Retransmission system, selection device, and retransmission method

Abstract

To retransmit terrestrial digital broadcast signals with low latency and stability. [Solution] In the retransmission system, a symbol transmitting device generates binary data by acquiring multiple carrier signals from a first broadcast signal and demodulating the symbols, and generates a symbol frame containing the binary data and a symbol number. A selection device selects one of the multiple symbol frames generated by each of the multiple symbol transmitting devices, and a broadcast signal transmitting device acquires the binary data from the selected symbol frame, generates a second broadcast signal by modulating an OFDM frame containing the acquired binary data, and transmits the generated second broadcast signal.

Description

Technical Field

[0001] The present disclosure relates to a retransmission system, a selection device, and a retransmission method.

Background Art

[0002] Conventionally, technologies for retransmitting terrestrial digital broadcasts have been proposed. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-114469) discloses the following transmission device. That is, the transmission device is a transmission device that transmits a broadcast signal of terrestrial digital broadcast via a communication network, and includes IQ data extraction means for extracting in-phase component data (I data) and quadrature component data (Q data) for each carrier for each symbol of OFDM from the RF signal of terrestrial digital broadcast, and IP output means for packetizing the extracted in-phase component data and quadrature component data into IP packets and outputting them on the communication network. [[ID=I3]]

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Beyond the technologies described in Patent Documents 1 and 2, a technology that can retransmit a broadcast signal of terrestrial digital broadcast with low latency and stability is desired.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a retransmission system, a selection device, and a retransmission method capable of retransmitting a broadcast signal of terrestrial digital broadcast with low latency and stability.

Means for Solving the Problems

[0006] The retransmission system of the present disclosure is a retransmission system for retransmitting terrestrial digital broadcasts, comprising a plurality of symbol transmitting devices that receive an OFDM (Orthogonal Frequency Division Multiplexing) modulated first broadcast signal at different locations, a selection device, and a broadcast signal transmitting device, wherein each of the plurality of symbol transmitting devices acquires a plurality of carrier signals from the received first broadcast signal, generates binary data for each symbol in the first broadcast signal by symbol demodulating the plurality of carrier signals, and generates a symbol frame including the binary data and a symbol number corresponding to the binary data, the selection device performs a selection process to select one of the plurality of symbol frames from which the same symbol number is included among the plurality of symbol frames generated by each of the plurality of symbol transmitting devices, the broadcast signal transmitting device acquires the binary data from the symbol frame selected in the selection process, generates an OFDM frame including the acquired binary data, generates an OFDM modulated second broadcast signal by modulating the generated OFDM frame, and transmits the generated second broadcast signal.

[0007] One aspect of this disclosure can be implemented not only as a selection device equipped with such characteristic processing, but also as a retransmission method with such characteristic processing as a step, or as a program for causing a computer to execute such steps. Furthermore, one aspect of this disclosure can be implemented as a semiconductor integrated circuit that implements part or all of the selection device. [Effects of the Invention]

[0008] According to this disclosure, terrestrial digital broadcast signals can be retransmitted with low latency and stably. [Brief explanation of the drawing]

[0009] [Figure 1]Figure 1 is a diagram showing the configuration of a retransmission system according to the first embodiment of this disclosure. [Figure 2] Figure 2 shows an example of an OFDM frame included in a broadcast signal that is retransmitted in a retransmission system according to the first embodiment of this disclosure. [Figure 3] Figure 3 shows the configuration of a retransmission device according to the first embodiment of this disclosure. [Figure 4] Figure 4 shows an example of symbol information generated by the symbol demodulation unit in a retransmission device according to the first embodiment of this disclosure. [Figure 5] Figure 5 shows an example of an IP packet generated by the packet generation unit in a retransmission device according to the first embodiment of this disclosure. [Figure 6] Figure 6 shows IP packets stored in a buffer in a retransmission device according to the first embodiment of this disclosure. [Figure 7] Figure 7 shows an example of a retransmission sequence in a retransmission system according to the first embodiment of this disclosure. [Figure 8] Figure 8 shows the configuration of a retransmission system according to a second embodiment of the present disclosure. [Figure 9] Figure 9 shows the configuration of a retransmission device according to a second embodiment of the present disclosure. [Figure 10] Figure 10 shows the configuration of a retransmission device according to a second embodiment of the present disclosure. [Figure 11] Figure 11 shows the configuration of a retransmission system according to a third embodiment of the present disclosure. [Figure 12] Figure 12 shows the configuration of a retransmission device according to a third embodiment of the present disclosure. [Figure 13] Figure 13 shows an example of a symbol packet generated by a packet generation unit in a retransmission device according to a third embodiment of the present disclosure. [Figure 14] Figure 14 shows symbol packets stored in a buffer in a retransmission device according to a third embodiment of the present disclosure. [Figure 15] FIG. 15 is a diagram showing the configuration of a retransmission system according to a fourth embodiment of the present disclosure. [Figure 16] FIG. 16 is a diagram showing the configuration of a retransmission device according to a fourth embodiment of the present disclosure. [Figure 17] FIG. 17 is a diagram showing an example of correction processing by a correction unit in a retransmission device according to a fourth embodiment of the present disclosure.

Embodiments for Carrying Out the Invention

[0010] First, the contents of the embodiments of the present disclosure will be listed and described. (1) A retransmission system according to an embodiment of the present disclosure is a retransmission system that performs retransmission of terrestrial digital broadcasting, and includes a plurality of symbol transmission devices that receive a first broadcast signal modulated by OFDM at different points, a selection device, and a broadcast signal transmission device. Each of the plurality of symbol transmission devices acquires a plurality of carrier signals from the received first broadcast signal, generates binary data for each symbol in the first broadcast signal by symbol-demodulating the plurality of carrier signals, generates a symbol frame including the binary data and a symbol number corresponding to the binary data, the selection device performs a selection process of selecting one symbol frame from the plurality of symbol frames generated by the plurality of symbol transmission devices, where the plurality of symbol frames include the same symbol number, the broadcast signal transmission device acquires the binary data from the symbol frame selected in the selection process, generates an OFDM frame including the acquired binary data, generates a second broadcast signal modulated by OFDM by modulating the generated OFDM frame, and transmits the generated second broadcast signal.

[0011] In this way, by the symbol transmission device demodulating a plurality of carrier signals obtained from the first broadcast signal to generate binary data and generating a symbol frame including the binary data, and the broadcast signal transmission device generating and transmitting a second broadcast signal based on the symbol frame, it is possible to reduce the delay in retransmitting terrestrial digital broadcasts compared to a configuration in which the broadcast signal is demodulated into MPEG-2 TS and digitally transmitted. Also, for example, by selecting one symbol frame from a plurality of symbol frames generated based on the first broadcast signal received at different locations while seamlessly switching, and generating a second broadcast signal based on the selected symbol frame, the first broadcast signal can be made redundant and the second broadcast signal can be transmitted stably. Therefore, the broadcast signal of terrestrial digital broadcasts can be retransmitted with low latency and stability.

[0012] (2) In (1) above, the symbol transmission device may generate the symbol frame further including quality information regarding the reception quality of the first broadcast signal, and the selection device may perform the selection process based on the quality information included in the symbol frame.

[0013] With such a configuration, it is possible to generate and transmit a high-quality second broadcast signal using a symbol frame based on the first broadcast signal with high reception quality among a plurality of symbol frames.

[0014] (3) In (1) or (2) above, the selection device may be provided for each symbol transmission device and include a plurality of reception buffers for storing the symbol frames received from the corresponding symbol transmission device, and in the selection process, the selection device may select one of the plurality of symbol frames stored in the plurality of reception buffers, which are the plurality of symbol frames including the same symbol number.

[0015] This configuration allows for the absorption of time differences in the arrival of multiple symbol frames in the selection device. Furthermore, when switching the receiving buffer from which the symbol frames are read, it is possible to read symbol frames with consecutive symbol data content before and after the switch, thus enabling the switching of the receiving buffer from which the symbol frames are read without causing a momentary interruption in the second broadcast signal.

[0016] (4) In any of (1) to (3) above, the selection device may generate a modulation clock, the broadcast signal transmitting device may modulate the OFDM frames according to the modulation clock generated by the selection device, and the selection device may adjust the frequency of the modulation clock based on a count value obtained by counting the period until a predetermined number of the symbol frames arrive from the broadcast signal transmitting device using the modulation clock.

[0017] This configuration allows for frequency correction of the modulation clock to track fluctuations in the sample frequency used to generate broadcast signals at terrestrial digital broadcasting stations.

[0018] (5) In any of (1) to (4) above, the selection device may switch the selected symbol frame without interruption during the selection process.

[0019] With this configuration, even when switching the selected symbol frame, the receiver receiving the second broadcast signal can play back the terrestrial digital broadcast content without interruption.

[0020] (6) The selection device according to the embodiment of the present disclosure is a selection device used for retransmission of terrestrial digital broadcasting and comprises: a receiving unit that receives a plurality of symbol frames, each including binary data for each symbol in an OFDM modulated broadcast signal and a symbol number corresponding to the binary data, via different transmission paths; a plurality of receiving buffers provided for each transmission path and storing the symbol frames received by the receiving unit via the corresponding transmission path; and a selection unit that performs a selection process to select one of the plurality of symbol frames, each stored in the plurality of receiving buffers, from among the plurality of symbol frames that include the same symbol number.

[0021] Thus, by receiving symbol frames containing binary data based on the broadcast signal from another device, the delay in retransmission of terrestrial digital broadcasts can be reduced compared to a configuration in which the broadcast signal is demodulated into MPEG-2 TS and digitally transmitted. Furthermore, for example, by selecting one symbol frame from among multiple symbol frames generated based on the broadcast signal and received via different transmission paths, while switching between them without interruption, the transmission paths of the symbol frames can be made redundant, and the broadcast signal can be stably generated and retransmitted based on the selected symbol frame. Therefore, terrestrial digital broadcast signals can be retransmitted with low latency and stably.

[0022] (7) A retransmission method according to an embodiment of the present disclosure is a retransmission method in a retransmission system for retransmitting terrestrial digital broadcasts, comprising the steps of: a plurality of symbol transmitting devices that receive an OFDM-modulated first broadcast signal at different locations each acquire a plurality of carrier signals from the received first broadcast signal, generate binary data for each symbol in the first broadcast signal by symbol demodulating the plurality of carrier signals, and generate a symbol frame including the binary data and a symbol number corresponding to the binary data; a selection device performing a selection process to select one of the plurality of symbol frames, each of the plurality of symbol frames generated by the plurality of symbol transmitting devices, which include the same symbol number; and a broadcast signal transmitting device acquiring the binary data from the symbol frame selected in the selection process, generating an OFDM frame including the acquired binary data, generating an OFDM-modulated second broadcast signal by modulating the generated OFDM frame, and transmitting the generated second broadcast signal.

[0023] In this way, the symbol transmitter generates binary data by symbol demodulating multiple carrier signals acquired from the first broadcast signal, generates a symbol frame containing the binary data, and the broadcast signal transmitter generates and transmits a second broadcast signal based on the symbol frame. This method reduces the delay in retransmission of terrestrial digital broadcasts compared to the method of demodulating the broadcast signal to MPEG-2 TS and digitally transmitting it. Furthermore, for example, by selecting one symbol frame from multiple symbol frames generated based on the first broadcast signal received at different locations, switching between them seamlessly, and generating a second broadcast signal based on the selected symbol frame, the first broadcast signal can be made redundant, and the second broadcast signal can be transmitted stably. Therefore, terrestrial digital broadcast signals can be retransmitted with low latency and stably.

[0024] Embodiments of this disclosure will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated. Furthermore, at least some of the embodiments described below may be combined in any way.

[0025] <First Embodiment> [Configuration and Basic Operation] Figure 1 is a diagram showing the configuration of a retransmission system according to a first embodiment of the present disclosure. Referring to Figure 1, the retransmission system 301 comprises a plurality of retransmission devices 101. In the example shown in Figure 1, the retransmission devices 101 are shown as retransmission devices 101A, 101B, 101C, and 101D. A retransmission device 101 is an example of a symbol transmission device, an example of a selection device, and an example of a broadcast signal transmission device. The retransmission system 301 performs retransmission of terrestrial digital broadcasts.

[0026] The retransmission devices 101 are installed in an area where the terrestrial digital broadcast signal S1 can be received. For example, each retransmission device 101 is installed at a different location. As an example, the retransmission devices 101A, 101B, 101C, and 101D are installed in the cable television station buildings 111A, 111B, 111C, and 111D, respectively. Hereinafter, each of the buildings 111A, 111B, 111C, and 111D will also be referred to as building 111.

[0027] Each retransmitter device 101 receives an OFDM-modulated RF band broadcast signal S1 at different locations via its corresponding antenna. Broadcast signal S1 is an example of a first broadcast signal. For example, broadcast signal S1 is a signal following OFDM mode 3 and contains 5616 carrier signals Sc. The 5616 carrier signals Sc can be divided into 13 segments Sg, each containing 432 carrier signals Sc, and the modulation method can be changed on a segment Sg basis.

[0028] Figure 2 shows an example of an OFDM frame included in a broadcast signal retransmitted in a retransmission system according to the first embodiment of the present disclosure. Referring to Figure 2, the OFDM frame contains 204 symbols Sy, from symbol Sy0 to Sy203. A guard interval GI is inserted between each symbol Sy. One symbol Sy contains information for 13 segments Sg, from segment Sg00 to segment Sg12, i.e., information for 5616 carrier signals Sc. The broadcast signal S1 is generated at a terrestrial digital broadcasting station by processing the OFDM frame with an IFFT (Inverse Fast Fourier Transform) according to the sample frequency fs.

[0029] Referring again to Figure 1, the retransmitter 101 generates an IP packet Pt containing a signal based on the received broadcast signal S1, and transmits the generated IP packet Pt to other retransmitter 101s via a wired transmission path such as an IP network. In the example shown in Figure 1, retransmitter 101B, 101C, and 101D transmit the IP packet Pt to retransmitter 101A. Retransmitter 101A transmits the IP packet Pt to other retransmitter 101s other than retransmitter 101A, 101B, 101C, and 101D.

[0030] Furthermore, retransmission device 101A may transmit the IP packet Pt to at least one of retransmission devices 101B, 101C, or 101D. Also, retransmission device 101 may generate a packet conforming to another protocol instead of the IP packet Pt and transmit it to another retransmission device 101.

[0031] Furthermore, the retransmission device 101 generates an OFDM-modulated broadcast signal S2 based on the signal contained in the IP packet Pt received from another retransmission device 101 and the received broadcast signal S1. Broadcast signal S2 is an example of a second broadcast signal. The retransmission device 101 transmits the generated broadcast signal S2 to receivers in each home via the cable television network. More specifically, the retransmission device 101 transmits the broadcast signal S2 to receivers in homes within the area corresponding to the station 111 where the retransmission device 101 is installed.

[0032] [assignment] There is a need for technology that can retransmit terrestrial digital broadcast signals with low latency and stability.

[0033] More specifically, the transmitting device in the broadcast signal transmission system described in Patent Document 1 generates a TS signal by demodulating the terrestrial digital broadcast signal into MPEG-2 TS. The transmitting device then generates an OFDM frame based on the TS signal and transmits the OFDM frame via IP without IFFT processing. Because the transmitting device in Patent Document 1 demodulates the broadcast signal into MPEG-2 TS, a significant delay occurs in the retransmission of terrestrial digital broadcasts.

[0034] Furthermore, the technologies described in Patent Documents 1 and 2 may not be able to retransmit broadcast signals stably due to interference from the sporadic E layer and fading of broadcast signals. In this case, reception problems of the broadcast signal may occur in the receiver.

[0035] Therefore, the retransmission system 301 according to the first embodiment of this disclosure solves the above problem with the following configuration.

[0036] (Retransmission device) Figure 3 shows the configuration of a retransmission device according to a first embodiment of the present disclosure. Referring to Figure 3, the retransmission device 101 comprises an RF receiving unit 11, a receiving quality measurement unit 12, a symbol demodulation unit 13, a packet generation unit 14, an IP transmission unit 15, a receiving unit 20, a storage unit 23, a selection unit 25, a frame generation unit 26, a broadcast signal generation unit 27, an RF transmission unit 28, a switching control unit 29, a counting unit 30, and a clock generation unit 31. The receiving unit 20 includes an IP receiving unit 21 and a sorting unit 22. The storage unit 23 includes buffers 24A, 24B, 24C, and 24D, which are buffers 24. Buffers 24 are examples of receiving buffers. Some or all of the RF receiving unit 11, the receiving quality measurement unit 12, the symbol demodulation unit 13, the packet generation unit 14, the IP transmission unit 15, the IP receiving unit 21, the sorting unit 22, the selection unit 25, the frame generation unit 26, the broadcast signal generation unit 27, the RF transmission unit 28, the switching control unit 29, the counting unit 30, and the clock generation unit 31 are implemented, for example, by a processing circuit (Circuitry) including one or more processors.

[0037] (Generation and transmission of IP packets Pt) The retransmission device 101 acquires multiple carrier signals Sc from the received broadcast signal S1 and generates symbol data Sd for each symbol in the broadcast signal S1 by symbol demodulating the multiple carrier signals Sc. The retransmission device 101 generates a symbol frame Sf containing the symbol data Sd and the symbol number corresponding to the symbol data Sd, and transmits the generated symbol frame Sf to another retransmission device 101. The details of the process of generating and transmitting IP packets Pt in the retransmission device 101 will be described below.

[0038] The RF receiver 11 receives the OFDM-modulated broadcast signal S1 via the antenna. The RF receiver 11 quadrature demodulates the received broadcast signal S1 to generate a quadrature signal, for example, a 64QAM (Quadrature Amplitude Modulation) modulated signal, and then generates a digital quadrature signal by digitally converting the quadrature signal. This digital quadrature signal includes an I component and a Q component that is 90° out of phase with the I component. The RF receiver 11 outputs the generated digital quadrature signal to the reception quality measurement unit 12 and the symbol demodulation unit 13.

[0039] The reception quality measurement unit 12 measures the reception quality Qr of the broadcast signal S1 in the RF reception unit 11. More specifically, the reception quality measurement unit 12 measures the reception quality Qr periodically or irregularly based on the digital quadrature signal received from the RF reception unit 11. As the reception quality Qr, the reception quality measurement unit 12 measures at least one of the following: the reception level of the broadcast signal S1, the CNR (Carrier to Noise Ratio) of the broadcast signal S1, or the BER (Bit Error Rate) of the broadcast signal S1. When the reception quality measurement unit 12 measures the reception quality Qr, it outputs quality information indicating the reception quality Qr to the packet generation unit 14.

[0040] The symbol demodulation unit 13 removes the guard interval GI from the digital quadrature signal received from the RF receiver 11. The symbol demodulation unit 13 performs FFT processing on the digital quadrature signal from which the guard interval GI has been removed to generate 5616 carrier signals Sc, which are 5616 digital quadrature signals corresponding to 5616 carriers.

[0041] Here, the broadcast signal S1 consists of 432 carrier signals Sc for each segment: 384 carrier signals Sc1 containing broadcast data, 36 carrier signals Sc2 containing pilot signals, 4 carrier signals Sc3 containing TMCC (Transmission and MultipleXing Configurative Control) signals, and 8 carrier signals Sc4 containing AC (Auxiliary Channel) signals. The TMCC signals contain TMCC information indicating the modulation scheme, etc. The AC signals contain AC information indicating earthquake warning information, etc. The frequencies assigned to carrier signals Sc1, Sc2, Sc3, and Sc4 are predetermined.

[0042] The symbol demodulation unit 13 selects each carrier signal Sc from the generated carrier signals Sc1, Sc2, Sc3, and Sc4 based on the frequency of each carrier signal Sc.

[0043] The symbol demodulation unit 13 symbolically demodulates the carrier signal Sc1. That is, the symbol demodulation unit 13 detects the amplitude and phase of the carrier signal Sc1. More specifically, the symbol demodulation unit 13 uses the carrier signal Sc2 as a reference to perform a correction process to correct the detected amplitude and phase. Based on the corrected amplitude and phase, the symbol demodulation unit 13 detects the amplitude Ai of the I component of the carrier signal Sc1 and the amplitude Aq of the Q component of the carrier signal Sc1. After performing the correction process, the symbol demodulation unit 13 discards the carrier signal Sc2 used in the correction process.

[0044] The symbol demodulation unit 13 converts the detected amplitudes Ai and Aq into symbol data Sd, which is binary data corresponding to those amplitudes Ai and Aq, according to the 64QAM modulation scheme. The symbol demodulation unit 13 generates symbol data Sd of a predetermined number of bits for each symbol Sy.

[0045] Furthermore, the symbol demodulation unit 13 generates TMCC information and AC information by symbol demodulating and decoding the carrier signals Sc3 and Sc4. The symbol demodulation unit 13 generates one TMCC information and one AC information for each symbol Sy.

[0046] For example, broadcast signal S1 includes information indicating the first symbol Sy among the 204 symbols Sy in the OFDM frame. The symbol demodulation unit 13 obtains this information from the carrier signal Sc and identifies the first symbol Sy among the 204 symbols Sy in the OFDM frame based on this information. The symbol demodulation unit 13 assigns a symbol number to each symbol Sy, which is sequentially incremented from zero to 203 starting from the identified symbol Sy.

[0047] Figure 4 shows an example of symbol information generated by the symbol demodulation unit in a retransmission device according to the first embodiment of this disclosure.

[0048] Referring to Figure 4, the symbol demodulation unit 13 generates symbol information Ss which includes the symbol number of symbol Sy and the TMCC information, AC information, and symbol data Sd corresponding to symbol Sy. The symbol demodulation unit 13 generates symbol information Ss for each symbol period Cs obtained by dividing the frame period Cf of the OFDM frame by 204, and outputs the generated symbol information Ss to the packet generation unit 14.

[0049] Figure 5 shows an example of an IP packet generated by the packet generation unit in a retransmission device according to the first embodiment of this disclosure.

[0050] Referring to Figure 5, the packet generation unit 14 generates an IP packet Pt that includes symbol information Ss received from the symbol demodulation unit 13 and quality information received from the reception quality measurement unit 12. The IP packet Pt is an example of a symbol frame.

[0051] An IP packet Pt includes a MAC header, IP header, UDP header, RTP header, payload, and FCS (Frame Check Sequence). The payload of an IP packet Pt contains the symbol number, packet number, quality information, TMCC information, AC information, and symbol data Sd.

[0052] For example, each time the packet generation unit 14 receives symbol information Ss from the symbol demodulation unit 13, it generates three IP packets Pt in which the received symbol information Ss is divided and stored.

[0053] More specifically, the packet generation unit 14 obtains the symbol number, TMCC information, AC information, and symbol data Sd from the received symbol information Ss. The packet generation unit 14 generates three IP packets Pt in which the latest quality information received from the reception quality measurement unit 12, the obtained symbol number, and the packet number are stored in the payload, and the TMCC information, AC information, and symbol data Sd are stored separately. For example, the packet generation unit 14 stores "0", "1", and "2" as the packet numbers of the three IP packets Pt in the order in which the IP packets Pt are generated. The packet generation unit 14 outputs the three generated IP packets Pt to the IP transmission unit 15 and the sorting unit 22 in the order in which they were generated.

[0054] Referring again to Figure 3, the IP transmission unit 15 receives an IP packet Pt from the packet generation unit 14 and transmits the received IP packet Pt to another retransmission device 101 via the IP network.

[0055] (Generation and transmission of broadcast signal S2) The retransmission device 101 performs a selection process to select one IP packet Pt from among multiple IP packets Pt that contain the same symbol number, which are generated by each of the multiple retransmission devices 101. For example, the retransmission device 101 switches the selected IP packet Pt without interruption. The retransmission device 101 obtains symbol data Sd from the IP packet Pt selected in the selection process, generates an OFDM frame containing the obtained symbol data Sd, and generates a broadcast signal S2 by modulating the generated OFDM frame. The retransmission device 101 transmits the generated broadcast signal S2 via the cable television network. The details of the process of generating and transmitting the broadcast signal S2 in the retransmission device 101 will be described below.

[0056] The receiving unit 20 receives multiple IP packets Pt via different transmission paths. More specifically, the IP receiving unit 21 in the retransmission device 101 receives IP packets Pt from other retransmission devices 101 via the IP network. In the example shown in Figure 1, the IP receiving unit 21 in the retransmission device 101A receives IP packets Pt from retransmission devices 101B, 101C, and 101D via the IP network. The IP receiving unit 21 outputs the received IP packets Pt to the sorting unit 22.

[0057] The sorting unit 22 receives IP packets Pt from the IP receiving unit 21. The sorting unit 22 also receives IP packets Pt from the packet generation unit 14. Based on the MAC header of the received IP packets Pt, the sorting unit 22 sorts the IP packets Pt and stores them in the storage unit 23.

[0058] More specifically, the buffers 24 in the storage unit 23 are provided for each transmission path of the IP packet Pt. That is, a buffer 24 is provided for each retransmission device 101 that generates the IP packet Pt. Each buffer 24 stores the IP packet Pt received by the receiving unit 20 via the corresponding transmission path. In the example shown in Figure 1, buffers 24A, 24B, 24C, and 24D in the retransmission device 101A are provided corresponding to retransmission devices 101A, 101B, 101C, and 101D, respectively.

[0059] The sorting unit 22 stores the received IP packets Pt in a buffer 24 corresponding to the source address of the IP packet Pt. The sorting unit 22 also outputs IP packets Pt containing a predetermined source address from among the received IP packets Pt to the counting unit 30.

[0060] Figure 6 shows IP packets stored in a buffer in a retransmission device according to the first embodiment of this disclosure. In Figure 6, the numbers written in the IP packet Pt indicate the symbol number and packet number of the IP packet Pt. Specifically, for example, an IP packet Pt labeled "11 / 0" indicates an IP packet Pt with a symbol number of "11" and a packet number of "zero".

[0061] Referring to Figure 6, buffer 24 has multiple buffer areas. Each buffer area is assigned a memory address Ma, which is represented, for example, by a predetermined bit value. The sorting unit 22 stores the IP packet Pt in the buffer area among the multiple buffer areas in buffer 24 that is assigned a memory address Ma determined by a combination of the symbol number and packet number of the IP packet Pt. More specifically, for example, the sorting unit 22 stores an IP packet Pt with a symbol number of "11" and a packet number of "zero" in the buffer area with memory address Ma of "31".

[0062] Referring again to Figure 3, the clock generation unit 31 generates a modulated clock CLfs. The frequency of the modulated clock CLfs is, for example, eight times the sample frequency fs mentioned above. More specifically, the clock generation unit 31 receives a reference clock CL1 of a predetermined frequency from an oscillator (not shown) and generates a reference clock CL2 by dividing the frequency of the reference clock CL1. The clock generation unit 31 is also a PLL synthesizer and includes a phase comparator, a loop filter, a voltage-controlled oscillator, and a frequency divider. The reference clock CL2 is supplied to the phase comparator as a reference signal. The voltage-controlled oscillator generates the modulated clock CLfs. The frequency divider is provided between the output of the voltage-controlled oscillator and the input of the phase comparator.

[0063] The clock generation unit 31 outputs the generated modulated clock CLfs to the selection unit 25, frame generation unit 26, broadcast signal generation unit 27, RF transmission unit 28, and counting unit 30. The selection unit 25, frame generation unit 26, broadcast signal generation unit 27, and RF transmission unit 28 operate according to the modulated clock CLfs generated by the clock generation unit 31.

[0064] The clock generation unit 31 adjusts the frequency of the modulated clock CLfs based on a count value CntA obtained by counting the period until a predetermined number of IP packets Pt arrive using the modulated clock CLfs.

[0065] More specifically, the counting unit 30 periodically or irregularly counts the pulses of the modulated clock CLfs during the period P1 required for N IP packets Pt to arrive from the sorting unit 22, and outputs the count value CntA to the clock generation unit 31. N is an integer of 2 or more. For example, N is the number of IP packets Pt required to transmit 12969 OFDM frames via IP. In this case, the period P1 is approximately 3000 seconds.

[0066] The clock generation unit 31 receives a count value CntA from the count unit 30 and compares the received count value CntA with a predetermined reference value St1. The reference value St1 is preset based on the sample frequency fs and the period P1. The difference between the count value CntA and the reference value St1 is a statistical value of the difference between the sample frequency fs at a terrestrial digital broadcasting station and the frequency of the modulation clock CLfs.

[0067] The clock generation unit 31 adjusts the frequency division ratio Dv of the reference clock CL1 used to generate the reference clock CL2 based on the comparison result between the count value CntA and the reference value St1. Specifically, if the count value CntA is greater than or equal to a predetermined value, the clock generation unit 31 lowers the frequency of the modulated clock CLfs by adjusting the frequency division ratio Dv to a larger value. On the other hand, if the count value CntA is less than or equal to a predetermined value than the reference value St1, the clock generation unit 31 raises the frequency of the modulated clock CLfs by adjusting the frequency division ratio Dv to a smaller value. This makes it possible to adjust the frequency of the modulated clock CLfs in accordance with fluctuations in the sample frequency fs at terrestrial digital broadcasting stations.

[0068] The selection unit 25 acquires an IP packet Pt from the buffer 24 in the storage unit 23 at an acquisition timing Tm that follows the modulated clock CLfs received from the clock generation unit 31, and outputs it to the frame generation unit 26.

[0069] The selection unit 25 selects one IP packet Pt from among the four IP packets Pt stored in buffers 24A, 24B, 24C, and 24D, which contain the same symbol number. The selection unit 25 reads the selected IP packet Pt from buffer 24 and outputs it to the frame generation unit 26.

[0070] Referring again to Figure 6, for example, the selection unit 25 waits after the retransmission device 101 is started until the number of IP packets Pt accumulated in a predetermined buffer 24 reaches a predetermined value or more. When the number of IP packets Pt accumulated in the buffer 24 reaches the predetermined value, the selection unit 25 starts reading IP packets Pt from the buffer 24. More specifically, at the acquisition timing Tm, the selection unit 25 reads IP packets Pt from the buffer 24 while incrementing the memory address Ma of the buffer area from which the data is read.

[0071] For example, the retransmission device 101 performs selection processing based on quality information contained in the IP packet Pt. More specifically, the switching control unit 29 refers to the quality information in the IP packet Pt stored in each buffer 24 and determines the buffer 24 from which the selection unit 25 will read based on the quality information.

[0072] For example, when the selection unit 25 is reading IP packets Pt from buffer 24A at each acquisition timing Tm, if the switching control unit 29 detects that the received quality Qr indicated by the quality information of the IP packets Pt stored at memory address MaX of buffer 24A is less than a predetermined threshold Th, it outputs a switching instruction to the selection unit 25 to switch the source buffer 24.

[0073] As an example, the switching control unit 29 refers to the quality information of the IP packet Pt stored at the memory address MaX of buffers 24B, 24C, and 24D, and determines that buffer 24B is the buffer in which the IP packet Pt containing quality information indicating the highest received quality Qr, and in which the received quality Qr is greater than or equal to the threshold Th, is stored. The switching control unit 29 then decides to switch the source buffer 24 from buffer 24A to buffer 24B, and outputs a switching instruction to the selection unit 25 to switch the source buffer 24 to buffer 24B.

[0074] Furthermore, for example, if the switching control unit 29 detects that IP packets Pt are missing from buffer 24A while the selection unit 25 is reading IP packets Pt from buffer 24A at each acquisition timing Tm, it outputs a switching instruction to the selection unit 25 to switch the source buffer 24. As an example, the switching control unit 29 outputs a switching instruction to the selection unit 25 to switch the source buffer 24 to buffer 24B, where no IP packets Pt are missing.

[0075] The selection unit 25 receives a switching instruction from the switching control unit 29 and switches the source buffer 24 from buffer 24A to buffer 24B according to the switching instruction. The selection unit 25 also increments the memory address Ma of the source buffer area before and after switching the source buffer. That is, if the selection unit 25 reads an IP packet Pt from the buffer area in buffer 24A where memory address Ma is "33" and then switches the source buffer 24 from buffer 24A to buffer 24B, at the next acquisition timing Tm, it reads an IP packet Pt from the buffer area in buffer 24B where memory address Ma is "34".

[0076] Referring again to Figure 3, the frame generation unit 26 receives an IP packet Pt from the selection unit 25 and obtains the symbol number, symbol data Sd, TMCC information, and AC information from the received IP packet Pt.

[0077] The frame generation unit 26 modulates the acquired symbol data Sd according to the modulation scheme indicated by the TMCC information. The frame generation unit 26 also generates a pilot signal and modulates the generated pilot signal according to the BPSK (Binary Phase Shift Keying) modulation scheme. Furthermore, the frame generation unit 26 generates a TMCC signal by encoding the acquired TMCC information and modulates the TMCC signal according to the DBPSK (Differential BPSK) modulation scheme. Furthermore, the frame generation unit 26 generates an AC signal by encoding the acquired AC information and modulates the AC signal according to the DBPSK modulation scheme.

[0078] The frame generation unit 26 generates an OFDM frame based on the symbol number obtained from the IP packet Pt, which includes symbol data Sd corresponding to each of the 204 symbol numbers from 0 to 203, pilot signals corresponding to each of the 204 symbol numbers from 0 to 203, TMCC signals corresponding to each of the 204 symbol numbers from 0 to 203, and AC signals corresponding to each of the 204 symbol numbers from 0 to 203. The frame generation unit 26 outputs the generated OFDM frame to the broadcast signal generation unit 27.

[0079] The broadcast signal generation unit 27 generates an OFDM modulated signal by performing IFFT processing on the OFDM frame received from the frame generation unit 26 according to the modulation clock CLfs generated by the clock generation unit 31. The broadcast signal generation unit 27 adds a guard interval GI to the generated OFDM modulated signal and outputs the OFDM modulated signal with the guard interval GI to the RF transmission unit 28.

[0080] The RF transmission unit 28 generates an analog modulated signal by converting the OFDM modulated signal received from the broadcast signal generation unit 27 to an analog signal, and generates a broadcast signal S2 by quadrature modulating the generated analog modulated signal. The RF transmission unit 28 transmits the generated broadcast signal S2 to receivers in each home via the cable television network.

[0081] For example, the IP transmission unit 15 in retransmission device 101A transmits IP packets Pt to IP retransmission devices 101B, 101C, and 101D; the IP transmission unit 15 in retransmission device 101B transmits IP packets Pt to IP retransmission devices 101A, 101C, and 101D; the IP transmission unit 15 in retransmission device 101C transmits IP packets Pt to IP retransmission devices 101A, 101B, and 101D; and the IP transmission unit 15 in retransmission device 101D transmits IP packets Pt to IP retransmission devices 101A, 101B, and 101C. This allows retransmission devices 101A, 101B, 101C, and 101D to compensate for each other's IP packets Pt, thus creating redundancy and enabling each retransmission device 101 to generate and transmit a high-quality second broadcast signal.

[0082] [Operation Flow] Figure 7 is a diagram showing an example of a retransmission sequence in a retransmission system according to the first embodiment of the present disclosure. Figure 7 shows the sequence of processing between retransmission devices 101A, 101B, 101C, and 101D.

[0083] Referring to Figure 7, first, each retransmitter 101 receives the OFDM-modulated broadcast signal S1 via its antenna (step S11).

[0084] Next, each retransmission device 101 measures the reception quality Qr of the received broadcast signal S1 (step S12).

[0085] Next, each retransmission device 101 generates a digital quadrature signal by quadrature demodulating the broadcast signal S1, and generates a carrier signal Sc by performing FFT processing on the digital quadrature signal (step S13).

[0086] Next, each retransmitter 101 generates symbol data Sd by symbol demodulating the carrier signal Sc1, and also generates TMCC information and AC information by symbol demodulating and decoding the carrier signals Sc3 and Sc4 (step S14).

[0087] Next, each retransmitting device 101 generates symbol information Ss, which includes the symbol number of symbol Sy and the TMCC information, AC information, and symbol data Sd corresponding to symbol Sy (step S15).

[0088] Next, each retransmission device 101 generates an IP packet Pt in which the symbol information Ss is divided and stored (step S16).

[0089] Next, the retransmission devices 101B, 101C, and 101D transmit the generated IP packet Pt to the retransmission device 101A via the IP network (step S17).

[0090] Next, the retransmission device 101A stores the generated IP packet Pt in buffer 24A. The retransmission device 101A also stores the IP packets Pt received from retransmission devices 101B, 101C, and 101D in buffers 24B, 24C, and 24D, respectively (step S18).

[0091] Next, the retransmission device 101A selects one IP packet Pt from among the four IP packets Pt containing the same symbol number stored in buffers 24A, 24B, 24C, and 24D, respectively, and reads out the selected IP packet Pt (step S19).

[0092] Next, the retransmission device 101A obtains the symbol number, symbol data Sd, TMCC information, and AC information from the read IP packet Pt (step S20).

[0093] Next, the retransmitter 101A generates an OFDM frame containing symbol data Sd, pilot signal, TMCC signal, and AC signal (step S21).

[0094] Next, the retransmission device 101A generates a broadcast signal S2 by modulating the OFDM frame (step S22).

[0095] Next, the retransmission device 101A transmits the broadcast signal S2 to the receivers in each home via the cable television network (step S23).

[0096] In the retransmission device 101 according to the first embodiment of this disclosure, the packet generation unit 14 is configured to generate IP packets Pt that include quality information, but the invention is not limited to this configuration. The packet generation unit 14 may also be configured to generate IP packets Pt that include a symbol number, packet number, TMCC information, AC information, and symbol data Sd, but do not include quality information.

[0097] Furthermore, although the retransmission device 101 according to the first embodiment of this disclosure is configured to include a buffer 24, it is not limited to this configuration. The retransmission device 101 may also be configured without a buffer 24. In this case, the selection unit 25 selectively outputs IP packet Pt from one of the four IP packet Pt systems output from the sorting unit 22 to the frame generation unit 26. Even with such a configuration, if the IP packet Pt of the currently selected system is interrupted, the transmission of the broadcast signal S2 can be continued by switching the selected system. However, if the retransmission device 101 does not include a buffer 24, it cannot absorb the time difference in the arrival of IP packet Pt from other retransmission devices 101, so a momentary interruption of the broadcast signal S2 may occur when the selected system is switched.

[0098] Furthermore, in the retransmission device 101 according to the first embodiment of this disclosure, the clock generation unit 31 is configured to adjust the frequency of the modulated clock CLfs based on a count value CntA obtained by counting the period until a predetermined number of IP packets Pt arrive using the modulated clock CLfs, but the invention is not limited to this configuration. The clock generation unit 31 may also be configured not to adjust the frequency of the modulated clock CLfs.

[0099] Furthermore, although the retransmission device 101 according to the first embodiment of this disclosure is configured to include a frame generation unit 26, a broadcast signal generation unit 27, and an RF transmission unit 28, it is not limited thereto. Instead of the retransmission device 101, a broadcast signal transmission device separate from the retransmission device 101 may be configured to include a frame generation unit 26, a broadcast signal generation unit 27, and an RF transmission unit 28. In this case, the selection unit 25 in the retransmission device 101 transmits the IP packet Pt read from the buffer 24 to the broadcast signal transmission device.

[0100] Next, other embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0101] <Second Embodiment> This embodiment relates to a retransmission system 302 that selects one IP packet Pt from among multiple IP packets Pt transmitted via IP, compared to the retransmission system 301 according to the first embodiment. Except for the contents described below, it is the same as the retransmission system 301 according to the first embodiment.

[0102] Figure 8 shows the configuration of a retransmission system according to a second embodiment of the present disclosure. Referring to Figure 8, compared to retransmission system 301, retransmission system 302 includes retransmission device 102 instead of retransmission device 101A, and retransmission devices 103B, 103C, and 103D, which are retransmission devices 103, instead of retransmission devices 101B, 101C, and 101D. Retransmission device 102 is an example of a selection device and an example of a broadcast signal transmission device. Retransmission device 103 is an example of a symbol transmission device.

[0103] Figure 9 is a diagram showing the configuration of a retransmission device according to a second embodiment of the present disclosure. Referring to Figure 9, the retransmission device 103 does not include a receiving unit 20, a storage unit 23, a selection unit 25, a frame generation unit 26, a broadcast signal generation unit 27, an RF transmission unit 28, a switching control unit 29, a counting unit 30, and a clock generation unit 31, compared to the retransmission device 101.

[0104] The IP transmission unit 15 in the retransmission device 103 receives an IP packet Pt from the packet generation unit 14 and transmits the received IP packet Pt to the retransmission device 103 via the IP network.

[0105] Figure 10 shows the configuration of a retransmission device according to a second embodiment of the present disclosure. Referring to Figure 10, the retransmission device 102 does not include an RF receiving unit 11, a reception quality measurement unit 12, a symbol demodulation unit 13, a packet generation unit 14, and an IP transmission unit 15, compared to the retransmission device 101. In the example shown in Figure 10, the storage unit 23 in the retransmission device 102 includes buffers 24B, 24C, and 24D. Buffers 24B, 24C, and 24D in the retransmission device 102 are provided corresponding to retransmission devices 103B, 103C, and 103D, respectively.

[0106] The IP receiving unit 21 in the retransmission device 102 receives IP packets Pt from the retransmission device 103 via the IP network. In the example shown in Figure 8, the IP receiving unit 21 receives IP packets Pt from retransmission devices 103B, 103C, and 103D via the IP network. The IP receiving unit 21 outputs the received IP packets Pt to the sorting unit 22.

[0107] The sorting unit 22 receives IP packets Pt from the IP receiving unit 21, sorts the IP packets Pt based on the MAC header of the received IP packets Pt, and stores them in the storage unit 23.

[0108] The selection unit 25 selects one IP packet Pt from among the three IP packets Pt stored in buffers 24B, 24C, and 24D, respectively, that contain the same symbol number. The selection unit 25 reads the selected IP packet Pt from buffer 24 and outputs it to the frame generation unit 26.

[0109] While the retransmission system 302 according to the second embodiment of this disclosure is configured to include retransmission devices 102, 103B, 103C, and 103D, it is not limited thereto. The retransmission system 302 may also be configured to include a retransmission device 101 instead of at least one of the retransmission devices 103B, 103C, and 103D.

[0110] Next, other embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0111] <Third Embodiment> This embodiment relates to a retransmission system 303 in which IP transmission of terrestrial digital broadcasting is not performed between station buildings 111, compared to the retransmission system 301 according to the first embodiment. Except for the contents described below, it is the same as the retransmission system 301 according to the first embodiment.

[0112] Figure 11 shows the configuration of a retransmission system according to a third embodiment of the present disclosure. Referring to Figure 11, compared to retransmission system 301, retransmission system 303 includes retransmission device 104 instead of retransmission device 101A, and does not include retransmission devices 101B, 101C, and 101D. Retransmission device 104 receives an OFDM-modulated RF band broadcast signal S1 via a plurality of antennas located at different locations. Retransmission device 104 is an example of a symbol transmitter, an example of a selection device, and an example of a broadcast signal transmitter.

[0113] Figure 12 is a diagram showing the configuration of a retransmission device according to a third embodiment of the present disclosure. Referring to Figure 12, the retransmission device 104 has multiple sets of RF receiving units 11, receiving quality measuring units 12, and symbol demodulation units 13, a packet generation unit 41A, 41B, and 41C instead of a packet generation unit 14, a counting unit 42 instead of a counting unit 30, and does not have a receiving unit 20.

[0114] In the example shown in Figure 12, the retransmitter 104 comprises RF receiving units 11A, 11B, and 11C, which are RF receiving units 11 corresponding to each of the three antennas; receiving quality measuring units 12A, 12B, and 12C, which are receiving quality measuring units 12 corresponding to each of the three antennas; and symbol demodulation units 13A, 13B, and 13C, which are symbol demodulation units 13 corresponding to each of the three antennas. The storage unit 23 includes buffers 24A, 24B, and 24C. Buffers 24A, 24B, and 24C are provided, each corresponding to one of the three antennas.

[0115] Figure 13 shows an example of a symbol packet generated by a packet generation unit in a retransmission device according to a third embodiment of the present disclosure.

[0116] Referring to Figure 13, the packet generation unit 41 generates a symbol packet Ps that includes symbol information Ss received from the corresponding symbol demodulation unit 13 and quality information received from the corresponding reception quality measurement unit 12. The symbol packet Ps is an example of a symbol frame. The symbol packet Ps includes a symbol number, quality information, TMCC information, AC information, and symbol data Sd.

[0117] For example, each time the packet generation unit 41 receives symbol information Ss from the symbol demodulation unit 13, it generates a symbol packet Ps containing the received symbol information Ss. More specifically, the packet generation unit 41 generates a symbol packet Ps containing the received symbol information Ss and the latest quality information received from the reception quality measurement unit 12. The packet generation unit 41 stores the generated symbol packet Ps in the corresponding buffer 24. Alternatively, for example, the packet generation unit 41C outputs the generated symbol packet Ps to the counting unit 42.

[0118] Figure 14 shows symbol packets stored in a buffer in a retransmission device according to a third embodiment of the present disclosure. In Figure 14, the numbers written in the symbol packets Ps indicate the symbol number of the symbol packet Ps.

[0119] Referring to Figure 14, buffer 24 has multiple buffer areas. Each buffer area is assigned a memory address Ma, which is represented, for example, by a predetermined number of bits. The packet generation unit 41 stores the symbol packet Ps in one of the multiple buffer areas in buffer 24, in which the memory address Ma is determined by the symbol number of the symbol packet Ps. More specifically, for example, the packet generation unit 41 stores a symbol packet Ps with symbol number "11" in the buffer area where memory address Ma is "31".

[0120] Referring again to Figure 12, the counting unit 42 periodically or irregularly counts the pulses of the modulated clock CLfs during the period P2 required for M symbol packets Ps to arrive from the packet generation unit 41C, and outputs the count value CntB to the clock generation unit 31. M is an integer of 2 or more. For example, M is the number of symbol packets Ps corresponding to 12969 OFDM frames.

[0121] The clock generation unit 31 receives a count value CntB from the count unit 42 and compares the received count value CntB with a predetermined reference value St2. The reference value St2 is preset based on the sample frequency fs and the period P2. The difference between the count value CntB and the reference value St2 is a statistical value of the difference between the sample frequency fs at a terrestrial digital broadcasting station and the frequency of the modulation clock CLfs. Based on the comparison result between the count value CntB and the reference value St2, the clock generation unit 31 adjusts the frequency division ratio Dv of the reference clock CL1 used to generate the reference clock CL2.

[0122] The selection unit 25 acquires symbol packets Ps from the buffer 24 in the storage unit 23 at an acquisition timing Tm that follows the modulated clock CLfs received from the clock generation unit 31, and outputs them to the frame generation unit 26.

[0123] The selection unit 25 selects one symbol packet Ps from among the three symbol packets Ps stored in buffers 24A, 24B, and 24C, respectively, that contain the same symbol number. The selection unit 25 reads the selected symbol packet Ps from buffer 24 and outputs it to the frame generation unit 26.

[0124] Referring again to Figure 14, for example, the selection unit 25 waits after the retransmission device 104 is started until the number of symbol packets Ps accumulated in a predetermined buffer 24 reaches a predetermined value or more. When the number of symbol packets Ps accumulated in the buffer 24 reaches the predetermined value, the selection unit 25 starts reading the symbol packets Ps from the buffer 24. More specifically, at the acquisition timing Tm, the selection unit 25 reads the symbol packets Ps from the buffer 24 while incrementing the memory address Ma of the buffer area from which the data is read.

[0125] For example, the switching control unit 29 refers to the quality information in the symbol packets Ps stored in each buffer 24 and, based on the quality information, determines the buffer 24 from which the selection unit 25 will read the data.

[0126] For example, when the selection unit 25 is reading symbol packets Ps from buffer 24A at each acquisition timing Tm, if the switching control unit 29 detects that the received quality Qr indicated by the quality information in the symbol packets Ps stored at memory address MaX of buffer 24A is less than a predetermined threshold Th, it outputs a switching instruction to the selection unit 25 to switch the source buffer 24.

[0127] As an example, the switching control unit 29 refers to the quality information in the symbol packet Ps stored at the memory address MaX of buffers 24B and 24C, and determines that buffer 24B is the buffer in which the symbol packet Ps containing quality information indicating the highest received quality Qr is stored, and where the received quality Qr is equal to or greater than the threshold Th. The switching control unit 29 then decides to switch the source buffer 24 from buffer 24A to buffer 24B, and outputs a switching instruction to the selection unit 25 to switch the source buffer 24 to buffer 24B.

[0128] Furthermore, for example, if the switching control unit 29 detects that a symbol packet Ps is missing from buffer 24A while the selection unit 25 is reading symbol packets Ps from buffer 24A at each acquisition timing Tm, it outputs a switching instruction to the selection unit 25 to switch the source buffer 24. As an example, the switching control unit 29 outputs a switching instruction to the selection unit 25 to switch the source buffer 24 to buffer 24B, where no symbol packets Ps are missing.

[0129] The selection unit 25 receives a switching instruction from the switching control unit 29 and switches the source buffer 24 from buffer 24A to buffer 24B according to the switching instruction. The selection unit 25 also increments the memory address Ma of the source buffer area before and after switching the source buffer. That is, if the selection unit 25 reads a symbol packet Ps from the buffer area in buffer 24A where memory address Ma is "33" and then switches the source buffer 24 from buffer 24A to buffer 24B, at the next acquisition timing Tm, it reads a symbol packet Ps from the buffer area in buffer 24B where memory address Ma is "34".

[0130] Referring again to Figure 12, the frame generation unit 26 receives a symbol packet Ps from the selection unit 25 and obtains the symbol number, symbol data Sd, TMCC information, and AC information from the received symbol packet Ps.

[0131] The frame generation unit 26 generates an OFDM frame based on the acquired symbol number, symbol data Sd, TMCC information, and AC information, and outputs the generated OFDM frame to the broadcast signal generation unit 27.

[0132] Next, other embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0133] <Fourth Embodiment> This embodiment relates to a retransmission system 304 that stores IP packets Pt according to the sequence number Sn in the RTP header, compared to the retransmission system 301 according to the first embodiment. Except for the contents described below, it is the same as the retransmission system 301 according to the first embodiment.

[0134] Figure 15 shows the configuration of a retransmission system according to a fourth embodiment of the present disclosure. Referring to Figure 15, the retransmission system 304, compared to the retransmission system 301, includes retransmission devices 105A, 105B, 105C, and 105D, which are retransmission devices 105 instead of retransmission device 101. Retransmission device 105 is an example of a symbol transmission device, an example of a selection device, and an example of a broadcast signal transmission device.

[0135] Figure 16 is a diagram showing the configuration of a retransmission device according to a fourth embodiment of the present disclosure. Referring to Figure 16, the retransmission device 105 further comprises a number correction unit 50 and a correction control unit 52 compared to the retransmission device 101. The number correction unit 50 includes correction units 51A, 51B, 51C, and 51D, which are correction units 51. The correction units 51A, 51B, 51C, and 51D are provided in correspondence with buffers 24A, 24B, 24C, and 24D, respectively. That is, the correction units 51A, 51B, 51C, and 51D are provided in correspondence with retransmission devices 105A, 105B, 105C, and 105D, respectively.

[0136] The sorting unit 22 receives IP packets Pt from the IP receiving unit 21. The sorting unit 22 also receives IP packets Pt from the packet generation unit 14. Based on the MAC header of the received IP packets Pt, the sorting unit 22 sorts the IP packets Pt and outputs them to the correction unit 51. More specifically, the sorting unit 22 outputs the received IP packets Pt to the correction unit 51 corresponding to the source address of the IP packets Pt.

[0137] The correction unit 51 receives IP packets Pt from the sorting unit 22 and stores the received IP packets Pt in the corresponding buffer 24. When the correction unit 51 receives a correction instruction from the correction control unit 52, it holds the received correction instruction. Each time the correction unit 51 receives an IP packet Pt from the sorting unit 22, it performs a correction process to correct the sequence number Sn included in the RTP header of the received IP packet Pt according to the correction instruction it holds. The correction unit 51 then stores the IP packet Pt after the correction process in the corresponding buffer 24.

[0138] The correction control unit 52 determines the correction value Mv for the sequence number Sn determined by each correction unit 51. For example, the correction control unit 52 determines the correction value Mv so that the sequence number Sn of IP packets Pt containing the same symbol data Sd is the same. The following describes in detail the procedure for determining the correction value Mv by the correction control unit 52.

[0139] First, the correction control unit 52 monitors the IP packets Pt stored in the buffer 24 by the correction unit 51. The correction control unit 52 searches for IP packets Pt_00 among the IP packets Pt stored in the buffer 24A by the correction unit 51A, where the symbol number is "zero" and the packet number is "zero".

[0140] When the correction control unit 52 detects an IP packet Pt_00 in buffer 24A, it determines a predetermined search period Tse based on the storage timing t1 at which the IP packet Pt_00 was stored in buffer 24A. The search period Tse is the period for searching for IP packets Pt_00 stored in each buffer 24. The search period Tse is set according to the length of the frame period Cf and guard interval GI of the OFDM frame.

[0141] For example, if the length of a symbol including the guard interval GI is 1260 microseconds and the frame period Cf is 257.040 milliseconds, the search period Tse is set to a 100-millisecond period centered on the reference time when the frame period Cf has elapsed from the save timing t1. Alternatively, if the length of the guard interval GI and the frame period Cf are unknown, the search period Tse is set to a 139-millisecond period starting from time t2, which is 169 milliseconds after the save timing t1.

[0142] During the set search period Tse, the correction control unit 52 waits for IP packets Pt_00 to be stored in buffers 24A, 24B, 24C, and 24D by the correction units 51A, 51B, 51C, and 51D. During the search period Tse, when the correction control unit 52 detects IP packets Pt_00A, Pt_00B, Pt_00C, and Pt_00D, which are IP packets Pt_00 stored in buffers 24A, 24B, 24C, and 24D respectively, it acquires the IP packets Pt_00A, Pt_00B, Pt_00C, and Pt_00D. The IP packets Pt_00A, Pt_00B, Pt_00C, and Pt_00D each contain symbol data Sd with the same content. Furthermore, if the correction control unit 52 fails to detect IP packets Pt_00A, Pt_00B, Pt_00C, and Pt_00D during the search period Tse, it searches for a new IP packet Pt_00 in buffer 24A and determines a new search period Tse based on a new storage timing t1.

[0143] The correction control unit 52 determines the correction values ​​MvB, MvC, and MvD, which are correction values ​​Mv to be given to the correction units 51B, 51C, and 51D, based on the sequence number Sn included in the RTP header of the acquired IP packets Pt_00A, Pt_00B, Pt_00C, and Pt_00D.

[0144] More specifically, the correction control unit 52 determines the correction value MvB as the difference obtained by subtracting the sequence number Sn of IP packet Pt_00B from the sequence number Sn of IP packet Pt_00A. The correction control unit 52 outputs a correction instruction indicating the determined correction value MvB to the correction unit 51B.

[0145] Furthermore, the correction control unit 52 determines the correction value MvC as the difference obtained by subtracting the sequence number Sn of IP packet Pt_00C from the sequence number Sn of IP packet Pt_00A. The correction control unit 52 outputs a correction instruction indicating the determined correction value MvC to the correction unit 51C.

[0146] Furthermore, the correction control unit 52 determines the correction value MvD as the difference obtained by subtracting the sequence number Sn of IP packet Pt_00D from the sequence number Sn of IP packet Pt_00A. The correction control unit 52 outputs a correction instruction indicating the determined correction value MvD to the correction unit 51D.

[0147] Figure 17 shows an example of correction processing by a correction unit in a retransmission device according to a fourth embodiment of the present disclosure. In Figure 17, the upper numbers written in the IP packet Pt indicate the symbol number and packet number of the IP packet Pt. Specifically, for example, an IP packet Pt labeled "11 / 0" indicates an IP packet Pt with a symbol number of "11" and a packet number of "zero". The lower numbers written in the IP packet Pt indicate the sequence number Sn of the IP packet Pt.

[0148] Referring to Figure 17, the correction units 51B, 51C, and 51D each receive a correction instruction and hold the correction values ​​MvB, MvC, and MvD indicated by the received instruction. The correction units 51B, 51C, and 51D each receive an IP packet Pt from the sorting unit 22 and perform a correction process by adding the held correction values ​​MvB, MvC, and MvD to the sequence number Sn of the received IP packet Pt. As a result, in the IP packets Pt after correction processing by each correction unit 51, the sequence number Sn of IP packets Pt containing the same symbol data Sd will be the same value.

[0149] The correction units 51B, 51C, and 51D each store the IP packet Pt in a buffer area among multiple buffer areas in buffers 24B, 24C, and 24D, which is assigned a memory address Ma determined by the sequence number Sn of the IP packet Pt after correction processing.

[0150] Furthermore, the correction unit 51A receives the IP packet Pt from the sorting unit 22 and stores the IP packet Pt in one of the multiple buffer areas in the buffer 24A, in which the memory address Ma, determined by the sequence number Sn of the IP packet Pt, is assigned.

[0151] For example, the correction control unit 52 periodically or irregularly determines the correction value Mv as described above and outputs a correction instruction to the correction unit 51 indicating the determined correction value Mv. The correction unit 51 receives the correction instruction from the correction control unit 52 and updates the held correction value Mv to the correction value Mv indicated by the received correction instruction.

[0152] The embodiments described above should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0153] Each process (each function) of the above-described embodiment is implemented by a processing circuit (Circuitry) including one or more processors. The processing circuit may consist of one or more memories, various analog circuits, various digital circuits, etc., in addition to the one or more processors, as well as an integrated circuit. The one or more memories store programs (instructions) that cause the one or more processors to execute each of the above processes. The one or more processors may execute each of the above processes according to the programs read from the one or more memories, or they may execute each of the above processes according to logic circuits that have been pre-designed to execute each of the above processes. The processors may be various processors suitable for computer control, such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), and ASIC (Application Specific Integrated Circuit). Furthermore, the physically separated multiple processors may cooperate with each other to execute each of the above processes. For example, the processors installed in each of several physically separated computers may cooperate with each other via a network such as a LAN (Local Area Network), WAN (Wide Area Network), and the Internet to perform the above processes. The program may be installed in the memory via the network from an external server device, or it may be distributed on a recording medium such as a CD-ROM (Compact Disc Read Only Memory), DVD-ROM (Digital Versatile Disk Read Only Memory), and semiconductor memory, and then installed in the memory from the recording medium.

[0154] The above description includes the following features. [Note 1] A retransmission system that retransmits terrestrial digital broadcasts, Multiple symbol transmitters receive a first broadcast signal modulated with OFDM at different locations. Selection device and Equipped with a broadcast signal transmission device, Each of the aforementioned multiple symbol transmitting devices acquires multiple carrier signals from the received first broadcast signal, generates binary data for each symbol in the first broadcast signal by symbol demodulating the multiple carrier signals, and generates a symbol frame including the binary data and the symbol number corresponding to the binary data. The selection device performs a selection process to select one of the multiple symbol frames, each of which is generated by the multiple symbol transmission devices and which contains the same symbol number. The broadcast signal transmitting device acquires the binary data from the symbol frame selected in the selection process, generates an OFDM frame containing the acquired binary data, generates an OFDM-modulated second broadcast signal by modulating the generated OFDM frame, and transmits the generated second broadcast signal. The aforementioned symbol frame includes a sequence number, The selection device is provided for each symbol transmitting device and includes a plurality of receiving buffers for storing the symbol frames received from the corresponding symbol transmitting device. A retransmission system comprising: a selection device that performs a correction process to correct the sequence number so that the sequence numbers of the symbol frames containing the same binary data have the same value, and a receiving buffer that stores the symbol frames after the correction process. [Explanation of Symbols]

[0155] 11 RF Receiver 12. Reception Quality Measurement Unit 13 Symbol Demodulation Unit 14. Packet generation unit 15 IP Transmission Unit 20 Receiver 21 IP receiving unit 22 Sorting section 23 Storage section 24, 24A, 24B, 24C, 24D buffers 25 Selection Section 26 Frame generation unit 27 Broadcast signal generation unit 28 RF Transmitter 29 Switching Control Unit 30 count section 31 Clock generation unit 41, 41A, 41B, 41C Packet generation unit 42 count section 50 Number Correction Section 51,51A,51B,51C,51D Correction section 52 Correction Control Unit 101, 101A, 101B, 101C, 101D Retransmission device 102 Retransmission device 103, 103B, 103C, 103D Retransmission Device 104 Retransmission device 105, 105A, 105B, 105C, 105D Retransmission Device 111,111A,111B,111C,111D Station building 301, 302, 303, 304 Retransmission System Cf frame period Cs Symbol Period Ss Symbol Information Pt IP packet Ps Symbol Packet

Claims

1. A retransmission system that retransmits terrestrial digital broadcasts, Multiple symbol transmitting devices that receive the OFDM-modulated first broadcast signal at different locations, Selection device and Equipped with a broadcast signal transmission device, Each of the multiple symbol transmitting devices acquires multiple carrier signals from the received first broadcast signal, generates binary data for each symbol in the first broadcast signal by symbol demodulating the multiple carrier signals, and generates a symbol frame including the binary data and the symbol number corresponding to the binary data. The selection device performs a selection process to select one of the multiple symbol frames, each of which is generated by the multiple symbol transmission devices and which contains the same symbol number. The broadcast signal transmitting device is a retransmission system that acquires the binary data from the symbol frame selected in the selection process, generates an OFDM frame containing the acquired binary data, generates an OFDM-modulated second broadcast signal by modulating the generated OFDM frame, and transmits the generated second broadcast signal.

2. The symbol transmission device generates the symbol frame which further includes quality information relating to the reception quality of the first broadcast signal. The retransmission system according to claim 1, wherein the selection device performs the selection process based on the quality information contained in the symbol frame.

3. The selection device is provided for each symbol transmission device and includes a plurality of receive buffers for storing the symbol frames received from the corresponding symbol transmission device. The retransmission system according to claim 1 or 2, wherein the selection device, in the selection process, selects one symbol frame from among the plurality of symbol frames, each of which is stored in the plurality of receiving buffers and which contains the same symbol number.

4. The selection device generates a modulated clock, The broadcast signal transmitting device modulates the OFDM frame according to the modulation clock generated by the selection device. The retransmission system according to claim 1 or 2, wherein the selection device adjusts the frequency of the modulation clock based on a count value obtained by counting the period of time until a predetermined number of the symbol frames arrive from the broadcast signal transmitting device using the modulation clock.

5. The retransmission system according to claim 1 or 2, wherein the selection device switches the selected symbol frame without interruption during the selection process.

6. A selection device used for retransmitting terrestrial digital broadcasts, A receiving unit that receives multiple symbol frames, each containing binary data for each symbol in an OFDM-modulated broadcast signal and a symbol number corresponding to the binary data, via different transmission paths. A plurality of receive buffers are provided for each transmission path and store the symbol frames received by the receiving unit via the corresponding transmission path, A selection device comprising: a selection unit that performs a selection process to select one symbol frame from among the plurality of symbol frames, each of which is stored in the plurality of receiving buffers and which contains the same symbol number.

7. A retransmission method in a retransmission system that retransmits terrestrial digital broadcasts, A step in which multiple symbol transmitting devices, each receiving an OFDM-modulated first broadcast signal at different locations, each acquire multiple carrier signals from the received first broadcast signal, generate binary data for each symbol in the first broadcast signal by symbol demodulating the multiple carrier signals, and generate a symbol frame including the binary data and the symbol number corresponding to the binary data, The selection device performs a selection process to select one symbol frame from among a plurality of symbol frames, each of which is generated by the plurality of symbol transmission devices and which contains the same symbol number. A retransmission method comprising the steps of: a broadcast signal transmitting device acquiring the binary data from the symbol frame selected in the selection process; generating an OFDM frame containing the acquired binary data; generating an OFDM-modulated second broadcast signal by modulating the generated OFDM frame; and transmitting the generated second broadcast signal.

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