FR2515452A1 - INTERFERENCE REDUCTION DEVICE AND ASSOCIATED DETECTOR - Google Patents

Abstract

The invention relates to techniques for reducing interference in telecommunications. AN ECHO CANCELER INCLUDES IN PARTICULAR A TRANSVERSAL FILTER 18 WHICH SYNTHETIZES AN ESTIMATION OF AN ECHO Y (K) REPRODUCTION SIGNAL, A COMBINATION CIRCUIT 20 WHICH SUBTRACTS THE ECHO REPRODUCTION SIGNAL FROM THE ECHO SIGNAL REEL Y (K) ON A TRANSMIT SIGNAL CHANNEL 14, AND A NEAR END SPEAKER DETECTOR 24. THE SPEECH DETECTOR INCLUDES A COMBINATION CIRCUIT 28 AND A CROSS-FILTER 26, ACCORDING TO A CONFIGURATION THAT REDUCES THE RATE. ERRORS IN THE DISCRIMINATION BETWEEN A HIGH LEVEL ECHO SIGNAL AND THE NEAR END SPEECH SIGNAL. APPLICATION TO TELEPHONE NETWORKS.

Description

15452

  The present invention relates to interference reduction devices and detectors used in these devices. Echoes commonly appear in a telecommunication system when electrical signals present in a receive signal path encounter impedance imperfectly matched at a differential junction and are partially reflected to the remote source on a signal path of a signal. emission so that the reflected signal, or echo, is heard at the far end of the transmit channel some time after the original signal is transmitted When the distance between the speaker and the speaker increases , the echo takes more time to reach the person speaking and, as a result, the echo becomes more embarrassing for the speaker,

less subjectively.

  It is therefore generally attempted to reduce the echoes. An echo control configuration which is described in US Pat. No. 4,005,277 comprises a device actuated by the speech signal which is called an echo canceller. characteristically involves some form of selective attenuation, performed under the influence of the vocal levels in the transmission path, so that the echo which would return by

  elsewhere to the speaker is attenuated Such a configuration

  This is usually satisfactory for terrestrial telecommunication paths, in which the echo delay, corresponding to the round trip delay between the signal transmission and the return of the echo,

  However, in the telecommunication

  satellite delays, transmission delays are much longer and the echo is more annoying and may even interrupt the conversation by chopping the return signal during intervals during which both parties are talking, ie say in

case of simultaneous speech.

  On the other hand, instead of interrupting the

  aunt, another echo control configuration, called

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  Echosynthesizer typically resets a reproduction signal of the impulse response of the echo signal and algebraically subtracts the estimate from the outgoing signal to obtain an echo canceled signal Most conventional echo cancellers, such as the configuration described in US Patent 3,499,999, synthesize the echo reproduction signal using

  a delay line to be taken with adjustable multipliers

  in a downstream reaction configuration of

  adaptive type, which is still called a transversal filter.

  The multipliers are set automatically by a control signal which is elaborated from the difference between the echo and the reproduction signal Because the impulse response of an echo path can be quite long, a precise synthesis of the signal transverse filter may require a large number of associated sockets and multipliers, which is a

  complex and expensive configuration.

  In addition, the speech coming from the user of the near end is generally speaking for an echo canceller, because the canceller considers that this speech is the echo signal and tries to establish a model. based on speech, so his estimate of the impulse response of the echo path deviates from the true impulse response of the echo path To solve this problem, we currently use speech detectors from the near end that block the modeling function of the echo canceller echo path impulse response, when the detector considers near-end speech presence US Patent 4,129,753 describes an echo canceller configuration that includes an active near-end speech detector This near-end speech detector comprises

  memory and other active circuits, and the memory

  records the values of a number of echo signals passed during operation, the detector compares the value of a current signal on the transmit signal channel with the past echo signals that are recorded in the

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  memory, and produces a blocking signal for the process.

  echo path modeling when the comparison

  determines that the current signal is speech from the

  close and not an echo signal.

  Although this configuration solves the problem associated with other earlier configurations of mistakenly indicating the presence of near end speech when the signal is actually a high amplitude echo signal, the speech detector of the near end the near end which is used is of very complex design because, in addition to the fact that it requires active circuits, the precision is directly proportional to the size of the memory used (that is to say to the number of values echo

past which are retained).

  One aspect of the invention is an interference reduction device for substantially canceling

  a scrambling signal of a real feedback signal is

  paging on a transmission channel of a near end transmitter / receiver, in which, during operation, a scrambling reproduction signal is subtracted from the return signal to produce a canceled scrambled signal, the signal scrambling reproduction

  is produced as a result of the annoying interference signal

  When an input signal is present on a receive channel of the transceiver, an additional interference reproduction signal is subtracted from the feedback signal to produce an additional canceled interference signal, the interference reproduction signal. additional output is generated by the additional canceled interference signal and the input signal, and the

  conditions in which the reproduction signal is produced

  interference is blocked by reliance on a rela-

  predetermined difference between the input signal and the

additional canceled interference.

  According to another aspect of the invention, a detector for blocking the adjustment of a scrambling reduction device and providing an atremity-poch signal on a transmit signal channel of a transmitter / receiver near end, includes means for subtracting from a real feedback signal propagating on the transmit signal path, a scrambling reproduction signal from the detector, for generating a canceled scrambled signal from the detector, means for receiving the canceled interference signal from the detector and an input signal propagating on a receive signal path of the transmitter / receiver, for recording a first set of M sample values of the signal of input, and to combine the set of M values and the canceled scrambled signal of the detector, to generate the scrambling reproduction signal of the detector, and control means for s to receive the canceled interference signal from the detector and the input signal, to record a

  set of sample values of the delayed input signal

  increasingly, and to produce a signal for

  adjusting the interference reduction device

  in a predetermined relation between the canceled scrambled signal of the detector and the set of values

  of increasingly delayed samples.

  An embodiment of the invention provides an echo canceller with improved performance for the near-end speech detector, and includes a near-end speech detector that does not exhibit the high detection rate. erroneous near end word that is associated with the configurations of

the prior art.

  The invention provides a near-end speech detector which is capable of distinguishing near-end speech from high-amplitude echo signals by the incorporation of a second-end speech detector. echo canceller in the near-end speech detector, to form a close-end speech detector of the correlation type, in front of the echo canceller

  active The echo canceller incorporated in the speech detector

  the end of the near end is in front of a

  A prior art speech detector and receives as an input signal the signal propagating in the transmission signal channel. The near end speech detector modifies this signal which is then applied. as an input signal to the speech detector of the prior art. The invention will be better understood on reading the

  description that follows of an embodiment and in

  reference to the attached drawings, in which the elements

  The logs are designated by the same references and in which: FIG. 1 is a block diagram of an exemplary echo cancellation configuration of the prior art, including a near-end speech detector. prior; FIG. 2 is a block diagram of an example of an echo canceller comprising a speech detector of

  the near end of the advanced type, in accordance with the invention

  tion; and Figures 3 and 4, which form Figure 5,

  represent an example of a detailed realization of the

their echo of Figure 2.

  FIG. 1, which basically represents a single transmission terminal intended to interconnect a near-end transmitter / receiver, 10, with a reception signal channel 12 and a transmission signal channel 14, by FIG. intermediate of a

  Differential network 16 The differential network 16 can

  generally take a balancing network (no

  shown) for performing the impedance matching.

  Theoretically, all signals propagating on the receive signal path 12 are transmitted by the differential network 16 only to the near-end transmitter / receiver, 10, and the signals from the transceiver 10 are transmitted by the differential network 16 only to the transmit signal path 14 However, because impedance mismatches can not be avoided in the actual signal paths 12 and 14 which are connected to the differential network 16 a part of the signal energy present on the reception channel 12 appears on the transmission channel 14 and is sent back to the far-end transmitter / receiver (not shown) in the form of an echo, in the absence of some kind of cancellation or echo cancellation An echo cancellation device, as shown in FIG. 1, can therefore be used to eliminate the echo signal appearing on the way

  transmission signal 14, and this device comprises a detection

  spokesperson of the near end.

  As shown in Figure 1, the echo canceller com-

  takes a transverse filter 18, a combination circuit 20 and a near-end speech detector, 22 The transverse filter 18, also called a tap delay line, receives and records successive samples of the signal x (k ) which approaches the near-end transmitter / receiver, 10, on the receive signal path 12, and processes these samples to form, as an output signal, an estimate of the echo signal on the transmission signal path 14, which is called a signal of

echo reproduction y (k).

  The combining circuit 20, which is placed in the transmission signal channel 14, subtracts the echo reproduction signal y (k) produced by the transversal filter 18, with respect to the real feedback echo signal y ( k) which propagates in the transmit signal path 14, to form a difference signal which is called an echo signal

  canceled e (k) The canceled echo signal e (k) is then applied

  than to propagate on the remaining portion of the transmit signal path 14, to be received by a far end transmitter / receiver (not shown).

  the same canceled echo signal is sent back to the trans-

  versal 18 to provide the latter with the information necessary to improve the estimation of the echo signal, that is to say the echo reproduction signal y (k) produced by the transversal filter 18 Under the ideal conditions , y (k) would be able to reproduce exactly y (k), the canceled echo signal e (k) would be zero, and the transmitter / receiver of

  the far end would receive no echo signal.

  However, in actual practice, some residual canceled echo signal is always sent back to the end

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distant.

  The word of the near end that can be pre-

  on the transmit signal channel 14 has a typical

  it is a much higher level than the echo and it is a parasitic noise with respect to the transversal filter 18 If the transverse filter 18 continued to operate in the presence of near end speech, the echo reproduction signal (k) would deviate from the actual feedback echo signal y (k) and, instead of reproducing this signal, would attempt to reproduce the near-end speech signal. To mitigate this problem, the word of the near end, 22, in order to prevent the continuation of the update operation

  transverse filter 18 in the presence of speech of the

  As shown, the speech detector

  the near end, 22, reacts both to the signal of

  x (k) and the actual return echo signal y (k), and by employing an algorithm establishing a relationship between these

  two signals, it blocks the operation of the cross-filter

  sal 18 when he considers that there is presence of word of

the near end.

  An example of a speech detection algorithm,

  known in the art, that can implement the detection

  the near-end speech word, 22, is given by the relation y (k)> 1/2 maxx (k), x (k-1), x (k- (N-1)), (1 ) In accordance with relation (1), the speech detector of

  the near end, 22, would include a transversal filter

  similar to the transversal filter 18, to generate the sequence

  jx (k), x (k- (N-1)) J, and a comparator for comparing separately

  the signal y (k) to each of the recorded values of the input signal, and to generate a blocking signal

  when y (k) is greater than half the value of the maximum

  mum of recorded values of the sequence.

  relationship (1) is satisfied, the detector of

  near-end speech, 22, sends a "blocking" signal

  ge "towards the trensversal filter 18, and the latter suspends its operation until the inequality of the relation (1)

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  no longer satisfied, and the near-end speech detector, 22, transmits a "validation" signal to

  the transversal filter 18, to reactivate the process

  update of this filter when the inequality of relation (1) is no longer satisfied The factor 1/2 in relation (1) is based on the assumption that there is

  at least 6 dB attenuation of the signal in the different network

  16, from the transmit signal channel 12 to the channel

  However, there is a problem

  in this configuration when the initial return echo signal y (k) is very high, because the near end speech detector, 22, may erroneously block the

  operation of the transverse filter 18.

  Referring now to FIG. 2, there is shown a transversal filter 18 which receives and records samples of the input signal x (k) and synthesizes therefrom an echo reproduction signal y (k). The combination of this signal then subtracts this signal from the actual feedback echo signal y (k) to form a canceled echo signal e (k) which is then applied to propagate over the remainder of the signal path. transmission 14, to a far-end transmitter / receiver (not shown) As shown in FIG. 2, a near-end speech detector, 24, includes a transversal filter 26 and a combination circuit 28, more than the near-end speech detector, 22, of the prior art The transversal filter 26 operates in a manner

  similar to the transverse filter 18 described above, that is,

  that is, it receives and records successive samples of the input signal x (k) and synthesizes therefrom an echo-reproducing signal from the speech detector, yd (k). The combining circuit 28, which is not in the transmit signal channel 14, and therefore does not disturb the signal propagating on that channel, subtracts this reproduction signal from the speech detector, yd (k), with respect to the signal from real feedback echo y (k) on the transmit signal path 14, which leaks through the differential grating 16, to form a canceled echo signal of the speech detector, ed (k) The canceled echo signal of the detector of speech, ed (k),

  is then returned to the transverse filter 26 to provide

  inform the latter to the information necessary to improve the estimate that it forms of the echo path. In addition, the canceled echo signal of the speech detector, ed (k), which the combination circuit 28 produces, is applied. as an input signal to the near-end near-end speech detector, 22, which also responds to the input signal x (k) The near-end near-end speech detector , 22, recognizes the word of the near end and

  blocks the operation of the transversal filter 18 in accordance with

  the relation: ed (k)> 1/2 maxix (k), x (k-1) ,, x (k- (N-1)) J (2) In particular, when the echo signal canceled by speech detector, ed (k), becomes greater than half of the largest individual delayed value of the input signal that is recorded in the end-of-end speech detector

  close to the prior art, 22, it is considered that there is

  near-end speech, and the cross-talk filter

  sal 18 is blocked in order to stop updating during

  the whole period during which the inequality of the relationship

tion (2) is satisfied.

  As can be seen by comparing the relations (1) and (2), the invention differs from the prior art by the use of a canceled echo signal ed (k), instead of the echo signal of real return y (k), in relation to the speech detector of the near end of the prior art, 22 Thus, by the fact that it uses ed (k), the detector of

  near-end word 24 is less likely to con-

  melt a high level echo signal with the word of

  the near end and block the trans-filter by mistake.

  versal 18, in comparison with a close-end speech detector of the prior art employing the signal y (k). FIGS. 3 and 4, which form FIG.

  represent a detailed embodiment of the invention.

  and show the delay line structure to

  transversal filter 18 and the transversal filter 26 of the

  As shown in FIG. 3, the transverse filter 18 comprises a set of (N-1) delay elements, denoted by the references 301-30 N-1 'N multipliers 321-32 N'. N generators

  weighting coefficients of catches 341-34 N 'and an accumu-

  The signal propagating on the reception channel 12 is introduced into the transversal filter 18 and passes through

  the (N-1) delay elements 30130 N_ 1 to form, in association with

  with the input signal value present x (k), a sequence of length N comprising the values {x (k),

  x (k-1, x (k- (N-1)}, as shown in Figure 3.

  As described above in connection with the figures

  1 and 2, the canceled echo signal e (k) is returned to the transversal filter 18 to assist in updating the echo reproduction signal y (k), in order to improve the reproduction of the signal of Real feedback echo y (k) However, the echo canceled signal e (k) is not suitable, by itself, to improve the echo reproduction signal y (k). Therefore, the signal is passed to canceled echo e (k) by the set of N 34134 N tap weighting factor generators which function individually to form a set of N coefficient values of

  weighting of catches h (k) to h N 1 (k), and these values can be

  can be used in relation to the set of N sampled and delayed input signal values, x (k) to x (k- (N-1)), to form the echo reproduction signal

  y (k) after being added to the accumulator 36.

  As shown in detail in association with the tap weight coefficient generator 341, a tap weight coefficient h O (k), taken as an example, is formed from the canceled echo signal e (k) multiplying this signal by the associated input signal sample value x (k) in a multiplier 3519 and averaging the resulting composite signal, in an integrator network 371, to produce the coefficient value of take weighting h O (k), whose polarity and absolute value indicate the appropriate correction that is required, based on the input signal sample value x (k) Each of these weighting factor values of takes ho (k) -h N 1 (k) produced by the respective generators 341-34 N, is then multiplied by the delayed input signal value associated therewith, xk) -x (k- (N- 1), in the associated multiplier 321 32 N 'More

  precisely, the value of the weighting coefficient of

  where h O (k) is multiplied by the input sample x (k) in the multiplier 321, h 1 (k) is multiplied by x (k-1) in the multiplier 322, and so on, with the take weight coefficient value h Nl (k) multiplied by the input sample x (k- (N1)) in the multiplier 32 N.

  The N output signals of the multipliers 321-

  32 N are then applied as separate input signals to the accumulator 36 which summed the N products h O (k) x (k) to h N 1 (k) x (k- (Nl)) for producing the echo reproduction signal y (k) as an output signal of the transversal filter 18 As indicated above in connection with FIG. 2, the echo reproduction signal y (k) is subtracted the actual feedback echo signal y (k) in the combining circuit 20 to form subsequently updated values of the canceled echo signal e (k) as an output signal of the canceller echo which is then

emitted towards the far end.

  FIG. 4 shows a detailed embodiment of the near-end speech detector 24, in which the transversal filter 26 comprises components similar to those of the transversal filter 18, including a

  set of (M-1) delay elements 401-40 M 1, multiplier M

  421-42 M, M generators of weighting coefficients.

  Socket tap 441-44 M (only the tap weight coefficient generator 441, comprising a multiplier 41 and an integrator network 431, is shown in detail in FIG. 4 to avoid complicating the representation), and an accumulator 46 During operation, the signal

  input x (k) which propagates on the receive signal

  12 is introduced into the transversal filter 26 and

  pays the elements of delay 401-40 M 1 to form, in association

  with the present value of the input signal x (k), a sequence of length M {x (k), x (k1), x (k- (M-1)) Dependent on the canceled echo signal of the speech detector, ed (k), produced by the combination circuit 28 of the detector

  close-end speech, and by an identi-

  than that described above in association with the general

  the weighting factor 341, the generators

  441-44 M tap weight factors

  a set of M weighting coefficient values.

  taking of the speech detector, jo (k) to j Mi (k).

  Each tap weight coefficient value of the speech detector is then multiplied by the associated delayed value of the input signal, in the associated multiplier 421-42 M More precisely, the tap weight coefficient value of the speech detector (k) is multiplied by the input sample value x (k) in the multiplier 421, Jl (k) is multiplied by x (k-1) in the multiplier 422, and so on, with the value of tap coefficient of the speech detector j M l (k) multiplied by the delayed input value x (k- (M-1)) in the multiplier 42 M. The M output signals of the multipliers

  421-42 M are then applied in the form of

  tred to the accumulator 46 which summed the M products jo (k) x (k) to j M l (k) x (k- (M1)) to produce the output signal of the transverse filter 26, which corresponds to to the echo reproduction signal of the speech detector of

  near end, yd (k) As indicated above in relation to

  2, the echo reproduction signal of the speech detector yd (k) is subtracted from the actual feedback echo signal y (k) in the combination circuit 28, to

  form the signal that is applied as a signal of

  to the near-end speech detector, 22, i.e. the canceled echo signal of the

speech detector, ed (k ?.

  As indicated above in connection with the figure

  2, the canceled echo signal of the speech detector of the

  near miss, ed (k), is returned to the cross filter

  26 and it is applied as an input signal to the detection

  speaker of the near end of the prior art, 22.

  In association with the transverse filter 26, the echo signal canceled from the speech detector, ed (k), is applied as an input signal to each tap weight coefficient generator 441-44 MY, which allows a setting Continuous update of the values of the weights

  by means of which the signal of reproduc-

  echo of the speech detector yd (k) converges con-

  nil to the actual feedback echo signal y (k) As indicated above in relation to Figure 2, the echo canceled signal of the ed (k) speech detector, applied as an input signal to the speech detector the near end of the prior art, 22, and in conjunction with the relationship (2), allows the near-end speech detector 24 to better distinguish between a high-level echo and the speech of the close end Thus, because the speech detector of the near end 24 reaches a false detection rate of the speech of

  the near end which is less than the one of the configura-

  of the prior art, this detector will block less

  mistakenly the operation of the transversal filter 18.

  It goes without saying that many modifications can

  can be made to the device described and represented,

  without departing from the scope of the invention.

Claims (6)

  A scrambling reduction device for practically canceling a scrambling signal of a real feedback signal propagating in a transmission channel of a near end transmitter / receiver, in which, during operation , a scrambling reproduction signal is subtracted from the feedback signal to produce a canceled scrambled signal, the scrambling reproduction signal is produced in response to the canceled scrambled signal and an input signal present on a noise channel. receiving the transceiver, and setting the conditions under which the scrambling reproduction signal is produced, is blocked in dependence on a predetermined relationship between signals generated from the transmit and receive signal paths ; characterized   in that an interference reproduction signal * ipplemened   (yd (k)) is subtracted from the return signal (y (k)) to produce an additional canceled interference signal   (ed (k)), the additional scrambling reproduction signal   is produced in response to the additional canceled interference signal and the input signal (x (k)), and the   setting the conditions under which the reproduction signal   interference ducting (y (k)) is generated is blocked under the dependence of a predetermined relationship between the signal   input and the additional canceled interference signal.   2 Device according to claim 1, characterized   in that it comprises means (20) for subdividing   milking the scrambling reproduction signal (y (k)) with respect to the feedback signal (y (k)), to generate the canceled scrambled signal (e (k)), first processing means (18) for receiving the canceled scrambled signal (e (k)) and the input signal (x (k)), recording a set of N sample values of the input signal, which are increasingly delayed, and combining this set of values with the scrambled signal canceled, to generate   the scrambling reproduction signal (y (k)), and a detection   controller (24) comprising means (28) for subtracting the additional scrambling reproduction signal (yd (k)) from the return signal to generate the additional canceled scrambled signal (ed (k)), second processing means (26) for receiving the additional canceled scrambled signal and the input signal, for storing an incrementally delayed set of M sample values of the input signal, and for   combine this set of M values and the signal to scramble   additional time, to generate the reproduction signal   additional interference ducting (yd (k)), and control means (22) for receiving the additional canceled scrambled signal and the input signal, for recording a set of sample values of the input signal, steadily retarded, and blocking the processing means (18) in accordance with a predetermined relationship   between the additional canceled interference signal and the   seemingly "delayed sample values in a health.   3 Device according to claim 2, characterized   in that the second processing means (26) comprises   take a set of (M-1) delay elements (40140 M 1) forming a transversal filter that responds to the input signal by generating the set of M input sample values, which are increasingly delayed, and a set of M tap decision coefficient generators (44144 M) each responsive to the further canceled interference signal by generating a respective one of a set of M tap weight coefficient values (jo (k) - M (k)>, a set of M multipliers (42142 M), each of which responds to a respective one of the M values of progressively delayed samples, and to a respective one of the M values of   weighting of catches, in order to generate   values of these values, and means (46) for summing the M products to generate the reproduction signal additional interference.   4 Device according to any one of the 15452   2 or 3, characterized in that the control means (22) have the function of blocking the first processing means (18) when the additional canceled interference signal is greater than one half of a maximum sample value of the set of sample values   Ion progressively delayed the input signal.   A detector for blocking the setting of a scrambling reduction device in the presence of a near-end signal on a transmission signal channel of a near-end transmitter / receiver, characterized in that it comprises means (28) for subtracting a scrambling reproduction signal from the detector (yd (k)), with respect to a real feedback signal (y (k)) which propagates on the signal path d transmission, in order to generate a canceled interference signal from the detector (ed (k)), processing means (26) for receiving the jamming signal   canceled detector and an input signal (x (k)) which   receiving signal (12) of the transmitter / receiver (10), recording a first set of M input sample values, which are delayed in an increasing manner, and combining the set of M values and the canceled scrambled signal of the detector, for generating the scrambling reproduction signal of the detector, and control means (22) for receiving the canceled scrambled signal from the detector and the input signal to record a set of input sample values, which are increasingly delayed, and to provide a   signal intended to block the adjustment of the reduction device   jamming according to a predetermined relationship   between the canceled interference signal of the detector and the   of increasingly delayed sample values.   6 detector according to claim 5, characterized in that the processing means comprise a set of (M-1) delay elements (401 -40 M) forming a transverse filter which reacts to the input signal by generating the set of M sample values of the input signal, increasingly delayed, a set of M tap coefficient generators (44144 M), each 15452   of them responsive to the canceled scrambled signal of the detector by generating a respective one of a set of M tap weight coefficient values (jo (k) -j M 1 (k)), a set of M multipliers (421- 42 M), each of which responds to a respective one of the set of M incrementally delayed sample values and to a respective one of the set of M   catch weight coefficients, in general   respective products of these values, and means (46) for summing the M products to generate   the scrambling reproduction signal.   Detector according to any one of the claims   5 or 6, characterized in that the control means have the function of providing a signal for blocking the adjustment of the interference reduction device when the canceled interference signal of the detector is greater than half a value of maximum sample out of the set of sample values, which has been steadily of the input signal.