JPH02295317A - Echo canceler for data over-voice system - Google Patents

Abstract

PURPOSE:To prevent a waveform tail from being generated for a long period in the echo of a sent signal or the inter-code interference of a received signal by connecting a high-pass filter of low order to the line echo path between an input and an output and performing the preceding of sent data matching the high-pass filter. CONSTITUTION:Both a shaping filter 7 and a DC cutoff filter 8 use primary high-pass filters and the shaping filter 7 is used in common for partial response waveform shaping to prevent a large unnecessary signal from being generated nearby a main signal. Consequently, a long tail shown by a solid-line waveform A is generated at the reception output terminal of hybrid circuit 5, but the tail is passed through the DC cutoff filter 8 to shorten the duration of the tail as shown by a broken-line waveform B, thereby performing equalization by an equalizer 11 without requiring a large number of taps.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an echo canceler for data over voice system;
In particular, in the data-over-voice system in which both the transmitting and receiving circuits of the data channel are connected via a hybrid circuit to a two-wire line that connects the voice channel, the data channel transmitting circuit passes through the hybrid circuit to the receiving circuit. The present invention relates to an echo canceller for a data over voice system for canceling line echoes caused by echo loops.

[Conventional technology]

Conventional echo cancellers for this type of data-over-voice system are designed to suppress the long tails of the waveforms of received signals and echo signals that occur due to the DC cutoff characteristics of hybrid circuits and lines. A transmission line code without spectrum is used. [Problems to be Solved by the Invention] The conventional echo canceller for the data over voice system described above attempts to suppress the influence of the direct current cutoff characteristics on the line side only by selecting the transmission line code to be used, so the suppression effect is small. , there is a drawback that there is a limit to the improvement of transmission quality such as bit error rate.

[Means to solve the problem]

The echo canceller of the present invention is for voice channel transmission.
A hybrid circuit in which both data transmission and reception circuits are connected to a two-wire line through a low-order high-pass filter, and a partial circuit that matches the response characteristics of the high-pass filter placed in front of the high-pass filter of the data transmission circuit. The apparatus includes a response precoder and an echo canceller that generates a pseudo-line echo in response to a signal sent from the precoder and subtracts the pseudo-line echo from the signal sent from the high-pass filter of the data receiving circuit. [Example] Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, in which reference number 1 is a terminal for data input, 2 is a terminal for data reproduction output, 3 is a precoder for partial response, and 4 is a terminal for data reproduction output.
is an echo canceller for line echo cancellation, 5 is a hybrid circuit, 6 is a terminal for two-wire line connection, 7 is a shaping filter for partial response waveform shaping, 8 is a DC blocking filter, 9 is a subtracter, 11 is etc. 12 is a terminal for audio signals, 13 is a reduction filter for audio signals, and 14 is an adaptive filter for generating pseudo echoes.

The data signal input from the terminal 1 is a binary pulse, subjected to partial response precoding by the programmer 3, and sent to the shaping filter 7 of the echo canceller 4. FIG. 2 is a block diagram showing an example of the configuration of the precoder 3 and the shaping filter. The input data signal is sent to the adder 31
and output through the delay circuit 32 and the adder 3.
It has been returned to 1. Adder 31 is modulo 2 (mod 2)
The adder uses an exclusive OR gate, for example. The delay circuit 32 provides a delay of one time slot (T). The output signal of the precoder 3 is multiplied by +1 in the multiplier 72, and after passing through the delay circuit 71 of one time slot, it is multiplied by -1 in the multiplier 72, and the double multiplier output signal is
The signals are added by an adder 74 and sent out. Based on the principle of partial response, if the output signal level of the shaping filter/tough is determined and a value of mod 2 is taken, the original signal is reproduced. Figure 3 shows another example of the configuration of the precoder 3 and shaping filter. The difference from FIG. 2 is that the delay circuits 32 and 71
The only difference is that the number of stages is changed to 2, but everything else is exactly the same. The frequency transfer characteristic H(ω) of the shaping filter 7 in FIGS. 2 and 3 is given by the following equation (1). However, n=1(
In the case of Fig. 2), n = 2 (in the case of Fig. 3).H(ω) in equation (1) indicates a high pulse filter characteristic with a first-order cutoff characteristic. If the line echo signal circulating through the circuit 5 or the received signal input from the terminal 6 contains a DC component, an extremely long tail will be generated in the signal waveform due to the influence of the DC cutoff of the hybrid circuit 5. ．If this tail is left as it is, residual echo or intersymbol interference will occur, resulting in a change in transmission quality.Furthermore, in order to cancel and equalize this tail, echo canceller 4, etc., which has a huge number of taps, etc. will be required to cancel and equalize this tail. The DC blocking filter 8 is effective in suppressing this tail, and the higher the order, the more effective it is in suppressing the tail. However, if the DC blocking filter 8 is used, a large Therefore, in this embodiment, both the shaping filter 7 and the DC blocking filter 8 are used as first-order high-pass filters, and the shaping filter 7 is also used for partial response waveform shaping, so that the main signal is This prevents large unnecessary signals from being generated in the vicinity. Fig. 4 is a signal waveform diagram for explaining the effect of the above-mentioned filter. At the reception output terminal of the hybrid circuit 5, as shown by solid line waveform A, Although a long tail is generated, by passing it through the DC blocking filter 8, the duration of the tail can be shortened as shown by the broken line waveform B, and equalization can be performed without requiring a huge number of taps in the equalizer 11.Also, line echo A similar waveform change occurs in the signal, but this can also be canceled by the echo canceller 4 without requiring a huge number of taps.

Since a high pulse filter is used in the data transmitting/receiving section of this embodiment, a reduction filter 13 is provided on the audio channel side.
can be connected to configure a data over voice system.

〔Effect of the invention〕

As explained above, the present invention connects a low-order high-pass filter to the line echo path between the input and output of an echo canceller, and applies bricoding to the transmitted data that matches the filter, thereby reducing the echo of the transmitted signal and the received signal. This has the effect of preventing long-term waveform tails from occurring in intersymbol interference and reducing the number of taps in echo cancellers and equalizers.

Furthermore, since the high-pass filter is provided on the data channel side, the voice channel can be connected via the reduction filter, and a data-over-voice system with less residual echo and residual intersymbol interference can be realized.

[Brief explanation of the drawing]

1 to 3 are block diagrams showing an embodiment of the present invention, and FIG. 4 is a signal waveform diagram for explaining the operation of the embodiment of the present invention. 1, 2, 6. 12...Terminal, 3...Precoder, 4
...Echo canceller, 5...Hybrid circuit,
7... Shaping filter, 8... DC blocking filter, 9
... Adder, 11... Equalizer, 13... Reduction filter, 14... Adaptive filter.

Claims (1)

[Claims] A hybrid circuit in which both data transmission and reception circuits are connected to a two-wire line for voice channel transmission through a low-order high-pass filter, and a response of the high-pass filter placed before the high-pass filter of the data transmission circuit. A precoder for partial response that matches the characteristics, and an echo canceller that generates a pseudo-line echo in response to a signal sent out from the precoder and subtracts the pseudo-line echo from the signal sent out from the high-pass filter of the data receiving circuit. Echo canceller for data over voice system.