JP2737140B2 - Uplink carrier frequency control method for bidirectional CATV system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional CATV system, and more particularly to an uplink carrier frequency control method for a dual CATV system.

[Conventional technology]

Information signals from a plurality of transmitters having different transmission carrier frequencies (channels) are multiplexed by a center device at a head end through an up line, and the multiplexed signal is transmitted to a plurality of receiving terminals by a down line. Conventionally, in a bidirectional CATV system, the upstream carrier frequency of a transmitter is fixed by each transmitter, and the center device has the same number of receivers corresponding to each transmitter.
In the case where the number of transmitters is larger than the number of channels that can be multiplexed in the center device, the channel is switched to the center device, and the center device has an aggregation device.

[Problems to be solved by the invention]

In the conventional bidirectional CATV system described above, since the transmission carrier frequency of the transmitter is fixed, the center device has the same number of receivers as the transmitter or the number of transmitters is smaller than the number of channels that can be multiplexed. If there are many, a switch for switching the channel is required, the size of the center device is increased, and with the increase in the number of transmitters, the number of uplink carriers to be allocated increases, so in a CATV system in which a frequency band is allocated, It has the disadvantage of lacking expandability.

An object of the present invention is to eliminate such disadvantages.
An object of the present invention is to provide an uplink carrier frequency control method for a bidirectional CATV system.

[Means for solving the problem]

The present invention multiplexes information signals from a plurality of transmitters having different transmission carrier frequencies with a center device at a head end through an up line, and multiplexes the multiplexed signal to a plurality of receiving terminals via a down line. In a bidirectional CATV system for transmitting, a bidirectional common control channel for control data transmission is provided between each transmitter and a center device, and the center device transmits the control data from each transmitter through the bidirectional common control channel. When receiving a transmission request, a channel allocation process for the transmitter is performed, and transmission carrier frequency information indicating the allocated channel is transmitted to the transmitter via the bidirectional common control channel. Controlling the voltage-controlled oscillator based on the transmission carrier frequency information sent from the center device, The wave number is set.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a bidirectional CATV applied to an embodiment of the present invention.
It is a block diagram of a system.

The center apparatus 1 having the number of multiplexed channels N is connected to the head end 11, and from the head end 11, a CATV
The trunk line extends, and branches off at tap-offs 12-1 to 12-M.
M (N ≦ M) receiving terminals 13-1 to 13-M and M transmitters 14-1 to 14-M are connected. Thus, it is assumed that the number of transmitters is larger than the number of multiplexed channels.

The center apparatus 1 includes control data modems 7 and 8, a controller 6 for performing channel assignment processing, a distributor 9 for distributing signals, and N (N ≦ M) demodulators 4-1 to 4-1-4.
-N, a distributor 5 for distributing signals to these demodulators, a distributor 10 for distributing signals, a multiplexer 3 and a modulator 2
And

On the other hand, each transmitter 14 includes a control data modem 15, 16;
It has a distributor 19 for distributing signals, a modulator 17, and a distributor 18 for distributing signals. The modulator 17 has a VCO (Voltage Controlled Oscillator) based on PLL (Phase Lock Loop) control, which can change the transmission carrier frequency by control data from the center device 1.

In the bidirectional CATV system having the above-described configuration, the transmission request transmitted through the control data modem 16 of the transmitter 14 and the distributors 19 and 18 has a tap-off 12 → a head end 11 →
The data is input to the controller 6 via the distributor 10 → the distributor 9 → the control data modem 7 of the center device 1. Upon receiving the transmission request from the transmitter, the controller 6 performs channel allocation processing for the transmitter, and transmits the allocated channel, that is, the transmission carrier frequency condition indicating the transmission carrier frequency, to the control data modem 8, the distributor 9, The data is transmitted to the head end 11 through 10. This transmission carrier frequency information is transmitted from the head end 11 → tap off 12 → transmitter 14
Distributors 18 and 19 → control data via modem 15 and modulator 1
Entered in 7. The modulator 17 sets a transmission carrier frequency by controlling a voltage controlled oscillator (VCO) based on transmission carrier frequency information sent from the center device 1.

The transmitter 14 transmits information according to the transmission carrier frequency set as described above. This information is sent to the center device 1 via the up line.

In the center device 1, the demodulator 4 demodulates the signal from the transmitter input through the distributors 10 and 5, multiplexes the obtained information in the multiplexer 2, modulates the information in the modulator 2, The signal is transmitted to the receiving terminal 13 via the down line.

〔The invention's effect〕

As described above, the present invention controls the transmission carrier frequency (channel) of each transmitter from the center device so that even if the number of transmitters is larger than the number of multiplexed channels, the receiver of the center device And the number of switches can be reduced to the same as the number of channels.
This is effective for system scalability.

[Brief description of the drawings]

FIG. 1 is a block diagram of a bidirectional CATV system applied to one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Center apparatus 2 ... Modulator 3 ... Multiplexer 4-1 to 4-N ... Demodulator of each channel 5, 9, 10 ... Divider 6 ... Controller 7, 8 ... Control data Modem 11 Head end 12-1 to 12-M Tap-off 13-1 to 13-M Receiver terminal 14-1 to 14-M Transmitter 15 and 16 Modem for control data 17 … Modulators 18,19 …… Distributors

Claims (1)

(57) [Claims] An information signal from a plurality of transmitters having different transmission carrier frequencies is multiplexed by a center device at a head end through an up line, and the multiplexed signal is transmitted to a plurality of receiving terminals by a down line. In the bidirectional CATV system, a bidirectional common control channel for control data transmission is provided between each transmitter and the center device, and the center device transmits the bidirectional common control channel from each transmitter. Receiving a transmission request via the transmitter, performs channel allocation processing for the transmitter, transmits transmission carrier frequency information indicating the allocated channel to the transmitter via the bidirectional common control channel, Controls the voltage-controlled oscillator based on the transmission carrier frequency information sent from the center device, An uplink carrier frequency control method for a bidirectional CATV system, wherein a frequency is set.