JP2012049734A - Transmitter and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmitter and a receiver which can switch reading directions of a bit interleaver in a transmission system for time division multiplex of multiple kinds of digital modulation systems.SOLUTION: A transmitter 100 comprises: an LDPC encoder 101 to perform LDPC encoding to a main signal; a two-direction-switching type bit interleaver 104 which can switch a forward-direction reading function and a reverse-direction reading function in relation to an LDPC encoding bit row depending on the received state. A receiver 400 comprises: a two-direction-switching bit deinterleaver 406 which can switch forward-direction writing and reverse-direction writing to the main signal by a row number corresponding to the modulation degree of the bit interleaving; a bit deinterleaver 407 for reading which performs bit deinterleaving by reading sequentially by the row number corresponding to the modulation degree of the bit interleaving; and an LDPC decoder 408 which performs LDPC decoding.

Description

  The present invention corresponds to the technical field of error correction codes for digital transmission for wideband transmission, and particularly relates to a transmission apparatus and a reception apparatus including a bit interleaver.

  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.

  Furthermore, one factor of transmission deterioration in the satellite transmission path is co-channel interference caused by simultaneously receiving a plurality of modulated signals in the same frequency bandwidth. As an example of co-channel interference in a satellite transmission path, multiple satellites share the same frequency bandwidth, and multiple signals modulated by different modulation schemes are received at a specific reception point at the same time. (Interfered signal) gives a signal transition different from white noise due to an interference wave (interfering signal) and causes transmission deterioration.

  In satellite digital broadcasting currently used, information correction is performed in a receiver 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 one of powerful error correction codes having 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.

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

  However, although a strong error correction code such as the LDPC code has an excellent correction capability for white noise, the correction capability for signal degradation caused by transmission line distortion other than white noise such as distortion inherent in satellite transmission lines and co-channel interference is not. Not enough. As a measure for improving transmission performance against distortion inherent in a satellite transmission path, processing for canceling distortion inherent in the transmission path, such as waveform equalization, is usually performed on the transmission side or the reception side. These are techniques for deteriorating distortion mainly by acquiring a transfer function specific to a satellite transmission path and adding its inverse characteristic to a signal in advance and afterwards.

  However, the satellite launch situation and frequency utilization situation are highly uncertain, and it is difficult to predict in advance what kind of interference signal will be added to the desired wave. Therefore, it is very difficult to specify co-channel interference as inherent transmission path distortion. As an example of co-channel interference, the constellation when the interfered signal: C is 8PSK, the interfering signal: I is 8PSK, and both are received simultaneously under the conditions of C / I = 8 dB and C / N = 30 dB. As shown in FIG.

  C represents the power of the interfered signal, I represents the power of the interfering signal, and N represents the white noise power. C / I represents the ratio of “interfered signal power” to “interfering signal power”. From FIG. 1, under the co-channel interference according to the above example, the interfered signal undergoes signal transition by the interfering signal, and 8PSK, which is usually the transition point of 8 points, undergoes 64 point transition according to the interfering signal. Become.

  In the transmission system of advanced broadband satellite digital broadcasting described in ARIB STD-B44 (hereinafter referred to as “advanced satellite broadcasting system”), as a performance improvement technique under white noise of an LDPC code, a higher-order modulation system of 8 PSK or higher is used. In addition, a bit interleaver is inserted between the LDPC encoding unit and the modulation mapper (refer to Radio Industry Association Standard: ARIB-STD B44 1.0 “Transmission System for Advanced Broadband Satellite Digital Broadcasting”).

  FIG. 2 shows an example of 8PSK coding rate 3/4 as an example of a bit interleaver in the advanced satellite broadcasting system. The bit interleaver 10 forcibly writes a bit string having a large column weight of the LDPC code by writing an LDPC encoded bit string in the vertical direction (20 in the figure) and reading it in the horizontal direction (forward direction) (in the figure 30). It becomes possible to assign the most significant bit (MSB) and the least significant bit (LSB) in the Gray code mapping.

  In the advanced satellite digital broadcasting system, a reading direction that provides the best performance under white noise is selected for each “coding rate”. For example, in the case of 8PSK coding rate 3/4, “forward reading” is selected, in which bits are read from the interleaver in ascending order.

  However, at the time of low C / I where a large interfering signal is applied to the interfered signal as shown in FIG. 1, since the modulation signal transitions according to the I level, the bit error tolerance of MBS and LSB in the Gray code mapping is improved. The difference is larger than in the case of white noise, and the reading direction that is optimal under white noise may be different in a low C / I environment.

  Accordingly, an object of the present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a transmitting apparatus and a receiving apparatus for switching the reading direction of a bit interleaver.

  The present invention inserts a bit interleaver between an LDPC code having a different column weight and a modulation symbol mapper under the same channel interference that simultaneously receives a plurality of modulation signals in the same frequency band, and reads out the bit interleaver. By changing the modulation mapping, the bit error tolerance between the modulation mapping bits is changed, and the transmission performance under the same channel interference can be improved.

  The present invention focuses on the influence of the reading direction of the bit interleaver as a technique for improving transmission performance even in a low C / I environment assuming co-channel interference. The standard of the conventional readout method in the advanced satellite digital broadcasting system was to select a readout method that obtains optimum performance under white noise. As an example, in the case of 8PSK coding rate 3/4, forward reading is selected as the reading method. This is because, in the case of Gray code 8PSK, the MSB that is the most significant bit has the weakest bit error resistance and the LSB that is the second and least significant bit has the strongest bit error resistance in the 3 bit mapping. This is because the performance under white noise is compensated for by assigning a bit string having a large column weight of an LDPC code having a different column weight to an MSB having low bit error resistance.

  FIG. 3 shows the C / N versus bit error rate characteristics obtained for each bit mapping position of the uncoded Gray code 8PSK. FIG. 3 also shows that the performance of the first bit (MSB) is inferior to the second bit and the third bit (LSB). On the other hand, FIG. 4 shows C / N vs. bit error rate characteristics obtained in a state where uncoded 8PSK is superimposed as an interference signal on uncoded 8PSK at C / I = 10 dB. Focusing on the bit error rate of 0.1 to 0.01 in FIGS. 3 and 4, it can be seen that the characteristic difference between the MSB and the LSB is large in the co-channel interference state. Therefore, in a situation where the influence of an interfering signal having a small C / I level under the same channel interference is large, it can be expected that the reading direction of the interleaver that actively utilizes the above characteristic difference will show a greater performance improvement. I understood.

  Therefore, in the present invention, in order to improve the transmission performance under co-channel interference, the reading direction is set to the opposite direction to the conventional one. As a result, it is possible to assign bits having a large column weight of the LDPC code to LSBs having high bit error resistance, and performance improvement in a low C / I environment can be expected. Further, since the interference state changes from moment to moment, the interleaving direction is switched depending on the reception state. The transmitting device of the present invention is based on the “interleaver read change flag” obtained from a specific receiving device, and the extension area (or the empty area) of the TMCC signal that can use information indicating the reading direction in the advanced satellite digital broadcasting system. The reception apparatus of the present invention performs switching of deinterleaver writing based on bit interleaver read direction information (or bit deinterleaver write direction information) obtained from the TMCC signal. It is configured as follows.

  That is, the transmission apparatus of the present invention is a transmission apparatus that switches the reading direction of a bit interleaver in a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes, and has a plurality of different column weights in a predetermined slot. An LDPC encoder that performs LDPC encoding on the main signal, and a bit length composed of the slot length / modulation order for the LDPC encoded bit string, a vertical row, and a modulation order M A two-dimensional bit interleaver having a size in the horizontal direction is configured, and writing of the bit length in the vertical direction is performed M times in the horizontal direction, and then reading of M bits from the horizontal direction is performed. When performing bit interleaving for the number of times corresponding to the bit length in the vertical direction, depending on the reception state, from the first row toward the LSB from the MSB of the slot Bidirectional switchable bit interleaver capable of switching between the function of performing forward reading to be read next and the function of performing backward reading to sequentially read from the last row from the LSB to the MSB of the slot, and the LDPC subjected to the bit interleaving A modulation symbol mapper that maps the encoded bit sequence to a complex symbol sequence according to the Mth-order modulation, and a TMCC signal that includes information indicating in which reading order, the forward reading or the backward reading, bit interleaving is performed. And a quadrature modulation unit configured to form a complex symbol sequence of the main signal subjected to bit interleaving as a transmission frame and to perform quadrature modulation according to the Mth-order modulation.

  Furthermore, the receiving apparatus of the present invention is a receiving apparatus that receives a broadcast wave from a transmitting apparatus that switches the reading direction of a bit interleaver in a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes. An orthogonal demodulator that demodulates the main signal and TMCC signal of the broadcast wave in accordance with a modulation scheme according to the next modulation, a TMCC decoder that decodes a TMCC signal that stores information indicating the reading direction of the bit interleave on the transmission side, and the transmission Bidirectional switching type bit that switches forward writing or backward writing with the number of columns corresponding to the modulation order of the bit interleaving for the main signal so as to correspond to the information indicating the reading direction of the bit interleaving on the side Read sequentially with deinterleaver and the number of columns corresponding to the modulation order of the bit interleave And a bit deinterleaver readout performing bit deinterleaving by, with respect to the bit deinterleaving the bit sequence subjected, characterized in that it comprises a LDPC decoder for performing LDPC decoding, a.

  In the receiving apparatus of the present invention, a constellation / MER evaluation unit for evaluating the modulation error ratio (MER) of the demodulated main signal, and error rate information (BER) of the received signal obtained when the LDPC decoding is performed. A reading direction change instruction generating unit that determines a reception state based on the modulation error ratio (MER) and notifies an interleaver read change flag that instructs the transmission side to change the reading direction of the bit interleave on the transmission side; Is further provided.

  In the receiving apparatus of the present invention, the reading direction change instruction generating unit may be configured to read the bit direction on the transmitting side when the MER value is equal to or greater than a predetermined value and the BER value is equal to or smaller than the predetermined value. It is determined that no change is necessary, and if not, it is determined that a change is necessary, and the interleaver read change flag is generated.

  According to the present invention, it is possible to improve transmission characteristics under co-channel interference for various modulation schemes having a plurality of amplitude levels.

It is a figure which shows the example of a received signal under the same channel interference in a prior art (interfered wave: 8PSK, interfering wave: 8PSK). It is a figure which shows operation | movement of the bit interleaver in the advanced satellite digital broadcasting system 8PSK encoding rate 89/120 in a prior art. It is a figure which shows the uncoded Gray code 8PSK C / N versus bit error rate characteristic. It is a figure which shows the uncoded Gray code 8PSK C / N vs. bit error rate characteristic (interference wave: 8PSK) in C / I = 10dB. It is an example of schematic structure of the transmitter of one Example by this invention, and a receiver. It is a block diagram of the transmitting apparatus and receiving apparatus of one Example by this invention. It is operation | movement explanatory drawing of the bidirectional | two-way switching type bit interleaver in the transmitter of one Example by this invention. It is operation | movement explanatory drawing of the bidirectional | two-way switching type bit deinterleaver in the receiver of one Example by this invention. It is an operation | movement flowchart of the transmitter of one Example by this invention, and a receiver. It is a figure which shows the C / I = 8dB LDPC coding Gray code 8PSK C / N versus bit error rate characteristic according to the interleaver reading direction (forward direction and reverse direction) in the 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.

  FIG. 5 is a schematic configuration example of a transmission apparatus and a reception apparatus according to an embodiment of the present invention. In a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes called advanced satellite digital broadcasting schemes, the transmission device 100 of this embodiment is connected via a satellite repeater 200 (hereinafter referred to as “transmission path”). The broadcast wave is transmitted to the receiving devices 300 and 400 of the present embodiment. It is assumed that the transmission path distortion occurs only in the process from the transmission side to the receiving apparatuses 300 and 400 via the transmission path. In addition, as one form of distortion generated on the satellite transmission path, co-channel interference caused by simultaneously receiving a plurality of modulated signals in the same frequency bandwidth is assumed. As an example embodiment, an advanced satellite digital broadcasting gray code 8PSK coding rate 89/120 will be described as an interfered signal, and an uncoded gray code 8PSK spread with a PN signal as an interfering signal will be described as an example. The influence of signal degradation due to co-channel interference is as shown in the constellation of FIG. 1 and the C / N versus bit error rate characteristic of FIG.

  Here, the receiving apparatus 400 evaluates the reception state to determine whether or not it is necessary to change the reading direction of the transmission side bit interleaver, and when it is determined that the change is necessary, the “interleaver read change flag” indicating that fact. Is different from the receiving apparatus 300 in that it has a means for transmitting to the transmitting apparatus 100 (described later in detail).

  FIG. 6 is a block diagram of a transmitting apparatus and a receiving apparatus according to an embodiment of the present invention. The transmitting apparatus 100 includes an LDPC encoder 101 that performs LDPC encoding on a main signal, a write bit interleaver 102, switching SWs 103-1 and 103-2, a bidirectional switching bit interleaver 104, and a TMCC. A signal generation / modulation unit 105, a modulation symbol mapper 106, and a transmission framing / orthogonal modulation unit 107 are provided. The receiving apparatus 400 receives broadcast waves from the transmitting apparatus 100 via the transmission path 201, evaluates the reception state, and sends a “bit interleaver read direction change instruction” to the transmitting apparatus 100 in a wired or wireless manner. The orthogonal demodulation unit 401, the log likelihood ratio calculation unit 402, the TMCC decoding unit 403, the constellation / MER evaluation unit 404, and the switching SW 405-1. , 405-2, a bidirectional switching bit deinterleaver 406, a read bit deinterleaver 407, an LDPC decoder 408 for performing LDPC decoding on the main signal, and a read direction change instruction generation unit 409. . In addition, although the transmission apparatus 100 and the reception apparatus 400 have shown only the component which concerns on this invention in FIG. 6, it does not intend removing the function similar to the past.

[Transmitter]
The LDPC encoder 101 has a function of performing LDPC encoding on the main signal.

  The write bit interleaver 102 writes data to a memory in which one slot is arranged with the number of columns corresponding to the modulation order (for example, Mth order) of bit interleaving for a main signal having a predetermined code length subjected to LDPC encoding. Have

  The switching SWs 103-1 and 103-2 have a function of switching the reading direction of bit interleaving in the bidirectional switching type bit interleaver 104 based on the “interleaver reading change flag” from the receiving device 400.

  The bidirectional switching type bit interleaver 104 has a function of performing forward reading sequentially reading from the first row from the left (MSB) to the right (LSB) of one slot written in the memory, and 1 written in the memory. It has a function of performing reverse-direction reading that sequentially reads from the last row from the right (LSB) to the left (MSB) of the slot, and each function is switched by switching SWs 103-1 and 103-2. As a more specific example, the bidirectional switching bit interleaver 104 inserts a two-dimensional bit interleaver having a bit length of 44,880 / M in the vertical direction and a modulation order size in the horizontal direction, 44,880 / M bit writing is performed M times in the horizontal direction, and then M bit reading from the horizontal direction is performed 44,880 / M times in the vertical direction to supply the LDPC encoded bit string to the modulation symbol mapper 106. To do.

  The TMCC signal generation / modulation unit 105 has a function of adding information indicating the reading direction of bit interleaving in the bidirectional switching bit interleaver 104 to the extension area (or vacant area) of the TMCC signal and performing π / 2 shift BPS modulation. Have.

  The modulation symbol mapper 106 has a function of mapping a digital bit string of the main signal subjected to bit interleaving to a complex symbol string according to the Mth-order modulation.

  The transmission framing / orthogonal modulation unit 107 configures a transmission frame by time-division-multiplexing a TMCC signal subjected to π / 2 shift BPS modulation and a complex symbol sequence of a main signal subjected to bit interleaving to form a transmission frame. It has a function of performing quadrature modulation according to the modulation and sending it out as a broadcast wave.

[Receiver]
The orthogonal demodulation unit 401 has a function of demodulating a broadcast wave received from the transmission apparatus 100 according to a modulation scheme according to the Mth-order modulation.

  The log likelihood ratio calculation unit 402 obtains the log ratio of the probability of 1 and the probability of 0 of each bit for each demodulated main signal symbol, and sends it to the switch SW 405-1 as the log likelihood ratio. And a function of generating a likelihood table used for likelihood calculation in LDPC decoding representing the log likelihood ratio, and storing or updating the table in a predetermined memory. The likelihood table is individually generated according to the modulation scheme and coding rate with a predetermined slot length, and the modulation scheme and coding rate information is a signal according to the TMCC information in the TMCC signal detected in advance. (Referred to as modulation scheme / coding rate selection signal).

  The TMCC decoding unit 403 has a function of demodulating the main signal and demodulating the demodulated TMCC signal. The TMCC decoding unit 403 extracts information indicating the reading direction of the bit interleave on the transmission side, and switches SW405-1 and 405- 2 has a function of controlling switching.

  The constellation / MER evaluation unit 404 has a function of evaluating the modulation error ratio (MER) of the demodulated main signal and sending the evaluation result to the reading direction change instruction generation unit 409.

  The switching SWs 405-1 and 405-2 have a function of switching the writing direction of the bit deinterleave in the bidirectional switching type bit deinterleaver 406 according to the information indicating the reading direction of the bit interleaving on the transmitting side.

  The bidirectional switching type bit deinterleaver 406 is a memory in which one slot is arranged with the number of columns corresponding to the modulation order (for example, Mth order) of the bit interleave so as to correspond to the information indicating the reading direction of the bit interleave on the transmission side. Has a function of performing forward writing or backward writing. As a more specific example, the bi-directional switching bit deinterleaver 406, on the contrary to the transmission side, writes the log likelihood ratio obtained from the received signal in the horizontal direction and M-value writing in the vertical direction to 44,880 / M. Next, 44,880 / M value reading from the vertical direction is read M times, thereby enabling data reading consistent with the transmitting side interleaver.

  The read bit deinterleaver 407 has a function of performing bit deinterleave by sequentially reading with the number of columns corresponding to the modulation order (for example, Mth order) of the bit interleave.

  The LDPC decoder 408 has a function of performing LDPC decoding on the main signal, and in particular has a function of sending error rate information (BER) of the received signal to the reading direction change instruction generation unit 409.

When the MER value is equal to or greater than a predetermined value (for example, 25 dB or more) and the BER value is equal to or less than the predetermined value (for example, 2.00 × 10 ⁻⁴ or less), the reading direction change instruction generation unit 409 If it is determined that a change in the reading direction of the bit interleave on the transmission side is not necessary, it is determined that a change is not required otherwise. It has a function of transmitting to the transmission device 100 by any wired or wireless communication method.

  The reception device 400 is configured as a device for monitoring the reception state and transmitting the information to the transmission device 100. Therefore, the constellation / MER evaluation unit 404 and the read direction change instruction generation unit 409 are configured as constituent elements. It is said. Therefore, the receiving apparatus 300 that does not need to monitor the reception state does not need to include the constellation / MER evaluation unit 404 and the reading direction change instruction generation unit 409 as components, and bidirectionally switchable bit deinterfacing from the TMCC decoded information. What is necessary is just to control the forward or reverse writing in the Lever 406.

  FIG. 7 is a diagram for explaining the operation of the bidirectional switching bit interleaver in the transmission apparatus according to the embodiment of the present invention. FIG. 8 is an explanatory diagram of the operation of the bidirectional switching bit deinterleaver in the receiving apparatus according to the embodiment of the present invention. Referring to FIG. 7, the bidirectional switching type bit interleaver 104 is a bit interleaver having both forward reading (illustrated (a)) and backward reading (illustrated (b)), and an interleaver reading change flag. Thus, for the bit string obtained from the write bit interleaver 102, the forward reading (illustration (a)) and the reverse reading (illustration (b)) are instructed in units of transmission slots having a length of 44,880 bits. . The specification of the bit interleaver is a two-dimensional interleaver in which the vertical direction is 44,880 bits / M and the horizontal direction is M bits. Here, M indicates the modulation order. In the case of 8PSK, M = 3, in the case of 16APSK, M = 4, and in the case of 32APSK, M = 5. As can be seen from FIG. 8, the bidirectional switching bit interleaver 104 and the bidirectional switching bit deinterleaver 406 are configured so as to correspond between transmission and reception, and “write” and “read” in FIGS. The direction of "" is configured to select a direction that can be matched with each other in transmission and reception.

  By superimposing the “read direction” information identified from the interleaver read flag shown in FIG. 7 on the TMCC signal and transmitting it before the main signal, the “read” and “write” directions of the interleaver in both transmission and reception And the reading direction of the bit interleaver can be changed according to the reception state, and in particular, the transmission performance at low C / I under the same channel environment can be greatly improved.

  FIG. 9 is an operation flowchart of the transmitting apparatus and the receiving apparatus according to an embodiment of the present invention. FIG. 9 illustrates an example of an operation performed by the transmission apparatus 100 and the reception apparatus 400 in cooperation. First, the transmitting apparatus 100 defines initial reading (forward reading or backward reading) as an interleaver reading direction in the transmitting apparatus 100 to be used first, sets the initial reading direction, and generates a main signal (step S1). Subsequently, when the interleaver read change flag indicates “change not required” (this flag value is referred to as “OFF”), the transmission device 100 generates a main signal in the read direction of step S1 (step S2). ). Subsequently, the transmitting apparatus 100 describes the reading direction designated in the initial setting in the TMCC signal, and transmits the TMCC signal in a frame preceding the main signal (step S3).

  Subsequently, receiving apparatus 400 first decodes the TMCC signal prior to the main signal, and uses the reading direction superimposed in step S3 as the interleaver writing direction for subsequent main signal decoding (step S4). Subsequently, the receiving apparatus 400 applies the writing direction acquired in step S4 to the deinterleaver, and decodes the main signal (step S5). Subsequently, the receiving apparatus 400 determines the presence / absence of C / I interference based on indices such as a received signal constellation, a modulation error ratio (MER) and a bit error rate (BER), and the like. The transmission side is notified of "necessity of change of interleaver reading on transmission side" by an interleaver change flag. As this notification means, a transmission / reception apparatus can be installed at the same place, and wired transmission, remote connection using a public communication network, or the like can be used. The interleaver change flag is fed back to step S2. When the flag indicates “change required” (this flag value is referred to as “ON”), the interleaver reading direction is switched in units of transmission slots. Also in this case, by describing the reading direction in the TMCC signal prior to the main signal, the receiving side can use the writing direction of the deinterleaver that is consistent with the transmitting side.

FIG. 10 is a diagram illustrating C / I = 8 dB LDPC coded Gray code 8PSK C / N vs. bit error rate characteristics for each interleaver reading direction (forward direction and reverse direction) in the receiving apparatus according to an embodiment of the present invention. Yes, as an effect of improving the transmission performance when the reading direction is changed at low C / I, the transmission characteristics of C / I = 8 dB, LDPC coded Gray code 8PSK coding rate 89/120 due to the difference in reading direction It is a computer simulation result. The LDPC code of coding rate 89/120 utilized the LDPC code prescribed | regulated by an advanced satellite broadcasting system. From FIG. 10, it can be confirmed that the reverse reading characteristic to which the present invention is applicable is improved by about 2.5 dB at a bit error rate of 10 ^{−6 with} respect to the forward reading characteristic corresponding to the conventional method. According to the present invention, it is possible to improve transmission characteristics after waveform equalization for various modulation schemes having a plurality of amplitude levels, not limited to 8PSK.

  According to the present invention, it is possible to improve transmission characteristics under the same channel interference with respect to various modulation schemes having a plurality of amplitude levels, which is useful for a transmission apparatus and a reception apparatus that employ a multilevel digital modulation scheme. is there.

DESCRIPTION OF SYMBOLS 100 Transmission apparatus 101 LDPC encoder 102 Bit interleaver for writing 103-1 and 103-2 switching SW
104 Bidirectional switching type bit interleaver 105 TMCC signal generation / modulation unit 106 Modulation symbol mapper 107 Transmission framing / orthogonal modulation unit 200 Satellite repeater 201 Transmission path 300,400 Receiver 401 Orthogonal demodulation unit 402 Log likelihood ratio calculation unit 403 TMCC decoding unit 404 Constellation / MER evaluation unit 405-1, 405-2 switching SW
406 Bidirectional switching type bit interleaver 407 Read bit deinterleaver 408 LDPC decoder 409 Read direction change instruction generation unit

Claims (4)

A transmission device that switches a reading direction of a bit interleaver in a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes,
An LDPC encoder that performs LDPC encoding on the main signal to have a plurality of different column weights in a given slot;
For the LDPC encoded bit string, a two-dimensional bit interleaver is formed in which the bit length consisting of the slot length / modulation order is a vertical row and the size of the modulation order M is a horizontal column. When performing bit interleaving for writing the bit length in the direction M times in the horizontal direction, and subsequently performing reading of M bits from the horizontal direction in the vertical direction for the number of times corresponding to the bit length, According to the reception state, a function of performing forward reading that sequentially reads from the first row from the MSB to the LSB of the slot, and a function of performing backward reading that sequentially reads from the last row from the LSB to the MSB of the slot. A switchable bidirectional switchable bit interleaver;
A modulation symbol mapper that maps the bit-interleaved LDPC encoded bit sequence to a complex symbol sequence according to the Mth-order modulation;
A TMCC signal including information indicating whether bit interleaving is performed in the reading order of the forward reading and the backward reading, and a complex symbol sequence of the main signal subjected to the bit interleaving are configured as a transmission frame, A quadrature modulation unit that performs quadrature modulation according to the Mth-order modulation;
A transmission device comprising: A receiving device that receives a broadcast wave from a transmitting device that switches a reading direction of a bit interleaver in a transmission system that time-division-multiplexes a plurality of types of digital modulation schemes,
An orthogonal demodulator that demodulates the main signal and TMCC signal of the broadcast wave in accordance with a modulation scheme according to the M-order modulation;
A TMCC decoding unit for decoding a TMCC signal storing information indicating a reading direction of bit interleaving on the transmission side;
Bidirectional switching that switches between forward writing and backward writing with the number of columns corresponding to the modulation order of the bit interleave for the main signal so as to correspond to information indicating the reading direction of bit interleaving on the transmitting side Type bit deinterleaver,
A bit deinterleaver for reading that performs bit deinterleaving by sequentially reading with the number of columns corresponding to the modulation order of the bit interleaving;
An LDPC decoder that performs LDPC decoding on the bit sequence subjected to the bit deinterleaving;
A receiving apparatus comprising: A constellation / MER evaluation unit for evaluating a modulation error ratio (MER) of the demodulated main signal;
The reception state is determined based on the error rate information (BER) of the received signal obtained when performing the LDPC decoding and the modulation error ratio (MER), and an instruction to change the reading direction of the bit interleave on the transmitting side is given. A read direction change instruction generation unit for notifying the transmission side of an interleaver read change flag;
The receiving apparatus according to claim 2, further comprising:   When the MER value is equal to or greater than the predetermined value and the BER value is equal to or smaller than the predetermined value, the read direction change instruction generation unit determines that the change of the read direction of the bit interleave on the transmitting side is unnecessary, and so The receiving apparatus according to claim 3, wherein if it is determined that a change is necessary, the interleaver read change flag is generated.