JP2633706B2 - Audio / video transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to simultaneous transmission of image data and audio signals using a low-speed and narrow-band transmission line such as a general telephone line or a wireless communication line. The present invention relates to a video / audio transmission device suitable for use.

[Prior Art] As a modulation method of a modem for a low-speed and narrow-band transmission line such as a general telephone line, many methods currently used include phase shift keying (PSK) and frequency shift keying (PSK). FSK),
There are quadrature amplitude modulation (QAM) and amplitude phase modulation (AM-PM).

Of these, frequency shift keying has a relatively small spread of spectrum, and there is a telewriting terminal as a simultaneous voice / data transmission device using this frequency shift keying. However, since the baud rate is low-speed transmission of about 300 bps, it takes a long time to transmit large-capacity data such as image data, which is not practical.

Still image transmission devices using amplitude phase modulation (multiple amplitude two-phase modulation) are commercially available as still image videophones.

The spectrum distribution of this modulation method is as follows: carrier frequency fc = 1747.8 Hz, maximum baseband frequency fb = 1747.8 / 2 Hz, and the first sideband is distributed above and below the carrier frequency, and the band is 1747.8 Hz.

This amplitude-phase modulation allows high-speed transmission suitable for still image transmission by allowing an error in the amplitude level due to a deterioration factor in the characteristics of a transmission line such as a radio wave circuit to be recognized as a redundancy like an error in the luminance level of an image. Modulation method.

However, this modulation method requires a wide transmission band (1747.8 Hz) occupying more than half of the frequency band of a general telephone line (analog line) of about 300 Hz to 3400 Hz. It is not practical to perform simultaneous transmission of image data and audio signal using the same.

[Problems to be Solved by the Invention] As described above, in the related art, an appropriate method of simultaneously transmitting an audio signal and image data through a general telephone line has not been realized.

In view of the above, the present invention provides an image and sound transmission device having a narrow data transmission band and a high transmission speed.

[Means for Solving the Problems] On the transmission side, a multi-frequency value modulation means for converting image data into an audio band signal having a frequency value corresponding to the data value, and the multi-frequency value modulation means from the audio signal A band removing filter for removing a component of a used frequency band of the voice band signal in the above, and a signal combining means for combining a voice band signal from the multi-frequency value modulating means and a voice signal from the band removing filter to obtain a transmission signal And the receiving side:
A signal separating unit for separating the audio band signal and the audio signal from a transmission signal transmitted from the transmitting side; and a multi-frequency value demodulating unit for converting the audio band signal from the signal separating unit into the image data. In the audio and video transmission apparatus, the multi-frequency value modulating means converts the image data values to respective frequency values within the use frequency band such that a period difference between frequency values representing data values having adjacent values is constant. And a voice band signal having a frequency value representing the data value of one data is output continuously for a plurality of cycles.

[Operation] In the above configuration, since the image data is converted into an audio band signal and frequency-division multiplexed and transmitted to the audio signal, the image data and the audio signal can be transmitted simultaneously.

Further, since the image data is converted into the audio band signal by the multi-frequency value modulation, it is possible to increase the baud rate of the data transmission.

In addition, image data is modulated by assigning data values indicating each gradation to frequency signals within the used frequency band, and a frequency signal indicating each data value is output continuously for a plurality of cycles. It is possible to suppress the spread of the transmission band at the time.

Embodiment An embodiment of the present invention will be described below with reference to FIG. This example is an example of transmission using a general telephone line.

In the figure, 100A and 100B are transmission / reception sets as terminal devices connected to a general telephone line (analog line) 200.

 The transmission / reception set 100A is configured as follows.

103 is an image memory. The video signal from the video camera 101 is converted into, for example, a 6-bit digital signal per sample by the A / D converter 102 and supplied to the image memory 103, and image data for one screen is written.

The image data read from the image memory 103 is D
Monitor TV 1
Supplied to 05.

Reference numeral 106 denotes a modem constituting multi-frequency value modulation / demodulation means. This modem 106 is configured, for example, as shown in FIG.

In the figure, reference numeral 106a denotes a modulation counter. 6-bit image data indicating 64 steps (gradations) is supplied from the image memory 103 to the counter 106a.

The counter 106a counts down from a predetermined value corresponding to the image data. The counter 106a outputs a square wave signal having a frequency corresponding to the data value (step). As described later, this square wave signal is transmitted as a sine wave signal via a band-pass filter.

This is because, when using a general telephone line network as a communication link, both ends of the transmission band of 300 Hz to 3400 Hz are affected by group delay distortion, and a frequency link of up to about 10 Hz in the positive and negative directions as a communication link. Have.

Therefore, as the frequency band of the image data, the influence of the group delay is avoided, and the concentrated portion (first formant; low band around 1 kHz) on the energy distribution during a call is removed to be 2000H.
Set to z ~ 2400Hz.

The frequency of the square wave signal output corresponding to each data value described above is set such that the period difference t between the square wave signals indicating adjacent data values (steps) is constant (fourth).
Illustrated in the figure).

The period difference t is, for example, a value obtained by dividing the period difference of 83 μsec (shown in FIG. 5) between the square wave signals of 2000 Hz and 2400 Hz into 63 equal parts.
1.3 μsec.

As a result, the frequency of the square wave in the first step is 2000H
z The frequency of the square wave in the second step is 2005 Hz,..., the frequency of the square wave in the 63rd step is 2393 Hz, and the frequency of the square wave in the 64th step is 2400 Hz (shown in FIG. 6A).

It is also conceivable to make the frequency difference between square wave signals indicating adjacent data values constant. However, in this case, the higher the frequency, the smaller the period difference between adjacent data values, and it is not possible to maintain uniform conditions with respect to disturbance factors such as jitter.

By the way, multi-frequency value modulation can be realized by outputting a sine wave signal having a frequency corresponding to each data value one cycle at a time, and consider the occupied band assuming random data as actual data.

For example, black (2000 Hz) and white (24
00Hz) (shown in FIG. 7A)
The repetition period is 1/1100 Hz, which is 22
(2200-1100) Hz and (2200 + 1100) Hz around 00Hz,
Upper and lower first sidebands are respectively generated (shown in FIG. B).
In this case, a band of 2200 Hz is required to include both first sidebands, and the transmission band at the time of data modulation is too wide compared to the data band of 400 Hz.

When the black and white states are alternately repeated every two cycles (shown in FIG. 8A), the repetition cycle is 1/550 Hz.
And centering around 2200Hz which is equivalent to the carrier frequency (2200-55
First upper and lower sidebands are generated at 0) Hz and (2200 + 550) Hz, respectively (shown in FIG. B). In this case, the band required to include both first sidebands is 1100 Hz, and the transmission data band is narrower than in the case where the black and white states are alternately repeated one period at a time.

Generally, in the multi-frequency value modulation, the frequency interval of the sideband is expressed by the following equation.

｛(F1 + f2 + ... + fn) 1 / n｝ (1 / n) (1 / m) (f1 + f2 + ... + fn) 1 / n: Average frequency within the modulation period (corresponding to carrier frequency) n: Number of different data values to be sent m: Number of repetitions of the same data value From this, it is understood that the frequency interval of the sideband is determined by the number of different data values to be transmitted and the number of repetitions of the same data value.

In this example, in order to narrow the transmission data band,
For example, the modulation counter 106a outputs a square wave signal having a frequency corresponding to each data value every two periods.

Reference numeral 106c denotes a waveform shaping circuit.
A voice band signal supplied from the transmission side via the general telephone line 200 is supplied to 106c via an amplifier 106d for automatic gain adjustment. This audio band signal, as described later,
The above-mentioned square wave signal is a sine wave signal obtained through a band-pass filter. In the waveform shaping circuit 106c, the original square wave signal is reproduced based on the zero cross point of the sine wave signal.

Then, the square wave signal from the waveform shaping circuit 106c is supplied to a demodulation counter 106b. As described above, the square wave signal has a cycle corresponding to the value (step) of the image data. The counter 106b performs a counting operation in each cycle period of the square wave signal, and calculates the period of the square wave signal from the count value. The counter 106 outputs 6-bit image data having a value corresponding to the cycle, and the 6-bit image data is supplied to the image memory 103.

Returning to FIG. 1, the square wave signal output from the counter 106a of the modem 106 is transmitted to a two-wire / four-wire conversion unit 108 via a band-pass filter 107 having a frequency characteristic indicated by a solid line a in FIG. Supplied as a signal. This audio band signal becomes a sine wave signal as shown in FIG. 6B.

Further, the audio signal from the handset 109 is amplified by the amplifier 111 and the maximum level is limited by the limiter 112, and then is passed through the band emissive filter 110 having frequency characteristics shown by solid lines b and c in FIG. It is supplied to the conversion unit 108.

In this case, the fundamental frequency range of the data value is 2000Hz to 2400
Hz, but 100 Hz is secured for the upper and lower sidebands. The audio band is 1500 Hz or less and 3000 Hz or more, and mutual interference between the audio signal in the audio band and the audio signal in the data band is prevented.

The band-pass filter 107 has a slope of 100 dB / oct or more and a suppression gain of 50 dB or more. The gain at the cross point (intersection of the slope) between the band pass filter 107 and the band emissive filter 110 is set to 40 dB or more.

By the way, if the required transmission data band is band-limited (band reduction), if the data value Ao currently being transmitted changes to a different data value Bo, the response characteristic of the data value becomes broad. In other words, after the data value changes transiently from the data value Ao to a different data value, the data value Bo
Is reached. The number of transient data values (responsiveness) in this case is related to the frequency interval of the sideband and the bandwidth to be restricted.

For example, if the number of data repetitions, that is, the repetition period per data, is 2 in the case of alternating black and white data, as described above, the frequency interval between the sidebands is 550 Hz, and the required band is 1100 Hz (No. 10 shown in Figure A).

The transmission data band is set to 600 by the bandpass filter 107.
When the frequency is limited to Hz (shown in FIG. B), the reproduced data value becomes as shown in FIG. D with respect to the transmission data value shown in FIG. C, and the number of transient data values becomes about 2-3.

The screen resolution decreases as the number of transient data values increases. That is, the screen configuration of the transmission image is, for example,
In the case of 256 bits (pixels), the transmission has a resolution of 128 to 85 dots.

The influence of the group delay characteristics of the band pass filter 107 and the band emissive filter 110 on the transmission data value includes a transient response characteristic accompanied by vibration. That is, the reproduced data value becomes as shown in FIG. 11B with respect to the indicated data value shown in FIG. 11A.

However, the actual image data is not completely random, but has a change in value based on the context of the data.
An acceptable group delay value is around 200 μsec.

Next, the conversion unit 108 will be described. The conversion unit 108 is configured, for example, as shown in FIG.

In the figure, reference numeral 108a denotes a synthesizing circuit.
To 108a, the audio band signal from the band-pass filter 107 is supplied via an amplifier 108f for adjusting the transmission level, and the audio signal from the band emissive filter 110 is supplied via an amplifier 108g for adjusting the transmission level. The signals are supplied and combined to form a transmission signal. This transmission signal is a signal obtained by frequency division multiplexing the audio band signal and the audio signal.

The transmission signal from the combining circuit 108a is transmitted to a general telephone line via the hybrid balance circuit 108b and the circuit transformer 108c.
Supplied to 200.

The transmission signal supplied from the transmission side via the general telephone line 200 is supplied to buffers 108d and 108e via the line transformer 108c and the hybrid balance circuit 108b.

Returning to FIG. 1, the transmission signal from the buffer 108d of the conversion unit 108 is supplied to a band-pass filter 107 to extract an audio band signal, and this audio band signal is supplied to a modem 106. Then, as described above, the image data is demodulated from the audio band signal and supplied to the image memory 103.

Further, the transmission signal from the buffer 108e of the conversion unit 108 is supplied to a band emissive filter 110 to extract an audio signal. The audio signal is amplified by an amplifier 113 and then supplied to a handset 109.

Although the transmission / reception set 100A is configured as described above, the transmission / reception set 100B is configured similarly to the transmission / reception set 100A.

In the above configuration, an operation in the case where the transmission / reception set 100A is the transmission side and the transmission / reception set 100B is the reception side will be described.

First, the transmission operation in transmission / reception set 100A will be described.

The video signal from the video camera 101 is converted by the A / D converter 102 into 6
Image memory 10 after being converted to digital signals of bits
3 and stored in the image memory 103 for one screen, for example,
Image data of 256 × 240 dots is written.

Then, 6-bit image data of each dot is sequentially read out from the image memory 103 and supplied to the modem 106. The modem 106 outputs a square wave having two periods each having a period corresponding to the value (step) of the image data. A signal is output.

Then, the square wave signal output from the modem 106 is converted into a sine wave signal, that is, a voice band signal by the band-pass filter 107, and supplied to the conversion unit 108.

The audio signal output from the handset 109 is supplied to the conversion unit 108 after the above-mentioned frequency band component of the audio band signal has been removed by the band elimination filter 110.

Then, in the conversion unit 108, the voice band signal and the voice signal are frequency-division multiplexed to form a transmission signal.
Is transmitted to

Next, the operation of the transmission / reception set 100B will be described. A transmission signal transmitted from the transmission / reception set 100A via the analog line 200 is supplied to a band elimination filter 110 via a conversion unit 108, and an audio signal extracted by the elimination filter 110 is supplied to a handset 109. , An audio signal is output.

In this case, since the audio band signal is removed by the band elimination filter 110, the handset 109 does not output an unpleasant sound due to the audio band signal (squealing sound).

Further, a transmission signal transmitted from the transmission / reception set 100A via the general telephone line 200 is supplied to a band-pass filter 107 via a conversion unit 108, and the band-pass filter 107
The voice band signal extracted at is supplied to the modem 106.

Then, the modem 106 demodulates 6-bit image data from the audio band signal. In this case, since the audio signal is removed by the band-pass filter 107, the audio signal does not cause the modem 106 to malfunction.

Then, the 6-bit image data demodulated by the modem 106 is supplied to the image memory 103 and written.

Then, 6-bit image data of each dot is sequentially read from the image memory 103, converted into an analog signal by the D / A converter 104, and supplied to the monitor television 105,
An image based on the image data is displayed.

As described above, according to this example, since the audio band signal obtained by multi-frequency value modulation of the image data and the band-limited audio signal are frequency-division multiplexed and transmitted, the image data and the audio signal are transmitted simultaneously. Can be.

Further, since the audio band signal is formed by modulating image data with multi-frequency values, the baud rate of data transmission can be increased, and the image transmission time can be greatly reduced.

In addition, each data value of the image data is set to 2000 Hz to 24
When performing modulation by allocating to a frequency signal within 00 Hz, the period difference between frequency signals indicating adjacent data values is made constant, so that each data value must be uniform with respect to disturbance factors such as jitter. Can be kept.

In addition, a frequency signal corresponding to each data value is provided for a plurality of cycles,
For example, since the output is performed every two cycles, the spread of the transmission band at the time of modulation can be suppressed. As a result, a sufficient voice band can be ensured, and simultaneous transmission of a voice signal and image data can be favorably performed without deteriorating the intelligibility of the call.

By the way, as described above, a general telephone line as a communication link has a frequency jitter of up to 10 Hz. In the case of multi-frequency value modulation as in this example, this frequency jitter is 1st.
It has a great effect on the cycle per data. However, since it is generally a frequency jitter in the entire frequency band of the transmission line, it appears as a change in luminance of image information, and a change in a luminance signal of 10 Hz with respect to a data band of 400 Hz does not cause much problem.

In the above-described embodiment, the image data having 6 bits has been described, but an image data having an arbitrary number of bits can be similarly configured. Also, the data bandwidth is 2000-2400
Hz, but the frequency and range are not limited to this.

Further, in the above-described embodiment, two sets of transmission / reception sets are shown. However, those in which more transmission / reception sets are provided can be similarly configured.

Further, in the above-described embodiment, the transmission using a general telephone line has been described. However, the present invention can be similarly applied to a system for simultaneously transmitting image data and audio signals using another transmission medium. For example, it can be applied to a system that handles image data and audio signals, such as an amateur band wireless communication, a home appliance and a remote control transmitter, a home security information system using a power line (100 V), and the like. it can.

[Effects of the Invention] As described above, according to the present invention, since an audio band signal and an audio signal obtained by modulating image data are frequency-division multiplexed and transmitted, the image data and the audio signal are transmitted simultaneously. Thus, the broadcast of the image and the voice can be secured.

Thereby, it is possible to talk while watching the image.
In addition, since there is no interruption in the transmission of images, the conventional method of transmitting images manually has been repeated so that image transmission-reception-transmission-reception-... It becomes possible, and the operation can be simplified.

Also, since the audio band signal is formed by modulating the image data with multi-frequency values, the baud rate in data transmission can be increased, the image transmission time can be greatly reduced, and the waiting time is cumbersome. Can be reduced.

Also, when modulating by assigning each data value of the image data to the corresponding frequency signal, the period difference between the frequency signals indicating adjacent data values is made constant, so that each data value is affected by a disturbance factor such as jitter. Can be kept uniform.

In addition, a frequency signal corresponding to each data value is provided for a plurality of cycles,
For example, since the output is performed every two cycles, the spread of the transmission band at the time of modulation can be suppressed. As a result, a sufficient voice band can be ensured, and simultaneous transmission of a voice signal and image data can be favorably performed without deteriorating the intelligibility of the call.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram of a modem, FIG. 3 is a block diagram of a two-wire / four-wire converter, FIG.
8 are diagrams for explaining multi-frequency value modulation, FIG. 9 is a diagram showing frequency characteristics of a filter, FIG. 10 is a diagram for explaining responsiveness due to band limitation, and FIG. 11 is a filter. FIG. 6 is a diagram for explaining overresponse characteristics based on the group delay characteristics of FIG. 100A, 100B ...... Transmission / reception set 101 Video camera 102 A / D converter 103 Image memory 104 D / A converter 105 Monitor TV 106 Modem 107 Band pass filter 108 … 2-wire 4-wire conversion unit 109… Handset 110… Band Elminate Filter

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-116547 (JP, A) JP-A-63-160454 (JP, A) JP-A-62-125762 (JP, A)

Claims (1)

(57) [Claims] 1. A transmitting side comprising: a multi-frequency value modulating means for converting image data into a voice band signal having a frequency value corresponding to the data value; A band rejection filter that removes components of the used frequency band, and a signal synthesizing unit that synthesizes an audio band signal from the multi-frequency value modulation unit and an audio signal from the band rejection filter to obtain a transmission signal, On the receiving side, signal separating means for separating the audio band signal and the audio signal from the transmission signal transmitted from the transmitting side,
A multi-frequency value demodulating means for converting the audio band signal from the signal separating means into the image data, wherein the multi-frequency value modulating means comprises an inter-frequency value representing a data value having an adjacent value. The image data values are respectively assigned to the audio band signals having the respective frequency values within the above-mentioned used frequency band so that the period difference of the data is constant, and the audio band signal having the frequency value representing the data value is assigned to one data. An image and sound transmission device characterized by outputting continuously for a plurality of cycles.