WO2003096692A1

WO2003096692A1 - Noise filtering apparatus for internet service using master antenna television network

Info

Publication number: WO2003096692A1
Application number: PCT/KR2003/000936
Authority: WO
Inventors: Sin-Yul Park; Dong-Hee Choi; Kyung-Keon Park
Original assignee: Dexter Communications, Inc.
Priority date: 2002-05-13
Filing date: 2003-05-12
Publication date: 2003-11-20
Also published as: KR100411339B1; AU2003230331A1

Abstract

Disclosed is a noise filtering apparatus for Internet service using an MATV network, which is provided between an HFC network and CMTS in Internet communication using the MATV network wired in a composite building and includes a band-pass filter for eliminating noise components introduced in upstream signals, and an amplifier connected to the rear of the band-pass filter for amplifying a level of the filtered upstream signals in order to restore a level of the upstream signal attenuated in the band-pass filter into its original signal level. Using this apparatus, it is possible to provide Internet communication service of better quality since various noises generated on introduction lines or connection lines are eliminated in the upstream signals.

Description

NOISE FILTERING APPARATUS FOR INTERNET SERVICE USING

MASTER ANTENNA TELEVISION NETWORK

TECHNICAL FIELD

The present invention relates to a filtering apparatus used for structuring an

Internet communication network by use of a master antenna television network (MATV

network) equipped during construction of a building such as an apartment, an office building, a shopping building, a school, a hotel or an inn, which are commonly called a

complex building.

BACKGROUND ART

Generally, a complex building is provided with a master antenna television

network (MATV network) so that multiple households or dwellers may watch programs

of various channels. The MATV network is a single signal receiving system for

connecting a plurality of TV receivers in one building or dense building area. This

MATV network includes one main antenna and a cable network for distributing TV

signals from the main antenna to a plurality of TV receivers so as to watch TV.

hi particular, an apartment in which many households are clustered frequently

uses the MATV network in connection to many regional cable TV service providers in order to satisfy the desire of the households. The regional cable TV service providers

generally send TV signals through an optical cable from a cable radio relay station to nods close to the end users, and also send the TV signals through a coaxial cable from the nods to a TV signal receiving set-top box of each user. This technique enabling to use both of the optical cable and the coaxial cable in

different parts of network in order to transmit TV signals composed of video and audio data to users is called "HFC (Hybrid Fiber Coaxial) communication technique".

According to the HFC communication technique, a signal with trustworthy

superior transmission property of the optical cable may be advantageously transmitted close to the users without changing the existing coaxial cable which is already installed

in offices and houses.

In addition, since the optical cable is used as a backbone pipe, more data may be

transmitted at a high bandwidth in the HFC technique than the case using only the

coaxial cable. Thus, the HFC technique may support the mutual-directional data transmission service based on the server/client model. Moreover, since the infrastructure in which the optical cable is installed has better reliability than the coaxial

cable, the HFC technique is efficient in mutually connecting networks of cable TV

service providers or telephone service providers closely located. Thus, many cable TV

service providers and telephone service providers are currently upgrading the existing

network into the HFC network.

On the other hand, there is recently commonly used the technique for providing

the high-speed Internet service using the HFC network, and the Internet service thereby

spreads all over the country. The process of transmitting Internet upward/downward signals through the HFC

network in order to realize the high-speed Internet service is described below in detail with reference to FIG. 1.

At first, Internet data packets transmitted through the Internet network 5 pass a router 10, and the Internet data packets transmitted through the router 10 are converted through CMTS (Cable Modem Termination System) 20 into a data having a format

receivable by a cable modem 60.

The converted Internet data is combined at a combiner 25 with cable TV signals

sent from a CATV transmitting station 15 and then transmitted to an optical network 40

through an optical transmitter 30. This transmitted combined signal is also transmitted to a building, in which Internet service is willing to be provided, through a directional coupler 55 via an optical network unit 45 and a coaxial cable network 50.

The combined signal split in the directional coupler 55 is separated into an

Internet signal and a cable TV signal at a signal separator 80, and then transmitted

through individual cable lines, respectively. The Internet signal among the separated

signals is converted into a signal recognizable by a user terminal 75 by means of a cable

modem 60, and then input to the user terminal 75. The cable TV signal is also input to

a TV receiver 70 via a converter 65.

On the other hand, the Internet upward signal transmitted from the user terminal

75 is firstly input to the optical network unit 45 via the cable modem 60 through the coaxial cable network 50. The Internet upward signal input to the optical network unit

45 is converted into an optical signal and then transmitted to the optical network 40.

After that, the Internet upward signal is input to the CMTS 20 through an optical

receiver 35 so as to be converted into Internet data packets, and then transmitted to the

Internet network 5 through the router 10.

The Internet upward signal is carried by a band used for transmission from the

user terminal 75 to a broadcasting station, which is hardly used in the past. However, along with the rapid propagation of high-speed Internet service, the upward band shows very increased use in recent days.

Nevertheless, the short wave band used for the upward signal has very weak structure to data communication because of much inflow of noise. Thus, only the

bandwidth 22MHz between 20MHz ~ 42MHz is practically used in the upward band.

The upward band of the HFC network is a short wave band showing a strong frequency property which may penetrate into the coaxial cable network, and many

domestic or overseas radio wave services such as HAM, TRS, short wave broadcasting

and special wireless service are existing in the band. Thus, the radio waves are combined with the upward transmission signal, which affects on the quality of the

upward signal. Here, various noises are generated at connecter portions of trunk lines or drop lines, fastened portions of various elements and portions not sufficiently

shielded in the indoor installations, and these generated noises are mixed in the upward band.

In other words, the current induced on the coaxial cable surface of trunk line,

drop line or indoor line is mixed in the connection portion of a connector, or an indoor

line, indoor device or protector having insufficient shielding.

In addition, it is also possible that the current induced in a drop line or an indoor line of the regular power source is mixed through a power line of a converter or a TV

receiver. This is generated when the indoor installation is not suitably constructed. At this time, the current caused by the voltage induced between the power line and a ground line is flowed to the ground through the indoor line or the drop line of the HFC transmission network. The difference between the upward signal and the downward signal is that all upward signals of a system may be stopped due to the interference at one point.

Transmission errors of the upward signal data are mostly caused by an impulse

noise. The impulse noise is characterized to have a rapid increasing time and a short

persistence time (mostly within lOμm) and loads significant wideband energy to the

upward band. The impulse noise may be generated in combination of impulse component which generates strong electronic wave at a specific user end connected to a

drop line or a feeder line, or when the connector or the passive element is loosely

fastened. In addition, the impulse noise may also be generated due to passive factors such as engine ignition device, power switch or neon sign.

In the upward signal of the HFC transmission network, noises generated or

penetrated in the transmission line are aggregated to one point of the headend. This is

a noise accumulation phenomenon specific to the upward line, called a streamed noise.

In other words, the noise in a complex building in which the noise inflow is serious and a local amplifier is not adjusted becomes a serious problem in the transmission of the Internet upward signal.

Thus, Internet service is provided to the complex building by use of ADSL,

home LAN, outer wall-wired cable modem and so on, not using the MATV network.

The above-mentioned currently attempted methods nevertheless have various

defects. For example, installation cost is increased in order to construct a new network.

In addition, the installation construction is very sophisticated since there is required for

finding out each line toward each household and applying signals to the line respectively, in case of a large apartment development. Moreover, extension of installations is impossible though subscribers increase. In addition, since the headend is positioned in

a basement of the apartment development which having a limited space, the installation space of the headend continuously occupies the basement as subscribers increase. Furthermore, though the coaxial cable installed in the existing MATV network is used

as the Internet line, the noises are introduced into the Internet upward signal which gives

significant influences on the Internet communication and is not effectively eliminated.

DISCLOSURE OF INVENTION

The present invention is designed to solve the problems of the prior art, and

therefore an object of the invention is to provide a filtering apparatus for Internet service, which is capable of providing high-quality data communication by use of the existing

MATV network without any additional installation.

In order to accomplish the above object, the present invention provides a noise

filtering apparatus for Internet service which is provided between an HFC (Hybrid Fiber

Coaxial) network and a CMTS (Cable Modem Termination System) in Internet

communication using an MATV network (master antenna television network) installed

in a complex building, which includes a band-pass filter for eliminating noise

introduced into an upward signal; and an amplifier connected to a rear end of the

band-pass filter for amplifying a level of the filtered upward signal in order to restore the level of the upward signal, which is attenuated through the band-pass filter, to an original signal level.

Preferably, the noise filtering apparatus is provided with a plurality of band-pass

filters and amplifiers. At this time, the noise filtering apparatus may further include a mixer for mixing

the upward signal with an oscillation frequency generated by a local oscillator at a front

end of the band-pass filter and then modulating the mixed signal in order to filter the upward signal at an intermediate frequency.

The noise filtering apparatus for Internet service may also further include

low-pass filters provided at both ends of the band-pass filter for separating the upward

signal in order to filter noise included in the upward signal.

In addition, it is also possible that the noise filtering apparatus for Internet

service further includes a level adjusting unit connected to a rear end of the amplifier for adjusting the frequency level of the upward signal to a predetermined reference level.

At this time, the level adjusting unit may include a level measuring means for

generating a signal showing an intensity of the upward signal so as to measure the upward frequency level; a control means for comparing the upward signal level

measured by the level measuring means with the predetermined reference level and

generating a level control signal when the levels are not identical; and a level converting

unit for adjusting the frequency level of the upward signal into a conversion frequency

by controlling an output frequency of a local oscillator based on the level control signal

generated by the control means.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of preferred embodiments of

the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings: FIG. 1 shows network architecture for illustrating a conventional Internet service

providing method using the HFC (Hybrid Fiber Coaxial) network;

FIG. 2 shows network architecture for providing Internet service through the

MATV network realized using a filtering apparatus according to the present invention;

FIG. 3 is a block diagram showing the filtering apparatus for Internet service

using the MATV network according to a preferred embodiment of the present invention;

and

FIG. 4 is a block diagram showing a level adjusting unit equipped in the filtering

apparatus for Internet service using the MATV network according to a preferred embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be concretely described, particularly with reference to the accompanying drawings in order to help

understanding the invention. However, the embodiments according to the invention

may be modified in various other ways, and the scope of the invention should be not

interpreted to be limited to the embodiments. The embodiments of the invention are

provided for explaining this invention more definitely and easily to those having an ordinary knowledge in the art. The same reference numeral in the drawings designates

the same element.

FIG. 2 shows network architecture for providing Internet service using the

MATV network (the master antenna television network) realized using a filtering apparatus according to the present invention. Referring to FIG. 2, the network architecture for realizing the present invention

includes the above-mentioned conventional network architecture together with the

filtering apparatus for achieving the technical object of the present invention.

Internet data packets transmitted through Internet network 5 pass through a

router 10, and the data packets transmitted through the router 5 are converted through

CMTS 20 into a data having a format receivable by a cable modem 60.

The converted data packets are combined with a cable TV signal at a combiner

25, and then transmitted to an optical network 40 through an optical transmitter 30.

The transmitted combined signal passes through a directional coupler 55 via an optical

network unit 40 and a coaxial cable network 50 by means of the HFC (Hybrid Fiber

Coaxial) communication technique so as to be transmitted to an MATV network in each

complex building.

The Internet data transmitted to the MATV network 85 is a downward signal,

which transmitted to each household through the MATV network 85 and separated into

the Internet signal and the cable TV signal at the signal separator 80.

The Internet signal separated at the signal separator 80 is converted through a

cable modem 60 into a signal recognizable by a user terminal 75 so that the user

terminal may receive the downward signal of the Internet data.

In addition, an Internet upward signal transmitted from the user terminal 75 is

transmitted in a reverse order to the Internet downward signal. In other words, the

Internet upward signal is transmitted to the coaxial cable network 50 through the cable modem 60 via the MATV network 85.

The upward signal transmitted to the coaxial cable network 50 is converted into an optical signal at the optical network unit 45, and then transmitted to an optical

receiver 35 through the optical network 40. The Internet upward signal transmitted to the optical receiver 35 is input to an upward signal noise processing unit 90 at which the noise introduced during transmission is eliminated, and then converted into Internet data

packets at the CMTS 20 through the optical receiver 35, and then transmitted to the

Internet network 5 through the router 10.

The Internet signal is classified into upward signal and downward signal, in which the upward signal is in a predetermined low frequency band of 5 ~ 52MHz, and the downward signal is in a predetermined high frequency band of 55 ~ 750MHz.

Now, the configuration of the upward signal noise processing unit, which is the

filtering apparatus according to the present invention, is described in detail with reference to FIG. 3.

FIG. 3 is a block diagram showing the filtering apparatus for Internet service

using the MATV network according to a preferred embodiment of the present invention.

Referring to FIG. 3, the upward signal noise processing unit 90, which is the

filtering apparatus of the present invention, is configured as follows. The upward

signal noise processing unit 90 includes a band-pass filter 115 for eliminating noise

introduced to the Internet upward signal transmitted from the user terminal 75 through

the MATV network 85 via the HFC network; low-pass filters 100a and 100b provided at

both ends of the band-pass filter 115 for filtering an upward signal in a low frequency band from the Internet signal received from the optical receiver 35; a first mixer 105a for mixing the upward signal with an oscillation frequency generated by a local

oscillator 125 at a front end of the band-pass filter 115 to convert the frequency band into intermediate frequency (IF) for the purpose of filtering the upward signal at the

intermediate frequency; an amplifier 110a for restoring a signal level, which is

attenuated while being modulated into the intermediate frequency by the first mixer 105a, up to the signal level before the modulation; a second mixer 105b for mixing the upward signal, of which noise is eliminated by the band-pass filter 115, with the

frequency generated by the local oscillator 125 for the purpose of down-conversion of

the frequency band so that the upward signal is converted into an original frequency

band; an amplifier 110b connected to a rear end of the band-pass filter 115 for

amplifying the level of the filtered upward signal in order to restore the attenuated

upward signal level to an original signal level; and a level adjusting unit 120 for

controlling an output frequency of the local oscillator 125 in order to convert a frequency level of the upward signal output from the amplifier 110b identically to a

predetermined frequency level.

The upward signal noise processing unit 90 according to the present invention is

preferably provided with a plurality of band-pass filters and amplifiers for signal level

compensation and more desirable noise filtering at the rear end of the band-pass filter

115 shown in FIG. 3. In this case, the upward signal noise processing unit 90 may eliminate the noise introduced in the upward signal more effectively.

In the above configuration, the level adjusting unit 120 provides an upward

signal level adjusting function so that the upward signal is matched with various Internet upward signal frequency bands adopted by many ISPs, when Internet service is provided through the HFC network. This level adjusting unit 120 is described in detail with

reference to FIG. 4. FIG. 4 is a block diagram showing the level adjusting unit equipped in the filtering apparatus for Internet service using MATV network according to a preferred

embodiment of the present invention.

Referring to FIG. 4, the level adjusting unit 120 includes a limiter 130 for

blocking input of signals over a predetermined level; a detector 135 for receiving a

signal output through the limiter 130 and generating a meta current signal which

expresses the intensity of the upward signal; a converter 140, which is configured with a resistor and an electrolytic condenser, for converting the meta current signal into a

voltage signal at the output end of the detector 135; an A/D converter (or, analog to digital converter) 145 for receiving and converting the voltage signal, which is an analog

voltage signal, into a digital upward signal level; an MCU (or, micro controller unit) 150

for comparing a predetermined upward frequency level with the digital upward signal

level, and then generating a level control signal when the levels are not coincident

within an allowable error; and a level converting unit 155 for receiving the level control

signal generated from the MCU 150 and controlling an output frequency of the local

oscillator 125 in order to adjust the level of the filtered upward signal to a conversion frequency signal level, and then outputting it to the low-pass filter 100b.

The operation of the filtering apparatus configured as above is now described in more detail with reference to FIGs. 3 and 4.

At first, the process for eliminating noise signals from the upward signal

transmitted through the MATV network 85 via the HFC network from the user terminal 75 is described with reference to FIG. 3. When the upward signal transmitted from the

user terminal 75 is input to the MATV network 85 composed of coaxial cable, noises generated by various electric equipments or electronic wave generating devices are introduced into the upward signal. This significantly lowers a signal to noise ratio

(S/N ratio) and thus abruptly increases data loss, so reliable signal transmission through

the MATV network 85 is substantially not easy. Due to this problem, the upward signal is filtered by the band-pass filter 115 to eliminate the noises introduced into the

upward signal while being transmitted through the MATV network 85 after the upward

signal in the low frequency band is separated by the low-pass filter 100a.

To explain the process of eliminating noise of the upward signal in more detail,

the upward signal separated by the low-pass filter 100a via the optical receiver 35

through the HFC network is mixed at the fist mixer 105a with frequency component provided from the local oscillator 125 so that the frequency is up-converted into an

intermediate frequency band. If noises are filtered after converting the upward signal into the intermediate frequency band, the filtering process is more easily and accurately

conducted. The upward signal of which a signal level is attenuated while being converted

into the intermediate frequency is amplified by the amplifier 110a to restore the signal

level before the modulation, and noise of this upward signal is filtered through the

band-pass filter 115. This band-pass filter 115 preferably adopts an SAW filter, which may realize high-quality signal passing, effective noise elimination and perfect signal

cutoff of unnecessary band.

The upward signal of which noise is eliminated by the band-pass filter 115 is again mixed at the second mixer 105b with the frequency provided from the local

oscillator 125 so that its frequency is down-converted into the original frequency band. The upward signal, of which noise is eliminated through the amplifier 110a and the band-pass filter 115 and demodulated into the original frequency band, is amplified by

the amplifier 110b once more in order to restore the signal level attenuation caused by the second mixer 105b, and then this upward signal is transmitted to the CMTS 20

through the level adjusting unit 120 and the low-pass filter 100b.

On the other hand, the level adjusting unit 120 provides an upward frequency band converting function when the Internet service is provided through the HFC

network in order to cope with the Internet upward frequency band adopted by ISP better.

Now, the operation of the level adjusting unit is described in detail with

reference to FIG. 4. In order to match the frequency band of the upward signal with

the frequency band of ISP, the limiter 130 blocks a signal over a predetermined level

among the filtered upward signals, and the detector 135 generates a meta current signal

for expressing the intensity of the upward signal of which the signal over a

predetermined level is blocked by the limiter 130.

The meta current signal generated at the detector 135 is converted into a voltage

signal at the converter 140, and the analogue voltage signal is converted into a digital upward signal level at the A/D converter 145.

The upward signal converted into the digital upward signal level at the A/D

converter 145 is compared with a predetermined upward signal level at the MCU 150

within an allowable error, and if the levels are not identical, an oscillator control signal for matching the levels is transmitted to the local oscillator 125.

The local oscillator 125 receiving the oscillator control signal transmitted from the MCU 150 outputs an oscillation frequency according to the control signal so that the level of the upward signal is coincided with the predetermined frequency level.

h addition, if the levels compared by the MCU 150 are identical to each other, the filtered upward signal is transmitted to the CMTS 20 through the low-pass filter

100b as it is.

Accordingly, the upward signal output from the upward signal noise processing unit 90 is matched with the frequency of ISP, so data communication from the user

terminal 75 to a server of ISP (not shown) becomes possible through the Internet

network 5. hi the upward signal noise processing unit 90 of the present invention, the first

and second mixers 105a and 105b preferably adopt DBM (Double Balanced Mixer), which minimizes noise of the local oscillator 125 and shows excellent RF (Radio

Frequency)/-F(Intermediate Frequency)/LO(Local Oscillator) isolation property. hi addition, the upward signal noise processing unit 90 of the present invention

may further include at least one amplifier/band-pass filter pair at the output end of the

band-pass filter 115. In this case, the S/N ratio may be kept higher while filtering the

upward signal to eliminate noise, so the noise introduced in the upward signal may be

more reliably eliminated.

If passing through all of the above-mentioned operations, the upward signal band

may be tuned to an Internet upward signal frequency band adopted by the ISP which

operates the Internet network, by the filtering apparatus for Internet service using the MATV network according to the present invention.

In addition, since the noise included in the upward signal is eliminated, it is

possible to provide more qualified Internet data communication. The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating

preferred embodiments of the invention, are given by way of illustration only, since

various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

INDUSTRIAL APPLICABILITY

According to an aspect of the present invention, since the MATV network

installed in an apartment or a building may be used as an Intemet network, it is possible to provide Internet service without installing any separate Internet network in an area

where the MATV network is already installed.

According to another aspect of the present invention, since various noises

generated on the lead-in line or the connection line are eliminated from the upward

signal, more qualified Internet communication service may be provided.

Claims

What is claimed is:

1. A noise filtering apparatus for Internet service which is provided between

an HFC (Hybrid Fiber Coaxial) network and a CMTS (Cable Modem Termination

System) in Internet communication using an MATV network (master antenna television

network) installed in a complex building, the apparatus comprising:

a band-pass filter for eliminating noise introduced into an upward signal; and an amplifier connected to a rear end of the band-pass filter for amplifying a level

of the filtered upward signal in order to restore the level of the upward signal, which is

attenuated through the band-pass filter, to an original signal level.

2. A noise filtering apparatus for Internet service according to claim 1,

wherein the noise filtering apparatus is provided with a plurality of band-pass filters and

amplifiers.

3. A noise filtering apparatus for Internet service according to claim 2,

further comprising:

a mixer for mixing the upward signal with an oscillation frequency generated by

a local oscillator at a front end of the band-pass filter and then modulating the mixed

signal in order to filter the upward signal at an intermediate frequency.

4. A noise filtering apparatus for Internet service according to claim 2, further comprising: low-pass filters provided at both ends of the band-pass filter for separating the

upward signal in order to filter noise included in the upward signal.

5. A noise filtering apparatus for Internet service according to claim 2, further comprising:

a level adjusting unit connected to a rear end of the amplifier for adjusting the frequency level of the upward signal to a predetermined reference level.

6. A noise filtering apparatus for Internet service according to claim 5,

wherein the level adjusting unit includes:

a level measuring means for generating a signal showing an intensity of the upward signal so as to measure the upward frequency level;

a control means for comparing the upward signal level measured by the level

measuring means with the predetermined reference level and generating a level control signal when the levels are not identical; and

a level converting unit for adjusting the frequency level of the upward signal into a conversion frequency by controlling an output frequency of a local oscillator based on

the level control signal generated by the control means.