Broadcasting system, relay equipment, and calculation equipment

Abstract

To make it possible to measure a transmission time difference of broadcast signals between relay devices with higher accuracy without increasing facility cost or modifying transmission signals.SOLUTION: A broadcasting system 1 includes: a master station 20 that transmits a broadcast signal composed of OFDM frames at a first frequency; a plurality of relay devices 30 that receives the broadcast signal transmitted from the master station 20 and transmits the received broadcast signal at a second frequency; and a calculation device 10 that calculates a transmission time difference of the broadcast signal from the plurality of relay devices 30. Each of the plurality of relay devices 30 measures a time difference between transmission time at which the received broadcast signal is transmitted and a reference time signal, and transmits time information indicating the time difference to the calculation device 10. The calculation device 10 calculates the transmission time difference of the broadcast signal between the plurality of relay devices 30 on the basis of the time difference measured by each of the plurality of relay devices 30.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a broadcast system, a relay device, and a calculation device.

Background Art

[0002] In order to improve the quality and functionality of terrestrial digital broadcasting, studies have been underway on a transmission method for next-generation terrestrial broadcasting (hereinafter referred to as the "advanced method") that inherits the features of the current ISDB-T (Integrated Services Digital Broadcasting - Terrestrial) method, which is the transmission method of terrestrial digital broadcasting (see Non-Patent Document 1).

[0003] Similar to the current terrestrial digital broadcasting, the advanced method adopts an OFDM (Orthogonal Frequency Division Multiplexing) transmission method with high multipath resistance, and it is possible to construct a broadcast network using SFN (Single Frequency Network). SFN refers to a network that transmits the same signal on the same broadcast channel in adjacent broadcast areas. In order to realize SFN, it is necessary to synchronize the signal waveforms from multiple transmitters. However, the transmitted OFDM signal includes a time interference mitigation component called a guard interval. When constructing SFN, it is only necessary that the time difference between multiple identical incoming waves to the receivers in the service area is within the range of the guard interval. Therefore, it is necessary to adjust the transmission timing between relay devices that construct SFN to keep the time difference within a certain range.

[0004] As a method for adjusting the transmission timing in the ISDB-T method, it is known to multiplex a network synchronization information (NSI), which is a time information signal, on a broadcast signal and adjust the time based on the NSI (see Patent Document 1). In the SFN in ISDB-T described in Patent Document 1, time information is transmitted as an NSI packet using an AC (Auxiliary Channel) carrier.

[0005] In terrestrial broadcasting networks, there are two signal relay methods: one that transmits broadcast signal information via a dedicated line called TTL (Transmitter to Transmitter Link), and another called broadcast wave relay, which receives and retransmits broadcast waves from higher-level stations. Broadcast wave relay that retransmits broadcast waves at a frequency different from the frequency of the received broadcast wave from the higher-level station is called MFN (Multi Frequency Network) broadcast wave relay. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] NHK Science & Technology Research Laboratories R&D, No. 172, pp. 2-47, November 2018. [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2006-14140 [Overview of the project] [Problems that the invention aims to solve]

[0008] In the advanced system, it is being considered to construct an SFN using multiple relay devices that relay MFN broadcast waves. To realize such a configuration, it is necessary to adjust and synchronize the transmission timing of broadcast waves among multiple relay devices, and it is necessary to know the transmission timing of each station.

[0009] However, if a method is used to transmit time information as an NSI packet, as described in Patent Document 1, in order to realize such a configuration, multiplexing of NSI packets is required separately from the broadcast signal. Therefore, multiplexing NSI packets in the advanced system increases equipment costs and requires the allocation of redundant bits separately.

[0010] The purpose of this disclosure is to provide a broadcasting system, relay equipment, and calculation device that can measure the transmission time difference of broadcast signals between relay devices with higher accuracy without increasing equipment costs or altering the transmitted signals. [Means for solving the problem]

[0011] (1) A broadcasting system as an embodiment of the present disclosure comprises a master station that transmits a broadcast signal composed of OFDM frames at a first frequency, a plurality of relay devices that receive the broadcast signal transmitted from the master station and transmit the received broadcast signal at a second frequency, and a calculation device that calculates the transmission time difference of the broadcast signal from the plurality of relay devices, wherein each of the plurality of relay devices measures the time difference between the transmission time of the received broadcast signal and a reference time signal, and transmits time information indicating the time difference to the calculation device, and the calculation device calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the time difference measured by each of the plurality of relay devices.

[0012] (2) In the broadcasting system described in (1), the calculation device calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the time difference indicated by the time information received from each of the plurality of relay devices at the time closest to each other.

[0013] (3) In the broadcasting system described in (2), the plurality of relay devices transmit the time information indicating the time difference to the calculation device in association with the identification information that identifies the OFDM frame, and the calculation device calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the time difference indicated by the time information associated with the same identification information.

[0014] (4) In the broadcasting system described in (3), the calculation device extracts a time difference from the set of time differences indicated by the plurality of time information that reflects the actual transmission time difference between the plurality of relay devices, and calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the extracted time difference.

[0015] In the broadcasting system described in (5)(3) or (4), the plurality of relay devices transmit the time information to the calculation device, as identification information for identifying the OFDM frame, associating at least one of the FEC block pointer of the OFDM frame, the demodulation results of some or all of the Lch in the OFDM frame, and the demodulation results of some or all of the main line signals in the OFDM frame.

[0016] (6) A relay device in one aspect of the present disclosure receives a broadcast signal consisting of OFDM frames transmitted from a master station at a first frequency, transmits the received broadcast signal at a second frequency, measures the time difference between the transmission time of the received broadcast signal and a reference time signal, and transmits time information indicating the time difference to a calculation device that calculates the transmission time difference of the broadcast signals from a plurality of relay devices.

[0017] (7)(6) The relay device described above transmits the time information indicating the time difference to the calculation device in association with the identification information that identifies the OFDM frame.

[0018] (8) A calculation device in one aspect of the present disclosure receives time information from each of a plurality of relay devices that relay a broadcast signal composed of an OFDM frame, indicating the time difference between the transmission time of the broadcast signal and a reference time signal, and calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the time difference received from each of the plurality of relay devices.

[0019] In the calculation device according to (9)(8), based on the time difference indicated by the time information received at the closest times from each of the plurality of relay devices, the transmission time difference of the broadcast signal between the plurality of relay devices is calculated.

[0020] (10) In the calculation device according to (8), the time information indicating the time difference, which is associated with the identification information for identifying the OFDM frame, is received from each of the plurality of relay devices. Based on the time difference indicated by the time information associated with the same identification information, the transmission time difference of the broadcast signal between the plurality of relay devices is calculated.

Advantages of the Invention

[0021] According to one embodiment of the present disclosure, it is possible to measure the transmission time difference of the broadcast signal between relay devices with higher accuracy without increasing the equipment cost or involving modification of the transmission signal.

Brief Description of the Drawings

[0022] [Figure 1] It is a block diagram showing a configuration example of a broadcast system according to one embodiment. [Figure 2] It is a block diagram showing a configuration example of the time information acquisition unit 35 included in the relay device 30 of FIG. 1. [Figure 3] It is a diagram schematically showing the time difference between an OFDM frame and a reference signal. [Figure 4A] It is a diagram schematically showing an example of the time information transmitted from the relay device 30a of FIG. 1. [Figure 4B] It is a diagram schematically showing an example of the time information transmitted from the relay device 30b of FIG. 1. [Figure 5] It is a diagram showing an example of the time information transmitted from each relay device 30 of FIG. 1 and the difference thereof. [Figure 6] It is a flowchart showing an example of the operation procedure of the relay device 30 of FIG. 1. [Figure 7] [[ID=四十二]]It is a flowchart showing an example of the operation procedure of the calculation unit 12 of FIG. 1. [Figure 8] This is a block diagram showing an example of the configuration of the time information acquisition unit 35 included in the relay device 30 in Figure 1. [Figure 9] This diagram schematically shows the time difference between the OFDM frame and the reference signal. [Figure 10A] This figure schematically shows an example of time information transmitted from the relay device 30a in Figure 1. [Figure 10B] This figure schematically shows an example of time information transmitted from the relay device 30b in Figure 1. [Figure 11] This figure shows an example of the time information transmitted from each relay device 30 in Figure 1 and the difference therebetween. [Figure 12] This figure shows an example of the time information transmitted from each relay device 30 in Figure 1 and the difference therebetween. [Figure 13] This is a block diagram showing an example of the configuration of the time information acquisition unit 35 included in the relay device 30 in Figure 1. [Figure 14] This is a block diagram showing an example of the configuration of the time information acquisition unit 35 included in the relay device 30 in Figure 1. [Figure 15] Figure 1 is a flowchart showing an example of the operation procedure of the relay device 30. [Figure 16] Figure 1 is a flowchart showing an example of the operation procedure of the calculation unit 12. [Modes for carrying out the invention]

[0023] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, parts having the same configuration or function are denoted by the same reference numerals. In the description of this embodiment, redundant descriptions of the same parts may be omitted or simplified as appropriate.

[0024] <First Embodiment> Figure 1 is a block diagram showing an example configuration of a broadcasting system 1 according to one embodiment of the present disclosure. The broadcasting system 1 is provided in a broadcasting network for realizing an advanced system and comprises a studio 10, a master station 20, and a plurality of relay devices 30 (30a, 30b). The studio 10 generates a broadcast signal and transmits the broadcast signal to the master station 20. The master station 20 modulates the broadcast signal received from the studio 10 into an OFDM frame and transmits the OFDM frame as a broadcast wave using the Xch (first frequency) communication channel to the relay devices 30 (30a, 30b). Each relay device 30 (30a, 30b) performs processing such as delay control on the received OFDM frame and then retransmits it using the Ych (second frequency) communication channel. In addition, each relay device 30 (30a, 30b) acquires time information indicating the time difference between a reference time signal and the transmission time of the OFDM frame and transmits it, for example, to a calculation unit 12 provided in the studio 10. Each relay device 30 (30a, 30b) and the calculation unit 12 are connected by a dedicated line such as a monitoring line, and time information may be transmitted via this dedicated line. Each relay device 30 (30a, 30b) constitutes an SFN that simultaneously transmits the same signal on the same frequency channel (Ych).

[0025] The broadcasting system 1 measures the transmission time difference between multiple relay devices 30 (30a, 30b) that relay MFN broadcast waves in the broadcasting network. In this embodiment, an example of measuring the transmission time difference between relay devices 30a, 30b of two MFN broadcast waves is described, but the configuration according to this embodiment is also applicable to TTL relay devices. Furthermore, the broadcasting system 1 may include three or more relay devices 30. The broadcasting system 1 may also include two or more studios 10 and master stations 20.

[0026] The studio 10, as a calculation device according to this embodiment, comprises a generation unit 11 and a calculation unit 12. The generation unit 11 generates broadcast signals representing video, audio, and text information to be broadcast. The studio 10 transmits the broadcast signals generated by the generation unit 11 to the master station 20 via STL (Studio to Transmitter Link). The calculation unit 12 calculates the transmission time difference of the broadcast signals between the relay devices 30 (30a, 30b) based on the time information received from each of the multiple relay devices 30 (30a, 30b). The studio 10 may transmit the transmission time difference calculated by the calculation unit 12 to each relay device 30 (30a, 30b), for example. In this embodiment, an example in which the calculation unit 12 is provided in the studio 10 is described, but the calculation unit 12 may be provided in a location other than the studio 10. If the calculation unit 12 is provided in a device other than the studio 10, that device functions as a calculation device.

[0027] The master station 20 comprises an OFDM modulation unit 21 and a transmission unit 22. The OFDM modulation unit 21 modulates the broadcast signal received from the studio 10 to generate an OFDM frame. The advanced method is being considered to improve transmission tolerance from ISDB-T by using LDPC (Low-Density-Parity-Bit) coding for the inner code and BCH coding for the outer code of the error correction code. In such error correction coding, the FEC (Forward Error Correction) block is configured as a unit block including an FEC block header, a main signal, and a parity bit. The FEC block pointer described in the TMCC (Transmission and Multiplexing Configuration Control), which contains information such as transmission parameters, specifies the starting position of the FEC block in the OFDM frame. The value of this FEC block pointer changes for each OFDM frame. The OFDM modulation unit 21 adds such an FEC block pointer to each OFDM frame.

[0028] The transmitting unit 22 transmits the OFDM frame generated by the OFDM modulation unit 21 as a broadcast wave using the Xch communication channel to multiple relay devices 30 (30a, 30b).

[0029] Each relay device 30 (30a, 30b) comprises a receiving conversion unit 31 (31a, 31b), a compensation unit 32 (32a, 32b), a delay control unit 33 (33a, 33b), a transmitting unit 34 (34a, 34b), and a time information acquisition unit 35 (35a, 35b). The following describes an example where multiple relay devices 30 (30a, 30b) have the same configuration, but each relay device 30 (30a, 30b) may have a different configuration.

[0030] The receiving conversion unit 31 (31a, 31b) converts the frequency of the signal indicating the OFDM frame received from the master station 20 to an intermediate frequency (for example, 37.15 MHz) which is a frequency common to all relay devices 30 (30a, 30b) in the broadcasting system 1. The receiving conversion unit 31 (31a, 31b) may perform frequency conversion using any frequency conversion process.

[0031] The compensation unit 32 (32a, 32b) performs compensation processing on the received signal to improve the signal quality that has deteriorated in the transmission path between the master station 20 and the relay devices 30 (30a, 30b). The compensation unit 32 (32a, 32b) may perform compensation processing using any compensation processing method.

[0032] The delay control units 33(33a,33b) control the signal transmission time. For example, the delay control units 33(33a,33b) delay the transmission signal based on the transmission time difference received from the calculation unit 12 of the studio 10, so that the time difference of the same transmission signal transmitted from each relay device 30(30a,30b) is within the guard interval range.

[0033] The transmitting unit 34 (34a, 34b) transmits the signal output from the delay control unit 33 (33a, 33b) as a broadcast wave using the Ych communication channel. The transmitting unit 34 (34a, 34b) may, for example, convert the signal output from the delay control unit 33 (33a, 33b) from the intermediate frequency to the transmission frequency (Ych frequency), amplify the signal power, and then transmit it.

[0034] The time information acquisition unit 35 (35a, 35b) acquires time information indicating the time difference between the transmission time of the OFDM frame and the reference time signal. The time information acquisition unit 35 (35a, 35b) receives the transmission signal from the transmission unit 34 (34a, 34b) and also receives a reference time signal indicating the reference time from an external source. As such a reference time signal, the time information acquisition unit 35 (35a, 35b) may receive, for example, the 1PPS (Pulse Per Second) signal used in GPS (Global Positioning System). The 1PPS (Pulse Per Second) signal is a signal transmitted from NAVSTAR (Navigation Satellites with Time And Ranging) satellites in GPS, and is a signal that outputs exactly one pulse per second. When using the 1PPS signal as the reference time signal, the time information acquisition unit 35 (35a, 35b) may receive the 1PPS signal using a GPS receiver. Furthermore, the time information acquisition unit 35 (35a, 35b) may acquire a signal other than the GPS 1PPS signal as a reference time signal, as long as it is time information synchronized in all relay devices 30 (30a, 30b). For example, the time information acquisition unit 35 (35a, 35b) may acquire a signal synchronized to UTC (Coordinated Universal Time) as a reference time signal.

[0035] The time information acquisition unit 35(35a,35b) acquires the time difference between the transmission time and the reference time signal for each OFDM frame. In addition to the reference time signal, the time information acquisition unit 35(35a,35b) may also acquire a reference frequency signal of a fixed frequency. For example, the time information acquisition unit 35(35a,35b) may acquire the reference time signal and the reference frequency signal, count the time difference between the start timing of the OFDM frame and the reference time signal using the reference frequency signal, and acquire the counted value as the time difference between the transmission time of the OFDM frame and the reference time signal. The time information acquisition unit 35(35a,35b) may receive such a reference frequency signal from a GPS Navstar satellite. In this embodiment, as an example, a case in which a 1PPS signal is used as the reference time signal and a signal indicating 10MHz is used as the reference frequency signal will be described.

[0036] The time information acquisition unit 35 (35a, 35b) transmits time information indicating the time difference between the calculated OFDM frame transmission time and the reference time signal to the calculation unit 12 installed in the studio 10 via a monitoring and control line installed in the relay device 30 (30a, 30b). As described above, in this embodiment, an example in which the calculation unit 12 is installed in the studio 10 is described, but the calculation unit 12 does not need to be installed in the studio 10 and may be installed in another location.

[0037] Figure 2 is a block diagram showing an example configuration of the time information acquisition unit 35 (35a, 35b) provided in the relay device 30 (30a, 30b) of Figure 1. The time information acquisition unit 35 in Figure 2 includes a frame synchronization unit 351 and a time difference measurement unit 352. The frame synchronization unit 351 synchronizes with the transmitted signal. For example, the frame synchronization unit 351 may output a synchronization signal synchronized with the transmission each time an OFDM frame is transmitted from the transmission unit 34. The frame synchronization unit 351 may also output a synchronization signal in response to the transmission of a specific part of the OFDM frame, such as the leading bit or trailing bit of the OFDM frame.

[0038] The time difference measurement unit 352 measures the difference between the time at which it receives the synchronization signal output from the frame synchronization unit 351 and the time at which it received the reference time signal immediately before receiving the synchronization signal. In other words, for each synchronization signal, the time difference measurement unit 352 measures the elapsed time from when it receives the reference time signal earlier and closest to the time it receives the synchronization signal. The time difference measurement unit 352 generates time information indicating this time difference and transmits it to the calculation unit 12.

[0039] Figure 3 schematically shows the time difference between OFDM frames and reference signals. Figure 3 shows the temporal relationship between each OFDM frame 101 (101a to 101e) transmitted from relay device 30a, 1PPS signals 105a and 105b received by relay device 30a, each OFDM frame 102 (102a to 102e) transmitted from relay device 30b, and 1PPS signals 105c and 105d received by relay device 30b. Figure 4A schematically shows an example of time information transmitted from relay device 30a in Figure 1. Figure 4B schematically shows an example of time information transmitted from relay device 30b in Figure 1.

[0040] In the example shown in Figure 3, the relay device 30a receives a 1PPS signal 105a immediately before transmitting the last bit of OFDM frame 101a. OFDM frame 101a is transmitted at a time t1_k elapsed from the time the 1PPS signal 105a was received. Similarly, OFDM frames 101b to 101d are transmitted at times t1_k+1 to t1_k+3 elapsed from the time the 1PPS signal 105a was received. After the transmission of OFDM frame 101d, the 1PPS signal 105b is received before the transmission of OFDM frame 101e. OFDM frame 101e is transmitted at a time t1_k+4 elapsed from the time the 1PPS signal 105b was received. In this manner, the time difference measurement unit 352 of the time information acquisition unit 35a of the relay device 30a measures the time difference T1 (t1_k to t1_k+4) for OFDM frames 101a to 101e, generates time information indicating these time differences T1, and transmits it to the calculation unit 12. That is, as shown in Figure 4A, the time difference measurement unit 352 of the relay device 30a sequentially generates time information indicating the time difference T1 (t1_k to t1_k+4) and transmits it to the calculation unit 12.

[0041] Similarly, in the example in Figure 3, the relay device 30b sequentially transmits OFDM frames 102a to 102e. As mentioned above, the 1PPS signals 105c and 105d received by the relay device 30b are synchronized with the 1PPS signals 105a and 105b received by the relay device 30a. In the example in Figure 3, OFDM frame 102a is transmitted at a time t2_l elapsed from the time the 1PPS signal 105c was received. Similarly, OFDM frames 102b to 102d are transmitted at times t2_l+1 to t2_l+3 elapsed from the time the 1PPS signal 105c was received. After the transmission of OFDM frame 102d, the 1PPS signal 105d is received before the transmission of OFDM frame 102e. OFDM frame 102e is transmitted at a time t2_l+4 elapsed from the time the 1PPS signal 105d was received. Accordingly, the time difference measurement unit 352 of the time information acquisition unit 35b of the relay device 30b measures the time difference T2 (t2_l ~ t2_l + 4) for OFDM frames 102a ~ 102e, generates time information indicating these time differences T2, and transmits it to the calculation unit 12. That is, as shown in Figure 4B, the time difference measurement unit 352 of the relay device 30b sequentially generates time information indicating the time difference T2 (t2_l ~ t2_l + 4) and transmits it to the calculation unit 12.

[0042] The calculation unit 12 calculates the difference |T1-T2| between the time differences T1 and T2 received from the relay devices 30a and 30b. In this embodiment, the calculation unit 12 receives the time differences T1 and T2 between the transmission time when each relay device 30 (30a, 30b) transmitted the OFDM frame and the reference time signal from each relay device 30 (30a, 30b), but does not receive the OFDM frame identification information. However, since the transmission and reception of broadcast waves are performed at high speed in a broadcast network, the transmission time difference between the relay devices 30 (30a, 30b) is generally small enough to be sufficient with respect to the OFDM frame length. Therefore, if the difference |T1-T2| is less than a predetermined value (e.g., 500ms), the time differences T1 and T2 are considered to be time differences relating to the same broadcast signal. Therefore, in this embodiment, the calculation unit 12 determines whether the difference |T1-T2| is less than a predetermined value, and if it is less than the predetermined value, it calculates T1-T2 as the transmission time difference between the relay devices 30 (30a, 30b).

[0043] In this embodiment, the transmission time difference between the relay devices 30 can be calculated simply by each relay device 30 (30a, 30b) calculating the time difference between the transmission time of the OFDM frame and the reference time signal, and aggregating the time information indicating that time difference in the calculation unit 12. Therefore, according to the configuration of this embodiment, it is possible to measure the transmission time difference of the broadcast signal between the relay devices 30 with higher accuracy without increasing equipment costs or modifying the transmission signal, as is the case when NSI packets are multiplexed.

[0044] Figure 5 shows an example of the time information transmitted from each relay device 30 in Figure 1 and the difference between them. In the example in Figure 5, the master station 20 transmits one OFDM frame every 0.3s (300ms). For example, the frame length of an OFDM frame is 300ms. That is, the transmission times of OFDM frames from the master station 20 are 0s, 0.3s, 0.6s, 0.9s, 1.2s, ... as shown in Figure 5. In this case, the difference between the transmission time when the master station 20 transmits an OFDM frame and the reception time of the reference time signal 1PPS immediately preceding the last bit of that OFDM frame is 0s, 0.3s, 0.6s, 0.9s, 0.2s, ...

[0045] In the example shown in Figure 5, the relay device 30a retransmits the OFDM frame with a delay of 0.1s after the master station 20 has transmitted the OFDM frame. That is, the (re)transmission times of the OFDM frame from the relay device 30a are 0.1s, 0.4s, 0.7s, 1s, 1.3s, ... as shown in Figure 5. In this case, the difference T1 between the transmission time when the relay device 30a (re)transmits the OFDM frame and the reception time of the reference time signal 1PPS immediately preceding the last bit of the OFDM frame is 0.1s, 0.4s, 0.7s, 0s, 0.3s, ... The time information acquisition unit 35a of the relay device 30a transmits information indicating this difference T1 as time information to the calculation unit 12.

[0046] In the example shown in Figure 5, the relay device 30b retransmits the OFDM frame 0.11s after the master station 20 has transmitted the OFDM frame. That is, the (re)transmission times of the OFDM frame from the relay device 30b are 0.11s, 0.41s, 0.71s, 1.01s, 1.31s, ... as shown in Figure 5. In this case, the difference T2 between the transmission time when the relay device 30b (re)transmits the OFDM frame and the reception time of the reference time signal 1PPS immediately preceding the last bit of the OFDM frame is 0.11s, 0.41s, 0.71s, 0.01s, 0.31s, ... The time information acquisition unit 35b of the relay device 30b transmits information indicating this difference T2 as time information to the calculation unit 12.

[0047] The calculation unit 12 compares the difference T1 and T2 indicated by the time information received from multiple relay devices 30 (30a, 30b), and associates the one with the smaller difference as the time information for the same OFDM frame. For example, when the calculation unit 12 receives the difference T1 and T2 from relay devices 30a and 30b, and lists the values ​​of the difference T1 and T2 in the same column of the table for each difference T1 and T2 as shown in Figure 5, it may also synchronize the two signals by searching for the nearest neighbor value for the received T1 and T2 and aligning the rows.

[0048] In the example shown in Figure 5, the difference T2-T1(-(T1-T2)) between the difference T1 sent from relay device 30a and the difference T2 sent from relay device 30b is +10ms. Therefore, the calculation unit 12 can determine that the transmission time of relay device 30b is 10ms behind that of relay device 30a.

[0049] Figure 6 is a flowchart showing an example of the operation procedure of the relay device 30 (30a, 30b) in Figure 1. Each of the following steps is performed based on the control of the time difference measurement unit 352. Specifically, for example, the time difference measurement unit 352 may include a control unit that includes one or more processors, and each of the following steps may be performed based on the control of this control unit. This processor may be a general-purpose processor such as a CPU (Central Processing Unit), or a dedicated processor specialized for a specific process. Each of the following steps is performed each time the relay device 30 (30a, 30b) receives an OFDM frame from the master station 20.

[0050] In step S1 of Figure 6, the time difference measurement unit 352 of the relay device 30 (30a, 30b) receives the synchronization signal of the OFDM frame. For example, the time difference measurement unit 352 may receive the synchronization signal output by the frame synchronization unit 351.

[0051] In step S2, the time difference measurement unit 352 acquires the reception time of the reference time signal received immediately before the synchronization signal of the OFDM frame received in step S1.

[0052] In step S3, the time difference measurement unit 352 calculates the time difference between the reception time of the synchronization signal received in step S1 and the reception time of the reference time signal acquired in step S2. Specifically, the time difference measurement unit 352 of relay device 30a calculates the time difference T1, and the time difference measurement unit 352 of relay device 30b calculates the time difference T2.

[0053] In step S4, the time difference measurement unit 352 transmits time information indicating the time difference calculated in step S3 to the calculation unit 12. Then, the time difference measurement unit 352 terminates the flowchart processing.

[0054] Figure 7 is a flowchart showing an example of the operation procedure of the calculation unit 12 in Figure 1. Each of the following steps is performed based on the control of the calculation unit 12. Specifically, for example, the calculation unit 12 may include a control unit that includes one or more processors, and each of the following steps may be performed based on the control of this control unit. This processor may be a general-purpose processor such as a CPU, or a dedicated processor specialized for a particular process. Each of the following steps is performed each time the calculation unit 12 acquires time information from the relay device 30 (30a, 30b).

[0055] In step S11, the calculation unit 12 receives time information from the first relay device (for example, relay device 30a) and obtains the time difference T1 indicated by that time information.

[0056] In step S12, the calculation unit 12 receives time information from the second relay device (for example, relay device 30b) and obtains the time difference T2 indicated by that time information.

[0057] In step S13, the calculation unit 12 determines whether the absolute value of the difference between T1 obtained in step S11 and T2 obtained in step S12, |T1-T2|, is less than a predetermined value. This predetermined value is a value smaller than the time interval of the reference time signal, and may be, for example, 500ms or a value smaller than 500ms. If the absolute value |T1-T2| is less than the predetermined value (YES in step S13), the calculation unit 12 proceeds to step S14; otherwise (NO in step S13), it terminates the flowchart processing.

[0058] In step S14, the calculation unit 12 calculates T1-T2 as the transmission time difference between the relay devices 30a and 30b. The calculation unit 12 may also transmit the calculated transmission time difference to the delay control units 33(33a, 33b) of each relay device 30(30a, 30b) to perform delay control according to the transmission time difference. Then, the calculation unit 12 finishes processing the flowchart.

[0059] As described above, the broadcast system 1 comprises a master station 20, a plurality of relay devices 30 (30a, 30b), and a studio 10 as a calculation device. The master station 20 transmits a broadcast signal composed of OFDM frames at a first frequency (communication channel Xch). The plurality of relay devices 30 (30a, 30b) receive the broadcast signal transmitted from the master station 20 and transmit the received broadcast signal at a second frequency (communication channel Ych). The calculation unit 12 of the studio 10 calculates the transmission time difference of the broadcast signals from the plurality of relay devices 30. Here, each of the plurality of relay devices 30 (30a, 30b) measures the time difference between the transmission time at which it transmits the received broadcast signal and a reference time signal, and transmits time information indicating this time difference to the calculation unit 12 of the studio 10. The calculation unit 12 of the studio 10 calculates the transmission time difference of the broadcast signal between the multiple relay devices 30 (30a, 30b) based on the time difference measured by each of the multiple relay devices 30 (30a, 30b).

[0060] In this way, each relay device 30 (30a, 30b) calculates the time difference between the transmission time of the OFDM frame and the reference time signal, and by aggregating the time information indicating this time difference in the calculation unit 12, the transmission time difference between the relay devices 30 can be calculated. Therefore, according to the configuration of this embodiment, it is possible to measure the transmission time difference of broadcast signals between the relay devices 30 with higher accuracy without increasing equipment costs or modifying the transmission signal, as is the case when NSI packets are multiplexed.

[0061] Furthermore, in this embodiment, the calculation unit 12 of the studio 10 calculates the transmission time difference of the broadcast signal between the multiple relay devices 30 (30a, 30b) based on the time difference indicated by the time information received from each of the multiple relay devices 30 (30a, 30b) at the time closest to each other. Therefore, according to the configuration of this embodiment, it is possible to measure the transmission time difference of the broadcast signal between the relay devices 30 with higher accuracy by simple processing without identifying OFDM frames.

[0062] <Second Embodiment> In the first embodiment, assuming that the transmission time difference between the relay devices 30 (30a, 30b) is sufficiently small compared to the OFDM frame length, it was determined whether the time differences T1 and T2 were time differences relating to the same broadcast signal based on the magnitude of the difference |T1-T2|. However, in such a configuration, if the transmission time difference between the relay devices 30 (30a, 30b) happens to become large, there is a possibility of mismatching the OFDM frames between the relay devices 30 (30a, 30b), and consequently the time differences T1 and T2. Furthermore, as mentioned above, when the calculation unit 12 synchronizes the two signals by searching for the nearest neighbor value for the received T1 and T2 and aligning the rows, it is necessary to predetermine the search range for the nearest neighbor value, and a search process is also required.

[0063] Therefore, in this embodiment, each relay device 30 (30a, 30b) acquires identification information to identify an OFDM frame from the contents of the OFDM frame. Then, each relay device 30 (30a, 30b) associates the time difference T1, T2 related to the OFDM frame with the identification information and transmits it to the calculation unit 12. As a result, according to this embodiment, it is possible to prevent errors in time difference calculation without complicating the processing and to measure the transmission time difference of the broadcast signal between the relay devices 30 (30a, 30b) with even higher accuracy.

[0064] Most of the configurations in this embodiment are the same as those in the first embodiment. Therefore, the explanation will focus on the configurations that differ from those in the first embodiment, and the same reference numerals will be used for the configurations that are common to both embodiments, and detailed explanations will be omitted. The broadcasting system 1 in this embodiment is shown in Figure 1, just as in the first embodiment, so a detailed explanation of it will be omitted.

[0065] Figure 8 is a block diagram showing an example configuration of the time information acquisition unit 35 included in the relay device 30 of Figure 1. As shown in Figure 8, the time information acquisition unit 35 includes a frame synchronization unit 351, a time difference measurement unit 352, a TMCC demodulation unit 353, and an FEC pointer identification unit 354. The example configuration in Figure 8 focuses on the fact that the value of the FEC block pointer changes for each OFDM frame, and uses this value of the FEC block pointer as identification information to identify OFDM frames.

[0066] The frame synchronization unit 351 synchronizes with the transmitted signal, similar to the first embodiment (Figure 2). For example, the frame synchronization unit 351 may output a synchronization signal synchronized with the transmission each time an OFDM frame is transmitted from the transmission unit 34. The frame synchronization unit 351 may also output a synchronization signal in response to the transmission of a specific part of the OFDM frame, such as the leading bit or trailing bit.

[0067] The TMCC demodulation unit 353 demodulates the TMCC included in the OFDM frame.

[0068] The FEC pointer identification unit 354 acquires the FEC block pointer described in the TMCC obtained by demodulation. This identifies the FEC block pointer of the OFDM frame input to the time information acquisition unit 35. In this embodiment, this FEC block pointer is used as identification information for the OFDM frame.

[0069] The time difference measurement unit 352 measures the difference between the time at which it receives the synchronization signal output from the frame synchronization unit 351 and the time at which it received the reference time signal immediately before the synchronization signal was received. That is, for each synchronization signal, the time difference measurement unit 352 measures the elapsed time from when it received the reference time signal earlier and closest to the synchronization signal until it receives the synchronization signal. The time difference measurement unit 352 generates time information indicating this time difference and transmits it to the calculation unit 12 along with the FEC block pointer, which is the identification information for the OFDM frame.

[0070] In the example shown in Figure 8, the FEC pointer identification unit 354 identifies the OFDM frame before inputting a signal to the time difference measurement unit 352, but the configuration is not limited to this. For example, the time difference measurement unit 352 may measure the time difference before identifying the OFDM frame to be measured.

[0071] Figure 9 schematically shows the time difference between OFDM frames and reference signals. Figure 9 shows the temporal relationship between each OFDM frame 101 (101a~101e) transmitted from relay device 30a, 1PPS signals 105a, 105b received by relay device 30a, each OFDM frame 102 (102a~102e) transmitted from relay device 30b, and 1PPS signals 105c, 105d received by relay device 30b. OFDM frames 101a~101e and 102a~102e are associated with pointers a~e as identification information. Figure 10A schematically shows an example of time information transmitted from relay device 30a in Figure 1. Figure 10B schematically shows an example of time information transmitted from relay device 30b in Figure 1.

[0072] In the example shown in Figure 9, the relay device 30a receives a 1PPS signal 105a immediately before transmitting the last bit of OFDM frame 101a. OFDM frame 101a is transmitted at a time t1_b elapsed from the time the 1PPS signal 105a was received. Similarly, OFDM frames 101b to 101d are transmitted at times t1_c to t1_e elapsed from the time the 1PPS signal 105a was received. After the transmission of OFDM frame 101d, the 1PPS signal 105b is received before the transmission of OFDM frame 101e. OFDM frame 101e is transmitted at a time t1_f elapsed from the time the 1PPS signal 105b was received. In this way, the time difference measurement unit 352 of the time information acquisition unit 35a of the relay device 30a measures the time difference T1 (t1_b~t1_f) for OFDM frames 101a~101e, generates time information indicating these time differences T1, and transmits it to the calculation unit 12 in association with pointers a~e, which are FEC block pointers. That is, as shown in Figure 10A, the time difference measurement unit 352 of the relay device 30a sequentially generates time information indicating the time difference T1 (t1_b~t1_f) and transmits it to the calculation unit 12 in association with pointers a~e.

[0073] Similarly, in the example in Figure 9, the relay device 30b sequentially transmits OFDM frames 102a to 102e. As mentioned above, the 1PPS signals 105c and 105d received by the relay device 30b are synchronized with the 1PPS signals 105a and 105b received by the relay device 30a. In the example in Figure 9, OFDM frame 102a is transmitted at a time t2_b elapsed from the time the 1PPS signal 105c was received. Similarly, OFDM frames 102b to 102d are transmitted at times t2_c to t2_e elapsed from the time the 1PPS signal 105c was received. After the transmission of OFDM frame 102d, the 1PPS signal 105d is received before the transmission of OFDM frame 102e. OFDM frame 102e is transmitted at a time t2_f elapsed from the time the 1PPS signal 105d was received. Accordingly, the time difference measurement unit 352 of the time information acquisition unit 35b of the relay device 30b measures the time difference T2 (t2_b~t2_f) for OFDM frames 102a~102e, generates time information indicating these time differences T2, and transmits it to the calculation unit 12 in association with pointers a~e, which are FEC block pointers. In other words, as shown in Figure 10B, the time difference measurement unit 352 of the relay device 30b sequentially generates time information indicating the time difference T2 (t2_b~t2_f) and transmits it to the calculation unit 12 in association with pointers a~e.

[0074] The calculation unit 12 calculates the difference T1-T2 between the time differences T1 and T2 received from the relay devices 30a and 30b for each OFDM frame identified by the same identification information, i.e., the FEC block pointer. Based on the difference T1-T2 calculated for each OFDM frame, the calculation unit 12 measures the transmission time difference of the broadcast signal between the relay devices 30 (30a, 30b).

[0075] In this embodiment, each relay device 30 (30a, 30b) calculates the time difference between the transmission time of the OFDM frame and the reference time signal, and aggregates the time information indicating this time difference, along with the OFDM frame identification information, in the calculation unit 12. The calculation unit 12 associates the time information received from each relay device 30 (30a, 30b) with the OFDM frame identification information and calculates the transmission time difference between the relay devices 30. Therefore, according to the configuration of this embodiment, even when there is a large difference in the transmission time of the broadcast signal between the relay devices 30, it is possible to measure the transmission time difference of the broadcast signal between the relay devices 30 with higher accuracy.

[0076] Figure 11 shows an example of time information transmitted from each relay device 30 in Figure 1 and the difference therebetween. In the example in Figure 11, the master station 20 transmits one OFDM frame every 0.3s (300ms). For example, the frame length of an OFDM frame is 300ms. That is, the transmission times of OFDM frames a, b, c, d, e, ... from the master station 20 are 0s, 0.3s, 0.6s, 0.9s, 1.2s, ... as shown in Figure 11.

[0077] In the example shown in Figure 11, the relay device 30a retransmits the OFDM frame with a delay of 0.1s after the master station 20 has transmitted the OFDM frame. That is, the (re)transmission times of OFDM frames a, b, c, d, e, etc. from the relay device 30a are 0.1s, 0.4s, 0.7s, 1s, 1.3s, etc., as shown in Figure 11. In this case, the difference T1 between the transmission time when the relay device 30a (re)transmits the OFDM frame and the reception time of the reference time signal 1PPS immediately preceding the last bit of the OFDM frame is 0.1s, 0.4s, 0.7s, 0s, 0.3s, etc. The time information acquisition unit 35a of the relay device 30a transmits to the calculation unit 12 the time information obtained by associating the information indicating such a difference T1 with the identification information (FEC block pointer) of the OFDM frame.

[0078] In the example shown in Figure 11, the relay device 30b retransmits the OFDM frame 0.15s after the master station 20 has transmitted it. That is, the (re)transmission times of OFDM frames a, b, c, d, e, ... from the relay device 30b are 0.15s, 0.45s, 0.75s, 1.05s, 1.35s, ... as shown in Figure 11. In this case, the difference T2 between the transmission time when the relay device 30b (re)transmits the OFDM frame and the reception time of the reference time signal 1PPS immediately preceding the last bit of the OFDM frame is 0.15s, 0.45s, 0.75s, 0.05s, 0.35s, ... The time information acquisition unit 35b of the relay device 30b transmits to the calculation unit 12 the time information obtained by associating the information indicating such a difference T2 with the identification information (FEC block pointer) of the OFDM frame.

[0079] The calculation unit 12 associates the difference T1 and T2 indicated by the time information received from multiple relay devices 30 (30a, 30b) with each OFDM frame using the OFDM frame identification information. Then, the calculation unit 12 calculates the difference T1-T2 for each corresponding OFDM frame. In the example in Figure 11, the difference T2-T1 (=-(T1-T2)) between the difference T1 sent from relay device 30a and the difference T2 sent from relay device 30b is +50ms. Therefore, the calculation unit 12 can determine that the transmission time of relay device 30b is 50ms behind that of relay device 30a.

[0080] Furthermore, if the delay in transmission time at the relay device 30 becomes large relative to the interval of the reference time signal, the pulses of the reference time signal used to calculate the time differences T1 and T2 for the same OFDM frame may differ between the relay devices 30 (30a, 30b). In such cases, considering that the temporal variation in the transmission time difference of the broadcast signal between the relay devices 30 (30a, 30b) is gradual, the calculation unit 12 extracts from the set of T1-T2 that reflects the actual transmission time difference and measures the transmission time difference based on the extracted information.

[0081] Figure 12 shows an example of the time information transmitted from each relay device 30 in Figure 1 and the difference therebetween. In Figure 12, the transmission time delay in relay device 30b is large. In the example in Figure 12, as in Figure 11, the master station 20 transmits one OFDM frame every 0.3s (300ms). As in Figure 11, relay device 30a retransmits the OFDM frame with a delay of 0.1s after the master station 20 has transmitted the OFDM frame. In this case, the difference T1 between the transmission time when relay device 30a (re)transmits the OFDM frame and the reception time of the reference time signal 1PPS immediately preceding the last bit of the OFDM frame is 0.1s, 0.4s, 0.7s, 0s, 0.3s, ...

[0082] In the example shown in Figure 12, the relay device 30b retransmits the OFDM frame 0.55s after the master station 20 has transmitted it. That is, the (re)transmission times of OFDM frames a, b, c, d, e, etc. from the relay device 30b are 0.55s, 0.85s, 1.15s, 1.45s, 1.75s, etc., as shown in Figure 12. In this case, the difference T2 between the transmission time when the relay device 30b (re)transmits the OFDM frame and the reception time of the reference time signal 1PPS immediately preceding the last bit of the OFDM frame is 0.55s, 0.85s, 0.15s, 0.45s, 0.75s, etc.

[0083] In this case, the T1-T2 for OFDM frames a, b, c, d, e, ... will be -0.45s, -0.45s, 0.55s, -0.45s, -0.45s, ... The correct transmission time difference between relay devices 30a and 30b is 0.1s - 0.55s = -0.45s, therefore, T1-T2 = 0.55s for OFDM frame c does not reflect the actual transmission time difference.

[0084] Therefore, the calculation unit 12 may extract from the set of T1-T2 that reflect the actual transmission time difference for T1 and T2 acquired within a certain time range, and measure the transmission time difference based on the extracted information. For example, the calculation unit 12 may exclude from the set of T1-T2 any values ​​|T1-T2| whose absolute value is greater than or equal to a predetermined threshold, extract the remaining values, and measure the transmission time difference based on the extracted information. Specifically, for example, the calculation unit 12 may use half the time interval of the reference time signal (e.g., 1 s) as the threshold (e.g., 500 ms). For example, the set of T1-T2 acquired for OFDM frames a to e is {-0.45s, -0.45s, 0.55s, -0.45s, -0.45s}. Of these, the T1-T2 values ​​less than the threshold of 500ms are {-0.45s,-0.45s,-0.45s,-0.45s}, so the calculation unit 12 may measure the transmission time difference based on these. For example, the calculation unit 12 may calculate the average value of the extracted T1-T2 (-0.45s) as the transmission time difference of the broadcast signal between the relay devices 30 (30a, 30b).

[0085] The calculation unit 12 may also extract the T1-T2 with the highest frequency from the set of T1-T2 obtained within a certain time range as the T1-T2 that reflects the actual transmission time difference. In this case, the calculation unit 12 may evaluate the frequency of occurrence by ignoring the difference in values ​​less than a certain value (e.g., 10ms) between T1 and T2. For example, suppose the set of T1-T2 obtained for OFDM frames a to e is {-0.451s, -0.458s, 0.552s, -0.452s, -0.455s}. In this case, the T1-T2 with the highest frequency of occurrence when values ​​less than 10ms are ignored (e.g., truncated) is -0.45s. The calculation unit 12 may measure the transmission time difference based on this value. For example, the calculation unit 12 may calculate the average value of {-0.451s, -0.458s, -0.452s, -0.455s}, which is -0.454s, as the transmission time difference of the broadcast signal.

[0086] In the example above, we described the case where an FEC block pointer is used as the identification information for identifying an OFDM frame, but the information used to identify an OFDM frame is not limited to an FEC block pointer. Since the same OFDM frame is transmitted to each of the multiple relay devices 30 (30a, 30b), any information that is unique to each OFDM frame may be used as the identification information for the OFDM frame. For example, the identification information for identifying an OFDM frame may be the Lch (equivalent to AC in ISDB-T) or the demodulated result of the main line signal.

[0087] Figure 13 is a block diagram showing an example configuration of the time information acquisition unit 35 when an OFDM frame is identified by the demodulation result of the Lch. In Figure 13, the time information acquisition unit 35 comprises a frame synchronization unit 351, a time difference measurement unit 352, and an Lch demodulation unit 355. The example configuration in Figure 13 focuses on the fact that the value of Lch changes for each OFDM frame, and uses this Lch value as identification information to identify an OFDM frame.

[0088] The frame synchronization unit 351 synchronizes with the transmitted signal, similar to the first embodiment (Figure 2). For example, the frame synchronization unit 351 may output a synchronization signal synchronized with the transmission each time an OFDM frame is transmitted from the transmission unit 34. The frame synchronization unit 351 may also output a synchronization signal in response to the transmission of a specific part of the OFDM frame, such as the leading bit or trailing bit.

[0089] The Lch demodulation unit 355 demodulates the Lch included in the OFDM frame. This identifies the Lch value of the OFDM frame input to the time information acquisition unit 35. In this embodiment, this Lch value is used as identification information for the OFDM frame.

[0090] Figure 14 is a block diagram showing an example configuration of the time information acquisition unit 35 when OFDM frames are identified by the demodulation result of the main line signal. In Figure 14, the time information acquisition unit 35 includes a frame synchronization unit 351, a time difference measurement unit 352, and a main line signal demodulation unit 356. The configuration example in Figure 14 focuses on the fact that the value of the main line signal changes for each OFDM frame, and uses the value of the main line signal as identification information to identify OFDM frames.

[0091] The frame synchronization unit 351 synchronizes with the transmitted signal, similar to the first embodiment (Figure 2). For example, the frame synchronization unit 351 may output a synchronization signal synchronized with the transmission each time an OFDM frame is transmitted from the transmission unit 34. The frame synchronization unit 351 may also output a synchronization signal in response to the transmission of a specific part of the OFDM frame, such as the leading bit or trailing bit.

[0092] The main line signal demodulation unit 356 demodulates the main line signals included in the OFDM frame. The main line signal demodulation unit 356 does not demodulate all OFDM symbols in the OFDM frame, but may demodulate only the minimum necessary OFDM symbols, such as a specific number of symbols in the OFDM frame, to identify the OFDM frame, and use this as identification information for the OFDM frame. This results in the value of the main line signal of the OFDM frame being identified and input to the time information acquisition unit 35. In this embodiment, the value of this main line signal is used as identification information for the OFDM frame.

[0093] The method using the Lch and main line signals described above can identify OFDM frames not only in advanced systems but also in ISDB-T broadcast networks. In the case of ISDB-T, since mobile broadcasting is operated using a portion of the frequency band (one segment), OFDM frames can be identified using signals only in this band. On the other hand, since the ISDB-T TMCC does not contain OFDM frame-specific information, the FEC block pointer cannot be used as OFDM frame identification information in ISDB-T.

[0094] Figure 15 is a flowchart showing an example of the operation procedure of the relay device 30 (30a, 30b) in Figure 1. Each of the following steps is performed based on the control of the time difference measurement unit 352. Specifically, for example, the time difference measurement unit 352 may include a control unit that includes one or more processors, and each of the following steps may be performed based on the control of this control unit. This processor may be a general-purpose processor such as a CPU, or a dedicated processor specialized for a specific process. Each of the following steps is performed each time the relay device 30 (30a, 30b) receives an OFDM frame from the master station 20.

[0095] In step S21 of Figure 15, the time difference measurement unit 352 of the relay device 30 (30a, 30b) receives the synchronization signal and frame identification information of the OFDM frame. For example, the time difference measurement unit 352 may receive the synchronization signal output by the frame synchronization unit 351.

[0096] In step S22, the time difference measurement unit 352 acquires the reception time of the reference time signal received immediately before the synchronization signal of the OFDM frame received in step S21.

[0097] In step S23, the time difference measurement unit 352 calculates the time difference between the reception time of the synchronization signal received in step S1 and the reception time of the reference time signal acquired in step S22. Specifically, the time difference measurement unit 352 of relay device 30a calculates the time difference T1, and the time difference measurement unit 352 of relay device 30b calculates the time difference T2.

[0098] In step S24, the time difference measurement unit 352 transmits the time information indicating the time difference calculated in step S23, along with the identification information received in step S2, to the calculation unit 12. Then, the time difference measurement unit 352 completes the flowchart processing.

[0099] Figure 16 is a flowchart showing an example of the operation procedure of the calculation unit 12 in Figure 1. Each of the following steps is performed based on the control of the calculation unit 12. Specifically, for example, the calculation unit 12 may include a control unit that includes one or more processors, and each of the following steps may be performed based on the control of this control unit. This processor may be a general-purpose processor such as a CPU, or a dedicated processor specialized for a particular process. Each of the following steps is performed each time the calculation unit 12 acquires time information from the relay device 30 (30a, 30b).

[0100] In step S31, the calculation unit 12 receives time information and OFDM frame identification information from the first relay device (for example, relay device 30a) and obtains the time difference T1 indicated by the time information.

[0101] In step S32, the calculation unit 12 receives time information and OFDM frame identification information from the second relay device (for example, relay device 30b) and obtains the time difference T2 indicated by the time information.

[0102] In step S33, the calculation unit 12 calculates T1-T2 for each set of OFDM frames identified by the same identification information and obtains a set of T1-T2. The calculation unit 12 may, for example, calculate T1-T2 for each T1 and T2 received within a certain period of time (e.g., 1 second to several seconds) and obtain a set of T1-T2.

[0103] In step S34, the calculation unit 12 extracts the true time difference from the set of T1-T2. For example, the calculation unit 12 may extract the true time difference by excluding |T1-T2| that exceeds a predetermined threshold and those that occur infrequently.

[0104] In step S35, the calculation unit 12 calculates the transmission time difference of the broadcast signal between the multiple relay devices 30 (30a, 30b) based on the true time difference extracted in step S34. For example, the calculation unit 12 may calculate the average value of the true time differences extracted in step S34 as the transmission time difference of the broadcast signal. Then, the calculation unit 12 finishes processing the flowchart.

[0105] As described above, in this embodiment, the multiple relay devices 30 (30a, 30b) transmit time information indicating the time difference, associated with identification information that identifies OFDM frames, to the calculation unit 12 of the studio 10. The calculation unit 12 calculates the transmission time difference of the broadcast signals between the multiple relay devices 30 (30a, 30b) based on the time difference indicated by the time information associated with the same identification information.

[0106] Therefore, in this embodiment, OFDM frames are identified by identification information, and the transmission time difference of the broadcast signal between multiple relay devices 30 (30a, 30b) is calculated by associating time information corresponding to the same OFDM frame. Thus, even if the transmission time difference between relay devices 30 (30a, 30b) becomes large by chance, it is possible to prevent errors in time difference calculation without complicating the process and to measure the transmission time difference of the broadcast signal between relay devices 30 (30a, 30b) with even higher accuracy.

[0107] Furthermore, the calculation unit 12 of the studio 10 extracts a time difference from the set of time differences indicated by multiple time information that reflects the actual transmission time difference between the multiple relay devices 30 (30a, 30b). Then, the calculation unit 12 calculates the transmission time difference of the broadcast signal between the multiple relay devices 30 (30a, 30b) based on the extracted time difference. As described above, if the delay in the transmission time at the relay devices 30 (30a, 30b) becomes large relative to the interval of the reference time signal, the pulses of the reference time signal used to calculate the time differences T1 and T2 for the same OFDM frame may differ between the relay devices 30 (30a, 30b). Even in such cases, the configuration according to this embodiment makes it possible to measure the transmission time difference of the broadcast signal between the relay devices 30 (30a, 30b) with even higher accuracy.

[0108] Furthermore, the multiple relay devices 30 (30a, 30b) transmit time information to the calculation unit 12 by associating at least one of the following as identification information for identifying OFDM frames: the FEC block pointer of the OFDM frame, the demodulation results of some or all of the Lch in the OFDM frame, and the demodulation results of some or all of the main line signals in the OFDM frame. Therefore, the calculation unit 12 can distinguish OFDM frames by the identification information and calculate the transmission time difference of the broadcast signal between the multiple relay devices 30 (30a, 30b) by associating the time information corresponding to the same OFDM frame.

[0109] As described above, in each embodiment of this disclosure, each relay device 30 (30a, 30b) identifies an OFDM frame, obtains the time difference from 1PPS, and by comparing the time differences of the same OFDM frame, it becomes possible to grasp the precise transmission time difference between the relay devices 30 (30a, 30b). Addition of NSI packets and devices for decoding are not required, contributing to the simplification of equipment and eliminating the need for additional bit allocation to the broadcast signal. As mentioned above, the method using NSI packets required an OFDM demodulator on the relay device side and required the addition of time information. In contrast, in each embodiment of this disclosure, the addition of time information and the multiplexing of new information to the transmission signal are not required.

[0110] This disclosure is not limited to the embodiments described above. For example, multiple blocks shown in the block diagram may be combined, or one block may be divided. Multiple steps shown in the flowchart may be performed in parallel or in a different order, depending on the processing capacity of the device performing each step, or as necessary, instead of being performed in chronological order as described. Other modifications are possible without departing from the spirit of this disclosure. [Explanation of Symbols]

[0111] 1. Broadcasting System 10 Performance Hall 11 Generation part 12 Calculation Section 20 Master station 21 OFDM Modulation Section 22 Transmitter 30 Relay device 31 Receiving and conversion unit 32 Compensation Department 33 Delay Control Unit 34 Transmitter 35-hour information acquisition unit 351 Frame synchronization section 352 Time difference measurement section 353 TMCC Demodulation Unit 354 FEC Pointer Identification Unit 355 Lch demodulation unit 356 Main line signal demodulation section

Claims

1. A master station that transmits a broadcast signal composed of OFDM frames at a first frequency, Multiple relay devices that receive the broadcast signal transmitted from the aforementioned master station and transmit the received broadcast signal at a second frequency, A calculation device for calculating the transmission time difference of the broadcast signals from the plurality of relay devices. Equipped with, Each of the aforementioned relay devices measures the time difference between the transmission time, which is the time when a specific part of the OFDM frame constituting the received broadcast signal was transmitted, and a reference time signal, and transmits time information indicating the time difference to the calculation device. The calculation device calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the time difference measured by each of the plurality of relay devices. Broadcasting system.

2. The broadcasting system according to claim 1, wherein the calculation device calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the time difference indicated by the time information received from each of the plurality of relay devices at the time closest to each other.

3. The plurality of relay devices transmit the time information indicating the time difference to the calculation device, in association with the identification information that identifies the OFDM frame. The calculation device calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the time difference indicated by the time information associated with the same identification information. The broadcasting system according to claim 2.

4. The calculation device is, From the set of time differences indicated by the multiple time information, extract the time difference that reflects the actual transmission time difference between the multiple relay devices. Based on the extracted time difference, the transmission time difference of the broadcast signal between the plurality of relay devices is calculated. The broadcasting system according to claim 3.

5. The broadcasting system according to claim 3, wherein the plurality of relay devices transmit the time information to the calculation device, as identification information for identifying the OFDM frame, associating at least one of the FEC block pointer of the OFDM frame, the demodulation results of some or all of the Lch in the OFDM frame, and the demodulation results of some or all of the main line signals in the OFDM frame.

6. A broadcast signal consisting of OFDM frames transmitted from the master station on a first frequency is received. The received broadcast signal is transmitted at a second frequency. For each OFDM frame constituting the received broadcast signal, the time difference between the transmission time (the time when a specific part of the OFDM frame was transmitted) and a reference time signal is measured, and time information indicating this time difference is transmitted to a calculation device that calculates the transmission time difference of the broadcast signals from multiple relay devices. A relay device.

7. The relay device according to claim 6, which transmits the time information indicating the time difference to the calculation device in association with the identification information that identifies the OFDM frame.

8. From each of the multiple relay devices that relay a broadcast signal composed of OFDM frames, time information is received for each OFDM frame constituting the broadcast signal, indicating the time difference between the transmission time, which is the time when a specific part of the OFDM frame was transmitted, and a reference time signal. Based on the time difference received from each of the plurality of relay devices, the transmission time difference of the broadcast signal between the plurality of relay devices is calculated. Calculation device.

9. The calculation device according to claim 8, which calculates the transmission time difference of the broadcast signal between the plurality of relay devices based on the time difference indicated by the time information received from each of the plurality of relay devices at the time closest to each other.

10. From each of the plurality of relay devices, the time information indicating the time difference, which is associated with the identification information that identifies the OFDM frame, is received. Based on the time difference indicated by the time information associated with the same identification information, the transmission time difference of the broadcast signal between the plurality of relay devices is calculated. The calculation apparatus according to claim 8.

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