Relay device, communication system, control circuit, storage medium, and communication method

Abstract

The relay device (3) relays a signal between a transmission device (1) that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction encoding process on an information sequence, and a receiving device (4) that is a destination device of the first modulated signal, and is characterized in comprising: a first soft demodulation unit (7) that generates a first soft demodulation sequence having reliability information corresponding to the first modulated signal; a second error correction encoding unit (8) that performs a second error correction encoding process on an information sequence including the first soft demodulation sequence to generate a second error correction code sequence; and a second modulation unit (9) that transmits the second modulated signal modulated with the second error correction code sequence.

Description

[Technical field]

[0001] The present disclosure relates to a relay device, a communication system, a control circuit, a storage medium, and a communication method that perform error correction processing on communication data. [Background technology]

[0002] In the field of data communications, a technology is generally used in which data is error-correcting coded at a transmitting device and then error-correcting decoded at a receiving device to correct errors that occur during data transmission. As the data transmission distance becomes longer, the errors that occur during transmission become larger, and transmission quality often deteriorates. For this reason, a technology for error-correcting coding has been proposed not only for receiving devices, but also for relay devices that relay data between transmitting devices and receiving devices.

[0003] For example, Patent Document 1 discloses a communication system in which data that has been error-correction coded in a transmission device based on hard-decision decoding is further error-correction coded in a relay device without error-correction decoding. This communication system has multiple relay devices, and the intermediate relay devices use hard-decision decoding, while only the final relay device uses soft-decision decoding to code the data, before transmitting the data to a receiving device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5933862 Summary of the Invention [Problem to be solved by the invention]

[0005] However, according to the above conventional technology, when the transmission distance from the transmission device to the relay device is long, the probability of error occurrence increases, and there is a high possibility that the error correction coding based on hard decision decoding will not be able to correct the error, which may result in a decrease in the reliability of communication. For example, when the transmission device is installed on the moon and the relay device is mounted on an artificial satellite orbiting the earth, the transmission distance from the transmission device to the relay device becomes long, and there is a high possibility that the error correction coding based on hard decision decoding will not be able to correct the error.

[0006] The present disclosure has been made in consideration of the above, and aims to obtain a relay device that can suppress a decrease in communication reliability even when the transmission distance from a transmission device to the relay device is long. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the objective, a relay device according to the present disclosure is a relay device that relays signals between a transmission device that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction encoding process on an information sequence, and a receiving device that is the destination device of the first modulated signal, and is characterized in having a first soft demodulation unit that generates a first soft demodulation sequence having reliability information corresponding to the first modulated signal, a second error correction encoding unit that performs a second error correction encoding process on an information sequence including the first soft demodulation sequence to generate a second error correction code sequence, and a second modulation unit that transmits a second modulated signal modulated with the second error correction code sequence. Effect of the Invention

[0008] The relay device according to the present disclosure has an advantage that it is possible to suppress a decrease in communication reliability even when the transmission distance from a transmission device to the relay device is long. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a configuration of a communication system according to a first embodiment; [Diagram 2]FIG. 2 is a diagram showing the functional configurations of the transmission device, the relay device, and the receiving device shown in FIG. 1; [Diagram 3] FIG. 1 illustrates dedicated hardware for implementing the functions of a transmission device, a relay device, and a receiving device according to a first embodiment. [Figure 4] FIG. 1 is a diagram showing a configuration of a control circuit for implementing each function of a transmission device, a relay device, and a receiving device according to a first embodiment; [Diagram 5] FIG. 13 is an explanatory diagram of a second error correction coding process according to the second embodiment; [Figure 6] FIG. 13 is an explanatory diagram of a second modulation process according to the third embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A relay device, a communication system, a control circuit, a storage medium, and a communication method according to embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0011] Embodiment 1 1 is a diagram showing a configuration of a communication system 100 according to a first embodiment. The communication system 100 includes a transmission device 1 of a transmitting station installed on the moon, a relay satellite 2 orbiting the moon, a relay device 3 mounted on an artificial satellite orbiting the earth, and a receiving device 4 of a receiving station installed on the earth. A signal transmitted by the transmission device 1 is transmitted to the receiving device 4 via the relay device 3.

[0012] The transmission device 1 performs a first error correction coding on an information sequence of transmission data to generate a first error correction code sequence, and transmits a modulated signal obtained by modulating the generated first error correction code sequence to the reception device 4. The transmission device 1 may transmit the modulated signal directly to the relay device 3, or may transmit the modulated signal to the relay device 3 via a relay satellite 2. The first error correction coding is coding using a first error correction code that assumes soft decision decoding.

[0013] When the relay satellite 2 receives the modulated signal from the transmission device 1, it can perform processes such as amplifying the modulated signal and converting the transmission medium of the modulated signal, and transmit the processed signal to the relay device 3. The transmission medium conversion is, for example, a process of converting the transmission medium of the modulated signal from wireless to spatial optical communication. In the communication between the transmission device 1 and the relay satellite 2, the transmission device 1 may add an error correction code that can relatively reduce the circuit scale and power consumption and has a small processing load, in addition to the first error correction code. In this case, the relay satellite 2 transmits the decoded first error correction coding sequence to the relay device 3.

[0014] The relay device 3 relays a signal between the transmission device 1 and the receiving device 4. At this time, the relay device 3 demodulates the modulated signal generated by the transmission device 1 and generates a soft demodulation sequence by adding reliability information to the hard decision result of the modulated signal. The relay device 3 also performs second error correction encoding using the generated soft demodulation sequence as an information sequence to generate a second error correction code sequence, modulates the generated second error correction code sequence, and transmits it to the receiving device 4.

[0015] The receiving device 4 decodes the signal received via the relay device 3 into an error correcting code corresponding to the second error correcting coding, and then decodes the signal into an error correcting code corresponding to the first error correcting coding.

[0016] Here, if the transmission speed from the transmission device 1 of the transmitting station on the moon to the relay device 3 of the artificial satellite orbiting the earth is XGbps, taking into consideration the installation position and transmission distance, the transmission speed from the relay device 3 of the artificial satellite to the receiving device 4 of the receiving station installed on the earth can be 5XGbps or more. For example, if the signal transmitted in the first section between the transmission device 1 and the relay device 3 is modulated by BPSK (Binary Phase Shift Keying) and the signal transmitted in the second section between the relay device 3 and the receiving device 4 is modulated by, for example, 16QAM (Quadrature Amplitude Modulation), the modulation speed of the second section can be suppressed to 1.25 times the modulation speed of the first section, and if the signal transmitted in the second section is modulated by QPSK (Quadrature Phase Shift Keying), the modulation speed of the second section can be suppressed to 2.5 times the modulation speed of the first section.

[0017] Fig. 2 is a diagram showing the functional configurations of the transmission device 1, relay device 3, and receiving device 4 shown in Fig. 1. The transmission device 1 has a first error correction coding unit 5 and a first modulation unit 6. The relay device 3 has a first soft demodulation unit 7, a second error correction coding unit 8, and a second modulation unit 9. The receiving device 4 has a second soft demodulation unit 10, a second LLR (Log-Likelihood Ratio) generation unit 11, a second error correction soft decoding unit 12, a first LLR generation unit 13, and a first error correction soft decoding unit 14.

[0018] The first error correction coding unit 5 performs a first error correction coding process on the information sequence of the transmission data to generate a first error correction code sequence, and outputs the generated first error correction code sequence to the first modulation unit 6. Here, the first error correction coding process is a coding process using a first error correction code that is based on soft decision error correction decoding. The first error correction code may be a low-density-parity-check (LDPC) code, a polar code, a turbo code, a convolutional code, a block code, or a combination of the above codes. The first error correction coding unit 5 adds a synchronization capture signal or the like to the first error correction code sequence, and outputs it to the first modulation unit 6.

[0019] The first modulation unit 6 performs a first modulation process to modulate the first error correcting code sequence using multi-level modulation such as OOK (On-Off Keying), BPSK, QPSK, or QAM, taking into consideration the transmission distance between the transmission device 1 and the relay device 3, the state of the transmission space, and the like, and transmits the modulated signal. The transmission medium used here may be wireless or optical.

[0020] Here, it is assumed that a signal transmitted from a transmission device 1 is received directly by a relay device 3 without passing through a relay satellite 2.

[0021] The first soft demodulation unit 7 demodulates the modulated signal generated by the first modulation unit 6. The first soft demodulation unit 7 performs a soft demodulation process that corresponds to the first modulation process and generates a soft demodulation sequence in which reliability information is added to the hard decision result of the modulated signal. Here, the soft demodulation process that corresponds to the first modulation process and is performed by the first soft demodulation unit 7 is referred to as the first soft demodulation process. Also, the soft demodulation sequence generated by the first soft demodulation process is referred to as the first soft demodulation sequence. The first soft demodulation unit 7 outputs the generated soft demodulation sequence to the second error correction coding unit 8. For example, in the case of BPSK, a soft demodulation sequence can be generated in which multiple bits of reliability information based on the Euclidean distance between the ideal signal point and the receiving point are added to a 1-bit symbol indicating the hard decision result. For example, when the reliability information is represented by 3 bits, the soft demodulation sequence is 4 bits in which 3 reliability bits are added to 1 hard decision bit.

[0022] If soft decision error correction decoding is performed based on the hard decision result and reliability information included in the first soft demodulation sequence obtained by the first soft demodulator 7, it is possible to correct errors by soft decision error correction decoding even when the error rate of the hard decision result is high, but the circuit that performs soft decision error correction decoding is large in circuit scale and consumes a lot of power. Therefore, in the communication system 100, the relay device 3 has a function of further error correction coding and modulation of the soft demodulation sequence output by the first soft demodulator 7 as an information sequence and transmitting it to the receiving device 4 without performing soft decision error correction decoding.

[0023] The second error correction encoding unit 8 performs a second error correction encoding process using, as an information sequence, the first soft demodulation sequence including the hard decision result and reliability information obtained by the first soft demodulation unit 7. The second error correction encoding unit 8 generates a second error correction code sequence by the second error correction encoding process, and outputs the generated second error correction code sequence to the second modulation unit 9.

[0024] The second modulation unit 9 modulates the second error correction code sequence output by the second error correction encoding unit 8, and transmits the modulated signal to the receiving device 4. The modulation process performed by the second modulation unit 9 is referred to as second modulation process.

[0025] In this case, when the signal transmitted in the first section from the transmission device 1 to the relay device 3 is modulated by BPSK, if the first soft demodulation unit 7 of the relay device 3 adds 3 bits of reliability information to 1 bit of hard decision bit, the amount of information transmitted in the second section from the relay device 3 to the receiving device 4 becomes four times, so the transmission speed in the second section needs to be four times or more faster than that of the first section. However, if the signal transmitted in the second section is 16QAM, the modulation speed in the second section can be suppressed to an increase of about the overhead due to the second error correction coding compared to the first section. Therefore, it is preferable that the modulation method used by the second modulation unit 9 has a higher degree of multi-value than the modulation method used by the first modulation unit 6.

[0026] The second soft demodulation unit 10 of the receiving device 4 performs a second soft demodulation process, which is a soft demodulation process corresponding to the second modulation process performed by the second modulation unit 9 of the relay device 3, generates a second soft demodulation sequence having reliability information, and outputs the generated second soft demodulation sequence to the second LLR generation unit 11.

[0027] The second LLR generating unit 11 generates reliability information such as an LLR corresponding to the second error correcting code sequence from the second soft demodulation sequence output by the second soft demodulating unit 10. The second LLR generating unit 11 outputs the generated LLR to the second error correcting soft decoding unit 12.

[0028] The second error correction soft decoding unit 12 decodes the second error correction code sequence based on the LLR output by the second LLR generating unit 11, and restores a first soft demodulation sequence of the first error correction code sequence output by the first soft demodulation unit 7 of the relay device 3. The second error correction soft decoding unit 12 outputs the restored first soft demodulation sequence to the first LLR generating unit 13.

[0029] The first LLR generating unit 13 generates reliability information such as an LLR corresponding to the first error correcting code sequence from the first soft demodulation sequence output by the second error correcting soft decoding unit 12. The first LLR generating unit 13 outputs the generated LLR to the first error correcting soft decoding unit 14.

[0030] The first error correction soft decoding unit 14 performs a first error correction soft decoding process corresponding to the first error correction encoding process, thereby decoding the first error correction code sequence based on the LLR output by the first LLR generating unit 13, and generates and outputs received data.

[0031] Here, the hardware configuration of each unit of the transmission device 1, the relay device 3, and the reception device 4 will be described. The first error correction coding unit 5, the first modulation unit 6, the first soft demodulation unit 7, the second error correction coding unit 8, the second modulation unit 9, the second soft demodulation unit 10, the second LLR generation unit 11, the second error correction soft decoding unit 12, the first LLR generation unit 13, and the first error correction soft decoding unit 14 are realized by processing circuits. These processing circuits may be realized by dedicated hardware, or may be control circuits using a CPU (Central Processing Unit).

[0032] When the above processing circuits are realized by dedicated hardware, they are realized by a processing circuit 90 shown in Fig. 3. Fig. 3 is a diagram showing dedicated hardware for realizing each function of the transmission device 1, the relay device 3, and the receiving device 4 according to the first embodiment. The processing circuit 90 is a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination of these.

[0033] When the above processing circuit is realized by a control circuit using a CPU, the control circuit is, for example, a control circuit 91 having a configuration shown in FIG. 4. FIG. 4 is a diagram showing the configuration of the control circuit 91 for realizing each function of the transmission device 1, the relay device 3, and the receiving device 4 according to the first embodiment. As shown in FIG. 4, the control circuit 91 includes a processor 92 and a memory 93. The processor 92 is a CPU, and is also called an arithmetic device, a microprocessor, a microcomputer, a DSP (Digital Signal Processor), etc. The memory 93 is, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), an EEPROM (registered trademark) (Electrically EPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD (Digital Versatile Disk), etc.

[0034] When the above processing circuit is realized by the control circuit 91, it is realized by the processor 92 reading and executing a program corresponding to the processing of each component, which is stored in the memory 93. The memory 93 is also used as a temporary memory for each processing executed by the processor 92. The program executed by the processor 92 may be provided in a state stored in a storage medium, or may be provided via a communication path such as the Internet.

[0035] In the first embodiment, the receiving device 4 has the first LLR generating unit 13, but the first LLR generating unit 13 may be implemented between the first soft demodulator 7 and the second error correction encoder 8 of the relay device 3. When the first LLR generating unit 13 is implemented between the first soft demodulator 7 and the second error correction encoder 8 of the relay device 3, the second error correction encoder 8 performs the second error correction encoding process using the LLR data of the first error correction code sequence as an information sequence.

[0036] In addition, in embodiment 1, the receiving device 4 performs soft demodulation processing in the second soft demodulation unit 10. However, when the probability of error occurrence between the relay device 3 and the receiving device 4 is assumed to be low, the receiving device 4 may perform hard decision demodulation processing, omit the function of generating an LLR corresponding to the second error correcting code sequence, and directly generate the second error correcting code sequence from the result of the hard decision demodulation processing, and perform second error correction hard decision decoding to generate LLR data of the first soft demodulation sequence or the first error correcting code sequence.

[0037] As described above, according to the first embodiment, it is possible to provide a relay device 3 that relays a signal between a transmission device 1 that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction coding process on an information sequence, and a receiving device 4 that is a destination device of the first modulated signal. The relay device 3 has a first soft demodulation unit 7 that generates a first soft demodulation sequence having reliability information corresponding to the first modulated signal, a second error correction coding unit 8 that generates a second error correction code sequence by performing a second error correction coding process on an information sequence including the first soft demodulation sequence, and a second modulation unit 9 that transmits a second modulated signal modulated with the second error correction code sequence. This makes it possible to apply a first error correction code that assumes soft decision decoding between the transmission device 1 and the relay device 3. In addition, the relay device 3 transmits a second modulated signal modulated by performing a second error correction coding process on an information sequence including a soft demodulation sequence without performing a soft decision decoding process, so that the relay device 3 does not need to be equipped with a soft decision error correction decoding circuit with a large circuit scale. Therefore, even if the transmission distance between the transmission device 1 and the relay device 3 is long and the probability of error occurrence is high, it is possible to improve the reliability of communication while suppressing an increase in the circuit scale of the relay device 3. Also, the soft-decision error correction decoding circuit not only has a large circuit scale but also consumes a large amount of power. Therefore, the power consumption of the relay device 3 can be reduced compared to the case where the relay device 3 is equipped with a soft-decision error correction decoding circuit.

[0038] The relay device 3 may be equipped with a first LLR generating unit 13 which is a reliability information generating unit that generates an LLR as a reliability information sequence corresponding to the first error correcting code sequence from a first soft demodulation sequence for the first error correcting code sequence, and the second error correction encoding unit 8 may perform a second error correction encoding process on the reliability information sequence.

[0039] The relay device 3 may also be mounted on a satellite. In this case, the relay device 3 can relay the first modulated signal transmitted from the transmission device 1 installed on the moon to the receiving device 4 installed on the earth, and the satellite on which the relay device 3 is mounted can be an artificial satellite orbiting the earth.

[0040] Moreover, according to the first embodiment, it is possible to provide a communication system 100 including a transmission device 1 that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction encoding process on an information sequence, a receiving device 4 that is a destination device of the first modulated signal, and a relay device 3 that relays a signal between the transmission device 1 and the receiving device 4. In this communication system 100, the relay device 3 generates a first soft demodulation sequence having reliability information corresponding to the first modulated signal, and performs a second error correction encoding process on an information sequence including the first soft demodulation sequence without performing decoding to generate a second error correction code sequence, and transmits a second modulated signal obtained by modulating the second error correction code sequence.

[0041] Furthermore, according to the first embodiment, it is also possible to provide a control circuit 91 that controls a relay device 3 that relays a signal between a transmission device 1 that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction encoding process on an information sequence, and a receiving device 4 that is a destination device of the first modulated signal. This control circuit 91 can cause the relay device 3 to execute the steps of generating a first soft demodulation sequence having reliability information corresponding to the first modulated signal, performing a second error correction encoding process on an information sequence including the first soft demodulation sequence to generate a second error correction code sequence, and transmitting the second modulated signal obtained by modulating the second error correction code sequence.

[0042] Furthermore, according to the first embodiment, it is also possible to provide a storage medium storing a program for controlling a relay device 3 that relays a signal between a transmission device 1 that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction encoding process on an information sequence, and a receiving device 4 that is a destination device of the first modulated signal. The program stored in the storage medium can cause the relay device 3 to execute the steps of generating a first soft demodulation sequence having reliability information corresponding to the first modulated signal, performing a second error correction encoding process on an information sequence including the first soft demodulation sequence to generate a second error correction code sequence, and transmitting the second modulated signal obtained by modulating the second error correction code sequence.

[0043] Moreover, according to the first embodiment, a communication method can be provided. This communication method can include the steps of: a transmission device 1 performing a first error correction coding process on an information sequence to generate a first error correction code sequence; a transmission device 1 modulating the generated first error correction code sequence to generate a first modulated signal; a transmission device 1 transmitting the first modulated signal; a relay device 3 relaying the first modulated signal generating a first soft demodulated sequence having reliability information corresponding to the first modulated signal; a relay device 3 performing a second error correction coding process on an information sequence including the first soft demodulated sequence to generate a second error correction code sequence; a relay device 3 modulating the second error correction code sequence to generate a second modulated signal; a relay device 3 transmitting the second modulated signal; and a receiving device 4 receiving the second modulated signal.

[0044] Embodiment 2 In the second embodiment, the communication system 100 differs from the communication system 100 according to the first embodiment only in a part of the processing performed by the second error correction coding unit 8 of the relay device 3, and the basic configuration is the same as that of the first embodiment. For this reason, the communication system 100 according to the second embodiment will be described here using the same reference numerals as those in the first embodiment shown in Fig. 2. The following mainly describes the parts that are different from the first embodiment.

[0045] The second error correction coding unit 8 generates a second error correction code sequence by adding an error correction code parity bit to the first soft demodulation sequence output by the first soft demodulation unit 7 as an information sequence. Here, the higher the error correction ability of the second error correction coding process, the greater the overhead in the second error correction code sequence. Also, each bit included in the first soft demodulation sequence has a different influence, i.e., importance, in soft decision error correction decoding. Therefore, in the second embodiment, the second error correction coding unit 8 performs second error correction coding with an error correction ability according to the influence of each bit included in the first soft demodulation sequence in soft decision error correction decoding. Hereinafter, when "the influence of each bit included in the first soft demodulation sequence" or simply "the influence" is mentioned, it means "the influence of each bit included in the first soft demodulation sequence in soft decision error correction decoding". Specifically, the second error correction encoding unit 8 can perform second error correction encoding with an error correction capability according to the degree of influence by using an error correction code parity, which is a parity bit of a bit length according to the degree of influence of each bit included in the first soft demodulation series.

[0046] FIG. 5 is an explanatory diagram of the second error correction coding process according to the second embodiment. Here, the first soft demodulation sequence 20 is a soft demodulation symbol composed of four soft decision bits per one hard decision bit of BPSK modulation. The four bits included in the first soft demodulation sequence 20 are called MSB (Most Significant Bit), 2ndSB, 3rdSB, and LSB (Least Significant Bit) in order from the most significant bit. For example, the MSB of the first soft demodulation sequence 20 is a hard decision bit indicating the hard decision result of the modulated signal generated by the first modulation process, and the 2ndSB, 3rdSB, and LSB are reliability bits indicating the reliability of the hard decision bit. Here, among the four bits constituting the first soft demodulation sequence 20, the MSB has the greatest influence, followed by the 2ndSB, 3rdSB, and LSB in order of decreasing influence.

[0047] In the example shown in FIG. 5, the second error correction coding unit 8 performs second error correction coding with different error correction capabilities on the MSB, 2ndSB, 3rdSB, and LSB. That is, the parity bit 21 with the highest error correction capability is added to the MSB, which has the greatest influence on the soft decision error correction decoding, and the parity bit 22 generated for the 2ndSB, the parity bit 23 generated for the 3rdSB, and the parity bit 24 generated for the LSB are added according to the influence of each of the 2ndSB, 3rdSB, and LSB. The bit lengths of the parity bits 21 to 24 are, in order from longest to longest, the parity bit 21, the parity bit 22, the parity bit 23, and the parity bit 24, as shown in FIG. 5. As a result, the second error correction coding unit 8 performs second error correction coding with higher error correction capability on the 2ndSB, 3rdSB, and LSB, which are reliability bits, than on the MSB, which is a hard decision bit.

[0048] In the second embodiment, the second error correction coding unit 8 performs second error correction coding with different error correction capabilities on the MSB, 2ndSB, 3rdSB, and LSB, respectively, and generates a second error correction code sequence for each bit included in the soft demodulation sequence by adding parity bits 21 to 24 with different lengths to the MSB, 2ndSB, 3rdSB, and LSB, respectively. However, as long as the second error correction coding unit 8 can perform second error correction coding with error correction capabilities according to the influence of each of the MSB, 2ndSB, 3rdSB, and LSB in the soft decision error correction decoding, the method is not important. For example, the second error correction coding unit 8 may perform error correction coding on the MSB and 2ndSB together, and error correction coding on the 3rdSB and LSB together. The second error correction coding unit 8 may also add a parity bit to the MSB to form one second error correction code sequence, and add parity bits collectively to the 2ndSB, 3rdSB, and LSB to form one second error correction code sequence. In this case, by making the bit length of the parity bit added to the MSB the same as the bit length of the parity bit added collectively to the 2ndSB, 3rdSB, and LSB, the error correction capability for the MSB can be made higher than the error correction capability for each of the 2ndSB, 3rdSB, and LSB.

[0049] As described above, according to the second embodiment, the second error correction coding unit 8 of the relay device 3 can perform the second error correction coding process with an error correction capability according to the influence of each bit included in the first soft demodulation sequence 20 on the soft decision error correction decoding. This makes it possible for the relay device 3 to suppress the overhead in the second error correction code sequence, for example, by imparting the error correction capability required for the MSB to all bits so that all bits included in the first soft demodulation sequence 20 have high error correction capability.

[0050] Furthermore, according to the second embodiment, the first soft demodulation unit 7 generates a first soft demodulation sequence 20 including hard decision bits, e.g., the MSB, indicating the hard decision result of the first modulated signal, and reliability bits, e.g., the 2ndSB, 3rdSB and LSB, indicating the reliability of the hard decision bits, and the second error correction encoding unit 8 can perform a second error correction encoding process on the hard decision bits, which has a higher error correction capability than the reliability bits.

[0051] Furthermore, when the first soft demodulation unit 7 generates a first soft demodulation sequence 20 including hard decision bits indicating a hard decision result of the first modulated signal and reliability bits indicating the reliability of the hard decision bits, and the second error correction coding unit 8 performs the second error correction coding process on multiple bits together, the second error correction coding unit 8 can perform the second error correction coding process with higher error correction capability on an information sequence including hard decision bits than on an information sequence not including hard decision bits.

[0052] Embodiment 3 In the third embodiment, the communication system 100 differs from the communication system 100 according to the first embodiment only in a part of the processing performed by the second modulation unit 9 of the relay device 3, and the basic configuration is the same as that of the first embodiment. For this reason, the communication system 100 according to the third embodiment will be described here using the same reference numerals as those in the first embodiment shown in Fig. 2. The following mainly describes the parts that differ from the first embodiment.

[0053] In the third embodiment, the second modulation unit 9 performs multi-level modulation processing to generate a second modulation symbol, which is a multi-level modulation symbol, from the second error correction code sequence. For example, the modulation method used by the second modulation unit 9 is multi-level modulation such as QAM. The second modulation unit 9 assigns each bit included in the second error correction code sequence to each bit of the multi-level modulation symbol based on the influence of each bit of the first error correction code sequence included in the second error correction code sequence on soft decision decoding and the error occurrence probability of each bit included in the second modulation symbol.

[0054] FIG. 6 is an explanatory diagram of the second modulation process according to the third embodiment. The first soft demodulation sequence 20, which is a soft demodulation sequence of the first error correction code sequence output by the first soft demodulation unit 7, is a soft demodulation symbol consisting of four bits, MSB, 2ndSB, 3rdSB, and LSB, and the second error correction coding unit 8 generates a second error correction code sequence by adding parity bits 21 to 24 to the first soft demodulation sequence 20. Here, the configuration of the second error correction code sequence is the same as that of the second embodiment, but the bit length, i.e., the error correction capability, of the parity bits 21 to 24 is the same for each bit. The second error correction coding unit 8 outputs the second error correction code sequence having the configuration shown in FIG. 6 to the second modulation unit 9. The second modulation unit 9 assigns each bit of the second error correction code sequence to each bit of the second modulation symbol so that the influence of each bit of the first error correction code sequence included in the second error correction code sequence in soft decision error correction decoding corresponds to the error occurrence probability of each bit in the second modulation symbol. Specifically, the second modulation unit 9 performs mapping so that the bit with a higher influence of the second error correction code sequence is assigned to the bit with a lower error occurrence probability in the second modulation symbol. Specifically, the second modulation unit 9 considers the influence of the parity bits 21 to 24 to be the same as the influence of each bit of the first soft demodulation sequence 20 corresponding to each parity bit 21 to 24.

[0055] Here, the second modulation unit 9 uses 16QAM as a modulation method. In this case, the second modulation unit 9 assigns the MSB, the parity bit 21 generated for the MSB, the 2ndSB, and the parity bit 22 generated for the 2ndSB of the first soft demodulation sequence 20 to the MSB of the second modulation symbol. In addition, the second modulation unit 9 assigns the 3rdSB, the parity bit 23 generated for the 3rdSB, the LSB, and the parity bit 24 generated for the LSB of the first soft demodulation sequence 20 to the LSB of the second modulation symbol. This makes it possible to generate a second error correction code sequence that is consistent with the influence of the first error correction code sequence in soft decision decoding.

[0056] As in the second embodiment, the MSB and 2ndSB may be subjected to the second error correction encoding process together, and the 3rdSB and LSB may be subjected to the second error correction encoding process together.

[0057] As described above, according to the third embodiment, the second modulation unit 9 performs a multi-level modulation process to generate a multi-level modulation symbol from the second error correction code sequence, and can assign each bit included in the second error correction code sequence to each bit of the multi-level modulation symbol based on the influence of each bit of the first error correction code sequence included in the second error correction code sequence in soft decision decoding and the error occurrence probability of each bit included in the multi-level modulation symbol. This makes it possible to simplify the configuration of the second error correction encoding unit 8 and to improve the error correction ability in the soft decision error correction decoding of the first error correction code sequence.

[0058] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or the embodiments may be combined with each other. Also, parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0059] In the above embodiment, the transmission device 1 is installed on the moon, which is a satellite of the earth, the receiving device 4 is installed on the earth, and the relay device 3 is mounted on an artificial satellite orbiting the earth, but the installation locations of each device are not limited to this example. The transmission device 1, the relay device 3, and the receiving device 4 may all be installed on the earth, or on a planet other than the earth. Also, the receiving device 4 may be installed on a planet other than the earth, the transmission device 1 may be installed on a satellite of the planet on which the receiving device 4 is installed, and the relay device 3 may be mounted on an artificial satellite orbiting the planet on which the receiving device 4 is installed. The installation locations of the transmission device 1, the relay device 3, and the receiving device 4 do not matter, but are particularly suitable when the transmission distance between the transmission device 1 and the relay device 3 is long. [Explanation of symbols]

[0060] 1 transmission device, 2 relay satellite, 3 relay device, 4 receiving device, 5 first error correction encoding unit, 6 first modulation unit, 7 first soft demodulation unit, 8 second error correction encoding unit, 9 second modulation unit, 10 second soft demodulation unit, 11 second LLR generation unit, 12 second error correction soft decoding unit, 13 first LLR generation unit, 14 first error correction soft decoding unit, 20 first soft demodulation sequence, 21, 22, 23, 24 parity bits, 90 processing circuit, 91 control circuit, 92 processor, 93 memory, 100 communication system.

Claims

1. A relay device that relays a signal between a transmission device that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction encoding process on an information sequence, and a receiving device that is a destination device of the first modulated signal, a first soft demodulation unit that generates a first soft demodulation sequence having reliability information corresponding to the first modulated signal; a second error correction encoding unit that performs a second error correction encoding process on an information sequence including the first soft demodulation sequence to generate a second error correction code sequence; a second modulation unit that transmits a second modulated signal obtained by modulating the second error correction code sequence; A relay device comprising:

2. a reliability information generating unit that generates, from the first soft demodulation sequence for the first error correcting code sequence, a reliability information sequence corresponding to the first error correcting code sequence; Further equipped with The second error correction coding unit performs a second error correction coding process on the reliability information sequence.

2. The relay device according to claim 1 .

3. The second error correction encoding unit performs the second error correction encoding process with an error correction capability according to the degree of influence of each bit included in the first soft demodulation sequence in soft decision error correction decoding.

3. The relay device according to claim 1, wherein the relay device is a relay unit.

4. the first soft demodulation unit generates the first soft demodulation sequence including hard decision bits indicating a hard decision result of the first modulated signal and reliability bits indicating reliability of the hard decision bits; The second error correction encoding unit performs the second error correction encoding process on the hard decision bits, the second error correction encoding process having a higher error correction capability than that on the reliability bits.

4. The relay device according to claim 3.

5. the first soft demodulation unit generates the first soft demodulation sequence including hard decision bits indicating a hard decision result of the first modulated signal and reliability bits indicating reliability of the hard decision bits; The second error correction encoding unit performs the second error correction encoding process with a higher error correction capability on an information sequence including the hard decision bits than on an information sequence not including the hard decision bits.

4. The relay device according to claim 3.

6. The second modulation unit performs a multi-level modulation process to generate a multi-level modulation symbol from the second error correction code sequence, and assigns each bit included in the second error correction code sequence to each bit of the multi-level modulation symbol based on a degree of influence of each bit of the first error correction code sequence included in the second error correction code sequence in soft decision decoding and an error occurrence probability of each bit included in the multi-level modulation symbol.

3. The relay device according to claim 1, wherein the relay device is a relay unit.

7. The relay device is mounted on a satellite.

3. The relay device according to claim 1, wherein the relay device is a relay unit.

8. The relay device relays the first modulated signal transmitted from the transmission device installed on the moon to a receiving device installed on the earth.

8. The relay device according to claim 7,

9. a transmission device that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction encoding process on an information sequence; a receiving device that is a destination device for the first modulated signal; a relay device that relays signals between the transmission device and the reception device; Equipped with The relay device generates a first soft demodulation sequence having reliability information corresponding to the first modulated signal, performs a second error correction encoding process on an information sequence including the first soft demodulation sequence without performing decoding, generates a second error correction code sequence, and transmits a second modulated signal obtained by modulating the second error correction code sequence. A communication system comprising:

10. A control circuit for controlling a relay device that relays a signal between a transmission device that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction encoding process on an information sequence, and a receiving device that is a destination device of the first modulated signal, comprising: generating a first soft demodulation sequence having reliability information corresponding to the first modulated signal; performing a second error correction encoding process on an information sequence including the first soft demodulation sequence to generate a second error correction code sequence; transmitting a second modulated signal obtained by modulating the second error correcting code sequence; A control circuit that causes the relay device to execute the above.

11. A storage medium storing a program for controlling a relay device that relays a signal between a transmission device that transmits a first modulated signal obtained by modulating a first error correction code sequence generated by performing a first error correction coding process on an information sequence, and a receiving device that is a destination device of the first modulated signal, the program comprising: generating a first soft demodulation sequence having reliability information corresponding to the first modulated signal; performing a second error correction encoding process on an information sequence including the first soft demodulation sequence to generate a second error correction code sequence; transmitting a second modulated signal obtained by modulating the second error correcting code sequence; A storage medium for causing the relay device to execute the above.

12. A transmission device performs a first error correction encoding process on an information sequence to generate a first error correction code sequence; a step of the transmission device modulating the generated first error correction code sequence to generate a first modulated signal; the transmission device transmitting the first modulated signal; A relay device that relays the first modulated signal generates a first soft demodulation sequence having reliability information corresponding to the first modulated signal; the relay device performing a second error correction encoding process on an information sequence including the first soft demodulation sequence to generate a second error correction code sequence; the relay device modulating the second error correcting code sequence to generate a second modulated signal; the relay device transmitting the second modulated signal; receiving the second modulated signal by a receiving device; A communication method comprising:

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