JPH06253306A - Automatic detecting method for incoming noise of two-way catv system - Google Patents

Abstract

PURPOSE:To easily and exactly detect a noise and to speedily detect the cause of the noise and makes a recovery by judging that a noise is mixed with an incoming signal once a noise detection part detects the incoming signal continu ously for longer than a certain time. CONSTITUTION:The noise detection part 1 is added on the output side of the carrier detection part 20 of a modem 10. Then this noise detector 1 is a timer counter and counts the continuance of detection data outputted from the detection part 20. In this case, when the counted continuance is longer than the transmission time of the up system by a polling system, it can be decided that its excessive signal part is not the normal up signal, but a noise. Therefore, when the carrier detection part 20 outputs an error signal, it can be known that the error is caused by the error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for automatically detecting upstream noise in a two-way CATV system, which allows a center to automatically detect upstream noise in the two-way CATV system.

[0002]

2. Description of the Related Art In a bidirectional CATV system, not only a downlink signal is sent from a center to a terminal, but also an uplink signal such as a TV signal and a data signal is sent from the terminal to the center. When noise is mixed in the upstream signal from each terminal, the noise is collected in the center and becomes a large collective noise. If the aggregate noise becomes large, the upstream C / N characteristic may be deteriorated, or the communication noise may occur due to the noise.
There was a problem that it covered the entire ATV system. Therefore, it is necessary to detect this collective noise as quickly as possible and eliminate the cause.

[0003]

However, conventionally, there is no suitable method for detecting the noise at the center, so that the noise can be confirmed unless the noise is measured by using a measuring instrument such as a spectrum analyzer. I couldn't. Therefore, it takes time to detect noise,
There was a problem that the noise detection was delayed.

An object of the present invention is to constantly detect automatically the noise included in the upstream direction at the center, to quickly find the noise and its cause, and to quickly eliminate the same cause, thereby making it possible to communicate by noise. It is intended to suppress abnormalities to a minimum and further to suppress deterioration of upstream C / N characteristics due to noise.

In order to achieve the above-mentioned object, the inventor of the present invention repeatedly studied the upstream signal transmission method of the bidirectional CATV system prior to the development of the present invention, and as a result, obtained the following findings. That is, when a data signal is sent as an uplink signal on the uplink of a bidirectional CATV system, normally,
As the upstream signal, a signal from a two-way converter installed in the terminal or a signal from a status monitor unit built in the amplifier is used. Moreover, since the communication method of the upstream signal is a polling method, that is, a method in which many devices use the same frequency in a time-division manner, the upstream signal is always turned on / off and continuously output for a certain time or longer. There is no. Therefore, in this upstream signal transmission method,
When the upstream signal continues for a certain time or longer, it can be determined that the upstream signal contains a signal other than the original data signal, that is, noise. The present invention was developed by paying attention to the characteristics of this upstream signal transmission method.

[0006]

Bidirectional CATV of the present invention.
As shown in FIG. 2, the method of automatically detecting the upstream noise in the system is such that in the two-way CATV system in which the upstream signal is intermittently sent from the terminal 2 to the center 3, the upstream signal is mixed into the upstream signal in the center 3. A noise detector 1 for detecting existing noise is provided as shown in FIG. 1, and the noise detector 1 determines that noise is mixed when an upstream signal is continuously detected for a predetermined time or longer. Is.

[0007]

According to the automatic upstream noise detecting method in the bidirectional CATV system of the present invention, when the upstream signal is continuously detected for a predetermined time or longer by the noise detecting section 1 provided in the center 3 of the CATV system, the upstream signal is detected. Since it is determined that the noise is mixed in, it is possible to always automatically detect the noise in the center 3.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for automatically detecting upstream noise in a bidirectional CATV system according to the present invention will be described in detail with reference to the embodiment shown in FIG. FIG. 1 shows an embodiment in which a noise detecting section 1 is provided in a broadband modem 10 installed in a center 3 of a bidirectional CATV system and used for processing an upstream signal.

The modem 10 shown in FIG. 1 mixes the upstream signal input from the bandpass filter 11, the amplifier 12, the local signal generator 13 and the input terminal 14 with the local oscillator signal generated from the local signal generator 13. Mixer for frequency conversion
5, bandpass filter 16, amplifier 17, amplifier 17
Demodulator 18 for demodulating the output signal of the output signal, branching device 19 for extracting part of the output of the amplifier 17 as a monitor signal
The monitor signal taken out by the
At the time of FF or when the level thereof is extremely low, the carrier detection unit 20 prevents the detection data from being output, and the output of the carrier detection unit 20 and the output from the demodulator 18 are ANDed and both are output. An AND circuit 21 that outputs a signal only when there is an output is provided.

However, in the modem 10, even if there is no regular upstream signal or the same signal is below a predetermined level, noise of the same frequency as the upstream signal and other signals are above the specified level to the upstream line. Once in, the carrier detector 2
At 0, the noise and other signals are detected and the same detection data as when there is a normal upstream signal is output. Therefore, the output of the AND circuit 21 becomes an error. Similarly, the detection data of the carrier detection unit 20 is also output to the carrier detection terminal. That is, the detection data output to the same detection terminal also becomes an error.

Therefore, in the present invention, as shown in FIG.
The noise detection unit 1 is newly added to the output side of the carrier detection unit 20 of 0. The noise detection unit 1 is a timer counter, which counts the duration of the detection data output from the detection unit 20. In this case, if the counted duration is longer than the transmission time of the upstream signal by the polling method, it can be determined that the signal corresponding to the longer duration is noise instead of the regular upstream signal. Therefore, when an error signal is output from the carrier detection unit 20 as described above, it can be known that the error is due to noise.

When noise is detected by the noise detector 1, a noise detection signal is output from the noise detector 1, and the signal notifies the occurrence of an abnormality by blinking a lamp or a buzzer. It is done.

[0013]

The automatic upstream noise detecting method in the bidirectional CATV system of the present invention has the following effects. ． Even if you do not detect noise one by one using a measuring instrument,
The noise mixed in the upstream signal can always be automatically detected at the center. Therefore, noise can be detected easily and accurately, and the cause of noise can be detected and recovered quickly. ． Since the communication abnormality due to noise can be suppressed to a minimum, the deterioration of the upstream C / N characteristic can also be suppressed to a minimum.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a method for automatically detecting upstream noise in a bidirectional CATV system according to the present invention.

FIG. 2 is an explanatory diagram showing an example of inserting a modem of a bidirectional CATV system.

[Explanation of symbols]

 1 Noise detector

Claims (1)

[Claims] 1. In a two-way CATV system in which an upstream signal is intermittently sent from a terminal to a center, the center is provided with a noise detection section 1 for detecting upstream noise mixed in the upstream signal. The noise detecting unit 1 determines that the upstream signal is contaminated with noise when the upstream signal is continuously detected for a predetermined time or longer, and the method for automatically detecting upstream noise in a bidirectional CATV system. .