JP4112290B2 - Receiving device in center of CATV transmission system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a center receiver of a CATV transmission system. In particular, the present invention relates to a receiving apparatus that suppresses generation of error data with respect to upstream inflow noise.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is known a bidirectional CATV transmission system capable of transmitting a video signal and a data signal from a head end to a consumer side by frequency division multiplexing and transmitting a data signal from the consumer side to the head end side.
[0003]
[Problems to be solved by the invention]
However, in such a CATV transmission system, the data signal transmitted from the consumer side to the head end side is modulated and transmitted to a high frequency, or transmitted from a large number of consumers to the head end in a tree-like network. Therefore, it is affected by communication failure due to distortion of the multi-channel high-frequency signal and inflow noise. In particular, the center has a problem that inflow noise increases.
[0004]
On the other hand, a high-frequency signal obtained by modulating a carrier wave with a baseband data signal is usually used as the uplink data signal in the transmission path. This high frequency signal is demodulated into a baseband data signal at the center by a receiving device such as an RF center modem that demodulates the upstream data signal. In this receiving apparatus, normally, the gate switch is in a passing state only when a carrier wave is received, that is, when a high-frequency data signal is received, and when the carrier wave is not received, the gate switch Is in a state of blocking the passage of the upstream signal. In this way, when there is no uplink data signal, demodulation processing is executed to prevent a baseband data signal from being obtained as error data. Performing demodulation processing only when a carrier wave is received in this way is usually called squelch.
[0005]
In order to control the passage and blocking of the gate switch, it is necessary to compare the reception level of the carrier wave with a predetermined level. Conventionally, this predetermined level has been fixed.
[0006]
For this reason, if the predetermined level is set high, there is a problem that if the reception level of the carrier wave decreases for some reason, the reception level of the carrier wave easily falls below the predetermined level, and normal data cannot be demodulated. On the other hand, if the predetermined level is set low, there is a problem that the gate switch is in a passing state due to noise even though no carrier wave is received, and error data is generated by demodulating the noise.
[0007]
Therefore, the predetermined level is set in a delicate balance between the normal reception level of the carrier wave and the upstream inflow noise in the transmission path, and there is a problem that this setting is not easy. In addition, the magnitude of the upstream inflow noise should be different for each system of the transmission path. However, in the past, a predetermined level that is uniformly fixed is set without considering this situation, and as a result, the above-described problems have occurred.
[0008]
The present invention has been made to solve the above-described problems, and an object of the present invention is to prevent the generation of error data and prevent the normal data from being demodulated. Further, an optimum predetermined level for controlling proper passage and blocking of the data signal is set for a plurality of systems having different magnitudes of upstream inflow noise.
[0009]
[Means for Solving the Problems]
The present invention provides a receiver for receiving data signals of upstream bandwidth by the center of CATV transmission system, the gate switch device for pass or block the data signal at the input side of the gate switch device, to detect the level of the upstream bandwidth and Relais bell detector, the outputs of the level detection device, in accordance with the recognized noise level noise level and recognizing level recognition device is a level of the received signal, the level recognition apparatus according nonexistent period of the carrier wave, A level control device that outputs a default voltage or generates a higher voltage according to a recognized noise level, a comparison device that subtracts the output of the level control device from an output of the level detection device, and an output of the comparison device is the gate switch device and the signal passing state when it is determined that high, the output of the comparator is low If it is a constant having a gate controller for the gate switch device and the signal blocking state, the receiving apparatus is characterized in that a device provided for each system in CATV transmission system.
[0011]
[Action and effect of the invention]
Is detected by the level Gale level detector of upstream bandwidth at the input of the gate switch device (terminal), the outputs of the level detection device, the noise level is level recognition is the level of a received signal in a non-existent period of the carrier wave Recognized by the device. The level control device outputs a default voltage according to the noise level recognized by the level recognition device, or generates and outputs a higher voltage according to the recognized noise level. Then, the output of the level control device is subtracted from the output of the level detection device by the comparison device. When it is determined that the output of the comparison device is high, the gate switch device enters a signal passing state. On the other hand, when it is determined that the output of the comparison device is low, the gate switch device is in a signal cutoff state. In such control, the level control device controls the predetermined level to be higher as the noise level recognized by the level recognition device is higher.
[0012]
As a result, the higher the noise level is, the higher the predetermined level is within a range that does not exceed the reception level of the carrier wave, so that the gate switch does not pass through even if the upstream inflow noise increases. For this reason, when there is no upstream data signal, it is not passed, so that error data is prevented from passing . In this case, if the predetermined level is increased, if the reception level of the carrier wave is lowered for some reason, the gate switch is cut off, and data may not pass even though there is an upstream data signal. The probability of occurrence increases. Therefore, when the noise level is low, the predetermined level is also lowered, so that data demodulation and passage are reliably performed when an upstream data signal is present. As described above, the present invention has an effect that data demodulation and passage in which error data is prevented from being optimally performed can be performed optimally when upstream inflow noise fluctuates with time or varies depending on the system. is doing.
Furthermore, a shall issue detects the noise level as the level of the received signal in the non-existing duration of the carrier wave. Thereby, it is possible to detect the reception level and noise level of the carrier wave in the same frequency band.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on specific embodiments. The present invention is not limited to this embodiment.
FIG. 1 shows a configuration of a receiving apparatus 100 provided in the center of the CATV system. The transmission line 10 is connected to a duplexer 12, and a downlink system device 14 and a receiving device 100 that is an uplink system device described below are connected to the duplexer 12. Hereinafter, the uplink system apparatus will be described. The upstream signal is input to the gate switch device 16, demodulated into a baseband data signal by the RF demodulator 18, input to the computer device 20, and processed as an upstream data signal. This path is a normal path through which signals flow.
[0014]
On the other hand, a branching device 22 and a branching device 24 are disposed on the input side of the gate switch device 16. The signal branched by the branching device 22 is input to the band pass filter 26. The band pass filter 26 separates a signal in a band that does not include a carrier wave in the upstream band. That is, noise is obtained from the output of the band pass filter 26. This noise is integrated after rectification by an integrating circuit 28 to obtain a noise level. The noise level output from the integration circuit 28 is output to the level generator 30. Then, it is converted into a predetermined level corresponding to the noise level received by the level generator 30 and output to the comparator 36.
[0015]
On the other hand, the signal branched by the branching device 24 is input to the band pass filter 32. The band pass filter 32 is a filter that separates the carrier wave of the upstream data signal. Then, the carrier wave extracted by the band pass filter 32 is integrated after rectification in the integration circuit 34 and output to the comparator 36 as the reception level of the carrier wave. In the comparator 36, the reception level of the carrier wave is compared with a predetermined level determined from the received noise level. If the reception level of the carrier wave exceeds the predetermined level, the gate switch device 16 is set in a signal passing state. A control signal for output is output to the gate switch device 16. On the other hand, when the reception level of the carrier wave is lower than the predetermined level, a control signal for setting the gate switch device 16 in a signal cutoff state is output to the gate switch device 16.
[0016]
Thereby, when the reception level of the carrier wave of the data signal is higher than a predetermined level, the data signal passes through the gate switch device 16 and is demodulated by the RF demodulator 18 to obtain a baseband data signal. If the reception level of the carrier wave of the data signal is lower than the predetermined level, no signal is input to the RF demodulator 18, so that the data is not demodulated. That is, even if noise is input to the gate switch device 16, generation of error data due to demodulation of the noise is prevented.
[0017]
The predetermined level is changed as shown by a curve A in FIG. 2 with respect to the noise level. A straight line B is the lowest predicted value of the reception level of the carrier wave. As described above, the predetermined level is set higher as the noise level is higher in the range not exceeding the predicted minimum value of the reception level of the carrier wave. That is, when the noise level is low, the margin for determining the reception level of the carrier wave is large, and when the noise level is high, the margin for determining the reception level of the carrier wave is small. In this way, when the noise is small, the reception state continues even when the reception level of the carrier wave is unpredictable, and when the noise is large, the gate switch is erroneously caused by the noise when there is no carrier wave. The probability that the device is prevented from going through is increased.
[0018]
Next, another embodiment will be described. In the above embodiment, the reception level of the carrier wave and the noise level are detected by separating the frequency band. However, in the present embodiment, the reception level and noise level of the carrier wave are separated and detected according to the difference in period without separating the frequency bands.
[0019]
The transmission path 10, the duplexer 12, and the downstream system 14 are the same as those in FIG. The receiving apparatus 200 according to the present embodiment is configured as follows. The upstream signal passes through the band-pass filter 50, is amplified by the amplifier unit and the frequency conversion unit 52, and is frequency-converted from the upstream frequency band to a predetermined frequency band. Then, it is demodulated into a baseband data signal by the demodulator 54, shaped into a rectangular wave by the data shaver 56, and data is output to the computer device 20 via the digital filter 66. This is the normal signal path.
[0020]
On the other hand, the following apparatus is provided for detecting the reception level and noise level of the carrier wave. The signal output from the amplifier unit and frequency conversion unit 52 is input to the level detection unit 58. The level detection unit 58 is the same as the integration circuits 28 and 34 in FIG. As shown in FIG. 4, the output of the level detector 58 is an integration level after rectification of a signal divided into a period A in which uplink data (carrier wave) exists and a period B in which data (carrier wave) does not exist. is there. The output of the level detection unit 58 is input to the level recognition unit 62, and the level recognition unit 62 extracts the signal level in the period B in which no data exists. Since one data length is known in advance, it can be regarded as a period B in FIG. 4 when a predetermined time has elapsed after the end of the data length after the high level signal is detected. The noise level detected in this way is input to the level voltage generator 64, and a predetermined level is output. This is the same configuration as the level generator 30 of FIG. When the noise level exceeds 35 dBμ, a predetermined level output from the level voltage generator 64 is output to the comparator 60. When the noise level is 35 dBμ or less, the fixed level output from the default squelch circuit 68 is output to the comparator 60. With this configuration, the higher the noise level, the higher the predetermined level, which is output to the comparator 60.
[0021]
On the other hand, the comparator 60 compares the output of the level detector 58 with a predetermined level. That is, since the reception level of the carrier wave is higher than the noise level, the level detection unit 58 compares the reception level of the carrier wave with a predetermined level. Then, a high level signal is output to the data shaver 56 during a period when the reception level of the carrier wave is higher than the predetermined level, that is, during the period A in FIG. The data shaver 56 is an AND circuit, and is a circuit that passes a signal output from the demodulator 54 during a period A in which one input terminal is at a high level. Therefore, the demodulated baseband data signal is output to the computer device 20 during the period in which the carrier wave is detected. On the other hand, in the period B in which no carrier wave exists, the signal level output from the level detector 58 is always lower than the predetermined level. Therefore, since the output of the comparator 60 is at the tee level, the data shaver 56 does not pass the baseband data signal output from the demodulator 54 during this period B. Therefore, error data obtained by demodulating noise is not input to the computer device 20.
[0022]
Since the predetermined level is changed according to the noise level in this way, the same effect as described in the first embodiment can be obtained.
[0023]
Upstream noise changes with time zone and also with system. Therefore, by using the present invention, it becomes a system that is robust against time-varying upstream noise. Furthermore, when the upstream inflow noise varies depending on the system, the communication apparatus having the above-described noise resistance performance can be provided for each system by providing the receiving apparatus of FIG. 1 for each system.
[0024]
In the above embodiment, the band pass filter 32 and the integrating circuit 34 constitute a carrier level detection device. The band pass filter 26 and the integrating circuit 28 constitute a noise level detection device. The comparator 36 constitutes a level comparison device, the level generator 30 constitutes a level control device, the comparator 36 and the gate switch device 16 constitute a gate control device, and the gate switch If the device 16 is composed of a transistor, a voltage generation mechanism for turning on or off the transistor by the output of the comparator 36 corresponds to the gate control device. The level generator 30, the comparator 36, and the like can be realized by software processing by a computer. In addition, although the present invention has been described as the receiving device 100 in the center, only the receiving function is focused because only the upstream signal is focused, and a device for actually processing the downstream signal is added. It may be. That is, even a transmission / reception device having a reception unit therein corresponds to the reception device of the present invention. The receiving apparatus 100 may also be called a center RF modem. In short, the present invention is not limited by the name.
[0025]
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a receiving device in a center according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing a relationship between a predetermined level and a noise level in the embodiment.
FIG. 3 is a configuration diagram of a receiving device in a center according to another embodiment of the present invention.
FIG. 4 is a timing chart showing a detection method of a carrier wave reception level and a noise level in the reception apparatus according to the embodiment;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Transmission path 12 ... Divider 16 ... Gate switch apparatus 18 ... RF demodulator 22, 23 ... Branch device 26, 32 ... Band pass filter 30 ... Level generator 36 ... Comparator

Claims (1)

In a receiving apparatus for receiving an upstream band data signal at the center of a CATV transmission system,
A gate switch device that passes or blocks the data signal;
The input side of the gate switch device, and Relais bell detector detecting the level of the upstream band,
A level recognizing device for recognizing a noise level which is a level of a received signal in a period in which the carrier does not exist among outputs of the level detecting device;
A level controller that outputs a default voltage or generates a higher voltage according to the recognized noise level according to the noise level recognized by the level recognition device; and
A comparator for subtracting the output of the level controller from the output of the level detector;
When the output of the comparison device is determined to be high, the gate switch device is set to a signal passing state, and when the output of the comparison device is determined to be low, the gate control is set to set the gate switch device to a signal cutoff state. Having a device ,
The receiving apparatus is an apparatus provided for each system in the CATV transmission system .

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