JPH01220591A - Up carrier frequency control system for bidirectional catv system - Google Patents

Abstract

PURPOSE:To miniaturize a device and to facilitate system extension by controlling transmission channels of transmitters by a center equipment to equalize the number of receivers of the center equipment to the number of channels even in case of the number of transmitters smaller than the number of multiplexed channels. CONSTITUTION:A transmission request passing a MODEM 16 and distributors 19 and 18 of a transmitter 14 is inputted to a controller 6 through a tap-off 12, a head end 11, and distributors 10 and 9 and a MODEM 7 of a center equipment 1. The controller 6 performs the channel assignment processing and sends transmission carrier frequency information to the head end 11 through a MODEM 8 and distributors 9 and 10, and it is inputted to a modulator 17 through the tap-off 12 and distributors 18 and 19 and a MODEM 15 of the transmitter 14. The modulator 17 controls a voltage controlled oscillator based on frequency information of the equipment 1 to set a transmission carrier frequency, and the transmitter 14 transmits information. The signal of the transmitter is demodulated by a demodulator 4 of the equipment 1 and is sent to a reception terminal 13 through a multiplexing device 3 and a modulator 2. Thus, the device is miniaturized and system extension is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a two-way CATV system, particularly a two-way CATTV system.
This invention relates to an upstream carrier frequency control method for the V system.

[Conventional technology]

Information signals from multiple transmitters with different transmission carrier frequencies (channels) are multiplexed by a center device at the head end via the upline, and the multiplexed signals are transmitted to multiple receiving terminals via the downline. Conventionally, in a two-way CATV system, the upstream carrier frequency of the transmitter is fixed for each transmitter, and the center device has the same number of receivers corresponding to each transmitter.

When the number of transmitters is greater than the number of channels that can be multiplexed by the center device, the center device has an aggregation device that switches and narrows down the channels.

[Problem to be solved by the invention]

In the conventional two-way CATV system described above, the transmission carrier frequency of the transmitter is fixed, so the center equipment side must be equipped with the same number of receivers as transmitters, or have more transmitters than the number of channels that can be multiplexed. If there are a large number of transmitters, a switch is required to switch channels, and as the scale of the center equipment increases and the number of transmitters increases, the number of uplink carriers to be allocated increases. In CATV system,
The drawback is that it lacks extensibility.

SUMMARY OF THE INVENTION An object of the present invention is to provide an uplink carrier frequency control method for a bidirectional CATV system in order to eliminate such drawbacks.

[Means to solve the problem]

The present invention multiplexes information signals from multiple transmitters with different transmission carrier frequencies through an upline at a center device located at the head end, and transmits the multiplexed signals to multiple receiving terminals through a downline. In a two-way CATV system that transmits data, a two-way common control channel for transmitting control data is provided between each transmitter and the center device, and this control channel transmits transmission carrier frequency instruction data to each transmitter. It is characterized by

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a bidirectional CAT applied to an embodiment of the present invention.
FIG. 2 is a block diagram of the V system.

The center device 1 with the number of multiplexed channels N is connected to the head end 11, and from the head end 11, C
The ATV main line extends, branches off at tap-offs 12-1 to 12-M, and receives M (N5M) receiving terminals 13-1 to 13-.
M or M transmitters 14-1 to 14-M are connected. In this way, it is assumed that the number of transmitters is greater than the number of multiplexed channels.

The center device 1 includes a control data modem 7.8, a controller 6 that performs channel allocation processing, a distributor 9 that performs signal distribution, and N (N5M) demodulators 4-1 to 4.
-N, a distributor 5 that distributes signals to these demodulators, a distributor 10 that distributes signals, a multiplexer 3, and a modulator 2.

On the other hand, each transmitter 14 has a modem 15, 16 for control data.
, a distributor 19 for distributing signals, a modulator 17, and a distributor 18 for distributing signals. The modulator 17 is
There is a VCO (voltage controlled oscillator) controlled by PLL (phase locked loop), whose transmission carrier frequency can be changed by control data from the center device 1.

In the two-way CATV system configured as above,
Modem 16 for control data of transmitter 14. Distributor 19.1
A transmission request sent through 8 is input to the controller 6 via the tap-off 12 -> the head end 11 -> the distributor 10 of the center device 1 -> the distributor 9 - the modem 7 for control data. When controller 6 receives a transmission request from a transmitter, it performs channel allocation processing for this transmitter, and transmits transmission carrier frequency information indicating the allocated channel, that is, transmission carrier frequency, to control data modem 8, distributor 9. 10 to the headend 11. This transmit carrier frequency information is transmitted from the headend 11 to the tap-off 12 to the distributor 18.19 of the transmitter 14.
- Input to modulator 17 via modem 15 for control data. The modulator 17 generates a voltage controlled oscillator (V) based on the transmission carrier frequency information sent from the center device 1.
CO) to set the transmission carrier frequency.

The transmitter 14 transmits information using the transmission carrier frequency set as described above, and this information is sent to the center device 1 via the up line.

In the center device 1, the signal from the transmitter input via the distributors 1O and 5 is demodulated by the demodulator 4, the obtained information is multiplexed by the multiplexer 2, and modulated by the modulator 2. It is sent to the receiving terminal 13 via the down line.

〔Effect of the invention〕

As explained above, the present invention allows the center device to control the transmission carrier frequency (channel) of each transmitter, so that even if the number of transmitters is greater than the number of multiplexed channels, the receiver of the center device can The number of channels can be reduced to the same as the number of channels, and the number of switches for aggregation can be reduced, which is effective in reducing the size of the device and increasing the expandability of the system.

[Brief explanation of the drawing]

FIG. 1 shows a bidirectional CAT applied to an embodiment of the present invention.
FIG. 2 is a block diagram of the V system. l... Center equipment W 2... Modulator 3... Multiplexer 4-1 to 4-N... Demodulator 5.9.10 for each channel.
・Distributor 6...Controller 7.8...Control data modem 11...Head end 12-1 to 12-M...Tap 13-1 to 13-M ...Receiving terminals 14-1 to 14-1, transmitters 15, 16, control data modem 17, etc.
・Modulators 18, 19...Distributor agent Yoshiyuki Iwasa, patent attorney

Claims (1)

[Claims] (1) Information signals from multiple transmitters with different transmission carrier frequencies are multiplexed by a center device at the head end via the upline, and the multiplexed signals are transmitted to multiple receiving terminals via the downline. Two-way CA
In the TV system, a two-way common control channel for transmitting control data is provided between each transmitter and a center device, and transmission carrier frequency instruction data is transmitted to each transmitter through this control channel. Two-way C
Upstream carrier frequency control method for ATV systems.