JPH1028105A - Synchronization system for single frequency network and encoding device and transmitter for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain transmission and reception of an OFDM signal in a single frequency network using plural transmitters by uniquely deciding the inserting position of a synchronizing symbol. SOLUTION: A multiplexing circuit 3 converts the speed of a signal inputted from an encoder 1 so that the time division multiplexing of a synchronizing packet can be attained, time division multiplexes it with a synchronizing packet from a synchronizing packet generating circuit 5, and transmits a TS(transport stream) to a transmission path. The TS transmitted to the transmission path is inputted to an OFDM(orthogonal frequency division multiplexing) transmitting device. A synchronizing packet detecting circuit 6 detects the synchronizing packet from the input TSP. A mapping circuit 7 successively allocates the data of the TS to each carrier wave of an OFDM signal by using the detecting timing signal of the synchronizing packet as a reference. A switch circuit 9 adds a synchronizing symbol to a data symbol string from an IFFT(inverse fast Fourier transforming) 8 based on the output timing signal of the synchronizing packet detecting circuit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronization system for a single frequency network and an encoding apparatus and a transmission apparatus thereof. And its encoding device and transmission device.

[0002]

2. Description of the Related Art In digital television broadcasting, it is necessary to establish various types of synchronization. The types of synchronization include bit synchronization (clock recovery), frame synchronization required by performing transmission in a frame configuration, and, in OFDM transmission, each bit constituting a data stream to be transmitted and each bit to which it is assigned. Carrier wave synchronization and the like.

[0003] For a digital transmission receiving system, various synchronization systems have been proposed. For example, as a method of synchronizing a frame for reception of FM multiplex broadcasting or the like, there is a method of knowing the head position of a frame from differences in header portions of a plurality of packets constituting the frame. In this synchronization method, since the header of a packet constituting a frame is known and the arrangement of the headers of the group constituting the frame is not uniform, the boundary of the group is specified, and the synchronization of the frame is performed based on the boundary. Take it. The purpose of this synchronization method is to enable synchronization of frames even when the beginning of a frame indicating a frame boundary is lost.

[0004] In the transmission of the OFDM system, there is a system in which symbol synchronization is obtained by using correlation of guard interval periods. This synchronization method utilizes the fact that at least a part of the effective symbols required for information transmission is repeatedly transmitted in the guard interval period, and the correlation between the signal in the guard interval period and the effective symbol period is synchronized with the symbol period. As a result, a timing signal for synchronization is obtained. However, the above-mentioned synchronization method relates to synchronization on the receiving side, not synchronization on the transmitting side.

[0005]

The OFDM system is a system that is resistant to ghost (multipath) because a redundant period called a guard interval in the time axis direction can be added. It is also said that this is a method that can realize a single frequency network (SFN). SFN is a method of transmitting the same signal from a plurality of transmitting stations or relay stations using the same frequency. At the receiving point, the arrival times of the signals transmitted from a plurality of transmitting stations or relay stations at the receiving point do not always coincide with each other, so that the signal becomes the same as a signal having a ghost (multipath). Reception is possible because the system is resistant to ghost (multipath).

In this case, signals transmitted from a plurality of transmitting stations or relay stations need to be equal.
Since the method uses a plurality of carriers, the combination of each bit and each carrier constituting the data stream to be transmitted is not uniquely determined, and each bit constituting the data stream to be transmitted and each carrier of the OFDM signal are used. It becomes necessary to synchronize with the assignment to the. In the case of a frame configuration, it is necessary to synchronize the insertion position of the synchronization symbol.

Conventionally, however, the synchronization of the insertion position of a synchronization symbol (signal for frame synchronization) when forming a frame, and each bit constituting a data stream required when SFN is performed by the OFDM method There is no proposal for a method of synchronizing the OFDM signal with each carrier of the OFDM signal.

[0008]

According to the present invention, in order to achieve the above object, digital signals having the same contents are respectively transmitted from a plurality of transmitting stations or relay stations using the same frequency and received by a receiver. A synchronization system for one frequency network,
In a packet sequence obtained by converting a desired information signal into a digital signal, an identifiable synchronization packet is time-division multiplexed and transmitted to a plurality of transmitting stations or relay stations. And transmitting a orthogonal frequency division multiplexed signal by sequentially allocating an input packet sequence to each carrier of the orthogonal frequency division multiplexed signal based on the detected synchronization packet.

According to the present invention, a relative position with respect to each data packet obtained by converting a desired information signal into a digital signal can be specified by identifying a synchronization packet from an input packet sequence. By allocating each data of the data packet to each carrier of the orthogonal frequency division multiplexed signal (OFDM signal) based on the synchronization packet, each data of the data packet and each carrier of the OFDM system can be transmitted at a plurality of transmitting stations or relay stations. Can be uniquely determined.

According to the present invention, in order to achieve the above object, a plurality of transmitting stations or relay stations detect a synchronization packet from an input signal, calculate the input signal, convert the input signal into a data symbol sequence, and It is characterized in that a synchronization symbol is inserted and added into a sequence based on the detected synchronization packet and transmitted.

In the present invention, when a frame structure is used,
Since the insertion position of the synchronization symbol is determined based on the synchronization packet, the insertion position of the synchronization symbol can be uniquely determined.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a first embodiment of the present invention. FIG. 1A is a block diagram of an encoding device, and FIG. 1B is a block diagram of an OFDM transmission device. The analog video signal and the analog audio signal to be transmitted are encoded by an encoder, and then OFDM is transmitted by an OFDM transmitter.
It is converted to a DM signal and transmitted.

That is, first, an analog video signal and an analog audio signal are compression-encoded into a digital signal by an encoder 1 shown in FIG. 1A and output in a packet format. The timing control circuit 4 detects a packet boundary from the digital signal in the packet format, and causes the synchronous packet generating circuit 5 to generate a synchronous packet for each prescribed number of packets. The output packet of the encoder 1 is time-division multiplexed in the multiplexing circuit 3 together with the synchronization packet generated by the synchronization packet generation circuit 5 and output to the transmission line as the output of the encoding device. Shown in FIG.

From the multiplexed signal input through the transmission path, a synchronization packet is detected by a synchronization packet detection circuit 6 and the multiplexed signal input from the transmission path is mapped by a mapping circuit 7 based on the detected timing. OFD
The signal is allocated to each carrier of the M signal, and is converted into an orthogonal complex data symbol sequence (ODDM signal) by an inverse fast Fourier transform (IFFT) circuit 8. The data symbol sequence and the signal of the synchronization symbol generated by the synchronization symbol generation circuit 10 are switched by the switching circuit 9 based on the output signal of the synchronization packet detection circuit 6. The output signal of the switching circuit 9 is supplied to the quadrature modulator 11, where it is quadrature-modulated into a final OFDM signal, which is then subjected to frequency conversion and amplification by the transmission high-frequency circuit 12 and transmitted from the antenna. .

Next, an application example and operation of the above embodiment will be described with reference to FIGS. FIG. 2 shows a system configuration diagram of an example of SFN to which the present invention is applied. The output signal of the encoding device shown in FIG.
Respectively. The transmitting stations 16 and 17 are shown in FIG.
The OFDM transmission apparatus shown in FIG.
FDM digital signals are transmitted from the antennas 18 and 19. This transmission signal is received by the receiver 21 via the antenna 20.

In this case, in order for the receiver 21 to receive the digital signals transmitted from the transmitting stations 16 and 17,
That the delay time difference between the digital signals from the transmitting stations 16 and 17 is within the guard interval length,
And 17 need to be identical. Here, “identical” means that the position of the synchronization symbol inserted in the transmitted data sequence is the same,
This means that the OFDM signal to be transmitted has the same assignment to each carrier.

That is, for example, as a data string to be transmitted from the music playing place 14, MPE, which is an international standard for moving images, is used.
G2 TS (Transport Stream)
When the TS is transmitted to the transmitting stations 16 and 17, if the TS is only information of video and audio to be transmitted, and has no information for synchronization, the position and data of the synchronization symbol to be inserted at each transmitting station 16 and 17 are transmitted. The assignment of the OFDM signal of the column to each carrier cannot be uniquely determined, and each of the transmitting stations 16 and 17
Are no longer identical.

FIG. 3 shows the TS and the like of MPEG2. FIG.
(A) shows a TS of MPEG2, and shows an output signal of the encoder 1 shown in FIG. MPEG2 TS
Is a series of TSPs (TS packets, transport stream packets) as shown in FIG. Each TSP includes a PID (packet ID, packet identifier) as shown in FIG.
Can be determined.

FIG. 3C shows a TS after adding a synchronization packet, and shows an output signal of the multiplexing circuit 3 in FIG. 1A. Although the data packet DP and the synchronization packet SP shown in FIG. 3C are both TSPs, they are referred to here as DP and SP for identification. DP is T shown in FIG.
It is the same as the SP, and has video and audio information. SP is a packet for synchronization.
This is added by the encoding device shown in FIG.

Returning to FIG. 1A, the analog video signal and the analog audio signal are converted into a digital signal by the encoder 1 and compressed, and the output signal is divided into a packet format, which is used as TS. Is output. This output signal is input to the multiplexing circuit 3 and the timing control circuit 4, respectively. The timing control circuit 4 detects a packet boundary by detecting a synchronization byte of the TSP, and outputs a signal for generating a synchronization packet to the synchronization packet generation circuit 5 for each predetermined number of TSPs.

The synchronous packet generating circuit 5 generates a synchronous packet by using this signal as a trigger and outputs the synchronous packet to the multiplexing circuit 3. The synchronization packet generated by the synchronization packet generation circuit 5 has the same configuration as that of the TS, but a code that can be distinguished from other TSPs is assigned to the PID portion. Since the synchronization packet is eventually deleted by the OFDM transmission device, the code assigned to the PID may be any code that can be identified.

The multiplexing circuit 3 converts the speed of the signal input from the encoder 1 so that time division multiplexing of the synchronization packet is possible, and time multiplexes the signal with the synchronization packet from the synchronization packet generation circuit 5 to obtain a transmission path. To send TS. The TS transmitted to the transmission path is input to the OFDM transmission device.

In the OFDM transmitting apparatus shown in FIG.
The input TS is input to the synchronous packet detection circuit 6 and the mapping circuit 7, respectively. The synchronization packet detection circuit 6 detects the PID of the input TSP, and detects a synchronization packet by its code. The synchronization packet detection circuit 6 outputs a timing signal for detecting the synchronization packet to the switching circuit 9 and the mapping circuit 7. The mapping circuit 7 sequentially assigns the data of the TS to each carrier of the OFDM signal based on the timing signal. The output signal of the mapping circuit 7 is converted into a data symbol sequence which is a signal on the time axis by an inverse fast Fourier transform (IFFT) circuit 8 and output to the switching circuit 9.

The switching circuit 9 switches between the data symbol sequence output from the IFFT circuit 8 and the synchronization symbol generated by the synchronization symbol generation circuit 10 in accordance with the output timing signal of the synchronization packet detection circuit 6, as shown in FIG. As schematically shown, a synchronization symbol is added to the data symbol sequence. The output signal of the switching circuit 9 is supplied to a quadrature modulator 11, where the signal is quadrature-modulated to obtain a high-frequency OFD signal.
The signal becomes an M signal, is subjected to frequency conversion and amplification by the transmission high-frequency circuit 12, and is transmitted from the antenna.

Next, a second embodiment of the encoding apparatus according to the present invention will be described in detail. FIG. 4 is a block diagram showing a second embodiment of the encoding apparatus according to the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals.
This embodiment is characterized in that a speed converter 2 and a switching circuit 13 are provided instead of the multiplexing circuit 3 of the first embodiment.

Next, the operation of the second embodiment shown in FIG. 4 will be described with reference to the timing chart of FIG. The analog video signal and the analog audio signal are converted into a digital signal by the encoder 1 shown in FIG. 4 and compressed, and the output signal is divided into a packet format and composed of data packets as shown in FIG. Output as TS. This output TS is supplied to the speed converter 2 and converted into a double speed. As a result, the signal after the speed conversion becomes a signal having an empty TS, and an empty packet having no information is inserted into the empty portion. FIG.
(B) shows an output packet of the speed converter 2, and an empty packet EP is inserted in the data packet DP.
This empty packet EP is identified by the PID.

The timing control circuit 4 detects a packet boundary by detecting a TS (DP) synchronization byte from the encoder 1 and outputs a signal for generating a synchronization packet for each predetermined number of TSPs. Output to the synchronous packet generation circuit 5. TS supplied to the speed converter 2 and subjected to speed conversion
Is supplied to the switching circuit 13, where the empty packet EP is replaced by the synchronization packet generated by the synchronization packet generation circuit 5. Thereby, as schematically shown in FIG. 5C, a signal in which the synchronization packet SP is replaced at a predetermined position from the empty packet EP is transmitted via the transmission path to the OF.
It is transmitted to the DM transmitter.

The configuration of the OFDM transmission apparatus is the same as that of the first embodiment shown in FIG.
As shown in (D), an OFDM signal having the same format configuration as the transmission OFDM signal of the first embodiment is transmitted.
However, when processing the signal of the encoding device shown in the second embodiment, unnecessary empty packets are discarded in the mapping circuit 7.

In the second embodiment, the case where the synchronization symbol is replaced has been described. However, it is not necessary to replace the entire empty packet EP with the synchronization packet SP, and other codes capable of identifying only the PID of the empty packet EP are used. It is clear that it can be replaced with The reason for this is that the information necessary for implementing the present embodiment in the synchronization packet SP is only in the synchronization byte and the PID.

Further, also in the first embodiment, it is apparent that the method of the present invention can be realized by replacing only the PID of some of the packets of the TS having information to be transmitted with another identifiable code. . However, in this case, it is necessary to finally return the PID to the original code.
Since D is known, it is easy to restore the original code.

In the above embodiment, the TS
A case has been described in which P and data symbols correspond one-to-one, that is, a case where the number of bits of the TSP is equal to the number of carriers of the OFDM signal, but the TSP and the data symbols are n: 1 (n is a natural number). Or it is clear that the present invention can be implemented even with 1: n. The former is OFDM
By allocating a plurality of TSPs to the data symbols of the signal, the latter is realized by allocating the TSPs to the plurality of data symbols. Similarly, the present invention can be applied to a case where the TSP and the data symbol are n: m (m is a natural number).

FIG. 6 shows a case where the ratio between TSP (DP) and data symbols is 5: 2. The five DPs 31 to 35 shown in FIG. 6A are allocated to the two data symbols 36 and 37 shown in FIG.
33 is allocated over two data symbols 36 and 37. FIGS. 6C and 6D show the DP in the above case.
FIG. 6 shows the relationship between OFDM and OFDM carriers.
The center DP 33 shown in (C) is allocated over two data symbols 38a and 38b shown in FIG. 6 (D).

Further, even when the TSP and the data symbol do not have a natural number ratio (n: m), the system of the present invention can be implemented by making a carrier wave to which no TSP data is allocated.

[0034]

As described above, according to the present invention,
By allocating each data of the data packet to each carrier of the orthogonal frequency division multiplexed signal (OFDM signal) on the basis of the synchronization packet, at each of a plurality of transmitting stations or relay stations, each data of the data packet and each carrier of the OFDM scheme are transmitted. Can be uniquely determined. Furthermore, by determining the insertion position of the synchronization symbol with reference to the synchronization packet, the insertion position of the synchronization symbol can be uniquely determined. Can be realized in a single frequency network using the transmitting device of (1).

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of an encoding device according to the present invention and a first embodiment of an OFDM transmission device.

FIG. 2 is a system configuration diagram showing a single frequency network to which the present invention is applied.

FIG. 3 is a timing chart for explaining the operation of FIG. 1;

FIG. 4 is a block diagram of a second embodiment of the encoding device according to the present invention.

FIG. 5 is a timing chart for explaining the operation of FIG. 4;

FIG. 6 is a timing chart for explaining the operation of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Encoder 2 Speed converter 3 Multiplexer 4 Timing control circuit 5 Synchronous packet generation circuit 6 Synchronous packet detection circuit 7 Mapping circuit 8 Inverse fast Fourier transform (IFFT) circuit 9 Switching circuit 10 Synchronous symbol generation circuit 11 Quadrature modulator 12 Transmitting high-frequency circuit 13 Switching circuit 14 Performer 16,17 Transmitter 21 Receiver

Claims (7)

[Claims] 1. A single frequency network synchronization system in which digital signals having the same contents are respectively transmitted from a plurality of transmitting stations or relay stations using the same frequency and received by a receiver, and a desired information signal is transmitted. In a packet sequence obtained by converting into a digital signal, an identifiable synchronization packet is time-division multiplexed and transmitted to the plurality of transmitting stations or relay stations. Detect packet,
A synchronization method for a single frequency network, wherein a packet sequence input based on the detected synchronization packet is sequentially allocated to each carrier of the orthogonal frequency division multiplex signal, and the orthogonal frequency division multiplex signal is transmitted. 2. The plurality of transmitting stations or relay stations detect the synchronization packet from an input signal, calculate the input signal and convert the input signal into a data symbol sequence, and include the detected synchronization packet in the data symbol sequence. 2. A single frequency network synchronization system according to claim 1, wherein a synchronization symbol is inserted and added on the basis of. 3. The packet stream is a transport stream, and the synchronization packet has the same configuration as each transport stream packet constituting the transport stream, and its packet identifier is a packet of the transport stream packet. 2. The method according to claim 1, wherein the value is set to a specific value different from the identifier.
Or a synchronization method for a single frequency network according to 2. 4. An encoder for converting and compressing a desired information signal into a digital signal to output a transport stream packet in a packet format, detecting a boundary of the transport stream packet, and determining a predetermined transport stream. A synchronization packet generating means for generating a synchronization packet for each number of packets, and a multiplexing circuit for time-division multiplexing the synchronization packet with the transport stream packet, wherein an output signal of the multiplexing circuit uses the same frequency. Encoding apparatus for supplying digital signals having the same contents to a plurality of transmitting stations or relay stations of a single-frequency network, as signals to be transmitted. 5. An encoder for converting and compressing a desired information signal into a digital signal to output a transport stream packet in a packet format, detecting a boundary of the transport stream packet, and determining a predetermined transport stream. A synchronous packet generating means for generating a synchronous packet identifiable for each number of packets, and a rate conversion of an output transport stream packet of the encoder to insert and output an empty packet in a vacant section. And a switching circuit that replaces part of the empty packets in the output packet sequence of the speed converter and the synchronization packet, and outputs the output signal of the switching circuit using the same frequency. Signals to be transmitted to multiple transmitting stations or relay stations of a single frequency network each transmitting the same digital signal An encoding device, characterized in that the encoding device is supplied as a code. 6. A transmitting device provided in each of a plurality of transmitting stations or relay stations constituting a single frequency network in which digital signals having the same content are respectively transmitted using the same frequency and received by a receiver. A synchronization packet detection circuit for receiving, as an input signal, a transport stream in which a synchronization packet identifiable in a transport stream packet sequence is time-division multiplexed, and detecting the synchronization packet from the input signal; A mapping circuit for sequentially allocating a packet in the input signal to each carrier of the orthogonal frequency division multiplexed signal based on the synchronization packet detected by the method, converting an output signal of the mapping circuit into an orthogonal frequency division multiplexed signal and transmitting A transmission device comprising: a conversion and transmission unit that performs conversion and transmission. 7. The conversion and transmission means includes: an operation unit that converts an output signal of the mapping circuit into a data symbol sequence; a synchronization symbol generation circuit that generates a synchronization symbol;
A switching circuit for switching an output data symbol sequence of the arithmetic unit to an output synchronization symbol of the synchronization symbol generation circuit with reference to a timing of detecting a synchronization packet by the synchronization packet detection circuit; and transmitting the output symbol sequence of the switching circuit. The transmitting device according to claim 6, comprising a circuit.