JP2006333232A - Digital broadcasting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital broadcasting system capable of providing a viewer with broadcast contents, without requiring immense equipment investment and construction expense, even in areas where broadcast radio waves cannot reach easily, such as tunnels and underground passages. <P>SOLUTION: A gap filler GF1 is arranged near an entrance to a tunnel TN, that is, a position where the digital terrestrial broadcast signal sent from a broadcasting main station, a gap filler GF2 is arranged within the broadcast service area of the gap filler GF1, that is, an area where the digital terrestrial broadcast signal from the broadcasting main station in the tunnel TN is receivable, gap fillers GF3 to GFn are arranged sequentially along a road RD, up to the proximity of an exit of the tunnel TN, and the digital terrestrial broadcast signal sent from the broadcasting main station BS is transmitted sequentially via the gap fillers GF1 to GFn. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital broadcast system that transmits a digital broadcast signal to an area where broadcast radio waves are difficult to reach, such as a tunnel or an underground passage.

In recent years, digital broadcasting has become widespread in satellite broadcasting systems using communication satellites and broadcasting satellites, and digital broadcasting has also started in terrestrial broadcasting systems.
In such a digital broadcasting system, there is a strong demand for a measure that allows a user to view a digital broadcast program even in an area where broadcast radio waves are difficult to reach, such as a tunnel or an underground passage. Therefore, a digital broadcasting that installs a broadcast transmission device that transmits digital broadcast waves in tunnels and underpasses, connects the broadcast transmission device and the broadcast main station with a communication cable, and broadcasts at the broadcast main station. A system for transmitting a program to a broadcast transmission apparatus via a communication cable is conceivable.

Also, a technique has been proposed in which a broadcast receiver displays an alternative program stored in advance when entering a radio wave-impossible area such as a tunnel or an underground passage (for example, Patent Document 1).
Japanese Patent Application Laid-Open No. 2004-112502.

  However, in the above system, it is necessary to secure a place for installing the broadcast transmission device in the tunnel or underpass, and to lay the communication cable, so a huge capital investment is required. Has become a major obstacle. In addition, maintenance of the broadcast transmission device is also necessary, and a large amount of expenses such as labor costs are required.

  Further, in the method of displaying an alternative program on the broadcast receiver side, a program different from the program viewed before entering the tunnel or the underground passage is displayed, which is uncomfortable for the viewer.

  Accordingly, an object of the present invention is to provide digital broadcasting that can provide broadcast contents to viewers without requiring huge capital investment and construction costs even in areas where broadcast radio waves are difficult to reach, such as tunnels and underpasses. To provide a system.

In order to achieve the above object, the present invention is configured as follows.
(1) A digital broadcast signal in a building that blocks digital broadcast signals coming from outside is arranged at a position where the digital broadcast signal can be received, receives the digital broadcast signal, and uses the received signal as a retransmission signal for a predetermined broadcast in the building. A first retransmission apparatus that retransmits to the service area, and a retransmission signal that is arranged in the broadcast service area of the first retransmission apparatus and that is transmitted from the first retransmission apparatus, receives this received signal as a retransmission signal And a second retransmission device that retransmits to a broadcast service area different from the broadcast service area of the first retransmission device in the building.

  According to the configuration of (1), the first retransmission device is arranged near the entrance in the building, that is, the position where the digital broadcast signal transmitted from the broadcasting station can be received, and the broadcast of the first retransmission device is performed. Since the second retransmission device is arranged in the service area, that is, the area where the digital broadcast signal from the broadcast station in the building cannot be received, the digital broadcast signal sent from the broadcast station is the first retransmission. It is transmitted to the second retransmission device via the device. For this reason, even when a viewer's broadcast receiving device is mounted on a moving body, for example, it is possible to reproduce the broadcast content without omission even when it passes through a building that cannot receive radio waves. In addition, it is possible to eliminate the need for laying communication cables, thereby reducing the cost of equipment for the system. In addition, since the retransmission apparatus is small, it is easy to install, thereby reducing the installation cost of the retransmission apparatus and maintaining it easily.

  (2) The second retransmission device is arranged in the broadcast service area of the second retransmission device, receives a retransmission signal transmitted from the second retransmission device, and uses the received signal as a retransmission signal for the first and second retransmissions in the building. The apparatus further comprises a third retransmission device for retransmitting to a broadcast service area different from the broadcast service area of the device.

  According to the configuration of (2), even in a long-distance tunnel or an underpass of a complicated route, it is possible to reproduce broadcast content without causing a loss by increasing the number of retransmission devices.

(3) The first to third retransmission apparatuses each include a reception antenna and a retransmission antenna each having directivity characteristics, and the maximum directivity direction of the reception antenna is opposite to the traveling direction of the mobile broadcast receiver in the building. And the maximum directivity direction of the retransmission antenna is set to the traveling direction of the mobile broadcast receiver.
According to the configuration of (3), it is possible to reduce degradation of signal quality due to wraparound of a retransmission signal from a retransmission antenna to a reception antenna.

(4) When the building is a tunnel road, the first to third retransmission apparatuses are sequentially arranged along the traveling direction of the mobile broadcast receiver.
According to the configuration of (4), the fluctuation speed of the received electric field in the mobile receiver can be suppressed.

  As described above in detail, according to the present invention, broadcast contents can be provided to viewers without enormous capital investment and construction costs even in areas where broadcast radio waves are difficult to reach such as tunnels and underpasses. A digital broadcasting system can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic configuration diagram of a terrestrial digital broadcasting system according to the first embodiment of the present invention. This system relays a gap filler GF1 installed in a tunnel TN as a retransmission apparatus and performs digital broadcasting. The terrestrial digital broadcast signal transmitted from the broadcast main station BS as the master station is broadcast toward the broadcast service area. Broadcast receivers RS1 and RS2 in this broadcast service area receive and reproduce terrestrial digital broadcast signals coming from the broadcast main station BS.

  Note that the broadcast receivers RS1 and RS2 are mounted on a vehicle traveling on the road RD or used by being carried by the viewer himself (user). The broadcast receivers RS1 and RS2 can be fixedly installed in the home.

  The terrestrial digital broadcast signal transmitted from the broadcast main station BS is relayed by the gap filler GF1 and broadcast toward the broadcast service area in the tunnel TN.

  FIG. 2 is a block diagram showing an arrangement example of n gap fillers GF1 to GFn arranged in the tunnel TN.

  That is, n gap fillers GF1 to GFn are arranged at predetermined intervals along the road RD in the tunnel TN.

  The terrestrial digital broadcast signal arriving from the broadcast main station BS is received by the receiving antenna 11 of the gap filler GF 1, and the received signal is supplied to the amplifier 12. The amplifier 12 amplifies the input received signal to a predetermined amplitude level, and outputs the amplified signal to the retransmission antenna 13 as a retransmission signal. Then, the retransmission antenna 13 radiates the input retransmission signal as a retransmission wave to the broadcast service area.

  This retransmitted wave is received by the receiving antenna 21 of the gap filler GF 2, and the received signal is supplied to the amplifier 22. The amplifier 22 amplifies the input received signal to a predetermined amplitude level, and outputs the amplified signal to the retransmission antenna 23 as a retransmission signal. Then, the retransmission antenna 23 radiates the input retransmission signal as a retransmission wave to the broadcast service area.

  Then, the retransmitted wave is sequentially retransmitted by the retransmit antenna n3 of the gap filler GFn through the gap fillers GF3 to GFn sequentially.

Next, the operation in the above configuration will be described.
It is assumed that a vehicle equipped with the broadcast receiver RS1 passes through the tunnel TN during the reception period of the terrestrial digital broadcast signal from the broadcast main station BS by the broadcast receiver RS1, thereby temporarily interrupting signal reception. Then, in this reception interruption period, a part of broadcast data that should be received is lost.

  Therefore, in the first embodiment, if the retransmitted waves from the gap fillers GF1 to GFn can be normally received, the received broadcast data can be reproduced.

  As described above, in the first embodiment, the gap filler GF1 is disposed near the entrance in the tunnel TN, that is, at a position where the terrestrial digital broadcast signal transmitted from the broadcast main station BS can be received, and the gap filler GF1. Gap filler GF2 is arranged in the broadcasting service area of the tunnel TN, that is, the area where the terrestrial digital broadcasting signal from the broadcasting main station BS cannot be received in the tunnel TN, and the gap fillers GF3 to GFn are set on the road RD to the vicinity of the exit of the tunnel TN. The terrestrial digital broadcast signals sent from the broadcast main station BS are transmitted in order from the gap fillers GF1 to GFn.

  Therefore, even when the viewer's broadcast receiver RS1 is mounted in a car, for example, even when the user passes through the tunnel TN that cannot receive radio waves, the broadcast content can be reproduced without being lost. .

  Furthermore, the installation cost of the system can be reduced without laying a communication cable in the tunnel TN. In addition, since the gap fillers GF1 to GFn are small in size, they can be easily attached, thereby reducing the installation cost of the gap fillers GF1 to GFn and facilitating maintenance.

(Second Embodiment)
FIG. 3A shows the structure of the gap filler according to the second embodiment of the present invention. FIG. 3B is a diagram showing the directivity characteristics of the reception antenna and the retransmission antenna of the gap filler (retransmission device) according to the second embodiment. Here, the gap filler GF2 will be described as a representative, and the same parts as those in FIG.

  In FIG. 3A, the gap filler GF2 is provided with a receiving antenna 101 and a retransmission antenna 102 having directivity characteristics.

  As shown in FIG. 3B, the maximum directional direction of the receiving antenna 101 is set to the traveling direction of the tunnel TN or the like, that is, the direction opposite to the traveling direction of the broadcast receivers RS1 and RS2, and the maximum directional direction of the retransmission antenna 102 is set. By directing the direction in the traveling direction, the reception level of the signal transmitted from the previous stage gap filler GF1 is increased and the sneak component of the retransmitted signal is reduced.

  FIG. 4 is a block diagram showing the operation of the gap filler GF2. Here, an example in which a canceller for canceling the wraparound component is provided is shown.

In general, the coupling amount C of the retransmission antenna 102 in the gap filler GF2 is expressed as follows.
C = {Gt (θ ₁ ) · K · Gr (θ ₂ )} / L2 (1)
Accordingly, the amount of wraparound (Pi / Po) when the canceller is not operated is given by the following equation (2).
Pi / Po = {Gt (θ ₁ ) · K · Gr (θ ₂ )} · Ga / L ² (2)
Where Pi is the power of the wraparound component at the input point of the receiving antenna 101, Po is the transmission output at the input point of the retransmitted antenna 102 after amplification, and Gt (θ ₁ ) is the gain of the retransmitting antenna 102 in the θ ₁ direction. , Gr (θ ₂ ) is the gain of the receiving antenna 101 in the θ ₂ direction, K is the conversion coefficient from power to power flux density, Ga is the power gain of the amplifier 22, and L is the distance between the transmitting and receiving antennas. .

  A condition for the retransmission apparatus to operate stably is that the loop gain is 1 or less.

From equation (1), if there is no canceller,
{Gt (θ ₁ ) · K · Gr (θ ₂ )} · Ga / L ² <1 (3)
Is a condition for stable operation.

As can be seen from the equation (3), by reducing Gt (θ ₁ ), Gr (θ ₂ ), and Ga, the amount of the wraparound component can be further reduced.

The output power Po is determined by the cover range of the gap filler GF2. In general, when the gap fillers GF1 to GFn are arranged at the distance R, the power gain of the amplifier 22 is proportional to R2 and inversely proportional to the gain of the receiving antenna 101 and the retransmission antenna 102 in a predetermined direction. Given.
Ga = Po / Pi = M · R ² / {Gt (0) · Gr (0)} (4)
Here, R is the distance from the preceding retransmission apparatus, Gr (0) is the maximum gain of the receiving antenna 101, Gt (0) is the maximum gain of the retransmitting antenna 102, and M is a coefficient.

Conditions for stable operation against wraparound when maintaining a predetermined gap filler distance R are given by substituting Equation (4) into Equation (3) as follows.
{Gt (θ ₁ ) · K · Gr (θ ₂ )} · M · R ² / {L ² · Gt (0) · Gr (0)} <1 (5)
Equation (5) can be converted as follows.
K · M · {R ² / L ² } · {Gt (θ ₁ ) / Gt (0)} · {Gr (θ ₂ ) / Gr (0)} <1 (6)
As can be seen from the equation (6), it is understood that the reception antenna 101 and the retransmission antenna 102 can operate more stably with respect to the wraparound as the directivity gain in the transmission / reception antenna coupling direction is lower. Therefore, a stable transmission network system with reduced wraparound can be realized by using the re-transmission antenna 102 as a directional antenna and setting the maximum directivity directions to the direction of the gap fillers GF1 and GF3 in the previous stage and the next stage. Can do.

  If the condition of equation (5) cannot be realized only by the directivity gain difference between the receiving antenna 101 and the retransmitting antenna 102, as shown in FIG. 4, a wraparound canceller is added to tune the transmission / reception wraparound characteristics. Stable operation can be obtained. Even in the case of adding a canceller, the smaller the required cancellation amount, the larger the allowable range of setting accuracy of the wraparound canceller, so that the canceller can be manufactured and tuned at a lower cost.

(Third embodiment)
FIG. 5 shows radio wave arrival paths in the system according to the third embodiment of the present invention. In FIG. 5, td1 to td3 indicate delay times for propagating each path.

  In FIG. 5, the gap fillers GF1 to GFn are sequentially arranged along the traveling direction of the broadcast receivers RS1 and RS2 in the tunnel TN.

  On the other hand, FIG. 6 shows an example of a system for comparison with the third embodiment. Each retransmission apparatus constituting the system is supplied with a signal through a feeder line or the like and is transmitted with the same delay time. Similarly, td1 to td2 in FIG. 6 indicate delay times for propagating each path.

  In the system shown in FIG. 5, since the radio waves from the plurality of gap fillers GF1 to GFn are received at the reception point, the received wave is a composite wave of a plurality of waves.

  FIG. 7 shows a change state of the combined received signal level in both cases.

  In the third embodiment, since the change in the difference between td1 and (td2 + td3) at the reception point is small, the level of the combined electric field hardly changes. On the other hand, in the case shown in FIG. 6, the level fluctuation of the combined electric field is large because the difference between td1 and td2 varies greatly depending on the reception point. For this reason, in the example of FIG. 6, when the signal is received by a mobile body or the like, the electric field fluctuates and the reception characteristics are deteriorated.

  On the other hand, the third embodiment has an advantage that the reception characteristic is less deteriorated because the fluctuation of the electric field is small.

  As described above, according to the third embodiment, the above-described effects can be realized by arranging the gap fillers GF1 to GFn and the retransmission antennas 13 to n3 in one direction.

(Other embodiments)
The present invention is not limited to the above embodiments. In the above embodiment, an example in which a plurality of gap fillers are arranged in the tunnel has been described. However, for example, a plurality of gap fillers may be arranged in an underpass of a complicated route or in a large number of buildings. In particular, in an underpass with many bends, installing a gap filler for each bend is very effective when carrying a broadcast receiver.

  In addition, the system type and the gap filler configuration can be variously modified and implemented without departing from the scope of the present invention.

1 is a schematic configuration diagram of a terrestrial digital broadcasting system according to an embodiment of the present invention. The block diagram which shows the example of arrangement | positioning of the several gap filler in the tunnel shown in FIG. The figure which shows the arrangement | positioning and directivity characteristic of the receiving and re-transmission antenna concerning 2nd Embodiment of this invention. The block diagram which shows the operation | movement in the structure of the said FIG. The figure explaining the relationship between the general | schematic structure concerning arrangement | positioning of the several gap filler apparatus concerning 3rd Embodiment of this invention, and the arrival distance to a receiving point. The figure explaining the relationship between the general | schematic structure in connection with arrangement | positioning of the several gap filler apparatus in another example, and the arrival distance to a receiving point. The figure shown in order to demonstrate the example of calculation of the receiving point electric field strength in arrangement | positioning of this invention shown in FIG.5 and FIG.6.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11-n1 ... Reception antenna, 12-n2 ... Amplifier, 13-n3 ... Retransmission antenna, BS ... Broadcast main station, GF1-GFn ... Gap filler, RS1, RS2 ... Broadcast receiver, TN ... Tunnel, RD ... Road.

Claims (5)

The digital broadcast signal in the building that blocks the digital broadcast signal coming from the outside is arranged at a position where the digital broadcast signal can be received, receives the digital broadcast signal, and uses the received signal as a retransmission signal for predetermined broadcast in the building A first retransmission device to retransmit to the service area;
The first retransmission apparatus is arranged in the broadcast service area of the first retransmission apparatus, receives a retransmission signal transmitted from the first retransmission apparatus, and uses the received signal as a retransmission signal of the first retransmission apparatus in the building. A digital broadcast system comprising: a second retransmission device that retransmits to a broadcast service area different from the broadcast service area. The second retransmission apparatus is disposed in the broadcast service area of the second retransmission apparatus, receives a retransmission signal transmitted from the second retransmission apparatus, and uses the received signal as a retransmission signal for the first and second in the building. 2. The digital broadcasting system according to claim 1, further comprising a third retransmission device for retransmitting to a broadcast service area different from the broadcast service area of the retransmission device. When the building is a tunnel or an underpass,
3. The digital broadcasting system according to claim 2, wherein the first, second, and third retransmission apparatuses are arranged along the tunnel road or the underground road. The first to third retransmission apparatuses each include a reception antenna and a retransmission antenna having directivity characteristics,
The maximum directional direction of the receiving antenna is set to be opposite to the traveling direction of the mobile broadcast receiver in the building, and the maximum directional direction of the retransmission antenna is set to the traveling direction of the mobile broadcast receiver. The digital broadcasting system according to claim 2, wherein: When the building is a tunnel road,
4. The digital broadcasting system according to claim 3, wherein the first to third retransmission apparatuses are sequentially arranged along the traveling direction of the mobile broadcast receiver.

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