JP2002185556A - Modulation agile method and up modulation agile circuit of communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the state of communication by speedily shifting to a modulation method by which the impact of up merging noise in a transmission channel is small. SOLUTION: An up tuner circuit 10 receives up data modulated by a terminal. The noise level in output signals S10 from the tuner circuit 10 is measured by an up noise level measuring circuit 40. A modulation agile judging circuit 50 outputs judgment signals S50 according to the noise level. When the noise level is high, a message requiring the stop of transmission of up data is prepared by a terminal message generating circuit 60 and the terminal is notified through a down data multiplexer circuit 80 and down data transmission modulating circuit 30. A modulation selecting circuit 70 selects the modulation method for change to be used by the terminal. The result of selection is also transmitted to the terminal and the modulation method of up data is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an upstream modulation agile method and an upstream modulation agile circuit in a communication device such as a center communication control device of a CATV communication system.

[0002]

2. Description of the Related Art In recent years, the transmission path of a CATV (cable television) system has been connected to a terminal device located at home, and downstream communication from the center communication control device to the terminal device and center communication control from each terminal device have been performed. Attention has been paid to high-speed communication using a transmission path in two-way communication including upstream communication to a device. In order to provide communication services, it is necessary to improve communication quality. However, the upstream ingress noise of the CATV transmission line often interferes with upstream communication (reception), and communication may be interrupted by the influence of the noise. The upstream ingress noise is obtained by accumulating diving noise generated in the vicinity of the terminal device in the vicinity of the center communication control device.
And it is difficult to remove. Such a problem exists not only in the CATV system but also in other communication devices that perform two-way communication.

[0003]

As a method for preventing communication disturbance due to upstream ingress noise and maintaining a good communication state,
For example, a frequency agile method described in JP-A-2000-69443 is known.

This frequency agile method monitors upstream inflow noise and, when detecting that communication quality in an upstream frequency band is degraded by the upstream inflow noise, quickly changes the upstream frequency band to a band with less noise. (Agile)
It is a method to do. However, this frequency agile method suffers if there is no changeable frequency band. Such a problem occurs not only in the CATV system but also in other communication systems that perform two-way communication.
Inherent.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and prevents a communication apparatus such as a CATV system from interrupting upstream communication due to upstream ingress noise and maintaining a good communication state. The purpose is to provide.

[0006]

According to a first aspect of the present invention, a terminal device receives uplink data modulated using a predetermined modulation method via a transmission line. At the same time, a communication device that transmits downlink data to the terminal device via the transmission path employs the following up-modulation agile method of the communication device.

That is, the noise level of a signal provided from the terminal device via the transmission line is measured, and when the noise level exceeds a predetermined value, an instruction is issued to the terminal device via the transmission line. The point is that the modulation method used by the terminal device is changed. By adopting such a method, during normal operation, the terminal device modulates uplink data with a predetermined modulation method and transmits the data to the communication device, but the communication device measures the noise level of the received signal. . As a result of the measurement, if the noise level exceeds a predetermined value, an instruction is given to the terminal device, and the modulation method used by the terminal device to modulate uplink data is changed. Therefore, communication using uplink data modulated by a modulation method different from the predetermined modulation method is performed, and the uplink communication is not interrupted.

According to a second aspect of the present invention, in the upstream modulation agile method of the first aspect, the following is performed. That is, when the noise level exceeds a predetermined value, a first stop process of giving an instruction to stop the transmission of the uplink data to the terminal device via the transmission path, and the first stop process, During the period when the terminal device is stopping the transmission of the uplink data, the terminal device has been instructed to change the modulation scheme used for the transmission of the uplink data from the predetermined modulation scheme to another modulation scheme, and the instruction has been stopped. An instruction to restart transmission of uplink data is created, a modulation scheme change process of transmitting these instructions to the terminal device via the transmission path, and the terminal device transmits the uplink data using the changed modulation scheme. When the period of the modulated transmission is equal to or longer than a predetermined time, a second stop process for instructing the terminal device to stop transmission of the uplink data via the transmission path, and the second stop process Terminal During the period in which the terminal device stops transmitting the uplink data, the terminal device causes the modulation method used for the uplink data to return to the predetermined modulation method, and restarts the transmission of the stopped uplink data. And a modulation scheme return process of creating these instructions and transmitting these instructions to the terminal device via the transmission path.

By taking such a method, the first
The terminal device stops transmission of uplink data by the stop processing of. The modulation method used in the terminal device is changed during this period, and the modulation method is returned to the original predetermined modulation method during the period when the terminal device stops transmitting uplink data in the second stop processing. Therefore, the modulation scheme can be changed without deteriorating the quality of uplink data transmission.

In the third invention, the following method is employed in the upstream modulation agile method of the first or second invention. That is, in the modulation scheme change processing, one modulation scheme is selected from a plurality of modulation schemes, and the noise level of the signal when the terminal apparatus modulates the uplink data using the selected modulation scheme is set. The process of investigating is repeated by changing the selection of the modulation method until the noise level becomes less than the predetermined value, and the terminal device uses the modulation method in which the noise level becomes less than the predetermined value when the terminal device transmits the uplink data. The point is to set the modulation method. By adopting such a method, an optimal modulation method that can be used is selected from a plurality of modulation methods, and uplink data is modulated using the selected modulation method.

According to a fourth aspect of the present invention, in the upstream modulation agile method according to any one of the first to third aspects, the communication device may constitute a cable television system in cooperation with a plurality of the terminal devices. Make a summary. When such a method is adopted, a CA that provides services to a plurality of terminal devices is provided.
It is more likely that disconnection of uplink data transmitted by the terminal device due to ingress noise, which is a problem in the TV system, can be prevented.

According to a fifth aspect of the present invention, the upstream modulation agile circuit has the following configuration. That is, a circuit provided in a communication device for receiving, via a transmission line, uplink data modulated by a terminal device using a predetermined modulation scheme, and transmitting downlink data to the terminal device via the transmission line. Receiving means connected to the transmission path for receiving a signal transmitted from the terminal device; demodulating means for demodulating an output signal of the receiving means; and noise for measuring a noise level of an output signal of the receiving means. A measuring unit, a signal control unit that reads a noise level measured by the noise measuring unit at a predetermined timing, and outputs a determination signal indicating whether the noise level exceeds a predetermined value, and the terminal based on the determination signal. When the apparatus detects that the noise level in a signal transmitted using the predetermined modulation scheme exceeds a predetermined value, the terminal apparatus refers to the determination signal and sets the terminal apparatus to the predetermined level. A modulation scheme selecting means that can be used in place of the modulation scheme, and a modulation scheme selecting means for selecting the predetermined modulation scheme when a certain time has elapsed since the selection of the modulation scheme, and the modulation scheme Message creating means for creating a message corresponding to each of the changing modulation scheme and the predetermined modulation scheme selected by the selecting means, and control data transmitting means for sequentially transmitting the message to the terminal device via the transmission path The gist is to have

By adopting such a configuration, during normal operation in which the terminal device modulates and transmits uplink data by a predetermined modulation method, the uplink data is received by the receiving means via the transmission path, and the demodulation means Is demodulated. Here, the noise level in the output signal of the receiving means is measured by the noise measuring means, and the signal control means outputs a judgment signal corresponding to the noise level. When the noise level of the signal transmitted by the terminal device using the predetermined modulation scheme exceeds a predetermined value, a modulation scheme for changing in place of the predetermined modulation scheme is selected by modulation scheme selection means, and the selected change mode is selected. A message corresponding to the modulation scheme is created by the message creating means. This message is transmitted from the control data transmitting means to the terminal device, and the terminal device uses the modulation scheme for change.

[0014] When a period during which the terminal device modulates the uplink data using the change modulation scheme becomes a fixed time,
The modulation scheme selection means selects a predetermined modulation scheme, and a message corresponding to the predetermined modulation scheme is created by the message creation means. This message is transmitted to the terminal device by the control data transmitting means, and the terminal device again uses the predetermined modulation method.

According to a sixth aspect of the present invention, in the upstream modulation agile circuit according to the fifth aspect of the present invention, the message creating means performs processing for selecting the change modulation method based on the determination signal. Detecting, before the start thereof, a function of generating a stop message for stopping the transmission of the uplink data to the terminal device and notifying the terminal device via the control data transmitting means and the transmission path, When creating a message corresponding to the modulation method, a function to create a restart message to restart the transmission of the uplink data to the terminal device, and to notify the terminal device via the control data transmission means and the transmission path, When a certain period of time has elapsed since the modulation method selection means selected the change modulation method, the stop message is created and the control data Data transmission means and the function of notifying the terminal device via the transmission path, and when creating a message corresponding to the predetermined modulation scheme, the control data transmission means and the transmission path by creating the restart message And a function of notifying the terminal device via the terminal device.

By adopting such a configuration, when the modulation scheme selecting means performs the process of selecting the changing modulation scheme based on the determination signal, the transmission of the uplink data to the terminal apparatus is stopped before the start. A stop message is generated and sent to the terminal device. When the selection of the modulation scheme for change is completed, a message corresponding to the modulation scheme for change and a restart message for starting transmission of uplink data are created and provided to the terminal device. As a result, no uplink data is transmitted during the period in which the change modulation scheme is selected. Similarly, no uplink data is transmitted during a period when the modulation scheme used by the terminal device is switched from the modulation scheme for change to the predetermined modulation scheme.

According to a seventh aspect of the present invention, in the upstream modulation agile circuit according to the fifth or sixth aspect, the following configuration is provided. That is, a modulation table storing a plurality of information of the modulation scheme for change and information indicating the predetermined modulation scheme,
By the determination signal, when it is determined that the predetermined modulation method used by the terminal device is inappropriate, sequentially scan the change modulation method stored in the modulation table, the output signal of the receiving means A pointer control circuit that selects a modulation scheme for which the noise level does not exceed a predetermined value as a modulation scheme to be used by the terminal device thereafter; and a fixed time after the pointer control circuit selects the modulation scheme for change. And the pointer control circuit selects the predetermined modulation scheme as a modulation scheme to be used by the terminal device thereafter when the return timer counts the fixed time. Configuration.

By employing such a configuration, when it is determined from the determination signal that the predetermined modulation scheme used by the terminal device is inappropriate, the plurality of changing modulation schemes stored in the modulation table are sequentially changed. A scanning modulation method is selected in which the noise level of the output signal of the receiving means does not exceed a predetermined value. When the return timer measures a certain time, the pointer control circuit selects a predetermined modulation method. According to an eighth aspect of the present invention, in any one of the fifth to seventh upstream modulation agile circuits, the following configuration is provided. That is, the signal control means includes: a first timer for generating a first timing signal at a constant interval; a second timer for generating a second timing signal at a shorter interval than the first timer; During a period in which the terminal device is modulating the uplink data with the predetermined modulation method, the noise level measured by the noise measurement means is read in synchronization with the first timing signal, and the modulation method selection means During the period for selecting the modulation scheme for change, a noise level monitoring control circuit that reads the noise level in synchronization with the second timing signal is compared with a noise level read by the noise level monitoring control circuit and a threshold value. And a threshold value judgment circuit for outputting the judgment signal.

By adopting such a configuration, the noise level monitoring and control circuit performs the noise measurement in synchronization with the first timing signal during the period when the terminal device is modulating the uplink data by the predetermined modulation method. The noise level measured by the means is read, and the noise level is read and output in synchronization with the second timing signal during a period in which the modulation scheme selection means selects the modulation scheme for change. Therefore, during the period until the change modulation method is selected, the noise level is measured at smaller intervals than in the normal operation.

[0020]

FIG. 1 is a block diagram showing a configuration of a modulation agile circuit according to an embodiment of the present invention. This modulation agile circuit constitutes a transmission / reception unit of a communication control device installed in a CATV communication center, monitors a noise level in an operating uplink frequency band, and prepares in advance when it is determined that the noise level cannot be operated. Has the function of changing to the changed modulation method. The transmission / reception unit of the communication control device includes:
An uplink tuner circuit 10 which is a receiving unit for receiving a signal from a terminal device (not shown) via a transmission path, an uplink data demodulation circuit 20 which is a demodulation unit connected to the uplink tuner circuit 10, and transmits data to the terminal device. And a downstream data transmission modulation circuit 30. The modulation agile circuit includes an upstream tuner circuit 10 to a downstream data transmission modulation circuit 30 and an upstream noise level measurement circuit 40 which is a noise measurement unit connected to an output terminal of the upstream tuner circuit 10.
And a modulation agile determination circuit 50 as signal control means
A terminal control message generating circuit 60 as a message creating means;
And a downlink data multiplexing circuit 80 as a control data transmitting means.
And it is comprised.

A terminal control message generation circuit 60 and a modulation selection circuit 70 are connected to the output side of the conversion agile determination circuit 50. The downlink data multiplexing circuit 80 is connected to the output side of the terminal control message generation circuit 60, and the downlink data transmission modulation circuit 30 is connected to the output side of the downlink data multiplexing circuit 80. An output terminal of the modulation selection circuit 70 is connected to the modulation agile circuit 50, the terminal control message generation circuit 60, and the uplink data demodulation circuit 20. The functions and configuration examples of the circuits 40 to 80 will be described below.
The upstream noise level measuring circuit 40 uses the interval between the upstream burst signals from the terminal device to output the output signal S of the upstream tuner circuit 10 when the upstream data signal SDu does not exist.
It has a function of measuring noise levels in ten frequency bands. FIG. 2 shows the conversion agile determination circuit 50 in FIG.
FIG. 3 is a block diagram illustrating a configuration example of FIG.

The conversion agile determination circuit 50 determines whether or not the noise level S40 output from the upstream noise level measurement circuit 40 exceeds a predetermined value, and outputs a determination signal S50. A circuit 51, a first timer 52, a second timer 53, and a timer 54
And a threshold determination circuit 55. The noise level monitoring control circuit 51 supplies a read signal (not shown) to the upstream noise level measurement circuit 40 at a predetermined timing, captures the noise level measurement result S40, and converts the captured measurement value S40 into a threshold value determination circuit 55. Output to The threshold determination circuit 55 determines the acquired noise level as
Compared with a predetermined threshold value, if it is larger than the threshold value, it is determined that it is too large, and if it is smaller than the threshold value, it is determined that it is too small. Monitoring control circuit 51, terminal control message generation circuit 6
0 or output to the modulation selection circuit 70.

In the normal operation state, the noise level monitoring and control circuit 51 outputs the timing signal S52 output from the timer 52.
The measurement result S40 of the noise level is read at a timing synchronized with the timing signal S. However, while the modulation method is being changed, the measurement result S40 is read at a timing synchronized with the timing signals S54 and S55 output from the timer 53 or the timer 54. Specifically, the noise level value monitoring control circuit 51 outputs the determination signal S5
When 0 indicates an excessive level, the return signal S74 indicating that the original modulation scheme is to be returned is provided from the modulation selection circuit 70 in accordance with the timing of the timer 53, and the noise level measurement result is provided in accordance with the timing of the timer 54. The reading of S40 is started. The interval between the timing signals S53 output from the timer 53 is shorter than the interval between the timing signals S52 output from the timer 52, and the interval between the timing signals S54 output from the timer 54 is equal to the interval between the timing signals S52.
Is set longer than the interval. The terminal control message generation circuit 60 of FIG. 1 generates a message instructing stop of transmission of uplink data according to the determination signal S50 supplied from the modulation agile determination circuit 50, and modulates a modulation parameter given from the modulation selection circuit 70. A function of generating a message indicating a modulation method for modulating uplink data according to the number S72 and a message instructing restart of transmission of uplink data, and outputting these as a control signal S60 to the downlink data multiplexing circuit 80. have.

FIG. 3 is a block diagram showing a configuration example of the modulation selection circuit 70 in FIG. The modulation selection circuit 70 includes a pointer control circuit 71, a modulation table 72 composed of a memory, a modulation setting circuit 73, and a recovery timer 74, and converts the original modulation method used in the terminal device to another modulation method. A function to select the modulation method to change to the method,
A function of returning to the original modulation method at a predetermined timing. The pointer control circuit 71 sets the initial address value of the modulation table 72 as an initial value, and
When 50 indicates an excessive value, a function of adding 1 to the current address value and outputting the result to the modulation table 72 is provided. Also,
The pointer control circuit 70 also has a function of determining whether the address value given to the modulation table 72 is the maximum address value.

The modulation table 72 stores a plurality of modulation parameter numbers for indicating a plurality of modulation schemes in association with addresses, and stores a modulation parameter number S72 corresponding to an output address value of the pointer control circuit 71 in a modulation setting circuit 73.
Is output to the terminal control message generation circuit 60. The modulation setting circuit 73 converts the supplied modulation parameter number S72 into a modulation setting signal S73,
Output to The timer 74 sets the operation time from when the operation is resumed after the change of the modulation method to when the operation returns to the original modulation method. When the set time has elapsed, the timer 74 modulates the return timing signal S74. It has a function of supplying to the agile determination circuit 50 and the pointer control circuit 71.

It should be noted that the change of the modulation method is specifically described in QPS.
It is assumed that a modulation rate change is included in addition to a method change such as a K (Quadrature Phase Shift Keying) method or a QAM (Quadrature Amplitude Modulation) method. FIG. 4 is a flowchart illustrating an uplink modulation agile method of a communication device performed by the uplink modulation agile circuit of FIG. The modulation agile method of the communication device will be described with reference to FIG. During normal operation, the terminal device modulates the uplink data SDu using a predetermined modulation scheme set in advance and transmits the modulated data SDu to the communication control device via the transmission line L. The uplink tuner circuit 10 of the receiving unit of the communication control device selects a frequency of the uplink data SDu modulated from the terminal device, and outputs an output signal S10 to the uplink data demodulation circuit 20 and the uplink noise level measurement circuit 40. The upstream data noise level measurement circuit 40 measures the noise level of the signal S10 and outputs a measurement result S40. The upstream data demodulation circuit 20 demodulates the output signal S10 of the upstream tuner circuit 10 and outputs upstream data S20. The demodulation processing performed by the uplink data demodulation circuit 20 is set according to the modulation setting signal S73 supplied from the modulation setting circuit 73, and corresponds to the modulation processing performed by the terminal device.

In step ST1, the noise level monitoring control circuit 51 in the modulation agile determination circuit 50 controls the timing signal S5 of the timer 52 used during normal operation.
2. Read the noise level measurement result S40 in synchronization with
It is sent to the threshold value judgment circuit 55. In step ST2, the threshold value determination circuit 55 determines whether or not the measurement result S40 is larger than the threshold value, and outputs a determination signal S50. At this time, if the noise level measurement result S40 is smaller than the threshold value (NO), the noise level monitoring control circuit 51 reads the noise level measurement result S40 at the timing set by the timer 52 continuously. repeat. When the measured value S40 is larger than the threshold value (YES), the threshold value determination circuit 55 supplies the terminal control message generation circuit 60 and the pointer control circuit 71 with a determination signal S50 indicating an excessive amount.

In step ST3, the terminal control message generating circuit 60 generates a message indicating the stop of uplink transmission to the corresponding terminal device, and outputs this to the downlink data multiplexing circuit 80 as an output signal S60. The downlink data multiplexing circuit 80 converts the signal S60 into the downlink data SDd.
Multiplex. Downlink data transmission modulation circuit 30 modulates output signal S80 of downlink multiplexing circuit 80 and transmits the modulated signal to terminal equipment. Steps ST1 to ST3 described above constitute a first stop process. When the noise level is high, the terminal device stops the transmission. In step ST4 after step ST3, the pointer control circuit 71 adds 1 to the current address value (pointer value) of the modulation table 72 and outputs the result to the modulation table 72. Step ST
In 5, the pointer control circuit 71 determines whether or not the pointer value is the maximum address value. If the pointer value is the maximum address value (YES), a later-described step ST1
Move to 6. If the pointer value is not the maximum address value (NO), in step ST6, the modulation table 72 selects a modulation method corresponding to the pointer value, and outputs a modulation parameter number indicating the selected modulation method to the output signal S72. To the modulation setting circuit 73 and the terminal control message generation circuit 60.

In step ST7, the modulation setting circuit 7
3 converts the supplied modulation parameter number S72 into a modulation setting signal S73 and outputs it to the uplink data demodulation circuit 20. The uplink data demodulation circuit 20 changes the setting of the modulation scheme. That is, the demodulation method for demodulating the uplink data is changed. Further, the terminal control message generation circuit 60
The message corresponding to the modulation parameter number is sent to signal S60.
And transmits it to the terminal device via the downlink data multiplexing circuit 80 and the downlink data transmission modulation circuit 30. Thereby, the terminal device switches the modulation method on a trial basis. In step ST8, the noise level value monitoring control circuit 51 in the modulation agile determination circuit 50 reads the noise level measurement result S40 at the timing set by the timing signal S53 output from the timer 53, and in step ST9, sets the threshold value. The determination circuit 55 determines whether the measurement result S40 is larger than a threshold. If the measurement result S40 is larger than the threshold value in step S9 (NO), the process returns to step ST4, selects the next modulation method stored in the modulation table 72, and the threshold determination result becomes too small. Investigate the noise level repeatedly up to. Thus, by repeating steps ST4 to ST9, the inside of the modulation table 72 is scanned.

If the measurement result S40 is smaller than the threshold value in step S9 (YES), the noise level monitoring control circuit 51 sets the measurement result S4 at the timing of the timer 53.
0 is read, and in step ST10, the threshold value determination circuit 55 repeats the operation of determining whether the measurement result S40 is larger than the threshold value a predetermined number of times. When the noise level value is stabilized and the noise level investigation is completed (YES)
In step ST11, the terminal control message circuit 11 creates a message corresponding to the parameter number indicating the change modulation method in step ST11. Then, this is output to the downlink data multiplexing circuit 80 as an output signal S60. The downlink data multiplexing circuit 80 multiplexes the signal S60 into the downlink data SDd. Downlink data transmission modulation circuit 3
0 modulates the output signal S80 of the downlink multiplexing circuit 80 and transmits it to the terminal device. Further, the terminal control message circuit 1
In step ST12, 1 generates a message indicating resumption of uplink transmission, outputs it as a signal S60, and outputs it to the downlink data multiplexing circuit 80. The downlink data multiplexing circuit 80 multiplexes the signal S60 into the downlink data SDd. The downlink data transmission modulation circuit 30 modulates the output signal S80 of the downlink data multiplexing circuit 80 and transmits it to the terminal device.

Steps ST4 to ST at this time
Reference numeral 12 denotes a modulation scheme change process.
By ST12, the corresponding terminal device is notified of the change of the uplink modulation scheme and the restart of the uplink transmission.
The terminal device changes the modulation scheme for the uplink data, and restarts transmission of the uplink data SDu modulated by the changed modulation scheme.

After the operation is resumed, after the time set by the timer 54 has elapsed (step ST13), the process returns to step ST1. If the time set in the timer 74 of the modulation selection circuit 70 has elapsed after the restart of operation (step S14), the terminal control message generation circuit 60 stops the uplink transmission to the corresponding terminal device in step ST15. A message to be transmitted is generated and the downlink data multiplexing circuit 8
Output to 0. The downlink data multiplexing circuit 80 outputs the output signal S60 of the terminal control message generation circuit 60 to the downlink data S
Multiplex to Dd. Downlink data transmission modulation circuit 30 modulates output signal S80 of downlink multiplexing circuit 80 and transmits the modulated signal to terminal equipment. Steps ST14 and ST15 are a second stop process, whereby the terminal device stops transmitting uplink data.

In step ST16, the pointer control circuit 71 sets a pointer value to an initial value. Thereby, the modulation table 72 selects the original modulation method before changing the modulation method in step ST17. Next, when the process of step S17 is completed, the process returns to step ST7. If the noise level is smaller than the threshold value and is stable, the operation is resumed by the original predetermined modulation method.

According to the above-described embodiment, the following effects can be obtained. ○ When transmitting uplink data from the terminal device, if there is ingress noise or the like, the modulation method is changed instead of changing the transmission frequency of the terminal device. The transmission can be prevented from being interrupted. ○ When changing the modulation method, stop transmission of uplink data to the corresponding terminal device, and while changing the modulation method, check the noise level in the absence of uplink data each time. Searches for operable modulation schemes,
During the search, no uplink data from the terminal device is sent to the communication control device side. Therefore, the search for the modulation method can be executed in a short time. Further, since the modulation method used by the terminal device is changed in a state where the transmission of the uplink data is stopped, the uplink data does not deteriorate.

When investigating the noise level, communication disconnection due to authentication of the terminal device does not occur. Therefore, communication becomes possible immediately after the restart of operation. O It is not necessary to have a separate receiving circuit for noise level measurement, and unnecessary hardware is not required, and the hardware scale is small. Note that the present invention is not limited to the above embodiment, and various modifications are possible. There are the following modifications.

(1) In the above embodiment, an up-modulation agile circuit provided in a communication control device of a CATV system connected to a plurality of terminal devices via a transmission line L has been described as an example. It can be applied to other communication devices connected to the terminal device. For example, 1
The present invention can also be applied to a communication device that performs communication only with the terminal devices. Further, the present invention can be applied to a case where a system other than the CATV system is configured. By changing the modulation method, the same effects as those of the above embodiment can be obtained. (2) In the above embodiment, the threshold value determination circuit 55 determines the magnitude relationship between the threshold value and the noise level. In addition, a circuit for counting the number of times the noise level becomes larger than the threshold value is added. Alternatively, a counting condition for judging the inoperability based on the count value may be added.

(3) The modulation agile determination circuit 50, the terminal control message generation circuit 60, and the modulation selection circuit 70
Instead of a circuit configuration using hardware, it may be realized using software means using a CPU. (4) The upstream noise level measurement circuit 40 may measure the noise level from the output signal of the upstream data demodulation circuit 20.

[0038]

As described above in detail, according to the first aspect of the present invention, the modulation method is changed even if noise enters the transmission line, so that the terminal device can communicate even when there is no frequency to change. Communication of uplink data to be transmitted to the device can be secured. According to the second invention, the modulation scheme change processing is performed after the transmission of the uplink data is stopped in the first stop processing, and the modulation scheme return processing is performed after the transmission of the uplink data is stopped in the second stop processing. Since it is performed, the uplink data is not damaged. Third
According to the invention, since a modulation method that substitutes for a predetermined modulation method is selected from a plurality of modulation methods, a modulation method that is resistant to noise can be selected, and communication quality can be stably maintained.

According to the fourth aspect, since the CATV system is configured by the communication device and the terminal device, it is easy to maintain the upstream communication in the CATV system even if there is ingress noise. According to the fifth aspect, the receiving means, the demodulating means,
Noise measurement means for measuring the noise level, signal control means for outputting a discrimination signal according to the noise level, modulation method selection means for selecting a modulation method for change, message creation means, and control data transmission means Since the upstream modulation agile circuit is configured, the modulation method is changed even if noise enters the transmission line, so that even when there is no frequency to be changed, communication of the upstream data transmitted by the terminal device to the communication device is ensured. it can.

According to the sixth aspect, the message creation means creates the stop message and the restart message.
The messages are provided to the terminal. Therefore,
The modulation method of the terminal device can be changed while transmission is stopped. Therefore, the uplink data is not damaged by the modulation scheme change processing. Further, the selection of the modulation method can be performed quickly. According to the seventh aspect, since the modulation method selecting means is configured by using the modulation table, the pointer control circuit, and the return timer, the changed modulation method can be selected by scanning the change table.

According to the eighth aspect, the signal control means is constituted by the first and second timers, the noise level monitoring and control circuit, and the threshold value judgment circuit, so that the period for selecting the modulation scheme for change is provided. Since the noise level monitoring and control circuit reads the noise level using the second timing signal output at a shorter interval than the first timing signal output from the second timer, the speed at which the modulation scheme is selected can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a modulation agile circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a modulation agile determination circuit in FIG. 1;

FIG. 3 is a block diagram illustrating a configuration of a modulation selection circuit in FIG. 1;

FIG. 4 is a flowchart illustrating a flow of an uplink modulation agile method of a communication device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Up tuner circuit as reception means 20 ... Up data demodulation circuit as demodulation means 30 ... Down data transmission modulation circuit 40 ... Up noise level measurement circuit as noise measurement means 50 ... Modulation agile judgment circuit 51 as signal control means 51 ··· Noise level monitoring and control circuit 52 ··· First timer 53 ··· Second timer 55 ··· Threshold decision circuit 60 ··· Terminal control message generation circuit as message creation means 70 ··· Modulation selection circuit 71 as modulation scheme selection means ... Pointer control circuit 72 ... Modulation table 74 ... Recovery timer 80 ... Downlink data multiplexing circuit as control data transmitting means

Claims (8)

[Claims] 1. A communication apparatus for receiving, via a transmission path, uplink data modulated by a terminal apparatus using a predetermined modulation scheme, and transmitting downlink data to the terminal apparatus via the transmission path, Measure the noise level of the signal given from the terminal device via a channel, and when the noise level exceeds a predetermined value, issue an instruction to the terminal device via the transmission line, and use the terminal device An up-modulation agile method for a communication device, characterized by changing a modulation method. 2. A first stop process for giving an instruction to stop transmission of the uplink data to the terminal device via the transmission line when a noise level of a signal given from the terminal device exceeds a predetermined value. And during the period in which the terminal device stops transmitting the uplink data due to the first stop processing, the terminal device changes the modulation method used for transmitting the uplink data from the predetermined modulation method to another modulation method. And a modulation scheme change process of transmitting these instructions to the terminal device via the transmission path, and creating an instruction to restart the transmission of the suspended uplink data to the terminal device, When a period during which the uplink data is modulated and transmitted by the changed modulation scheme is equal to or longer than a predetermined time, a second instruction for giving an instruction to stop transmission of the uplink data to the terminal device via the transmission path is provided. Stop processing, and during the period when the terminal device stops transmitting the uplink data by the second stop process, the modulation method used by the terminal device for the uplink data is returned to the predetermined modulation method. An instruction and an instruction to restart transmission of uplink data that has been stopped are created, and a modulation scheme return process of transmitting these instructions to the terminal device via the transmission path is performed. Item 3. An uplink modulation agile method for a communication device according to item 1. 3. The modulation scheme changing process, wherein one modulation scheme is selected from a plurality of modulation schemes, and the signal of the signal when the terminal apparatus modulates the uplink data using the selected modulation scheme. The process of investigating the noise level is repeated by changing the selection of the modulation method until the noise level becomes less than the predetermined value, and the terminal device transmits the uplink data to the modulation method in which the noise level becomes less than the predetermined value. 3. The up-modulation agile method for a communication device according to claim 1, wherein the modulation method is set as the modulation method used at that time. 4. The uplink modulation of a communication device according to claim 1, wherein said communication device constitutes a cable television system in cooperation with a plurality of said terminal devices. Agile way. 5. A communication apparatus for receiving, via a transmission path, uplink data modulated by a terminal apparatus using a predetermined modulation method and transmitting downlink data to the terminal apparatus via the transmission path. A circuit connected to the transmission line, receiving means for receiving a signal transmitted from the terminal device, demodulating means for demodulating an output signal of the receiving means, and a noise level of an output signal of the receiving means. Noise measuring means for measuring, signal control means for reading the noise level measured by the noise measuring means at a predetermined timing, and outputting a judgment signal indicating whether or not the noise level exceeds a predetermined value; and the judgment signal When the terminal device detects that the noise level in a signal transmitted using the predetermined modulation scheme exceeds a predetermined value, the terminal device refers to the determination signal and A modulation method selecting means for selecting an available modulation method in place of the predetermined modulation method, and selecting a predetermined modulation method again when a certain time has elapsed after selecting the change modulation method; and A message creation unit that creates and outputs messages indicating the change modulation scheme and the predetermined modulation scheme selected by the modulation scheme selection unit to change the modulation scheme used by the terminal device; An up-modulation agile circuit, comprising: a control data transmitting unit that inputs a message created by a message creating unit and sequentially transmits the message to the terminal device via the transmission path. 6. The message creation means detects that the modulation scheme selection means performs a process of selecting the modulation scheme for change based on the determination signal, and notifies the terminal device before starting the processing. A function of creating a stop message for stopping the transmission of uplink data and notifying the terminal device via the control data transmitting means and the transmission path, and creating a message indicating the modulation scheme for change, the terminal device A function to also create a restart message to restart the transmission of the uplink data and output it to the control data transmitting means together with a message indicating the change modulation scheme, and the modulation scheme selection means selects the change modulation scheme. A function to generate the stop message when a predetermined time has elapsed from the control data transmission means, and to output the control message to the control data transmission means; 6. The up-modulation agile according to claim 5, further comprising a function of, when generating a message indicating the formula, generating the restart message and outputting the restart message together with a message indicating the predetermined modulation scheme to the control data transmitting means. circuit. 7. The modulation method selection means includes: a modulation table for storing a plurality of information on the change modulation method and information indicating the predetermined modulation method; When it is determined that the predetermined modulation method is inappropriate, the modulation method for modulation stored in the modulation table is sequentially scanned, and the noise level of the output signal of the receiving means does not exceed a predetermined value. A pointer control circuit that selects a method as a modulation method to be used by the terminal device thereafter; and a return timer that measures a certain time after the pointer control circuit selects the change modulation method, The pointer control circuit is configured to select the predetermined modulation scheme as a modulation scheme to be used by the terminal device thereafter when the return timer measures the fixed time. The up-modulation agile circuit according to claim 5 or 6, wherein: 8. A signal control means comprising: a first timer for generating a first timing signal at a constant interval; and a second timer for generating a second timing signal at a shorter interval than the first timer. Reading the noise level measured by the noise measuring means in synchronization with the first timing signal during a period in which the terminal device is modulating the uplink data with the predetermined modulation method, and selecting the modulation method. A noise level monitoring control circuit for reading the noise level in synchronization with the second timing signal during a period in which the means selects the modulation scheme for change; a noise level and a threshold value read by the noise level monitoring and control circuit; And a threshold value judgment circuit which outputs the judgment signal by comparing with the threshold value.
3. The upstream modulation agile circuit according to claim 1.