JPS5930345B2 - PCM encoder/decoder monitoring method - Google Patents

Description

[Detailed Description of the Invention] This invention provides a PC that is commonly used by a plurality of channels.
' This relates to a monitoring method for monitoring the operating status of an M encoder/decoder.

In the conventional well-known PCM-24B system, when monitoring the operating status of an encoder/decoder (hereinafter referred to as C0DEC), when one channel is idle, the frequency is set at a specific level at the time slot position of that channel. is 4K
The reference DC voltage corresponding to the positive and negative peak values of the Hz sine wave signal is supplied to the encoder and encoded, and the encoded P
When a CM signal is decoded by a decoder on the other side and the decoded signal deviates from a reference level by more than a certain value, it is determined that there is some kind of failure between the encoder input and the decoder output, and an alarm is issued. That's what I was doing.

However, since the portion of the CODEC that is used differs depending on the level of the input signal, a monitoring signal of a specific level does not mean that all portions of the CODEC have been monitored.

For example, regarding the 15-fold line companding C0DEC recommended by CCITT, there are 15 fold line sections including positive and negative lines, and it is desirable to monitor each of them.

To monitor the C0DEC, one station gives a PCM encoded monitoring signal to an empty time slot of the C0DEC decoder, decodes it, and sends the decoded PAM input signal to the C0DEC encoder in the empty time slot. It is conceivable to provide the signal, encode it, and compare the encoded output with the monitoring signal.

In this monitoring system, the path from the decoder to the PAM input signal encoder is of course frequency-limited, so that the PAM input signal form may be rounded and crosstalk to other time slots may occur.

If the amplitude value of the monitoring signal is changed to a value corresponding to each broken line section of the broken line companding of the encoder, the crosstalk signal changes due to the change, so monitoring cannot be performed while the C0DEC is in operation.

In the present invention, the basic period of the monitoring signal is set to 1/2 of the sampling period, and furthermore, the constant positive and negative amplitude values are taken alternately, and the amplitude is changed, but the change is made over a long period so that it is outside the signal band. become

In this way, the operating status of each part of the CODEC can be monitored using multiple monitoring signals with different levels,
Furthermore, the influence of aliasing noise on the main signal is eliminated, and furthermore, the influence of crosstalk of the monitoring signal on the characteristics of the CODEC is eliminated.

FIG. 1 shows a first embodiment of the invention, in which CCITT
Recommendation 15 is for C0DEC for fold line companded audio.

This C0DEC has 15 broken line sections including positive and negative lines, and one monitoring signal is used for each section to calculate the C0D
Monitor EC.

That is, in the quantization characteristic of the 15-fold line companding C0DEC shown in FIG. 2, a monitoring signal of a specific level within the 8th fold line section 2 is sent out alternately between positive and negative at a period of 1/2 of the sampling period.

For example, assuming that the sampling frequency of the CODEC is 8 KHz, the repetition period (hereinafter referred to as the fundamental period) T1 of the monitoring signal is □ KHz.

This process of sending out the monitoring signal with the positive and negative alternately shifted is continued, for example, 64 times.

The duration T2 (hereinafter referred to as level repetition period) is approximately □.

Similarly, within the remaining 7th to 1st broken line sections (3 Hz) to I, monitoring signals of a specific level in each section are continued to be sent alternately between positive and negative signals at a period T1 over a period T.

In this way, the period (hereinafter referred to as basic repetition period) T3 of the monitoring signal for monitoring the operating state of the CODEC over all 15 broken line sections (positive and negative) is approximately 8 Hz.

Each such supervisory signal is supplied as a reference PCM signal to an empty time slot of the decoder of the CODEC.

For example, if the number of operating time slots of CODEC is 128 but the number of channels being used is 120, one of the remaining 8 time slots is used.

Alternatively, if all the time slots of the CODEC are assigned to channels, the time slots of the channels in the idle state are used for supplying the reference PCM signal.

P of the reference PCM signal decoded by the decoder in this way
The AM signal is supplied to an empty time slot of the CODEC encoder and PCM encoded.

A table comparing the coded peak and the reference pCM signal in the digital signal state.The values of the reference PCM signal mentioned above change as shown in FIG. The signals are stored in a memory in advance, one of them is read out repeatedly at a period of T, /2, and l and O are alternately given as sign bits to each read reference PCM signal and sent to the decoder, and the above-mentioned reading is performed. When the level repetition period T2 is repeated, that is, 128 times, the next reference PCM signal is repeatedly read out.

The same applies hereafter.

As explained above, the fundamental period T of the monitoring signal is C0D
1 of the sampling period in one time slot of the EC
/ 2, the return signal due to sampling is the audio signal sent in that time slot (bandwidth is 300 to 3
400Hz).

Furthermore, since positive and negative monitoring signals of the same level are sent out alternately, the crosstalk caused by the waveform distortion of the decoded PAM signal is reversed and canceled by the positive monitoring signal and the negative monitoring signal. Ru.

Furthermore, since the level repetition period T2 and the basic repetition period T3 of the monitoring signal are selected to be sufficiently lower than the audio band, there is no fear that the leakage of the monitoring signal will affect the audio signal.

FIG. 3 shows a second embodiment of the invention, in which CCITT
Recommendation 15 In order to improve the monitoring accuracy of the C0DEC for companding audio, two monitoring signals are used in each of the 15 fold line sections (positive and negative) to monitor the operating state of the C0DEC.

That is, in the quantization characteristic of the 15-fold line companding C0DEC shown in FIG. 2, the first monitoring signal of the specific level 11 within the 8th fold line section ■ is sent out alternately between positive and negative at a period of 1/2 of the sampling period. .

For example, assuming that the sampling frequency of C0DEC is 8KH2, the fundamental period T of the monitoring signal becomes □ as in the case ① of the first embodiment.

By continuing to send the first monitoring signal KHz alternately in positive and negative directions, for example, 64 times, the level repetition period T2 becomes approximately □ as in the case of the first embodiment.

The second monitoring signal at a different level 12 in the eighth 3KHz broken line section ■ and the remaining monitoring signals in the seventh to first broken line sections ■ to I are generated in the same way. The basic repetition period T3 is approximately □.

Hz As explained above, since the fundamental period T of the monitoring signal is selected to be 1/2 of the sampling frequency, the return signal due to sampling does not affect the audio signal.

In addition, since the level repetition period T2 and basic repetition period T3 of the monitoring signal are selected to be sufficiently lower than the voice band, the crosstalk of the monitoring signal is reduced to the voice signal.

It becomes possible to eliminate the influence on

Furthermore, the PAM signals demodulated from each reference PCM signal also appear alternately positive and negative with almost the same amplitude, and due to the waveform distortion caused by the band limit, the influence on adjacent time slots is that of positive and negative PA.
Due to the M signal, the magnitudes are almost the same, but the polarities are opposite, and on average they cancel each other out, so there is no effect of these.

Also, to monitor each broken line section. All parts of CODEC can be monitored.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of a monitoring signal in a C0DEC monitoring system according to the present invention, FIG. 2 is a quantization characteristic curve diagram of a 15-fold line drawn C0DEC, and FIG. 3 is a diagram showing a C0DEC monitoring method according to the present invention. FIG. 4 is a diagram showing a second example of a monitoring signal in the method. T1: fundamental period, T2 two-level repetition period, T3: basic repetition period.

Claims (1)

[Claims] 1 Reference PC at the receiving side monitoring time slot position
The M signal is supplied to a decoder, and the reference PCM signal decoded by the decoder is supplied to an encoder at a monitoring time slot position on the PAM input signal side for encoding, and the encoded PCM signal and the reference PCM signal are encoded. A plurality of reference PCM signals having different amplitude values are prepared by comparing with a reference PCM signal, and the reference PCM signal is sampled in one time slot of the encoder/decoder so that positive and negative signals of the same amplitude value are sampled in one time slot of the encoder/decoder. A monitoring system for a PCM encoder/decoder, characterized in that the amplitude value is sent to the decoder at half a cycle and is changed at a long cycle outside a band of a transmission signal of the encoder/decoder.