JP2010258742A - Transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for preventing increase in the influence on the surroundings, when connecting a different antenna, while enlarging a service area and suppressing cost increase. <P>SOLUTION: A modulator 10 generates signals of an intermediate frequency band by orthogonally modulating data which is a processing object and outputs the signals of the intermediate frequency band. A distributor 12 distributes the inputted signals of the intermediate frequency band into a plurality of ends and outputs the signals of the intermediate frequency band thus distributed from a plurality of other ends, respectively. Each of a plurality of transmitters 14 generates the signals of a radio frequency band, by frequency-converting the inputted signals of the intermediate frequency band and transmits the signals of the radio frequency band from an antenna 16. Each of the plurality of transmitters 14 sets only the antenna 16 as an interface for the signals of the radio-frequency band. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a transmission system, and more particularly to a transmission system that transmits signals from a plurality of antennas.

  A broadcasting system for passengers in a railway vehicle to receive a television broadcast or the like with a portable receiver has been proposed. In order to improve the reception characteristics, for example, a relay device is mounted on a railway vehicle, and the relay device amplifies the received television signal or the like and transmits it to the vehicle. In addition, a train data server is installed in order to distribute information and the like suitable for each passenger's taste in the vehicle. Distribution data is broadcast from the train data server to the relay device, and the relay device extracts the distribution data in response to a request from the portable receiver and returns it to the portable receiver (for example, Patent Documents). 1).

JP 2005-203911 A

  In order to reduce the interference to the surroundings, it is required to broadcast a television signal only in a desired area. One means for realizing this is to use weak radio waves. For example, the power of weak radio waves is set so that the radius of the area is several tens of centimeters. In order to realize such a service in a plurality of areas, a plurality of transmission apparatuses are installed. When the television signal is compatible with terrestrial digital television broadcasting, since each transmission device includes an OFDM modulator, the cost generally increases.

  On the other hand, in order to suppress an increase in cost, it is effective to connect a plurality of antennas to one transmitter via a cable. At that time, the transmission device generates a radio frequency signal and outputs the radio frequency signal to the plurality of antennas via the cable. However, in such a form, when a user or a third party connects another antenna having a large gain via a cable, a radio wave with a large power exceeding the range of the weak radio wave is easily transmitted. As a result, the influence on the surroundings becomes large.

  The present invention has been made in view of such a situation, and an object of the present invention is to prevent an increase in influence on the surroundings when another antenna is connected while expanding a service area and suppressing an increase in cost. Is to provide.

  In order to solve the above problems, a transmission system according to an aspect of the present invention includes a modulation device that generates an intermediate frequency band signal by orthogonally modulating data to be processed, and outputs the intermediate frequency band signal; A modulation device is connected to one end, the input intermediate frequency band signal is divided into a plurality of distribution devices, and the divided intermediate frequency band signals are output from the plurality of other ends, respectively, and a plurality of distribution devices Each of the plurality of transmission devices is connected to the other end, generates a radio frequency band signal by frequency-converting the input intermediate frequency band signal, and transmits the radio frequency band signal from the antenna. The modulation device is connected to one end of the distribution device via a cable, each of the plurality of transmission devices is connected to each of the plurality of other ends of the distribution device via a cable, and only the antenna is a signal in the radio frequency band. Interface.

  According to this aspect, a modulation device, a distribution device, and a plurality of transmission devices are connected by a cable. In the transmission device, only the antenna is used as a radio frequency band signal interface, so the service area is expanded and the cost is increased. It is possible to prevent an increase in the influence on the surroundings when another antenna is connected.

  Each of the plurality of transmitting apparatuses may adjust the magnitude of the input intermediate frequency band signal so that the magnitude of the radio frequency band signal approaches a certain value. In this case, since the magnitude of the signal in the intermediate frequency band is adjusted, even if the magnitude of the input signal in the intermediate frequency band changes, it can conform to the weak radio wave standard.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, it is possible to prevent an increase in influence on the surroundings when another antenna is connected while expanding a service area and suppressing an increase in cost.

It is a figure which shows the structure of the transmission system which concerns on the Example of this invention. It is a figure which shows the structure of the modulation apparatus of FIG. It is a figure which shows the structure of the transmitter of FIG.

  Before describing the present invention in detail, an outline will be described. Embodiments of the present invention relate to a transmission system for transmitting a signal in a radio frequency band (hereinafter referred to as “broadcast signal”) compatible with digital television broadcasting. The transmission system according to the present embodiment includes only one OFDM modulator in order to suppress an increase in cost. In order to expand the service area, a plurality of antennas are connected to the OFDM modulator via cables.

  In such a situation, in order to prevent an increase in the influence on the surroundings when another antenna is connected, the transmission system according to the present embodiment is configured as follows. The OFDM modulator generates an intermediate frequency band signal (hereinafter referred to as “intermediate signal”), not a broadcast signal. Further, the OFDM modulator outputs an intermediate signal via a cable. Each antenna connected to the cable converts the frequency of the intermediate signal into a broadcast signal and transmits the broadcast signal. Even if an antenna corresponding to a radio frequency band is connected to the OFDM modulator by a third party, only an intermediate signal is input to the antenna, and a broadcast signal is not transmitted from the antenna. Increase in impact is prevented.

  FIG. 1 shows a configuration of a transmission system 100 according to an embodiment of the present invention. The transmission system 100 includes a modulation device 10, a distribution device 12, and a first transmission device 14a, a second transmission device 14b, a third transmission device 14c, and an Nth transmission device 14n, which are collectively referred to as a transmission device 14. The first transmitting device 14a is connected to the first antenna 16a, the second transmitting device 14b is connected to the second antenna 16b, the third transmitting device 14c is connected to the third antenna 16c, An Nth antenna 16n is connected to the Nth transmitter 14n. Here, the first antenna 16a, the second antenna 16b, the third antenna 16c, and the Nth antenna 16n are collectively referred to as the antenna 16.

  The modulation device 10 corresponds to the above-described OFDM modulator, and generates an OFDM signal in which a predetermined program is stored. The predetermined program may be stored in advance in the modulation device 10 or may be input from the outside. Here, the OFDM signal has a format corresponding to digital television broadcasting. Digital television broadcasting is a system defined by, for example, ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) and DVB (Digital Video Broadcasting). The OFDM signal in ISDB-T includes 13 segments having a width of 429 kHz. The OFDM signal may be formed by frequency division multiplexing a plurality of channels with 13 segments as one channel.

  When performing one-segment broadcasting for portable receivers in ISDB-T, one segment in the center (segment number 0) is used, but any number of 1-segment width modulation signals can be It is not excluded in the present embodiment that data is transmitted in the segment. In one-segment broadcasting, for example, QPSK is used as the modulation method of the OFDM carrier. The modulation device 10 generates an intermediate signal by orthogonally modulating the OFDM signal. The modulation device 10 is connected to one end of the distribution device 12 via a cable, and outputs an intermediate signal via the cable. For example, a coaxial cable is used as the cable.

  The distribution device 12 is connected to the modulation device 10 at one end via a coaxial cable, and receives an intermediate signal from the modulation device 10. The distribution device 12 distributes the intermediate signal into a plurality of signals. Each of the intermediate signals distributed in a plurality is a signal having the same frequency and the same content. The distribution device 12 outputs intermediate signals distributed in plural from the plural other ends. Here, the transmission device 14 is connected to each of the other ends of the distribution device 12 via a coaxial cable. Therefore, the distribution device 12 outputs an intermediate signal to each of the plurality of transmission devices 14 via the coaxial cable.

  As described above, each of the plurality of transmission devices 14 is connected to each of the plurality of other ends of the distribution device 12 via coaxial cables, and receives an intermediate signal from the distribution device 12. The transmission device 14 generates a broadcast signal by frequency-converting the intermediate signal. The transmission device 14 transmits a broadcast signal from the antenna 16. Here, each of the plurality of transmission apparatuses 14 is installed in an area where a service is to be provided. Further, since the transmission device 14 outputs a broadcast signal with weak radio waves, an area with a radius of about 10 cm is formed according to the number of the transmission devices 14. The transmission device 14 uses only the antenna 16 as an interface for broadcast signals, and does not output broadcast signals from other than the antenna 16.

  When an image receiving device (not shown) enters the area formed by the transmission device 14, it receives a broadcast signal from the transmission device 14. The image receiving apparatus reproduces a program included in at least one channel component or at least one segment component by demodulating at least one channel component or at least one segment component in the broadcast signal. The image receiving apparatus displays a program on the monitor.

  In such a configuration, a coaxial cable is used for connection between the modulation device 10 and the distribution device 12 and between the distribution device 12 and the transmission device 14. Further, in the coaxial cable, an intermediate signal is transmitted and a broadcast signal is not transmitted. Therefore, even if a third party disconnects one of the coaxial cables and connects a device (hereinafter referred to as “transmitter”) including an amplifier and an antenna to the modulation device 10 or the distribution device 12, the transmitter Only intermediate signals are input. Therefore, the transmitter transmits an intermediate signal and does not transmit a broadcast signal. Note that the power of the intermediate signal may also be reduced. As a result, an increase in influence on the surroundings when another antenna is connected is prevented.

  In addition, since the modulated analog signal is distributed, the time difference between broadcast signals output from each transmitter is small, so the signal of the modulation system that is resistant to multipath interference (such as OFDM modulation with a guard interval period added) Is used, it is possible to receive a broadcast even at a point where the service areas of each transmission device overlap by simply making the frequency difference between the transmission devices less than a specified value. On the other hand, in the conventional configuration, that is, in the case where each transmission device includes an OFDM modulator, this time difference is generally large in the modulation processing in each modulator, and when this exceeds the guard interval period, the service area of each transmission device overlaps. The broadcast cannot be received at the point. In order to solve this, it is necessary to synchronize the time between the transmitting apparatuses, which complicates the system.

  FIG. 2 shows the configuration of the modulation device 10. The modulation device 10 includes a modulation unit 20, a storage unit 22, an IFFT unit 24, an orthogonal modulation unit 26, an output terminal 30, and a control unit 32.

  The storage unit 22 stores a predetermined program. The program is, for example, moving image data and is formed as digital data. In addition, since a well-known technique should just be used for such moving image data or digital data, description is abbreviate | omitted here. The modulation unit 20 extracts a program from the storage unit 22, and then sequentially generates a TS (Transport Stream) signal. Since a known technique may be used for the TS signal, description thereof is omitted here. Further, the modulation unit 20 may input a TS signal including a predetermined program from the outside instead of generating the TS signal. The modulation unit 20 generates a frequency-domain OFDM signal by performing mapping on the TS signal. For example, QPSK is used as the modulation method in the mapping. The modulation unit 20 sequentially outputs the frequency domain OFDM signal to the IFFT unit 24.

  The IFFT unit 24 receives the OFDM signal in the frequency domain from the modulation unit 20. The IFFT unit 24 generates an OFDM signal in the time domain by performing IFFT on the OFDM signal in the frequency domain. Here, the OFDM signal in the frequency domain and the OFDM signal in the time domain correspond to OFDM signals determined in digital television broadcasting. The IFFT unit 24 sequentially outputs time-domain OFDM signals to the orthogonal modulation unit 26. The oscillating unit 28 is a local oscillator that generates a carrier wave of quadrature modulation, and its frequency is an intermediate frequency.

  The quadrature modulation unit 26 receives the time-domain OFDM signal from the IFFT unit 24 and the local oscillation signal from the oscillation unit 28. Further, the orthogonal modulation unit 26 generates an intermediate frequency band OFDM signal by orthogonally modulating the time domain OFDM signal with the local oscillation signal. The OFDM signal in the intermediate frequency band corresponds to the above-described intermediate signal. The quadrature modulation unit 26 outputs the intermediate signal to the output terminal 30. The output terminal 30 receives the intermediate signal from the quadrature modulation unit 26. Further, the output terminal 30 is connected to a coaxial cable, and an intermediate signal is output to the distribution device 12 (not shown) via the coaxial cable. The control unit 32 controls the overall operation of the modulation device 10.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it is realized by a program having a communication function loaded in the memory. Describes functional blocks realized by collaboration. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 3 shows the configuration of the transmission device 14. The transmission device 14 includes an input terminal 40, an input level adjustment unit 42, a frequency conversion unit 44, an output level adjustment unit 46, a setting unit 48, an oscillation unit 50, and a control unit 52.

  The input terminal 40 is connected to a coaxial cable, and receives an intermediate signal from a distribution device 12 (not shown) via the coaxial cable. The intermediate signal is input from the modulation device 10 to the input terminal 40 via the distribution device 12. The input terminal 40 outputs the input intermediate signal to the input level adjustment unit 42. The input level adjustment unit 42 inputs an intermediate signal from the input terminal 40 and also receives a broadcast signal from the frequency conversion unit 44. The input level adjustment unit 42 sets the gain so that the size of the broadcast signal approaches a certain value. If the size of the broadcast signal is larger than a certain value, the gain is decreased. If the size of the broadcast signal is smaller than the certain value, the gain is increased. The input level adjustment unit 42 adjusts the magnitude of the intermediate signal with the set gain. Thereby, even if the signal input to the input terminal 40 is lowered due to the loss of the coaxial cable, the size of the broadcast signal can be made constant, so that the coaxial cable can be of any thickness and length. Can be used.

  The oscillation unit 50 outputs a local oscillation signal corresponding to the frequency for converting the signal in the intermediate frequency band to the signal in the radio frequency band to the frequency conversion unit 44. The frequency of the local oscillation signal is preset by the setting unit 48. The frequency conversion unit 44 receives the local oscillation signal from the oscillation unit 50 and the intermediate signal from the input level adjustment unit 42. The frequency conversion unit 44 generates a broadcast signal by converting the frequency of the intermediate signal into a radio frequency band using the local oscillation signal. The frequency converting unit 44 outputs the broadcast signal to the output level adjusting unit 46.

  The output level adjustment unit 46 receives the broadcast signal from the frequency conversion unit 44. The broadcast signal is amplified with the gain set by the output level adjusting unit 46 and the setting unit 48. Here, the setting unit 48 may set the gain so as to correct the frequency characteristic of the gain of the antenna 16. The setting unit 48 also sets the frequency of the local oscillation signal in the oscillation unit 50. The output level adjustment unit 46 transmits the amplified broadcast signal (hereinafter also referred to as “broadcast signal”) from the antenna 16. As a result, broadcast signals having the same frequency and the same content are transmitted from the plurality of transmission devices 14. The control unit 52 controls the operation of the entire transmission device 14.

  According to the embodiment of the present invention, a modulation device, a distribution device, and a plurality of transmission devices are connected by a coaxial cable, and a broadcast signal is transmitted from each of the plurality of transmission devices. The area can be expanded. In addition, since a weak radio wave is used, interference to the surroundings can be reduced. In addition, since a plurality of transmission devices are connected to one modulation device, the modulation function can be shared. Moreover, since the modulation function is shared, an increase in cost can be suppressed. Further, since the intermediate signal is transmitted to the coaxial cable, transmission of the broadcast signal can be avoided even if a transmitter is connected.

  Moreover, since transmission of broadcast signals is avoided, an increase in influence on the surroundings can be prevented. Further, in the transmission apparatus, since only the antenna is used as the broadcast signal interface, it is possible to avoid transmission of the broadcast signal from other parts. Moreover, since it is avoided to transmit a broadcast signal from other than the antenna, an increase in influence on the surroundings can be prevented. In addition, since the magnitude of the signal in the intermediate frequency band is adjusted before conversion into the broadcast signal, the magnitude of the broadcast signal can be limited to a predetermined value. In addition, since the size of the broadcast signal is limited to a predetermined value, it can be adapted to the weak radio wave standard.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

  10 modulation device, 12 distribution device, 14 transmission device, 16 antenna, 20 modulation unit, 22 storage unit, 24 IFFT unit, 26 orthogonal modulation unit, 28 oscillation unit, 30 output terminal, 32 control unit, 40 input terminal, 42 input Level adjustment unit, 44 frequency conversion unit, 46 output level adjustment unit, 48 setting unit, 50 oscillation unit, 52 control unit, 100 transmission system.

Claims (2)

A modulation device that generates an intermediate frequency band signal by orthogonally modulating data to be processed and outputs the intermediate frequency band signal;
A distribution device that connects the modulation device to one end, distributes the input intermediate frequency band signal to a plurality, and outputs the divided intermediate frequency band signals from the plurality of other ends, respectively;
A plurality of transmissions that are respectively connected to a plurality of other ends of the distribution device, generate a radio frequency band signal by frequency-converting an input intermediate frequency band signal, and transmit the radio frequency band signal from the antenna With the device,
The modulation device is connected to one end of the distribution device via a cable,
Each of the plurality of transmission devices is connected to each of a plurality of other ends of the distribution device via a cable, and only the antenna is used as a radio frequency band signal interface.   2. The transmission device according to claim 1, wherein each of the plurality of transmission devices adjusts the magnitude of an input intermediate frequency band signal so that the magnitude of a radio frequency band signal approaches a certain value. Transmission system.

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