JP2005150853A - Communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system suitable for a building having a plurality of housings receiving video/audio signals of a high-frequency band in community. <P>SOLUTION: The communication system uses as a signal transmission path an in-house communication line 110 laid in the building 90 having a plurality of housings 200, 210 receiving the video/audio signals of a high-frequency band in community. The building 90 is provided with a community receiving terminal unit (amplifier 101, distributor 102) for receiving the video/audio signals of a high-frequency band in community, and a plurality of branch communication lines 111-114 for transmitting the video/audio signals from the receiving terminal unit to each of the housings in community. The building 90 is also provided with a first communication apparatus (master modem 10) for modulating the digital video/audio signals into signals of a low-frequency band lower than the high-frequency band, and implanting the modulated signals into the vicinity of the receiving terminal in community. The housing 210 is provided with a second communication apparatus (slave modem 20) which is connected to the terminal 121 of the branch communication line 114 and is capable of demodulating the signals modulated by the master modem 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a communication system suitable for a building including a plurality of houses that jointly receive high-frequency video and audio signals such as TV signals and CATV signals. In particular, the present invention relates to a communication system that reduces attenuation of a transmission signal and is not easily affected by inflow noise.

  2. Description of the Related Art Conventionally, in a building such as an apartment house or a commercial building having a plurality of houses, a form called joint reception is used as a reception form of video and audio signals such as TV signals and CATV signals. In this form, generally, a video / audio signal transmitted from a signal distribution side such as a TV station is distributed by a distributor and received by a plurality of houses. FIG. 2 is an explanatory diagram showing an outline of a joint reception mode of CATV signals. In the drawings, the same reference numerals denote the same items. In the form shown in FIG. 2, a video / audio signal is transmitted from a building such as a TV station having an antenna for receiving a video / audio signal from an artificial satellite to each house via a communication line such as an optical fiber cable or a coaxial cable. It is a wired form. In this form, distribution of head-end devices and servers that can distribute video and audio signals from the office building 500 to the outside of buildings 90 and 91 such as multi-family houses and detached houses 92 are usually provided. Devices 600 and 601 are arranged. These distribution apparatuses 600 and 601 are connected to the buildings 90 and 91 and the detached house 92 through the communication line 150, and transmit the video and audio signals from the station building 500 to the building 90 and the like through the communication line 150. . The building 90 includes an amplifier 101 that amplifies the video / audio signal from the distribution device 600, a distributor 102 that distributes the video / audio signal to each house in the building 90, and an indoor that transmits the video / audio signal to each house. The communication line 110 is provided. The indoor communication line 110 is branched into a plurality of branch communication lines 111 to 114 via the distributor 102, and a plurality of houses share one branch communication line. For example, the house 200 can receive a CATV signal by connecting a receiver 300 such as a television to the terminal unit 120 included in the branch communication line 111. In the example shown in FIG. 2, an example in which video and audio signals are distributed from the roof of the building 90 is shown. However, when the communication line is buried underground, the underground part of the building or the first floor It may be delivered from

  On the other hand, in recent years, communication using a power line, for example, power line communication (PLC) that transmits a communication signal to a low-voltage distribution line and performs high-speed communication has been studied (for example, see Non-Patent Document 1). ). This communication system usually includes a PLC modem that modulates and demodulates the frequency of the communication signal at several tens of MHz or less, and the communication signal is appropriately modulated and demodulated by the PLC modem, thereby enabling high-speed communication using the power line as a signal transmission path.

Kiyoshi Eto, “Current Status of Power Line Communication (PLC)”, Interface, CQ Publisher, September 2000, p.70-81

  As described above, in the conventional joint reception mode, a plurality of houses are connected to one distribution apparatus. Therefore, when noise called daily noise occurs in each house, these noises are collected in the distribution apparatus via the communication line. In addition, so-called inflow noise is generated which is collected in the station. The inflow noise may affect the distribution device, the distribution facility of the station, and the like, and the signal transmission characteristics may be deteriorated. This infusion noise becomes large in a low frequency band, specifically in a frequency band of less than 70 MHz. Therefore, conventionally, TV signals and CATV distribution signals use a frequency band of 70 MHz or higher to reduce the infusion noise and make it less susceptible to influencing noise.

  However, signals such as video and audio signals can generally reduce signal attenuation when the frequency band used is lower. Accordingly, in order to reduce the attenuation of the transmission signal, it is desired to lower the use frequency band. However, if the use frequency band is lowered, there is a problem that the deterioration of the transmission characteristics is unavoidable due to the influence of the inflow noise. There is. In addition, the higher the frequency band used, the more difficult the device is manufactured. From the viewpoint of manufacturability, it is desirable that the frequency band used be low.

  Therefore, a main object of the present invention is to provide a communication system that reduces the attenuation of a transmission signal and is less susceptible to inflow noise when an indoor communication line of a building is used as a signal transmission path.

  The present invention achieves the above object by lowering the use frequency band and specifying the arrangement position of the distribution device.

  That is, the communication system of the present invention is arranged in a building having a plurality of houses and jointly receives a high frequency band video and audio signal, and the video and audio signals from the joint receiver terminal to each house. And a plurality of branch communication lines for transmitting. A first communication device that modulates the digital video / audio signal into a low frequency band that is lower than the high frequency band and injects the digital video and audio signal in the vicinity of the joint receiving terminal unit; and a branch communication line disposed in each house. A second communication device connected to the terminal unit and capable of demodulating the signal modulated by the first communication device.

  Conventionally, it has not been considered to distribute a video / audio signal in a frequency band of less than 70 MHz due to the problem of inflow noise. However, the present inventors have studied to lower the use frequency band of the video / audio signal. As a distribution device, we attempted to use a PLC modem that can modulate and demodulate communication signals at several tens of MHz or less. However, the influence of inflow noise cannot be reduced only by replacing the conventional distribution device with the PLC modem. Therefore, the present inventors arrange a communication device capable of modulating the digital video / audio signal such as the PLC modem to a frequency lower than the frequency band of the TV signal or CATV signal in the building itself, not in a place other than the building. . With such an arrangement, the house that receives the transmission signal from the communication device on the downstream side as viewed from the distribution side of the TV signal or the like is limited, and the influence of inflow noise is reduced. The present invention will be described in detail below.

  The present invention is a building having a plurality of houses, for example, a commercial building such as an apartment house, an office building, a multi-purpose building, etc., and the plurality of houses are images of a high frequency band such as a TV signal or a CATV signal. For buildings that jointly receive audio signals. That is, a building comprising a joint receiving terminal unit for jointly receiving the video and audio signal in the high frequency band and a plurality of branch communication lines connected to the joint receiving terminal unit and transmitting the signal to each house. Use.

  Examples of the video and audio signals in the high frequency band include TV signals and CATV (Community Antenna TV) signals. Examples of the joint receiving terminal unit include an amplifier (amplifier) that amplifies the video / audio signal in the high frequency band, and a distributor that distributes the signal to each house. Examples of the distributor and amplifier include an amplifier generally used for amplifying TV signals and CATV signals, and a distributor generally used for distributing the signals. In the present invention, each branch communication line is used as a signal transmission path. Examples of the branch communication line include a coaxial cable that is generally used for transmission of a TV signal or a CATV signal. The arrangement state of the branch communication line is a state in which one end side of each branch communication line is connected to the joint receiving terminal unit (usually a distributor), that is, a so-called tree shape in which each branch communication line branches from the joint receiving terminal unit. The arrangement form is mentioned. In addition, a form in which a plurality of houses share one branch communication line is common. At this time, a plurality of terminal units are provided on one branch communication line, and these terminal units are arranged in each house, thereby enabling reception of video and audio signals such as CATV signals.

  In the building in which the above-mentioned joint reception form of video and audio signals in the high frequency band is constructed, the branch communication line is used as a signal transmission path. The present invention uses a first communication device that can modulate a low frequency band, which is a frequency lower than the high frequency band, for injection of a digital video / audio signal. The first communication device has a configuration capable of injecting a modulation signal into the signal transmission path, for example, a power source for obtaining power for operating each component such as a receiver and a receiver for receiving the signal. Examples include a power supply unit composed of a circuit and an interface necessary for communication with the outside.

  In particular, the first communication device has a configuration capable of modulating a digital video / audio signal to a frequency lower than a high frequency band used for the video / audio signal. An object of the present invention is to reduce the attenuation of a transmission signal. Therefore, in the present invention, it is defined that the digital video / audio signal is modulated to a frequency band lower than the use frequency band (high frequency band) of the video / audio signal. Specifically, for example, the frequency band of the TV signal is 90 MHz to 222 MHz in the VHF band, 470 MHz to 770 MHz in the UHF band, and the frequency band of the CATV signal is 70 to 770 MHz in the distribution signal. Therefore, the frequency band in which the first communication device performs modulation includes less than 70 MHz. In particular, 1.7 MHz to 50 MHz is preferable. If it is 50 MHz or less, it is effective in reducing signal attenuation, and if it is 1.7 MHz or more, interference with AM radio broadcasting can be avoided. In the CATV signal, the frequency band of the reply signal is 10 to 50 MHz, and about 40 MHz is often used. Therefore, when performing modulation at 10 to 50 MHz, the first communication device uses the frequency band used in the video / audio signal so that the frequency band of the digital video / audio signal is different from the frequency band used in the video / audio signal. It may be modulated by masking.

  As a modulation method, for example, a method of modulating a digital video / audio signal with a carrier frequency of 50 MHz or less at any one of a single frequency, a plurality of frequencies, and a continuous frequency can be mentioned. Specifically, a single frequency sine wave is distributed and transmitted over a wide frequency and restored to the original single frequency sine wave at the time of reception. OFDM (Orthogonal Frequency Domain Multiplex) method, other FSK (Frequency shift keying) method, PSK (Phase Shift Keying) method, which divides into frequency sine waves and densely superimposes the divided wave data Modulation) method.

  As the first communication device having the above configuration, a known PLC modem used as a so-called parent modem can be used.

  One object of the present invention is to reduce the influence of inflow noise. Therefore, in the first communication device, the modulation signal is injected in the vicinity of the joint receiving terminal unit where a plurality of branch communication lines are collected, and the houses that can sufficiently receive the injected signal are limited. When the modulation signal is injected in the vicinity of the joint reception terminal unit, the injected signal is generally transmitted to a branch communication line connected to the joint reception terminal unit. That is, a house having a branch communication line located downstream of the first communication device as viewed from the high frequency band video / audio signal distribution side can receive a signal from the first communication device. As described above, in the present invention, by defining the signal injection location of the first communication device, the range in which the signal from the first communication device can be received is limited, thereby reducing the influence of inflow noise. Depending on the capacity of the first communication device, the number of branch communication lines, etc., in the case of a known PLC modem, if it is provided in a building with about 20 to 100 houses, it will be included in one ratio. Less susceptible to inflow noise.

  As the vicinity of the joint reception terminal unit, for example, the upstream side of the amplifier as viewed from the signal distribution side of the video and audio signal in the high frequency band, between the amplifier and the distributor (the downstream side of the amplifier and the upstream side of the distributor), Examples include the downstream side of the distributor. When the joint receiving terminal unit such as an amplifier or a distributor is a device for video and audio signals in a high frequency band such as a TV signal or a CATV signal, the loss of the frequency band other than the frequency band of the signal may not be considered. . In such a case, it is preferable to inject the modulated signal directly into the branch communication line, bypassing the joint reception terminal unit. At this time, attenuation of the signal by the joint reception terminal unit can be prevented.

  According to the regulation of the signal injection location of the first communication device, the first communication device is arranged in the building itself including the joint reception terminal unit. Specific examples of the location include locations where the joint receiving terminal unit, which is a signal injection location, is located, for example, the vicinity of a rooftop, a basement, or the like.

  The present invention further includes a second communication device connected to a terminal portion of a branch communication line provided in each house and capable of demodulating the signal modulated by the first communication device. That is, the second communication device can extract the modulation signal transmitted from the first communication device to the branch communication line. For example, a receiving unit for receiving a modulated signal, a power supply unit including a power supply circuit for obtaining power for operating each component such as a receiving unit, and the like can be given. As such a second communication device, a known PLC modem used as a so-called child modem can be used. The second communication device is connected to a terminal unit of a branch communication line provided in each house, for example, a branching device that branches a video / audio signal such as a TV signal or a CATV signal, and extracts and demodulates a modulation signal. .

  A plurality of houses including the second communication device may exist in the building. At this time, the first communication device is configured to transmit a modulation signal to the plurality of second communication devices, specifically, for example, by controlling time sharing of each second communication device, It is good to use what has the structure which transmits a modulated signal to each of two communication apparatuses. In addition, in this invention, a house does not necessarily mean only a general residence but the inside of a building is divided | segmented into several space, and let it be this divided | segmented small space. Specifically, for example, individually independent homes, companies, offices, rooms, etc. that require communication.

  The first communication device and the second communication device each have impedance matching so as to match the impedance of the branch communication line serving as the signal transmission path.

  The present invention can reduce signal attenuation by using a communication apparatus such as a PLC modem that can modulate a digital video / audio signal in a low frequency band (low frequency band) as a distribution facility. In particular, in the present invention, by providing the communication device in the building itself, it is possible to achieve an excellent effect that the influence of inflow noise can be reduced while the transmission signal is in a low frequency band.

  Embodiments of the present invention will be described below.

  FIG. 1 is a schematic diagram showing an outline of the communication system of the present invention. The system of the present invention modulates a digital video / audio signal into a low frequency band having a frequency lower than the high frequency band in a building 90 having a plurality of houses (200, 210) that jointly receive high frequency band video / audio signals. A possible communication device (parent modem 10) is used as a distribution device, and an indoor communication line 110 used for transmission of a high-frequency band video / audio signal is used as a signal transmission path. In particular, in the present invention, a modulation signal is injected by the parent modem 10 in the vicinity of the joint reception terminal unit (amplifier 101, distributor 102) arranged in the building 90. This will be described in detail below.

  The building 90 includes a plurality of houses 200 and 210 that perform joint reception of TV signals and CATV signals. The amplifier 101 receives and amplifies the TV signals and CATV signals transmitted from the signal distribution side, and the TV signal. And a distributor 102 for distributing the CATV signal to each house, and an indoor communication line 110 for transmitting the TV signal and the CATV signal to each house. The indoor communication line 110 is branched into a plurality of branch communication lines 111 to 114 via the distributor 102, and a plurality of houses share one branch communication line. Each branch communication line 111 to 114 includes a plurality of terminal units 120, and each terminal unit 120 is arranged in each house. Therefore, the house 200 can receive a TV signal or a CATV signal by connecting the receiver 300 such as a television to the terminal unit 120 included in the branch communication line 111. In this example, the distributor 102 is a known one that can distribute TV signals and CATV signals. The branch communication lines 111 to 114 are known coaxial cables used for transmission of TV signals and CATV signals.

  In the building 90 that jointly receives high-frequency video / audio signals such as TV signals and CATV signals, the system of the present invention can modulate the digital video / audio signals and inject the modulated signals in the vicinity of the joint receiving terminal unit. A simple parent modem 10 is provided. Further, the house 210 includes a child modem 20 that can extract and demodulate a modulated signal that is modulated from the parent modem 10 and transmitted to the branch communication line 114.

  In particular, in the present invention, in order to reduce the attenuation of the transmission signal (digital video / audio signal), the parent modem 10 converts the digital video / audio signal into a low frequency band that is lower than the frequency band of the TV signal and the CATV distribution signal. Modulate. In this example, the parent modem 10 is a PLC modem that can modulate a digital video / audio signal to a frequency lower than the frequency band used for the TV signal and the CATV signal and can inject the modulated signal into the signal transmission path. In this example, the modulation method of the parent modem 10 is the OFDM method, and modulation is performed at a carrier frequency of 50 MHz or less.

  Also, in the present invention, since the modulated signal in the low frequency band is transmitted as described above, the receiving range of the modulated signal is limited in order to reduce the influence of inflow noise. Specifically, the parent modem 10 injects a modulation signal in the vicinity of the joint reception terminal unit included in the building 90. By injecting a signal in the vicinity of the joint receiver in this way, the modulated signal is generally transmitted to the branch communication lines 111 to 114 connected to the joint receiver. That is, the branch communication lines 111 to 114 on the downstream side of the parent modem 10 when viewed from the CATV signal distribution side are the main transmission range of the modulation signal, and compared to the conventional CATV signal distribution device, from the CATV signal distribution side Since the houses on the downstream side are limited, the influence of inflow noise is reduced. In this example, the parent modem 10 is arranged on the upstream side of the amplifier 101 as viewed from the CATV signal distribution side, and the modulation signal is injected.

  As the slave modem 20, a PLC modem capable of extracting a modulated signal transmitted to the branch communication lines 111 to 114 and demodulating the modulated signal to a frequency lower than the use frequency band of the TV signal or the CATV signal is used. In this example, the demodulation method of the child modem 20 is the OFDM method, and modulation is performed at a carrier frequency of 50 MHz or less.

  The child modem 20 is connected to the terminal unit 121 of the branch communication line 114 arranged in the house 210 and extracts a modulation signal from the terminal unit 121. In this example, the terminal unit 121 is a known branching device that can branch a TV signal and a CATV signal. Note that the impedances of the parent modem 10 and the child modem 20 are matched so as to match the impedance of the branch communication line.

  With the above configuration, when the digital video / audio signal is distributed from the upper network NT, the digital video / audio signal is transmitted to the parent modem 10 via the optical fiber cable 150 connected to the upper network NT, and the TV signal and Modulated to a frequency lower than the frequency band of the CATV signal. In this example, modulation is performed by the OFDM method with a carrier frequency of 50 MHz or less. The modulated signal is transmitted to each of the branch communication lines 111 to 114, extracted and demodulated by the child modem 20 via the terminal unit 121 included in the house 210, and extracted by the terminal device 400 such as a personal computer. Received. In this example, demodulation is performed by the OFDM method with a carrier frequency of 50 MHz or less. In this example, the parent modem 10 includes a media converter (MC) that can convert an optical signal / electrical signal, but the MC may be provided separately.

  As described above, according to the present invention, it is possible to reduce the attenuation of a distribution signal by performing distribution using a communication device that can modulate to a low frequency band that is a lower frequency than a video / audio signal of a high frequency band such as a TV signal or a CATV signal. it can. In particular, in the present invention, by arranging the communication device in the building itself and limiting the transmission range of the modulation signal from the communication device, it is possible to reduce the influence of inflow noise. Therefore, the present invention can perform distribution of a low-frequency video / audio signal in a better state.

  In the example shown in FIG. 1, an example is shown in which one house in a building that receives digital video and audio signals is provided, but a plurality of houses may be provided. At this time, each house is provided with a child modem and may be connected to a terminal portion of a branch communication line provided in each house, and the parent modem has a configuration capable of controlling the time sharing of each child modem. Good. In this example, the OFDM method is used as the modulation method and the demodulation method, but an SS method, an FSK method, a PSK method, etc. can be used as appropriate. Further, when there is a place where the frequency band of the digital video / audio signal overlaps with the use frequency band of the video / audio signal of the high frequency band, the frequency band may be modulated so as to be different from the use frequency band by masking or the like.

  In addition, in this example, the case where the modulation signal is injected on the upstream side of the amplifier 101 has been described. However, the modulation signal may be injected between the amplifier 101 and the distributor 102, on the downstream side of the distributor 102, or the like. In particular, if there is a risk of attenuation when the modulated signal is transmitted through the amplifier 101 or the distributor 102, the modulated signal is sent to the branch communication line by bypassing the joint receiving terminal unit such as the amplifier 101 or the distributor 102. It may be injected. In addition, in this example, the case where the video / audio signal is conveyed from the roof of the building 90 where the joint receiving terminal unit is arranged is described. However, in the case where a communication line such as an optical fiber cable is buried underground In some cases, the common reception terminal unit is arranged in the basement or first floor of the building 90. In such a case, the parent modem 10 may be arranged in the basement part or the first floor part of the building 90 where the joint reception terminal part is arranged.

  The system of the present invention is most suitable for receiving digital video / audio signals in a building having a plurality of houses that jointly receive high-frequency video / audio signals such as TV signals and CATV signals.

It is a schematic diagram which shows the outline | summary of this invention communication system. It is explanatory drawing which shows the outline of the joint reception form of a CATV signal in the building which provides a some house.

Explanation of symbols

10 parent modem 20 child modem
90,91 Building 92 Detached house
101 Amplifier 102 Divider 110 Indoor communication line 111 to 114 Branch communication line
120,121 Terminal 150 Communication line
200,210 House 300 Receiver 400 Terminal equipment 500 Station 600,601 Distribution device

Claims (4)

A joint receiving terminal unit that is arranged in a building having a plurality of houses and jointly receives video and audio signals in a high frequency band;
A plurality of branch communication lines for transmitting the video and audio signals from the joint reception terminal unit to each house;
A first communication device that modulates a digital video / audio signal into a low frequency band that is a frequency lower than the high frequency band and injects the digital video / audio signal in the vicinity of the joint receiving terminal unit;
A communication system comprising: a second communication device connected to a terminal portion of a branch communication line arranged in each house and capable of demodulating a signal modulated by the first communication device.   2. The communication system according to claim 1, wherein the low frequency band is less than 70 MHz.   2. The communication system according to claim 1, wherein the low frequency band is 1.7 MHz to 50 MHz.   2. The communication system according to claim 1, wherein the first communication device modulates the digital video / audio signal to a single frequency, a plurality of frequencies, or a continuous frequency with a carrier frequency of 50 MHz or less.

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