CN1708920A - Echo canceller with mobile crosstalk control - Google Patents

Abstract

The device of the invention for canceling echo generated by a first telecommunication device located at a first end of a connection, comprises: a first adaptive filtering unit (36; 56) outputting an echo estimate, which unit is supplied with a first error signal (E)_MCC1；E_MCC2) Control of (2); a delay estimation unit (44; 54) outputting an echo delay estimate, adapted to determine a signal originating from a second end of the connection and destined for the first end and the first error signal (E)_MCC2) The offset between; a delay unit (46; 57) for delaying the signal (Y') destined for the first terminal by the echo delay estimate, an output of the delay unit being connected to an input of the first adaptive filtering unit (36; 56); and an echo cancellation unit (38; 58) for subtracting an estimate of the echo from a signal (Xin) received from the first telecommunication device.

Description

Echo eliminator with mobile cross-talk control

The present invention relates to have the echo eliminator of mobile cross-talk control.

Echo eliminator is a kind of device that is usually used in restraining or removing in the telephone system echo in the long-distance service.For example, in honeycomb public land mobile net network (PLMN), echo eliminator is used for mobile services switching centre (MSC), with the echo in supression or the removal speech business.Echo eliminator also is used for compensating sound or mechanical echoes in mobile radio phone and " hands-free " telephone plant.

On the principle, the digital mobile radio phone handset should not produce echo, connects and does not mix because have to the duplex of this hand-held device, and reasoning does not have echo source thus.But in the actual conditions, many these type of mobile phones can produce the echo that is derived from sound in the hand-held device or mechanical cross-talk.This type of echo makes user's worry, especially when the Systems Operator selects to improve downlink signal levels.Improve downlink signal levels and become usual practice, because many clients complain that the level of loud speaker output of mobile handsets is not high.

Since adopt in the transmission path two speech coders/decoders (codec) to and radio interface, so the echo path of digital mobile phone is non-linear, and changes in time.In addition, in the digital mobile phone level of echo well below echo level from PSTN (public switched telephone network).For example, digital cellular global system for mobile communications (GSM) requirement is the pure tone of 0dBm for level in the 300-3400Hz frequency band, and measured echo reflection loss (ERL) of arriving is 46dB (for mobile phone).But if adopt non-pure tone signal to measure, then this ERL may be lower, but still need the supression level of about 40dB.In other words, quantizing noise seemingly causes the nonlinear important root of echo path.

For eliminating echo, many solutions have been proposed.

For example, the long-term average that document EP-A-0 746 133 has introduced filter factor is used to estimate echo delay, and document WO-A-96 27951 has then introduced the result of calculation of FFT (fast fourier transform) is estimated as a step length of delay.But these solutions are very complicated, and it is very difficult to make real-time implementation get up, because they will expend the plenty of time of processor.

In document US-A-6 064 873, proposed a kind of solution preferably, but it is still very complicated.In addition, also do not provide the details of relevant mobile cross-talk control.Moreover this solution can not be finely tuned the delay of mobile network's side.

Fig. 1 shows the schematic diagram of the general networks echo eliminator with mobile cross-talk control.A plurality of this echo eliminators can constitute echo canceller pool (ECP), and can be integrated in the digital exchange system.

Input originates from the signal Xin of distal side (for example may be cellular link or satellite link) in mobile cross-talk control (MCC) unit 10.MCC unit 10 also receives the output of nonlinear processor (NLP) 12 as input.Near-end (for example its can corresponding to PSTN), mixedcell 14 be 2 line circuits with 4 line line transfer.The output that mixedcell 14 receives as theMCC unit 10 of input, and output signal Yin.Two talk detector (DTD)unit 16 andmixed cell 14 also connect.Input delay (D)unit 18 is gone back in the output ofMCC unit 10, and the output ofdelay cell 18 offers finite impulse response (FIR) (FIR) filter 20.FIR filter 20 is adaptive, because it is controlled by the error signal E ofsubtrator 22outputs.Subtrator 22 calculates output poor of the signal Yin that starts from far-end and FIR filter 20.NLP 12 is also imported in the output ofsubtrator 22.

This echo eliminator is simpler than the equipment that proposes in the above-mentioned prior art document.But it can't obtain the adaptation value of echo delay.

The present invention is intended to overcome above-mentioned shortcoming.

For this reason, the invention provides a kind of echo eliminator in the communication network, be used to eliminate echo, it should be noted that described cancellation element comprises by first telecommunication installation generation of first end that is positioned at connection:

The first adaptive-filtering unit, it is controlled by first error signal, described first error signal signal that to be the signal that receives from described first telecommunication installation export with the described first adaptive-filtering unit poor; The estimation that described echo is exported in the described first adaptive-filtering unit;

Postpone estimation unit, it is suitable for determining that second end by described connection starts and mails to the signal of described first end and the side-play amount between described first error signal, and described delay estimation unit is exported the estimation of described echo delay;

Delay cell is used to make the described echo delay estimator of the signal delay that mails to described first end, and the output of described delay cell is connected to the input of the described first adaptive-filtering unit; And

Echo-cancellation unit is used for deducting from the signal that is received from described first telecommunication installation estimation of described echo.

Thus, because the present invention, real-time implementation is oversimplified.Moreover echo signal delay value is estimated with adaptive mode.The present invention also makes and can finely tune echo signal delay value.In addition, the echo-signal level value is estimated with adaptive mode.

According to special characteristic, described echo eliminator also comprises another adaptive-filtering unit, this filter unit only is subjected to be used to estimate that in the incipient stage of echo cancellation process another error signal of described delay controls, described another error signal signal that to be the signal that receives from described first telecommunication installation export with described another adaptive-filtering unit poor, the signal that described another adaptive-filtering unit will mail to described first end receives as input, and in the described incipient stage, described delay estimation unit is suitable for determining to mail to the signal of described first end and the side-play amount between described another error signal.

The invention enables the coefficient estimation that can obtain described another adaptive-filtering unit more quickly in the incipient stage.

According to certain special characteristic, described delay estimation unit is suitable for calculating described first error signal and mails to the cross-correlation of the signal of described first end, and is suitable for calculating described another error signal and the cross-correlation that mails to the signal of described first end in the described incipient stage.

The calculating of described cross-correlation is simple, makes real-time implementation easy.

Based on purpose same as described above, the present invention also provides a kind of echo cancellation system in the communication network, wherein first telecommunication installation is positioned at first end of connection, and second telecommunication installation is positioned at second end of described connection, and described echo cancellation system comprises the echo eliminator of above summary.

This echo cancellation system has the advantage identical with above-mentioned echo eliminator.

Based on purpose same as described above, the present invention also provides a kind of communication network, and it comprises the echo cancellation system of above summary.

This communication network has the advantage identical with described echo eliminator.

According to certain special characteristic of described network, extremely the link of above-mentioned first telecommunication installation comprises cellular link or satellite link.

Owing in this type of link, postpone very long and variation in time (particularly being), so the present invention is valuable especially because the continuous radio transmission conditions that changes.

Below reading by non-limiting example provide at DETAILED DESCRIPTION OF THE PREFERRED, be appreciated that other features and advantages of the present invention.

Following description references accompanying drawing, in the accompanying drawing:

The Fig. 1 that had described schematically shows the conventional echo eliminator with mobile cross-talk control;

Fig. 2 is the difference in demonstration sound cross-talk echo path and the PSTN echo path schematically;

Fig. 3 schematically shows echo eliminator according to a particular embodiment of the present invention, has wherein shown all entities in the work of the incipient stage of echo cancellation process;

Fig. 4 illustrates schematically how particular embodiments of the inventions herein estimates echo delay; And

Fig. 5 schematically shows echo eliminator according to a particular embodiment of the present invention, has wherein only shown the entity of working during the fine setting stage after the incipient stage of echo cancellation process finishes.

Hereinafter, term " far-end " and " only end " they are not in order to limit, but the relative two ends of two-way communication path.

Having relatively high expectations of mobile cross-talk control task.It should eliminate the cross-talk echo from cell phone, but if there is no echo, and it should not reduce voice quality, and should not cause slicing or make it distortion in the voice signal of input.

From the angle of switching system, as shown in Figure 2, the echo that has many features to make to be derived from the cross-talk in the mobile digital hand-held device is distinguished mutually with network echo.

Fig. 2 shows the travelling carriage (MS) 24 that is connected with the base station system (BSS) 26 of cellular network.(MSC) 28 of mobile switching centre is connected with echo canceller pool 30.The input and output arrow of MSC 28 and echo canceller pool 30 represent the to come in and go out signal path (left side of MSC 28) of BSS 26 and local exchange center (LE) signal path of the public switched telephone network (PSTN) 32 of coming in and going out.LE comprises and is used for 4 line line transfer is the mixed cell H of 2 line circuits.Landline telephone ST 34 is connected to LE.

The arrow of MS 24 and BSS 26 tops is represented crosstalk path, and the arrow of PSTN 32 and ST 34 belows is represented the echo path of PSTN.Very little signal only takes place in the echo path of network echo canceller to be disturbed.But the echo path of the echo eliminator of control cross-talk comprises wireless radio transmission.This causes moving back to the feature of wave path and the difference that network echo relatively has essence.

Delay in the handset echo is very long, and this is because wireless radio transmission need be encoded and interweave.Actual echo delay may with (such as but not limited to) hand-held device, system hardware, extra treatment facility be with to call out route different and different.

Because the change of hand-held device position, the feature that therefore moves back to wave path often changes fast and continually.This feature also may be subjected to the influence of the transmission of error code, switching or interruption in the wireless radio transmission for example.The MS echo delay may for example change in 120 to 320 milliseconds the scope.The duration of MS echo is generally short than the duration of PSTN echo, and its level is generally lower.

Fig. 3 has shown echo eliminator according to a particular embodiment of the present invention, this echo eliminator is handled this two kinds of echoes respectively according to the above-mentioned difference between the echo of echo that originates from portable terminal and fixed network, and uses in the so-called incipient stage of echo cancellation process.

Consider to comprise respectively that the far-end of first and second telecommunication installations and the communication network between the near-end connect.Link to first telecommunication installation that is positioned at far-end comprises cellular link or satellite link, and second telecommunication installation that is positioned at near-end is assumed to the fixed telecommunication device.When the incipient stage occurred in connection between near-end and the far-end and begins, it had predetermined lasting time.

In order to eliminate the echo that originates from near-end one side, adopt and the identical conventional echo eliminator of before having described with reference to figure 1 300 of conventional echo eliminator, it comprisesnonlinear processor 12, twotalk detector 16,delay cell 18, finiteimpulse response filter 20 andsubtrator 22.

In order to eliminate the echo that originates from far-end one side, according to the present invention, described echo eliminator comprises theecho eliminator 302 with first adaptive-filteringunit F MCC1 36, and its output originates from the estimation of the echo of far-end.FMCC1 unit 36 is subjected to the first error signal E_MCC-1 control, this first error signal signal that to be the signal Xin that receives from first telecommunication installation export withFMCC1 unit 36 poor.The calculating of this difference is carried out by subtrator 38.The first error signal E_MCC1Be used to adjust the coefficient of filter FMCC1 36.

Echo eliminator 302 also comprises another adaptive-filtering unit F t 40.Ft unit 40 will originate from near-end and mail to the signal Y ' conduct input reception of far-end.Ft unit 40 is subjected to another error signal E_tControl, this another error signal signal that to be signal Xin export withFt unit 40 poor.The calculating of this difference is carried out by another subtrator 42.Described another error signal E_tBe used to adjust the coefficient of filter Ft 40.Being noted that filter Ft40 can be designed as only calculates a coefficient subclass, and for example in ten coefficients provides the rough estimate of echo with the incipient stage in echo cancellation process.

Echo eliminator 302 also comprises delayestimation unit C 44, and its output originates from the delay of the echo of far-end and estimates.The signal Y ' thatC unit 44 receives as first input, and receive another error signal E that imports as second_t, this element is suitable for determining signal Y ' and described another error signal E_tBetween side-play amount.

Echo eliminator 302 also comprises delay cell DELAY 46, is used to the echo delay estimator that signal Y 'delay C unit 44 is exported.The output ofDELAY unit 46 is connected to the input ofFMCC1 unit 36.

Subtrator 38 estimates to serve as echo-cancellation unit by the echo that deducts 36 outputs of FMCC1 unit from signal Xin.

Echo delay is for example being estimated during theDTD unit 16 detected near end talk byC unit 44.

As shown in Figure 4, estimate echo delay.In a plurality of time intervals (for example blanking time between two samples), calculate described another error signal E_tWith the cross-correlation of signal Y ', the cross correlation value that will so obtain is stored in the random access memory 460 ofDELAY unit 46 then.Comparator 462 is the value of all storages relatively then, and definite maximum cross-correlation value, and it is corresponding to echo delay.In fact, when the distant echo signal peak takes place when, described another error signal E_tAnd originate from cross-correlation maximum between the signal Y ' of near-end.

During determining this echo delay, all coefficients ofFMCC1 unit 36 equal 0, so that this filter is had no effect.Postpone to estimate thatFMCC1 unit 36 just begins the calculating filter coefficient value in case carried out.

As previously mentioned, the echo-signal that originates from far-end is shorter, and its level is lower than the echo-signal that originates from the PSTN side.Therefore, the quantity of transversary sef-adapting filter joint that is used for estimating being derived from the echo-signal of far-end obviously is less than the used quantity of conventional echo eliminator on the PSTN side 300.In addition, used number of filter sections can be than used number of filter sections much less in theFMCC1 unit 36 in theFt unit 40.

Can be with normalization LMS (NLMS, normalization minimum mean-square) algorithm application in two sef-adapting filters.For example, therefore two filters can be realized by using individual digit signal processor (DSP).

Fig. 5 has shownecho eliminator 502 according to a particular embodiment of the present invention, and it is corresponding to the fine setting stage of echo cancellation process, and wherein the entity in work lacks than the work entity in the incipient stage shown in Figure 3.

In order to eliminate the echo that originates from near-end one side, adopt with shown in Figure 3 and previous with reference to the described identicalconventional echo eliminator 300 of figure l, it comprisesnonlinear processor 12, twotalk detector 16,delay cell 18, finiteimpulse response filter 20 andsubtrator 22.

In order to eliminate the echo that originates from far-end one side, according to the present invention, this echo eliminator comprises theecho eliminator 502 with single adaptive-filteringunit F MCC2 56, and this device output originates from the estimation of the echo of far-end.When incipient stage of echo cancellation process finished, the coefficient initialization ofFMCC2 unit 56 was the coefficient of theFt unit 40 that obtains when finishing the incipientstage.FMCC2 unit 56 is subjected to error signal E_MCC2Control, this error signal signal that to be the signal Xin that receives from first telecommunication installation that is positioned at far-end export withFMCC2 unit 56 poor.The calculating of this difference is carried out by subtrator 58.The first error signal E_MCC2Be used to adjust the coefficient of filter FMCC256.

Echo eliminator 502 also comprises delayestimation unit C 54, and this element output originates from the delay of the echo of far-end and estimates.The signal Y ' thatC unit 54 will originate from near-end and mail to far-end receives as first input, and with error signal E_MCC2Receive as second input,C unit 54 is suitable for determining signal Y ' and error signal E_MCC2Between side-play amount, for example by coming error signal E with reference to the described mode of Fig. 4 with similar_MCC2Cross-correlation with signal Y '.

Echo eliminator 502 also comprisesdelay cell DELAY 57, is used to the echo delay estimator that signal Y 'delay C unit 54 is exported.The output ofDELAY unit 57 is connected to the input ofFMCC2 unit 56.

Subtrator 58 estimates to serve as echo-cancellation unit by the echo that deducts 56 outputs of FMCC2 unit from signal Xin.

Echo delay is for example being estimated during the 16 detected near-end conversations of DTD unit byC unit 54.

Claims (6)

1. a kind of echo eliminator in the communication network is used to eliminate the echo that first telecommunication installation on first end that is positioned at connection produces, and it is characterized in that it comprises:

The first adaptive-filtering unit (36; 56), it is subjected to the first error signal (E_MCC1E_MCC2) control, described first error signal is the signal (Xin) and the described first adaptive-filtering unit (36 that receives from described first telecommunication installation; 56) Shu Chu signal is poor; The estimation that described echo is exported in the described first adaptive-filtering unit;

Postpone estimation unit (44; 54), it is suitable for signal (Y ') and the described first error signal (E that definite second end by described connection starts and mails to described first end_MCC2) between side-play amount, described delay estimation unit is exported the estimation of the described delay of described echo;

Delay cell (46; 57), be used to make the signal (Y ') that mails to described first end to postpone described echo delay estimator, the output of described delay cell is connected to the described first adaptive-filtering unit (36; 56) input; And

Echo-cancellation unit (38; 58), be used for deducting the described estimation of described echo from the signal (Xin) that is received from described first telecommunication installation.

2. echo eliminator as claimed in claim 1 is characterized in that: it also comprises adaptive-filtering unit (40), and this filter unit is subjected to only to be used to estimate in the incipient stage of described echo cancellation process another error signal (E of described delay_t) control, described another error signal (E_t) to be the signal (Xin) that receives from described first telecommunication installation with the signal of described another adaptive-filtering unit (40) output poor, the described signal (Y ') that described another adaptive-filtering unit (40) will mail to described first end receives as input; And, in the described incipient stage, described delay estimation unit (44; 54) signal (Y ') that is suitable for determining to mail to described first end and described another error signal (E_t) between side-play amount.

3. echo eliminator as claimed in claim 2 is characterized in that: described delay estimation unit (44; 54) be suitable for calculating the described first error signal (E_MCC2) and mail to the cross-correlation of the described signal (Y ') of described first end, and be suitable for calculating described another error signal (E in the described incipient stage_t) with mail to the cross-correlation of the signal (Y ') of described first end.

4. a kind of echo cancellation system in the communication network, wherein: first telecommunication installation is positioned at first end of connection, and second telecommunication installation is positioned at second end of described connection, and described echo cancellation system is characterised in that: it comprises as described above any one described echo eliminator in the claim.

5. communication network, it is characterized in that: it comprises echo cancellation system as claimed in claim 4.

6. any one described communication network in the claim as described above, it is characterized in that: the link to described first telecommunication installation comprises cellular link or satellite link.

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