JPH0582789B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention not only transmits data downstream from a center to the subscriber side, but also transmits data upstream from the subscriber side, thereby achieving two-way data communication. The present invention relates to a so-called two-way CATV that performs this, and in particular to a two-way CATV that detects an abnormality in data transmission from the subscriber side when transmitting data from the subscriber side to a center and prevents noise from concentrating on the main cable.

[Summary of the invention]

In this invention, for example, in a two-way CATV in which a center and a subscriber side can communicate in both directions, when the subscriber side sends data to the center side, the data generated by the CPU 25 and to be sent is transmitted as shown in FIG. Multiplier 3 via low-pass filter 31
Add to 0. The oscillation output from the oscillator 29, which continues oscillation for the period of the transmission request signal (RTS signal) sent from the CPU 25, is applied as a carrier wave to the multiplier 30, and modulation for data transmission is performed. The transmission data obtained as the output of the multiplier 30 is transmitted to the center side by the upstream, but in order to prevent the carrier wave from being unnecessarily transmitted even after the transmission data, the carrier wave transmission time setting circuit 28 is configured to After a predetermined time has elapsed, the oscillation of the oscillator 29 is forcibly stopped. This prevents a specific subscriber from monopolizing the data transmission path for the upstream by continuing to send out unnecessary carrier waves, thereby preventing communications of other subscribers from being obstructed.

[Technical background of the invention and its problems]

Generally, in a CATV system, in addition to television signals from a center, individual data to subscribers is transmitted, and on the other hand, two-way communication is performed in which data signals are transmitted from the subscriber side to the center. This two-way system is called urban CATV, and allows subscribers to make program reservations and billing from the center under the pay-TV system.In addition, the center monitors the subscriber's condition to prevent abnormalities such as fires. It also enables a so-called security system in which the center detects the state and controls the fire extinguishing equipment accordingly. Furthermore, mail-order sales and the like are also possible by transmitting shopping information from the subscriber side to the center and having the center process the information.

This kind of two-way CATV system is characterized by the fact that in addition to the transmission of broadcast waves from the center, it also enables data communication between the center and the subscriber side.

However, in a two-way CATV system,
Since there are many subscribers who generate data in the upstream direction to the center, if one subscriber's data generation circuit goes out of control and the upstream line is occupied, data transmission by other subscribers will be inhibited. This will damage the two-way communication function.

FIG. 2 is a circuit diagram showing an example of a general two-way CATV, in which normal on-air signals are applied to the center side 100 via an antenna, and satellite broadcast signals are applied to the head end 3 via a parabolic antenna 1. , where it is converted into a retransmission channel and sent to the trunk cable 4 as a retransmission signal.
In addition to the above-mentioned retransmission signal, a signal from a transmitter 5 that transmits an independent broadcast signal such as a pay program is added to this trunk cable.

In addition, for bidirectional data communication, the modulator 6 and the demodulator 7
, the center side 1 is connected via the bidirectional coupler 8.
This is done by exchanging data between 00 and the subscriber side 200. For example, data communication from the center side to the subscriber side as a town stream is FSK.
(Frequency Shift Keying) method is used to transmit data by making binary digital data correspond to two different frequencies f ₁ and f ₂ . On the other hand, in the upstream that transmits data from the subscriber side 200 to the center side, for example, a two-phase digital phase modulation method is used, so-called PSK (Phase Shift Keying).
method is used. The subscriber terminal 20 on the subscriber side 200 and the center side 100 are connected by a trunk cable, and trunk amplifiers 30 are provided at predetermined cable length intervals to compensate for signal attenuation depending on the cable length. The trunk amplifier 30 performs level control such as signal amplification in both the downstream and upstream directions. The trunk amplifier 30 also performs frequency compensation for the frequency characteristics of the cable.

For data transmission using the PSK method from the subscriber terminal 20 to the center side 100 using the upstream, the center computer 9 of the center side 100 performs polling, and only specified subscribers are permitted to send data as response data. . The response data collected at the center side 100 is processed by the center computer 9, and if necessary, an output device 1 configured by an output means such as an image display or a line printer is provided.
Output by 0.

Note that each terminal 20 receives and receives data for the downstream and upstream via the bidirectional coupler 19. Looking at the television signal in the town stream, the television signal passes through the bidirectional coupler 21. The television signal, which is converted into a predetermined frequency by the converter tuner 22, is applied to a television receiver 23 for image reproduction and audio reproduction.

On the other hand, looking at upstream and downstream data communication, the center side
The data transmitted from the bidirectional coupler 21
is applied to demodulator 24 by. This demodulator 2
4 consists of an FSK receiver, which detects a frequency signal corresponding to binary data from the center side and demodulates the data. And the demodulated center side 1
The data from 00 is applied to the CPU 25, where data processing is performed. At this time, a unique address is determined for each subscriber unit by the address section 26, and only the CPU 25 of the subscriber corresponding to the corresponding address is accessed.
For example, in the case of paid broadcasting, etc., the center side sends the subscriber address with which the contract was made to the subscriber side via downstream, and the subscriber terminal 20 of the corresponding address checks whether the address matches with the CPU 2.
5 and control is permitted in order to view the reserved pay program.

Regarding the upstream at the unit of the subscriber terminal 20, data to be sent to the center side 100 is phase modulated by a modulator 27 that performs phase modulation, and the data is transmitted according to the PSK method.

Upstream data transmission using this PSK method is performed by, for example, making digital data "1" and "0" correspond to carrier wave phases of 0° and 180°.

Data transmission from the subscriber side 200 to the center side 100 in the above-mentioned upstream is performed by a subscriber designated by the center side 100 by boring sending data to the upstream. This data transmission from the subscriber side 200 is performed, for example, by PSK modulation, but in this case, the data to be transmitted on the subscriber side 200 is generated by an oscillator (not shown) that generates a carrier wave, and this and the data are The multiplication is performed, phase modulation is performed, and data is transmitted.

In this case, the oscillator of the subscriber terminal 20
Data transmission request signal (RTS) generated by CPU25
The signal will continue to oscillate for a period of
If the oscillation continues beyond the RTS signal, the unnecessary oscillation output will occupy the upstream, making it impossible for other subscribers to send data. Also,
Even if the control by which the RTS signal controls the oscillator is not properly performed, the carrier wave will unnecessarily occupy the upstream and interfere with the data transmission of other subscribers regarding the upstream data transmission. .

Therefore, it is necessary to control the oscillator of the subscriber terminal 20 so that the subscriber does not unnecessarily transmit carrier waves.

[Purpose of the invention]

This invention was made in view of the above points, and is intended to prevent noise from being concentrated in the upstream of the main line when subscribers carry out unnecessary carrier waves to the upstream in two-way CATV, and to The purpose is to provide two-way CATV that does not interfere with the data transmission of subscribers.

[Embodiments of the invention]

Hereinafter, with reference to the drawings, the bidirectional structure according to this invention will be explained.
An example of CATV will be described.

FIG. 3 is a circuit diagram showing an embodiment of the bidirectional CATV according to the present invention, and is a circuit diagram showing one subscriber terminal on the subscriber side.

Note that the parts having the same functions as those in FIG.

First, regarding the downstream, the signal sent from the center side passes through the bidirectional coupler 21, the television signal is added to the television receiver 23, and the FSK data signal is sent to the demodulator 24 which performs FSK demodulation. Added. The data demodulated by this demodulator 24 is sent to the data input terminal of the CPU 25.
Added to IN. An example of control performed via the downstream in the FSK method is address control for identifying subscribers who are permitted to send data to the center by polling or the like. This address control detects a match between the address data sent by the FSK method and the center of the address section 26 of the subscriber terminal 20, and if a match is detected, the subscriber terminal that is allowed to send data is specified. Ru. Next, a case will be described in which data is sent from the subscriber terminal 20 specified by, for example, polling from the center side.

The data sent from the corresponding subscriber terminal 20 that sends the data is generated at the data output terminal OUT of the CPU 25. This data includes, for example, preset data for pay programs and status data of fire sensors generated on the subscriber terminal side in the security system, and this data is sent to the center side via an upstream.

For data modulation in this case, for example, a phase keying (PSK) method is adopted. The PSK method is a modulation method that changes the phase of the carrier wave according to the data, but if the carrier wave continues to be generated even after the data transmission period has elapsed, the subscriber in question will be unable to send out data. Nevertheless, it occupies the upstream line and interferes with other subscribers' upstream data transmission. In order to deal with this problem, in this embodiment, the relevant subscriber terminal 20
This prevents unnecessary signals from concentrating on the trunk cable by specifying the period during which carrier waves can be sent out. In the example shown in FIG. 3, the carrier wave transmission period is determined by a carrier wave transmission time setting circuit 28 provided in the PSK modulator 27.

In the above PSK method, for example, in the two-phase PSK, the phase modulation of the transmitted data at the subscriber terminal 20 is performed by the oscillator 2.
Carrier wave generated in 9 and output terminal OUT of CPU25
This is done by multiplying the data obtained by That is, the data to be transmitted obtained through the low-pass filter 31 is multiplied by the oscillator output of the oscillator 29 to perform phase modulation on the data to be transmitted.

The phase-modulated transmission data obtained at the output of the multiplier 30 is amplified by an amplifier 32 and then transmitted to the main cable via a bandpass filter 33.
Data is transmitted to the center via the upstream.

Here, the oscillator 29 basically constitutes a Colpitts oscillator, the oscillation frequency is approximately determined by the crystal resonator 40, and the oscillation is sustained by the amplification operation of the oscillation transistor 41. Furthermore, resistors R ₁ and R ₂ are bias resistors, capacitor C ₁ functions as a feedback capacitor, and the oscillation output is taken out from the collector of transistor 41 whose load is a resonant circuit consisting of capacitor C ₂ and inductance L ₁ . . An oscillation control transistor 42 is provided on the emitter side of the oscillation transistor 41, and a collector-emitter current path of the transistor 42 conductively connects the emitter of the transistor 41 to the ground potential via a resistor _R3 . Furthermore, the emitter of the transistor 41 is connected to ground potential via a capacitor _C3 , forming a bypass capacitor.
The output of the oscillator configured in this manner is applied to one input terminal of the multiplier 30, with the DC component removed by the capacitor _C4 .

Data to be sent out via the upstream is applied to the other input terminal of the multiplier 30, and a phase modulation operation is performed by the multiplication operation. Further, the CPU 25 outputs a data transmission request signal (RTS signal) to control the oscillator 29.

That is, when the CPU 25 operates in response to polling and sends out data, a negative pulse is generated at the set terminal SET of the CPU 25 at the initial stage, and accordingly, the RS flip-flop FF is set and its output becomes a high potential. Become. Therefore, the transistor 42 becomes conductive and the transistor 41
An emitter bias is applied to the As a result, both transistors 41 and 42 become conductive, allowing oscillation. A data transmission request signal (RTS signal) is applied to the base of the transistor 41 via an inductance L ₂ and a diode D ₂ . While this RTS signal is at a high level, in other words, while a voltage higher than the diode voltage of diode _D0 is applied, the transistor 4
1 conducts and continues oscillation. At this time, the diode D ₀ is provided to set a threshold value to prevent the oscillator 29 from starting oscillation due to noise, etc., and the inductance L ₂ is provided to act as a choke effect against high frequency noise. On the other hand, it works to prevent the oscillator 29 from erroneously oscillating.

As mentioned above, the series circuit consisting of the inductor L ₂ and the diode D ₀ connected to the RTS terminal of the CPU 25, and the transistor 41 whose base is connected to the RTS terminal via this series circuit, outputs the RTS data transmission request signal. It operates as a first control means that operates the oscillator 29 in response to the signal generation period. While the RTS is at a high level, the base potential of the transistor 41 is increased and the oscillator 29 continues to oscillate. In this way, the oscillation of the oscillator 29 is controlled so that the oscillation period of the oscillator 29 corresponds to the RTS signal generation period. For this reason, the oscillator 29
The generation of unnecessary carrier waves from the carrier wave prevents generation of carrier waves other than the carrier wave as data in the upstream.

However, if the RTS signal itself becomes unstable, such as when the RTS signal is generated longer than necessary due to an abnormality in the CPU 25, unnecessary carrier waves may be concentrated in the upstream. Furthermore, a carrier wave transmission time setting circuit 28 is provided to prevent the carrier wave from being unnecessarily transmitted to the upstream and interfering with communications of other subscribers. Carrier wave sending time setting circuit 28
controls the conduction state of the transistor 42 of the oscillator 29 by the output of the output terminal Q of the reset flip-flop FF. This control is
When a negative pulse is supplied from the set terminal SET of the CPU 25, the output Q of the flip-flop FF is
becomes high level, the transistor 42 becomes conductive, and the oscillator 29 becomes ready for oscillation. When the RTS signal is supplied in this state, the oscillator 29 continues to oscillate while the RTS signal is at a high level.

The time corresponding to the RTS signal is determined by the resistances R ₂₀ , R ₃₀ of the carrier wave sending time setting circuit 28,
It is set by a time constant circuit approximately determined by the capacitor _C30 , and the time constant of this time constant circuit is equal to the above-mentioned RTS signal period, but is slightly longer than this. Furthermore, the output of an amplifier 32 that amplifies the output of the multiplier 30 is input to the carrier wave transmission time setting circuit 28 . This amplifier 32 outputs a PSK signal, but in the two-phase PSK signal, the phase of the carrier wave is inverted according to the data value, and the frequency is the same as the oscillation frequency of the oscillator 29. The output signal of the amplifier 32 whose phase changes from 0° to 180° according to this data is smoothed by a diode D ₁₀ , a capacitor C ₁₀ , and a resistor R ₁₀ and converted into data. This data is inverted by an inverter 51 and applied to the base of a transistor 53 via a resistor 52. The base input signal is inverted by this transistor 53 and obtained on the collector side. When the amplifier 32 loses the data to be sent, the base potential of the transistor 53 becomes high level, the transistor 53 becomes conductive, and the charge in the capacitor C ₃₀ is discharged, and the transistor 5 in the subsequent stage becomes conductive.
4 blocks it. At this time, resistor R ₄₀ and capacitor C ₂₀
The collector potential of the transistor 54, which is the connection point of the transistor 54, is at a high level, and the flip-flop FF is not reset.

That is, the carrier wave output of the multiplier 30 is
Carrier wave transmission is stopped at the falling edge of the RTS signal,
If unnecessary carrier waves are properly prevented from being sent to the upstream, the above flip-flop FF
does not change state. At this time, the RST signal period has passed and the level has become low, so the oscillator 29
Regardless of the base potential of the transistor 42 being at a high level, the transistors 41 and 42 are in a cut-off state and oscillation is stopped, thereby preventing unnecessary carrier waves from being transmitted to the upstream.

On the other hand, if the oscillator 29 malfunctions and continues to oscillate even after the RTS signal period has elapsed, unnecessary carrier waves will be sent out to the upstream, interfering with other subscribers' upstream communications.
It is desirable to reliably stop the transmission of carrier waves that exceed the period.

The carrier wave sending time setting circuit 28 cooperates with a transistor 42 and is connected to a multiplier 30 via an amplifier 32.
When the data output from is detected and the data is output beyond the RTS signal generation period,
It operates as a second control means for stopping the application of the carrier wave from the oscillator 29 to the multiplier 30. This carrier wave sending time setting circuit 28 is configured as described above.
When the transmission of the carrier wave continues beyond the RTS signal period, the presence of the unnecessary carrier wave is detected by an envelope detection operation using a diode D ₁₀ , a capacitor C ₁₀ , and a resistor R ₁₀ .

As a result of this detection, the input side of the inverter 51 becomes a high level, and the output level of the inverter 51 becomes a low level. As a result, the transistor 53
is cut off, resistor R ₂₀ against capacitor C ₃₀ , resistor
Charging takes place via R ₃₀ and the above capacitor C ₃₀
terminal voltage increases. When the voltage at the terminal of capacitor _C30 increases to exceed the Zener voltage of Zener diode _D20 , transistor 54 becomes conductive and a negative pulse is generated at the reset terminal of flip-flop FF. The flip-flop 13 is reset by this negative pulse, and the output of the output terminal Q of the flip-flop FF becomes low level, the transistor 42 forming the oscillator 29 is cut off, oscillation is stopped, and unnecessary carrier waves are sent to the upstream. can be reliably prevented.

〔Effect of the invention〕

As described above, according to this invention, bidirectional
In CATV, etc., it is possible to prevent subscribers from sending unnecessary carrier signals to the center outside of the data period, and by sending unnecessary carrier waves to the upstream, data transmission of other subscribers who have requested communication can be prevented. Therefore, it is possible to provide a two-way CATV system that can avoid situations that cause interference.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an overview of an embodiment of a two-way CATV according to the present invention, FIG. 2 is a circuit diagram showing a conventional two-way CATV, and FIG. 3 is a circuit diagram showing an example of a two-way CATV according to the present invention. FIG. 2 is a circuit diagram showing an example. 20... Subscriber terminal 28... Carrier wave transmission time setting circuit 25... CPU 29... Oscillator 3
0... Multiplier.

Claims (1)

[Claims] 1. In a two-way CATV that performs two-way communication between a center and a plurality of subscribers via a communication line, data to be sent to the communication line is set,
a data processing means for generating a data transmission request signal for a predetermined period of time; an oscillator for generating a carrier wave; a modulating means for modulating the data by applying the carrier wave from the oscillator to an input terminal; and a modulating means for modulating the data; a circuit for controlling transmission of the carrier wave, the circuit comprising: first control means for operating the oscillator for the predetermined period in response to the data transmission request signal; and a circuit for detecting data transmission from the modulation means; and a second control means for stopping the application of the carrier wave to the modulating means when the carrier wave is transmitted for a predetermined period of time. A two-way CATV characterized in that communication of other subscribers is prevented from being hindered due to transmission of unnecessary carrier waves on the communication line.