RU2412546C1 - Adaptive echo canceller on recursive filter - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: adaptive echo canceller (AEC) on recursive filter consists of N≥2 channel filters (CF) (1), N-exhaust delay line (DL) (2), M-input adder (3), subtracting unit (SU) (4) and adaptive control unit (ACU) (5). In AEC there formed are direct and return signal (echo) passage circuits, estimated value of signal level is calculated, on the basis of which by means of method of quickest descent there calculated are corrective weight coefficients for deeper suppression of echo signal.

EFFECT: deeper suppression of echo signal within the whole range of voice spectrum.

3 cl, 4 dwg

Description

The invention relates to the field of radio communications and can be used in telecommunication lines of two-way communication.

Adaptive echo cancellers are known, described, for example, in EP No. 0412691 A2 of 02.13.91 with priority of 07.08.89; in US patent No. 4964118 from 10.16.1990,

Adaptive echo canceller according to the application EP No. 0412691 consists of a first block for dividing the primary signal into a set of signals divided within the spectrum of the primary signal, and a second block that performs the function of the secondary signal similarly to the first block. The echo canceller also includes many adaptive filters designed for primary and secondary signals and providing the generation of an error signal.

The disadvantage of this filter is the relatively high level of uncompensated echo.

Adaptive echo canceller according to US Pat. US No. 4964118 consists of the first and second channel filters, providing suppression of the echo signal due to the generation of compensating signals. The echo canceller generates a compensating signal in accordance with a given function, which allows to reduce it exponentially.

The disadvantage of this analogue is the relatively high level of uncompensated echo.

The closest in technical essence to the claimed is the adaptive echo canceller according to ed. St. SU No. 1436277, IPC Н04В 3/20, publ. 11/7/1988, Bull. No. 41. The closest analogue consists of M≥2 channel filters (CF), N-tap delay line (NO LZ), adder, amplifier, subtraction unit. Each CF contains the first and second multipliers, the channel adder (CS), the channel integrator and the channel N-tap LZ.

After processing and comparing it with the residual signal in the closest analogue, the far end subscriber’s speech signal is generated to evaluate the impulse response of the echo path and an echo signal is generated based on the current estimate of the cross-correlation function of the generated signals taking into account the values of the impulse response of the echo path.

However, the prototype echo canceller has an insufficient level of echo suppression, which is due to the linear dependence of the feedback on the error signal and a fixed level of amplitude limitation of the generated signal.

The technical result from the use of the claimed device is the development of an adaptive echo canceller that provides deeper suppression of the echo signal in the entire range of the speech spectrum due to more accurate convergence of the iterative process of compensating the echo signal.

The claimed device extends the arsenal of funds for this purpose.

This goal is achieved by the fact that in the known adaptive echo canceller (AEC) containing M≥2 KF, N-tap LZ, where N = M-1, the input of which is the input "distant subscriber signal" (SDA) AEC, M-input adder (MVkh.SUM), the output of which is connected to the output of the subtraction unit (BV), the second input and the output of which are respectively the input "reflected signal" (In. OTs) and the output "error signal" (output SO), n-th tap NO LZ, where n = 1, 2, ..., N, is connected to the signal input of the (n + 1) -th KF, and the signal input of the first KF is connected to the input NO LZ, the signal output of the m-th KF, where m = 1, 2, ..., M, is connected to the m-th entry VCM. SUM, an adaptive control unit (BAU) is additionally introduced. The BAU is equipped with M-bit signal input (MR SVx.), The first and second outputs are the signal of modeling coefficients (1 MR Output QMS and 2 MR Output QMS), the output is “correction signal” (MR Output QSC) and the input is “training signal ”(MR Vh.Obs). To the signal input of the m-th KF is connected the m-th discharge of MR CBx. BAU, and m-th categories IMP Out. QMS and 2MR Output QMS, MR O.K.S. and MR In.ObS BAU are connected respectively to the first and second inputs "signal modeling coefficients" (1 input. QMS and 2 inputs. QMS), input "correction signal" (Vkh.SK ) and the output of the “training signal” (Output OBS) m-th KF. The BAU is equipped with an additional input “error signal” (Bx.CO), which is connected to the output of the BO, which is the output of the AEC.

KF consists of the first, second, third, fourth and fifth multipliers (UM), the first and second channel adders (KSUM), the first and second adders (SUM), the first and second delay lines (LZ).

The first input of the first PA is the signal input KF. The second KSUM, the first KSUM, the first SUM and the second SUM are cascaded along the signal inputs. The first input of the first PA is connected to the input of the second LZ, the output of which is connected to the first input of the third PA. The inverse output of the third PA is connected to the second input of the second KSUM.

The inverse output of the fifth PA is connected to the second input of the first SUM. The output of the second SMS is connected to the input of the first LZ and is the signal output of the CF. The output of the second PA is connected to the first input of the fifth PA and to the second input of the second SUM. The output of the first LZ is connected to the first input of the second PA, to the first input of the fourth PA and is the output of the CCF. The second inputs of the third and fourth PA are combined and are 2 Vkh.SMK KF. The second input of the second PA is Vkh.SK KF. The second input of the fifth multiplier and the second input of the first multiplier are combined and are 1Bx.CMK KF.

BAU consists of the first and second weight shapers (FVC), the first and second weight corrector (KVK) of the direct signal shaper (FPS) and the feedback signal shaper (FSOS). The M-bit inputs of the FPS and FSOS are respectively MR CBx. and Mr Bh. OBS BAU. M-bit input FPS is connected to the M-bit input of the first FVC. The FPS output is connected to the first input of the first FAC, the output of which is connected to the “correction” input of the first FVC. The M-bit first and second outputs of the QMS of the first FVC are respectively IMP Out. QMS and 2MP Out. QMS BAU. The M-bit input of the FSOS is connected to the M-bit input of the second FVC. The M-bit output of the second FVK is MR Vykh.SK BAU. The output of the FSOS is connected to the first input of the second KVK, the output of which is connected to the input "correction" of the second FVK. The second inputs of the first and second KVK are combined and are Vkh.SO BAU.

Thanks to this new set of essential features, the claimed device provides adaptive regulation of weight coefficients in real time, which in turn provides deeper echo cancellation.

The claimed adaptive echo canceller is illustrated by drawings, which show:

figure 1 is a General block diagram of an adaptive echo canceller;

figure 2 is a structural diagram of a channel filter;

figure 3 is a structural diagram of an adaptive control unit;

figure 4 is a block diagram of the algorithm of the BAU.

The adaptive compensator on the recursive filter, shown in figure 1, consists of M≥2 KF 1 ₁ , 1 ₂ , ..., 1 _M , NO LZ 2, MVx. SUM 3, BV 4 and BAU 5. Input NO LZ 2 is connected to the signal input of the first (m = 1) KF 11 and is Vh. SDA AEC. The signal input of the (n + 1) -th CF 1 _{n + 1 is} connected to the nth tap of NO LZ 2 and the (n + 1) -th discharge of MR CBx. BAU 5. The first discharge (m = 1) MR SVh. BAU 5 is connected to the input NO LZ 2. The signal output of the m-th KF 1 _{m is} connected to the m-th input of MVx. SUM 2, the output of which is connected to the first input of the BV 4. The second input of the BV 4 is Bx. From AEC. The output of BV 4 is connected to Vkh.SO BAU 5 and is Vykh.SO AEK. Out ОС, 1 In.СМК, 2В.СМК and Вх.СК of the m-th KF 1 _{m are} connected to the m-th bits respectively МР В.ОBS, IMP O.СМК, 2МР O.СМК and МР Output.СК БУУ 5.

Channel filters 1. ₁ -1 _m are designed to simulate a pre-emptive speech echo signal.

Each channel filter 1 is made in accordance with the model of the speech signal, in particular, as shown in figure 2. CF 1 consists of the first 1.2, the second 1.10, the third 1.7, the fourth 1.8 and the fifth 1.9 UM, the first 1.4 and the second 1.3 KSUM, the first 1.5 and the second 1.6 QMS, the first 1.11 and the second 1.1 LZ.

The first UM 1.2, the second KSUM 1.3, the first KSUM 1.4, the first SUM 1.5 and the second SUM 1.6 are cascaded along the signal (first) outputs (inputs). The first input of the first PA 1.2 is the signal input of CF 1. The first input of the first PA 1.2 is connected to the input of the second LZ 1.1, the output of which is connected to the first input of the third PA 1.7. The inverse output of the third UM 1.7 is connected to the second input of the second KSUM 1.3. The output of the fourth UM 1.8 is connected to the second input of the first KSUM 1.4. The inverse output of the fifth UM 1.9 is connected to the second input of the first SUM 1.5. The output of the second SUM 1.6 is connected to the input of the first LZ 1.11 and is the signal output of CF 1. The output of the second UM 1.10 is connected to the first input of the fifth UM 1.9 and the second input of the second SUM 1.6. The output of the first LZ 1.11 is connected to the first input of the second PA 1.10 and to the first input of the fourth PA 1.8 and is Output.ObS KF 1.

The second inputs of the third 1.7 and fourth 1.8 PAs are combined and are 2 Vx. SMK KF 1. The second input of the fifth PAs 1.9 and the second input of the first PA 1.2 are combined and 1Bx.CMK CF 1. The second input of the second PA 1.10 is VH.SK CF 1.

BAU 5 is designed to calculate and form weight coefficients for each channel filter along the direct and feedback circuits. BAU 5, shown in figure 3, consists of the first 5.1 and second 5.2 FVK, the first 5.4 and second 5.5 KVK, FPS 5.3 and FSOS 5.6. M-bit inputs of FPS 5.3 and FSOS 5.6 are respectively M-bit signal input and MP Vh. OBS BAU 5. M-bit input FPS 5.3 is connected to the M-bit input of the first FVC 5.1. The output of FPS 5.3 is connected to the first input of the first KVK 5.4, the output of which is connected to the input "correction" of the first FVK 5.1. IMP Output QMS and 2MP Output QMS of the first FVC are respectively IMP Output QMS and 2MP Output QMS of BAU 5. The M-bit input of FSOS 5.6 is connected to the M-bit input of the second FVC 5.2, the M-bit output of which is MP Output. SC BAU 5.

The output of FSOS 5.6 is connected to the first input of the second KVK 5.5, the output of which is connected to the input "correction" of the second KVK 5.2. The second inputs of the first 5.4 and second 5.5 KVK are combined and are Vkh.SO BAU 5.

The elements included in the BAU 5 have the following purpose.

и

в цепях соответственно прямой и обратной связи для каждого m-го канального фильтра в период времени выборки Т.The first 5.1 and the second 5.2 FVK are designed to calculate weighting factors

and

in the chains of direct and feedback, respectively, for each m-th channel filter during the sampling time period T.

The first 5.4 and second 5.5 KVK are designed to calculate, at each sampling period, T correction signals X _k and Y _k, respectively, for the direct and feedback circuit, taking into account the residual level of the reflected signal (error signal) U _co .

FPS 5.3 and FSOS 5.6 are intended for calculation in each sampling period T of the total signals X _Σ and Y _Σ, respectively, along the direct and feedback circuits.

Other elements that are part of the general AEC scheme and the CF scheme: multipliers, adders, delay lines and a subtraction unit, are known and described, for example, in the book by B. Widrow, S. Stearns, “Adaptive Signal Processing”: Per. from English // M .: "Radio and communications", 1989, 440 p. or Chao J., Shigeo T., A new IIR adaptive echo canceler: GIVE., IEEE journal on selected areas in communications. vol. 12, no. December 9, 1994.

BAU 5 can also be implemented as a processor, the algorithm of which is shown in Fig.4. Ports P 1 and P 2 correspond to MP C In. and MR. OBA BAU 5. Upon receipt of signals at these ports via direct and feedback circuits, respectively, their total values X _Σ and Y _Σ are calculated (blocks 2 and 3 of the algorithm).

Then, taking into account the error signal received at port P 3 from BV 4, correction signals X _k and Y _d are calculated for the direct and feedback circuits _, respectively (algorithm blocks 4, 5). Then, according to the least squares method, the weighting coefficients for the direct V ^p and feedback V ^o circuits for each m-th KF 1 are calculated, which through the processor ports P 6 and P 5 are sent to 1 Vh QMS and Vh SK of each m-th KF 1 In addition, from port P 4, the calculated value of the weight coefficient, which has a time delay with respect to the corresponding weight coefficient of port P6 for one period T, is supplied to the 2 Vx QMS of each of the CF 1 ₁ -1 _M.

The claimed device operates as follows.

The distant subscriber's speech signal x (t) is fed to the input of the N-tap LZ 2 and to the signal input of the first (m = 1) KF 1, as well as to the first bit of the MPx. BAU 5 (figure 1). The signal inputs of other KF 1 are connected to the corresponding taps of the N-tap LZ 2, namely the n-th tap of the N-tap LZ 2 is connected to the signal input of the (n + 1) -th KF 1 _{n + 1} . This achieves a delay of the signal x (t) between the nth and (n + 1) -th taps of the N-branch line for the time T.

The second input of the first UM 1.2 from the corresponding discharge 1 MR Output. SMK BAU 5 receives the calculated weight coefficient. At the signal output of the second SUM 1.6, a signal is generated for evaluating the impulse response of the echo path x '(t), which is fed to the corresponding input MVx. SUM 3 and to the input of the first LZ 1.11 of the corresponding KF 1. The signal from the output of the first LZ 1.11 is fed to the first inputs of the second UM 1.10 and the fourth PA 1.8 and on to the corresponding bit MP Vh. OBS BAU 5. The second input of the second PA 1.10 receives the calculated coefficients from the corresponding bit MP Vykh.SK BAU 5. From the output of the second multiplier 1.10, the converted signal of the impulse response goes to the first input one of the fifth UM 1.9 and the second input of the second SUM 1.6. The second input of the fifth UM 1.9 from the corresponding discharge 1 MR Output. SMK BAU 5 receives the calculated weighting coefficients.

As a result of the secondary conversion of the pulse sequence in the fifth PA 1.9, the generated signal through the inverse output is fed to the second input of the first SMS 1.5. The second inputs of the fourth UM 1.8 and the third UM 1.7 receive a “signal of modeling coefficients” from the corresponding discharge 2MP Output QMS BAU 5. These signals convert the impulse response received from the output of the first LZ 1.11, and then transmit it to the second input of the first KSUM 1.4 . The pulse sequence signal from the inverse output of the third PA 1.7 comes to the second input of the second KSUM. This signal is the result of a multiplication in the third PA 1.7 of the impulse response received from the output of the second LZ 1.1 to the first input of the third PA 1.7 by the gain obtained at the second input of the third PA 1.7. From the signal outputs of all KF 1, the signals are fed to the corresponding inputs of MVkh.SUM 3, the output of which is formed a signal corresponding to the level of the echo signal y (t), and then fed to the first input of the BV 4. At the second input of the BV 4 the echo signal y (f) subject to compensation. The residual signal y (t) at the output of the BV 4 is fed to Vh.OS BAU 5 and to the output of the device.

T.O. In AEC, a signal for evaluating the impulse response of an echo path is generated not only on the basis of current estimates of the cross-correlation function of the signals x (t) and e (t), but also taking into account the values of the estimates of the impulse response of the echo path obtained at the M previous tuning steps. This provides a "prediction" of the echo signal estimation values at time t based on its known values in M previous time instants x (t-T), x (t-2T), ..., x (t-M · T).

The gain coefficients obtained from the outputs of the BAU 5 to the inputs of the PA are prediction factors, the values of which are determined by the least squares method in real time.

Moreover, an accurate determination of the signal energy at each iteration ensures both the stable operation of the echo canceller filter and deeper suppression of the echo signal, i.e. the achievement of the formulated technical result is ensured.

Claims (3)

1. Adaptive echo canceller on a recursive filter, containing M≥2 channel filters, N-tap delay line, where N = M-1, the input of which is the “far-end signal” of the adaptive echo canceller, M-input adder, the output of which is connected to the input a subtraction unit, the second input and output of which are the reflected signal input and the error signal output of the adaptive echo canceller, the nth tap of the N-tap delay line, where n = 1, 2, ..., N, is connected to the signal input ( n + 1) -th channel filter, and the signal input is first channel filter is connected to the input of the N-branch delay line, the signal output of the m-th channel filter is connected to the m-th input of the M-input adder, where m = 1, 2, ..., M, characterized in that an adaptive control unit is additionally introduced equipped with M-bit signal input, first and second outputs “signal of modeling coefficients”, output “correction signal” and input “training signal”, the m-th bit of the M-bit signal input of the adaptive control unit is connected to the signal input of the m-th channel filter, and m-th digits M-times core first and second outputs “signal of modeling coefficients”, output “correction signal” and input “training signal” of the adaptive control unit are connected respectively to the first and second inputs “signal of modeling coefficients”, the input “correction signal” and the output of “training signal” m -th channel filter, and the adaptive control unit is equipped with an additional input "error signal" connected to the output of the subtraction unit. 2. The adaptive echo canceller according to claim 1, characterized in that the channel filter consists of the first, second, third, fourth and fifth multipliers, the first and second channel adders, the first and second adders and the first and second delay lines, the first input of the first multiplier is the signal input of the channel filter, the second and first channel adders, the first and second adders are cascaded along the signal outputs, the first input of the first multiplier is connected to the input of the second delay line, the output of which is connected to the first input the third multiplier, the inverse output of which is connected to the second input of the second channel adder, the output of the fourth multiplier is connected to the second input of the first channel adder, the inverse output of the fifth multiplier is connected to the second input of the first adder, the output of the second adder is connected to the input of the first delay line and is the signal output of the channel filter, the output of the second multiplier is connected to the first input of the fifth multiplier and the second input of the second adder, the output of the first delay line is connected to the first input the second multiplier and to the first input of the fourth multiplier and is the channel filter training signal, the second inputs of the third and fourth multipliers are combined and are the second input of the channel filter modeling coefficients signal, the second input of the fifth multiplier and the second input of the first multiplier are combined the first input is the “signal of modeling coefficients” of the channel filter, and the second input of the second multiplier is the input of the correction signal of the channel filter. 3. The adaptive echo canceller according to claim 1, characterized in that the adaptive control unit consists of first and second weight shapers, first and second weight correctors, direct signal shaper and feedback shaper, M-bit inputs of the direct signal and signal shapers feedback are M-bit, respectively, the signal input and the input of the "training signal" of the adaptive control unit, the M-bit input of the direct signal driver is connected to the M-bit input ode to the first weight former, the output of the direct signal former is connected to the first input of the first weight corrector, the output of which is connected to the input “correction” of the first weight former, the M-bit first and second outputs of which are “M modeling signals” are respectively M-bit the first and second outputs "signal modeling coefficients" of the adaptive control unit, the M-bit input of the feedback former is connected to the M-bit input of the second of the first shaper of the weighting coefficients, the M-bit output of which is the second M-bit output of the “correction signal” of the adaptive control unit, the output of the shaper of the feedback signal is connected to the first input of the second corrector of the weighting factors, the output of which is connected to the input of the “correction” of the second shaper of the weighting factors and the second inputs of the first and second weight corrector are combined and are the input "error signal" of the adaptive control unit.

Images