JP2008236244A - Mobile relay transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile relay transmission system capable of relaying only by radio waves of two waves regardless of the number of relay stations. <P>SOLUTION: Whey performing relaying from a mobile station M to a broadcasting center C via a plurality of relay stations Ra and Rb, the mobile station M is provided with a GPS device 2 to detect a position of the mobile station M, a radio wave propagation time delay caused by a difference between the length of a radio wave propagation route via the relay station Ra and the length of a radio wave propagation route via the relay station Rb is corrected to suppress a phase shift when a microwave transmitted from the relay station Ra to the broadcasting center C and a microwave transmitted from the relay station Rb to the broadcasting center C are made to have the same frequencies. In such a case, an evaluation result of a receiving state of the relay station is transmitted through other line, and only the relay station the radio wave quality of which is relatively satisfactory is allowed to perform retransmission. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a television relay transmission system, and more particularly to a mobile relay transmission system for television relay targeting a moving subject.

  In recent years, for example, in the case of live broadcasts of a wide range of outdoor events such as marathons, a mobile station is equipped with a transmission device as a mobile station, and the moving runner is tracked with a television camera. In this case, depending on the situation, it may be difficult to wirelessly transmit the video signal directly from the mobile station to the broadcast center. In such a case, the mobile relay transmission system as shown in FIG. Is used.

  Here, in the mobile relay transmission system shown in FIG. 4, the transmission device 11 is mounted on the car A to form the mobile station M, and comparison is made between the hills and high-rise buildings that have a line-of-sight relationship with the marathon runway W. A high location is selected as a relay point X, and a receiver 13 and a transmitter 14 are installed here as a relay station R. A marathon runner image captured by the television camera TV of the mobile station M is transmitted by the mobile station M. The data is transmitted from the device 11, received by the receiving device 13 of the relay station R, transmitted again from the transmitting device 14 to the broadcast center C serving as a base station, and received by the receiving device 16.

  In the case of the system shown in FIG. 4, for example, an OFDM system using an 800 MHz Hertz wave is used for transmission between the mobile station M and the relay station R, and analog transmission using microwaves is performed between the relay station R and the broadcast center C. The method is usually used. Here, this OFDM system (orthogonal frequency division multiplex modulation system) is a type of multi-carrier modulation system in which a large number of digital modulation waves are added. According to this, it is resistant to signal level fluctuations and is stable even during movement. Therefore, it has been widely used for mobile relays.

  By the way, for example, when the moving distance is long, such as the above-mentioned marathon competition, the moving range of the mobile station M is widened, so that transmission between the mobile station M and the relay station R is difficult depending on the positional relationship with the relay station R. It may become. In particular, in recent years, the television system has also shifted from the conventional SDTV (standard television system) to HD (for example, a high-definition system). At this time, the minimum reception electric field is about -90 dbm in the case of the SDTV system. However, although 8 Mbps DQPSK (Differential Quadrature Phase Shift Keying) is sufficient, in the HD method, the 16QAM method (16 Quadrature Amplitude Modulation: 16-valued orthogonal modulation) has a minimum received electric field of only about -85 dbm. (Amplitude modulation method) is required, and for this reason, relaying becomes more difficult.

  Therefore, in such a case, as shown in FIG. 5, a system in which a relay point Y is selected in addition to the relay point X and relay stations Ra and Rb are respectively installed is conventionally applied. In the case of the system shown in FIG. 5, one 800M Hertz wave is commonly used for transmission of signals from the mobile station M to the plurality of relay stations Ra and Rb, but from the plurality of relay stations Ra and Rb to the broadcasting center. For C, microwaves a and b having different frequencies are individually used. Note that the number of relay stations at this time is not limited to two stations, X and Y, and may be three or more.

  At this time, the reception device 13a and the transmission device 14a, and the microwave a indicate that the device and the microwave of the relay station Ra, and the reception device 13b and the transmission device 14b and the microwave b are the device of the relay station Rb. Represents. The broadcasting center C includes receiving devices 15a and 15b corresponding to the microwaves a and b, respectively, and the output is selected by the switching device 16, and one of the outputs is connected to the main line according to the situation. To send out.

Here, as a related art related to such a relay transmission system, for example, the disclosure of Patent Document 1 can be cited. Further, as a conventional technique in which the receiver of each relay station has a reception state determination unit and transmits the reception state of the relay station to the base station via another line, the disclosure of Patent Document 2 can be cited.
JP-A-10-276343 JP-A-2005-51755

  The above prior art cannot be said to take into consideration that radio wave resources are limited, but has a problem in the effective use of radio wave resources. In other words, the frequency channels that can be used as radio waves are limited. Therefore, they are regulated as public goods, and approval is required for usable frequencies. Therefore, it is better to use fewer frequency channels for relaying. However, in this case, in the prior art, as many microwave channels as the number of relay stations are used for transmission to the base station, a problem arises in the effective use of radio wave resources.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a mobile relay transmission system capable of relaying with only two radio waves from a relay station, a radio wave from a relay station and a broadcast center, regardless of the number of relay stations. is there.

  In the mobile relay transmission system using a plurality of relay stations for relaying from the mobile station, the object is to provide position detection means in the mobile station, and the radio wave propagation time in each radio wave propagation path passing through the plurality of relay stations This difference is achieved in such a way that it is corrected according to the detection result of the position detecting means.

  At this time, the relay station may stop the relay operation when the quality of the signal to be relayed is lowered.

  Further, in the above transmission system, the receiver of each relay station has a reception state determining means, and the relay station's reception state comparable evaluation results are transmitted to each other between the relay stations via separate lines. Each relay station has means for comparing the radio quality of the stations received, or the base station has means for transmitting the reception status of each relay station to the base station and comparing the radio quality of each relay station received Only the relay station with relatively good radio quality may be retransmitted to the base station.

  According to the present invention, since the phase shift due to the difference in transmission path can be corrected, carriers of the same frequency can be used for transmission from a plurality of relay points to the base station, which can contribute to effective use of radio resources. .

  Hereinafter, a mobile relay transmission system according to the present invention will be described in detail with reference to embodiments shown in the drawings. Here, FIG. 1 is a block diagram showing an embodiment of a mobile relay transmission system according to the present invention. In the figure, 1 is a transmitting device, which is mounted on a car A, and thereby functions as a mobile station M. In some respects, it is the same as in the case of the prior art shown in FIG. 4 and FIG. 5, or here the GPS device 2 is further mounted on the car A, thereby detecting the position of the car A, It differs from the prior art in that it is supplied to the transmitter 1.

  Next, also in the embodiment of FIG. 1, the relay points are set at two locations of X and Y, and the relay station Ra and the relay station Rb are installed respectively, and the receiving devices 3a and 3b and the transmitting device are respectively provided. 4a and 4b are provided so that the function as a relay station can be obtained. This is the same as the case of the prior art shown in FIGS. This is different from the prior art in that 5b and delay units 6a and 6b are provided.

  At this time, the transmitters 4a and 4b in each of the relay station Ra and the relay station Rb use the same frequency microwaves, for example, the same microwave a as in the prior art in FIG. Therefore, in this embodiment, although there are two relay stations, the relay station Ra and the relay station Rb, only one receiver 7 is installed in the transmission center C. This is also different from the prior art shown in FIG.

  Therefore, the equipment of the mobile station M will be described with reference to FIG. 2. In FIG. 2, the transmitter 1 first includes a 16QAM-OFDM modulation unit MOD and a high-frequency transmission unit TX with a frequency of 800 MHz as shown in the figure. The position information P supplied from the GPS device 2 is multiplexed with the video signal V supplied from the television camera TV, and the high frequency signal 800M (V, P) with the frequency of 800 MHz modulated by the 8 Mbps 16QAM-OFDM method is used. It works to transmit the radio wave 800M1 from the antenna.

  At this time, the GPS device 2 functions to detect the position of the automobile A, that is, the position of the mobile station M and output the position information P. Note that the position detection by the GPS device 2 at this time is given by receiving GPS signals from a plurality of GPS satellites. This can be said to be well-known, and will be described here. Will be omitted.

  Next, the devices in the relay station Ra and the relay station Rb will be described with reference to FIG. 3. In FIG. 3A, first, the receiving devices 3a and 3b receive a high-frequency front unit HF ( 800M) and 16QAM-OFDM demodulator DEM (16QAM-OFDM), and a high-frequency signal 800M (V, P) having a frequency of 800 MHz modulated by 8 Mbps 16QAM-OFDM is input from an antenna, and 16QAM-OFDM demodulation is performed. The video TS signals Va and Vb and the position information Pa and Pb are decoded.

  At this time, as shown in FIGS. 3 (b) and 3 (c), the transmission devices 4a and 4b are provided with delay units 6a and 6b for inputting the corrected video signals Va and Vb, a digital modulation unit MOD (16QAM-OFDM), and a microwave. a high-frequency transmission unit TX (microwave) that operates on a carrier of frequency a, and serves to supply a parabolic antenna directed in the direction of the broadcast center C, and as a result, required by each relay station Ra, Rb The relay function to perform is obtained. At this time, even if the delay units 6a and 6b are provided before the digital modulation unit MOD as shown in FIG. 3B, the digital modulation unit as shown in FIG. It may be provided after the MOD.

  In addition, at this time, although not shown in the figure, the high frequency transmission unit TX (microwave) uses a microwave carrier phase-locked to the 800M1 carrier received from the mobile station M, and this is used as the corrected video signal Va ′. , Vb ′ is 16QAM-OFDM modulated and supplied to the parabolic antenna.

Next, the calculation units 5a and 5b receive the position information Pa and Pb, and the straight lines from the mobile station M to the relay stations Ra and Rb based on the position of the mobile station M on the map data held inside. The distances Lma and Lmb are determined. Then, the linear distances Lac and Lbc from the respective relay stations Ra and Rb to the broadcasting center C are added to this to obtain distances Lmac and Lmbc, respectively. That means
Lmac = Lma + Lac
Lmbc = Lmb + Lbc
It is supposed to be.

  Then, the distance Lmac at this time is the propagation distance of radio waves from the mobile station M to the broadcasting center C when passing through the relay station Ra, while the distance Lmbc is the movement when passing through the relay station Rb. This is the propagation distance of radio waves from the station M to the broadcasting center C. At this time, it goes without saying that the straight line distances Lac and Lbc from the respective relay stations Ra and Rb to the broadcasting center C are immediately obtained as known values from a map or the like when the relay point X and the relay point Y are set.

  Therefore, the arithmetic units 5a and 5b convert these distances Lmac and Lmbc into radio wave propagation times, respectively, to obtain delay time data DTa and DTb, and supply these to the delay units 6a and 6b. Therefore, as will be described in detail later, the delay units 5a and 5b give delay amounts to the video signals Va and Vb according to the input delay time data DTa and DTb, respectively, and correct the corrected video signals Va ′ and Vb. 'Is supplied to the transmission devices 4a and 4b, respectively.

  Here, referring back to FIG. 1, in the receiving device 7 installed at the broadcasting center C at this time, the microwave a transmitted from one relay station Ra and the microwave a transmitted from the other relay station Rb. Will be received at the same time, but at this time, if the phase matching condition that the phase of both modulation signals and the phase of the carrier match with a certain degree of error is satisfied, Even when the microwave a transmitted from one relay station Ra and the microwave a transmitted from the other relay station Rb are superimposed and received, the video signal V can be obtained without any trouble.

A technique that enables multiple channel transmission using radio waves of the same frequency (microwave a) by satisfying the phase matching condition in this way is called SFN (Single Frequendy Network) transmission. Here, the above-mentioned “error below a certain level” will be explained. First, the radio wave has a delay of about 3 μs at a propagation distance of 1 km. On the other hand, in the OFDM method, for example, even in the 2k mode, there is only a guard interval of 12 μs, so it is necessary to suppress the delay time difference of 3 μs to 6 μs. Therefore, this defines the above-mentioned “a certain degree of error”. It becomes. In addition, in the case of the mobile station M, the influence of the Doppler effect accompanying the movement can be considered, but this is only a movement of about 10 m / s at the time of relay with respect to the radio wave propagation speed of 3 × 10 ⁸ m / s. If there is no mobile station M, it can be ignored.

  Therefore, next, how the above phase alignment conditions are guaranteed in this embodiment will be described. First, in order to satisfy this phase alignment condition, the frequency of both carriers is assumed as the premise. However, in the case of this embodiment, as described above, the high-frequency transmitters TX (microwaves) of the transmitters 3a and 3b are used in both the relay stations Ra and Rb. This is guaranteed by the fact that a phase locked microwave carrier is used for the 800M1 carrier received from the mobile station M. That is, in this case, it is operating with the same carrier source.

  At this time, from the recent situation in which the practical application of the rubidium atomic oscillator is proceeding, the rubidium atomic oscillator can be used as the carrier source in the transmitter 1 of the mobile station M. However, if necessary, radio waves of GPS satellites or Galileo satellites or radio waves of terrestrial digital broadcasting may be used.

  Next, the phase matching condition will be further described. In the case of such a relay system, as shown in the figure, the propagation path of the radio wave from the mobile station M to the broadcasting center C is the path through the relay station Ra and the relay station Rb. The length of the propagation path is different between the microwave a transmitted from one relay station Ra and the microwave a transmitted from the other relay station Rb. It becomes a problem of phase alignment. In addition, at this time, the mobile station M moves according to its name, so that the length changes in each propagation path, which is further problematic.

  Therefore, in this embodiment, the GPS device 2 is attached to the car A to detect the position information P indicating the position of the mobile station M, and as described above, from the mobile station M via the relay station Ra as described above. The propagation distance Lmac of the radio wave to the broadcasting center C and the propagation distance Lmbc of the radio wave from the mobile station M to the broadcasting center C via the relay station Rb are obtained, and the propagation time of the radio wave is calculated from these. These are converted into delay data Da and Db corresponding to the respective propagation times and supplied to the delay units 6a and 6b, so that the corrected video signals Va ′ and Vb ′ are supplied to the transmitters 3a and 3b, respectively. It is.

  At this time, for these corrected video signals Va ′ and Vb ′, the propagation time of the radio wave from the mobile station M to the broadcasting center C via the relay station Ra and the mobile station M via the relay station Rb. Are delayed by the delay units 5a and 5b by the delay time data DTa and DTb, respectively, so that the propagation time of the radio wave from to the broadcast center C is apparently the same. The microwaves a received by C are signals delayed by the same time, and therefore the phase matching condition is satisfied.

  More specifically, first, the delay units 6a and 6b are set so that each delay time becomes a preset maximum delay time DTmax when the delay time data DTa and DTb are not input. To do. When the delay time data DTa and DTb are input, the delay times are set to delay times DTx (= DTmax−DTa) and DTy (= DTmax−DTb) obtained by subtracting the delay time data DTa and DTb from the maximum delay time DTmax. So that The maximum delay time DTmax at this time is the larger of the propagation distance Lmac and the propagation distance Lmbc when the mobile station M moves to a place farthest from the relay stations Ra and Rb within the movement range of the mobile station M. Set to the radio wave propagation time at the propagation distance of.

  As a result, the microwave a received from the relay station Ra to the broadcast center C and the microwave a received from the relay station Rb to the broadcast center C are both the same delay time, that is, a delay time equal to the maximum delay time DTmax. Therefore, although the delay is accompanied by a phase-aligned signal, the phase matching condition is satisfied.

  Therefore, according to this embodiment, it becomes possible to obtain a reduction in the number of channels by SFN transmission, and as a result, it is possible to provide a mobile relay transmission system that can contribute to effective utilization of radio wave resources.

  By the way, when SFN transmission is applied in this way, for example, if a signal with a low reception level and poor quality is added to a friend of SFN transmission, other signals may be adversely affected. Therefore, in the embodiment of FIG. 1, when the quality of the signal to be relayed there decreases in each relay station Ra, Rb, for example, the transmission of microwaves by the transmission devices 4a, 4b is stopped, and the relay operation is stopped. May be.

  In this case, as in the embodiment of FIG. 6, the receiver (reception device) of each relay station has a reception state determination means, and the evaluation result that can be compared with the reception state of each relay station is transmitted between the relay stations on a separate line. Each relay station has means to compare the radio quality of each relay station that is transmitted to each other, and only the relay stations with relatively good radio quality are retransmitted to the base station. As shown in the embodiment of FIG. 7, the receiver of each relay station has a reception state determination means, and transmits the reception state of the relay station to the base station by superimposition or another line, The base station has a means to compare the radio wave quality of the relay station reception, select a relay station with relatively good radio wave quality at the base station, and instruct the base station to retransmit or stop radio waves on another line. It may be transmitted.

  More specifically, FIG. 6 shows an embodiment of the present invention in which the transmission of the microwave is stopped. In the figure, reference numerals 10a and 10b denote determination units, and other configurations are omitted here. This is the same as the embodiment of FIG. Therefore, in the case of this embodiment, in the embodiment of FIG. 1, the determination units 10a and 10b are respectively added to the relay stations Ra and Rb. These determination units 10a and 10b are installed in the relay stations Ra and Rb as shown in the figure, and receive the reception information A and B from the respective reception devices 3a and 3b, and separate relay lines La, They are connected to each other via Lb and can also receive reception information A and B of other relay stations.

  At this time, as described above, the OFDM scheme is used for transmission between the mobile station M and the relay stations Ra and Rb. Therefore, the reception information A and B can be easily extracted from the reception devices 3a and 3b. In this case, the separate relay lines La and Lb provided between the relay stations Ra and Rb are, for example, narrow lines approved by broadcasting stations such as RZ-SSB (Return Zero Single Side Band) radios and wireless intercoms. A transmission line using a band radio may be used, or a wireless LAN or a telephone line may be used. In any case, the determination unit 10a of the relay station Ra connects the separate relay line Lb from the receiving device 3b of the relay station Rb. The determination unit 10b of the relay station Rb can acquire the reception information A from the reception device 3a of the relay station Ra via another line La.

  Therefore, each determination unit 10a, 10b inputs both of the reception information A and B, compares and evaluates the reception quality at the own relay station and the reception quality at the other relay station, and determines the operation stop command according to the evaluation result. S is generated and supplied to each of the transmission devices 4a and 4b. Specifically, in the determination unit 10a of the relay station Ra, when the reception quality by the reception device 3a is worse than the reception quality by the reception device 3b, the operation stop command S is supplied to the transmission device 4a, and the relay station Rb When the reception quality by the reception device 3b is worse than the reception quality by the reception device 3a, the determination unit 10b supplies an operation stop command S to the transmission device 4b.

  Therefore, according to the embodiment of FIG. 6, it is possible to suppress the propagation of unnecessary radio waves while ensuring the transmission of radio waves necessary for relaying, and this can also contribute to the effective use of radio wave resources. .

  In the embodiment of FIG. 6, in addition to the above configuration, delay adders (delay profile adapters) 17a and 17b are provided in the broadcast center C so that the received information A and B can be monitored. According to the embodiment, it is possible to monitor the propagation status of relay radio waves at the broadcast center C.

  Next, in the case of the embodiment of FIG. 7, one determination unit 10c is used, which is installed in the broadcast center C, and both reception information A and B are input to this via separate relay lines La and Lb, respectively. It has come to be. Then, the determination unit 10c inputs both of the reception information A and B, compares and evaluates the reception quality at one relay station and the reception quality at the other relay station, and determines the operation stop command according to the evaluation result. S is generated and transmitted to the respective relay stations A and B via further separate relay lines Lca and Lcb, and supplied to the transmission devices 4a and 4b. Specifically, when the reception quality by the reception device 3a is worse than the reception quality by the reception device 3b, the operation stop command S is supplied to the transmission device 4a, and the reception quality by the reception device 3b is received by the reception device 3a. If it is worse than the quality, the operation stop command S is supplied to the transmission device 4b.

  Accordingly, the embodiment of FIG. 7 also contributes to the effective use of radio resources, as in the embodiment of FIG. 6, since it is possible to suppress the propagation of unnecessary radio waves while ensuring the transmission of radio waves necessary for relaying. can do.

  Also in the embodiment of FIG. 7, delay adders (delay profile adapters) 17a and 17b are provided in the broadcast center C so that the reception information A and B can be monitored in the broadcast center C. However, the propagation status of relay radio waves can be monitored.

It is explanatory drawing which shows 1st Embodiment of the mobile relay transmission system which concerns on this invention. It is a block diagram which shows the mobile station in 1st Embodiment of the mobile relay transmission system which concerns on this invention. It is a block diagram which shows the relay station in 1st Embodiment of the mobile relay transmission system which concerns on this invention. It is explanatory drawing which shows an example of the mobile relay transmission system by a prior art. It is explanatory drawing which shows another example of the mobile relay transmission system by a prior art. It is explanatory drawing which shows 2nd Embodiment of the mobile relay transmission system which concerns on this invention. It is explanatory drawing which shows 3rd Embodiment of the mobile relay transmission system which concerns on this invention.

Explanation of symbols

1: Transmitter (mobile station transmitter)
2: GPS device 3a, 3b: receiver (relay station receiver)
4a, 4b: Transmitting device (relay station transmitting device)
5a, 5b: arithmetic units 6a, 6b: delay unit 7: receiving device (receiving device of broadcasting center)
A: Automobile W: Marathon runway

Claims (3)

In a mobile relay transmission system using a plurality of relay stations for relaying from a mobile station,
The mobile station is provided with position detection means,
A mobile relay transmission system configured such that a difference in radio wave propagation time in each radio wave propagation path passing through the plurality of relay stations is corrected according to a detection result of the position detection means. The mobile relay transmission system according to claim 1,
The mobile relay transmission system, wherein the relay station stops the relay operation when the quality of a signal to be relayed is lowered. In the mobile relay transmission system according to claim 1 or 2,
The receiving device of each relay station has a reception state determination means,
Each relay station has means for transmitting the comparison results of the reception statuses of the relay stations to each other between the relay stations on a separate line and comparing the radio wave quality of each relay station received,
The base station has means for transmitting the reception status of each relay station to the base station and comparing the radio quality of each relay station received,
A mobile relay transmission system, wherein only the relay station with relatively good radio wave quality is retransmitted to a base station.

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