EP1570583A1 - Dispositif de suppression d'echo au moyen d'un controle de diaphonie mobile - Google Patents

Dispositif de suppression d'echo au moyen d'un controle de diaphonie mobile

Info

Publication number
EP1570583A1
EP1570583A1 EP02788447A EP02788447A EP1570583A1 EP 1570583 A1 EP1570583 A1 EP 1570583A1 EP 02788447 A EP02788447 A EP 02788447A EP 02788447 A EP02788447 A EP 02788447A EP 1570583 A1 EP1570583 A1 EP 1570583A1
Authority
EP
European Patent Office
Prior art keywords
echo
signal
unit
echo cancellation
delay
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Withdrawn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
EP02788447A
Other languages
German (de)
English (en)
Inventor
Dragan Topalovic
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.)
Telefonaktiebolaget LM Ericsson AB
Original Assignee
Telefonaktiebolaget LM Ericsson AB
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 Telefonaktiebolaget LM Ericsson AB filed Critical Telefonaktiebolaget LM Ericsson AB
Publication of EP1570583A1 publication Critical patent/EP1570583A1/fr
Withdrawn legal-status Critical Current

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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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/54—Systems for transmission via power distribution lines
    • H04B3/542—Systems for transmission via power distribution lines the information being in digital form
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2203/00—Indexing scheme relating to line transmission systems
    • H04B2203/54—Aspects of powerline communications not already covered by H04B3/54 and its subgroups
    • H04B2203/5404—Methods of transmitting or receiving signals via power distribution lines
    • H04B2203/5408—Methods of transmitting or receiving signals via power distribution lines using protocols

Definitions

  • the present invention relates to an echo cancellation device with mobile crosstalk control.
  • An echo canceller is a device that is commonly used in telephony systems to suppress or remove echoes in long distance traffic. For example, in cellular Public Land Mobile Networks (PLMNs), echo cancellers are used in Mobile services Switching Centres (MSCs) to suppress or remove echoes in speech traffic. Echo cancellers are also used in mobile radiotelephones and "handsfree" telephone equipment to compensate for acoustical or mechanical echoes.
  • PLMNs Public Land Mobile Networks
  • MSCs Mobile services Switching Centres
  • Echo cancellers are also used in mobile radiotelephones and "handsfree" telephone equipment to compensate for acoustical or mechanical echoes.
  • a digital mobile radiotelephone handset should not generate echoes, because there is a duplex connection to the handset and no hybrid, and therefore, a priori no source of echo.
  • many such mobile phones generate echoes that originate from acoustical or mechanical crosstalk in the handset. This type of echo is annoying to users, especially if the system operator has elected to raise the downlink signal levels. Raising the downlink signal levels has become an accepted practice, since many customers have complained about the low output levels from the mobile handsets' speakers.
  • the echo path for a digital mobile phone is non-linear and time- varying, due to the use of two speech coder/decoder (codec) pairs and radio interfaces in the transmission path. Additionally, the level of the echo in a digital mobile phone is much lower than that from a PSTN (Public Switched Telephone Network).
  • PSTN Public Switched Telephone Network
  • GSM Global System for Mobile Communications
  • ERL Echo Return Loss
  • the ERL can be lower if signals other than pure tones are used for the measurements, but suppression levels of about 40 dB can still be expected. In other words, the quantisation noise appears to be a considerable source for the echo path non-linearity.
  • document EP-A-0 746 133 describes the use of a long- term average value of filter coefficients in order to estimate the delay of the echo
  • document WO-A-96 27951 discloses the use of calculation of FFT (Fast Fourier Transformation) as a one-step delay value estimate.
  • FFT Fast Fourier Transformation
  • FIG. 1 shows a schematic view of a conventional network echo canceller with mobile crosstalk control.
  • a plurality of such echo cancellers may form an Echo Canceller Pool (ECP) and may be integrated in a digital switching system.
  • ECP Echo Canceller Pool
  • MCC Mobile Crosstalk Control
  • NLP Non- Linear Processor
  • a hybrid unit 14 converts the 4-wire line to a 2-wire line.
  • the hybrid unit 14 receives as input the output of the MCC unit 10 and outputs a signal Yin.
  • a Double Talk Detector (DTD) unit 16 is connected in parallel with the hybrid unit 14.
  • the output of the MCC unit 10 is also input in a Delay (D) unit 18, whose output is supplied to a Finite Impulse Response (FIR) filter 20.
  • the FIR filter 20 is adaptive, since it is controlled by an error signal E, which is the output of a subtraction unit 22.
  • the subtraction unit 22 computes the difference between the signal Yin originating from the near end and the output of the FIR filter 20.
  • the output of the subtraction unit 22 is also input in the NLP 12.
  • This echo canceller is simpler than the devices proposed by the above-mentioned prior art documents. However, it does not make it possible to obtain an adaptive value of the echo delay.
  • the present invention aims at overcoming the above-mentioned drawbacks.
  • the present invention provides an echo cancellation device in a telecommunications network, for cancelling an echo generated by first telecommunication means located on a first end of a connection, remarkable in that it comprises: first adaptive filtering means, controlled by a first error signal which is the difference between a signal received from the first telecommunication means and a signal output by the first adaptive filtering means, the first adaptive filtering means outputting an estimate of the echo; delay estimation means, adapted to determine a shift between a signal transmitted towards the first end and originating from a second end of the connection and the first error signal, the delay estimation means outputting an estimate of the delay of the echo; delaying means, for delaying by the echo delay estimate the signal transmitted towards the first end, the output of the delaying means being connected to an input of the first adaptive filtering means; and echo cancellation means, for subtracting the estimate of the echo from the signal received from the first telecommunication means.
  • the echo signal delay value is estimated in an adaptive fashion.
  • the invention also makes it possible to carry out a fine-tuning of the echo signal delay value.
  • the echo signal level value is estimated in an adaptive way.
  • the echo cancellation device comprises further adaptive filtering means, controlled by a further error signal that is used for estimating the delay only during a start phase of the echo cancellation process, the further error signal being the difference between the signal received from the first telecommunication means and a signal output by the further adaptive filtering means, the further adaptive filtering means receiving as an input the signal transmitted towards the first end, and during the start phase, the delay estimation means are adapted to determine a shift between the signal transmitted towards the first end and the further error signal. It makes it possible to obtain more quickly an estimate of the coefficients of the further adaptive filtering means during the start phase.
  • the delay estimation means are adapted to calculate the cross-correlation of the first error signal and the signal transmitted towards the first end and, during the start phase, to calculate the cross-correlation of the further error signal and the signal transmitted towards the first end.
  • the calculation of the cross-correlation is simple and makes real-time implementation easy.
  • the present invention also provides an echo cancellation system in a telecommunications network, wherein first telecommunication means are located on a first end of a connection, and second telecommunication means are located on a second end of the connection, said echo cancellation system comprising an echo cancellation device as succinctly described above.
  • the present invention also provides a telecommunications network, comprising an echo cancellation system as succinctly described above.
  • the link to the above- mentioned first telecommunication means comprises a cellular or a satellite link. Since, in such links, delays are long and time-varying, in particular because of changing radio transmission conditions, the invention is especially valuable.
  • FIG. 2 illustrates schematically the differences in the echo path of acoustical crosstalk and PSTN echo
  • FIG. 3 shows schematically an echo cancellation device according to the present invention, in a particular embodiment where all entities that operate during a start phase of the echo cancellation process are shown;
  • FIG. 4 shows schematically how the delay of the echo is estimated, according to the present invention in a particular embodiment
  • FIG. 5 shows schematically an echo cancellation device according to the present invention, in a particular embodiment, where only the entities that operate after the end of the start phase of the echo cancellation process, during a fine-tuning phase, are shown.
  • the expressions "far end” and “near end” are not intended to be limiting, other than to denote the opposite ends of a path for two- way communication.
  • the task of mobile crosstalk control is exacting. It should cancel acoustical crosstalk echo from the cellular telephone, but it should not degrade speech quality if echo is not present and it should not introduce clipping into or distort the incoming speech signal.
  • FIG. 2 shows a Mobile Station (MS) 24 connected to the Base
  • BSS Station System 26 of a cellular network.
  • a Mobile Switching Centre (MSC) 28 is connected to an echo canceller pool 30.
  • the arrows input in and output from the MSC 28 and the echo canceller pool 30 represent the path of the signals coming from and returned to the BSS 26 (on the left of the MSC 28) and coming from and returned to a Local Exchange (LE) of the Public Switched Telephone Network (PSTN) 32.
  • the LE contains a hybrid unit H for converting the 4-wire line to a 2-wire line.
  • a Stationary Telephone ST 34 is connected to the LE.
  • the arrow above the MS 24 and the BSS 26 represents the path of the acoustical crosstalk and the arrow below the PSTN 32 and the ST 34 represents the path of the PSTN echo.
  • the echo path of the echo canceller that controls acoustical crosstalk includes radio transmission. This gives rise to fundamental differences in the characteristics of the mobile echo path, in comparison with the network echo.
  • the delay in the handset echo is long, since radio transmission requires coding and interleaving.
  • the actual echo delay may vary, depending, by way of non-limiting examples, on the handset, system hardware, extra signal processing equipment, and the routing of the call.
  • the characteristics of the mobile echo path are liable to vary rapidly and frequently due to changes in the position of the handset.
  • the characteristics may also be affected by bit errors in the radio transmission, handover, or discontinuous transmission, for example.
  • the MS echo delay can for instance vary from 120 to 320 ms.
  • the duration of the MS echo is generally shorter than that of the PSTN echo, and its level is generally lower.
  • Figure 3 shows a particular embodiment of an echo cancellation device in accordance with the present invention, which, on the basis of the above-mentioned differences between the echoes originating from a mobile terminal and from a fixed network, handles the two kinds of echoes separately, and which is used during a so-called start phase of the echo cancellation process.
  • a connection in a telecommunications network is considered between a far end and a near end, comprising respectively first and second telecommunication means.
  • the link to the first telecommunication means, that are located on the far end comprise a cellular or a satellite link, whereas the second telecommunication means, that are located on the near end are assumed to be fixed telecommunication means.
  • the start phase takes place at the beginning of the connection between the near end and the far end, and has a predetermined duration.
  • a conventional echo canceller 300 identical to the one described earlier with reference to Figure 1 is used, comprising a non linear processor 12, a double talk detector unit 16, a delay unit 18, a finite impulse response filter 20 and a subtraction unit 22.
  • the echo canceller comprises an echo cancellation device 302 having a first adaptive filtering unit FMCC1 36, that outputs an estimate of the echo originating from the far end.
  • the FMCC1 unit 36 is controlled by a first error signal EMCC-I , which is the difference between a signal Xin received from the first telecommunication means and a signal output by the FMCC1 unit 36. The calculation of this difference is carried out by a subtraction unit 38.
  • the first error signal EMCCI is used for adjusting the coefficients of the filter FMCC1 36.
  • the echo cancellation device 302 also comprises a further adaptive filtering unit Ft 40.
  • the Ft unit 40 receives as an input a signal Y' transmitted towards the far end and originating from the near end.
  • the Ft unit 40 is controlled by a further error signal E t , which is the difference between the signal Xin and a signal output by the Ft unit 40. This difference is calculated by a further subtraction unit 42.
  • the further error signal Et is used for adjusting the coefficients of the filter Ft 40.
  • the filter Ft 40 can be designed so as to compute only a subset of coefficients, e.g. one coefficient out of ten, in order to supply a rough estimate of the echo, during the start phase of the echo cancellation process.
  • the echo cancellation device 302 also comprises a delay estimation unit C 44, outputting an estimate of the delay of the echo originating from the far end.
  • the C unit 44 receives as a first input the signal Y', and receives as a second input the further error signal Et, and is adapted to determine a shift between the signal Y' and the further error signal E t .
  • the echo cancellation device 302 also comprises a delaying unit DELAY 46, for delaying the signal Y 1 by the echo delay estimate output by the C unit 44.
  • the output of the DELAY unit 46 is connected to an input of the FMCC1 unit 36.
  • the subtraction unit 38 acts as an echo cancellation unit by subtracting the echo estimate output by the FMCC1 unit 36 from the signal Xin.
  • the echo delay is estimated by the C unit 44 for example during the near end talk, which is detected by the DTD unit 16.
  • the echo delay is estimated as shown in Figure 4.
  • the cross- correlation of the further error signal Et and the signal Y 1 is calculated in a plurality of intervals of time such as the intervals between two samples, and the cross-correlation values thus obtained are stored in a random access memory 460 of the DELAY unit 46.
  • a comparator 462 then compares all stored values and determines the maximum cross-correlation value, which corresponds to the echo delay. Indeed, when the peak of the far end echo signal occurs, the cross-correlation between the further error signal E t and the signal Y' originating from the near end is maximal.
  • the FMCC1 unit 36 starts calculating the value of the filter coefficients.
  • the echo signal originating from the far end is shorter and has a lower level than the echo signal originating from the PSTN side.
  • the number of segments of adaptive filters with transversal structure that are used for estimating the echo signal from the far end is significantly smaller than that used in the conventional echo canceller 300 on the PSTN side.
  • the number of segments used in the Ft unit 40 can be much smaller than that used in the FMCC1 unit 36.
  • the normalised LMS (NLMS, Normalised Least Mean Square) algorithm can be applied to both adaptive filters.
  • both filters can therefore be implemented through the use of a single Digital Signal Processor (DSP).
  • DSP Digital Signal Processor
  • Figure 5 shows a particular embodiment of an echo cancellation device 502 in accordance with the present invention, which corresponds to a fine-tuning phase of the echo cancellation process and in which less entities operate than during the start phase shown in Figure 3.
  • a conventional echo canceller 300 identical to the one shown in Figure 3 and described earlier with reference to Figure 1 is used, comprising a non linear processor 12, a double talk detector unit 16, a delay unit 18, a finite impulse response filter 20 and a subtraction unit 22.
  • the echo canceller comprises an echo cancellation device 502 having a single adaptive filtering unit FMCC2 56, that outputs an estimate of the echo originating from the far end.
  • the coefficients of the FMCC2 unit 56 are initialised with the coefficients of the Ft unit 40, obtained at the end of the start phase.
  • the FMCC2 unit 56 is controlled by an error signal EMCC2, which is the difference between a signal Xin received from first telecommunication means, located on the far end, and a signal output by the FMCC2 unit 56. The calculation of this difference is carried out by a subtraction unit 58.
  • the error signal E M cc 2 is used for adjusting the coefficients of the filter FMCC2 56.
  • the echo cancellation device 502 also comprises a delay estimation unit C 54, outputting an estimate of the delay of the echo originating from the far end.
  • the C unit 54 receives as a first input a signal Y 1 transmitted towards the far end and originating from the near end, and receives as a second input the error signal EMCC2, and is adapted to determine a shift between the signal Y' and the error signal EM CC 2, for example by calculating the cross-correlation of the error signal EM C C2 and the signal Y' in a similar fashion as described above with reference to Figure 4.
  • the echo cancellation device 502 also comprises a delaying unit DELAY 57, for delaying the signal Y' by the echo delay estimate output by the C unit 54.
  • the output of the DELAY unit 57 is connected to an input of the FMCC2 unit 56.
  • the subtraction unit 58 acts as an echo cancellation unit by subtracting the echo estimate output by the FMCC2 unit 56 from the signal Xin.
  • the echo delay is estimated by the C unit 54 for example during the near end talk, which is detected by the DTD unit 16.

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

Abstract

L'invention concerne un dispositif permettant de supprimer un écho généré par une unité de télécommunication située sur une première extrémité d'une connexion. Ce dispositif comprend : une première unité de filtrage adaptative (36, 56) qui sort une estimation d'écho, contrôlée par un premier signal d'erreur (EMCC1, EMCC2); une unité d'estimation de retard (44; 54) qui sort une estimation de retard d'écho et est conçue de manière à déterminer un décalage entre un signal (Y') transmis vers la première extrémité et issu d'une seconde extrémité de la connexion et le premier signal d'erreur (EMCC2); une unité de retard (46, 57) permettant de retarder, au moyen de l'estimation de retard d'écho, le signal (Y') transmis vers la première extrémité, la sortie de l'unité de retard étant connectée à une entrée de la première unité de filtrage adaptative (36, 56); et une unité de suppression d'écho (38, 58) permettant de soustraire l'estimation de l'écho d'un signal (Xin) reçu depuis l'unité de télécommunication.
EP02788447A 2002-12-09 2002-12-09 Dispositif de suppression d'echo au moyen d'un controle de diaphonie mobile Withdrawn EP1570583A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IB2002/005697 WO2004054127A1 (fr) 2002-12-09 2002-12-09 Dispositif de suppression d'echo au moyen d'un controle de diaphonie mobile

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EP1570583A1 true EP1570583A1 (fr) 2005-09-07

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EP (1) EP1570583A1 (fr)
CN (1) CN1708920A (fr)
AU (1) AU2002353422A1 (fr)
WO (1) WO2004054127A1 (fr)

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CN102760461B (zh) * 2012-05-28 2015-08-05 杭州联汇数字科技有限公司 一种自适应调节音量大小的音频播放设备和方法
KR20150002784A (ko) * 2012-06-08 2015-01-07 인텔 코포레이션 장기 지연된 에코에 대한 에코 소거 알고리즘
CN107331406B (zh) * 2017-07-03 2020-06-16 福建星网智慧软件有限公司 一种动态调整回声延时的方法

Family Cites Families (2)

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Publication number Priority date Publication date Assignee Title
US4970715A (en) * 1987-03-27 1990-11-13 Universal Data Systems, Inc. Modem with improved remote echo location and cancellation
US5896452A (en) * 1996-05-24 1999-04-20 Motorola, Inc. Multi-channel echo canceler and method using convolution of two training signals

Non-Patent Citations (1)

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Title
See references of WO2004054127A1 *

Also Published As

Publication number Publication date
CN1708920A (zh) 2005-12-14
AU2002353422A1 (en) 2004-06-30
WO2004054127A1 (fr) 2004-06-24

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