JP2990182B1 - Digital terrestrial broadcasting transmission system - Google Patents

Abstract

An information transmission rate capable of improving the same-channel interference protection ratio and operating a high-definition broadcasting service is realized. SOLUTION: In a terrestrial digital broadcast transmission system using an OFDM transmission system having a segment structure,
When an analog TV broadcast signal of the same channel is broadcast in an adjacent area and the energy of the video carrier and the audio carrier is concentrated and becomes a disturbance source, the modulation method or error correction of a specific segment affected by the video carrier and the audio carrier. Is different from the modulation scheme of other segments in the same channel or the coding rate of error correction. As a result, resistance to interference from analog TV signals is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terrestrial digital broadcasting system, and more particularly, to reducing interference from an existing analog TV signal during a so-called simulcast operation period in which analog TV broadcasting and digital TV broadcasting coexist. Technology for effective use of

[0002]

2. Description of the Related Art As a next-generation digital broadcasting system,
The development of digital terrestrial broadcasting using the TV band by the current terrestrial wave is being promoted. The transmission method is O
A scheme using FDM (Orthogonal Frequency Division Multiplexing) has already been adopted as a European standard scheme, and is considered to be a leading scheme in Japan.

[0003] In a digital broadcasting transmission system using OFDM, convolutional coding-Viterbi decoding and Reed-Solomon (hereinafter, RS) are used to digitally modulate a majority carrier forming an OFDM signal and further reduce transmission path errors. A so-called concatenated code obtained by combining codes is used.

In general, when the bandwidth is determined, the transmission rate is determined by the modulation scheme and the coding rate of the convolutional code, and the higher the transmission rate, the higher the signal-to-noise ratio required to maintain the service. Become. Table 1 shows the relationship between the coding rate and the transmission speed in the case of a 6 MHz bandwidth.

[0005]

[Table 1] In digital broadcasting, high-definition broadcasting such as high-definition broadcasting is expected. In the example of the United States, an information transmission rate of just over 19 Mbps is required. As shown in Table 1,
This can be realized by using 64QAM as a modulation method and 7/8 or 5/6 as a coding rate of a convolutional code. Therefore, in order to realize high-definition broadcasting in digital broadcasting, a transmission ER that realizes a reception electric field strength sufficient to maintain a service in a required service area is provided.
P (given as the product of effective radiation power, transmission power and antenna gain) is required.

On the other hand, the current analog broadcast service frequency plan usually uses frequencies alternately in adjacent areas to avoid co-channel interference as shown in FIG. When newly starting digital broadcasting, a so-called simulcast period is required, in which digital broadcasting is sequentially shifted while continuing the conventional analog broadcasting service. Available channels for analog broadcasting. Therefore, a channel assigned to digital broadcasting in a certain service area has a high probability of being used for analog broadcasting in an adjacent service area.

[0007] In starting digital broadcasting, the following measures are required so as not to interfere with existing analog broadcasting services. (1) Restrict transmission ERP of digital broadcasting. (2) Carrier holes (areas that do not use two segments where analog interference is prominent) are provided in digital broadcasting. (3) In the analog service area of the same channel, keep the digital transmitting stations apart so that digital radio waves attenuate to a level that does not cause interference.

[0008] In the case of (3), the transmitting station for analog broadcasting and the transmitting station for digital broadcasting are arranged at a distance from each other, which requires a correspondingly large number of channels. There is a problem that it is difficult to secure the space. Therefore, it is desirable to secure the channel according to (1). In this case, however, the ERP of the digital broadcast decreases, so that the same channel interference due to adjacent analog broadcast waves occurs in the fringe area of the service area. For this reason, it is desired that the transmission system of digital broadcasting has a high resistance to the same channel interference of the analog TV signal.

Table 2 shows an example of calculating the required D / U ratio for co-channel analog TV signal interference.

[0010]

[Table 2] As can be seen from Table 2, when the coding rate is reduced to 3/4 or less, the robustness is rapidly improved, and at a coding rate of 2/3, the robustness is improved by almost 20 dB as compared with the case of 7/8.

However, when the coding rate is 2/3, the information transmission speed in the 6 MHz band is only 16 Mbps when the guard interval is 1/8, which is insufficient for providing a high definition service.

According to (2), when carrier holes for two segments are provided, as shown in Table 3, 6 MHz
The information transmission rate in the band is: coding rate 7/8, guard 1 /
In the case of 8, it is still 18 Mbps, which is still insufficient for providing a high-definition service. Since the carrier hole has an area where carriers do not stand, the current ISDB
-There is a problem that the specification of T is changed and that reception synchronization becomes difficult.

[0013]

As described above, when starting terrestrial digital broadcasting, it is necessary to ensure the operation of a high-definition broadcasting service while reducing interference from existing analog TV signals. Yet, no effective means has been found.

SUMMARY OF THE INVENTION The object of the present invention has been made in view of the above circumstances, and has an object to improve the same-channel interference protection ratio and to realize an information transmission speed capable of operating a high-definition broadcasting service. Is to provide.

[0015]

In order to solve the above-mentioned problems, the present invention has the following characteristic configuration.

(1) A transmission band of one channel is divided into a plurality of cells.
OFDM transmission with segment structure divided into segments
Combine one or more segments using the transmission method
, One or more corresponding to one reception form
In terrestrial digital broadcasting transmission system that transmits a hierarchy forming a digital broadcast signal comprising the digital broadcast
Concentration of energy in a part of the band of the same channel as the signal
Interference source that emits a frequency signal
When a broadcast signal is disturbed, a specific segment affected by the disturbing source and the specific segment are included.
To separate from other segments in the same hierarchy
Layering and applying frequency interleaving for each layer
In addition, the modulation scheme of the layer by the specific segment or the coding rate of error correction is determined by another segment in the same layer .
It should be different from the modulation scheme or the error correction coding rate of a certain layer . As a result, the broadcasting area of digital broadcasting signals
Inside and outside of the band of the same channel as the broadcast signal
Interference sources that emit frequency signals with concentrated energy
Even if the
Increases resistance.

(2) In the configuration of (1), the interference source
Is broadcast on the same channel as the digital broadcast signal.
Video carrier, audio carrier, color of analog TV broadcast signal
Any of the subcarriers,
Each is treated as the specific segment. As a result, the video in the analog TV broadcast signal of the same channel is
Image carrier, audio carrier, chrominance subcarrier are interference sources
Also, their resistance to interference is increased.

[0018]

(3) In the configuration of (1) or (2) , the modulation scheme or coding rate of the specific segment is
Determined according to the strength of the interference source. Thus, it is possible to flexibly cope with various interference sources.

(4) In the configuration of (1) or (2) , when there are a plurality of the specific segments, the modulation scheme or the coding rate of each specific segment is set to be the same, and the signals are handled as signals belonging to the same layer. Thereby, the circuit of the receiving device can be simplified.

(5) In any one of the constitutions (1) to (4) , information on the segment position of the specific segment and its transmission parameter is stored in a mode designating signal (for example, TMCC (all OFD
Signal for designating the mode of ISDB-T inserted in M segment)). This allows
The switching control of the modulation method or the coding rate on the receiving side can be automatically performed.

(6) In the configuration of (5) , the modulation method or the coding rate of the specific segment is changed when the state of the interference source changes using the mode designation signal.
This makes it possible to select a transmission method that is adaptively matched to the state of the transmission path.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS.

FIG. 1 shows a terrestrial digital broadcasting transmission system in Japan currently under discussion by the Telecommunications Technology Council (hereinafter referred to as a draft tentative system). In this draft of the provisional scheme, the 6 MHz band is divided into 13 segments, and each segment has a structure in which an arbitrary modulation scheme and coding rate can be selected. Up to four combinations of modulation schemes and coding rates are possible, and segments belonging to the same combination are called layers.

The purpose of devising such a hierarchical division transmission system is mainly to select transmission parameters in accordance with the reception mode. For example, the layer for fixed reception emphasizes information transmission speed, and is set to 64QAM and the coding rate is 7/8. The layer for mobile reception is DQPSK, code capable of receiving in a poor propagation environment such as fading. Conversion rate 2 /
A combination of layers such as 3 is possible.

The present invention provides a transmission system utilizing such a segment structure and having a high information transmission rate and a good co-channel interference protection ratio.

FIG. 2A shows a digital signal by OFDM having a segment structure, and FIG. 2B shows a spectrum of an analog TV signal which interferes with the digital signal by the OFDM. As shown in FIG. 2B, it can be seen that most of the energy of the analog TV signal is concentrated near the video carrier and the audio carrier. for that reason,
On the digital broadcasting side, most of the errors that occur due to co-channel interference occur in carriers near the video carrier and near the audio carrier of the analog TV signal.

Therefore, for the segments including the frequencies near the video carrier and the audio carrier (segments 3 and 13 in FIG. 2A), the modulation method 64QAM and the convolutional coding rate 2 /
3 and the other segments are set to a modulation method of 64 QAM and a coding rate of 7/8, the information transmission rate over 6 MHz is as shown in Table 4, and the information transmission rate exceeds 19 Mbps capable of HDTV transmission. Speed can be achieved.

That is, in Table 1, the entire band 64QA
The transmission rate when the M modulation and the error correction coding rate are 2/3 is 16.357 Mbps. In Table 3, the transmission rate when the carrier hole is provided (error correction coding rate 7/8) is 18.17 Mbps. In Table 4, the transmission speed at the time of hierarchical division (correction coding rate for 11 segments: 7/8, for 2 segments: 2/3) is 20.68 Mbps.

[0030]

[Table 3]

[Table 4] As is clear from the above results, the transmission method of the present embodiment has the highest transmission capacity.

FIG. 3 shows the configuration of the transmitting side in the digital terrestrial broadcasting transmission system of the present embodiment. FIG.
, When a stream TS according to the MPEG2 system is input, the stream TS is supplied to the RS encoding processing unit 1. The RS encoding processing unit 1 applies the shortened Reed-Solomon code and encodes the input stream TS for each packet. The encoded output is sent to the hierarchical division processing unit 2.

The hierarchical division processing unit 2 divides the data into arbitrary layers (here, a maximum of four layers) in units of 204 bytes separated by a synchronization byte in accordance with separately provided layer information. The coded signals are subjected to delay time adjustment for each layer in the delay correction processing unit 3, and are randomly arranged with a pseudo-random code for each layer in the energy spread byte interleave processing unit 4 and subjected to interleaving. .

Subsequently, in the convolutional encoding processing section 5,
Convolutional coding with a constraint length of 7 and a coding rate of 1/2 to 7/8 is performed for each layer. Here, the disturbing segment is
For example, a coding rate of 2/3 is selected. For a segment without interference, for example, a coding rate of 7/8 is selected. In the carrier modulation processing unit 6, the bit data of each hierarchical output of the convolutional coding processing unit 5 is modulated and mapped. As the segment having the interference, for example, 16QAM is selected. For a segment without interference, for example, 64QAM is selected. Each layer output of the carrier modulation processing unit 6 is subjected to frequency interleaving in a frequency interleave processing unit 7.

Here, transmission parameters (coding rate, modulation method) can be selected from a plurality of types, and transmission is performed by dividing the same reception form into layers (characteristic of the present invention)
Performs frequency interleaving for each layer.

Each hierarchical output of the frequency interleave processing unit 7 is synthesized by the hierarchical synthesis processing unit 8,
The frame configuration processing unit 9 incorporates the pilot signal for detection synchronization, the pilot signal for detection, and the TMCC signal into an OFDM frame to become a frequency domain signal. The frequency domain signal is multiplexed by the IFFT processing unit 10, converted from a frequency domain to a time domain signal, and becomes a baseband OFDM modulated signal. Although not shown, the OFDM modulated signal generated in this manner is further added with guard time data, then placed on a carrier of a predetermined channel, and transmitted and output as a digital broadcast wave.

FIG. 4 shows the configuration of the receiving terminal side in the digital terrestrial broadcasting transmission system of the present embodiment.
In FIG. 4, a baseband OF selected by receiving and detecting a digital broadcast wave by a reception processing unit (not shown).
The DM modulation signal is demultiplexed by the FFT processing unit 11 and converted from a time domain to a frequency domain signal. The reproduction processing unit 21 performs timing reproduction from the input / output signals of the FFT processing unit 11.

The output of the FFT processing is separated into a pilot signal and a TMCC signal for reception synchronization and detection by an OFDM frame decoding processing unit 12, and a differential hierarchy / SP hierarchy processing is performed by a differential hierarchy / SP hierarchy processing unit 13. The signal is demodulated for each layer, and divided by the layer division processing unit 14 for each layer.

The demodulated signal divided into the respective layers is subjected to frequency deinterleaving in a frequency deinterleave processing unit 15. At this time, when transmission parameters (coding rate, modulation scheme) are selected from a plurality of types and are transmitted in the form of hierarchical division for the same reception form (a feature of the present invention), the frequency is determined for each hierarchical level. Deinterleaving is performed.

Subsequently, the data is converted into bit data in the demapping processing unit 16.
In accordance with the TMCC separated by the DM frame decoding processing unit 2, for a segment having a disturbance, for example, 16Q
AM is selected, and for a segment without interference, for example, 64QAM is selected. Each layer output subjected to the demapping process is subjected to Viterbi error correction by the Viterbi decoding unit 17 for each layer. At this time, TMC
According to C, a coding rate of 2/3 is selected, for example, for a segment with interference. For segments without interference, for example, a coding rate of 7/8 is selected.

After Viterbi decoding, each layer signal is randomly removed by a pseudo random code for each layer and deinterleaved by an energy spreading byte deinterleave processing unit 18. Further, the signal is synthesized according to the layer information by the layer synthesizing unit 19, and the RS decoding unit 20 performs error correction by Reed-Solomon to obtain a TS output by the MPEG2 system.

As is apparent from the above description, the main purpose of the prior art is to select a transmission parameter according to the reception mode and transmit the data in a hierarchical manner. Then, transmission parameters (coding rate, modulation method) are selected, and the data is divided into layers and transmitted. Therefore, it is possible to improve the same-channel interference protection ratio and realize an information transmission speed at which a high-quality broadcast service can be operated.

[0042]

As described above, according to the present invention, it is possible to provide a terrestrial digital broadcast transmission system which improves the same-channel interference protection ratio and realizes an information transmission speed at which a high-quality broadcast service can be operated. it can.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a terrestrial digital broadcast transmission system in Japan currently being deliberated by the Telecommunications Technology Council.

FIG. 2 shows a segment structure OF in the above transmission system.
FIG. 4 is a diagram showing a comparison between the spectrum of a digital signal by DM and the spectrum of an analog TV signal that interferes with this signal.

FIG. 3 is a block diagram showing a configuration of a transmission side in the digital broadcasting system according to the embodiment of the present invention.

FIG. 4 is an exemplary block diagram showing a configuration of a receiving side in the digital broadcasting system of the embodiment.

FIG. 5 is a conceptual diagram showing a frequency plan of a current analog broadcasting service.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 RS encoding processing unit 2 Layer division processing unit 3 Delay correction processing unit 4 Energy spread byte interleave processing unit 5 Convolutional encoding processing unit 6 Carrier modulation processing unit 7 Frequency interleave processing unit 8 Layer Synthesis processing unit 9 OFDM frame configuration processing unit 10 IFFT processing unit 11 FFT processing unit 12 OFDM frame decoding processing unit 13 Differential layer / SP layer processing unit 14 Layer division processing unit 15 Frequency deinterleaving processing unit DESCRIPTION OF SYMBOLS 16 ... Demapping processing part 17 ... Viterbi decoding processing part 18 ... Energy spreading byte deinterleave processing part 19 ... Hierarchy synthesis processing part 20 ... RS decoding processing part 21 ... Reproduction processing part

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04N 7/24 (72) Inventor Taku Suga 5-2-8 Akasaka, Minato-ku, Tokyo Next-generation digital television broadcasting system Inside the system laboratory (72) Inventor Kenshi Sawada 5-2-2-8 Akasaka, Minato-ku, Tokyo Inside the next-generation digital television broadcasting system laboratory (72) Inventor Hideki Ohno Toshiba Komukai, Saiwai-ku, Kawasaki-shi, Kanagawa 1-cho, Komukai, Toshiba Corporation (56) Reference "Transmission system for terrestrial digital broadcasting-Transmission characteristics in fixed reception and mobile reception-" Proceedings of Technical Open Lectures and Research Presentations, May 22, 1998, p. 67 −72 (58) Fields investigated (Int. Cl. ⁶ , DB name) H04J 11/00

Claims (6)

(57) [Claims] 1. A transmission band of one channel is divided into a plurality of segments.
OFDM transmission method with segment structure divided into
Combine one or more arbitrary segments using an expression
Thus, one or more floors corresponding to one reception mode
In a terrestrial digital broadcast transmission system for transmitting a digital broadcast signal having a layer formed, a part of a band of the same channel as the digital broadcast signal is used.
Interference sources that emit frequency signals with concentrated energy
And interferes with the digital broadcast signal
The specific segments affected by the interferer and their characteristics
With other segments in the same hierarchy that
Are further divided into layers, and the frequency interface is
And the hierarchy based on the specific segment
A terrestrial digital broadcast transmission system, wherein the modulation scheme or the error correction coding rate is different from the modulation scheme or the error correction coding rate of a layer by another segment in the same layer . 2. The digital broadcast signal according to claim 2 , wherein:
Video of analog TV broadcast signals broadcast on the same channel
One of an image carrier, an audio carrier, and a color subcarrier,
Each of the disturbed segments is the specific segment
2. The terrestrial digital broadcast transmission system according to claim 1, wherein the digital terrestrial broadcast transmission system is handled as a digital broadcast. 3. The terrestrial digital broadcast transmission system according to claim 1, wherein the modulation method or the coding rate of the specific segment is determined according to the strength of an interference source. 4. When there are a plurality of said specific segments, each of the specific segments has the same modulation scheme or coding rate, and is treated as a signal belonging to the same layer. A terrestrial digital broadcast transmission system according to any one of claims 1 and 2. 5. The method according to claim 1, wherein information on a segment position of the specific segment and transmission parameters thereof is described in a mode designation signal inserted in all segments. 4. The terrestrial digital broadcast transmission system according to any one of 4. 6. The terrestrial digital system according to claim 5, wherein the mode designation signal is used to change a modulation method or a coding rate of the specific segment when a state of an interference source changes. Broadcast transmission system.