JPH10145771A - Method for monitoring transmission quality for catv system and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve transmission efficiency, to shorten nonoperating time of a system and to improve the transmission quality of the incoming line of the system without performing an extensive modification work on the transmission line. SOLUTION: In the two-way CATV (community antenna television system) system in which a center station 1 and plural local stations 2 are connected via a tree-form transmission line 4, a relation between noise characteristic amount and code error ratio in the incoming line of the two-way CATV system is measured before starting communication service and previously making a neurocomputer 18 learn this relation, and after the system operation is started, making the neurocomputer 18 predict types of code errors using the noise characteristic amount observed in a flowing noise observation device 16, and an error correction or the change of control device is directed to the local stations based on this code errors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV system transmission quality monitoring method and apparatus for improving the uplink transmission quality of a bidirectional CATV system deteriorated by ingress noise.

[0002]

2. Related Art In a two-way CATV system, for example, as shown in FIG. 7, a center station 1 and a plurality of subscribed stations 2 are connected by a transmission line formed in a tree shape, and subscribe via the center station 1. Stations communicate with each other. Such a bidirectional CATV system distributes a broadcast wave received from an antenna 3 to each subscriber station 2 via a downlink, converts a signal transmitted from each subscriber station 2 via an uplink, and converts A central station 1 for transmitting signals to the center station 1, an amplifier 5 for compensating for attenuation of a signal transmitted via a transmission line (for example, a coaxial cable or an optical fiber) 4 connecting each of the subscriber stations 2 and the center station 1, Tap-off 6 for distributing signals to each subscriber station 2
And a protector 7 for electrically protecting each subscriber station 2. Reference numeral 8 denotes a two-way home terminal of the subscriber station 2.

[0003] For example, bidirectional C by the sub-split method
The approximate transmission band used for the uplink of the ATV system is 10 MHz to 50 MHz, and the transmission band used for the downlink is 70 MHz to 700 MHz. The signal transmitted from the subscriber station 2 using the uplink is converted by the center station 1 into a frequency used for the downlink and retransmitted.

[0004] Since the wiring form of the transmission path is tree-like,
The noise that has entered the end of the transmission line 4 or into the middle of the transmission line 4 joins at the branch point of the transmission line 4 (branch point of the amplifier 5 and the tap-off 6), and further approaches the center station 1 at each branch point. While repeating the addition of the noise in the transmission band used in the above, all the noises that have entered the uplink and the thermal noise of the amplifier 5 are collected in the center station 1. This noise is generally called ingress noise.

Therefore, the transmission quality of the uplink, for example,
Since it has been difficult to maintain the average bit error rate (BER) stably, several measures have conventionally been taken. For example, a bit for BER observation may be added to desired data to be transmitted, or data for BER observation may be prepared, and the center station 1 may use the bit to measure the degree of transmission quality degradation. The amplifier 5 counts the number of error bits per fixed time for each of the transmission lines 4 branched from its own device, and measures the number of error bits until the counted number of error bits falls below the threshold value. Transmission in a predetermined band.

[0006]

However, in the conventional method, bits for error observation are added to desired transmission data, and BER is observed using a specific frame. The amount of data transmitted within a certain period of time decreases, deteriorating transmission efficiency, and transmission lines that exceed the threshold set in the amplifier may temporarily become unable to transmit, increasing the system downtime. There was a problem to make it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a higher transmission efficiency, a reduced system downtime, and an upstream line without large-scale repair work on a transmission line. It is an object of the present invention to provide a CATV system transmission quality monitoring method and apparatus capable of improving transmission quality.

[0008]

In order to achieve the above object, according to the present invention, in a bidirectional CATV system in which a center station and a plurality of subscriber stations are connected via a tree-shaped transmission line, a noise spectrum (eg, The relationship between the BER and amplitude, phase, center frequency, noise generation timing, error-free interval, etc.) and the BER are measured by the center station before the communication service starts, and the relationship obtained from the measurement result is learned by the inference means composed of a neurocomputer. After the system operation starts, the neurocomputer predicts the type and magnitude of the code error from the noise spectrum observed at the center station, and based on the type and magnitude of the code error, changes the error correction and control measures to the subscriber station. And a CATV system transmission quality monitoring method for instructing a center station.

That is, the center station monitors the noise spectrum caused by a plurality of types of interference waves, and the neurocomputer predicts the BER caused by the above-mentioned interference waves, and instructs error correction and control measures to improve the transmission quality. Aim. Further, in the present invention, the noise spectrum (amplitude, phase, center frequency, noise generation timing, error-free interval, etc.)
The center station measures the relationship between the BER and the BER before the start of the communication service, and makes the neurocomputer learn the relationship obtained from the measurement result. After the system starts operating, it flows from the noise spectrum observed at the center station to the neurocomputer. The type and scale of the combined noise are predicted, the center frequency and phase of the predicted noise are matched, an amplitude having a polarity opposite to that of the noise is generated, and the noise is canceled by the center station.

That is, the center station monitors the noise spectrum due to a plurality of types of interference waves, the neurocomputer predicts the type and magnitude of the above-mentioned interference waves, and cancels the amplitude of the opposite polarity so as to cancel the above-mentioned interference waves. A signal is generated to improve transmission quality.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A transmission quality monitoring method and apparatus for a CATV system according to the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram showing an example of a configuration of a CATV system according to the present invention. 7 differs from the conventional example shown in FIG. 7 in that a bit error rate tester (hereinafter referred to as "transmitter") 9 is provided in the subscriber station 2, and the transmission quality of monitoring the transmission quality of the CATV system is provided in the center station 1. That is, the monitoring device 10 is provided. In the following drawings, the same components as those in FIG. 7 are denoted by the same reference numerals for convenience of explanation.

The transmission quality monitoring device 10 is, for example, shown in FIG.
As shown in the first embodiment, a mixer 12 connected in front of a head end modulator 11 and a demodulator 13
A bit error rate tester (hereinafter, referred to as a “receiver”) 14, a splitter 15, an ingress noise observation device 16,
It comprises a power meter 17, a neurocomputer 18, and a modulator 19.

In such a configuration, with the transmission of the baseband signal from the transmitter 9, noise collected via the plurality of amplifiers 5 and the tap-off 6 passes through the mixer 12 and the demodulator 13 of the center station 1. Received by the receiver 14. The baseband signal is received by the receiver 14 and the BER is measured. In parallel with that, mixer 1
The signal split by the splitter 15 installed at the front stage 2 is received by the ingress noise observation device 16 and the noise spectrum is measured. The power is also measured by the power meter 17.

In this embodiment, the neurocomputer 18 is made to learn the relationship between three types of data (BER, spectrum and power) measured simultaneously. That is, as shown in FIG. 2, the observation spectrum is normalized by the ingress noise observation device 16 based on the occupied bandwidth, half width and peak level of the noise spectrum. This normalized result is
For example (measured bandwidth) / (maximum occupied bandwidth),
It consists of data of (measured half width) / (maximum half width) and (measured peak level) / (maximum peak level). Also, the BE measured by the receiver 14 at the same time
The data obtained by normalizing the value of R is (measured BER) /
The data obtained by normalizing the power value measured by the power meter 17 includes (measured power) / (maximum noise power). The receiver 14, the ingress noise observation device 16, and the power meter 17 make the neurocomputer 18 learn these data together.

After the system operation is started, the noise spectrum is monitored by the ingress noise observation device 16 and the transmission quality degradation state (the type and scale of the code error, that is, the error bit Number and error duration). The noise spectrum observed by the ingress noise observation device 16 includes, for example, noise amplitude, phase, center frequency, noise generation timing, and error-free interval.

In the center station 1, based on the above prediction, the two-way home terminal 8 of the subscriber station 2 is transmitted from the neurocomputer 18 of the center station 1 via the modulator 19 and the mixer 12 through the down line (transmission line 4). It instructs the communication system to change the type and number of error correction codes (for example, burst error correction codes), packet length, transmission timing, and transmission interval. For example, in the case of burst mode packet communication, the change instruction may be a change in packet length, transmission interval, file transfer speed, or the like.

As described above, in this embodiment, the type of noise is predicted, and the length of the packet transmitted from the subscriber station, the code used for error correction, and the number of codes are specified from the center station. There is no need to add measurement bits to data or transmit a BER measurement frame, so that more optimal BER compensation can be performed under various noise environments, and transmission efficiency can be further improved. .

FIG. 3 is a configuration diagram showing the configuration of the second embodiment of the transmission quality monitoring device shown in FIG. Note that, in the transmission quality monitoring device 10 of FIG. 3, only devices used for two-way communication are shown. In FIG. 3, a head-end remodulator 11 demodulates an uplink signal to a baseband signal, performs a code error check by a method such as CRC, modulates the signal to a predetermined downlink frequency again, and transmits the signal. The apparatus 30 predicts the type and scale (noise level and duration) of the uplink noise, generates a corresponding ingress noise cancellation signal, cancels the uplink noise, cancels it, and cancels the neurocomputer 31. Then, even if the system is in operation, the correctness of the past learning and the type and scale of the noise that has not been experienced in the past are learned, and the learning result is transmitted to the ingress noise canceling device 30.

The ingress noise canceling device 30 includes the branching device 1
5. Ingress noise observation device 16, neurocomputer 1
8, modulator 19, ingress noise cancellation signal generator 2
0, cancel evaluation device 21, delay circuit 22, mixer 2
3 is comprised. Next, the operation of the above device will be described. An uplink signal is branched from the transmission line 4 by a branching device 15, and a noise spectrum (amplitude, phase, center, center, etc.) of a band adjacent to a band used for a communication service is analyzed by an ingress noise observation device 16 including, for example, a spectrum analyzer. Frequency, noise generation timing, error-free interval, etc.), and sends the observation result to the neurocomputer 18.

The neurocomputer 18, which has received the observation result, predicts noise that degrades transmission quality based on the learning result, and transmits information on the characteristic amount of the noise, such as amplitude, phase, duration, center frequency, etc. The signal is transmitted to the cancel signal generator 20. The ingress noise cancellation signal generator 20 that has received the information outputs a signal for canceling the noise predicted by the information to the uplink of the transmission line 4 via the mixer 23. That is, in the mixer 23, a signal for canceling the predicted ingress noise is added to the uplink signal, and the predicted ingress noise is canceled and the uplink signal from which the ingress noise has been considerably removed is converted. The signal is input to the head-end remodulator 11, is re-modulated to a signal of a predetermined frequency, and is transmitted to the downlink.

When the uplink signal is once demodulated into a baseband signal, the head-end remodulator 11 tests whether or not the data string contains an error. If the data string contains an error, the head-end remodulator 11 discards the data string. Processing such as notifying an error to the source subscriber station or the destination subscriber station is performed. The result of this processing is transmitted to the cancel evaluation device 21 and the neurocomputer 31 and used for correction of the prediction by the neurocomputer 18 or the neurocomputer 3
1 for new learning data.

In the cancellation evaluation device 21, for example, the relationship between the predicted target cancellation amount of the interference wave and the ratio of the spectrum after cancellation (remaining cancellation amount), or the cancellation remaining amount and C in the head end remodulator 11, for example.
The relationship with the sign test result such as RC, or the characteristic amount used for prediction, for example, the amount of energy change at a plurality of predetermined frequencies in the spectrum of the interference wave to be canceled or the peak voltage of the interference wave passes the predetermined threshold value The relationship between the pattern to be performed and the remaining amount of cancellation is set as an evaluation item, and the interference wave is evaluated from at least one of these evaluation items.

The neurocomputer 18 receives the data of the observation result of the ingress noise observation device 14 and the data of the evaluation result from the cancel evaluator 21, and corrects the past learning results from the neurocomputer 31 and outputs The relationship between the BER and the type, scale, duration and the like of the noise that has not been performed is learned, and a signal for canceling the noise is specified.

Even during the operation of the system, the new learning result is transmitted from the neuro computer 31 to the neuro computer 18 at any time or on a regular basis, and the newly specified cancellation signal is transmitted to the ingress noise cancellation signal generator. 20 is added as new data. Also,
The neurocomputer 31 is a neurocomputer 1
8 and data which are no longer valid in the ingress noise cancellation signal generator 20 are updated or corrected.

In this embodiment, as shown in FIG. 4, for example, when there is an illegal citizen band radio (interference wave) having a center frequency of 30 MHz for a communication wave of 30 MHz to 36 MHz, the neurocomputer 18 Can be output from the ingress noise cancellation signal generator 20 at the same level as that of the interference wave and of the opposite amplitude, based on the prediction result of Not limited to

That is, for example, when the baseband signal of the voice shown in FIG. 5A is AM-modulated by a sine wave carrier (carrier) shown in FIG. 5B, the neurocomputer 18 predicts the carrier wave shown in FIG. 5B, and based on the prediction result, the carrier wave and the inverse amplitude wave (cancellation wave indicated by the broken line in FIG. It is also possible to generate it from the generator 20 and combine it with the modulated wave of FIG. In this case, since the interference wave is canceled by a voltage of about the baseband of the voice, it is possible to substantially avoid the influence on the signal used for communication. In addition,
In the present embodiment, even if the predicted carrier does not exactly coincide with the center frequency of the interfering wave, the energy of the carrier can be almost canceled, and the above-described effect can be obtained.

As described above, the transmission quality monitoring device of the center station predicts the uplink noise and cancels the noise. Therefore, a large-scale construction is performed on the uplink having poor transmission quality to improve the transmission quality. You don't have to. In the present invention, as shown in FIG.
Transmission quality monitoring apparatus 1 of the third embodiment in which the embodiments are combined
It is also possible to provide 0. In this case, any method can be used depending on the type of signal to be transmitted. For example, in the case of normal data transmission, the method of the first embodiment capable of performing optimal BER compensation is used, and in the case of voice or image transmission, quick transmission quality improvement is performed. By using the method according to the second embodiment, the transmission quality can be improved.

In these embodiments, for the noise having a fixed pattern, the neurocomputer instructs the output of the signal for canceling the ingress noise each time, but the hardware logic or the microcomputer etc. It may be configured as an ingress noise prediction device. In addition, a probability statistic such as an amplitude probability density of noise or a numerical value of probability prediction may be used as the feature amount of noise.

Further, a computer that learns the relationship between the noise feature amount and the BER and predicts the type of noise is as follows:
The computer is not limited to the neurocomputer, and may be an inference computer used in an expert system or the like.

[0030]

As described above, according to the present invention, in a bidirectional CATV system in which a center station and a plurality of subscriber stations are connected via a tree-shaped transmission path,
The inference means learns the relationship between the characteristic amount of the uplink noise of the ATV system and the BER in advance, and after the system starts operating,
Using the feature amount of the noise observed at the center station, the inference means predicts the type and magnitude of the code error, and based on the type and magnitude of the code error, it is possible to change to an error correction or control measure. Since bits or frames for measuring quality are not required, it is possible to further improve the transmission efficiency of uplink data.

Further, the inference means predicts the type and scale of the ingress noise, and outputs a signal for canceling the noise to the uplink based on the predicted type and scale of the ingress noise. Since the ingress noise is canceled, the transmission quality of the uplink can be improved without repairing the transmission line on a large scale.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a first embodiment of a transmission quality monitoring device for a CATV system according to the present invention.

FIG. 2 is a diagram showing an example of observed values of a spectrum to be learned by the neurocomputer shown in FIG. 1;

FIG. 3 is a configuration diagram illustrating a configuration of a second embodiment of the transmission quality monitoring device illustrated in FIG. 1;

FIG. 4 is a waveform diagram showing a relationship between a communication wave, an interference wave, and a cancel signal according to the present invention.

FIG. 5 is a waveform diagram for explaining an embodiment of a transmission quality monitoring method according to the present invention for canceling an interference wave.

FIG. 6 is a configuration diagram showing a configuration of a third embodiment of the transmission quality monitoring device.

FIG. 7 is a configuration diagram showing a configuration of a conventional CATV system.

[Explanation of symbols]

 Reference Signs List 1 center station 2 joining station 3 antenna 4 transmission line 5 amplifier 6 tap-off 7 protector 8 two-way home terminal 10 transmission quality monitoring device 11 headend remodulator 12,23 mixer 13 demodulator 14 bit error rate tester (receiver) Reference Signs List 15 branching device 16 ingress noise observing device 17 power meter 18, 31 neurocomputer 19 modulator 20 ingress noise canceling signal generator 21 cancellation evaluating device 22 delay circuit 30 ingress noise canceling device

Claims (10)

[Claims] 1. A bidirectional CATV system in which a center station and a plurality of subscriber stations are connected via a tree-shaped transmission line, wherein a characteristic amount of an uplink noise and a bit error rate of the bidirectional CATV system are determined. Measure relationships before commencing communication services,
Let the inference means learn the relationship, and after the system starts operating,
Using the feature amount of the noise observed at the center station, the inference means predicts the type and magnitude of the code error, and based on the type and magnitude of the code error, corrects the error and changes the control measures based on the type and magnitude of the error. C instructing the center station
A transmission quality monitoring method for an ATV system. 2. A bidirectional CATV system in which a center station and a plurality of subscriber stations are connected via a tree-shaped transmission line, wherein a characteristic amount of an uplink noise and a code error rate of the bidirectional CATV system are determined. Measure relationships before commencing communication services,
Let the inference means learn the relationship, and after the system starts operating,
Using the characteristic amount of noise observed at the center station, the inference means predicts the type and magnitude of the ingress noise, and based on the predicted type and magnitude of the ingress noise, transmits a signal for canceling the noise to the uplink. A transmission quality monitoring method for a CATV system, wherein the transmission noise is output to the center station and the ingress noise is canceled by the center station. 3. The CATV system transmission according to claim 1, wherein the center station has second inference means, and always compares the predicted value with the actual value and corrects the predicted value. Quality monitoring method. 4. The apparatus according to claim 3, wherein the second inference means, when finding a relationship between noise and a bit error rate not experienced in the past, transmits to the inference means and adds data. 3. A method for monitoring transmission quality of a CATV system according to claim 1. 5. The CA according to claim 1, wherein the characteristic amount of the noise uses a noise spectrum.
A transmission quality monitoring method for a TV system. 6. The noise spectrum comprises: a noise amplitude;
The CA according to claim 5, comprising a phase, a center frequency, a noise generation timing, and an error-free interval.
A transmission quality monitoring method for a TV system. 7. In a two-way CATV system in which a center station and a plurality of subscriber stations are connected via a tree-shaped transmission line, the center station includes a feature amount of an uplink noise of the two-way CATV system. Measuring means for measuring the relationship with the bit error rate, learning the relationship measured by the measuring means before starting the communication service, and using the characteristic amount of the noise measured by the measuring means after the system operation starts. Transmission quality monitoring apparatus for a CATV system, comprising: inference means for predicting the type of a code error by using the code error; and instructing means for instructing the subscriber station to correct an error or change a control strategy based on the code error. . 8. In a bidirectional CATV system in which a center station and a plurality of subscriber stations are connected via a tree-shaped transmission line, the center station includes a feature amount of an uplink noise of the bidirectional CATV system. Measuring means for measuring the relationship with the bit error rate, learning the relationship measured by the measuring means before starting the communication service, and using the characteristic amount of the noise measured by the measuring means after the system operation starts. Inference means for predicting the type of ingress noise, and canceling means for outputting a signal for canceling the noise to the uplink based on the predicted type of ingress noise and canceling the ingress noise. C characterized by having
Transmission quality monitoring device for ATV system. 9. The transmission quality of a CATV system according to claim 7, wherein said center station includes second inference means for always comparing prediction with actual and correcting a prediction value. Monitoring device. 10. The apparatus according to claim 9, wherein said second inference means, when finding a relationship between noise and a bit error rate which has not been experienced in the past, transmits to said inference means and adds data. A transmission quality monitoring device for a CATV system according to claim 1.