JP2008211587A - Ip/rf converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a ground digital broadcast type OFDM signal from an IP-retransmitted broadcast TS packet. <P>SOLUTION: Each IP/FEC processor (32-1 to n) processes receiving IP packets in corresponding channels, and outputs RTP packets solving a jitter in an IP network 20. Time-stamp processors (34-1 to n) successively align and output each receiving broadcast TS packet in each RTP packet with time. Each clock extracting device (36-1 to n) extracts synchronous clocks from the receiving broadcast TS packets, and outputs the receiving broadcast TS packets and extracting clocks to OFDM modulators (38-1 to n). Each OFDM modulator (38-1 to n) OFDM-modulates the receiving broadcast TS packets from the corresponding devices (36-1 to n), and generates OFDM signals. A mixer 40 mixes the OFDM signals from each OFDM modulator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an IP / RF conversion apparatus in a terrestrial digital broadcast retransmission technique using IP multicast.

  Currently, for the purpose of early dissemination of digital terrestrial broadcasting, studies are being conducted on broadcast wave retransmission technology by IP multicast (hereinafter referred to as “IP retransmission”) mainly for difficult viewing areas. In the future, TVs with set-top boxes (STBs) and LAN interfaces that support IP retransmission will be developed, and users of broadband Internet services such as FTTH (Fiber To The Home) will be able to The broadcast is expected to be viewable.

  A conventional typical method for distributing a terrestrial digital broadcast signal via an IP network is a method in which an STB is installed on the receiving side and a TS signal is demodulated as it is. In this system, the PCR clock for MPEG demodulation is reproduced, but the high-accuracy IFFT sampling clock necessary for OFDM modulation is not reproduced (see Non-Patent Document 1).

  In the future, even when terrestrial digital broadcasts that have been retransmitted by IP are received and viewed on an STB or IP-compatible TV, there are still a few detached houses and condominiums where LAN wiring is provided in each room in the house. It is difficult for the user to view in any room.

  TVs with tuners compatible with digital terrestrial broadcasting are now steadily spreading, but it will take more than 10 years before these replacement demands occur. Considering video peripheral devices such as video recorders, for the time being, it is essential to support video devices with current RF signal inputs.

  Therefore, an IP / RF conversion method is being studied in which a broadcast signal transmitted to the home by IP multicast is again converted into an RF signal in a terrestrial digital broadcast format and can be distributed using an existing home coaxial wiring.

  In terrestrial digital broadcasting, OFDM (Orthogonal Frequency domain Multiplexing) modulation is adopted as broadcast wave output. A signal called a broadcast TS (Transport Stream) packet in which the bit rate is adjusted to 32.508 Mbps by adding a null packet or a dummy byte is input to the OFDM modulator. In broadcasting stations, the addition of PCR (Program Clock Reference) at the time of MPEG2 encoding, remultiplexing to broadcast TS packets, and inverse fast Fourier transform (IFFT) processing of OFDM modulators are common in high precision and high stability. It is synchronized using an oscillator. Thereby, a time-stable broadcast signal can be generated and transmitted.

  In the case of the IP / RF conversion method, it is necessary to extract data corresponding to a broadcast TS signal from an IP signal received via an IP network and reconvert it into an OFDM signal. The clock signal prepared locally on the IP signal receiving side and the TS signal extracted from the IP signal are asynchronous. Therefore, in order to perform a stable OFDM modulation operation in which neither buffer overflow nor underflow occurs, it is necessary to generate a dependent synchronization clock from the received TS packet.

There are STL (Studio-Transmitter Link) and TTL (Transmitter-Transmitter Link) as techniques for performing OFDM modulation in a remote place away from a performance place. A method for synchronizing a highly accurate and highly stable clock to the GPS, a method for transmitting the clock using a separate line from the data, and a performance / transmitting station for a synchronous clock using an SDH (Synchronous Data Hierarchy) line A method of synchronizing is conceivable (see Non-Patent Document 2).
“A Study on Digital Broadcasting Content Distribution Technology Using IP Multicast”, IEICE Technical Report, CS2005-69, pp. 49-54, 2005 "Transmission method for digital terrestrial television broadcasting", Radio Industry Association ARIB STD-B31

  The technique described in Non-Patent Document 2 cannot be realized at low cost, and cannot be used for an inexpensive IP / RF conversion device that can be used in a private house.

  An object of the present invention is to provide an IP / RF conversion device that can be realized at low cost.

  In order to solve the above-described problem, an IP / RF conversion apparatus according to the present invention includes an IP packet receiving apparatus that receives an IP packet carrying a broadcast TS packet, and an IP packet received by the IP packet receiving apparatus. The TS packet is extracted, and the broadcast TS packet processing apparatus that outputs the TS packets arranged in time order on the transmission side, and the synchronization clock necessary for OFDM modulation is extracted from the broadcast TS packet supplied from the broadcast TS packet processing apparatus. A clock extraction device for synchronously outputting the synchronous clock and the broadcast TS packet, and an OFDM modulation device for OFDM-modulating the broadcast TS packet from the clock extraction device in synchronization with the synchronous clock from the clock extraction device It is characterized by comprising.

  According to the present invention, an RF signal can be generated from a broadcast TS packet retransmitted by IP with a simple configuration. Since there is no need to transmit the clock synchronized with the broadcast TS packet from the transmission side from the transmission side, the system configuration is simplified and the cost can be greatly reduced.

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

  FIG. 1 shows a schematic block diagram of an IP retransmission system using an embodiment of the present invention. FIG. 2 shows the structure of a broadcast TS packet. FIG. 3 shows the transition of broadcast TS packets in the IP retransmission system shown in FIG.

  The transmission device 10 includes a plurality of terrestrial digital tuners 12-1 to 12-n that separate broadcast TS packets of individual channels from terrestrial digital broadcast waves. As shown in FIG. 2, the broadcast TS packet has a fixed length of 204 bytes, 1 synchronous byte ("0x47" in hexadecimal notation), 187 bytes of data part, 8 bytes of ISDB-T (Integrated Services). Digital Broadcasting for Terrestrial Television Broadcasting) information and 8-byte parity. The ISDB-T information section includes control information such as a modulation parameter for performing OFDM modulation again on the receiving side.

  The TS / IP converters 14-1 to 14-n convert the broadcast TS packets from the corresponding tuners 12-1 to 12-n into RTP (Real-time Transport Protocol) packets, and further convert them into IP packets. For example, each TS / IP converter 14-1 to 14-n collects, for example, seven broadcast TS packets into one RTP packet as shown in FIGS. As shown in FIG. 3B, an RTP header is added to each RTP packet. Each TS / IP converter 14-1 to 14-n further converts each RTP packet into an IP packet as shown in FIGS. 3 (2) and 3 (3). An IP header is added to each IP packet.

  The IP packets generated by the TS / IP conversion devices 14-1 to 14-n are supplied to the video distribution server 16. The video distribution server 16 sends the IP packets from the TS / IP converters 14-1 to 14-n to the IP / RF converter 30 at the user's home by unicast, multicast or broadcast via the IP network 20. Send. The video distribution server 16 performs error correction encoding of the IP packet by FEC (Forward Error Correction) in preparation for a transmission error in the IP network 20. Although a gateway such as a network termination device or an IP router may be interposed between the IP network 20 and the IP / RF conversion device 30, they are omitted in FIG.

  The IP / RF conversion device 30 receives the IP packet transmitted from the transmission device 10 via the IP network 20. Due to the jitter of the IP network 20, each IP packet reaches the IP / RF conversion device 30 before and after time as shown in FIG. 3 (4). To compensate for this, the RTP protocol is used.

  The IP / FEC processing devices 32-1 to 32-n are provided corresponding to the respective channels of terrestrial digital broadcasting. The IP / FEC processing devices 32-1 to 32-n function as the IP packet receiving device in the claims.

  Each IP / FEC processing device 32-1 to 32-n processes the received IP packet of the corresponding channel, corrects the transmission error by FEC, and outputs the packet in which the jitter in the IP network 20 is eliminated. More specifically, the loss of the arrived packet and the occurrence of the order change are detected. The lost packet is restored by FEC processing. Then, each packet is rearranged so that the packet order is the same as that on the transmission side. For example, in the case of RTP, packet loss and order change are detected from the sequence number in the RTP header. For the FEC processing, buffers of appropriate sizes are prepared in the IP / FEC processing devices 32-1 to 32-n. Using this buffer, as shown in FIG. 3 (5), the jitter of the RTP packet generated in the IP network 20 is absorbed.

  In FIG. 1, the IP / FEC processing devices 32-1 to 32-n are provided for each terrestrial digital channel, but processed RTP packets are provided for each channel after the single IP / FEC processing device. You may arrange | position the distribution apparatus distributed to the time stamp processing apparatuses 34-1 to 34-n. In this case, the single IP / FEC processing device and the subsequent distribution device are the IP packet receiving device in the claims.

  The time stamp processing devices 34-1 to 34-n extract time stamps from the RTP headers of the RTP packets from the corresponding IP / FEC processing devices 32-1 to 32-n and output timings based on the time stamps. As shown in 3 (6), the received broadcast TS packets in each RTP packet are sequentially output in time alignment. As a result, the received broadcast TS packet is reproduced at almost the same timing as the transmission interval on the transmission side. The time stamp processing devices 34-1 to 34-n function as broadcast TS packet processing devices in the claims.

  Each clock extractor 36-1 to 36-n extracts a clock from the received broadcast TS packet from the corresponding time stamp processor 34-1 to 34-n, and OFDM modulates the received broadcast TS packet and the extracted clock. Output to devices 38-1 to 38-n. The clock extracted or generated by each of the clock extracting devices 36-1 to 36-n is a so-called subordinate synchronous clock.

  FIG. 4 shows a schematic block diagram of the clock extractors 36-1 to 36-n. Received broadcast TS packets from the time stamp processing devices 34-1 to 34-n are input to the buffer 50 and the synchronization byte detection device 52.

  The buffer 50 sequentially captures incoming received broadcast TS packets. At this time, the write clock of the buffer 50 uses a local oscillator that operates at a frequency that does not cause buffer underflow, or an interface for transferring data from the preceding time stamp processing devices 34-1 to 34-n. The clock used in the above may be used.

  The synchronization byte detection device 52 detects a synchronization byte arranged in the first byte of the received broadcast TS packet and outputs a trigger signal to the PLL frequency synthesizer 54. The broadcast TS packet input to the synchronization byte detection device 52 has the same broadcast TS format as that input to the OFDM modulator at the broadcast station, and the bit rate is 32.508 (= 512 × 4/63) Mbps. It is fixed. Therefore, the rate of the trigger signal output from the synchronous byte detector 52 is 19.9 kHz (= 512 × 4/63 × 1 / (204 bytes × 8 bits)). The PLL frequency synthesizer 54 generates a subordinate synchronization clock of 32.508 MHz in synchronization with the trigger signal of 19.9 kHz.

  The 32.508 MHz output clock of the PLL frequency synthesizer 54 is supplied to the buffer 50 as a read clock. That is, the buffer 50 reads the received broadcast TS packet to be stored in accordance with the output clock of the PLL frequency synthesizer 54. The received broadcast TS packet read from the buffer 50 is supplied to the corresponding OFDM modulators 38-1 to 38-n.

  The output clock of the PLL frequency synthesizer 54 is also supplied to the frequency divider 56. The frequency divider 56 divides the output clock of the PLL frequency synthesizer 54 by ¼ to generate a clock having a frequency of 8.127 (= 512/63) MHz. The generated clock is supplied to the corresponding OFDM modulators 38-1 to 38-n as an extracted clock or a clock dependently synchronized with the transmission side.

  In this way, the 8.127 MHz clock dependently synchronized with the transmission side and the received broadcast TS packet synchronized with this clock are supplied to each of the OFDM modulators 38-1 to 38-n. Each of the OFDM modulators 38-1 to 38-n performs OFDM modulation on the received broadcast TS packet from the corresponding clock extractor 36-1 to 36-n, and generates the same OFDM signal as the broadcast wave. Extracted clocks from the corresponding clock extracting devices 36-1 to 36-n are used for the inverse Fourier transform processing (IFFT) of OFDM modulation. This makes it possible to generate an OFDM signal that carries broadcast TS packets with a very simple configuration.

  The mixer 40 mixes the OFDM signals output from the OFDM modulators 38-1 to 38-n. The mixing result of the mixer 40 is a so-called terrestrial digital broadcast RF signal. The output signal of the mixer 40 is transmitted, for example, to a terrestrial digital tuner or a terrestrial digital compatible television in each room via a coaxial cable compatible with digital terrestrial broadcasting in the house. Thereby, the terrestrial digital broadcast retransmitted by IP can be viewed in each room.

  Although an embodiment using RTP as means for compensating for delay in the IP network 20 has been described, it is obvious that other delay compensation means can be used. In the above embodiment, the time stamp for correcting the timing with respect to the jitter of the network is used, but other time stamp methods may be used.

  It is obvious that the digital terrestrial tuners 12-1 to 12-n are not necessary when the transmission device 10 can receive broadcast TS packets directly from each broadcasting station.

  The clock extracting devices 36-1 to 36-n can be applied to a system that distributes a broadcast TS signal using a transmission method other than the IP network and performs OFDM modulation at a remote location.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a schematic block diagram of one Example of this invention. It is a figure which shows the structure of a broadcast TS packet. It is a schematic diagram which shows the transition of the broadcast TS packet in a present Example. It is a schematic block diagram of the clock extracting devices 36-1 to 36-n.

Explanation of symbols

10: Transmitters 12-1 to 12-n: Terrestrial digital tuners 14-1 to 14-n: TS / IP converter 16: Video distribution server 20: IP network 30: IP / RF converters 32-1 to 32-2. n: IP / FEC processor 34-1 to 34-n: Time stamp processor 36-1 to 36-n: Clock extractor 38-1 to 38-n: OFDM modulator 40: Mixer 50: Buffer 52: Synchronous byte detector 54: PLL frequency synthesizer 56: Frequency divider

Claims (5)

IP packet receivers (32-1 to 32-n) for receiving IP packets carrying broadcast TS packets;
Broadcast TS packet processing devices (34-1 to 34-n) that extract the broadcast TS packets from the IP packets received by the IP packet receiving device and arrange them in time order on the transmission side;
A clock extraction device (36-1 to 36-36) that extracts a synchronization clock necessary for OFDM modulation from the broadcast TS packet supplied from the broadcast TS packet processing device and outputs the synchronization clock and the broadcast TS packet in synchronization. n) and
OFDM modulation device (38-1 to 38-n) that performs OFDM modulation on the broadcast TS packet from the clock extraction device in synchronization with the synchronous clock from the clock extraction device
An IP / RF converter characterized by comprising: For each channel of terrestrial digital broadcasting, comprising a unit comprising the broadcast TS packet processing device, the clock extraction device and the OFDM modulation device,
An IP / RF converter characterized by further comprising a mixer (40) for mixing the output signal of the OFDM modulator for each channel. The clock extractor is
A buffer (50) for temporarily storing the broadcast TS packet from the TS packet processing device;
A synchronization byte detection device (52) for detecting a synchronization byte of the broadcast TS packet from the TS packet processing device and outputting a trigger signal synchronized with the broadcast TS packet;
A clock generation device (54) for generating a clock used for reading the broadcast TS packet stored in the buffer according to the trigger signal;
A frequency divider (56) for dividing the clock generated by the clock generator into a predetermined frequency and outputting the synchronous clock
And
The IP / RF conversion apparatus according to claim 1 or 2, wherein the buffer reads a broadcast TS packet to be stored in accordance with the clock generated by the clock generation apparatus.   4. The IP packet receiving apparatus (32-1 to 32-n) is an IP / FEC processing apparatus that performs an order change process of the IP packets and corrects a transmission error. The IP / RF conversion apparatus according to claim 1.   The broadcast TS packet processing device is a time stamp processing device that arranges broadcast TS packets in time order on the transmission side according to the time stamp of the output signal of the IP packet receiving device (32-1 to 32-n). The IP / RF conversion device according to claim 1, wherein the IP / RF conversion device is characterized in that:

Images