JPH0370236A - Terminal equipment for digital communication - Google Patents

Abstract

PURPOSE:To prevent concentration of collected noise onto a cable by bringing an oscillator of a transmission means in a terminal equipment into the normal operating state just before the transmission is started after an operation stabilizing period. CONSTITUTION:When the necessity of reply is reconfirmed, a control section turns on switches 25, 27 to start data transmission. When the data transmission is finished, the transmission operation is finished, the reception function is restored and the reception standby state is caused. When it is decided that no reply is required and an error of a received data is detected, the control section activates an oscillation circuit 23. In the case of the operation above, the oscillation circuit 23 is activated only when the date transmission is required and the actual data transmission is started after the oscillation is made stable. Thus, the oscillation circuit 23 is activated only as required, then collected noise on a line is evaded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a data communication terminal device useful as a terminal for, for example, a cable television system (hereinafter referred to as a CATV system).

(Prior Art) A CATV system has a configuration in which a large number of terminals are connected to a center (central office) via cables, and the plurality of terminals share one line. In response to polling from the center, the called terminal modulates a carrier wave with data and sends it out to the line.

FIG. 3 shows the basic configuration of a conventional terminal.

A receiver 1 receives a signal from the center, and a data processing and control unit 2 judges the content of the received data. If this terminal is being called, switch 4 is controlled. Then, the output carrier wave of the oscillation circuit 3 is transmitted to the modulator (for example, F
SX modulator) 6. Further, the data processing and control section 2 supplies transmission data to the modulator 6 via the signal conversion section 5. The output modulation signal of the modulator 6 is transmitted to an excitation amplifier 7,
A transmission signal is sent out to the cable via the power amplifier 8.

FIG. 4 also shows an example of a conventional terminal. Although the configuration is almost the same as that shown in FIG. 3, this example differs in that the switch 3a of the oscillation circuit 3 is turned on when starting transmission. Since the other parts are the same as those in FIG. 3, they are given the same reference numerals as in FIG. 3 and their explanation will be omitted.

The terminal shown in FIG. 3 has a configuration in which the oscillation circuit 3 for generating a carrier wave is always in operation. According to this terminal, there is a problem in that oscillation leakage concentrates on the same frequency and appears as collective noise on the line. Therefore, measures are taken to suppress the leakage level of the oscillation signal as much as possible on the transmitting side, but this is insufficient. For this reason, it is necessary to limit the number of terminals connected on the same line to reduce the level of collective noise, depending on the relationship between the capture ratio on the receiving side and collective noise.

High levels of collective noise impede demodulation at the center.

FIG. 4 shows a terminal in which the switch 3a is controlled to operate the oscillation circuit 3 only when it is necessary to send data in order to avoid the above-mentioned problems. However, according to this terminal, there is a problem that it takes time for the oscillation operation to stabilize after the oscillation circuit 3 is turned on, and the communication speed becomes slow, that is, the communication efficiency of the overall system deteriorates. Further, there is a problem in that spurious signals are emitted during an unstable period of the oscillation circuit 3, which adversely affects signals in other frequency bands.

(Problems to be Solved by the Invention) As described above, in conventional terminals, if the oscillation circuit 3 that generates a carrier wave is always operated, there is an adverse effect due to collective noise, and the oscillation circuit 3 is operated only when necessary. However, there are problems in that the communication efficiency of the overall system deteriorates and spurious signals during unstable periods adversely affect signals in other frequency bands.

SUMMARY OF THE INVENTION An object of the present invention is to provide a digital communication terminal device that prevents collective noise from occurring and does not reduce communication efficiency.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a communication system in which a plurality of terminals share the same line, in which the terminal includes an oscillator for creating a carrier wave and a carrier wave for modulating the carrier wave with transmission data. an amplifier for transmitting the modulated output of this modulator to the center, and receives and processes polling signals and data from the center, and controls its own transmitter according to the data content. data processing and control means for controlling the oscillator from off to on in response to polling from a center, and means for supplying the modulator output to the amplification means when the operation of the oscillator is stable; It is equipped with the following.

(Function) By the above means, the oscillator of the transmission means from the terminal is brought into a normal operating state immediately before transmission starts and after a period of stable operation, so collective noise is concentrated on the cable. It will no longer be done.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The terminal in Figure 1 is
For example, this is an example of a terminal in a CATV system capable of two-way communication, and when it is designated by polling from the center, it starts responding. The transmission signal from the center is received by the receiver 21, and the received data is
It is introduced into the data processing and control section 22. The data processing unit and control unit 22 determines received data and performs various controls inside the terminal.

On the other hand, this terminal is equipped with a transmission function.

That is, the carrier wave of the oscillation circuit 23 is supplied to the modulator 24. Transmission data from the data processing and control section 22 is input to the modulator 24 via two signal conversion sections. In the modulator 24, the carrier wave is subjected to FSX modulation, for example, according to the data. The modulated output is supplied to an excitation amplifier 26 via a switch 25 to become a transmission frequency, and this output is input to a power amplifier 28 via a switch 27, where it is amplified and led out to a cable.

Here, the oscillation circuit 23 is turned on when necessary, and the switch 23a for this purpose is controlled by a control signal from the data processing and control section 22. . Next, switches 25 and 27 are provided between the modulator 24 and the excitation amplifier 26 and between the excitation amplifier 26 and the power amplifier 28, respectively. After reaching a stable state, it is turned on and controlled to configure the transmission signal path. The water 25 and 27 are also controlled by control signals from the data processing and control section 22.

FIG. 2 shows the data format (FIG. 2 (A)) received by the data processing and control unit 22, the operating period of the oscillation circuit 23 that operates in response to the data format, and the excitation and power amplifier 2.
6.28 operation period and data transmission period are shown in chronological order. Further, FIG. 3 shows an example of a flowchart in the data processing and control section 22. The operation will be explained below with reference to FIGS. 2 and 3.

First, the data processing and control unit 22 receives a polling signal from the center, inputs data, and stores it in a buffer memory. If the address content of the data specifies the own terminal, first switch 23a
is controlled to turn on the oscillation circuit 23 (steps Sl, S
2. S3).

Next, the command is read and it is determined whether a response is required from the center (steps S4 and S5).

If a response is required, read the checksum and determine whether there are any abnormalities in the received data in steps S6 and S7.
), if there is no response, it is determined whether a response is necessary again (step S8). When the necessity of a response is reconfirmed, the control unit turns on the switches 25 and 26 and starts transmitting data (step 39, 5IO). When the data transmission is completed, the transmission operation is completed, the reception function is restored, and the reception standby state is entered (step Sll, 512). If it is determined in steps S5 and S8 that there is no need for a response, and if an error in the received data is detected in step S7, the control section turns off the oscillation circuit 23 and ends the transmission operation.

When operating as described above, the oscillation circuit 23 is turned on only when data exit is necessary, and actual data transmission is started after the oscillation operation is stabilized.

As a result, since the oscillation circuit 23 is turned on only when necessary, collective noise on the line is eliminated compared to the conventional system in which it is turned on all the time. This means that
This leads to the ability to reduce reception errors at the receiver on the center side. This also means that it is easy to increase the number of terminals connected to the same line.

Further, after the operation of the oscillation circuit 23 is stabilized, data output and operation of the power amplifier etc. are started.

Therefore, the data transmission period of one terminal as seen from the line is T1 to T2 in FIG. 2, and the unstable period of the oscillation circuit does not play any role. When considering communication efficiency in a line that shares many terminals, T1 to T
2, it is sufficient to consider the period, and the efficiency does not decrease compared to the conventional system shown in FIG. in this way,
According to this terminal, it is possible to obtain secure data communication without reducing efficiency.

In the above embodiment, the switches 25 and 27 are provided on the input sides of the excitation amplifier 26 and the power amplifier 28, respectively, but the switch 25 and 27 are not limited to this, and the switches 25 and 27 are provided on the input sides of the excitation amplifier 26 and the power amplifier 28, respectively. The i-source may be turned on and off, or an attenuator in the signal path or a switch in the high frequency path may be controlled.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain a digital communication terminal device that prevents collective noise from occurring and does not reduce communication efficiency.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a timing chart shown to explain the operation of the terminal device in FIG. 1, and FIG. 3 is a diagram showing the operation of the terminal device in FIG. 1. Flowcharts shown to explain an example of operation, and FIGS. 4 and 5 are configuration explanatory diagrams of a conventional terminal device. 21... Receiver, 22... Data processing and control unit,
23...Oscillation circuit, 23a...Switch, 24...
- Modulator, 25. 27... Switch, 26... Excitation amplifier, 28... Power amplifier.

Claims (1)

[Claims] In a communication system in which a plurality of terminals share the same line, the terminal includes: an oscillator for creating a carrier wave, a modulator for modulating the carrier wave with transmission data, and a modulation output of the modulator. an amplifying device for transmitting data to the center; and a data processing and control means that receives polling signals and data from the center, processes the data, and controls its own transmitter according to the data content, for data communication, comprising means for controlling the oscillator from off to on in response to polling, and means for supplying the modulator output to the amplifying means when the operation of the oscillator is stabilized. Terminal device.