JP2012054681A - Transmitter and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmitter and a receiver that perform an LDPC coding to information bits including TMCC information, in a transmission system that performs time-division multiplexing of a plurality of kinds of digital modulation system.SOLUTION: A transmitter 100 has: a main signal LDPC coder 1005 that performs LDPC coding of a main signal symbol string; an TMCC LDPC coder 1004 that performs LDPC coding of information bits to generate a synchronization reinforcement burst signal; and a transmission framing and orthogonal modulation unit 1007 that inserts a symbol string of the synchronization reinforcement burst signal to form a predetermined slot length, performs time-division multiplexing to construct a transmission frame, performs orthogonal modulation, and then transmits it. The TMCC LDPC coder 1004 has means of inserting null data, which depends on a parameter prescribing an insertion rate of the symbol string of the synchronization reinforcement burst signal, and a predetermined coding rate, into the information bits, performing the LDPC coding at the predetermined coding rate, and then, deleting the null data to perform shortening.

Description

  The present invention relates to a forward error correction (FEC) technique in the technical field of error correction codes for digital transmission for wideband transmission, and in particular, a transmission system for time-division multiplexing a plurality of types of digital modulation schemes. The present invention relates to a transmitting apparatus that performs LDPC encoding on information bits including TMCC information, and a receiving apparatus thereof.

  In the digital transmission system, a multi-level modulation system is often used so that more information can be transmitted in the frequency bandwidth available for each service. In order to increase the frequency utilization efficiency, it is necessary to increase the number of bits allocated per modulation signal symbol (the number of modulation levels), but the relationship between the upper limit of the information rate that can be transmitted per frequency 1 Hz and the signal-to-noise ratio is Limited by Shannon limit. As an example of a transmission form of information using a satellite transmission path, satellite digital broadcasting can be cited.

  In satellite digital broadcasting, TWTA (traveling wave tube amplifier) with high power efficiency is often used due to hardware limitations of satellite repeaters. It is also desirable to operate the amplifier in the saturation region so that the satellite repeater output is maximized in order to take full advantage of the limited satellite repeater hardware limitations. However, since distortion generated in the amplifier leads to transmission degradation, phase modulation is often used as a modulation scheme that is resistant to transmission degradation caused by distortion generated in the power amplifier. Currently, a transmission system called ISDB-S is used as a transmission system for satellite digital broadcasting in Japan, and phase modulation such as BPSK, QPSK, and 8PSK can be used.

  In addition, DVB-S2, which is a European transmission method, uses an amplitude phase modulation called amplitude phase modulation (APSK), and a modulation method that further improves the frequency utilization efficiency has been put to practical use. For example, if 16 APSK is used, the maximum frequency utilization efficiency is 4 bps / Hz, and if 32 APSK, the maximum 5 bps / Hz transmission is possible.

  In satellite digital broadcasting currently used, information correction is performed in a receiving apparatus using an error correction code. By adding a redundant signal called a parity bit to information to be sent, it is possible to control the redundancy (coding rate) of the signal and increase the resistance to noise. Error correction codes and modulation systems are closely related, and the relationship between frequency utilization efficiency and signal-to-noise ratio with redundancy added is defined by the Shannon limit. As a powerful error correction code having a performance approaching the Shannon limit, an LDPC (Low Density Parity Check) code was proposed by Gallagher in 1962 (see, for example, Non-Patent Document 1).

  The LDPC code is a linear code defined by a very sparse check matrix H (the elements of the check matrix are 0 and 1 and the number of 1 is very small).

  The LDPC code is a powerful error correction code that can obtain transmission characteristics approaching the Shannon limit by increasing the code length and using an appropriate check matrix, and is a new European satellite broadcasting standard such as DVB-S2 and broadband wireless access standard. The LDPC code is also adopted in IEEE 802.16e. By combining multi-level phase modulation and a powerful error correction code such as an LDPC code, transmission with higher frequency utilization efficiency has become possible.

  By the way, the main cause of transmission deterioration in satellite broadcasting is attenuation of radio waves due to rainfall. Currently, the satellite digital broadcasting in Japan mainly uses the 12 GHz band, but the 21 GHz band is also regarded as a promising frequency band that can be used for satellite broadcasting. However, compared with the 12 GHz band, the 21 GHz band has a very large signal attenuation of 3 times in terms of dB. Therefore, in realization of 21 GHz band satellite broadcasting, a satellite repeater having a larger scale than that of the 12 GHz band and a rain attenuation countermeasure for improving line reliability are required.

R. G Gallager, “Low Density Parity Check Codes,” in Research Monograph series Cambridge, MIT Press, 1963

  Assuming a digital transmission system that assumes 21 GHz band satellite broadcasting, especially in the case of rain, the synchronization performance and transmission control signal of the receiving device under the condition that the dB value is three times worse than the 12 GHz band used in the current service. Communication needs to be realized.

  The advanced broadband satellite digital broadcasting transmission system described in ARIB STD-B44 (hereinafter referred to as "advanced satellite digital broadcasting system") is capable of stable synchronization performance and transmission of transmission control signals even under low C / N. An LDPC code having a code length of 31680 bits obtained by shortening an LDPC code having a code length of 44880 bits and a coding rate of 61/120 is used as an error correction code for transmission control signal transmission, and an error correction code for transmission control signal transmission Is assigned to the synchronization-enhanced burst signal to improve synchronization performance and realize transmission control signal transmission at low C / N while maintaining information efficiency (for example, Radio Industry Association Standard: ARIB-STD B44) 1.0 Refer to the transmission system of advanced broadband satellite digital broadcasting).

  FIG. 1 is a schematic configuration example of a transmission device and a reception device in the advanced satellite digital broadcasting system. In a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes called advanced satellite digital broadcasting schemes, a transmission device 100 transmits broadcast waves via a satellite repeater 200 (hereinafter referred to as “transmission path”). It transmits to the receiving apparatus 300 of a present Example. In the advanced satellite digital broadcasting system, three types of LDPCs of coding rates 101/120, 105/120, and 109/120 having different column weights with a slot length of 44880 bits in a transmission system that time-division-multiplexes a plurality of types of digital modulation systems. At least the code is adopted. FIG. 2 shows the configuration of a coding rate 61/120 shortened LDPC code in the advanced satellite broadcasting system. FIG. 3 shows a modulation signal format in the advanced satellite digital broadcasting system.

  Referring to FIG. 2, when performing LDPC encoding at a coding rate of 61/120 on a power spread TMCC signal (9614 bits), a total of 1870 + 11330 = 13200 bits of null data is inserted. At the time of LDPC encoding, 0 is inserted in these null data, and shortening is achieved by removing all after the encoding. Therefore, the shortened code length is 44880-13200 = 31680 bits, and a signal obtained by modulating the above bit string by π / 2 shift BPSK is used as a synchronization reinforcement burst signal in FIG.

  Referring to FIG. 3, “Data” represents a main signal, and “T” represents a synchronous reinforcement burst signal (a signal subjected to π / 2 shift BPSK modulation). In the case of the advanced satellite digital broadcasting system, four symbols of the synchronous reinforcement burst signal are allocated to the main signal 136 symbols at a frequency of 66 times in one slot, and the ratio of the synchronous reinforcement signal to the main signal is about 3%. Yes. Here, in all 120 slots, the total number of symbols of the synchronous reinforcement burst signal is 120 × 66 × 4 = 31680 symbols, and it can be seen that all the shortened LDPC codes are used for the synchronous reinforcement burst signal. As performance related to this function, it has been shown by a demonstration experiment using an actual satellite repeater that synchronization performance at C / N = −3 dB or less is maintained (for example, Hashimoto et al., “Advanced Satellite Digital Broadcasting System”). ARIB Demonstration Experiment, "Eiji Journal, pp. 958-966, vo. 63, No. 7, 2009).

  However, as described above, since the influence of rain attenuation in the 21 GHz band is three times larger in dB value, the altitude satellite digital that assumes the 21 GHz band synchronization performance under poor conditions far below C / N = -3 dB It is required in the broadcasting system. Therefore, in order to maintain strong synchronization performance in the 21 GHz band advanced satellite digital broadcasting system, it is necessary to increase the ratio of the synchronous reinforcement burst signal to the main signal and to improve the performance of the LDPC code that can be decoded at a lower C / N. It becomes.

  Therefore, the present invention superimposes the signal of the LDPC code shortened with respect to the information bits of the TMCC information on the synchronization reinforcement burst signal for improving the synchronization performance in the receiving apparatus, so that even in a very poor noise environment, It is an object of the present invention to provide a transmission device and a reception device that can achieve both synchronization performance and information transmission.

  In the present invention, since the ratio of the synchronous reinforcement burst signal to the main signal is flexibly changed and the encoding and decoding of the LDPC code is realized in a poor environment where C / N = -3 dB, Then, a shortening process is performed on an LDPC code having a high coding rate of a coding rate of 101/120 or more, and the shortened information bit + parity bit is used as a synchronization reinforcement burst signal.

  On the transmission side, in the three types of LDPC codes of coding rates 101/120, 105/120, and 109/120 having different column weights with a slot length of 44880 bits in a transmission system in which a plurality of types of digital modulation schemes are time-division multiplexed, By inserting all “0” s into predetermined information bit positions in the LDPC code, LDPC encoding is performed, and after the LDPC encoding, the encoded bit corresponding to the predetermined information bit position is discarded, thereby reducing the information bit amount required for transmission. Shorten to reduce the coding rate. In particular, information bits and parity bits of TMCC information LDPC-encoded at a reduced coding rate are phase-modulated, all of the phase-modulated signals are assigned to synchronization reinforcement burst signals, and this synchronization reinforcement burst signal is mainly used. The coding rate is reduced by intermittently inserting the signal. On the receiving side, for the three types of LDPC codes with shortened coding rates 101/120, 105/120, and 109/120, a predetermined shortened bit position is notified in advance from the transmitting side, or Alternatively, it is determined between transmission and reception, and likelihood values corresponding to a code length of 44880 bits are obtained by re-inserting likelihood values corresponding to the case where “0” is ideally transmitted at the bit position, and the three types LDPC decoding for the coding rate of is realized.

  That is, the transmission apparatus of the present invention is a transmission apparatus that performs LDPC encoding on information bits including TMCC information in a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes. An LDPC encoder for main signal that performs LDPC encoding on the LDPC, an LDPC encoder for TMCC that performs LDPC encoding on information bits including TMCC information at a predetermined encoding rate, and generates a synchronous reinforcement burst signal; A symbol sequence of the synchronous reinforcement burst signal is inserted into a symbol sequence of the main signal to be transmitted at a predetermined position to form a predetermined slot length, and a transmission frame is constructed by time-division multiplexing a plurality of slots. The TMCC LDPC encoder is a symbol for the main signal. After inserting a parameter defining the insertion rate of the symbol sequence of the synchronous reinforcement burst signal with respect to the sequence and null data corresponding to the predetermined coding rate into the information bits, and performing LDPC coding at the predetermined coding rate, It has a means for deleting and shortening the null data.

  In the transmitting apparatus of the present invention, the predetermined coding rate to be shortened is any one of 101/120, 105/120, and 109/120.

  In the transmitting apparatus of the present invention, the parameter that defines the insertion ratio of the synchronization reinforcement burst signal to the symbol sequence of the main signal is composed of a number of symbols that is a multiple of 2 with a lower limit value of 10 symbols and an upper limit value of 16. To do.

  Furthermore, the receiving apparatus of the present invention is a receiving apparatus that receives broadcast waves from a transmitting apparatus that performs LDPC encoding on information bits including TMCC information in a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes. A quadrature demodulator for demodulating the main signal and the synchronization reinforcement burst signal of the broadcast wave, and a symbol string of the synchronization reinforcement burst signal inserted at a predetermined position with respect to the symbol string of the main signal, and including TMCC information Extracting a symbol string of a synchronization-enhanced burst signal in which LDPC encoding is performed on the included information bits at a predetermined coding rate, and inserting a likelihood ratio corresponding to C / N = ∞, the likelihood of a predetermined slot length And an LDPC decoder for TMCC that performs LDPC decoding and a LDPC decoder for main signal that decodes the main signal using the decoded TMCC information.

  In the receiving apparatus of the present invention, the predetermined coding rate is any one of 101/120, 105/120, and 109/120.

  In the receiving apparatus of the present invention, the parameter that defines the insertion ratio of the symbol sequence of the synchronous reinforcement burst signal to the symbol sequence of the main signal is composed of the number of symbols that is a multiple of 2 with the lower limit value being 10 symbols and the upper limit value being 16. It is characterized by.

  According to the present invention, it is possible to improve the decoding performance of the transmission control signal while keeping the insertion rate of the synchronous reinforcement burst signal low even at a very low C / N as assumed in the 21 GHz band satellite broadcasting system.

It is a figure which shows the schematic structural example of the transmitter and receiver in an advanced satellite broadcast system. It is a figure which shows the structural example of the code rate 61/120 shortened LDPC code in an advanced satellite digital broadcasting system. It is a figure which shows the example of a modulation signal format of an advanced satellite digital broadcasting system. It is a figure which shows the example of a hierarchical transmission slot structure at the time of code length 44880 bits and QPSK / 8PSK application. It is a figure which shows the example of a hierarchical transmission slot structure which divides | segments and transmits at the time of applying LDPC code of code length 44880 bits assumed to be used with a 21 GHz band satellite broadcasting system and QPSK / 8PSK. It is a figure which shows the structural example of the transmitter of one Example by this invention, and a receiver. It is a figure which shows the operation | movement flow of the transmitter of one Example by this invention, and a receiver. It is a figure which shows the example of P = 10 and code rate 109/120 shortened LDPC code in the transmitter and receiver of one Example by this invention. It is a figure which shows the example of P = 12 and code rate 109/120 shortened LDPC code in the transmitter of one Example by this invention, and a receiver. It is a figure which shows the example of P = 14 and code rate 105/120 shortened LDPC code in the transmitter of one Example by this invention, and a receiver. It is a figure which shows the example of P = 16 and the code rate 101/120 shortened LDPC code in the transmitter and receiver of one Example by this invention. It is a figure which shows the example of the specification of the shortened LDPC code with respect to the insertion unit P of the synchronous reinforcement | strengthening burst signal in the transmitter and receiver of one Example by this invention. It is a figure which shows the example of the BPSK C / N versus bit error rate characteristic in P = 10, P = 12, P = 14, P = 16 in the transmitter and receiver of one Example by this invention.

  Hereinafter, a transmission apparatus and a reception apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  In the present invention, since the ratio of the synchronous reinforcement burst signal to the main signal is flexibly changed and the encoding and decoding of the LDPC code is realized in a poor environment where C / N = -3 dB, Then, a shortening process is performed on an LDPC code having a high coding rate of a coding rate of 101/120 or more, and the shortened TMCC information information bits + parity bits are used as a synchronization reinforcement burst signal. In the case of assuming a satellite broadcast system of 21 GHz band advanced satellite digital broadcasting system (hereinafter referred to as “21 GHz band satellite broadcast system”), description will be made assuming the use of multilevel phase modulation such as QPSK and 8PSK. Further, it is desirable that the hierarchical transmission that is also used in the current ISDB-S can be used in the 21 GHz band satellite broadcasting system.

  Therefore, a 2 × 3 = 6 slot configuration can be given as the minimum number of slots that can be used for hierarchical transmission of multiple modulation schemes. FIG. 4 shows an example of a hierarchical transmission slot configuration when an LDPC code having a code length of 48880 bits and QPSK / 8PSK are applied, assuming use in a 21 GHz band satellite broadcasting system. In FIG. 4, the slot header in each slot (Slot) is assumed to be 26 symbols, and the minimum unit of data symbols is assumed to be 187 symbols (symbol) in consideration of MPEG-2 TS transmission. QPSK transmission requires 44880/2 = 22440 symbols, and allocating 22440 × 2 symbols to 3 slots in FIG. 4 enables a QPSK and 8PSK hierarchical transmission configuration. When all LDPC codes having a code length of 48880 bits are transmitted with 8PSK modulation in the above slot configuration, 6 slots × 44880/3 = 89760 symbols are required.

  Also, referring to FIG. 4, when the minimum insertion unit of the synchronization reinforcement burst signal is “P symbol”, the total number of symbols of the synchronization reinforcement burst signal inserted in the hierarchical transmission slot is 480P symbols. The insertion rate P of the synchronization reinforcement burst signal with respect to the main signal symbol is preferably as small as possible in consideration of information efficiency, but the insertion rate of the synchronization reinforcement burst signal can be flexibly increased when a poor reception environment in the 21 GHz band is assumed. It is desirable. Therefore, assuming a C / N degradation of about 3 times in the dB value in the 21 GHz band and assuming the insertion ratio of the synchronous reinforcement burst signal of about 3 times from the conventional ratio of 3% as an upper limit guideline, 89760 × 0.09≈ It is necessary to insert a synchronous reinforcement burst signal equivalent to 8078 symbols. Further, 8078 / 480≈16.8, and when the possible value of P is limited to a multiple of 2, the assumed upper limit value of P is 16 symbols. In this case, the insertion rate of the synchronous reinforcement burst signal is about 8.6%. Here, assuming that the upper limit value of P is 16, and paying attention to an LDPC code with a coding rate of 101/120 or more, in the case of a coding rate of 101/120, the parity bit of the LDPC code = 7106 bits, the parity bit of the BCH code = 192 bits, and the sum of both falls within 480 × 16 = 7680 bits. In addition, in the case of the coding rate 101/120, the information bit length is 37774 bits, and it is possible to perform LDPC decoding at a low C / N lower than -3 dB by shortening most of the information bit length and lowering the coding rate. Become. By receiving the shortened bit position in advance on the receiving side, it becomes possible to insert a likelihood value in an ideal state with respect to the shortened bit position, and LDPC decoding can be started under more advantageous conditions. It becomes possible.

  Further, by using codes such as 105/120 and 109/120 which are high coding rates other than the coding rate 101/120, it is possible to shorten the parity bit length, that is, to reduce the synchronization reinforcement burst signal to be transmitted. Thus, the ratio of the synchronous reinforcement burst signal to the main signal can be reduced (the value of P can be reduced), and the information efficiency can be increased. As a lower limit value of P, it is necessary to transmit a minimum of 4306 bits in total, that is, a parity bit length of 4114 bits and a BCH parity bit of 192 bits at the maximum available coding rate 109/120, and a possible value of P Similarly, when it is limited to a multiple of 2, the lower limit value of P is preferably 10 symbols. In this case, the insertion rate of the synchronous reinforcement burst signal is about 5.3%.

  FIG. 5 shows an example of a hierarchical transmission slot configuration in which a slot is divided and transmitted when an LDPC code having a code length of 48880 bits and QPSK / 8PSK, which are assumed to be used in a 21 GHz band satellite broadcasting system. QPSK (occupies 120 symbols) is applied to the main signals (Data) of slots # 1 to # 3, and 8PSK (occupies 80 symbols) is applied to the main signals (Data) of slots # 4 to # 6. This is an example.

  Therefore, according to the present invention, a shortening process is performed on an LDPC code with a coding rate of 101/120 or higher, and the information bits and parity bits of the shortened TMCC information are set to a lower limit of 10 symbols and an upper limit of 16 symbols. By using it as a synchronous reinforcement burst signal consisting of a number of symbols that is a multiple of 2, even in a transmission line such as the 21 GHz band, where deterioration due to rain attenuation is large, the ratio of the synchronous reinforcement burst signal to the main signal is kept as low as possible. Decoding can be expected in an environment where N is less than −3 dB.

  Hereinafter, a transmitting apparatus and a receiving apparatus according to an embodiment of the present invention will be described more specifically.

〔Device configuration〕
FIG. 6 is a diagram illustrating a configuration example of a transmission device and a reception device according to an embodiment of the present invention. Transmitting apparatus 100 includes parameter setting section 1001, TMCC information generating section 1002, BCH encoder 1003, LDPC encoder 1004, main signal generation / main signal modulation mapping 1005, and π / 2 shift BPSK mapping 1006. And a transmission framing / orthogonal modulation unit 1007. The receiving device 300 is a device that receives a signal from the transmitting device 100 via the transmission path 200a, and includes a parameter setting unit 3001, an orthogonal demodulation unit 3002, a TMCC likelihood ratio calculation unit 3003, and a main signal signal. An LDPC decoder 3004, a NULL data likelihood ratio insertion unit 3005, a TMCC LDPC decoder 3006, and a TMCC BCH decoder 3007 are provided.

  The parameter setting unit 1001 is a functional unit that sets a value of P to be used in advance between transmission / reception devices. Since the value of P that defines the insertion ratio of the synchronization-enhanced burst signal symbol sequence to the main signal symbol sequence is a parameter related to the generation of the TMCC signal itself, it is desirable to share it in advance between the transmitting and receiving apparatuses.

  The TMCC information generation unit 1002 has a function of generating TMCC information as a transmission control signal. BCH encoding is performed on the information bits of the TMCC information, and in addition to the information bits + BCH parity bits, null data specified by the set P is added to a predetermined position according to the configuration for each coding rate in FIGS. FIG. 8 is a diagram showing an example of PPC = 10 and coding rate 109/120 shortened LDPC code in the transmitting apparatus and the receiving apparatus according to an embodiment of the present invention, and FIG. 9 is an embodiment according to the present invention. FIG. 10 is a diagram illustrating an example of an LDPC code with P = 12, coding rate 109/120 shortened in an example transmission apparatus and reception apparatus, and FIG. 10 is a diagram illustrating P = 14 in an exemplary transmission apparatus and reception apparatus according to the present invention. FIG. 11 is a diagram illustrating an example of a coding rate 105/120 shortened LDPC code, and FIG. 11 illustrates P = 16, a coding rate 101/120 shortened LDPC code in a transmitting apparatus and a receiving apparatus according to an embodiment of the present invention. It is a figure which shows the example of.

  The BCH encoder 1003 has a function of performing BCH encoding on the information bits of the generated TMCC information and adding a BCH parity bit to the information bits.

  The LDPC encoder 1004 inserts “null data” corresponding to the value of P and the coding rate into the information bits to which the BCH parity bits are added, and further “information bits + BCH parity bits + null data”. After performing LDPC coding at a predetermined coding rate (coding rate of 101/120 or higher), it has a function of generating shortened LDPC code bits in which the total number of symbols is 480P symbols by deleting null data .

  The main signal generation / main signal modulation mapping 1005 includes a main signal LDPC encoder (not shown) that generates a main signal to be transmitted and performs LDPC encoding on a main signal symbol having a predetermined slot length. It has a function of performing mapping according to a predetermined modulation process (for example, QPSK or 8PSK).

  The π / 2 shift BPSK mapping 1006 has a function of generating a synchronization-enhanced burst signal by performing mapping according to the modulation processing of π / 2 shift BPSK on the generated shortened LDPC code bits.

  The transmission framing / orthogonal modulation unit 1007 inserts a symbol sequence of the synchronization-enhanced burst signal into a complex symbol sequence of the main signal to be transmitted at a predetermined position to form a slot, and performs time division multiplexing of the plurality of slots. It has a function of constructing a transmission frame, performing orthogonal modulation of a predetermined order (for example, Mth order), and sending it out as a broadcast wave.

  Similar to the parameter setting unit 1001, the parameter setting unit 3001 is a functional unit that sets a value of P used in advance between the transmitting and receiving apparatuses. Since the value of P that defines the insertion ratio of the synchronous reinforcement burst signal is a parameter related to the generation of the TMCC signal itself, it is desirable to share it in advance between the transmitting and receiving apparatuses.

  The orthogonal demodulator 3002 has a function of establishing synchronization for a broadcast wave received from the transmission apparatus 100 using a synchronization reinforcement burst signal and demodulating according to a modulation scheme according to the Mth-order modulation.

  The likelihood ratio calculation unit 3003 for TMCC obtains the logarithmic ratio of the probability of 1 and the probability of 0 of each bit for each symbol for the demodulated synchronous reinforcement burst signal and calculates it as a log likelihood ratio. Then, a likelihood table used for likelihood calculation in LDPC decoding representing this log likelihood ratio is generated and sent to the TMCC LDPC decoder 3006.

  The main signal LDPC decoder 3004 has a function of acquiring the information bits of the TMCC information, determining the coding rate of the main signal in advance, and performing LDPC decoding on the main signal.

  The likelihood ratio insertion unit 3005 for NULL data inserts a likelihood ratio corresponding to C / N = ∞ to the null data deletion position corresponding to P that defines the insertion ratio of the synchronization reinforcement burst signal, and the likelihood for TMCC. In addition to the log likelihood ratio acquired by the frequency ratio calculation unit 3003, the likelihood ratio equivalent to 44880 bits is obtained.

  The LDPC decoder 3006 for TMCC uses the likelihood table acquired by the likelihood ratio calculation unit 3003 for TMCC, and shortens the LDPC from the likelihood ratio of the synchronous reinforcement burst signal acquired by the likelihood ratio insertion unit 3005 for NULL data. It has a function of decoding the sign bit.

  The TMCC BCH decoder 3007 deletes the null data inserted from the LDPC-decoded data for the shortened LDPC code bits, performs BCH decoding, extracts the information bits of the TMCC information, and sends them to the main signal LDPC decoder 3004 It has the function to do.

  FIG. 7 is a diagram illustrating an operation flow of the transmission apparatus and the reception apparatus according to an embodiment of the present invention. First, as step S1, the transmission apparatus 100 determines a value of P to be used in advance between transmission / reception apparatuses. Since the value of P is a parameter related to the generation of the TMCC signal itself, it is desirable to share it in advance between the transmitting and receiving apparatuses. Subsequently, in step S2, the transmitting apparatus 100 performs BCH encoding on the TMCC information bits, and in addition to the information bits + BCH parity bits, the null data designated by P set in step S1 is configured as shown in FIGS. To be added at a predetermined position.

  Subsequently, in step S3, the transmission apparatus 100 performs LDPC encoding based on a coding rate designated as P, acquires an LDPC encoded bit string, and deletes the null data inserted in step S2. Subsequently, in step S4, the transmitting apparatus 100 performs π / 2 shift BPSK modulation mapping on the shortened LDPC code bits obtained in step S3, and generates a synchronous reinforcement burst signal corresponding to the total number of symbols specified by P. Subsequently, in step S5, the transmission apparatus 100 inserts P symbols for every 187 symbols of the main signal using the main signal symbol sequence and the synchronization reinforcement burst signal acquired in step S4, and based on the transmission frame shown in FIG. A transmission signal is generated.

  In step S6, the receiving apparatus 300 receives the signal from the transmitting apparatus 100, grasps the insertion ratio and insertion position of the synchronization reinforcing burst signal on the receiving side based on P determined in advance from the received signal, and then performs synchronization reinforcement. Synchronization is established using a burst signal. After the synchronization is established, receiving apparatus 300 calculates the likelihood necessary for LDPC decoding using a synchronization reinforcement burst signal corresponding to one transmission frame (corresponding to “T” in all slots in FIG. 3) in step S7. Do. Subsequently, receiving apparatus 300 inserts a likelihood ratio corresponding to C / N = ∞ for the null data deletion position corresponding to the coding rate corresponding to P in step S8, and the likelihood ratio acquired in step S7. And a likelihood ratio equivalent to 44880 bits is obtained and LDPC decoding is performed.

  In this way, by sharing the specifications of the shortened LDPC code shown in FIG. 12 corresponding to each P and coding rate in advance between the transmitting and receiving apparatuses, the insertion rate of the synchronous reinforcement burst signal, the insertion position, and the null data The insertion and deletion positions can be grasped, and LDPC encoding and decoding can be performed with consistency between the transmitter and the receiver.

  That is, in the transmission apparatus 100 and the reception apparatus 300 of the present embodiment, it is assumed that the upper limit value Pmax of P is 16 and the lower limit value is Pmin = 10. The possible value of P is limited to a multiple of 2. Therefore, the possible values of P assumed in the present embodiment are four types of P = 10, 12, 14, and 16, and the insertion ratio of the synchronous reinforcement burst signal in P is 5.3%, 6.4%, 7.5% and 8.6%. For these four types of P, three types of LDPC codes of coding rates 101/120, 105/120, and 109/120 that can be used in the advanced satellite digital broadcasting system are shortened according to the value of P. Therefore, it is possible to realize low transmission and improve transmission performance at low C / N.

  Further, FIG. 12 shows that the shortened LDPC coding rate is very low for all Ps. Therefore, by using the shortened codes shown in FIGS. 8 to 11, it is possible to expect an improvement in LDPC decoding performance at an extremely low C / N while suppressing the insertion ratio of the synchronous reinforcement burst signal.

  Next, FIG. 13 shows C / N versus bit error rate characteristics when BPSK modulation is applied in the configurations of FIGS. From FIG. 13, it can be seen that in all cases of P = 10, 12, 14, and 16, error correction capability at C / N = −3 dB or less is shown.

  According to the present invention, LDPC decoding performance at low C / N can be improved, which is useful for a transmission apparatus and a reception apparatus that employ a multilevel digital modulation scheme.

100 Transmitting Device 200 Satellite Repeater 300 Receiving Device 1001 Parameter Setting Unit 1002 TMCC Information Generation Unit 1003 BCH Encoder 1004 LDPC Encoder 1005 Main Signal Generation / Main Signal Modulation Mapping 1006 π / 2 Shift BPSK Mapping 1007 Transmission Frame Orthogonal modulation unit 3001 Parameter setting unit 3002 Orthogonal demodulation unit 3003 Likelihood ratio calculation unit for TMCC 3004 LDPC decoder for main signal 3005 Likelihood ratio insertion unit for NULL data 3006 LDPC decoder for TMCC 3007 BCH decoder for TMCC

Claims (6)

A transmission device that performs LDPC encoding on information bits including TMCC information in a transmission system that performs time division multiplexing of a plurality of types of digital modulation schemes,
A main signal LDPC encoder that performs LDPC encoding on a main signal having a predetermined slot length;
An LDPC encoder for TMCC that performs LDPC encoding on information bits including TMCC information at a predetermined encoding rate, and generates a synchronous reinforcement burst signal;
A symbol sequence of the synchronous reinforcement burst signal is inserted into a symbol sequence of the main signal to be transmitted at a predetermined position to form a predetermined slot length, and a transmission frame is constructed by time-division multiplexing a plurality of slots. With a transmission framing / orthogonal modulation section that sends out to the outside as a broadcast wave,
The TMCC LDPC encoder inserts into the information bits a parameter that defines the insertion ratio of the symbol sequence of the synchronization-enhanced burst signal to the symbol sequence of the main signal and the predetermined coding rate into the information bits. A transmission apparatus comprising: means for deleting and shortening the null data after performing LDPC coding at a coding rate.   The transmission apparatus according to claim 1, wherein the predetermined coding rate to be subjected to the shortening is any one of 101/120, 105/120, and 109/120.   The parameter that defines the insertion ratio of the synchronous reinforcement burst signal with respect to the symbol string of the main signal includes a number of symbols that is a multiple of 2 with a lower limit of 10 symbols and an upper limit of 16 symbols. Transmitter. In a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes, a receiver that receives broadcast waves from a transmitter that performs LDPC encoding on information bits including TMCC information,
An orthogonal demodulator that demodulates the main signal of the broadcast wave and the synchronous reinforcement burst signal;
A synchronization-enhanced burst, which is a symbol sequence of a synchronization-enhanced burst signal inserted at a predetermined position with respect to the symbol sequence of the main signal, and in which information bits including TMCC information are subjected to LDPC encoding at a predetermined coding rate An LDPC decoder for TMCC that extracts a symbol sequence of a signal, inserts a likelihood ratio corresponding to C / N = ∞ to form a likelihood ratio of a predetermined slot length, and performs LDPC decoding;
A main signal LDPC decoder that decodes the main signal using the decoded TMCC information;
A receiving apparatus comprising:   The receiving apparatus according to claim 4, wherein the predetermined coding rate is one of 101/120, 105/120, and 109/120.   The parameter that defines the insertion ratio of the symbol sequence of the synchronization-enhanced burst signal with respect to the symbol sequence of the main signal comprises a number of symbols that is a multiple of 2 with a lower limit value of 10 symbols and an upper limit value of 16. 5. The receiving device according to 5.

Images