DE2163673C2 - Echo canceller for a communication system - Google Patents

Description

The invention relates to an echo canceller for a message transmission system a two-wire four-wire transition, in which one of the signals of the incoming direction of the Four-wire path fed branch network with a number of outputs, the systems with each other linearly independent impulse responses are provided. The output signals of the Branch network are each via an adjustment element fed to a summer, the output signal of which is a simulated echo signal in the subtracting sense the sign; I in the outgoing direction of the four-wire path is added. Here, each setting member is integrated by means of an integrating member Output signal of the respective output signal of the branching network with the residual echo signal adjustable in the outgoing direction of the four-wire path multiplying multiplier.

An echo canceller of the aforementioned type is z. B. through the article "An Adaptive Echo Canceller", by M. M. S o η d h i, from "The Bell System Technical Journal" 1967, pp. 497-511, known. However, since Dialing noises and the speech signals of the nearby participant the outgoing signal of the four-wire path make largely unusable for the correlation at times and can lead to a good setting of the adjustment members that has been achieved in the meantime is lost again, achieve the known ones Echo cancellers usually only have a low level of adjustment accuracy, which, moreover, only takes a long time can be achieved because the adjustment speed due to the aforementioned disturbances in moderate Limits must be kept.

It is the object of the invention. to specify an echo canceller of the type mentioned above, which shows a better converging setting behavior than known echo cancellers.

This object is achieved according to the invention in that averaged and then two-way equal

2 163 675 if

3 ⁴

Directed output signals of the multipliers in a parallel filter 21 ... 29 ^ but ^ ^

another totalizer to form a control signal - through a right runner. limb with a coarser

are released, which is used to control the speed number of taps (cf. ionü η ι rg .γ

fet of the adjustment process with monotonous "increasing or by Laguerre networks (cf. Sd ' Realize effect dif amplification of further actuators 5 page 506). In general, however, it is sufficient

sets one of each between one of the condition that the impulse responses of the filter

Multiply the following integrator »« ^ ™ ^ invented idea

^Eir these measures an adaptation of the isf an embodiment is chosen which, by setting speed to the already achieved degree,. going with analog signals work et.t '"' especially the approach to the optimal setting is achieved, advantageous, but not shown in detail A so that in the case of large deviations from the optimal management of the invention"! .by the d g.ta e setting in a very short time, a satisfactory operation and d through and feeding, it can be achieved S gnate state, which then by the incoming direction and the ^ g ™ ^'e ° γ disorders such awful noise during dialing or speech signals _l5 outgoing direction of the J' ^^^ ^ J ^ of the nearby subscriber can hardly be influenced, characterized by an analog-to-digital converter, but on the contrary continuously and slowly In this case, the output signals «·, ^» λ are improved, even with persistent, strong interfering noise in the branching network, for example by looking at the beginning of the connection an optimal shift register is generated. », _prt \ _e n

Setting can be achieved in a comparatively short time, zo The individual output signals e «·, ..." * * ™

Further details of the invention are given in the arrangement according to FIG. 1 and 2 from the branching network 21.29 generated and explained in more detail in the management example, FIG. 2 after each passage one of the sluice members 61 .. ^ » a detail of the embodiment according to F i g. 1 by the summer 7 ^ dems ™ '' ^{erten tch0} _shows 2 ₅ signal y combined. Since the actuators 61 ... oy

Fig. 1 shows an excerpt from a telephone - each with an adjustable gain c, ... rv, the long-distance connection over one or more transit times can be greater or less than 1, with four-wire lines affected by the transition from one to the output des Sum.erers7 the gescnaizic four-wire line with an incoming direction or simulated echo signal y to 1-2 and an outgoing direction 5-6 to a 30th ^ _n

Two-wire line 4 over a with a simulation y - "Σ ^Ci ' ^M ' ·

equipped fork 3. Here is the echo compensator, ·. 1

sator on the one hand in the incoming direction 1-2 .. c-iitri ^ Hpr

and also in the outgoing direction 5-6 one- Setting the Verstarf """^ ^s £ lgl." £

switched, but between this echo 35 61 ... 69 takes place in each case. ^{milte |} b ^ar ^ J Js Off compensator and fork 3 can still be the output signal of the _ associated ^M f'P ¹ ™ ^ / ^ a longer four-wire line. this multiplier 31 ... 39 becomes one

The adaptive quadrupole of the echo canceller is the corresponding output signal of the branched mgs, for example from a filter bank with a larger network 21 ... 29 and the other by the number * input side of parallel-connected filter 40 residual echo, gnal e in the outgoing R ^{'CHT "n} |" f 21 ... 29, then controlled by the four-wire path connected downstream of the filters. One output signal each for actuators 61 ... 69 and a subsequent e ■ w, the multiplier, ^ «^ * ⁰ * ^? Summing unit 7. The input of this quadrupole is fed from residual echoes.gnals e with the associated η output to the signal of the incoming direction 1-2 ge signal u, of the branching network, darglk controlled; the output of the quadrupole feeds a simulated 45 then via an ^αε \ ^ ' ^ι ^ ^η _Ιη ™ ^^^^^^^ echo signal Γ via the differential amplifier 8 in the sub- and one of the downstream integral elements 51 in the outgoing direction 5- 6 a. 59 the reinforcement c, of the associated stem.eto in the balanced state, the quadrupole has approximately De Multiplmerer 31 39 ^can ^ JJ ^ _e

the same transfer function as the transmission be configured such that the s R ^e ^ e os.gnai-cleaning function of the echo path from the input of 50 and / or A "sgangss.gnalIh, the delay" on supply quadripole fork 3 back to the difference - network in the We.se evaluate daU cdigiic amplifiers, so that at the output of the Γ i terenver- their sign function of s.gn e or signu, .nul amplifier 8 a substantial compensation of the over-multiplied _Uprkirq l of the invention

the fork 3 crossed echoes γ takes place. It is the de wesentl.ches feature ^de ™ "^ ^ng

from the nearby participant, who over the two-wire ₅₅ that the respective output signal ₁ ^ h 1 ^ dnen

line 4 is connected to fork 3. native multipliers 31. 39 with a J % right-handed appears in the 'outgoing path 5 of the fact, r k multiplies the following four-wire path as the signal ". The signals are fed to the Integnerghed. said _Au sgangdesDifferenzverstärkers8ergibtsichdaherzU ₆ ^^^^ J ^^^^

e = γ -y + n ----- e + n. _{sjgnal k we} ] _ches dj _e further actuators 41 ...

The most favorable conditions for the setting in each case to the multiplication with the Jj ^ ^ork de actuators 61 ... «9 by means of the still to be set, from the control signal ρ ^{at the} output of the c. frictional correction. the use of a branching network which contains 6 ₅ output signals e ■ «· ,, der Mu t pli« «^ ¹ ^ ³ » _d ^J _cn ches systems with orthogonal impulse responses ψ ^^^^^^^ ^ adration. Such a branching network leaves s.ch low pass 71 ... wound in. ^En ° "y ₈₉

present example by means of Doppelweggle.chncnter 81 on the input side

like in

are led. The size of the control signal ρ results from the output of the first ratio generator 10

therefore generally appears as the coming convergence ^{signal p} - is the multiplicative

_. '"^ ^V r ,, ₂ tive input of the second ratio generator 11 to-

P ~ '2- * _λ L "<J ■ 5, the dividing input of which is the other

Control signal r is supplied, which consists of the signal e

where the angle brackets represent the symbol for the respective outgoing direction 6 of the four-wire connection! The detection via a rectifier 18 with quadratic characteristics of all output signals W _{1 of} the multiplier line and a downstream low-pass filter 19 to 31 ... 39 for the formation of the control signal /) brings about a mean value. The value of the further control signal r , which is the most favorable for the control according to the invention, results from r = [e ² ]. Result, however, is not absolutely necessary. At the output of the second ratio generator 11 produces It is sufficient at low and claims, _{sjch therefore the Au} j_ ^ ,, ^ _the only part of the output signals e · w <respective ° ° ° r-q '
averaged and then full-wave rectified 15 to feed the essential portion of the further setting elements to the further adder, where ei; 41 ... 49 controlling factor signal k forms. By means of the quadratic characteristic curve of the Doppe! Wegghichrichter of _{the product line 13, the si} , _P_ _still 81 ... 89 are very advantageous, but not necessarily ⁶ _r . _q
necessary is. The generation of the factor signal k from the limit value stage 12 on the one hand and the timing stage 14 to the control signal ρ is carried out by means of the device 90, on the other hand, and together form an adjustment factor γ in the simplest case, a linear dependency. The invention is therefore based on the factor signal k given by the control signal ρ essentially the following law of formation for the can. In addition to the control factor k , this device 90 is:

signal ρ also the signal χ of the incoming 35 _ ρ _ Σ [e · n> ₍ ] *
Direction 1-2 of the four-wire path and the residual echo ~ ? ' _r . "~~ ^γ \ _χ ιγ. ~ 7 _e * \ '
signal e at the output of the differential amplifier 8 is supplied. The device 90 may be, for example wherein the manner of generation of the signal for the Anals decision means executed passungsfaktor γ hereafter described in greater detail which of those time intervals in which is the 30th
Signal χ on the incoming direction 1 smaller The limit value stage 12 is activated by the con-

^iS 7'l ^d? _n ^Si f ^{al e d to} f ^{ra "b} g f ^{eh ligand R} * i |" ⁿ 8 ί vergenzsignal representing output signal of the first P-

and also when the signal χ has a certain ^a ° ° _q

predetermined threshold level below which factor ratio generator 10 is driven and is such off signal k makes zero and formed by the setting 35, that it 61 ... still relies input values of the convergence members 69 so that the setting state p_ _unt best On for those time intervals, in which the signals ^b q «.» luiugnuic
Due to the disturbance of the setting elements 61 ... 69 arriving from the nearby subscriber, the limit value which gives the output signal zero can only be seen to a limited extent for the correlation, is frozen. According to a preferred 40 and thus the product former 13 blocks, so that the device 90 is also an embodiment of the invention, the factor signal k becomes zero. It is also possible, however, in the following with reference to FIG. 2 in more detail instead of the value zero in a manner explained with the convergence. signal, signal F i g, which falls approximately proportionally. 2 shows in detail the preferred embodiment to be generated. Above the intended limit width, the device 90, which essentially supplies the 45 for the convergence signal, the limit value stage 12, the first ratio generator 10, the second ratio to the product generator a constant value,
bildner II, the limit value stage 12 and the time stage 14 Contains the third multiplicative input of the product. The first ratio former 10 forms from former 13 is controlled by the timing stage 14, which is controlled by the signal χ of the incoming direction 1-2 control signalp and the additional control signal q 5 ° and is designed such that it is a time-

j τ, ■ 1 P r »1. · ·» jjj · · λ · emits dependent control signal which during

the convergence signal -. This is the dividie-, -, · »“ ·. , egg,

^{0 &} q of the times in which the signal jc has a predetermined η

Starting input of the first ratio generator 10 exceeds value, starting from a smaller η guided additional control signal q from the signal χ initial value monotonously a larger end value zi> the incoming direction 1 of the s four-wire path 55 strives, whereby it is achieved that at the beginning of the remote derived , namely via a rectifier 15 with a conversation initially with a reduced speed it square characteristic, a downstream low and only after a predetermined start-up time pass 16 for averaging and a subsequent Güed 17 with a square characteristic to determine the mean values to be formed π it . The maximum: r speed is set.
The value of the additional control signal q results in 60. The output signals of the time stage 14 and the limit therefore for value stage 12 result in the multiplied by one another

Adjustment factor, through its action under

q = [x ² ] * and the value of the convergence- the conditions under which the echo canceller

signals - to work, an optimally converging setting ratio It: n

1 65 can be achieved.

yr, 1 * W '^; already mentioned, there is a particularly ve -

P- = _ ^le liüiL, partial, but not shown execution -

1 [x ² t ² form of the invention in the digital embodiment

of the echo comparator, to which the signal χ of the incoming direction 1-2 and the signal e of the outgoing direction 6 of the Vierdralitweg can each be fed via an analog-to-digital converter. Here, the function of the actuators 61 ... 69, the integral actuators 51 ... 59, the further actuators 41 ... 49, the multipli-

zierer 31 ... 39, the Mittelweubildner 71 ... 79 and the squarer 81 ... 89 each by a single one digital actuator, digital integrator, digital additional actuator, single digital multiplier, single middleager and a single squarer in successive time intervals Fulfills.

1 sheet of drawings

809 681 II '.

Claims (9)

Patent claims: 1. Echo canceller for a communication system with a two-wire-four-wire junction, in which a branching network fed by the signals of the incoming direction of the four-wire path is provided with a series of outputs that correspond to systems with impulse responses that are linearly independent from one another and whose output signals j: over an adjusting element are fed to an adder, the output signal of which is added as a simulated echo signal in the subtracting sense to the signals of the outgoing direction of the four-wire path, each adjusting element by means of the output signal integrated by means of an integrating element, the respective output signal of the branching network with the residual echo signal in the outgoing direction of the four-wire path multiplying multiplication is adjustable, characterized in that averaged and then full-wave rectified output signals of the multipliers (31 ... 39) in a further adder (9) to a St euersignal (p) are summarized, which sets the gain (A) of further actuators (41 ... 49) to control the speed of the adjustment process with a monotonically increasing effect, one of which is switched on between one of the multipliers and the subsequent integrator. 2. Echo canceller according to claim 1, characterized in that the further control signal (r) the rectified and then averaged residual echo signal in the outgoing direction (6) of the four-wire path with reciprocal effect, the gain (A) of the other actuators (41 ... 49) additionally controls multiplicative. 3. Echo canceller according to claim 2, characterized in that as an additional control signal (q) the rectified and then averaged signal of the incoming direction (Π of the four-wire path with reciprocal monotonously increasing effect, the gain (A) of the further actuators (41 ... 49) additionally controls multiplicative. 4. Echo canceller according to claim 3, characterized in that the additional control signal (q ) controls the gain (A) of the further actuators (41 ... 49) with an approximately reciprocal quadratic effect. 5. Echo canceller according to claim 3 or 4, characterized in that a convergence signal C formed from the ratio of the control signal (p) to the additional control signal (i /) below a chaacteristic limit value for the best possible setting of the setting elements the gain of the further actuators (41 ... 4 ')) is reduced, preferably to zero stencil. 6. Echo canceller according to one of the preceding claims, characterized in that the rectification of the averaged output signals dei multiplier (31 ... 39), the rectification of the further control signal (r) and that of the additional control signal (q) are each carried out with a squaring effect. 7. Echo canceller according to one of the preceding claims, characterized in that that a time-dependent control signal, which starts from the beginning of the conversation starting from a smaller initial value monotonically tends towards a larger final value, the gain (A-) of the other actuators (41 ... 49) additionally controls in a multiplicative manner. 8. Echo canceller according to one of the preceding claims, characterized by digital Working method and by supplying the signals of the incoming direction and the Signals of the outgoing direction of the four-wire path each via an analog-digital converter. 9. Echo canceller according to claim 8, characterized in that the function of the actuators (61 ... 69), the integrating elements (51 ... 59), the further actuators (41 ... 49), the multiplier (31 .. . 39) "the averaging (71 ... 79) and the squarer (81 ... 89) each by a single digital actuator, ¹ digital integrator, additional digital actuator, single digital multiplier, single averaging and a single squarer in time successive intervals is met.