JP2010118903A - Broadcast system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a broadcast system in which a dead zone in a service area is reduced by canceling and reducing dead zones in one-segment local services. <P>SOLUTION: The broadcast system performs broadcasting to a specific area while utilizing a part of available transmission frequency bands, which includes a means for simultaneously transmitting a signal of the same contents also in another possible transmission frequency band portion of the available transmission frequency bands. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a broadcasting system that broadcasts a signal including a video signal and the like, and more particularly, to a broadcasting system that broadcasts to a specific area using a part of a transmission frequency band.

  In recent years, using the partial reception (one-segment) broadcasting system of digital terrestrial television broadcasting, the service “One” is limited to a specific area that is extremely smaller than ordinary television broadcasting, and is transmitted like broadcasting. The practical application of “segment local service” is under consideration. (Reference: Provisional Guidelines for Sending Operation of “One Segment Local Service” by Digital Broadcasting Promotion Association)

Conventionally, according to Patent Document 1 below, in a one-segment broadcasting system that transmits OFDM digital broadcasting including one-segment broadcasting in a band, considering attenuation of terrestrial digital broadcasting indoors or in a building, For the purpose of maintaining sufficient video quality even with a built-in antenna, there are already known a plurality of broadcasting means arranged in a facility and connected between them by a cable.
JP 2008-34898 A

  In a conventional broadcasting system that covers a specific area with a minute transmission power using a one-segment broadcasting system (hereinafter referred to as “area broadcasting”), a dead zone is likely to occur in the service area for the following reasons. There was a problem.

  First, the height of the transmitting antenna is lower than that of ordinary television broadcasting (for example, a few tens of meters), and the influence of the reflection of the ground, the shielding by the buildings inside and outside the service area, and the reflection are large. Second, the sampling frequency is insufficient in the first place against fading in the propagation path of the propagation distance that can be reached even with a minute transmission power. That is, when 512-point FFT is performed within an effective symbol length of 1.008 ms for one-seg reception, the sample rate in the time domain is about 2 μs, which corresponds to a propagation time of 590 m. Therefore, the frequency characteristics due to delay dispersion assumed in area broadcasts with a radius of about several hundred meters are flat within the one-segment band, and the level decreases uniformly when fading occurs, and frequency interleaving makes sense. It will not be.

  Accordingly, the present invention has been made to solve the above-described problems in the prior art, and an object of the present invention is to provide a broadcasting system capable of eliminating or reducing the dead zone when used for area broadcasting. That is.

  In order to achieve the above object, according to the present invention, first, there is provided a broadcasting system that broadcasts to a specific area by using a part of a usable transmission frequency band. There is provided a broadcasting system provided with means for simultaneously transmitting signals having the same contents in other active transmission frequency band portions.

  Further, in the present invention, in the broadcast system described above, it is preferable that the transmission unit is set at a plurality of positions in the specific area.

  That is, according to the above-described broadcasting system according to the present invention, it is possible to eliminate or reduce the dead zone in the area broadcasting by so-called frequency diversity that performs broadcasting in a plurality of frequency bands on the transmission side.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 shows the basic principle of the diversity method in the broadcasting system of the present invention, and shows a specific use segment arrangement.

  In the figure, in the one-segment local service capable of broadcasting service by using one part (1 segment out of 13 segments) of the used channel (bandwidth 6 MHz), as shown in FIG. ) And at least one segment other than the central segment (hereinafter referred to as sub-segments), the same content (excluding parts that cannot be made identical due to specifications) is transmitted.

  FIG. 2 shows a propagation path model assumed in the broadcasting system of the present invention. As shown in the figure, the receiving antenna 10 receives both the direct wave from the transmitting antenna 20 and the reflected wave from the ground. The As a result, when the central segment is received, a point at which viewing becomes impossible due to a decrease in the reception level occurs. In segments other than the central segment, the frequency is different, and the point at which viewing is not possible due to a decrease in reception level is different from the central segment.

  FIG. 3 shows an example of segment reception level calculation. The carrier frequency assumes the UHF band, fc and fH are the center frequencies of the center segment and the sub-segment, respectively, and fH is about 2.3 MHz away from fc. At the point where the distance from the antenna is around 100 meters (this is in the service area), the first level drop occurs, but if the better of fH and fc is selected, the level drop is improved by 10 dB or more. Therefore, by selecting a segment that can be viewed on the receiving terminal side, dead zones in the service area can be eliminated or reduced.

  The above is an example of ground reflection, but the same effect can be expected when there are buildings and walls inside and outside the service area where reflection occurs.

(Second Embodiment)
Next, a diversity broadcasting system according to the second embodiment of the present invention will be described.

FIG. 4 is an example of diversity transmission antenna arrangement according to the second embodiment of the present invention.
The second embodiment is characterized in that the frequency diversity transmission signal shown in the first embodiment is transmitted from two or more antennas 20 and 30 corresponding to the frequency.

  Between these antennas 20 and 30, although a ground plane (reflecting plate) is shared, a substantial radiating element portion is arranged with a quarter wavelength or more apart. In this example, the central segment is radiated from the antenna 20 and the sub-segment is radiated from the antenna 30. Arrangement may be any of vertical, horizontal, and diagonal directions, and may be determined so that the propagation path of the central segment and the sub-segment becomes more independent according to the required reception area and the place where the arrangement is possible. For example, it is also effective to make the polarization direction different between vertical and horizontal. When arranged up and down, it may be better to arrange the antenna corresponding to the higher frequency on the top. Furthermore, although not shown, when there are three or more antennas, they may be arranged not only in the same direction but also in a combination of up / down, left / right, and diagonal directions.

  As described above, the diversity system according to the present invention can eliminate or reduce the dead zone in the one-segment local service by performing diversity on the transmission side.

(Third embodiment)
Next, a diversity broadcasting system according to the third embodiment of the present invention will be described. FIG. 6 is a block diagram of a receiver suitable for a broadcasting system according to the third embodiment of the present invention. In this third embodiment, the circuit scale is slightly increased based on a conventional one-segment receiver. The frequency diversity transmission signal shown in the first and second embodiments can be received.

  The RF 41 amplifies a radio frequency reception signal input from an antenna, outputs a band-limited signal.

  The tuners 42a and 42b select a signal from the RF 41 at a frequency specified by a control unit 51 (described later), perform quadrature detection, sampling, and the like, and output a baseband digital complex signal. The individual configurations of the RF 41 and the tuners 42a and 42b are the same as those of the conventional one-segment receiver.

The symbol synchronization units 43a and 43b perform OFDM symbol synchronization from the signals from the tuners 42a and 42b, extract effective symbols, hold and output the latest effective symbol.
The switch 44a selects one of the signals from the symbol synchronization units 43a and 43b as instructed by the control unit.

  The double-speed one-segment FFT 45 is a circuit that performs an FFT operation on the signal selected by the switch 44a, for example, at 512 points, and operates at double speed according to an instruction from the control unit 51, and performs FFT for two symbols in one symbol time.

  The TMCC decoder 46 is a circuit that detects and decodes predetermined subcarriers to extract TMCC information, detects a partial reception flag, transmission parameter information for a plurality of layers, an emergency warning broadcast activation flag, and the like, and Pass to 51. The TMCC decoder 46 of this example can be operated separately from the double-speed one-segment FFT 45, but may receive only an input from the delay detection unit.

  The switch 44b outputs the signal from the double speed one-segment FFT 45 to one of the outputs from the delay detection units 47a and 47b, which is instructed by the control unit. The switches 44a and 44b operate so as to switch alternately in units of 0.5 OFDM symbol time during reception by the frequency diversity method.

  The delay detection units 47a and 47b perform differential demodulation for each subcarrier and hold the latest one OFDM symbol as a result.

  The comparison unit 48 roughly compares and compares the total power of the signals from the delay detection units 47a and 47b, and outputs a signal for selecting the higher power to the switch 44c. Furthermore, the result of QPSK determination of the signals from the delay detection units 47a and 47b may be compared to determine whether or not the signals from the delay detection units 47a and 47b are the same over all subcarriers.

  The switch 44c selects one of the signals from the delay detection units 47a and 47b instructed by the comparison unit 48.

  The deinterleaving / error decoding unit (TS decoder) 49 performs symbol determination, deinterleaving, layer separation / combination, decoding of transmission path coding, and the like on the signal from the switch 44c as appropriate based on the TMCC information, and TS. Output a stream.

  The PSI decoding unit 50 decodes the NIT (including PSI and the like) included in the TS stream and passes it to the control unit 51.

  For example, in the TMCC information from the TMCC decoder, the control unit 51 has a partial reception flag of 1 and B layer transmission parameters include predetermined information (desirably including information indicating the position number of the sub-segment). In this case, it is determined that the transmission is performed by the frequency diversity method of the present example, and a signal specifying the frequency of the sub-segment is given to the tuner 42b using the B layer transmission parameter or by trial, and the double speed one-segment FFT 45, the switch 44a, b is controlled. If the frequency diversity system is not used, the frequency of the central segment is designated only for the tuner 42a, the switches 44a and 44b are fixed to a predetermined one, and normal one-segment demodulation is performed. When the frequency diversity method is determined by trial, the determination is finally made based on the match of delay detection, the match of various IDs included in the TS, and the like. The control unit 51 also outputs necessary information such as PID to an MPEG decoder (not shown) so that the MPEG decoder can extract TS packets of appropriate PID. If the service ID is different between the central segment and the sub-segment, which causes a problem, a signal for ignoring it is output.

  Although the receiver of this example has been described as selection diversity, various types of selection criteria can be used. For example, when the power of the currently selected segment (the initial value is the central segment) falls below a predetermined value, When a TS decoding error occurs, it may be switched unconditionally to the other segment or may be combined diversity. With these methods, the amount of power calculation can be halved or eliminated.

(Fourth embodiment)
Next, a diversity broadcasting system according to the fourth embodiment of the present invention will be described. The fourth embodiment is characterized in that the frequency diversity transmission signals shown in the first and second embodiments can be received based on the conventional full-segment receiver and one-segment receiver. That is, 44a and b of the third embodiment are deleted, 42 to 47, 49, and 50 are replaced with those of a normal full segment receiver (for one wave), and one segment specified by the control unit 51 is further added. Is different from the third embodiment in that a cutout circuit 52 is provided that is fed to the comparator 48 and the switch 44c. Also in this example, the processing after the TS decoder 49 can be made the same as one reception operation of one segment, and power consumption can be reduced as compared with the operation at the time of full segment reception.

It is a figure which shows the basic principle of the diversity system in the broadcasting system of this invention. It is a figure which shows the propagation path model (1st Example) assumed with the broadcasting system of this invention. It is a figure which shows the result of the reception level calculation of the segment in said broadcast system. It is a figure which shows the propagation path model (2nd Example) assumed with the broadcasting system of this invention. It is a figure which shows the principle in the broadcast system using the broadcast system of the conventional 1seg. It is a block diagram of the receiver suitable for the broadcasting system concerning the 3rd Embodiment of this invention.

Explanation of symbols

  10: Receive antenna 20, 30 ... Transmit antenna.

Claims (2)

A broadcasting system that broadcasts to a specific area that is extremely smaller than normal television broadcasting by using an available transmission frequency,
First broadcasting means for transmitting a broadcast signal to the specific area using a part of the usable transmission frequency band;
A second signal that simultaneously transmits a signal having the same content as the broadcast signal to the specific area by using another capable transmission frequency band part different from the part of the usable transmission frequency band. And a broadcasting system.   2. The broadcasting system according to claim 1, wherein the first broadcasting unit and the second broadcasting unit are set at different positions in the specific area.

Images