JPS63119330A - Level adjusting device - Google Patents

Abstract

PURPOSE:To uniformize the level of a reception high frequency signal by adjusting the level of a transmission high frequency signal in the terminal side to which the signal level measured by a head end frequency converter part is given as information. CONSTITUTION:The level of the up high frequency signal transmitted from each data terminal is measured by a level measuring circuit 6 provided in a frequency converter part 4. The measured level is reported back to each terminal by a device consisting of a microcomputer, a communication LSI, or the like. Each terminal to which its own transmission level is reported back controls a level adjusting attenuator by the microcomputer to set the transmission signal to a proper level and tries this level adjustment several times. Since it is unnecessary to provide a pilot signal generator in the frequency converter side and to provide each data terminal with a pilot signal detector, the circuit constitution of the data terminal is simplified and the cost is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to data communication between a plurality of data terminals using bidirectional CATV, and in particular detects collisions of data transmitted from data terminals. The present invention relates to a signal level adjustment device suitable for various cases.

[Conventional technology]

As office equipment becomes more diverse and sophisticated, LAN
(Local area network: LocalArea
There is an emerging need for transmitting multiple information in networks. In traditional data-centered LANs, images (
In particular, it has been difficult to communicate (videos), so a system that uses CATV technology to transmit a variety of information such as data, audio, and videos is being considered.

However, the main purpose of the CATV system was originally to transmit television signals, and the subscriber terminal signal level was 60 to 8.
5 clBμ is an acceptable range. Therefore, the signal level will vary considerably depending on the location of the subscriber terminal.

On the other hand, using the CATV system, an international standard LAN
C8MA/CD (Carrier
5ense Multiple Access wit
In order to perform data communication using high-frequency signals by means of hColIsionDetaction), it is necessary that the received signal level difference of the high-frequency signals from any data terminal be within 6 dB (empirical value). This is due to the following reasons.

Collision detection (two or more data terminals transmitting data at the same time) is a very important function in C8MA/CD. However, if the level difference between high-frequency signals is 6 dB or more, the weaker data signal is ignored, so even if a collision occurs, it cannot be detected.
In order to perform C8MA/CD data communication using the system, it is essential to adjust the level of the high frequency signal.

As a method of level adjustment of high frequency signals, for example,
As shown in Publication No. 9-115633, a reference level signal (pilot signal) is sent from a head end that includes a frequency converter, and the data terminal that receives it adjusts the gain of the receiving amplifier so that the level becomes an appropriate value. A known method is to adjust the gain of the transmitting amplifier so that the signal level of the test signal transmitted from the data terminal when it returns via the frequency converter is equal to the reference level. ing. However, this method requires a pilot signal generator on the frequency converter side and also requires a device to detect this pilot signal at each data terminal, making the circuit configuration of the data terminal complex and increasing costs. be.

[Problem that the invention seeks to solve]

In order to utilize a bidirectional CATV system for data communication, it is an object of the present invention to provide information on the signal level measured at one frequency converter section so that the level difference of high frequency signals received at any data terminal does not exceed 6 dB. An object of the present invention is to provide a level adjustment device that adjusts the level of a transmitted high-frequency signal on a given terminal side and, as a result, equalizes the level of the received high-frequency signal.

[Means for solving problems]

When a specific data terminal receives a signal coming from any other data terminal, in order to prevent the level difference of the received high-frequency signals from exceeding 6 dB, it is necessary to 2. Adjust the level on the transmitting side of each data terminal so that the level of the upstream high-frequency signal from the data terminal remains constant regardless of which data terminal the upstream high-frequency signal came from 1. Originally, the reception level at the data terminal We will explain why the level should be adjusted using a frequency converter when the difference should be made into an intermediate layer. In two-way CATV, the logical transmission path is divided into uplink high-frequency signals and downlink high-frequency signals, and the amount of attenuation of the downlink high-frequency signals to a specific data terminal that is looped back at the frequency converter depends on each data terminal. This is because it does not depend on whether it is an upstream high-frequency signal transmitted from.

Therefore, in the present invention, the head-end frequency converter includes a measuring circuit for high frequency signals, a microcomputer that reads the signals and notifies each data terminal, and a communication function that notifies each terminal.

Level adjustment for performing C8MA/CD on broadband LAN is achieved by installing a device on each data terminal side that adjusts the level of the sending signal several times based on the informed level and adjusting it to the appropriate level. It is distinctive in that it is made to do.

[Effect]

As mentioned above, the level measuring circuit placed in the frequency converter section measures the level of the upstream high frequency signal transmitted from each data terminal. Next, a device composed of a microcomputer, a communication LSI, etc. notifies each terminal of the measured level as information. Each terminal that has been notified of its own output level controls the level adjustment attenuator with a microcomputer to adjust the output signal to an appropriate level.

Try this several times.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the configuration of a data communication system using a two-way CATV system embodying the present invention. The center equipment includes an antenna 1 that receives general broadcast waves, an independent program broadcaster 2 consisting of a VTR or the like for sending programs different from the broadcast waves to the terminal side, and amplifies the broadcast signals from the antenna 1 and the broadcaster 2. or the head end group [3] which is modulated and sent to the terminal side via the transmission system, and the transmission data from the computers 13a, 13b...13n installed on the terminal side as upstream high frequency signals, that is, the first high frequency signal. and a frequency converter 4 for converting the frequency of the signal F into a second high frequency signal FH and sending it back to the terminal side via the transmission system.

A synthesizer 5 that combines and distributes the signal from the headend device 3 and the signal from the frequency converter 4, a level measuring device that measures the level of the upstream high frequency signal input to the frequency converter, and a level measuring device that measures the result. It consists of an attached device 6 of a frequency converter which has a communication function to notify each terminal as information.

The transmission system is a trunk line 7a consisting of a coaxial cable.

7b... and branch lines 9a, 9b, 9c...
・9n and lead-in line 11a, flb...lln, 1
2 and a bidirectional trunk amplifier 8a...9 branch amplifiers 10a, 10b...Ion. Transmits high frequency signals to center equipment.

On the terminal side, computers 13a, 13b...1
3n are lead-in lines 11a from the branch amplifier, respectively.

11b...connected to lln. Furthermore, the television receiver 14 of the original CATV system is also connected to the lead-in line 12, and the broadcast waves received by the antenna 1 of the center equipment and the programs of the independent program broadcaster 2 can be viewed and viewed.

FIG. 2 shows an example of the configuration of the frequency converter 4 that converts an upstream high frequency signal from a terminal into a downstream high frequency signal.

The upstream high frequency signal Ft input from the synthesizer 5 to the frequency converter is amplified by an amplifier 41, mixed with a signal from a local oscillator 42 by a mixer 43, and then an intermediate frequency is generated. The intermediate frequency is extracted by a bandpass filter 44, amplified by an intermediate frequency amplifier 45, and then sent to a demodulation circuit 4.
6, it is converted into a digital signal. Further, the output from the low-pass filter 40 is input to a level detector 52, and is further used to control the variable attenuator 47 via an amplifier 53. These circuits allow the amplitude of normal digital data to be varied depending on the magnitude of the input level.

When performing this level adjustment, each data terminal that wants to perform level adjustment sends data to the communication function of one frequency converter. That is, the communication function 62 has an address, and each data terminal sends data in the same way as when communicating between terminals. When the microcomputer 61 is notified of the need for level measurement through the communication function, it operates the level measuring device 63, learns the level of the upstream high-frequency signal at the frequency converter section, and converts it into data to send to each data terminal. Notify me by return. Each terminal adjusts the output level based on the notified information.

FIG. 3 shows an example of the configuration of the computer 13a provided on the terminal side.

The processing device 139 is composed of a microcomputer, etc.
Performs data processing, communication control, etc. Data sent from the processing device 139 to the other computers 13a, 13b, . This first high frequency signal FL is sent to the drop-in line 11a via a line 133, a branching filter 132, and a zero branching filter 13.
2 branches the first high frequency signal FL and the second high frequency signal.

A second high-frequency signal FH sent from the center equipment via the transmission system lead-in line 11a is applied to a demodulation circuit 136 via a branching filter 132 and a line 134.

The demodulation circuit 136 has a function of detecting the presence or absence of the second high frequency signal FH and a function of demodulating the second high frequency signal into data, and outputs it to the processing device 139 via a line 138.

The processing device 139 receives the demodulated data and does not take in the data if it is addressed to another station. Also, if it receives data informing it of a collision, it immediately stops transmitting.

In this case, an attenuator 131 is placed in the part where data is sent from the duplexer 132 to the transmission line 11a, and a level measurement circuit placed in the frequency converter section measures the level of the upstream high frequency signal sent out. After being notified of this, the microcomputer 139 controls the controller 140,
A feature is that the transmission level can be adjusted by an attenuator 131.

FIG. 4 is a flowchart showing the operation of the frequency converter section and the microcomputer on the terminal side.

The frequency converter waits to see if the packet is received for its own station (step 71). If it is not addressed to its own station, it directly converts the frequency (step 72). If it is for its own station, it measures the level. Steps 73- 75) Read the level (step 76), use the level as information (step 77), perform carrier sense to make sure that no other data terminal is using the line (step 78), and send the data.Step 79 ), notifies each terminal of the signal level.

On the data terminal side, if you want to adjust the level 1
Send data to the frequency converter (Step 80) After receiving a packet from the frequency converter (Step 87)
) The level information therein is read (step 82), and if the level is within the allowable range, the adjustment is completed (step 83).
), and if not, make adjustments based on the level information (steps 84-86) and try this several times.

According to this embodiment, there is no need to provide a pilot signal generator on the frequency converter side, and there is no need for a device to detect this pilot signal at each data terminal.
This has the effect of simplifying the circuit configuration of the data terminal and lowering costs.

〔Effect of the invention〕

According to the present invention, there is no need to provide a pilot signal generator, which was conventionally placed on the frequency converter side, as described above.
In addition, since it is no longer necessary to provide a circuit for detecting this pilot signal in each data terminal, there is a possibility of cost reduction due to the simplification of the level adjustment method. It is possible to adjust the received level of the transmitted signal by the level measured by a frequency converter section in the head end.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a broadband LAN in a two-way CATV system that is one embodiment of the present invention, Fig. 2 is a block diagram of a frequency converter that converts uplink signals from terminals into downlink signals, and Fig. 3 is a block diagram of a frequency converter that converts uplink signals from terminals into downlink signals. FIG. 4 is an operational flowchart of the microcomputer in the frequency converter and the microcomputer of the terminal computer. 1...Antenna, 2...Independent program broadcaster, 3...
Head end, 4... Frequency converter, 5... Synthesizer, 6... Level measuring device, 7... Main line, 8... Main line amplifier, 9... Branch line, 10... Branch amplifier, 1
1... Lead-in line, 13... Computer, 14...
TV, 40...Low pass filter, 41...Amplifier, 42...Local oscillator. 43...Mixer, 44...Band pass filter, 4
5... Intermediate frequency amplifier, 46... Demodulation circuit, 47
... variable attenuator, 48 ... bypass filter, 49
...Amplifier, 50...Band pass filter, 51.
... Modulation circuit, 52 ... Level detector, 53 ... Amplifier, 61 ... Microcomputer, 62 ... Level measuring device,
131... Attenuator, 132... Duplexer, 13
5... Modulation circuit, 136... Demodulation circuit, 139...
・Microcomputer. No. 4

Claims (1)

[Claims] 1. Utilizing a bidirectional CATV network, the data terminal consists of a head end as a center device including a frequency converter, a transmission line connected to the head end, and a plurality of data terminals connected to the transmission line. In a data communication system that uses different frequencies for an upstream high-frequency signal from to the headend and a downstream high-frequency signal from the headend to the data terminal that has been converted by the frequency converter, an in-headend frequency converter is used. A circuit for measuring the level of the upstream high-frequency signal and a device for reading the level and notifying the level to the data terminal that sent the upstream signal are installed in the section, and the data terminal side uses the notified information to adjust the level of the transmitting side signal to an appropriate level. A broadband LAN characterized by being equipped with a device for adjusting a transmission level to match the value.
level adjustment device.