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

Abstract

A relay device (3) relays a signal between a transmission device (1), which transmits a first modulated signal that has been modulated with a first error-correcting code sequence generated by performing a first error-correcting coding process on an information sequence, and a reception device (4), which is the destination device of the first modulated signal. The relay device (3) is characterized by comprising: a first soft demodulation unit (7) that generates a first soft-demodulated sequence with confidence information corresponding to the first modulated signal; a second error-correcting coding unit (8) that performs a second error-correcting coding process on an information sequence including the first soft-demodulated sequence to generate a second error-correcting code sequence; and a second demodulation unit (9) that transmits a second modulated signal that has been modulated with the second error-correcting code sequence.

Description

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

[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.

[0002] In the field of data communications, a technique is commonly used in which data is error-correction coded at the transmitting device and then error-correction decoded at the receiving device to correct errors that occur during data transmission. As the data transmission distance increases, the number of errors that occur during transmission increases, often resulting in a decrease in transmission quality. For this reason, techniques for error-correction coding have been proposed not only for receiving devices but also for relay devices that relay data between transmitting 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 intermediate relay devices use hard-decision decoding, while only the final relay device performs error-correction coding based on soft-decision decoding, before transmitting the data to a receiving device.

[0004] Patent No. 5933862

[0005] However, with the above-mentioned conventional technology, when the transmission distance from the transmission device to the relay device is long, the probability of an error occurring increases, and there is a high possibility that the correction ability will be insufficient in error correction coding based on hard-decision decoding, which may result in a decrease in communication reliability. For example, if 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 will be long, and there is a high possibility that the correction ability will be insufficient in error correction coding based on hard-decision decoding.

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

[0007] In order to solve the above-mentioned problems and achieve the objectives, the relay device disclosed herein 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 by comprising: 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.

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

[0009] 1 is a diagram showing the configuration of a communication system according to a first embodiment; FIG. 2 is a diagram showing the functional configurations of the transmission device, relay device, and receiving device shown in FIG. 1; FIG. 3 is a diagram showing dedicated hardware for realizing each function of the transmission device, relay device, and receiving device according to the first embodiment; FIG. 4 is a diagram showing the configuration of a control circuit for realizing each function of the transmission device, relay device, and receiving device according to the first embodiment; FIG. 5 is an explanatory diagram of a second error correction coding process according to a second embodiment; and FIG. 6 is an explanatory diagram of a second modulation process according to a third embodiment.

[0010] Hereinafter, 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 with reference to the accompanying drawings.

[0011] 1 is a diagram showing the configuration of a communication system 100 according to a first embodiment. The communication system 100 includes a transmission device 1 at 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 at 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 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 receiving device 4. The transmission device 1 may transmit the modulated signal directly to the relay device 3, or may transmit it 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 performs processing such as amplifying the modulated signal and converting the transmission medium of the modulated signal, and transmits the processed signal to the relay device 3. Transmission medium conversion is, for example, processing to convert the transmission medium of the modulated signal from wireless to free-space optical communication. In 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 circuit size 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 coded sequence to the relay device 3.

[0014] The relay device 3 relays signals 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 correction code corresponding to the second error correction coding, and then decodes the signal into an error correction code corresponding to the first error correction coding.

[0016] Here, if the transmission rate from the transmission device 1 of the lunar transmitting station to the repeater device 3 of the artificial satellite orbiting the Earth is set to X Gbps, taking into account the installation location and transmission distance, the transmission rate from the repeater device 3 of the artificial satellite to the receiving device 4 of the receiving station installed on Earth can be set to 5X Gbps or more. For example, if the signal transmitted in the first section between the transmission device 1 and the repeater device 3 is modulated using BPSK (Binary Phase Shift Keying) and the signal transmitted in the second section between the repeater device 3 and the receiving device 4 is modulated using, for example, 16QAM (Quadrature Amplitude Modulation), the modulation rate in the second section can be suppressed to 1.25 times the modulation rate in the first section, and if the signal transmitted in the second section is modulated using QPSK (Quadrature Phase Shift Keying), the modulation rate in the second section can be suppressed to 2.5 times the modulation rate in the first section.

[0017] 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 encoder 5 performs a first error correction encoding 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 modulator 6. Here, the first error correction encoding process is an encoding process using a first error correction code that assumes soft-decision error correction decoding. Possible first error correction codes include low-density-parity-check (LDPC) codes, polar codes, turbo codes, convolutional codes, block codes, or combinations of the above codes. The first error correction encoder 5 adds a synchronization capture signal or the like to the first error correction code sequence and outputs it to the first modulator 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 transmit the modulated signal. The transmission medium used here may be wireless or optical.

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

[0021] The first soft demodulator 7 demodulates the modulated signal generated by the first modulator 6. The first soft demodulator 7 performs a demodulation process corresponding to the first modulation process, which generates a soft demodulation sequence by adding reliability information to the hard decision result of the modulated signal. Here, the soft demodulation process corresponding to the first modulation process and performed by the first soft demodulator 7 is referred to as the first soft demodulation process. The soft demodulation sequence generated by the first soft demodulation process is also referred to as the first soft demodulation sequence. The first soft demodulator 7 outputs the generated soft demodulation sequence to the second error correction encoder 8. For example, in the case of BPSK, a soft demodulation sequence can be generated by adding multiple bits of reliability information based on the Euclidean distance between the ideal signal point and the receiving point to a one-bit symbol indicating the hard decision result. For example, if the reliability information is represented by three bits, the soft demodulation sequence will be four bits, with one hard decision bit and three reliability bits added.

[0022] If soft-decision error correction decoding processing 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. However, the circuitry that performs soft-decision error correction decoding is large in scale and consumes a lot of power. For this reason, in the communication system 100, the relay device 3 has the function of not performing soft-decision error correction decoding, but instead using the soft-demodulation sequence output by the first soft demodulator 7 as an information sequence, further error-correcting encoding and modulation, and transmitting the information sequence to the receiving device 4.

[0023] The second error correction coding unit 8 performs a second error correction coding 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 coding unit 8 generates a second error correction code sequence by the second error correction coding 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, if the signal transmitted in the first section from the transmission device 1 to the relay device 3 is modulated using BPSK, when the first soft demodulator 7 of the relay device 3 adds 3 bits of reliability information to 1 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 larger, and therefore a transmission speed four times or more faster in the second section than in the first section is required. However, if the signal transmitted in the second section is 16QAM, the increase in the modulation speed in the second section can be suppressed to approximately the amount of 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 modulator 9 has a higher multi-level degree than the modulation method used by the first modulator 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 generation 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 demodulation unit 10. The second LLR generation 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 generation 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 generation 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 generation unit 13, and generates and outputs received data.

[0031] Here, we will explain the hardware configuration of each unit of the transmission device 1, relay device 3, and receiving device 4. The first error correction coding unit 5, first modulation unit 6, first soft demodulation unit 7, second error correction coding unit 8, second modulation unit 9, second soft demodulation unit 10, second LLR generation unit 11, second error correction soft decoding unit 12, first LLR generation unit 13, and 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 thereof.

[0033] When the processing circuit is realized by a control circuit using a CPU, the control circuit is, for example, a control circuit 91 having the configuration shown in FIG. 4 . FIG. 4 is a diagram showing the configuration of the control circuit 91 for realizing the functions 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 unit, 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 random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM), an electrically programmable programmable read-only memory (EEPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, 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 process 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 demodulating unit 7 and the second error correction encoding unit 8 of the relay device 3. When the first LLR generating unit 13 is implemented between the first soft demodulating unit 7 and the second error correction encoding unit 8 of the relay device 3, the second error correction encoding unit 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, but if it is assumed that the probability of error occurrence between the relay device 3 and the receiving device 4 is low, the receiving device 4 may perform hard decision demodulation processing, omitting the function of generating an LLR corresponding to the second error correcting code sequence, and instead generating the second error correcting code sequence directly from the result of the hard decision demodulation processing, and performing 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 encoding process on an information sequence, and a receiving device 4 that is the destination device of the first modulated signal. The relay device 3 includes 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 a second modulated signal obtained by modulating 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. Furthermore, because the relay device 3 transmits a second modulated signal modulated by performing a second error correction encoding process on an information sequence including the soft demodulation sequence without performing soft decision decoding, 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 size of the relay device 3. Furthermore, the soft-decision error correction decoding circuit not only has a large circuit size but also consumes a large amount of power. Therefore, it is possible to reduce the power consumption of the relay device 3 compared to when a soft-decision error correction decoding circuit is installed in the relay device 3.

[0038] The relay device 3 may be equipped with a first LLR generation unit 13, which is a reliability information generation unit that generates an LLR as a reliability information sequence corresponding to the first error correction code sequence from a first soft demodulation sequence for the first error correction 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] Furthermore, 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 the destination device of the first modulated signal, and a relay device 3 that relays signals 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 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 perform the following steps: 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 this 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] Furthermore, according to the first embodiment, a communication method can also be provided. This communication method includes the steps of: a transmission device 1 performing a first error correction encoding 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 demodulation sequence having reliability information corresponding to the first modulated signal; a relay device 3 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; 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] Second Embodiment In the second embodiment, the communication system 100 is basically the same as the first embodiment, except for a portion of the processing performed by the second error correction coding unit 8 of the relay device 3. For this reason, the communication system 100 according to the second embodiment will be described below using the same reference numerals as those in the first embodiment shown in FIG. 2. The following mainly describes the differences from the first embodiment.

[0045] The second error correction coding unit 8 uses the first soft demodulation sequence output by the first soft demodulation unit 7 as an information sequence and generates a second error correction code sequence by adding an error correction code parity bit. Here, the higher the error correction capability of the second error correction coding process, the greater the overhead in the second error correction code sequence. Furthermore, 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 capability according to the influence, in soft decision error correction decoding, of each bit included in the first soft demodulation sequence. Hereinafter, when referring to "the influence of each bit included in the first soft demodulation sequence" or simply "the influence," it refers to "the influence, in soft decision error correction decoding, of each bit included in the first soft demodulation sequence." Specifically, the second error correction coding unit 8 can perform second error correction coding with error correction capability according to the degree of influence by using 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] 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 hard decision bit of BPSK modulation. The four bits included in the first soft demodulation sequence 20 are referred to as the most significant bit (MSB), second bit (2ndSB), third bit (3rdSB), and least significant bit (LSB), in descending order. 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 second bit (2ndSB), third bit (3rdSB), and LSB are reliability bits indicating the reliability of the hard decision bit. Here, of the four bits constituting the first soft demodulation sequence 20, the MSB has the greatest influence, followed by the second bit (2ndSB), third bit (3rdSB), and LSB, in that order.

[0047] In the example shown in Figure 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 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 respective influences of the 2ndSB, 3rdSB, and LSB. As shown in Figure 5, the bit lengths of the parity bits 21 to 24 are, in order from longest to longest, parity bit 21, parity bit 22, parity bit 23, and parity bit 24. 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, 2nd SB, 3rd SB, and LSB, respectively, and adds parity bits 21 to 24 of different lengths to the MSB, 2nd SB, 3rd SB, and LSB, thereby generating a second error correction code sequence for each bit included in the soft demodulation sequence. However, the second error correction coding unit 8 can perform second error correction coding with an error correction capability according to the influence of each of the MSB, 2nd SB, 3rd SB, and LSB on soft decision error correction decoding, regardless of the method. For example, the second error correction coding unit 8 may perform error correction coding on the MSB and 2nd SB together, and error correction coding on the 3rd SB and LSB together. The second error correction encoding 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 second SB, the third SB, and the 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 second SB, the third SB, and the LSB, the error correction capability for the MSB can be made higher than the error correction capability for each of the second SB, the third SB, and the LSB.

[0049] As described above, according to the second embodiment, the second error correction coding unit 8 of the relay device 3 can perform second error correction coding processing with an error correction capability according to the influence of each bit included in the first soft demodulation sequence 20 on soft decision error correction decoding. This allows the relay device 3 to suppress overhead in the second error correction code sequence, for example, compared to 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., MSBs, indicating the hard decision results of the first modulated signal, and reliability bits, e.g., 2ndSB, 3rdSB, and LSBs, indicating the reliability of the hard decision bits, and the second error correction coding unit 8 can perform a second error correction coding process on the hard decision bits, which has a higher error correction capability than the reliability bits.

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

[0052] Third Embodiment In the third embodiment, the communication system 100 is basically the same as the first embodiment, except for a portion of the processing performed by the second modulation unit 9 of the relay device 3. For this reason, the communication system 100 according to the third embodiment will be described below using the same reference numerals as those in the first embodiment shown in FIG. 2. The following mainly describes the differences from the first embodiment.

[0053] In the third embodiment, the second modulation unit 9 performs multi-level modulation processing to generate second modulation symbols, which are multi-level modulation symbols, from the second error correcting 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 correcting code sequence to each bit of the multi-level modulation symbol based on the influence of each bit of the first error correcting code sequence included in the second error correcting 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: the MSB, the 2nd SB, the 3rd SB, and the LSB. 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 in 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 configured as shown in FIG. 6 to the second modulation unit 9. The second modulation unit 9 assigns each bit of the second error correcting code sequence to each bit of the second modulation symbol so that the influence of each bit of the first error correcting code sequence included in the second error correcting 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 correcting 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 the modulation method. In this case, the second modulation unit 9 assigns parity bits 21 generated for the MSB, MSB, and parity bits 22 generated for the 2nd SB, of the first soft demodulation sequence 20 to the MSB of the second modulation symbol. Also, the second modulation unit 9 assigns parity bits 23 generated for the 3rd SB, 3rd SB, and parity bits 24 generated for the LSB, 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 correcting code sequence that is consistent with the influence of the first error correcting code sequence on soft decision decoding.

[0056] As in the second embodiment, the MSB and the second SB may be subjected to the second error correction coding process together, and the third SB and the LSB may be subjected to the second error correction coding process together.

[0057] As described above, according to the third embodiment, the second modulation unit 9 performs multi-level modulation processing to generate multi-level modulation symbols from the second error correcting code sequence, and can assign each bit included in the second error correcting code sequence to each bit of the multi-level modulation symbol based on the influence of each bit of the first error correcting code sequence included in the second error correcting code sequence on 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 capability in soft decision error correction decoding of the first error correcting code sequence.

[0058] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist 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 Earth, and the relay device 3 is mounted on an artificial satellite orbiting the Earth. However, the installation locations of each device are not limited to this example. The transmission device 1, relay device 3, and receiving device 4 may all be installed on Earth, or on a planet other than the Earth. Alternatively, 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, relay device 3, and receiving device 4 are not important, but are particularly suitable when the transmission distance between the transmission device 1 and the relay device 3 is long.

[0060] REFERENCE SIGNS LIST 1 Transmission device, 2 Relay satellite, 3 Relay device, 4 Receiving device, 5 First error correction coding unit, 6 First modulation unit, 7 First soft demodulation unit, 8 Second error correction coding 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 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, the relay device comprising: 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.

2. The relay device according to claim 1, further comprising a reliability information generating unit that generates a reliability information sequence corresponding to the first error correcting code sequence from the first soft demodulation sequence for the first error correcting code sequence, wherein the second error correcting encoding unit performs a second error correcting encoding process on the reliability information sequence.

3. The relay device according to claim 1 or 2, characterized in that the second error correction encoding unit performs the second error correction encoding process with an error correction capability according to the degree of influence in soft decision error correction decoding of each bit included in the first soft demodulation series.

4. The relay device described in claim 3, characterized in that 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 the reliability of the hard decision bits, and the second error correction encoding unit performs the second error correction encoding process on the hard decision bits, which has a higher error correction capability than the reliability bits.

5. The relay device according to claim 3, characterized in that 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 the reliability of the hard decision bits, and the second error correction coding unit performs the second error correction coding process, which has a higher error correction capability for an information sequence including the hard decision bits than for an information sequence not including the hard decision bits.

6. The relay device according to claim 1 or 2, characterized in that the second modulation unit performs a multi-level modulation process to generate a multi-level modulation symbol from the second error correcting code sequence, and assigns each bit included in the second error correcting code sequence to each bit of the multi-level modulation symbol based on the influence of each bit of the first error correcting code sequence included in the second error correcting code sequence on soft decision decoding and the error occurrence probability of each bit included in the multi-level modulation symbol.

7. The repeater according to claim 1 or 2, characterized in that the repeater is mounted on a satellite.

8. The repeater device according to claim 7, characterized in that the repeater device repeats the first modulated signal transmitted from the transmission device installed on the moon to a receiving device installed on the earth.

9. A communication system comprising: 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 the destination device of the first modulated signal; and a relay device that relays signals between the transmission device and the receiving device, wherein 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 to generate a second error correction code sequence, and transmits a second modulated signal obtained by modulating the second error correction code sequence.

10. A control circuit for controlling 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, the control circuit causing the relay device to execute the following steps: 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 a second modulated signal modulated with the second error correction code sequence.

11. A storage medium storing a program for controlling 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, the program causing the relay device to execute the following steps: 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 a second modulated signal obtained by modulating the second error correction code sequence.

12. A communication method comprising the steps of: a transmission device performing a first error correction encoding process on an information sequence to generate a first error correction code sequence; a transmission device modulating the generated first error correction code sequence to generate a first modulated signal; a transmission device transmitting the first modulated signal; a relay device relaying the first modulated signal generating a first soft demodulated sequence having reliability information corresponding to the first modulated signal; a relay device performing a second error correction encoding process on an information sequence including the first soft demodulated sequence to generate a second error correction code sequence; a relay device modulating the second error correction code sequence to generate a second modulated signal; a relay device transmitting the second modulated signal; and a receiving device receiving the second modulated signal.

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