JPS6314544B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for transmitting analog telephone signals.

Adaptive delta modulation is a method for transmitting analog telephone signals with a simple configuration and at a lower transmission bit rate than the existing PCM method while maintaining sufficiently good speech quality.

Regarding adaptive delta modulation, the publication "Modulation characteristics of adaptive delta modulation method" published in October 1971, IEICE Communication Method Study Group Materials, CS-71
79, so a detailed explanation will be omitted here, but to briefly explain, by adaptively changing the quantization step size of the conventional delta modulation method according to the input signal level, it is possible to widen the input signal level. This is an encoding method that can obtain uniform quality over a range of levels and requires small hardware.

Now, when transmitting a telephone signal using such an adaptive delta modulation method, there is a possibility that not only a voice signal but also an in-band data signal is input as an input signal. It must be possible to transmit high quality data. However, the characteristics of voice signals and data signals are quite different, and the adaptive delta modulation method optimized for voice signals does not necessarily provide good characteristics for data signals.

In view of these drawbacks, the present invention automatically uses two types of modulation methods: an adaptive delta modulation method suitable for audio signals, and a modulation method suitable for data signals for data signals. It is an object of the present invention to provide a new and easy-to-implement analog telephone signal transmission system that modulates and demodulates while switching the frequency.

In the present invention, in order to obtain sufficiently good quality and dynamic range not only for the audio signal but also for the data signal, the audio signal and the data signal are encoded using different modulation methods. Whether or not an analog telephone signal is a data signal is known by detecting a specific sinusoidal signal transmitted prior to transmission of the data signal. Various types of this specific sine wave signal can be considered, and if these are transmitted prior to transmitting the data signal, it is possible to detect that the analog telephone signal is a data signal. It is also possible to detect that an analog telephone signal is a data signal by monitoring the spectral distribution of the analog telephone signal without using such a specific sine wave signal.

Here, as a specific example of a specific sine wave signal that is transmitted prior to data signal transmission, we will use the echo suppressor DISABLING TONE specified by the Consultative Committee on International Telegraph and Telephone (CCITT). , that is, transmitted prior to the transmission of the data signal in order to stop the operation of the echo suppression device at the beginning of the data signal transmission.
The case of using a 2100HZ sine wave signal will be explained in detail. When a 2100 HZ sine wave signal, which is the echo suppressor's disabling tone, is detected, the transmission method is switched to a different adaptive delta modulation method suitable for encoding audio signals. The reason for this is as follows. In other words, the adaptive delta modulation method suitable for encoding audio signals is designed to maximize the S/N ratio with respect to the input signal, but this does not mean that the input signal is almost overloaded. It is nothing but encoding in the state. However, when the input signal is a data signal, such nearly overloaded encoding tends to cause instantaneous waveform distortion, causing errors in the data signal. Therefore, when the input signal is a data signal, it is necessary to encode the data signal so as not to cause overload, and as a means of this invention, the average level of the data signal is approximately constant over time. The average level of the input data signal is used to determine a step size that does not cause overload during encoding, and delta modulation encoding is performed.

The step size may also be adaptively changed as the data signal varies from its average level, resulting in better encoding of the data signal when using adaptive delta modulation. Furthermore, in the present invention, when encoding such a data signal, since the signal level itself is not so important in data signal transmission unlike in the case of audio signals, the input data signal is encoded by the AGC circuit. After reaching a certain level, as described above, a fixed step size delta modulation method suitable for encoding this level or an adaptive delta modulation method in which the step size is adaptively changed according to fluctuations in the data signal level is used. Since the input data signal is encoded using the same method, the input dynamics range of the input data signal can be widened.

In this way, when a data signal is input, it is detected and encoded by switching to an encoding method suitable for the data signal, but the data signal ends after a certain period of time during data signal transmission. Detection is made when the signal level becomes equal to or less than a predetermined threshold over a period of time. When the end of the data signal is detected, the encoding method is switched to an adaptive delta modulation scheme suitable for encoding voice signals, and the telephone signal is encoded. The switching of the delta modulation method as described above is performed not only during encoding but also during decoding.

As described above, according to the present invention, it is possible to transmit voice signals and data signals in telephone signals while maintaining sufficiently good call quality at a transmission bit rate lower than that of the existing PCM system.

In addition, since the delta modulation method is easy to configure,
It is also possible to reduce the cost of the encoding circuit.

Next, the present invention will be explained in detail using the drawings.

FIG. 1 is an example of the implementation of the present invention. In the figure, the part surrounded by a broken line on the left side is a block diagram of the code/decoding circuit on the transmitting side, the part surrounded by a broken line on the right side is a block diagram of the code/decoding circuit on the receiving side, and the thick line is the block diagram of the code/decoding circuit on the receiving side. This shows the flow of data signals when

The analog telephone signal to be transmitted inputted to the terminal 100 is sent to the terminal 107 by the switch circuit 104.
to the adaptive delta modulation encoding circuit 109 via
Alternatively, at the same time, it is input to the automatic gain control circuit (AGC circuit) 106 via the terminal 105 and from the adaptive delta modulation decoding circuit 112 to the terminal 113.
The received analog telephone signal is added in an analog manner to the received analog telephone signal outputted via the terminal 101 and inputted to the data signal detection circuit 102 via the terminal 101.

The data signal detection circuit 102 determines whether the signal input via the terminal 101 is a 2100HZ sine wave signal, which is an echo suppressor disable tone specified by the Consultative Committee on International Telegraph and Telephone (CCITT). At the same time, the average level of the input signal is checked, and if the average level of the input signal is a 2100Hz sine wave signal exceeding a certain threshold, it is sent to the adaptive delta modulation encoding circuit via terminal 103. 109 and the adaptive delta modulation decoding circuit 112 to an operation suitable for encoding the data signal, the switch circuit 10
A signal for connecting the switch No. 4 to the terminal 105 is output. If the average level of the input signal is below the threshold value for a certain period of time or more, the adaptive delta modulation encoding circuit 109 and the adaptive delta modulation decoding circuit 112 operate via the terminal 103. It switches the operation to one suitable for encoding and decoding audio signals, and outputs a signal for connecting the switch of the switch circuit 104 to the terminal 107.

In this way, it is possible to detect whether the telephone signal to be transmitted is a data signal by detecting the 2100 HZ sine wave transmitted prior to the data signal when transmission of the data signal is started. Furthermore, analog telephone signals sent and received are added in an analog manner and inputted to the data detection circuit 102 . Therefore, no matter which side of the two opposing terminal stations the data transmission starts from, the code/decoding methods of both terminal stations can be switched for data signals. Normally, when a data signal from one terminal station is being transmitted to another terminal station, no audio signal is transmitted from the receiving terminal station, but a data signal is transmitted. In this embodiment, the encoding/decoding method of both terminal stations is switched to one for data signals so that both terminal stations can exchange data signals at the same time.

According to the signal output from the data signal detection circuit 102, the adaptive delta modulation encoding circuit 109 outputs a signal from terminal 1 when the input signal is a data signal.
The data signal that is input to the AGC circuit 106 through the AGC circuit 106 and has a constant level is encoded by an adaptive operation suitable for the data signal. The reason for using AGC here is to perform encoding without sacrificing quality even if the input signal level changes. A suitable adaptive operation for data signals is to encode them using a larger step size than for audio signals of the same input level. An example of a specific circuit that realizes this operation will be described later. Although this method is not necessarily optimal in terms of signal-to-noise ratio, it is possible to obtain better characteristics in terms of data error rate than encoding optimized for voice signals.

On the other hand, when the input telephone signal is not a data signal, it is encoded by an adaptive operation suitable for voice, and is encoded at the terminal 11.
Output via 0. Furthermore, if the input data signal is converted into a data signal of a constant level with high accuracy by the AGC circuit 106, it is also possible to encode it using a fixed step size delta modulation method without using adaptive delta modulation. .

The adaptive delta modulation decoding circuit 120 on the reception side converts the signal input via the terminal 114 according to the signal output from the data signal detection circuit 118.
The data signal and voice are decoded by adaptive operations suitable for each, and outputted via terminal 115.

The operation when a telephone signal is transmitted from the other party's terminal station is the same as that described above, and will therefore be omitted.

Through the operations described above, it is possible to encode and decode an analog telephone signal by switching to an adaptive operation suitable for each signal, whether it is a voice signal or a data signal. As a result, not only audio signals but also data signals can be
It is possible to maintain sufficient quality at a lower transmission bit rate than the PCM method, and to transmit over a wider dynamic range.

FIG. 2 shows details of an example of the configuration of the data signal detection circuit 102 in FIG. 1. The operation will be explained below using the time chart shown in FIG.

Assume that a data signal shown at 3A in FIG. 3 is input to the terminal 101. In signal 3A, T1 indicates the duration of the 2100HZ sine wave transmitted prior to the data signal transmission, and T2 indicates the pause time after the 2100HZ sine wave is transmitted until the data signal transmission starts. shows. T3 indicates the duration of the data signal.

The 2100HZ sine wave signal shown at 3A is connected to terminal 10.
1 to the tone detection circuit 201 and at the same time rectified by the rectifier circuit 210 and input to the integration circuit 206. When a 2100Hz sine wave signal is input to the tone detection circuit 201 via the terminal 101 for a certain period of time T4 or more, the potential at the terminal 202 becomes a high level as shown in 3B in FIG.
When the 2100HZ sine wave signal disappears, it returns to a low level after a short period of time.

A 2100Hz sine wave signal input to the integrating circuit 206 via the terminal 101 is integrated and then output to the terminal 2.
07 to the comparator 208. The integral signal is input to the comparator 208 via the terminal 207, and when the level thereof exceeds a certain threshold, the signal is input to the terminal 2.
The potential of 09 is set to high level. The signal waveform at the terminal 209 is as shown in 3C in FIG. At time T5 at 3C, the 2100HZ sine wave signal passes through the integration circuit 2.
06 until the comparator 208 exceeds the threshold value.

The voltage level at terminal 202 and terminal 209 is
The logical sum is taken by the logical sum circuit 203 and the terminal 2 is
04. The signal waveform at terminal 204 is the third
It will look like the 3D image.

Flip-flop 205 is set by the rise of the potential at terminal 204 and reset by the fall of the potential at terminal 209. flipflop 2
The internal state of 05 is output via terminal 103,
The signal waveform becomes as shown in 3E in FIG.

While the data signal is being transmitted as described above, the potential of the terminal 103 is kept at a high level. When a signal other than the 2100Hz fundamental wave signal is input to the terminal 101, the potential of the terminal 202 is at a low level, so the terminal 204 becomes a low level, and the flip-flop 205 is not set.
Terminal 103 is kept at a low level.

As long as the recommendations of the Consultative Committee on International Telegraph and Telephone (CCITT) are followed, T1 at 3A in Figure 3 should continue for at least 400 msec, and T2 should continue for at least 400 msec.
should be kept below 100msec.
Therefore, T4 and 3C in 3B of FIG.
T5 may be set to 400 msec or less. Furthermore, when the potential of the terminal 209 becomes low level during the period T2 at 3A, the flip-flop 205 is reset and the terminal 103 is reset.
The waveform shown in 3E in FIG. 3 cannot be obtained as a waveform. Therefore, the time constant of the integrating circuit 206 is set so that the potential at the terminal 209 remains at a high level even during the period T2.

As described above, the data signal can be detected by detecting the 2100 HZ sine wave signal sent prior to the data signal at the start of data transmission.

Adaptive delta modulation coding circuit 1 in FIG.
09, for example, Figure 6 on page 138 of "PCM Communication Technology" published by Sanposha in August 1976.
13 can be used. This is shown in FIG. In Figure 4, the input signal is at terminal 4.
01 and output from the local decoder 410 via the terminal 402. The difference signal thus obtained is input to a comparator 404 via a terminal 403. Comparator 404
responds to the sampling pulse inputted through the terminal 411 and outputs "1" if the input difference signal is larger than a certain threshold, and outputs "0" if it is smaller than the terminal 40.
5, and this becomes the delta modulation output. The "1" and "0" signals are also input to a level detector 406, which outputs a signal for changing the step size in accordance with the continuous pattern of "1" and "0". This signal is supplied to a multiplier circuit 408 after being added with a constant bias b by an adder circuit 407 . The multiplier circuit 408 outputs the product value of the “1” and “0” signals input via the terminal 405 and the step size control signal output from the adder circuit 407 to the local decoder 410 via the terminal 409. do. In this way, the multiplication circuit 40
8 changes the step size of delta modulation.

The local decoder 410 receives input “1” and “0”.
Local decoding is performed by integrating the signal, and the result is output to terminal 402. Therefore, by varying the output signal of level detector 406 with the signal flowing to terminal 103 in FIG. 1, the adaptive operation of the adaptive delta modulation encoder can be switched.

FIG. 5 shows a level detector 407 in this embodiment.
An example of a specific circuit is shown below. Other circuits similar to those shown in FIG. 4 can be used. In FIG. 5, the output of the comparator 404 shown in FIG. 4 is inputted to an audio level detection circuit 503 and a data level detection circuit 504 via a terminal 405. The audio level detection circuit 503 and the data level detection circuit 504 each output a signal for changing the step size suitable for encoding the audio signal and the data signal. The switch circuit 502 is connected to the terminal 10 in FIG.
3, if the input signal is audio, the output of the audio level detection circuit 503 is output, and if the input signal is data, the output of the data level detection circuit 504 is output via the terminal 501. Output to multiplier 408. An embodiment of the audio level detection circuit 503 and the data level detection circuit 504 is shown in FIG. In the figure, the delta modulation code (“1” or “0”) input from the signal line 405 is detected by the continuous pattern detection circuit 601 when a predetermined number or more of the “1” or “0” codes are consecutively generated. It is checked whether or not, and if it is more than a certain number “1”
Or if “0” continues, the integration circuit 60
A pulse is output for 0. The appropriate number of consecutive patterns is usually 3 to 4. Next, in the integration circuit 600, a continuous pattern detection circuit 60
The pulses output from 1 are integrated with a predetermined time constant and output. In this way, when a slope overload occurs in so-called delta modulation, in which delta modulation codes of the same polarity continue, it is detected, a pulse is generated, and the encoded step size is determined according to the load by integrating it. The method for obtaining PCM
It is also explained on page 138 of "Communication Technology". In such a level detection circuit, an integrator with a time constant of several tens of milliseconds may be used as the audio level detector 503, and one with an integrator time constant of several hundred milliseconds may be used as the data level detector 504. Furthermore, when encoding a data signal with a fixed step size, it is sufficient that the data level detector 504 simply outputs a signal of a constant value; in this case, the continuous pattern detector 601 or the integrating circuit 600
is not required, just output a fixed pattern from a register or read-only memory (ROM). As described above, the adaptive operation of the encoding step size can be switched between voice and data. Note that as the adaptive delta modulation decoding circuit 112 in FIG. 1, one corresponding to the adaptive delta modulation encoding circuit 109 may be used.

As described above, according to this embodiment, whether the input analog telephone signal is a voice signal or a data signal, it is encoded using a modulation method suitable for each. It is possible to transmit data with sufficiently good quality over a wide input dynamic range, and also at a lower transmission bit rate than the existing PCM method, making it possible to use the bandwidth effectively. Since the configuration of the required modulation circuit is simple, it is also possible to reduce the cost of the encoding circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating one embodiment of the present invention. In FIG. 1, each symbol indicates the following. 100... (transmission) input terminal, 101... input terminal of data signal detection circuit 102, 102...
Data signal detection circuit, 103... Output terminal of data signal detection circuit 102, 104... Switch circuit, 105... Input terminal of AGC circuit 106, 1
06...AGC circuit, 107...Input terminal of adaptive delta modulation encoding circuit 109, 108...
Output terminal of AGC circuit 106, 109...Adaptive delta modulation coding circuit, 110...Output terminal of adaptive delta modulation coding circuit 109, 111...Input terminal of adaptive delta modulation decoding circuit 112, 1
12...Adaptive delta modulation decoding circuit, 113...
...Output terminal of adaptive delta modulation decoding circuit 112, 114...Adaptive delta modulation decoding circuit 12
0 input terminal, 115... Output terminal of adaptive delta modulation decoding circuit 120, 116... Input terminal of data signal detection circuit 116, 117... Output terminal of data signal detection circuit 116, 118... Data signal detection circuit, 119...adaptive delta modulation coding circuit, 120...adaptive delta modulation decoding circuit, 121...switch circuit, 122...AGC
circuit. FIG. 2 shows the data detection circuit 102 in FIG.
FIG. 2 is a block diagram showing in detail an example of the configuration of the device. In FIG. 2, each symbol indicates the following. 201... Tone detection circuit, 202... Output terminal of the tone detection circuit, 203... OR circuit,
204... Output terminal of OR circuit 203, 205
...Flip-flop circuit, 206... Integrating circuit, 207... Output terminal of integrating circuit 206, 20
8... Comparator, 209... Output terminal of comparator 208, 210... Rectifier circuit. In Figure 3, 3A indicates the 2100HZ sinusoidal signal and the following data signal, 3B,
3C, 3D and 3E, the signal shown in 3A is the second
It shows signal waveforms at terminals 202, 209, 204, and 103, respectively, when input to terminal 101 in the figure. FIG. 4 is a block diagram showing an example of an adaptive delta modulation circuit. In FIG. 4, each symbol indicates the following. 401...Input terminal, 402...Decoder 41
0 output terminal, 403...Input terminal of comparator 404, 404...Comparator, 405...Comparator, 40
6... Level detector, 407... Bias circuit,
408... Multiplier, 409... Output terminal of multiplier 408, 410... Local decoder, 411... Input terminal of sampling pulse of comparator 404. FIG. 5 shows an example of a level detector in the adaptive delta modulation and encoding circuits 109 and 119 in this embodiment. In FIG. 5, each symbol indicates the following. 501... Output terminal of switch circuit 502,
502...Switch circuit, 503...Audio level detection circuit, 504...Data level detection circuit. FIG. 6 is a diagram showing an example of a data level detection circuit. In FIG. 6, each symbol indicates the following. 600...Integrator circuit, 601...Continuous pattern detection circuit.

Claims (1)

[Claims] 1 On the transmitting side, it is determined whether the input analog telephone signal is a data signal by detecting a specific sine wave signal transmitted prior to transmission of the data signal, and it is determined that the analog telephone signal is not a data signal. If the analog telephone signal is determined to be a data signal, the analog telephone signal is encoded using an adaptive delta modulation method, and the analog telephone signal is made to a constant level by automatic gain control and then encoded using a delta modulation method or a step encoder. The data signal is encoded using an adaptive delta modulation method in which the size adaptive operation is changed to an adaptive operation suitable for the data signal, and if the transmission of the data signal is stopped for a certain period of time or more, it is regarded as the end of the data signal. Encoding is performed using the adaptive delta modulation method used for encoding, and the receiving side determines whether the received telephone signal is a data signal by detecting the specific sine wave signal, similarly to the transmitting side. If it is determined that the telephone signal is not a data signal, the received signal is decoded using an adaptive delta modulation method used for decoding other than data signals, and if it is determined that the telephone signal is a data signal, the received signal is decoded using a delta modulation method or The data signal is decoded using an adaptive delta modulation method in which the step size adaptive operation is changed to an adaptive operation suitable for the data signal, and if the reception of the data signal stops for a certain period of time or more, it is regarded as the end of the data signal. 1. A transmission method for analog telephone signals, characterized in that decoding is performed using the adaptive delta modulation method used for encoding.