WO2005008960A1

WO2005008960A1 - Digital cable modem and bidirectional amplifier using hybrid coaxial cable

Info

Publication number: WO2005008960A1
Application number: PCT/KR2004/001731
Authority: WO
Inventors: Dongwoo Lee; Changyeong Kim
Original assignee: Global Telecom Co.,Ltd.
Priority date: 2003-07-16
Filing date: 2004-07-12
Publication date: 2005-01-27
Also published as: KR20050009350A

Abstract

Provided is a digital cable modem simultaneously connected to a plurality of houses via a cable. In each house, the cable modem is disposed between a customer premise equipment subscriber device such as a user computer and a headend device of a CATV system network such as a distributor and a divider to transmit and receive digital data via an analog link therebetween. The distributor and a hub are connected by a bidirectional coaxial cable so that bidirectional data transmission and reception is made possible. The hub is connected by an optical fiber capable of transmitting and receiving data in a bidirectional manner. A television is connected to the distributor or divider so that broadcasting can be viewed. The cable modem supports a speed of 11 Mbps, 54 Mbps, and 108 Mbps and improves stability in multiple connection. The upstream and downstream speeds are identical so that data can be transmitted farther with the same power, for example, a transmission distance over tens of kilometers.

Description

Description DIGITAL CABLE MODEM AND BIDIRECTIONAL AMPLIFIER USING HYBRID COAXIAL CABLE Technical Field

[1] The present invention relates to a digital cable modem and a bidirectional amplifier using a hybrid coaxial cable which uses as backbones a cable model (DOCSIS 1.0, 1J, and 2.0), an asymmetric digital subscriber line (ADSL), an exclusive network, and a gigabit optical Ethernet in an existing cable television (CATN) system network or a master antenna television (MATN), and more particularly, to a digital cable modem and a bidirectional amplifier using a hybrid coaxial cable which provides an Internet service without interference of other frequency using an existing cable installed in a building and can transmit a signal to a remote place. Background Art

[2] In general, an Internet service is provided through a cable modem (CM), an asymmetric digital subscriber line (ADSL), an exclusive network such as El and Tl, and a gigabit optical Ethernet. To provide the Internet service, a large number of additional apparatuses are used and an apparatus for connecting to a larger network to manage the service is needed together with installation of new cables. Accordingly, extra costs are generated, which may burden customers. Also, since these apparatuses are expensive and users have difficulty directly purchasing them, these apparatuses are usually used through rental services.

[3] Consequently, although supplying optical lines to each house is ideal for high speed broad band data communications, since a huge amount of capital and time is needed for the complete establishment of such a network, a solution that a cable modem system provides high speed data communications is suggested.

[4] HG. 1 is a view showing a general cable modem connection state. Referring to HG. 1, reference numeral 11 denotes a cable modem, reference numeral 12 denotes a user computer that is an example of a customer premise equipment (CPE), and reference numeral 13 denotes a distributor that is an example of a headend device in the CATN system network.

[5] The cable modem 11 is a connection apparatus that enables high speed data access such as the Internal by using the CATN system network only. The cable modem 11 is disposed between the user computer 12 and the distributor 13 and makes digital data transmitted and received therebetween through an analog link. [6] Also, reference numerals 14 and 15 denote a hub and a television, respectively. The distributor 13 and the hub 14 are connected by a bidirectional coaxial cable to make bidirectional data transmission and receiving possible. An optical fiber is connected to the hub 14 so that bidirectional data transmission and receiving is possible. A television 15 is connected to the distributor 13 so that broadcasting can be viewed.

[7] Since the cable model 11 connected as shown in the above enables not only connection through a station in a CATN system network, which is several hundred times faster than an existing telephone modem, but also maintains an on-line state, necessary information can be easily obtained anytime when needed. A down speed of a general cable model is normally 4 Mbps through 30 Mbps while an up speed is 500 Kbps through 10 Mbps.

[8] To describe the principle of the operation of the cable modem 11, in upstream, IP traffic is received from the CPE, that is, the user computer 12, through Ethernet, framed into a cable MAC frame, encoded, if necessary, digital-modulated in a quadrature phase shift keying (QPSK) or a quadrature amplitude modulation (QAM 16), and up transmitted between 5 MHz through 65 MHz.

[9] In downstream, an RF signal is received from a selected down channel, the QAM64/256 digital-modulated signal is demodulated to extract an MPEG packet, and a MAC frame is extracted with an MPEG packet toward the cable modem 11 or the user computer 12. When the signal is encoded, the signal is restored to the original data. A message toward the cable modem 11 is processed and data toward the user computer 12 is transmitted via the Ethernet. When the signal arrives at the cable modem 11, the cable modem 11 separates an Internet signal and a cable TV signal.

[10] The conventional cable modem is originally developed to use a cable in a building. However, due to interference with other signals and many other problems in the building, a separate cable is used to provide the Internet service. Accordingly, the user should pay for the additional installation.

[11] Also, in the conventional cable modem, since upstream and downstream frequencies are different, transmission capacities thereof are different, and an actually used distance is short, performance is deteriorated and only the cable is used.

[12] In particular, as the number of users increases, performance is sharply deteriorated due to architecture such as an Ethernet backbone. The distance in which signals can be transmitted without amplification is very short to be within 1 Km. Furthermore, if the signals are amplified, there is a limit to transmit the signal with amplification to a remote place due to noise. Disclosure of Invention Technical Problem

[13] To solve the above and/or other problems, the present invention provides a digital cable modem and a bidirectional amplifier using a coaxial cable in which an Ethernet signal is processed to IF, RF signal or Zero IF signal, or RF encoding so that a distance over tens of kilometers is supported and a user can use the Internet using a cable installed in a building.

[14] The present invention provides a digital cable modem and a bidirectional amplifier using a coaxial cable in which the upstream and downstream frequency are made identical and the transmission capacity is increased to be used with a TN channel band so as to have a transmission speed of 11 Mbps, 54 Mbps, or 108 Mbps and improve user's convenience.

[15] The present invention provides a digital cable modem and a bidirectional amplifier using a coaxial cable which can extend the distance of transmission.

[16] The present invention provides a digital cable modem and a bidirectional amplifier using a coaxial cable by which an existing cable installed in a building and a LAN card can be used so that burden of an installation cost to a user is reduced and the user can easily install the same with a simple operation. Thus, a financial burden to the user is reduced and, for an Internet service provider (ISP), manpower or costs needed to install supplementary devices at the initial stage are not needed. Technical Solution

[17] According to an aspect of the present invention, a digital cable modem using an coaxial cable comprises an RF signal amplifier which receives a signal transmitted from a digital portion of the modem, filters a signal in a TV channel band and amplifies a signal out of the TV channel band, and, during transmission, amplifies an output level so that a signal of a low level that is internally processed is transmitted to a system , an RF/IF converter which, during reception, converts the signal out of the TV channel band amplified by the RF signal amplifier to an intermediate frequency (IF) signal and, during transmission, uploads data to be internally processed and transmitted to an IF band, converts the same to the TV channel band, includes a content to be transmitted in a carrier frequency, and provides the same to the RF signal amplifier, an I/Q mod/demodulator which, during reception, compares a signal passed through I (in-phase) and Q (quadrature) component with the signal provided by the RF/IF converter and analyses as to which value that the received signal signifies using a QPSK (quadrature phase shift keying)/QAM (quadrature amplitude modulation) method and, during transmission, converts the signal to a signal in the QPSK method which has a 90 ° phase difference for each signal and transmits the same to the RF/IF converter, a baseband processor which, during reception, A/D converts a signal completing the QPSK analysis output from the I/Q mod/demodulator to a digital signal and extracts an original data by demodulating the digital signal using DSSS (direct sequence spread spectrum), OFDM (orthogonal frequency division multiplexing) methods and, during transmission, DSSS, OFDM modulates data to be transmitted, D/ A converts the same to an analog signal, and transmits the analog signal to the I/Q mod/demodulator, and a media access controller (MAC) which receives data to be transmitted from a PC and sends the received data to the PC, through an interface with a PC card such as a PCMCIA slot, and performs a function to control flow and switch in transmission and reception in a CSMA/CA (carrier sense multiple access/collision avoidance) method.

[18] A range of the carrier frequency uses 750 MHz through 1000 MHz in the TN channel band.

[19] The digital cable modem further comprises a means operating with a wired coaxial cable modem or an IP set top box using IEEE802.1 lb, 802.1 lg, 802.1 la, HIPER LAN 1, 2, IEEE 1394, and UWB (ultra wide band) that are existing wireless devices having a similar modulation method.

[20] In the present invention, a Zero IF method, that is, a direct RF modulation method, which directly uses an RF signal without using an IF signal, can be employed.

[21] According to another aspect of the present invention, a bidirectional amplifier to transmit a signal to a remote place using the digital cable modem comprises a band pass filter which performs filtering by passing only a signal in a desired band and blocking the other signals, a signal detector which detects an RF signal after the band pass filter performs filtering, and a switch and a gain controller which determines transmission or reception using strength of the RF signal detected by the signal detector and generates a particular output value. Advantageous Effects

[22] In the digital cable modem and a bidirectional amplifier using a coaxial cable, since the installation of the supplementary devices is not needed, the user can enjoy reduced costs while, in view of the ISP, manpower or costs for installation of s up- plementary devices at the initial stage are not needed.

[23] Also, the cable modem according to the present invention can support various speeds such as 11 Mbps, 54 Mbps, and 108 Mbps, support stable multiple connections, solve security problems, enable use of an existing LAN card, and provide a wired/ wireless combined service, so as to improve user's convenience.

[24] In the present invention, the upstream and downstream speed are made identical so that a signal can be transmitted farther using the same power through the bidirectional amplifier. Thus, the transmission distance is extended to tens of kilometers or more. Description of Drawings

[25] HG. 1 is a view for explaining a state in which a general cable modem is connected;

[26] HG. 2 is a view schematically showing the structure of a building to which the present invention is applied;

[27] HG. 3 is a view schematically showing the internal structure of a digital cable modem according to an embodiment of the present invention;

[28] HG. 4 is a view for explaining a switch operation between an RF signal and an IF signal according to an embodiment of the present invention;

[29] HG. 5 is a view for explaining a modulation and demodulation operation of DSSS according to the present invention;

[30] HG. 6 is a view for explaining .a data processing operation of OFDM according to the present invention;

[31] HG. 7 is a view showing the structure of a bidirectional amplifier according to an embodiment of the present invention; and

[32] HG. 8 is a view for explaining application of a product similar to a product according to the present invention. Best Mode

[33] A digital cable modem and a bidirectional amplifier using an coaxial cable according to an embodiment of the present invention will not be described with reference to the accompanying drawings.

[34] A product employing the present invention uses a band of 750 MHz through 1000 MHz that is a frequency band other than a present TV channel frequency. In other words, a frequency of an unused channel of the TV channel frequency is being used.

[35] HG. 2 shows the structure of a building in which the present invention is applied. Referring to HG. 2, a plurality of houses in a building like an apartment are simultaneously connected through a cable. Each house has the structure as shown in HG. 1. The cable modem 11, as shown in HG. 3, includes an RF signal amplifier 22 which receives a signal transmitted from an access point (AP) 21 that is a concentrator, filters and amplifies a signal in the above frequency band (750 MHz - 1000 MHz), and, during transmission, amplifies an output level so that a signal of a low level that is internally processed is transmitted to a system.

[36] The cable modem 11 also includes an RF/IF converter 23 which, during reception, converts the signal in the above frequency band amplified by the RF signal amplifier 22 to an intermediate frequency (IF) signal and, during transmission, uploads data to be internally processed and transmitted to an IF band, converts the same to the above frequency band, includes a content to be transmitted in a carrier frequency in the above frequency band, and provides the same to the RF signal amplifier 22.

[37] The cable modem 11 also includes an I/Q mod/demodulator 24 which, during reception, compares a signal passed through I (in-phase) and Q (quadrature) component with the signal provided by the RF/IF converter 23 and analyses as to which value that the received signal signifies using a QPSK (quadrature phase shift keying)/QAM (quadrature amplitude modulation) method and, during transmission, converts the signal to a signal in the QPSK, QAM method which has a 90 ° phase difference for each signal and transmits the same to the RF/IF converter 23.

[38] The cable modem 11 also includes a baseband processor 25 which, during reception, A/D converts a signal completing the QPSK, QAM analysis output from the I/Q mod/demodulator 24 to a digital signal and extracts the original data by demodulating the digital signal using DSSS (direct sequence spread spectrum), OFDM (orthogonal frequency division multiplexing) methods and, during transmission, DSSS, OFDM modulates data to be transmitted, D/A converts the same to an analog signal, and transmits the analog signal to the I/Q mod/demodulator 24.

[39] The cable modem 11 also includes a media access controller (MAC) 26 which receives data to be transmitted from a PC and sends the received data to the PC, through an interface with a PC card such as a PCMCIA slot, and performs a function to control flow and switch in transmission and reception in a CSMA/CA (carrier sense multiple access/collision avoidance) method.

[40] The operation of the cable modem having the above structure according to the embodiment of the present invention is described below. In the following description, the above frequency band (750 MHz - 1000 MHz), for example, is used.

[41] A signal transmitted from the access point (AP) 21 that is an concentrator is transferred through air and the signal is attenuated in the air so that a level of the signal is lowered. Since the signal of a low level is difficult to use directly, the signal transmitted from the access point (AP) 21 needs to be amplified. [42] The RF signal amplifier 22 amplifies a weak received signal to a signal suitable for use. Also, since the above frequency band is used, only a signal around the above frequency band is needed. Thus, a filter to distinguish such a signal is provided.

[43] During transmission, the output level of the internally processed low level signal should be increased so as to be transmitted to the system. The RF signal amplifier 22 amplifies the internally processed low level signal During transmission so as to be transmitted through an antenna.

[44] To load a content to be transmitted in a carrier frequency in the above frequency band, as shown in HG. 4, the frequency is converted to a frequency of an intermediate step that is the IF and then upgraded to the above frequency band. This is because the bandwidth used for the transmission of data is relatively lowered than the above frequency band. Accordingly, if the frequency is upgraded at once, a gain property of the amplifier and other various properties are deteriorated so that the signal is upgraded to the IF at about 10 MHz through 600 MHz and to the RF frequency band. Thus, during reception, the signal in the RF frequency band amplified through the antenna and RF signal amplifier 22 is converted to the IF frequency band and, during transmission, the internally processed data to be transmitted is uploaded to the IF frequency band and then converted to the RF frequency band.

[45] When noise is generated in the above conversion, an error exists in the content to be transmitted so that a low noise amplifier (LNA) exhibiting a superior amplification property and being strong at the noise is provided to the RF/IF converter 23.

[46] The signal converted to the IF signal by the above operation of the RF/IF converter 23 passes through the I/Q mod/demodulator 24 performing modulation and demodulation and analyzes a QPSK, QAM type signal. During reception, signals passing through the I (in-phase) component and the Q (quadrature) component that is different by 90 from the I component are compared and the value the received signal signifies is analyzed. The analyzed signal is transmitted to the baseband processor 25. During transmission, the signal from the baseband processor 25 is converted to a signal in the QPSK, QAM method which has a 90 ° phase difference for each signal and transmitted to the RF/IF converter 23.

[47] The IF signal completing the QPSK, QAM analysis by the operation of the I/Q mod/demodulator 24 still remains as an analog signal and the DSSS, OFDM analysis has not yet been performed. The baseband processor 25 converts an input IF signal to a digital signal through an A/D converter or, during transmission, a digital signal to an analog signal through a D/A converter and, as shown in HGS. 5 and 6, performs the DSSS, OFDM mod/demodulation. During reception, the analog signal completing the QPSK, QAM analysis is input to the baseband processor 25. The signal is A/D converted to a digital signal and DSSS, OFDM demodulated to extract the original data. During transmission, data to be transmitted is DSSS, OFDM modulated and D/A converted and then transmitted to the I/Q mod/demodulator 24.

[48] In the meantime, in a Zero IF method shown in HG. 4, a signal is directly converted to an RF signal without being converted to an IF signal.

[49] The cable modem 11 according to the present invention mixes a general TN signal, and an Internet and Ethernet signal, to an RF signal through an RF mixer and transmits the mixed signal to each subscriber's end. The RF signal only including the Internet and Ethernet signal is detected among the transmitted signal and converted to the Internet and Ethernet signal. A media signal to watch TN among various signals mixed in an existing cable for a master antenna TN system enables TN watching without filtering. In contrast, an RF signal including data passes through the cable modem 11 of the present invention and decoded to an Ethernet signal so that a user can use an Internet service.

[50] In the structure and operation of the bidirectional amplifier to extend a transmission distance, as shown in HG. 7, a TN frequency band is filtered by a band pass filter (BPF) and a signal of the present product only is passed. Next, the strength of an output of an RF signal is detected to operate an interior auto gain control (AGC). Also, an auto level control (ALC) is operated to generate a particular output value. When transmission and reception is determined based on the RF signal, a switch in the bidirectional amplifier is operated. Such operation can reduce power consumption by 70% or more since the bidirectional amplifier is not always operated but operated only when a signal is generated. When a reception level is appropriately about -70 dBm though 0 dBm, an output of +10 dBm is appropriate. This is because the signal must be transmitted with the TV signal and thus exist in the same range. The TV signal reception level is in a range of -45 dBm through -60 dBm.

[51] While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

[52] For example, since the technical concept of the present invention can be used for a wireless bridge and a wireless LAN card, the present invention can be used in both wired and wireless manners according to the type of a service to be used. [53] Also, as shown in HG. 8, as applications of the present product, existing wireless LAN devices such as IEEE802J lb, 802.1 lg, 802. Ha, HIPER LAN 1, 2, IEEE 1394, and UWB (ultra wide band) can be manufactured similar to the present product by being engaged with other modems or IP set top boxs. Mode for Invention [54] Industrial Applicability [55] As described above, the present invention can be used in the fields of a digital cable modem and a bidirectional amplifier using an coaxial cable. Sequence List Text [56]

Claims

[1] A digital cable modem using an coaxial cable comprising: an RF signal amplifier which receives a signal transmitted from a digital portion of the modem, filters a signal in a TN channel band and amplifies a signal out of the TN channel band, and, during transmission, amplifies an output level so that a signal of a low level that is internally processed is transmitted to a system ; an RF/IF converter which, during reception, converts the signal out of the TN channel band amplified by the RF signal amplifier to an intermediate frequency (IF) signal and, during transmission, uploads data to be internally processed and transmitted to an IF band, converts the same to the TN channel band, includes a content to be transmitted in a carrier frequency, and provides the same to the RF signal amplifier; an I/Q mod/demodulator which, during reception, compares a signal passed through I (in-phase) and Q (quadrature) component with the signal provided by the RF/IF converter and analyses as to which value that the received signal signifies using a QPSK (quadrature phase shift keying), QAM (quadrature amplitude modulation) method and, during transmission, converts the signal to a signal in the QPSK method which has a 90 ° phase difference for each signal and transmits the same to the RF/IF converter; a baseband processor which, during reception, A/D converts a signal completing the QPSK analysis output from the I/Q mod/demodulator to a digital signal and extracts an original data by demodulating the digital signal using DSSS (direct sequence spread spectrum), OFDM (orthogonal frequency division multiplexing) methods and, during transmission, DSSS, OFDM modulates data to be transmitted, D/A converts the same to an analog signal, and transmits the analog signal to the I/Q mod/demodulator; and a media access controller (MAC) which receives data to be transmitted from a PC and sends the received data to the PC, through an interface with a PC card such as a PCMCIA slot, and performs a function to control flow and switch in transmission and reception in a CSMA/CA (carrier sense multiple access/ collision avoidance) method.

[2] The digital cable modem of claim 1, wherein a range of the carrier frequency uses 750 MHz through 1000 MHz in the TN channel band.

[3] The digital cable modem of either claim 1 or 2, further comprising a means operating with a wired coaxial cable modem or an IP set top box using IEEE802J lb, 802.1 lg, 802. Ha, HIPER LAN 1, 2, IEEE 1394, and UWB (ultra wide band) that are existing wireless devices having a similar modulation method. [4] A bidirectional amplifier of a digital cable modem to transmit a signal to a remote place using the digital cable modem of claim 1 or 2, the bidirectional amplifier comprising: a band pass filter which performs filtering by passing only a signal in a desired band and blocking the other signals; a signal detector which detects an RF signal after the band pass filter performs filtering; and a switch and a gain controller which determines transmission or reception using strength of the RF signal detected by the signal detector and generates a particular output value.