JP5771134B2 - Transmitting apparatus and receiving apparatus - Google Patents

Description

  The present invention relates to the technical fields of satellite and terrestrial broadcasting, fixed and mobile communications, and more particularly, to a digital data transmitter and receiver.

  As a technique to improve transmission performance under white noise, a coding modulation technique that can improve transmission performance by combining error correction code strength and modulation mapping bits appropriately in digital modulation has been proposed. (For example, refer nonpatent literature 1).

  In particular, the encoding and modulation technique described in Non-Patent Document 1 is also adopted in the Japanese satellite digital broadcasting standard ISDB-S (for example, see Non-Patent Document 2), and is a technique that contributes to improving transmission performance. There is a track record.

  The basic principle of the technique described in Non-Patent Document 1 is that the Euclidean distance among signal bits (hereinafter referred to as symbol configuration bits) constituting a symbol is considered in consideration of the Euclidean distance between signal points after mapping the symbol. Strong error correction is applied to bits whose 1/0 is inverted between signal points with a short distance, while weak error correction is applied to bits whose 1/0 is inverted between signal points with a long Euclidean distance. In other words, noise tolerance is improved while maintaining the overall information efficiency by applying or not performing the encoding process.

  Further, Non-Patent Document 1 proposes a method for assigning symbols to signal points called a set division method using 8PSK as an example. As an example, an example of a method of assigning symbols to 8PSK signal points by the set division method will be described with reference to FIG.

  In FIG. 13, symbols (000, 001,..., 111) configured by 3 bits to be assigned to each signal point of 8PSK are already described. This is performed by using the following division procedure. This is obtained as a result of assigning symbols to and has not yet been determined at the time of performing set partitioning.

  In the first division, the eight signal points are divided into two signal point groups composed of four signal points so that the Euclidean distance between adjacent signal points is maximized. Here, of the two signal point groups, one signal point group is assigned a1 = 0 to the first bit of the symbol configuration bits and a1 = 1 is assigned to the other.

  Next, the two signal point groups composed of the four signal points obtained in the first division are each divided into four signals composed of two signal points so that the Euclidean distance between adjacent signal points is maximized. Divide into point clouds. Here, when a signal point group composed of four signal points is divided into two signal point groups, one signal point group is assigned a2 = 0 to the second bit of the symbol constituent bits and the other is assigned to the other signal point group. Assigns a2 = 1.

  Furthermore, although omitted in FIG. 13, four signal point groups composed of two signal points obtained by the second division are each divided into eight signal point groups each consisting of one signal point. Here, when dividing a signal point group composed of two signal points into one signal point, one signal point group is assigned a3 = 0 to the third bit of the symbol configuration bits, and the other Assign a3 = 1.

  As a result of the above three-stage set division, a unique symbol of 3 bits is assigned to each of the eight signal points.

  By assigning symbols to these signal points, in the case of 8PSK, the first bit (corresponding to a1 in FIG. 13) is the adjacent Euclidean distance in 8PSK, and the second bit (corresponding to a2 in FIG. 13) is QPSK. The adjacent Euclidean distance and the third bit (corresponding to a3 in FIG. 13) can be decoded under the BPSK Euclidean distance condition.

  The symbol assignment to the signal points obtained by the set division method is shared between the transmission and reception in advance, and the transmission side corrects the data transmitted by each bit constituting the symbol, suitable for the Euclidean distance between the corresponding signal points. A transmission system with high noise tolerance can be realized by performing encoding and modulation with an error correction code of capability and performing decoding corresponding to encoding on the transmitting side after demodulation on the receiving side.

  On the other hand, as a symbol allocation method that is often used in the same way as the set division method, there is a Gray code. As an example, FIG. 14 shows an example of assignment of symbols to 8PSK signal points by Gray code. Gray code is a technique for assigning symbols to signal points so that the symbols of adjacent signal points are always different from each other by one bit. Although there is no feature of transmitting at a different Euclidean distance for each bit in the set division method, it is assigned to 8PSK. The number of signal point pairs in the relationship of the minimum Euclidean distance of each bit in a given symbol is smaller than that in the set partitioning method. For example, focusing on the first bit in FIGS. 13 and 14, the number of pairs of signal points in the relationship of the minimum Euclidean distance is 8 in the set division, but only 4 in the Gray code. Therefore, as far as the first bit is concerned, since the Gray code has a smaller number of signal point pairs with the minimum Euclidean distance than the set partitioning method, the signal point arrangement provides a good bit error rate in the same noise environment. ing. On the other hand, with respect to the second and third bits, in the set division method, the signal point distances are equivalent to QPSK and BPSK, respectively, so that characteristics with a better bit error rate can be obtained in the same noise environment than the Gray code. Become. However, this is a performance on the assumption that the first bit can be received correctly. If the decoding performance of the first bit is insufficient, the decoding performance of the second and third bits is adversely affected. In particular, the bit error rate characteristic of the entire symbol constituent bits is worse than that of the Gray code.

  Therefore, in the transmission system of advanced wideband satellite digital broadcasting described in DVB-S2 and ARIB STD-B44 (hereinafter referred to as advanced satellite broadcasting system, see Non-Patent Document 3, for example), a technique for assigning symbols to signal points As a gray code is adopted.

G. Ungerboeck, “Channel coding with multilevel / phase signals”, IEEE Transaction Information Theory, Vol.IT-28, No.1, January 1982, p.55−67 “Satellite Digital Broadcasting Transmission Standards Standard ARIB STD-B20 3.0 Edition, [online], formulated November 6, 1998, ARIB, [Search June 21, 2011], Internet <URL: http: // www.arib.or.jp/english/html/overview/doc/2-STD-B20v3_0.pdf> "Transmission system of advanced broadband satellite digital broadcasting standard ARIB STD-B44 1.0 version, [online], formulated on July 29, 2009, ARIB, [searched on June 21, 2011], Internet <URL: http: //www.arib.or.jp/english/html/overview/doc/2-STD-B44v1_0.pdf>

  As described above, in the advanced satellite broadcasting system described in DVB-S2 or ARIB STD-B44, the Gray code is adopted instead of the set division method.

  FIG. 15 shows the C / N vs. bit error rate characteristics of each symbol component bit when the Gray code and the set division method are applied to 8PSK in the conventional technique. In the set division method shown in FIG. 15, the signal point is divided into three stages as shown in FIG. 13, and one of the three bits constituting the symbol is assigned to the first for each division. By assigning bits sequentially, the assignment of symbols to each signal point is determined. On the transmission side, it is assumed that mapping is performed based on the correspondence between the symbols and signal points obtained in this way, and on the reception side, it is assumed that the bits assigned to each division are sequentially decoded from the first bit. Here, in order to individually evaluate the noise immunity of the bits allocated to each division, the first bit is correctly received for the characteristics of the second bit, and the first bit and the second bit are correctly received for the performance of the third bit. The extracted characteristics are shown. From FIG. 15, in the set partitioning method according to the conventional technique, it can be expected that the performance improves as the Euclidean distance increases as the higher-order bits are reached. On the other hand, comparing the bit error rate of the Gray code 8PSK and the set division 8PSK with respect to the first bit, the latter performance is inferior. Therefore, in the set division, the error correction code applied to the first bit is made strong. Otherwise, it can be seen that the bit error of the first bit affects the decoding of the bits below it, and as a result, the bit error rate of the entire symbol may be deteriorated as compared with the Gray code.

  Therefore, it is important to assign symbols to signal points in consideration of the correction capability of the error correction code to be used and the propagation path environment.

  In addition, it is desirable to apply multilevel modulation from the viewpoint of improving frequency utilization efficiency. LDPC (Low Density Parity Check) codes and turbo codes are effective because they have performance close to the Shannon limit as the performance of error correction codes alone.

  Therefore, as an example of multi-level modulation, FIG. 16 shows an example of symbol assignment to each signal point by conventional set division in 32QAM, and FIG. 17 shows the set division used to perform this symbol assignment. FIG. 18 shows C / N versus bit error rate characteristics of each symbol constituent bit when the symbol allocation of FIG. 16 is applied. From FIG. 18, by applying the conventional set partitioning method to 32QAM, the second and subsequent bits can be decoded under more advantageous conditions, while the performance of the first bit is much worse than that of the second and subsequent bits. It can be seen that sufficient performance improvement cannot be expected unless the error correction code applied to the first bit is extremely strong.

  As an example, assuming that information of about 4 bits per symbol is transmitted, a combination of a conventional set division method and an LDPC code is transmitted under the condition of combining 32QAM and an error correction code corresponding to a coding rate of 4/5. Think about the case. For each bit of 32QAM, from the viewpoint of protecting all bits with error correction while considering the correction capability, the coding rate 61/120 is the first bit, the coding rate 89/120 is the second bit, and the coding rate 109/120 is applied to the third bit, the fourth bit, and the fifth bit. In this case, the overall coding rate is (61/120 + 89/120 + 109/120 + 109/120 + 109/120) /5=0.595. FIG. 19 shows the C / N versus bit error rate characteristics of this example. Further, FIG. 19 shows a C / N vs. bit error rate in a combination of a conventional 32QAM gray code and LDPC code as a case of a similar coding rate (coding rate 97/120 = 0.008). The characteristics are also shown.

  As is clear from FIG. 19, the 32QAM gray code is superior in performance to the 32QAM set partitioning method, and as far as this example is concerned, the superiority of the set partitioning method cannot be confirmed. This is considered to be a result of a decrease in overall performance mainly due to a lack of error correction capability of the first bit. When the application of the set partitioning method is considered, the bit error rate before error correction of the first bit is changed. How to reduce it is an important issue.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a digital data transmitter and receiver having excellent noise resistance.

  In order to solve the above-described problems, the present invention has at least one feature described below.

The first feature is
In a set division method for assigning symbols to signal points used for modulation in a transmitter that transmits digital data, the conventional technique uniformly divides the signal points so that the minimum Euclidean distance is increased. On the other hand, in the set division method according to the present invention, symbols are assigned to signal points by a set division method including division that reduces the signal point logarithm of the minimum Euclidean distance without increasing the minimum Euclidean distance. As a result, it is possible to reduce the bit error rate before error correction of the symbol constituent bits corresponding to signal points having a small minimum Euclidean distance.

The second feature is
The set division method according to the first feature is to perform symbol allocation to signal points by set division of the conventional technique, and then replace the symbol configuration bits. As a result, the characteristics of the symbol constituent bits after the replaced bits can be made the same characteristics as those of the conventional set division method, and the bit error rate of the symbol constituent bits corresponding to the signal points having a large minimum Euclidean distance is reduced. It becomes possible to do.

The third feature is
The symbol configuration bit replacement according to the second feature is performed between the first bit and the second bit. Thereby, the bit error rates of the first bit and the second bit can be made uniform, and the correction capability of the error correction code applied to the first bit can be reduced.

The fourth feature is
In a transmitter that performs modulation using a signal point arrangement in which symbols are assigned by at least one feature including the first feature among the first to third features, without increasing the minimum Euclidean distance, The purpose is to perform encoding with the same correction capability for the symbol constituent bits corresponding to the division for reducing the signal point pair number of the minimum Euclidean distance and the symbol constituent bits corresponding to the next stage of the division. Thereby, efficient error correction coding becomes possible. Here, in this specification, “equivalent correction capability” refers to the same or substantially equal correction capability. For example, if the difference is 20% or less with the same error correcting code and the difference is 20% or less with different error correcting code, the correction ability can be determined in advance.

The fifth feature is
In a receiving device that receives a signal transmitted by a transmitting device including at least one of the first to fourth features, the minimum Euclidean distance is not increased without increasing the minimum Euclidean distance. The decoding process corresponding to each symbol component bit is performed based on the correspondence between signal points and symbols obtained by set division including division that reduces the signal point logarithm of distance. As a result, optimal bit error distribution is possible for the symbol constituent bits corresponding to each division.

The sixth feature is
In the receiving device that receives the signal transmitted by the transmitting device configured by at least one feature including the first feature among the first to fourth features, the set division is performed on the transmission side for each division. After assigning symbols to the signal points by the first set division that divides the signal points so that the minimum Euclidean distance increases uniformly, by exchanging the symbol configuration bits, without increasing the minimum Euclidean distance, Performing a second set division including a division that reduces the signal point logarithm of the minimum Euclidean distance, and the decoding means, based on the correspondence relationship between the symbol and the signal point obtained by the second set division, Each symbol component bit is to be decoded. As a result, the characteristics of the symbol constituent bits after the replaced bits can be made the same characteristics as those of the conventional set division method, and the bit error rate of the symbol constituent bits corresponding to the signal points having a large minimum Euclidean distance is reduced. It becomes possible to do.

The seventh feature is
The symbol constituent bits are exchanged between the first bit and the second bit. Thereby, the bit error rates of the first bit and the second bit can be made uniform, and the correction capability of the error correction code applied to the first bit can be reduced.

The eighth feature is
In a receiving device that receives a signal transmitted by a transmitting device including at least one of the first to fourth features, the minimum Euclidean distance is not increased without increasing the minimum Euclidean distance. Decoding corresponding to the encoding having the same correction capability performed in the transmission apparatus is performed on the symbol constituent bits corresponding to the division for reducing the logarithm of the signal point of the distance and the symbol constituent bits corresponding to the next stage of the division. It is in. This enables efficient error correction decoding.

The ninth feature is
In the transmission apparatus configured by at least one feature including the first feature among the second to fourth features, a first signal point is divided so that the minimum Euclidean distance increases uniformly for each division. Whether it is digital data transmitted by the set division method or digital data transmitted by the second set division method that reduces the signal point logarithm of the minimum Euclidean distance without increasing the minimum Euclidean distance. The transmission is based on multiple control signals. As a result, it is possible to provide a transmission / reception apparatus that supports both encoding and decoding of the first set division technique (conventional set division method) and the second set division technique (set division method according to the present invention). .

The tenth feature is
In the receiving device that receives the signal transmitted by the transmitting device configured by the ninth feature, transmission is performed by the first set division method that divides the signal point so that the minimum Euclidean distance increases uniformly for each division. On the basis of the transmission multiplex control signal, whether the received digital data is digital data transmitted by the second set division method that reduces the signal point logarithm of the minimum Euclidean distance without increasing the minimum Euclidean distance. It is to discriminate. As a result, it is possible to provide a transmission / reception apparatus that supports encoding and decoding of both the first set division technique (conventional set division method) and the second set division technique (set division method according to the present invention). .

  By configuring the transmitting apparatus and the receiving apparatus by adopting the above technique, it becomes possible to improve the transmission performance of the set division method, which has been difficult to achieve the performance higher than that of the Gray code in the conventional technique.

That is, the transmitting apparatus of the present invention is a digital data transmitting apparatus, wherein a plurality of data sequences are generated by encoding means for generating a codeword sequence obtained by performing error correction on each of a plurality of data sequences at a predetermined coding rate. The word sequence is an input symbol sequence, and the input symbol sequence is not accompanied by the expansion of the minimum Euclidean distance, and the minimum Euclidean distance is reduced so as to reduce the logarithm of signal points in a relationship in which 1/0 of a specific symbol component bit is inverted Symbol / signal point conversion means for converting to a signal point series based on the correspondence between symbols and signal points obtained by performing set partitioning including partitioning to reduce the signal point logarithm of the signal point, and the symbol / signal point and a quadrature modulating means for quadrature modulating the generated signal point sequence by the conversion means, the symbol / signal point conversion means, the minimum Euclidean distance is evenly for each divided After assigning symbols to signal points by the first set division that divides signal points as much as possible, the signal point logarithm of the minimum Euclidean distance is not accompanied by the expansion of the minimum Euclidean distance by replacing the symbol configuration bits. Performing a second set division including a division to reduce the input symbol sequence, and converting the input symbol sequence into the signal point sequence based on a correspondence relationship between a symbol and a signal point obtained by the second set division. Features. Thus, it is possible to reduce the bit error rate before error correction symbol configuration bits corresponding to between small signal point having the minimum Euclidian distance Do Ri, it is possible to efficiently error correction coding.

  In the transmission apparatus of the present invention, the symbol / signal point conversion means performs the symbol configuration bit exchange between the first bit and the second bit. Thereby, the bit error rates of the first bit and the second bit can be made uniform, and the correction capability of the error correction code applied to the first bit can be reduced.

  Further, in the transmission apparatus of the present invention, the encoding means includes symbol configuration bits corresponding to the division that decreases the signal point logarithm of the minimum Euclidean distance without increasing the minimum Euclidean distance, and the next stage of the division. The corresponding symbol constituent bits are encoded by a code having the same correction capability. Thereby, efficient error correction coding becomes possible.

In addition, the receiving apparatus of the present invention includes a quadrature demodulating unit that orthogonally demodulates a modulated signal and outputs a received signal point sequence, and a relationship in which 1/0 of a specific symbol component bit is inverted without increasing the minimum Euclidean distance. each symbol on the basis of the signal points so that the logarithm is reduced, a corresponding relationship between the signal point and symbol was assigned symbol to set partitioning was carried out signal points including a split to reduce signal points logarithm of the minimum Euclidean distance in Decoding means corresponding to the constituent bits, and the set division is performed by the first set division for dividing the signal points so that the minimum Euclidean distance is uniformly increased for each division on the transmission side. After assigning symbols to, the signal point logarithm of the minimum Euclidean distance is reduced without changing the minimum Euclidean distance by replacing the symbol configuration bits And performing a second set partitioning including division to the decoding means, based on the correspondence between the obtained symbol and signal points obtained by set partitioning of the second, by performing the decoding of each symbol configuration bits It is characterized by. Thus, the symbol configuration bits corresponding to each divided stages, Ri Do can be received at an optimal bit error allocation, efficient error correction decoding is possible.

  In the receiver of the present invention, the symbol configuration bits are exchanged between the first bit and the second bit. Thereby, the bit error rates of the first bit and the second bit can be made uniform, and the correction capability of the error correction code applied to the first bit can be reduced.

  Further, in the receiving apparatus of the present invention, the decoding means corresponds to a symbol configuration bit corresponding to a division that reduces the signal point logarithm of the minimum Euclidean distance without increasing the minimum Euclidean distance, and the next stage of the division The symbol constituent bits to be decoded are decoded corresponding to the encoding having the same correction capability used on the transmission side. As a result, an optimum bit error rate characteristic is obtained for the symbol constituent bits corresponding to each division stage, and transmission with excellent noise resistance is possible.

  In the transmitter of the present invention, the orthogonal modulation means is digital data transmitted by a first set division method that divides signal points so that the minimum Euclidean distance uniformly increases for each division, Set division for transmitting by a transmission multiplex control signal (for example, TMCC signal) whether the digital data is transmitted by the second set division method that reduces the signal point logarithm of the minimum Euclidean distance without enlarging the minimum Euclidean distance. It comprises a discrimination signal multiplexing means. As a result, it is possible to provide a transmission apparatus that supports encoding and decoding of both the first set division technique (conventional set division method) and the second set division technique (set division method according to the present invention). .

  In the receiving apparatus of the present invention, the decoding means may be digital data transmitted by a first set division method that divides signal points so that the minimum Euclidean distance increases uniformly for each division, or the minimum A set for determining whether the digital data is transmitted by the second set division method that reduces the signal point logarithm of the minimum Euclidean distance without enlarging the Euclidean distance, based on a transmission multiplex control signal (for example, TMCC signal). A division discrimination means is provided. Accordingly, it is possible to provide a receiving apparatus that can decode both the first set division technique (conventional set division method) and the second set division technique (set division method according to the present invention).

  According to the present invention, it is possible to improve the performance of coded modulation in a combination of an error correction code and multilevel modulation, and to improve the transmission performance under white noise.

It is a block diagram of the transmitting apparatus and receiving apparatus of one Embodiment by this invention. According to the present invention, modulation scheme 32QAM, LDPC code rate 61/120 of the first bit, LDPC code rate 61/120 of the second bit, LDPC code rate 109/120 of the third bit, LDPC of the fourth bit It is a block diagram of the transmitter and receiver which show an example of one Embodiment by this invention in the case of assuming the case of the encoding rate 1/1 and the LDPC encoding rate 1/1 of the 5th bit. Modulation order 5, LDPC code rate 61/120 for the first bit, LDPC code rate 61/120 for the second bit, LDPC code rate 109/120 for the third bit, LDPC code rate 1/4 for the fourth bit It is a figure which shows the example of the codeword sequence in the case of LDPC coding rate 1/1 of 1 and the 5th bit. It is a figure which shows the example of the set division | segmentation for allocating a symbol to the signal point used with the transmitter and receiver which show an example of one Embodiment by this invention. It is a figure which shows the example of the set division | segmentation for allocating a symbol to the signal point used with the transmitter and receiver which show an example of one Embodiment by this invention. It is a figure which shows the example of the set division | segmentation for allocating a symbol to the signal point used with the transmitter and receiver which show an example of one Embodiment by this invention. It is a figure which shows the example of the set division | segmentation for allocating a symbol to the signal point used with the transmitter and receiver which show an example of one Embodiment by this invention. It is the example of symbol allocation to the signal point in the transmitter and receiver which show an example of one Embodiment by this invention. It is a figure which shows the C / N vs. bit error rate characteristic of each symbol component bit in the comparison with the set division | segmentation method based on this invention, and the conventional set division | segmentation method. It is a figure which shows the C / N vs. bit error rate characteristic in 32QAM which contrasted the set division | segmentation method based on this invention, the conventional set division | segmentation method, and the Gray code by setting the LDPC coding rate to about 0.8. It is a figure which shows the example of allocation of the symbol to the signal point by the conventional set division | segmentation method in 16QAM. It is a figure which shows the example of the set division | segmentation for allocating a symbol to the signal point used with the transmitter and receiver which show an example of one Embodiment by this invention. It is a figure which shows the example of a division | segmentation of the set division | segmentation method in conventional 8PSK. It is a figure which shows the example of the symbol allocation to the signal point by the conventional Gray code in 8PSK. It is a figure which shows the C / N versus bit error rate characteristic of the conventional set division | segmentation method in 8PSK, and a Gray code | cord | chord. It is a figure which shows the example of assignment of the symbol to the signal point by the conventional set division | segmentation method in 32QAM. It is a figure which shows the method of assigning a symbol to a signal point by applying the conventional set division | segmentation method in 32QAM. It is a figure which shows the C / N versus bit error rate characteristic for every bit at the time of performing symbol allocation to the signal point shown in FIG. A combination of a conventional set division method of 32QAM and an LDPC code (a1: coding rate 61/120, a2: coding rate 89/120, a3: coding rate 109/120, a4: coding rate 89/120, It is a figure which shows the C / N vs. bit error rate characteristic in the combination (coding rate 97/120) of the conventional gray code and LDPC code of a5: coding rate 89/120) and 32QAM.

  Hereinafter, a transmission device and a reception device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a transmission apparatus and a reception apparatus according to an embodiment of the present invention. It should be noted that the actual transmitter has a function for multiplexing the synchronization signal to the modulated wave signal to identify the head of the error correction code, and information such as the setting of the transmission method employed in ISDB-S etc. In many cases, it includes a function of multiplexing a transmission multiplex control signal (also referred to as a TMCC signal) for notification to a modulated wave signal. Also, the actual receiver detects the synchronization signal multiplexed with the modulated wave signal and detects the head of the error correction code, and detects information such as the transmission method setting from the transmission multiplex control signal. In many cases, a control function for setting a modulation scheme, a coding rate, and the like is included, but the illustration is omitted.

(Device configuration)
[Transmitter]
The transmission apparatus 10 according to the present embodiment is a forward error correction transmission apparatus, and includes a serial / parallel conversion unit 15, an error correction coding unit 16, a mapping unit 18, and an orthogonal modulation unit 20. That is, the functional block configuration of the transmission device is the same as that of the coded modulation transmission device according to the conventional technique, but the processing of the error correction coding unit 16 and the mapping unit 18 is different from the conventional technique.

The serial / parallel conversion unit 15 sets a multi-value number of a modulation method to be used as L for a 1-bit transmission data sequence, and M = log ₂ L-bit data sequence (in the case of 32-value modulation, M = log ₂ 32 = 5 bit sequence) and sent to the error correction coding unit 16 (M is hereinafter referred to as a modulation order).

  The error correction encoding unit 16 includes a first error correction encoding unit 16-1 to an Mth error correction encoding unit 16-M, and is encoded by a predetermined error correction code (for example, a BCH code and an LDPC code). The generated M codeword sequences are generated. In the case of the conventional technique, the noise immunity of each symbol constituent bit corresponding to the division differs depending on the set division, and accordingly, an error correction code having a different correction capability is applied to each symbol constituent bit. However, in the error correction coding unit 16 according to the present invention, since the correspondence relationship between symbols and signal points described later is different from the coding modulation of the conventional technique and performs division without enlarging the minimum Euclidean distance, There are a plurality of substantially equal symbol constituent bits, and an error correction code having an equivalent correction capability is applied to these symbol constituent bits. Therefore, the error correction encoding unit 16 functions as an encoding unit that generates a code word sequence obtained by performing error correction on each of a plurality of data sequences at a predetermined encoding rate.

  The mapping unit 18 uses the M codeword sequences as input symbol sequences, and outputs I-axis and Q-axis amplitude values of signal points corresponding to the symbols as modulated signal point sequences. Here, the correspondence between the symbol and the signal point to be used is different from that obtained by the set division method according to the conventional technique. That is, in the set division method according to the conventional technique, the correspondence between the symbol and the signal point is acquired by dividing the signal point so that the minimum Euclidean distance increases uniformly for each division. The increase in the minimum Euclidean distance by the division of the conventional technique is √2 times in the case of QAM, doubled in the case of ASK, and between the values of QAM and ASK in the case of PSK, that is, a value of √2 to 2 times. Is generally. On the other hand, in the set partitioning according to the present invention, instead of increasing the minimum Euclidean distance, by performing the partitioning so that the number of signal point pairs in which 1/0 of a specific symbol component bit is inverted is reduced, Get the correspondence between symbols and signal points. Therefore, the mapping unit 18 is not accompanied by the expansion of the minimum Euclidean distance, and based on the correspondence relationship between the symbol and the signal point obtained by performing the set division including the division that reduces the signal point logarithm of the minimum Euclidean distance, It functions as symbol / signal point conversion means for converting an input symbol sequence made up of a plurality of codeword sequences into a signal point sequence.

  There are a plurality of division methods in which the number of signal point pairs in which 1/0 of a specific symbol component bit is inverted is reduced instead of increasing the minimum Euclidean distance, but one method is as follows. This can also be realized by assigning symbols to signal points by a conventional set partitioning method in which the minimum Euclidean distance increases uniformly, and then exchanging bits between specific symbol constituent bits. In this case, since the symbol configuration bits after the bit after the replacement are the same as the characteristics of the conventional set division method before the replacement, among the symbol configuration bits in the conventional set division method, between the replaced bits The noise neutralization performance is neutralized. When the first bit and the second bit are exchanged, the noise resistance performance of these bits is neutralized. As a result, the correction capability of the error correction code required for the first bit can be reduced.

  The quadrature modulation unit 20 performs roll-off filter processing on the modulated signal sequence generated by the mapping unit 18, and then transmits the modulated wave signal subjected to quadrature modulation to an external transmission path.

[Receiver]
The receiving device 50 according to the present embodiment is a forward error correction receiving device, and includes an orthogonal demodulator 51, first to M-th bit log likelihood ratio calculators 54-1 to 54-M, M-th bit error correction decoding units 55-1 to 55-M and a parallel / serial conversion unit 56 are provided. That is, the functional block configuration of the receiving apparatus is the same as that of the coded modulation receiving apparatus according to the conventional technique, but the first to Mth bit log likelihood ratio calculation units 54-1 to 54-M and the first to Mth bit errors. The processing of the correction decoding units 55-1 to 55-M is different from the conventional technique.

  The orthogonal demodulator 51 receives a modulated wave signal obtained by modulating the modulated signal sequence based on the correspondence relationship between the symbol and the signal point obtained by the above-described set division method according to the present invention from the transmission device 10 via the transmission line. And quadrature demodulating and outputting a received signal point sequence corresponding to the symbol of the main signal. Therefore, the orthogonal demodulator 51 serves as an orthogonal demodulator that restores and outputs a modulated signal point sequence modulated based on the correspondence between the symbol and the signal point obtained by the set division method according to the present invention by orthogonal demodulation. Function.

  The first bit log-likelihood ratio calculation unit 54-1 determines that the first bit constituting the symbol is 1 and 0 based on the correspondence between the symbol and the signal point obtained by the set division method according to the present invention. Certain probabilities (likelihoods) P11 and P10 are obtained, and the natural logarithm (LLR: log likelihood ratio) of the ratio P11 / P10 is calculated and sent to the first bit error correction decoding unit 55-1.

  The first bit error correction decoding unit 55-1 uses the log likelihood ratio of the first bit by the first bit log likelihood ratio calculation unit 54-1 to perform error correction on the first bit constituting the symbol. The decoding process of the code (for example, the concatenated code of the LDPC code and the BCH code) is executed, and the decoding result of the first bit is sent to the second bit log likelihood ratio calculation unit 54-2 and the parallel / serial conversion unit 56.

  The second bit log-likelihood ratio calculation unit 54-2 uses the logarithmic likelihood of the second bit constituting the symbol in the same manner as the first bit based on the correspondence between the symbol and the signal point obtained by the set division method according to the present invention. The degree ratio is calculated and sent to the second bit error correction decoding unit 55-2.

  The second bit error correction decoding unit 55-2 performs error correction on the second bit constituting the symbol using the log likelihood ratio of the second bit by the second bit log likelihood ratio calculation unit 54-2. A code (for example, a concatenated code of an LDPC code and a BCH code) is decoded, and the decoding result of the second bit is converted into a bit log likelihood ratio calculation unit (for example, an Mth bit log likelihood ratio calculation unit 54 of the next stage). -M) and the parallel / serial converter 56. The M-th log likelihood ratio calculation unit 54-M and the M-th bit error correction decoding unit 55-M perform the same processing, and perform sequential decoding until all bits constituting the symbol are decoded.

  In this manner, the first to M-th bit log likelihood ratio calculation units 54-1 to 54-M and the first to M-th bit error correction decoding units 55-1 to 55-M can perform the set division method according to the present invention. On the basis of the correspondence relationship between the symbol and signal point obtained by the above, sequential decoding is performed using the decoding result obtained for each bit and the log likelihood ratio. Accordingly, the first to Mth bit log likelihood ratio calculation units 54-1 to 54-M and the first to Mth bit error correction decoding units 55-1 to 55-M perform set division according to the present invention and perform signal division. It functions as a decoding means that decodes each symbol constituent bit based on the correspondence between the signal point to which the symbol is assigned to the point and the symbol. Here, the decoding means is data transmitted by a conventional set division method that divides signal points so that the minimum Euclidean distance is uniformly increased for each division, or the minimum without increasing the minimum Euclidean distance. A set division discriminating means for discriminating whether the data is transmitted by the set division method according to the present invention that reduces the logarithmic signal point logarithm of the Euclidean distance can be provided based on the transmission multiplex control signal (see FIG. Not shown). In this case, the transmission device 10 is configured to include means for transmitting information indicating the type of the set division method to be used using the transmission multiplex control signal. In addition, when the set division determination means determines that the set division method according to the present invention, the decoding means is based on the correspondence between signal points and symbols obtained by exchanging the first bit and the second bit in the conventional set division method. Thus, each symbol component bit can be decoded.

  The parallel / serial conversion unit 56 performs parallel / serial conversion on the decoding result of the data series corresponding to the bits constituting the symbols obtained from the first to Mth bit error correction decoding units 55-1 to 55-M, and outputs 1 bit. The received data series is sent to the outside.

  Next, with reference to FIG. 2, a transmitting apparatus 10b and a receiving apparatus 50b illustrating an example of an embodiment according to the present invention when the modulation scheme is 32QAM will be described.

  FIG. 2 shows the LDPC coding rate 61/120 for the first bit and the second bit, the LDPC coding rate 109/120 for the third bit, the LDPC coding rate 1/4 for the fourth bit and the fifth bit according to the present invention. It is a figure which shows the example of the transmitter in the case where the case of 1 is assumed. Here, the LDPC coding rate 1/1 means that the transmitting side does not perform LDPC coding and the receiving side does not perform LDPC decoding. Therefore, in FIG. 2, the error correction coding unit (BCH, LDPC) is described in the transmitting apparatus 10b for the first to fifth bits, but the LDPC encoder is actually used for the fourth and fifth bits. Is unnecessary. Similarly, the log likelihood ratio calculation unit and the error correction decoding unit (LDPC, BCH) are described for the first to fifth bits in the receiving device 50b, but the log likelihood ratio for the fourth bit and the fifth bit. Instead of the calculation unit, a demapper that performs hard decision can be used, and an LDPC code decoder is not actually required. The transmission device 10b and the reception device 50b illustrated in FIG. 2 may be considered as an example of the transmission device 10 and the reception device 50 according to the embodiment illustrated in FIG. For this reason, the same reference numerals are given to the same components, and description will be made. Hereinafter, the transmission device 10b and the reception device 50b will be described in this order.

(Device configuration)
[Transmitter]
The transmission device 10b includes a serial / parallel conversion unit 15b, an error correction coding unit 16b, a mapping unit 18b, and an orthogonal modulation unit 20.

  2 is provided with a serial / parallel conversion unit 15b instead of the serial / parallel conversion unit 15 in place of the error correction encoding unit 16, as compared with the transmission device 10 shown in FIG. Is provided with an error correction encoding unit 16 b and a mapping unit 18 b instead of the mapping unit 18. Therefore, the constituent elements other than these differences are as described with reference to FIG. 1, and these differences will be described in detail below.

  The serial / parallel converter 15b converts the 1-bit transmission data sequence into a 5-bit data sequence and sends it to the error correction encoding unit 16b.

  The error correction encoding unit 16b sends the generated codeword sequence to the mapping unit 18b. The error correction encoding unit 16b of the present example includes a first error correction encoding unit 16b-1 to a fifth error correction encoding unit 16-5. In the set division according to the present invention, which will be described in detail later, division is first performed without enlarging the minimum Euclidean distance. For this reason, there are two symbol constituent bits with almost equal noise immunity. An error correction code having the same correction capability is applied to these two symbol constituent bits. Here, both the first error correction encoding unit 16b-1 and the second error correction encoding unit 16b-2 are concatenated codes combining a BCH code and an LDPC code with a code rate 61/120, and a codeword sequence ( a1) and (a2) are generated. For the other symbol component bits, the third error correction encoding unit 16b-3 generates a codeword sequence (a3) by using a concatenated code combining the BCH code and the LDPC code with the coding rate 109/120. . Further, the fourth error correction encoding unit 16b-4 and the fifth error correction encoding unit 16b-5 have a sufficiently low bit error rate as compared with the other 3 bit symbol constituting bits, so that the BCH code Codeword sequences (a4) and (a5) are generated. An example of the generated codeword sequence is shown in FIG.

  In this example, the mapping unit 18b uses the five codeword sequences (a5, a4, a3, a2, a1) generated by the error correction encoding unit 16b as input symbol sequences, and the correspondence between symbols and signal points described later. A modulation signal point sequence is generated according to the relationship. Thereafter, the quadrature modulation unit 20 performs the same processing as described in FIG. 1 to generate a modulated wave signal.

  Here, the set division method according to the present invention for acquiring the correspondence between symbols and signal points used in the mapping unit 18b will be described. Before that, the conventional set division method will be described. FIG. 17 shows set division according to the conventional technique of 32QAM as described above. The division after the third stage is omitted in the figure. In the conventional technique, signal points are divided obliquely in both the first stage and the second stage so that the minimum Euclidean distance becomes √2 times for each division. Based on the result of the set division of FIG. 17, the correspondence between the symbol and the signal point shown in FIG. 16 is acquired. In this case, since the symbol near the center of the constellation is surrounded from four directions by signal points in which 1/0 of the first bit is inverted, and there are 52 pairs of signal points in which 1/0 of the first bit is inverted. The bit error rate (BER) of the first bit is degraded. When performing multi-stage decoding, the decoding error of the first stage is propagated to the subsequent stage, so that it is important to improve the decoding characteristics of the first bit.

  Next, the set division method according to the present invention will be described. As a set division method for improving the noise resistance of the first bit, for example, divisions as shown in FIGS. 4, 5 and 6 can be considered, and signal points in a relationship in which 1/0 of the first bit is inverted are respectively There are 24, 16, and 12 pairs. In these figures, the division after the fourth stage is omitted. Since the number of signal point pairs in which 1/0 of the first bit is inverted can be greatly reduced from 52 pairs in the conventional technique, these are effective in reducing the error correction capability required for the first bit. On the other hand, since the minimum Euclidean distance of the upper bits is smaller than that of the conventional method set division method, the higher bits require stronger error correction than in the case of the conventional method set division.

  It is also possible to improve noise resistance characteristics of specific bits by assigning symbols to signal points by conventional set division and then exchanging bits. In order to improve the performance of the first bit instead of slightly degrading the performance of the second bit, the first bit and the second bit may be exchanged. In this case, the minimum Euclidean distance of the upper bits is equivalent to that of the conventional technique set division method, and the same code as that of the conventional technique set division can be used for the upper bits.

  FIG. 7 shows an example in which symbols are assigned to 32QAM signal points by conventional set division, and then the performance of the first bit is improved instead of slightly degrading the performance of the second bit. The division after the third stage is omitted in the figure. In this set division, signal points are divided horizontally in the first stage and vertically in the second stage. In the first division, the minimum Euclidean distance is the same as before the division. FIG. 8 shows the correspondence between symbols and signal points obtained as a result of the set division of FIG. Comparing FIG. 8 with FIG. 16 of the conventional technique, it can be confirmed that symbols in which the first bit and the second bit of FIG. 18 are exchanged are assigned in FIG. Further, according to FIG. 7, the signal point near the center of the constellation in the first stage is surrounded only by the two upper and lower directions with the signal point in which 1/0 of the first bit is inverted, and 1/0 of the first bit is inverted. Although there are 26 pairs of signal points in the above relationship, which is larger than in FIG. 4 to FIG. 6, it can be greatly reduced from 52 pairs in the case of the conventional technique. On the other hand, since the division in which the minimum Euclidean distance is not expanded in the first stage, the signal points of the Euclidean distance before the division are surrounded from the left and right after the division, and the bits corresponding to the division in the first stage and the second stage are Equivalent BER characteristics.

  FIG. 9 shows the C / N vs. BER characteristics (without error correction) of each symbol component bit when symbols are assigned to signal points using the conventional technique and the set division method according to the present invention. From the figure, it can be seen that when the present invention is applied, the BER characteristic of the first stage is improved, while the BER characteristic of the second stage is equivalent to that of the first stage.

[Receiver]
As illustrated in FIG. 2, the reception device 50b includes an orthogonal demodulation unit 51, first to fifth bit log likelihood ratio calculation units 54-1 to 54-5, and first to fifth bit error correction decoding units 55. -1 to 55-5 and a parallel / serial converter 56.

  Here, the receiving device 50b shown in FIG. 2 is different from the receiving device 50 shown in FIG. 1 in that the first to fifth bit log likelihood ratio calculation units 54-1 to 54-5 and M = 5 and 1 to 5 bit error correction decoding units 55-1 to 55-5 are different. Therefore, the constituent elements other than these differences are as described with reference to FIG. 1, and these differences will be described in detail below.

  The first to fifth bit log likelihood ratio calculation units 54-1 to 54-5 and the first to fifth bit error correction decoding units 55-1 to 55-5 are modulated signal points obtained through the orthogonal demodulation unit 51. For the sequence, the log likelihood ratio obtained for each symbol constituent bit and the error correction decoding section after the second bit are sequentially decoded from the first bit to the fifth bit using the preceding decoding result.

  The parallel / serial conversion unit 56 performs parallel / serial conversion on the decoding result of the data series corresponding to the bits constituting the symbols obtained from the first to fifth bit error correction decoding units 55-1 to 55-5, and outputs 1 bit. The received data series is sent to the outside.

  The effect of applying the set partitioning method according to the present invention will be described with reference to FIG. In FIG. 10, in addition to the characteristics of the present invention, the conventional 32QAM set partitioning method and the characteristics when using the Gray code are also shown. In the coded modulation method using the set division method according to the conventional technique, the C / N for securing the same bit error rate is high and the noise resistance is inferior compared with the case where the gray code according to the conventional technique is applied. It was a thing. On the other hand, the coding modulation method applying the set division of the present invention has a low C / N for securing the same bit error rate and excellent noise resistance compared to the case where the gray code according to the conventional technique is applied. It has become a thing.

As is apparent from FIG. 10, the transmitting apparatus 10b and the receiving apparatus 50b, which are examples of the present embodiment, are approximately 0.9 dB at a point of BER = 1 × 10 ⁻⁷ , for example, compared with the case where the gray code according to the conventional technique is applied. It has improved. In the comparison of FIG. 10, the transmission device 10b and the reception device 50b assume the codeword sequence shown in FIG. The total LDPC coding rate in this case is (22814 + 22814 + 40766 + 44880 + 44880) / (44880 * 5) = 0.786. On the other hand, since the LDPC coding rate of the conventional gray code is 36278/44880 = 0.0883, it is necessary to subtract the coding rate difference of 0.13 dB for fair comparison. Even in that case, there is an improvement of 0.77 dB, and the effectiveness of the transmission device 10 and the reception device 50 according to the present embodiment can be confirmed.

  Although the above embodiment has been described based on a specific example, various applications are possible. For example, the modulation method has been described by taking 32QAM as an example, but may be 16QAM. In this case, the assignment of symbols to signal points by the set division of the prior art is as shown in FIG. 11. In this case, the signal points near the center are 4 signal points with 1/0 of the first bit inverted. Since there are 24 pairs of signal points that are surrounded from the direction and in which 1/0 of the first bit is inverted, the bit error rate (BER) of the first bit deteriorates. On the other hand, in the set division method according to the present invention, division as shown in FIG. 12 can be considered, and there are 12 pairs of signal points in which 1/0 of the first bit is inverted. Therefore, since the number of signal point pairs in which 1/0 of the first bit is inverted can be greatly reduced from 24 pairs in the case of the conventional technique, it is effective in reducing the error correction capability required for the first bit. Similarly, the present invention is applicable to modulation schemes such as 8PSK, 64QAM, 128QAM, 256QAM, 512QAM, 1024QAM, 2048QAM,. In addition, regarding the error correction code used for the coding modulation, the LDPC code and the BCH code defined in the advanced satellite broadcasting system have been described as examples, but a turbo code, a Reed-Solomon code, and a convolutional code may be used. The present invention can also be applied to other transmission methods such as satellite broadcasting, terrestrial broadcasting, mobile communication, and fixed communication.

  According to the present invention, it is possible to improve the encoding modulation performance in the combination of the error correction code and the multi-level modulation and improve the transmission performance under white noise, so that the error correction code and the multi-level modulation are used. Useful for any application.

10, 10b Transmitting device 15, 15b Serial / parallel converter 16, 16b Error correction encoder 16-1, 16b-1 First error correction encoder 16-2, 16b-2 Second error correction encoder 16 -3, 16b-3 Third error correction coding unit 16-4, 16b-4 Fourth error correction coding unit 16-5, 16b-5 Fifth error correction coding unit 16-M Mth error correction coding Unit 18, 18b mapping unit 20 orthogonal modulation unit 50, 50b receiving apparatus 51 orthogonal demodulation unit 54-1 first bit log likelihood ratio calculation unit 54-2 second bit log likelihood ratio calculation unit 54-5 fifth bit log Likelihood ratio calculation unit 54-M Mth bit log likelihood ratio calculation unit 55-1 First bit error correction decoding unit 55-2 Second bit error correction decoding unit 55-5 Fifth bit error correction decoding unit 55-M Mth bit error Positive decoding unit 56 parallel / serial converter

Claims (8)

A transmission device for transmitting digital data,
An encoding means for generating a codeword sequence in which error correction is performed on each of a plurality of data sequences at a predetermined coding rate;
A plurality of codeword sequences are used as input symbol sequences, and the input symbol sequences are not accompanied by an increase in the minimum Euclidean distance, and the logarithm of signal points having a relationship in which 1/0 of a specific symbol component bit is inverted is reduced. A symbol / signal point conversion means for converting into a signal point series based on a correspondence relationship between a symbol and a signal point obtained by performing set partitioning including partitioning to reduce the signal point logarithm of the minimum Euclidean distance;
Orthogonal modulation means for orthogonally modulating signal points generated by the symbol / signal point conversion means ,
The symbol / signal point conversion means assigns symbols to signal points by first set division that divides signal points so that the minimum Euclidean distance increases uniformly for each division, and then replaces symbol configuration bits. Accordingly, the second set division including the division for reducing the signal point logarithm of the minimum Euclidean distance is performed without enlarging the minimum Euclidean distance, and the correspondence between the symbol and the signal point obtained by the second set division is performed. A transmission apparatus that converts the input symbol sequence into the signal point sequence based on a relationship . 2. The transmission apparatus according to claim 1 , wherein the symbol / signal point conversion unit exchanges the symbol constituent bits between a first bit and a second bit. 3. The encoding means does not increase the minimum Euclidean distance, and the symbol configuration bits corresponding to the division that reduces the signal point logarithm of the minimum Euclidean distance and the symbol configuration bits corresponding to the next stage of the division are equivalent. characterized by coding the sign of correction capability, the transmission device according to claim 1 or 2. The orthogonal modulation means is digital data transmitted by the first set division method that divides signal points so that the minimum Euclidean distance increases uniformly for each division, or is minimal without increasing the minimum Euclidean distance. 2. A set division discriminating signal multiplexing means for transmitting, by a transmission multiplexing control signal, whether the digital data is transmitted by the second set division method for reducing the signal point logarithm of the Euclidean distance. 4. The transmission device according to any one of items 1 to 3 . A digital data receiving device,
Orthogonal demodulation means for orthogonally demodulating the modulated signal output from the transmission device according to any one of claims 1 to 4 and outputting a received signal point sequence;
Perform set partitioning, including partitioning, which reduces the signal point logarithm of the minimum Euclidean distance so that the signal point logarithm of 1/0 of a specific symbol component bit is inverted without reducing the minimum Euclidean distance. Decoding means for decoding each symbol component bit based on the correspondence between the signal point and the symbol corresponding to the assignment of the symbol to the signal point ;
In the set division, on the transmission side, symbols are allocated to signal points by first set division in which signal points are divided so that the minimum Euclidean distance increases uniformly for each division, and then the symbol configuration bits are replaced. Thus, the second set division including the division for reducing the signal point logarithm of the minimum Euclidean distance is performed without increasing the minimum Euclidean distance, and the decoding means is obtained by the second set division. A receiving apparatus that decodes each symbol constituent bit based on a correspondence relationship between a symbol and a signal point . The receiving apparatus according to claim 5 , wherein the symbol constituent bits are exchanged between the first bit and the second bit. The decoding means is configured to transmit, on the transmitting side, a symbol configuration bit corresponding to a division that reduces the signal point logarithm of the minimum Euclidean distance without increasing the minimum Euclidean distance, and a symbol configuration bit corresponding to the next stage of the division. The receiving apparatus according to claim 5 or 6 , wherein the decoding apparatus performs decoding corresponding to encoding with the same correction capability used. The decoding means is digital data transmitted by the first set division method for dividing the signal point so that the minimum Euclidean distance increases uniformly for each division, or the minimum Euclidean distance is not increased without increasing the minimum Euclidean distance. 6. The apparatus according to claim 5 , further comprising set division discrimination means for discriminating based on the transmission multiplex control signal whether the digital data is transmitted by the second set division method that reduces the logarithmic signal point logarithm. receiving apparatus according to any one of 7.