JPS5832531B2 - Encoder/decoder monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for monitoring an encoder/decoder in a PCM terminal equipment.

In public telephone lines, terminal equipment using the PCM transmission system is always provided with a monitoring circuit to detect whether the equipment is operating normally.

This monitoring circuit is essential for user services and maintenance operations.

For example, the PCM currently in practical use in Japan
-24B method includes "Facility" Vol. 24, No. 9, No. 8, published by Electric Corporation.
As described on page 9, an AC pilot system is used as a monitoring system for encoders and decoders.

In this AC pilot method, when the first channel CHI of one system (24 channels) is idle, a 4KHz constant level sine wave signal is applied to the encoder on the transmitting side, and this is encoded and sent to the decoder on the receiving side. This encoded digital signal is decoded.

If the level of this decoded sine wave changes by ±3 dB or more, it is considered a failure.

This AC pilot system essentially monitors signal levels and does not correspond to the signal-to-quantization-noise ratio S/NQ of the encoder/decoder.

On the other hand, as seen in Japanese Patent Publication No. 52-13905, a digital reference signal is decoded by a decoder, and the decoded analog signal is supplied to an encoder via a folding circuit to encode it. There is a method of monitoring an encoder/decoder based on the difference between a converted digital output signal and a digital reference signal.

This method monitors level fluctuations in the digital output signal.

Therefore, if the gain of the folding circuit changes due to a change in ambient temperature, the digital output signal will have a digital pattern different from the digital reference signal even if the encoder/decoder is normal.

This results in a false fault signal.

Drift in the folding circuit also had the same drawback, leading to a decrease in monitoring accuracy.

The purpose of this invention is to provide a highly accurate and reliable encoder/decoder monitoring device that can eliminate the effects of gain changes and drifts in the folding circuit and obtain monitoring information corresponding to S/NQ. It is about providing.

According to this invention, a reference pattern is decoded by a decoder, and this decoded signal is supplied to an encoder through a folding circuit and encoded.

The monitoring circuit performs this for two reference patterns, detects the proportional relationship between the difference between the reference patterns and the difference between the output encoding patterns of the encoder corresponding to these reference patterns, and determines whether this is greater than a predetermined threshold. If so, send out an alarm signal.

In this way, since the proportional relationship between the difference in the reference pattern and the difference in the encoding pattern is used as monitoring information, it is possible to monitor the encoder and decoder regardless of the drift and gain changes in the folding circuit, resulting in highly reliable monitoring. will be held.

Next, let's explain with reference to the drawings.

FIG. 1 is a diagram showing the intensification characteristic on either the positive or negative side.

In FIG. 1, all input signals in the interval [aK-7, aK] are approximated (ie, quantized) to aKo.

Therefore, the quantization noise N in the interval [aK-1, aK]
QK is given by P(x): probability density function of input signal amplitude.

Therefore, the quantization noise NQ in the entire interval takes into account the positive and negative, However, m is represented by the maximum number of encoding steps.

Here, if the number of encoding steps m is large, the interval (aKt, a
Since the probability density function P(x) of the input signal amplitude at [K] can be considered to be almost constant, equation (1) can be approximately expressed as a tree.

The condition in which the above equation (3) is the minimum is clearly when the output level aKo is between the discrimination levels aK-1 and aK, that is, when the output level aKo is between the discrimination levels aK-1 and aK.

Therefore, in order to minimize the quantization noise NQ, the output level a
Each point of Ko is located on a straight line passing through the origin, as shown in FIG.

In actual encoders and decoders, aK
Each point of o is not a straight line, so the S/NQ is worse than the theoretical value.

In the following explanation, this invention will be explained based on the 15-fold line μ of the CCITT recommendation.
A case where this is applied to the m255 encoding rule will be explained.

First, the 15-fold line μm255 encoding rule will be explained.

Figure 2 shows the encoding characteristics of the μm255 encoding rule, where the sample value of the analog input signal is represented by ■ bits in the polarity display, and 3 bits (positive or 8-fold line section for each negative analog human input signal)
and 4 bits (16
The signal is then converted into an 8-bit PCM signal.

Δi indicates the encoding step size of the broken line section i.

FIG. 3 is a diagram showing the relationship between tE or negative polarity discrimination level y of the μm255 encoding rule and output level depth.

In the encoder, the sample values of the analog human signal are compared in magnitude using the identification level X shown in FIG. 3, and in the decoder, the output level is uniquely determined by the PCM signal output from the encoder.

For example, if the analog human input signal is in the range of 1 to 3 in the encoder, the decoder outputs an output level of 2, which is exactly the middle value.

These relationships are generally given by the following equation, where X is the discrimination level of the encoder and the corresponding output level of the decoder.

However, i: broken line section 1 (i=1.2,...8)
X: Quantization level within the broken line section (X-0, ■,...
...15) That is, in the μm255 encoding rule, the encoding step size Δi of the broken line section i- can be expressed as.

Furthermore, as shown in FIG. 2 or 3, when the analog input signal is at zero voltage, the output level of the encoder is at zero voltage, which is what is called mid-tread.

Therefore, at the output level of the decoder, when a broken line section changes to the next broken line section, the encoding step size becomes the arithmetic mean value of the encoding step sizes of adjacent broken line sections.

Next, a specific embodiment of the present invention will be described with reference to FIG.

Here, FIG. 4 shows an apparatus for encoding or decoding input signals of 120 channels in the voice band using one encoder/decoder.

The number of time slots is 128, with 120 time slots being allocated to 120 channels of PCM signals and the remaining 8 time slots being time slots for synchronization and encoder/decoder monitoring.

Also, a case where the transmitting side and the receiving side are asynchronous will be explained.

Note that the above conditions are unrelated to the principle of this invention and are provided for the purpose of making the explanation easier to understand.

In normal encoding/decoding operations, 120 channels of time-division multiplexed PAM signals are input from PAM signal input terminal 1, and are sequentially encoded into 8-bit PCM signals for each channel by encoder 2, and sent to the separation circuit. 3, and is sent to the PCM signal output terminal 4.

On the other hand, a 120-channel time-division multiplexed PCM signal from the other party is inputted from a PCM signal input terminal 5, passed through a combiner 6, decoded by a decoder 7, and sent to a PAM signal output terminal 8.

Here, when the control circuit 9 detects the monitoring time slot on the receiving side, the reference pattern generating circuit 10 supplies an 8-bit reference pattern Ai1 to the coupling circuit 6 and the subtraction circuit 16, respectively.

The combiner 6 supplies this reference pattern to the decoder 7 for decoding using the control signal C2 from the control circuit 9.

This decoded PAM signal is sampled and held in the sampling and holding circuit 12 in the folding circuit 11 in accordance with the control signal C2.

The sampled output is amplified by an amplifier 13 and supplied to a sampling gate 14.

When the control circuit 9 detects the monitoring time slot on the transmitting side, the sampling gate 1 is activated by the control signal C1 of the control circuit 9.
4 is opened and the amplifier 130 PAM signal output is output to encoder 2.
supplied to

At this time, there is no PAM signal from PAM signal input terminal 1.

Therefore, the PAM signal output of the folding circuit 110 is encoded by the encoder 2 to become an 8-bit encoded pattern Bi1.

This encoded pattern Bi1 is supplied to the subtraction circuit 15 and disconnection detection circuit 18 via the separator 3 in accordance with the control signal C1.

Next, the above operation is similarly performed for the reference pattern Ai2 generated by the reference pattern generator 10, and the encoded pattern Bi2 is input to the subtraction circuit 15.

The reference patterns Ai1 and Al1 are different patterns.

The subtraction circuit 16 subtracts the reference patterns Ai1 and Al1 of the reference pattern generator 10, and obtains the subtraction result (Ai
l-Al1) is supplied to the detection circuit 17.

Further, the subtraction circuit 15 similarly subtracts the encoding patterns Bi1 and Bi2 of the separation circuit 3, and the subtraction result (Bi
l-Bi, , ) is supplied to the detection circuit 17.

The above operation is performed N times.

That is, the reference patterns Ai1 and Al1 (i-2, 2,...
...N), the encoding patterns Bi1 and B1 are
2(i-1, 2, . . . N), respectively.

Here, the reference patterns Ai1 and Al1 are generally different patterns.

That is, as a result, N subtraction results (Ail-Al1) and N (Bi, -Bi2) are supplied to the detection circuit 17 every N operations, and the proportional relationship between them is determined by a predetermined threshold value. If this occurs, a fault signal is sent to the OR gate 19.

On the other hand, in case the monitoring circuit becomes a failure, disconnection detection circuit 1
Monitored by 8.

For example, if the return circuit 11 becomes a disconnection failure, the separation circuit 3
Since the encoded patterns from 1 to 2 are the same for different reference patterns, the disconnection detection circuit 18 sends a fault signal to the OR gate 19.

The OR gate 19 sends out an alarm signal to the alarm signal output terminal 20 in response to a failure signal from either the failure detection circuit 18 or the detection circuit 17.

Next, other embodiments of the invention will be described.

In the above embodiment, in order to subtract an 8-bit pattern, the 8-bit companding code is first converted into a linear code (15-bit line μm).
According to the H.255 encoding rule, the data is reduced after being converted to a 14-bit linear code.

This increases the circuit scale.

In the following embodiment, the circuit scale is reduced by utilizing the characteristics of the 15-fold line μm255 encoding rule.

Since the specific circuit block diagram is exactly the same as that in FIG. 4, the explanation will be made using FIG. 4.

The reference patterns Ai1 and Al1 are selected as codes of the same broken line section, and encoded patterns Bi1 and Bi2 are generated in the same manner as in the previous embodiment.

Here, for the 8-bit pattern, the lower 4 bits are linear codes as already explained.

Therefore, if the encoding patterns Bi and Bi2 are codes in the same broken line section, the subtraction circuit 15 can directly subtract the lower 4 bits, and the 8-bit companding code can be converted into 14 bits.
Subtraction is possible without converting bits into linear codes.

The subtraction circuit 16 is also used for the reference patterns Ai1 and Al1.
The lower 4 bits are subtracted at .

The same process is performed for other broken line sections.

Even if the line sections occasionally differ, if the lower four bits of the reference pattern are fixed, in an ideal encoder/decoder, the result of subtraction between the reference pattern and the encoded pattern will be exactly the same.

Therefore, in the detection circuit 17, the subtraction circuit 150 subtraction result (Bi
, -Bi2) is the subtraction result of the subtraction circuit 16 (Ail A1
2) is the median value, and if it is greater than a predetermined threshold value, a fault signal is sent to the OR gate 19.

The one-way break detection circuit 18 detects the broken line section of the encoded pattern from the separation circuit 3, and if it does not match the broken line section of the reference pattern of the reference pattern generator 100, ORs the fault signal.
Send to gate 19.

In the OR gate 19, the disconnection detection circuit 1 is connected as in the previous embodiment.
8 or the detection circuit 17, an alarm signal is sent to the alarm signal output terminal 20.

In this embodiment, the subtraction circuits 15 and 16 only need to process 4 bits, so the circuit scale is reduced.

On the other hand, if the drift and gain change of the folding circuit 11 change significantly, the broken line section to which the encoded pattern belongs will be different from the broken line section of the reference pattern, and the disconnection detection circuit 18 will generate a fault signal.

However, since the present invention detects the coincidence or mismatch of the broken line sections, it is less sensitive to the drift and gain change of the folding circuit 110 than the conventional monitoring system, and a highly reliable monitoring device can be obtained.

As explained above, the present invention uses the amount of difference between two encoding patterns as monitoring information, which corresponds to monitoring the differential coefficient of the quantization characteristic shown in FIG. 1.

Therefore, as already mentioned, the linearity of the quantization characteristic is S/N
Since it corresponds to Q, the monitoring device of the present invention has highly accurate monitoring ability.

Furthermore, even if drift and gain changes occur in the folding circuit 11, generation of false alarm signals is reduced.

Note that in the present invention, the method of selecting the reference pattern is completely arbitrary; for example, a specific pattern may be selected from among the reference patterns, and the amount of difference between this specific pattern and the like may be monitored.

As this specific pattern, for example, a reference pattern in which all voltages are O'', that is, the output of the decoder 7 is in principle zero voltage, can be considered.

Further, in the present invention, the case where the transmitting side and the receiving side are asynchronous has been described, but the same can be applied to a synchronous state.

As explained above, this invention does not detect the instantaneous value between the reference pattern and the encoded pattern, but uses the amount of difference between the reference pattern and the amount of difference between the encoded pattern as the monitoring information.
/NQ, high-precision monitoring can be performed, and the influence of the loopback circuit can be removed to provide a highly reliable monitoring device.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a part of the quantization characteristics, FIGS. 2 and 3 are diagrams each showing the 15-point line μm255 encoding rule recommended by the CCITT, and FIG. 4 is a circuit diagram of an embodiment of the monitoring device according to the present invention. It is a block diagram. 1: PAM signal input terminal, 2: encoder, 3: separation circuit,
4: PCM signal output terminal, 5: PCM signal input terminal, 6
: combination circuit, 7: decoder, 8: PAM signal output terminal, 9
: control circuit, 10: reference pattern generator, 11: folding circuit, 12: sampling holding circuit, 13: amplifier, 14: sampling gate, 15.16: subtraction circuit, 17: detection circuit,
18: disconnection detection circuit, 19: OR gate, 20: alarm signal output terminal.

Claims (1)

[Claims] 1. A reference input cover turn generator that sends out a reference input cover turn to a decoder, a folding circuit that sends a PAM output signal decoded by the decoder to an encoder, a difference between two different reference input cover turns, and the difference between two different reference input cover turns. Monitoring of an encoder/decoder, comprising: a monitoring circuit that monitors the encoder/decoder based on a proportional relationship with a difference between code output cover patterns respectively encoded by the encoder in correspondence with a reference input cover turn. Device.