EP 00977136A EP 00977136 A EP00977136 A EP 00977136A EP 1232644 A1 EP1232644 A1 EP 1232644A1
Authority
EP
European Patent Office
Prior art keywords
echo
line card
network
circuit
line
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.)
Withdrawn
Application number
EP00977136A
Other languages
German (de)
English (en)
Other versions
EP1232644A4 (fr
Inventor
Yatish Kumar
Scott Mcclennon
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.)
Ciena Corp
Original Assignee
Catena Networks Inc
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
Application filed by Catena Networks Inc filed Critical Catena Networks Inc
Publication of EP1232644A1 publication Critical patent/EP1232644A1/fr
Publication of EP1232644A4 publication Critical patent/EP1232644A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/20—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
    • H04B3/23—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers

Definitions

  • the present invention relates to a system and method for implementing echo cancellation in a communication network, and more particularly to a system for echo cancellation in a voice-over-data telephone network.
  • Voice over data communication utilizes existing data lines such as ISDN (Integrated Services Digital Network) in order to transport digitized voice signals along with data on a common communication line.
  • the analog voice signals are digitized using coding such as PCM (Pulse Code Modulation).
  • a user's telephone equipment is connected via a line card and a twisted pair telephone line to a Public Switching Telephone Network (PSTN).
  • PSTN Public Switching Telephone Network
  • the twisted pair circuit is normally a two-wire circuit, while sections between a PSTN is a four- wire circuit.
  • FIG. 1 shows a schematic diagram of a typical telephone network configuration 10.
  • a network echo path 12 is described from the perspective of one of the telephone users, referred to as "user A" 14.
  • the user A is connected via a twisted pair to line card A, which, in turn, is connected to the telephone network.
  • a user B is connected via a twisted pair and a line card B to the network.
  • the echo signal received at user A (or B) may be seen as the contribution of signals from various echo paths.
  • the user A is referred to as the "near end talker,” or simply “near end” while the user B is referred to as the “far end talker” or simply “far end.”
  • the near end echo is comprised of signals received from the near end line card, the network, and the far end line card.
  • the echo cancellation equipment When voice over data communication is used, such as voice over DSL, the echo cancellation equipment needs to be adapted to provide echo cancellation over the twisted pair wire, since the supe ⁇ osition of voice with data in DSL systems normally occurs at the line card. Because the echo cancellation equipment is contained within the network, the equipment to be provisioned for each new voice over data connection. Changes to the equipment is labour intensive and, therefore, expensive. The type of equipment available may also limit the number of changes thereby limiting the number of voice over data users. Therefore, there is a need for a method for canceling the line echo without burdening the network. Such a method would greatly enhance the deployment of the voice over data service, without the need to coordinate the availability of the service on specific subscriber lines with centralized network equipment.
  • a line card for coupling a subscriber line to a switching network the line card which has an echo canceling circuit for reducing an echo signal received from the network and perceived at a user instrument coupled to the subscriber line.
  • the present invention seeks to solve the problem having to provide new echo cancellation equipment in a switching network whenever any new voice over data services are added to the network.
  • Figure 1 is a schematic diagram of a typical network connection showing a connection path between a pair of subscribers
  • Figure 2 is a schematic diagram of a line card for far end network echo cancellation
  • Figure 3 is a schematic diagram of a line card for near end network echo cancellation
  • Figure 4 is a schematic diagram of a line card with near end network echo cancellation and balance filtering.
  • FIG. 1 a schematic diagram of a telecommunications network is shown generally by numeral 10.
  • the network 10 connects at least a pair of subscribers 14 and 15.
  • the network 10 is generally comprised of line card 22 connecting a digital switching network 17 (which may comprise more than one network) of a central office (CO) exchange to a plurality of subscriber lines 18.
  • CO central office
  • subscriber lines are typically twisted pair Tip and Ring copper lines that connect subscriber instruments (such as a telephone, fax, data modem, and the like) located at the subscriber location and thus remote to the CO.
  • a line card 22 may comprise a plurality of POTS subscriber line interface circuits (SLIC) and CODECS.
  • SLIC subscriber line interface circuits
  • CODECS CODECS
  • the SLIC connects a balanced two-wire transmission path (the path to and from the subscriber telephone handset) with an unbalanced four-wire transmission path (the path to and from the telephone central station).
  • SLICs perform various functions, including battery feed, overvoltage protection, ringing, signaling, hybrid and timing.
  • the line card may also include, for voice over data transmissions, an xDSL transceiver or integrated POTS/xDSL circuit such as for example described in the applicants co-pending U.S. Patent Application No. 09/614,927.
  • a forward communication path 18 is shown schematically from a first user A 14 to a second user B 15 ( Figure 1). Furthermore, an echo path 20 is defined between user A 14 and user B 15. From the point of view of user A, the echo signal is perceived as a contribution of at least four echo signals each due to segments of the echo path 20 between user A and user B, each segment is labeled el, e2, e3, and e4 in the drawing of Figure 1.
  • the present invention is based on the recognition that the line card 22 is the first circuit card to which a subscriber's twisted pair telephone line is coupled. It is the first point of access for either digital or analog communication over the twisted pair. Therefore, by implementing echo cancellation at the line card makes it possible to account for transport delays across the twisted pair loop to the subscriber set, without burdening the rest of the network with a requirement to perform echo cancellation.
  • a Line Card A for reducing the echo returned to user A from path segments e2, e3 or e4, according to an embodiment of the invention is shown generally by numeral 22.
  • This form of echo cancellation is referred to as "far end” echo cancellation, wherein the term “far end” refers to the path direction with the greater physical distance from user A.
  • FIG. 3 a schematic block diagram of A Line Card B 24 for reducing the echo returned to user A 14 from path segment 4 only is shown generally by numeral 25.
  • This form of echo cancellation is referred to a "near end” echo cancellation, wherein the term “near end” refers to the path direction with the lesser physical distance to user A.
  • a block diagram of a line card for "far end" network echo is indicated generally by numeral 22.
  • the line card 22 is coupled at one end to the subscriber line 18 and at the other end to the network 17 and includes an echo cancellation circuit 42 which is coupled at one end to the network 17, an analog interface circuit 43 for connecting at one end to a twisted pair subscriber line 18, and a digital interface transceiver 45 for processing analog signals coupled from the analog interface and passing it via the echo cancellation circuit 42 to the network 17.
  • Both the analog interface circuits 43 and digital interface circuits 45 are well known in the art.
  • the echo cancellation circuit 42 comprises transmit and receive paths 47 and 48, respectively, and a network delay model circuit 44 coupled to receive an input signal from the transmit path 47 and outputs a signal 46 to a sub tractor 49.
  • the subtractor is operative to subtract the signal received along the receive path 48 from the output 46 of the delay model circuit 44 to produce a receive signal to the digital interface 45.
  • the network delay model circuit 44 uses a digital circuit such as a FIR filter, IR filter, or other adaptive filter and is based on a model of the network delay.
  • the model 44 uses the signal transmitted to the network as its input and predicts the echo to be returned. These types of echo cancellation circuits are also well known in the art.
  • the echo canceller may also include a fax or modem detection circuit for disabling echo cancellation when the subscriber loop is used for communications other than voice; a speech activity detection for detecting the presence of a voice signal to activate the echo canceller; and a center clipper or some other non-linear processor for removing residual echo.
  • the output 46 of the network delay model 44 is subtracted from the signal received 48 from the network. Matching the magnitude and phase of the echo signal returned with the predicted echo 46 allows the output 46 of the network delay model 44 to cancel the echo returned from the network and provide a voice transmission that is virtually free of echo.
  • FIG. 3 a block diagram of a line card having a near end network echo cancellation circuit 52 is shown generally by numeral 24.
  • the near end Network Echo Canceller 52 on the Line Card operates in a similar way to the far end echo canceller 42 in that it also uses a digital circuit such as a FIR filter, IR filter or other adaptive filter as its model 53.
  • This model 53 uses the signal received 54 from the network 17 as its input and predicts the echo 56 to be returned.
  • the output of the network delay model is subtracted from the signal transmitted 57 to the network 17.
  • Matching the magnitude and phase of the actual echo signal with the predicted echo allows the output of the network delay model 53 to cancel the echo returned from the twisted pair 58 and provide a voice transmission that is virtually free of echo.
  • the near end echo cancellation aids in implementing echo cancellation on the line card. It is this function that allows the delays inherent in voice over data technology to be accounted for, thereby improving the quality of voice transmissions for DSL communication.
  • the near end network echo cancellation 24 as described with reference to figure 3 may also include a balance circuit which is provided in typical voice CODECS. Referring to Figure 4, a line card having near end echo cancellation and a balance function circuit is shown generally by numeral 60.
  • the line card 60 includes a balance function circuit 62 for coupling to the subscriber line 58 and an echo cancellation circuit 52 for coupling the balance function circuit to the network 17.
  • the echo cancellation circuit 52 provides some echo cancellation for voice communication. However, it may only cancel delays in the order of microseconds and is a compromise for a range of actual loops. Since the duration of the echo is typically in the order of a thousand times greater (1 ms), the balance function handles a signal that is large compared with the delay. In comparison, the network echo canceller cancels delays in the order of milliseconds. Therefore, the duration of the echo is relatively small compared to the delay.
  • the echo canceller 52 provides cancellation that enhances the performance of the balance function 62 and can take into account components of the system that are between the balance function 62, and the network echo canceller 52. Furthermore, it may be required that Line Card A 22 perform both far and near end echo cancellation. It is possible to implement both types of echo cancellation, as previously described, on one line card, further integrating and simplifying the architecture of the system. Both the delay model circuit and the balance function circuits are well known in the art.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Telephonic Communication Services (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

L'invention concerne une carte de ligne (22) permettant de coupler une ligne d'abonné (18) à un réseau de commutation (17), la carte de ligne (22) comprenant un circuit d'annulation d'écho (42) destiné à réduire un signal d'écho reçu du réseau et perçu au niveau d'un instrument d'utilisateur couplé à la ligne d'abonné. Le circuit d'annulation du réseau utilise un modèle (44) de réseau pour prédire un signal de réplique d'écho lequel est ensuite soustrait soit du signal de transmission (47) soit du signal de réception (49) sur le réseau. La carte de ligne (22) peut contenir un circuit d'annulation d'écho à l'extrémité distante, un circuit d'annulation d'écho à l'extrémité proche ou une combinaison des deux.
EP00977136A 1999-11-10 2000-11-09 Systeme et procede d'annulation d'echo Withdrawn EP1232644A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
CA 2289275 CA2289275A1 (fr) 1999-11-10 1999-11-10 Systeme et methode de suppression d'echo
CA2289275 1999-11-10
PCT/US2000/030898 WO2001035624A1 (fr) 1999-11-10 2000-11-09 Systeme et procede d'annulation d'echo

Publications (2)

Publication Number Publication Date
EP1232644A1 true EP1232644A1 (fr) 2002-08-21
EP1232644A4 EP1232644A4 (fr) 2004-09-15

Family

ID=4164593

Family Applications (1)

Application Number Title Priority Date Filing Date
EP00977136A Withdrawn EP1232644A4 (fr) 1999-11-10 2000-11-09 Systeme et procede d'annulation d'echo

Country Status (4)

Country Link
EP (1) EP1232644A4 (fr)
AU (1) AU1481501A (fr)
CA (1) CA2289275A1 (fr)
WO (1) WO2001035624A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004059866A1 (fr) * 2002-12-24 2004-07-15 Surf Communication Solutions, Ltd. Procede et appareil d'annulation d'echo au moyen d'une carte de ligne

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5323460A (en) * 1992-01-07 1994-06-21 Ag Communication Systems Corporation Enhanced subscriber line interface circuit
US5644596A (en) * 1994-02-01 1997-07-01 Qualcomm Incorporated Method and apparatus for frequency selective adaptive filtering
JP3359460B2 (ja) * 1995-03-20 2002-12-24 沖電気工業株式会社 適応フィルタ及びエコーキャンセラ
US5926464A (en) * 1996-04-04 1999-07-20 Lucent Technologies Inc. Customer telecommunication interface device with built-in network features
FR2758677B1 (fr) * 1997-01-21 1999-04-02 Matra Communication Procede d'annulation d'echo et annuleur d'echo mettant en oeuvre un tel procede
US6141406A (en) * 1997-03-27 2000-10-31 T-Netix, Inc. Method and apparatus for detecting a secondary destination of a telephone call based on changes in the telephone signal path
US6028929A (en) * 1997-11-14 2000-02-22 Tellabs Operations, Inc. Echo canceller employing dual-H architecture having improved non-linear echo path detection
US6067316A (en) * 1997-11-19 2000-05-23 Globespan, Inc. Circuit for combined xDSL and other services

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
No further relevant documents disclosed *
See also references of WO0135624A1 *

Also Published As

Publication number Publication date
EP1232644A4 (fr) 2004-09-15
CA2289275A1 (fr) 2001-05-10
AU1481501A (en) 2001-06-06
WO2001035624A1 (fr) 2001-05-17

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