JP2001145070A - Cable modem - Google Patents

Abstract

(57) [Problem] To provide a cable modem in which a converter and a cable modem are integrated to simplify the configuration of both, and that the C / N does not greatly deteriorate. SOLUTION: A converter unit 4 is QPSK / 16QAM.
An RF attenuator 8 controlled by the CPU 5 is provided on the output side of the modulation section 7, and a QPSK / 1
An RF switch 9 operating in synchronization with the 6QAM modulator 7 was provided and connected to the signal input / output terminal 1 of the cable modem.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a cable modem which enables two-way communication using a CATV network.

[0002]

2. Description of the Related Art In a bidirectional CATV system, a system in which a frequency band is expanded to increase an information transmission capacity is widely used. For example, in the case of down-flow, 70 MHz to 4
What was 50 MHz was expanded by about 150 MHz from 70 MHz to 602 MHz.
The frequency range from ５５55 MHz (LOW) to 650 MHz to 770 MHz (HIGH) is newly set as the upstream signal band. Further, with the provision of a new upstream band, the conventional band of 10 MHz to 55 MHz overlaps with the noise band originally generated in home appliances, so that all the bands are converted to the HIGH band in order to prevent such noise from being mixed. Or use it.

In the case of converting the upstream frequency LOW to HIGH as described above, as shown in FIG. 2, a method of connecting a cable modem 11 connected to a PC (personal computer) or the like to a CATV network 13 via an upstream converter 12 is known. In order to make the entire HIGH band available, frequency conversion is performed by a block converter system using three converters A, B and C. In this case, for example, in converter A, 10 MHz to 55 MHz is changed to 650.
MHz to 695 MHz.
MHz to 55 MHz converted to 69 to 740 MHz,
Further, in converter C, 10 MHz to 40 MHz or 25 MHz
MHz to 55 MHz was converted to 740 MHz to 770 MHz.

[0004]

As described above, the conventional one
In one converter, 120 of 650-770 MHz
Since only a range of 45 MHz in the MHz band can be converted, it is necessary to use three types of converters properly when constructing a system using the 120 MHz band. In addition, since the converter is separate from the cable modem and is an independent device, it is difficult to control the output level of the converter from the cable modem, and the output level of the converter varies greatly depending on the installation location of the CATV network. Thus, depending on the input level adjustment of the converter, the C / N may be greatly deteriorated or distortion may occur.

[0005] In view of the above problems, the present invention provides a cable modem in which the converter and the cable modem are integrated to simplify the configuration of both, and that the C / N is not significantly degraded. That is the task.

[0006]

In order to solve the above-mentioned problems, a first aspect of the present invention is a cable modem installed on each terminal side to enable two-way communication using a CATV network, An upstream converter for converting an upstream signal frequency from the terminal device to a frequency higher than the downstream frequency is provided in the upstream signal output unit.

The invention of claim 2 is characterized in that, in the invention of claim 1, the output frequency of the up converter is a frequency that can be received by a center modem installed in a center station.

According to a third aspect of the present invention, in the first or second aspect of the present invention, a switch for blocking output of a high-frequency signal is provided on the output side of the up converter.

A fourth aspect of the present invention is characterized in that, in the first or second aspect of the invention, the adjustment of the upstream signal level is performed by adjusting the output of the converter.

According to a fifth aspect of the present invention, in the first or second aspect of the present invention, the set frequency bandwidth of the up converter is substantially one.
The frequency is 20 MHz.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit block diagram of a cable modem according to the present invention.
A signal input / output terminal connected to a V network, 2 is a terminal connection terminal for connecting a terminal device such as a PC, 3 is a tuner unit, 4 is a converter unit, 5 is a CPU, and 6 is a media access control (MAC). is there. The converter unit 4
Provided on the output side of the PSK / 16QAM modulator 7,
The uplink signal is frequency-converted by L control. And
The frequency-converted upstream signal passes through the RF attenuator 8 and the RF switch 9 controlled by the CPU 5, and
It is sent to the V network. Note that the tuner section and the demodulation circuit for the output thereof are not the gist of the present invention, and thus description thereof is omitted.

The operation of the above cable modem will be described.
First, when the power of the cable modem is turned on, the cable modem sequentially changes the reception frequency and searches for the downlink signal frequency fd of the center modem. When the reception frequency of the cable modem becomes fd, the cable modem receives the down signal of the center modem. The center modem periodically transmits information such as the frequency, the modulation method, and the data transmission rate relating to the uplink signal.
By controlling L2, the uplink frequency is set to a frequency fu that can be received by the center modem. Also, QPSK / 16QAM
A modulation method and a data transmission speed are set for the modulation unit 7. The frequency fu is 1 from 650 MHz to 770 MHz.
It is set to be changeable in a 20 MHz band.

Next, an operation for determining an output level is performed, and the cable modem outputs an upstream signal at a frequency permitted by the center modem at a frequency fu. The output level is sequentially increased from the minimum value under the control of the CPU 5, and the RF attenuator 8 is controlled so as to end when the output level reaches a prescribed level that the center modem can receive. Thus, data communication between the contractor terminal and the center becomes possible. The RF switch 9 is a switch for blocking the output of the high-frequency signal, operates in synchronization with the QPSK / 16QAM modulator 7, and turns off when the QPSK / 16QAM modulator 7 is not operating.

As described above, since the upstream converter is provided in the cable modem, an external converter is not required, and the cable modem receives a signal from the center station,
Since the local oscillation frequency of the up converter can be controlled, it can be set to an arbitrary frequency. Also,
If the output frequency of the up converter is set to a frequency that can be received by the center modem, there is no need to install a new device in the center station, and by providing an RF switch that operates according to the operation of the QPSK / 16QAM modulator, During communication, the noise of the up converter can be cut, and the communication environment of the CATV line can be kept good. Further, by adjusting the output level on the output side of the upstream converter, C /
N can be minimized, and 120 MH
By having a z-bandwidth, any frequency can be set,
Even if the operating frequency changes, such as a system change, it can be easily handled.

[0015]

As described in detail above, according to the first aspect of the present invention, since the upstream converter is provided in the cable modem, an external converter is not required, and the cable modem receives signals from the center station. As a result, the local oscillation frequency of the up converter can be controlled, so that it can be set to an arbitrary frequency.

According to the invention of claim 2, in addition to the effect of the invention of claim 1, there is no need to install a new device in the center station. According to the invention of claim 3, in addition to the effect of claim 1 or 2, noise of the up converter can be cut during non-communication, and a favorable communication environment of the CATV line can be maintained.

According to the invention of claim 4, according to claim 1 or 2,
In addition to the effects of the present invention, by adjusting the output level on the output side of the up converter, the deterioration of C / N can be minimized. According to the invention of claim 5, in addition to the effect of the invention of claim 1 or 2, an arbitrary frequency of a 120 MHz bandwidth can be set.
Even if the operating frequency changes, it can be easily handled.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a cable modem showing an example of an embodiment of the present invention.

FIG. 2 is a circuit block diagram of a conventional cable modem.

[Explanation of symbols]

1. Signal input / output terminal, 2. Terminal connection terminal, 4. Converter part, 5. CPU, 8. RF attenuator,
9. RF switch.

Claims (5)

[Claims] 1. A cable modem installed on each terminal side to enable bidirectional communication using a CATV network, wherein the upstream converter converts an upstream signal frequency from the terminal device to a frequency higher than a downstream frequency. A cable modem comprising: an upstream signal output unit. 2. The cable modem according to claim 1, wherein the output frequency of the up converter is a frequency that can be received by a center modem installed in a center station. 3. The cable modem according to claim 1, further comprising a switch provided on an output side of the upstream converter to block output of a high-frequency signal. 4. The cable modem according to claim 1, wherein the upstream signal level is adjusted by adjusting an output of the converter. 5. The cable modem according to claim 1, wherein the set frequency bandwidth of the upstream converter is approximately 120 MHz.