JP3133960B2 - OFDM transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to integrated digital broadcasting (ISDB: Integrated Television Broadcasting) which integrates and broadcasts terrestrial digital television broadcasting, digital audio broadcasting, digital information and the like.
The present invention relates to an OFDM wave transmission device suitable for use in grated service digital broadcasting, and the like.

[Summary of the Invention] The present invention relates to a transmission device used in integrated digital broadcasting for integrating and broadcasting terrestrial digital television broadcasting, digital audio broadcasting, digital information, etc., and conforms to the MPEG2 standard. Modulate the transport stream packet (TSP)
When an OFDM wave having a frame structure is generated and transmitted on a transmission path, the OFDM wave is divided into a plurality of OFDM blocks having a fixed bandwidth, and a carrier modulation method and an error correction method can be changed for each OFDM block. And one OFDM frame, one OFDM
The frame length of an OFDM frame is set so that an integral number of transport stream packets can be transmitted per DM block, thereby improving transmission efficiency and facilitating hierarchical transmission.

[0003]

2. Description of the Related Art As a method of dividing an OFDM wave into a plurality of OFDM blocks and performing hierarchical transmission by changing a modulation method, transmission power, and the like for each OFDM block, a method disclosed in Japanese Patent Application Laid-Open Publication No. H10-207,972, proposed by the present applicant. 7-321765
Japanese Unexamined Patent Application Publication No. 6-116251 is known.

[0004] This prior application relates to layering of OFDM, and when performing layered modulation, for each transmission symbol included in a transmission frame, the power of which carrier is increased on the frequency axis and which carrier is increased. By changing the allocation pattern indicating whether to reduce the power, even after hierarchical modulation, the power spectral density of the OFDM wave is
Keep the characteristics close to white Gaussian noise in the transmission band, and do not impair the excellent feature of OFDM that the characteristics of interference with other services are almost the same as white Gaussian noise by layered modulation. It is like that. In addition, even when the modulation scheme of each carrier is changed for each carrier or each carrier block, and hierarchical modulation is performed, the assignment of the modulation scheme of a certain carrier is determined by the OFDM transmission symbol. Thus, even when only a specific frequency band within the transmission band is greatly affected by multipath interference, it is possible to minimize the deterioration of the bit error rate characteristics.

[0005]

However, in the conventional transmission technique using the OFDM wave, including the above-mentioned prior art, the conventional technique for transmitting packetized information such as a transport stream packet of the MPEG2 standard is used. When the content of the processing performed in each layer is changed, the size of each packet and the size of each OFDM block of the OFDM wave may cause a mismatch, and one of the OFDM blocks may become invalid. In some cases, efficient transmission cannot be performed.

For this reason, for example, using an OFDM wave,
When transmitting transport stream packets of the PEG2 standard, the number of bits of these transport stream packets, the bandwidth of an OFDM block,
The number of blocks, O
Development of technology that can easily perform hierarchical transmission by associating the number of bits of a transport stream packet to be transmitted with an OFDM frame as a unit in the time direction of an OFDM wave by associating the number of FDM symbols and the like. Was strongly desired.

The present invention has been made in view of the above circumstances, and has as its object to provide an OFDM wave transmission apparatus capable of improving transmission efficiency and facilitating hierarchical transmission.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is an apparatus for transmitting an OFDM wave in which a plurality of OFDM blocks having a fixed bandwidth are arranged continuously. For all the layering processes, the OFDM symbols included in the OFDM frame are set so as to be the least common multiple of the number of OFDM symbols required for each piece of information obtained by performing the layering process on a packet having a certain number of bits to be transmitted. Means for allocating the determined number of OFDM waves to a plurality of systems of OFDM blocks having a fixed bandwidth, means for independently performing error correction processing and carrier modulation processing for each of the allocated systems, Means for generating OFDM waves to be transmitted by combining OFDM blocks subjected to processing and carrier modulation processing. .

According to the above configuration, the OFDM wave is divided into frequency blocks, the carrier modulation method and the error correction method are independently designated for each frequency block, and the hierarchical transmission for simultaneously transmitting signals having different reception characteristics is performed. For example, the number of bits of information to be transmitted is associated with an OFDM frame that is a unit in the time direction of an OFDM wave, thereby improving transmission efficiency and facilitating hierarchical transmission.

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

<< Description of Premise of the Invention >> First, prior to the detailed description of the OFDM wave transmission apparatus according to the present invention, the OFDM wave transmission apparatus used in the present invention
The DM wave will be described briefly.

First, FIG. 6 shows a transmission system for an integrated digital broadcast to which the OFDM transmission apparatus according to the present invention is applied, such as terrestrial digital television broadcast, digital audio broadcast, digital information, etc. A predetermined bandwidth, for example, an integer number of OFDM blocks having a bandwidth of 100 kHz to 500 kHz on the frequency axis,
It has been studied to use an OFDM wave arranged continuously and transmit information to a receiving apparatus side in a unit of an integral number of frames (OFDM frames) on a time axis.

At the time of transmission, hierarchical transmission in which a carrier modulation method and an error correction method are optimized in accordance with the type of information such as terrestrial digital television broadcast, digital audio broadcast, digital information, etc. in units of each OFDM block. Adopt the method. As a result, while improving the transmission efficiency of the transmission path,
The receiving apparatus reproduces necessary information among these terrestrial digital television broadcasts, digital audio broadcasts, digital information, and the like.

As shown in FIG. 7, the signal format of these terrestrial digital television broadcasts, digital audio broadcasts, digital information, and the like is based on a data length of 188 bytes and an error correction code such as ( 204, 1
88) Use of a transport stream packet (TSP) of the MPEG2 standard having a data length of 204 bytes to which a check code such as a Reed-Solomon code is added has been studied.

Conventionally, these transport stream packets are hierarchized and processed using OFDM waves.
In the case of transmission in frame units, if the processing content of each layer, for example, the content of error correction processing or the content of carrier modulation processing is changed, the number of bits after the layering processing changes, and OF
Since there is an empty space in one of the DM blocks or the number of OFDM blocks becomes insufficient, once the processing contents of each layer are set once, the contents of error correction processing of each layer, the contents of carrier modulation processing, etc. There was a problem that it was difficult to change.

Therefore, the OFDM transmission apparatus according to the present invention associates the number of bits of each transport stream packet, the bandwidth of an OFDM block, the number of blocks of an OFDM block, the number of OFDM symbols constituting an OFDM frame, etc., with each other. Even if the content of the error correction process performed in the hierarchy and the content of the carrier modulation process are changed and the number of bits after the hierarchical process is changed, an empty space is generated in one of the OFDM blocks or a shortage occurs in the OFDM block. Thus, the transmission efficiency is increased and the hierarchical transmission is facilitated.

<< Description of Embodiments of the Invention >> FIG. 1 is a block diagram showing an embodiment of an OFDM wave transmission apparatus according to the present invention.

The transmission apparatus 1 shown in FIG. 1 has a transport stream (T) in which transport stream packets (188-bit TSP) of the MPEG2 standard are connected.
S), a switch 2 for distributing this to each system (three systems) specified for each transport stream packet, and a transport stream packet distributed to each system by this switch 2 is set in advance. The error correction circuit 3 for each system that performs error correction encoding in any of the four error correction methods described above, and the transport stream packets output from each error correction circuit 3 are set in advance. A carrier modulation circuit 4 for each system for performing carrier modulation in one of the four carrier modulation schemes, a combining circuit 5 for combining each OFDM block output from each carrier modulation circuit 4, and an OFDM wave on the receiving device side And a control synchronization information circuit 6 for generating control information and synchronization information necessary for synchronizing the frames. Based on the control information and synchronization information et output, continuous output from the synthesizing circuit 5 OFD
Temporal information (frame synchronization signal) during M blocks
Is selectively assigned, and the inverse FFT transform is performed to OF
An IFFT circuit 7 for generating a DM wave.

When a transport stream (TS) conforming to the MPEG2 standard is input, each transport stream packet (TSP) constituting this transport stream is distributed to one of three systems, and After performing the error correction process and the carrier modulation process specified in (1) and synthesizing each OFDM block obtained in each system, temporal information (frame synchronization signal) is selectively inserted between these OFDM blocks. In addition to the allocation, each OFDM carrier and the like are subjected to inverse FFT transform to generate an OFDM wave, which is transmitted on a transmission path.

Next, the operation of the transmission apparatus 1 will be described in detail with reference to the block diagram shown in FIG.

As shown in FIG. 2, when a transport stream (TS) conforming to the MPEG2 standard is input, the switching unit 2 performs a switching operation for each transport stream packet (TSP) constituting the transport stream. Then, each transport stream packet is distributed to one of the three systems.

Here, as an error correction method performed by each error correction circuit 3, a 信号 convolution coding method in which one signal is convolved into two signals, and three signals are convoluted into four signals. Either of the 3/4 convolutional coding method and the 7/8 convolutional coding method of convolving seven signals into eight signals are set. The carrier modulation method performed by each carrier modulation circuit 4 is QPSK.
Modulation method, DQPSK modulation method, 16QAM modulation method,
One of the 64QAM modulation schemes is set.
Therefore, the transport stream packets distributed for each system are processed by the error correction circuits 3 and the carrier modulation circuits 4 into 12 processing routes (processing routes indicated by three error correction methods × 4 carrier modulation methods). Is processed in each of three processing routes. After that, when converted into information on the frequency axis according to the bit rate, that is, the transmission capacity of each processing route, an integer number of OFs are considered in consideration of which block to allocate.
Assigned to DM block.

At this time, even if the transport stream packet passes through any of the 12 processing routes in which the error correction method and the carrier method are different, the number of the OFDM blocks is exactly an integer per transport stream packet. Next, the number of bits of the transport stream packet is made to correspond to the frame length of the OFDM frame in the following procedure.

First, OFDM per OFDM frame
If the number of symbols is “S”, the number of carriers in an OFDM block is “N”, the number of bits per carrier modulation symbol is “M”, and the error correction coding rate is “R”, one O
The total number of bits that can be transmitted in one FDM block and one OFDM frame is represented by N · M · S (1) and is represented by one OFDM block and one OFDM frame.
The number of information bits that can be transmitted in a frame is represented by R, N, M, S (2).

On the other hand, since the number of bits of the transport stream packet is “8 × 188” (3) bits, the number of bits represented by the equation (3) is smaller than the number of bits represented by the equation (3). If the number of bits to be obtained is an integral multiple (K times), then RNMS = 8 × 188 × K (4)

Thus, if the number of carriers “N” in the OFDM block is set to “24”, the following equation is obtained.

[0032]

S = (8 × 188 × K) / (R × M × 24) (5) where the number of bits per carrier modulation symbol “M”
Is "M = 2" when using the QPSK modulation method or the DQPSK modulation method as the carrier modulation method, becomes "M = 4" when using the 16QAM modulation method, and becomes "M = 4" when using the 64QAM modulation method. M = 6 "
Becomes Further, the error correction coding rate “R” is determined by selecting one of the １ ／ convolutional coding method, the ／ convolutional coding method, and the 7/8 convolutional coding method as the error correction method, and (20)
4, 188), the number of OFDM symbols per OFDM frame "S" shown in the above equation (5) becomes "3" as shown in FIG.
4 multiples, 68 multiples, 136 multiples, 2
72, that is, the least common multiple of the number of symbols required in each processing route.

Therefore, O per frame of OFDM frame
If "multiple of 272" is selected as the number of FDM symbols "S", the transport stream packet can be processed using any of the twelve processing routes, regardless of the error correction method and carrier modulation method. Each OFDM block can be used to transmit a fixed number of transport stream packets per OFDM frame.

The error correction circuit 3 and the carrier modulation circuit 4 perform error correction processing and carrier modulation processing on one of the processing routes, and combine the transport stream packets assigned to each OFDM block. After being synthesized by the circuit 5 and arranged in a line on the frequency axis, based on the control information and the synchronization information output from the control synchronization information circuit 6, the IFFT circuit 7 generates 272 pieces of data as shown in FIG. A frame synchronization signal is added to each OFDM frame constituted by OFDM symbols, and the resulting signal is subjected to inverse FFT transform, and the obtained OFDM wave is transmitted onto a transmission path.

As described above, in this embodiment, the OFD
When the M wave is divided into frequency blocks, a carrier modulation scheme and an error correction scheme are independently designated for each block, and hierarchical transmission for simultaneously transmitting signals having different reception characteristics is performed, the OFDM included in the OFDM frame is used. Since the number “S” of symbols is set to the least common multiple of the number of symbols required in each processing route, the error correction method of each error correction circuit 3 is １ ／ convolution coding method, ／ convolution coding method, 7 / Regardless of which of the eight convolutional coding systems is used, and as the carrier modulation system of each carrier modulation circuit 4, Q
Regardless of which of the PSK, DQPSK, 16QAM, and 64QAM modulation methods is used, and the transport stream packet to be transmitted is allocated to any system, the number of bits of the transport stream packet and the OFDM The OFDM frame, which is a unit in the time direction of the wave, can be associated with the OFDM frame, thereby improving transmission efficiency and facilitating hierarchical transmission.

In this embodiment, an OFDM wave is divided into frequency blocks, and a carrier modulation method and an error correction method are independently designated for each of these blocks, and signals having different reception characteristics are simultaneously transmitted. When performing hierarchical transmission,
The bandwidth of the OFDM block is 100 kHz to 500 kHz.
z, it is easy to associate the number of bits of the transport stream packet to be transmitted with the OFDM frame which is a unit in the time direction of the OFDM wave, thereby improving the transmission efficiency, Hierarchical transmission can be facilitated.

Further, in this embodiment, an OFDM wave is divided into frequency blocks, and a carrier modulation method and an error correction method are independently designated for each of these blocks, and signals having different reception characteristics are simultaneously transmitted. When performing hierarchical transmission,
Since the number of bits of the packet is defined as “188”,
When the information to be transmitted is a transport stream packet, the number of bits of the transport stream packet and the OFDM as a unit in the time direction of the OFDM wave
This facilitates the association with the DM frame, thereby improving the transmission efficiency and facilitating the layered transmission.

As described above, in this embodiment, based on the control information and the synchronization information output from the control synchronization information circuit 6, the IFFT circuit 7
Although a frame synchronization signal is added for each OFDM frame composed of two OFDM symbols, as shown in FIG. 5, the frame synchronization signal is distributed between each OFDM symbol in the OFDM frame. You may make it arrange | position.

In this manner, the number “S” of OFDM symbols constituting one OFDM frame is changed to “272”.
With this configuration, effects similar to those of the above-described embodiment can be obtained.

In the above-described embodiment, each transport stream packet is assigned to a specific OFDM block, and then processed as it is. However, in practice, the transport stream packet is assigned to a specific OFDM block. After allocating to the blocks, a process of switching in the frequency direction on a carrier basis (frequency interleaving process) is performed.

As a result, it is possible to disperse fading errors of frequency selectivity caused by multipath distortion.

Also, in the above-described embodiment, since the terrestrial digital television broadcasting, digital audio broadcasting, digital information, and the like need only be processed by integrated digital broadcasting, transport stream packets are processed by three systems. However, when these terrestrial digital television broadcasts, digital audio broadcasts, digital information, and the like are further subdivided for each information characteristic, the number of systems may be "3" or more.

By doing so, it is possible to perform a detailed broadcast using the integrated digital broadcast.

[0044]

As described above, according to the present invention, O
When FDM waves are divided into frequency blocks, carrier modulation and error correction are specified independently for each frequency block, information to be transmitted when performing hierarchical transmission, etc., for simultaneously transmitting signals with different reception characteristics is performed. And the OFD
The OFDM frame, which is a unit in the time direction of the M wave, can be associated with the OFDM frame, thereby improving the transmission efficiency and facilitating the layered transmission.

[0045]

[0046]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an OFDM transmission apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a relationship between a switching operation of the switch shown in FIG. 1 and each OFDM block.

FIG. 3 shows the number of carriers “N”, the number of bits per carrier modulation symbol “M”, the coding rate “R”, and the number of symbols per OFDM frame used in the OFDM transmission apparatus shown in FIG. It is a table | surface which shows the example of relationship with S ".

FIG. 4 is a schematic diagram showing a configuration example of an OFDM frame transmitted from the OFDM wave transmission device shown in FIG.

FIG. 5 is a schematic diagram showing another configuration example of the OFDM frame transmitted from the OFDM transmission apparatus shown in FIG. 1;

FIG. 6 is a schematic diagram showing a configuration example of an OFDM wave used in the OFDM wave transmission device according to the present invention.

FIG. 7 is a schematic diagram showing a configuration example of a transport stream used in the OFDM transmission apparatus according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmission device 2 switch 3 error correction circuit 4 carrier modulation circuit 5 synthesis circuit 6 control synchronization information circuit 7 IFFT circuit

Continuing on the front page (72) Inventor Shunji Nakahara 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Research Institute (72) Inventor Masayuki Takada 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Japan Broadcasting Corporation (72) Inventor Michihiro Uehara 1-1-10 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Japan Broadcasting Research Institute (72) Inventor Kenichi Tsuchida 1-110, Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Japan Broadcasting Corporation (72) Inventor Masahiro Okano 1-1-10 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Research Institute (72) Inventor Makoto Sasaki 1-110-11 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation JP-A-7-321765 (JP, A) JP-A-8-46655 (JP, A) JP-A-10-322388 (JP, A) JP-A-10-322306 (JP) , A) Technical Report of the Institute of Image Media Technology, Vol. 21, No. 30, p. 1-6 (58) Field surveyed (Int. Cl. ⁷ , DB name) H04J 11/00

Claims (1)

(57) [Claims] 1. A transmission apparatus for transmitting an OFDM wave in which a plurality of OFDM blocks having a constant bandwidth are continuously arranged, wherein a fixed number of bits to be transmitted is set for all possible hierarchical processes. To be the least common multiple of the number of OFDM symbols required for each piece of information obtained by layering the packets of
Means for distributing an OFDM wave, in which the number of OFDM symbols included in an OFDM frame is determined, to a plurality of systems of OFDM blocks having a fixed bandwidth, and independent error correction processing and carrier modulation processing for each distributed system And OFD that has been subjected to error correction processing and carrier modulation processing.
Means for generating an OFDM wave to be transmitted by combining M blocks. An OFDM wave transmission apparatus comprising: