JPS6010819A - Adaptive type echo cancellor - Google Patents

Abstract

PURPOSE:To relax as required a requested internal processing speed by providing a prescribed delay to an estimate operation of an echo line response at next time from the response of estimate echo line at a time by means of the study identification method so as to apply adaptive correcting processing. CONSTITUTION:An input signal is coded by an A/D converter 41 and stored in a register 42 as an input signal time series (xj). A prescribed operation is applied to an output x'j of the register 42 at a time jT ((j) is an integral number and T is a sample period) and an estimate echo response h'j from an echo response (h) register 43 at a convolution circuit 45, an estimated echo signal by D/A-converting 49 the output and the difference between said signal and an actual echo signal Y is operated by a subtractor 50. A specific formula is operated by operating circuits 44, 47 and a correction circuit 46 from a signal as result of A/D conversion 48 of a residual difference output of the subtractor 50 and a signal giving delays 51, 52 to the signal x'j so as to obtain an estimate echo line response h'j+1 at the next time (j+1)T.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an adaptive echo cancellation device using a learning identification method, and more particularly to an adaptive correction calculation method for an estimated echo path response.

[Technology background]

Generally, long-distance telephone lines have two wires.

In order to prevent part of the signal transmitted from the partner station from leaking at the 4-wire switching unit and being sent back to the partner station, an echo canceling device is installed in the 4-wire side circuit as shown in Figure 1. It has been inserted. Such an echo canceling device is designed using a learning identification method to determine the in-wave response, which is determined by the absolute amount of delay for the echo to return via the echo path seen from the installed station to the subscriber side, and the transfer characteristics of the echo path. An adaptive echo cancellation device is used to estimate the amount of noise. A schematic configuration of such an adaptive echo canceling device is shown in FIG.

[Conventional technology and problems]

In the adaptive echo canceling device of the prior art, the following is used as a calculation algorithm for adaptively correcting the estimated value of the impulse response of the echo path by the learning identification method. A circuit configuration for implementing this is shown in FIG. In FIG. 3, reference numeral 1 denotes a transmitting section of the opposite station, 2 a receiving section of the opposite station, 3 an echo path, and 4 an adaptive echo canceling device.

In the echo canceling device 4 shown in FIG. 3, it is necessary to complete a series of processes for filling holes within one sample period, and high-speed processing is required.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to improve the adaptive correction calculation method in an adaptive echo canceling device so that the required internal processing speed can be reduced as necessary. There's K things to do.

[Structure of the invention]

In order to achieve the above object, in the present invention'VC,
In an adaptive echo canceling device that estimates the echo path response using a learning identification method and subtracts the expected echo signal from the input signal time series X from the actual echo signal, T is the sampling period and j is As an integer, from the estimated echo path response 9j at time JT, α: correction coefficient (0<α<2), ej: cancellation residual signal at time JT, xj: time JT
An adaptive echo canceling device is provided, characterized in that an estimated echo path response Gj+1 at the next time (j+1)T is obtained by the calculation of an input signal time series, m: a natural number.

[Embodiments of the invention]

Before describing the present invention in detail, the prior art adaptive echo canceling device shown in FIG. 1 mentioned above will be described for comparison. The operation time chart of the device in Figure 3 is shown in Figure 5.
Shown in Figure (,). In the echo canceling device 4 of FIG. 3, an input signal is encoded in an N-code converter 41 and stored in a register 42 as an input signal time series xj.

At time JT, the output of register 42;
- I J is calculated (■), and the D/A converter 49 obtains the analog output y from the estimated echo output yj (■
).

The estimated value y is subtracted from the actual reverberation output y in the analog subtraction circuit 50, and a residual signal 9=y−y is obtained (■)
. This residual signal e is converted into a digital output ej by a width converter 48 (■).

On the other hand, +xj+2 is calculated in the arithmetic circuit 44,
The arithmetic circuit 47 obtains Δj=αej/1xj12 (■). In the prior art echo canceling device shown in FIG. 3, the h register correction circuit 46 requires an expensive high-speed arithmetic circuit because the series of serial processing described above must be performed during one sample period T (for example, 125 μB). , a high-speed converter and a high-speed D/A converter are required.

An adaptive echo cancellation system according to one embodiment of the present invention is shown in FIG. Corresponding parts in FIG. 4 have the same reference numerals as in FIG. 3. In the echo canceling device shown in Fig. 4, the series of processes that needed to be completed within one sample period in the device shown in Fig. It is sufficient to finish within the period. Note that the delay circuits 51 and 52 are
This prevents the data sampling position from shifting.

The operation time chart of each part of the device in Figure 4 is shown in Figure 5.
It is shown in (b) to 0) of the figure. In this embodiment, the series of processes ■ to ■ that needed to be completed within one sample period in (,) in FIG. Since the process only needs to be completed within T, the processing speed is significantly reduced. Input at time j; j is ■, [phase], @, @, @
, 8j+6 is generated at time j+4 through the processing of (1). Therefore, at time j, the estimated echo path response is modified by the following calculation. Compared to the original correction formula, the above formula only requires m = 5 fewer modifications to h at time j. Therefore, since the number of corrections is made, an increase of five times in the number of corrections does not pose any practical problem. As described above, according to the present invention, the convergence condition,
It is possible to significantly reduce the internal processing speed without causing a practical disadvantage in the number of convergence operations.

〔Effect of the invention〕

According to the present invention, it is possible to significantly reduce the required internal processing speed in an adaptive echo cancellation system, thereby allowing the use of low cost, slow circuit components.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of application of the adaptive echo canceling device, Fig. 2 is a diagram showing a general configuration of the adaptive echo canceling device, and Fig. t43 is a circuit of a conventional adaptive echo canceling device. 4 is a circuit diagram of an adaptive echo canceling device as an embodiment of the present invention, and FIG. 5 is a diagram showing an operation time chart of the device of FIGS. 3 and 4. (Explanation of symbols) 1: Transmitting section, 2: Receiving section, 3: Echo path, 4: Echo canceling device, 41: A, /11m converter, 42:; Register,
43: 1 registor, 44: arithmetic circuit, 45: ) convolution circuit, 46: correction circuit, 47: arithmetic circuit, 48:
A/D converter, 49: D/A converter, 50: Analog subtracter, 51.52: Delay circuit.

Claims (1)

[Claims] Adaptive echo α in which the echo path response is estimated by a learning identification method, and the echo signal expected from the input signal time series X is subtracted from the actual echo signal: Modification Coefficient (0kuα〈
2), ej: cancellation residual signal at time JT, xj: time JT
An adaptive echo canceling device characterized in that an estimated echo path response 9j+1 at the next time (j+1)T is obtained by an operation such as an input signal time series, m: a natural number.