Satellite optical communication system

Abstract

In a transmission terminal (1), a control unit (101) selects number of parallelizations, and a parallelization unit (103) parallelizes data according to the number of parallelizations selected by the control unit (101); and in a reception terminal (2), a demodulation unit (205) and a demapping unit (206) perform processing according to the number of parallelizations.

Description

Satellite optical communication system

[0001] This disclosure relates to a satellite optical communication system.

[0002] In inter-satellite communications, optical communication, which offers higher capacity compared to RF communication, is being increasingly adopted. Similar progress is expected in communications between satellites and ground stations. Polarization multiplexing and wavelength division multiplexing are used for high-capacity data transmission.

[0003] In order to achieve high-capacity data transmission, it is necessary to amplify the signal in the transmitting optical amplifier and transmit it with sufficient optical output. However, a single optical amplifier may not be able to provide sufficient optical output.

[0004] In such cases, as shown in Figure 32, for example, a method has been proposed in which signals with different wavelengths and polarizations are divided into multiple groups, amplified in parallel by the optical amplification unit 17, and transmitted in parallel from the optical system 18 (see, for example, Patent Document 1). In Figure 32, reference numeral 11 indicates the error correction coding unit, reference numeral 12 indicates the parallelization unit, reference numeral 13 indicates the optical modulation unit, reference numeral 14 indicates the polarization conversion unit, reference numeral 15 indicates the polarization multiplexing unit (PBC), and reference numeral 16 indicates the wavelength multiplexing unit.

[0005] As shown in the example in Figure 32, when reading data stored in memory and transmitting it as an 8-parallel signal, four wavelengths (λ) are used. １ ~λ ４ This can be achieved by utilizing two polarizations. In the example shown in Figure 32, the optical modulation unit 13 outputs right-hand circular polarization, and the polarization conversion unit 14 converts it to left-hand circular polarization.

[0006] International Publication No. 2021 / 245938

[0007] On the other hand, in communication between satellites and ground stations, the power budget may not be met and communication may not be possible depending on the performance of the optics at the ground station, atmospheric conditions or weather, or the elevation angle of the satellite as seen from the ground station. In the case of communication between low-Earth orbit satellites and ground stations, communication is only possible for a short time while the low-Earth orbit satellite passes over the ground station, and multiple ground stations are necessary to send larger amounts of data to the ground. However, if the performance of some ground stations is insufficient, the power budget may not be met and communication may not be possible.

[0008] This disclosure was made to solve the above-mentioned problems and aims to provide a satellite optical communication system that can avoid situations where communication is impossible due to an insufficient power budget.

[0009] The satellite optical communication system according to this disclosure comprises a transmitting terminal and a plurality of receiving terminals, the transmitting terminal comprising: a control unit for selecting the number of parallelizations; an error correction coding unit for error-correcting and coding the data; a parallelization unit for parallelizing the data after error-correction coding by the error correction coding unit according to the number of parallelizations selected by the control unit; an optical modulation unit provided one set per wavelength, which converts the corresponding data parallelized by the parallelization unit into an optical signal of the corresponding wavelength; a polarization conversion unit provided for each wavelength, which converts the polarization of the optical signal obtained by one of the corresponding optical modulation units into orthogonal polarizations; a polarization combining unit provided for each wavelength, which polarizes and combines the optical signal obtained by the other corresponding optical modulation unit and the optical signal converted by the corresponding polarization conversion unit; and a number of units provided for each group less than the number of wavelengths. The device comprises an optical amplification unit that amplifies a signal based on the polarization-multiplexed signal by a corresponding polarization-multiplexing unit, and an optical system provided for each group that transmits the amplified signal by the corresponding optical amplification unit to a receiving terminal, wherein the receiving terminal comprises a second optical system that collects the optical signal transmitted by the transmitting terminal, a second optical amplification unit that amplifies the optical signal collected by the second optical system, a detection unit provided for each wavelength that converts the optical signal based on the optically amplified optical signal by the second optical amplification unit into an electrical signal, a demodulation unit provided for each wavelength that demodulates the electrical signal obtained by the corresponding detection unit according to the number of parallelizations, a demapping unit that demmaps the demodulated signal by a plurality of demodulation units according to the number of parallelizations, and a decoding unit that decodes the demmapped signal by the demapping unit.

[0010] According to this disclosure, the above configuration makes it possible to avoid a situation where communication is impossible due to an insufficient power budget.

[0011] This figure shows an example configuration of a satellite optical communication system according to Embodiment 1. This figure shows an example configuration of a transmitting terminal according to Embodiment 1. This figure shows an example configuration of a receiving terminal according to Embodiment 1. This figure shows an example configuration of the detection and demodulation unit in Embodiment 1 when the modulation method is QAM. This figure shows an example configuration of the detection and demodulation unit in Embodiment 1 when the modulation method is intensity modulation. This figure shows another example configuration of the detection and demodulation unit in Embodiment 1 when the modulation method is intensity modulation. This figure shows an example configuration of the parallelization unit in Embodiment 1. This figure shows the detection and demodulation unit operating when the modulation method is QAM and 4 parallelization is performed. This figure shows an example configuration of a transmitting terminal according to Embodiment 2. This figure shows an example configuration of the detection and demodulation unit in Embodiment 2 when the modulation method is QAM. This figure shows an example configuration of the detection and demodulation unit in Embodiment 2 when the modulation method is intensity modulation. This figure shows another example configuration of the detection and demodulation unit in Embodiment 2 when the modulation method is intensity modulation. This figure shows an example configuration of a transmitting terminal according to Embodiment 3. This figure shows an example configuration of a receiving terminal according to Embodiment 3. This figure shows an example of state transitions for a receiving terminal according to Embodiment 3. This is a diagram showing an example configuration of a receiving terminal according to Embodiment 4. This is a diagram showing an example of state transitions for a receiving terminal according to Embodiment 4. This is a diagram showing an example configuration of a receiving terminal according to Embodiment 5. This is a diagram showing an example of state transitions for a receiving terminal according to Embodiment 5. This is a diagram showing an example of hardware configuration of a transmitting terminal according to Embodiments 1 and 2. This is a diagram showing an example of hardware configuration of a receiving terminal according to Embodiments 1 and 2. This is a diagram showing another example of hardware configuration of a transmitting terminal according to Embodiments 1 and 2. This is a diagram showing another example of hardware configuration of a receiving terminal according to Embodiments 1 and 2. This is a flowchart showing an example of operation of the processing circuit of a transmitting terminal according to Embodiments 1 and 2. This is a flowchart showing an example of operation of the processing circuit of a receiving diagram showing an example of hardware configuration of a transmitting terminal according to Embodiments 3 to 5. This is a diagram showing an example of hardware configuration of a receiving terminal according to Embodiments 3 to 5.This figure shows another hardware configuration example of the transmitting terminal according to Embodiments 3 to 5. This figure shows another hardware configuration example of the receiving terminal according to Embodiments 3 to 5. This flowchart shows an example of the operation of the processing circuit of the transmitting terminal according to Embodiments 3 to 5. This flowchart shows an example of the operation of the processing circuit of the receiving terminal according to Embodiments 3 to 5. This figure shows a conventional example of the transmitting terminal configuration.

[0012] The embodiments will be described in detail below with reference to the drawings. Embodiment 1. Figure 1 is a diagram showing an example of the configuration of a satellite optical communication system according to Embodiment 1. The satellite optical communication system is a wavelength division multiplexing satellite optical communication system. This satellite optical communication system includes, for example, a transmitting terminal 1 and a plurality of receiving terminals 2, as shown in Figure 1. In the example in Figure 1, two receiving terminals 2 are shown, but there may be three or more receiving terminals 2. Here, the explanation will be given as an example in which the transmitting terminal 1 is mounted on a satellite and the receiving terminals 2 are installed at multiple ground stations.

[0013] Figure 2 shows an example of the configuration of a transmitting terminal 1 according to Embodiment 1. As shown in Figure 2, for example, the transmitting terminal 1 includes a control unit 101, an error correction coding unit 102, a parallelization unit 103, an optical modulation unit 104, a polarization conversion unit 105, a polarization multiplexing unit (PBC) 106, a wavelength multiplexing unit 107, an optical amplification unit 108, and an optical system 109.

[0014] The control unit 101 selects the number of parallelizations in the parallelization unit 103. Here, the number of parallelizations that can be received by the receiving terminal 2 differs for each receiving terminal 2. Therefore, the control unit 101 selects the number of parallelizations in the parallelization unit 103 to match the number of parallelizations that can be received by the receiving terminal 2 that is the target of communication. In this case, for example, the control unit 101 selects the number of parallelizations specified by the user.

[0015] The error correction coding unit 102 performs error correction coding on the data to be transmitted. In this process, for example, the error correction coding unit 102 performs forward error correction coding (FEC).

[0016] The parallelization unit 103 parallelizes the data after error correction coding by the error correction coding unit 102. In this case, the parallelization unit 103 performs parallelization using the number of parallelizations selected by the control unit 101. In the example in Figure 2, the parallelization unit 103 is shown to be capable of 8 parallelizations.

[0017] Here, we assume that the satellite optical communication system handles 4 wavelengths, 2 polarizations, and 2 groups of wavelengths. In this case, if the control unit 101 selects 8-parallelization, the parallelization unit 103 divides the error-corrected encoded data into 8 distinct data sets and outputs each of the divided data sets to the corresponding optical modulation unit 104. If the control unit 101 selects 4-parallelization, the parallelization unit 103 divides the error-corrected encoded data into 4 distinct data sets and outputs each of the divided data sets to the corresponding optical modulation unit 104 on a wavelength basis. In this case, the same data is input to the optical modulation unit 104 corresponding to the same wavelength. If the control unit 101 selects 2-parallelization, the parallelization unit 103 divides the error-corrected encoded data into 2 distinct data sets and outputs each of the divided data sets to the corresponding optical modulation unit 104 on a group basis. In this case, the same data is input to the optical modulation unit 104 corresponding to the same group. Furthermore, if the control unit 101 selects the same data transmission, the parallelization unit 103 does not split the error-corrected encoded data, but outputs the data to each optical modulation unit 104. In this case, the same data is input to each optical modulation unit 104.

[0018] The optical modulation units 104 are provided in sets of 2 × N, one set for each wavelength, where N is the number of wavelengths. These optical modulation units 104 convert the corresponding data, parallelized by the parallelization unit 103, into optical signals of the corresponding wavelengths. In this process, the optical modulation units 104 map the data to symbols, for example, QPSK or OOK, perform waveform shaping, and then modulate the light of the corresponding wavelength to generate the optical signal. In the example in Figure 2, the wavelength is λ １ ~λ ４ These are the four points.

[0019] There are N polarization conversion units 105, one for each wavelength. Each polarization conversion unit 105 converts the polarization of the optical signal obtained by the corresponding optical modulation unit 104 into orthogonal polarization. For example, if the optical signal output by the optical modulation unit 104 is right-hand circularly polarized, the polarization conversion by the polarization conversion unit 105 results in a left-hand circularly polarized optical signal.

[0020] There are N polarization multiplexing units 106, one for each wavelength. These polarization multiplexing units 106 obtain a polarization multiplexed signal by polarization multiplexing the optical signal obtained by the other optical modulation unit 104 and the optical signal converted by the corresponding polarization conversion unit 105.

[0021] There is one wavelength multiplexer 107 for each group, i.e., M in total. M is the number of groups and is smaller than the number of wavelengths (N). This wavelength multiplexer 107 combines the polarization multiplexed signals obtained by the corresponding polarization multiplexer 106. In the example in Figure 2, there are 2 groups.

[0022] There is one optical amplification unit 108 for each of the above groups, i.e., M units in total. Each optical amplification unit 108 amplifies the signal after it has been combined by the corresponding wavelength multiplexing unit 107.

[0023] There is one optical system 109 for each of the above groups, i.e., M systems in total. This optical system 109 transmits the signal amplified by the corresponding optical amplification unit 108 to the receiving terminal 2.

[0024] Figure 3 shows an example of the configuration of a receiving terminal 2 according to Embodiment 1. The receiving terminal 2 includes, for example, an optical system (second optical system) 201, an optical amplification unit (second optical amplification unit) 202, a wavelength demultiplexer 203, a detection unit 204, a demodulation unit 205, a demapping unit 206, and a decoding unit 207, as shown in Figure 3.

[0025] The optical system 201 collects the optical signal transmitted by the transmitting terminal 1.

[0026] The optical amplification unit 202 amplifies the optical signal focused by the optical system 201.

[0027] The wavelength demultiplexing unit 203 demultiplexes the signal after optical amplification by the optical amplification unit 202 for each of the above wavelengths. In the example of FIG. 3, the wavelengths are λ １ to λ ４ .

[0028] The detection unit 204 is provided one by one for each of the above wavelengths, that is, N are provided. This detection unit 204 converts the optical signal of the corresponding wavelength obtained by the wavelength demultiplexing unit 203 into an electrical signal.

[0029] The demodulation unit 205 is provided one by one for each of the above wavelengths, that is, N are provided. This demodulation unit 205 demodulates the electrical signal obtained by the corresponding detection unit 204 to obtain symbols.

[0030] The demapping unit 206 demaps the symbols which are the signals after demodulation by the plurality of demodulation units 205.

[0031] Note that the demodulation unit 205 and the demapping unit 206 perform the above processes according to the parallelization number that can be received by the receiving terminal 2.

[0032] The decoding unit 207 decodes the signal after demapping by the demapping unit 206. At this time, for example, the decoding unit 207 performs decoding of a forward error correction code (FEC).

[0033] Next, a configuration example of the detection unit 204 and the demodulation unit 205 in Embodiment 1 will be described. First, when the modulation method is QAM such as QPSK, that is, when the optical signal obtained by the optical modulation unit 104 is a QAM signal, a configuration example of the detection unit 204 and the demodulation unit 205 is shown in FIG. 4. In this FIG. 4, the detection unit 204 has a local light source 2041 and a polarization multiplexed coherent detection unit 2042, and the demodulation unit 205 has an equalization unit 2051 and a phase compensation unit 2052.

[0034] The local light source 2041 inputs local light of the same wavelength as the optical signal input to the polarization multiplexed coherent detection unit 2042 to the polarization multiplexed coherent detection unit 2042.

[0035] Note that, in FIG. 4, the case where the local light source 2041 is provided inside the detection unit 204 is shown. However, the present invention is not limited to this, and the local light source 2041 may be provided outside the detection unit 204.

[0036] The polarization multiplex coherent detection unit 2042 converts the optical signal of the corresponding wavelength obtained by the wavelength demultiplexing unit 203 into electrical signals of the I component and the Q component of two orthogonal polarizations by interfering with the local light input by the local light source 2041.

[0037] The equalization unit 2051 compensates for the waveform distortion due to the frequency characteristics of analog components and the like for the electrical signal obtained by the corresponding polarization multiplex coherent detection unit 2042, and extracts the electrical signal of a specific polarization.

[0038] The phase compensation unit 2052 is provided one by one for each polarization, that is, two are provided. This phase compensation unit 2052 compensates for the phase variation depending on the phase noise of the light sources on the transmission side and the reception side, that is, compensates for the phase difference, for the electrical signal of the corresponding polarization extracted by the equalization unit 2051.

[0039] Here, when the parallelization number is 2×N, the equalization unit 2051 compensates for the waveform distortion for the electrical signal obtained by the corresponding polarization multiplex coherent detection unit 2042, and extracts the electrical signals of two polarizations, that is, the electrical signals of the right-handed circular polarization and the left-handed circular polarization. Then, each phase compensation unit 2052 compensates for the phase variation for each of the electrical signals of the two polarizations obtained by the equalization unit 2051.

[0040] Further, when the parallelization number is N, the parallelization unit 103 parallelizes the data in wavelength units. That is, the parallelization unit 103 inputs the same data to the two optical modulation units 104 for each wavelength. Then, the equalization unit 2051 compensates for the waveform distortion for the electrical signal obtained by the corresponding polarization multiplex coherent detection unit 2042, and extracts the electrical signal of a single polarization. Then, one of the phase compensation units 2052 compensates for the phase variation for the electrical signal of the single polarization obtained by the equalization unit 2051.

[0041] Furthermore, if the number of parallelizations is N / 2 or less, the parallelization unit 103 parallelizes the data in units of multiple wavelengths. That is, the parallelization unit 103 inputs the same data to the optical modulation unit 104 corresponding to the multiple wavelengths. The equalization unit 2051 then compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042 and extracts an electrical signal with a single polarization. The phase compensation unit 2052 then compensates for phase fluctuations in the electrical signal with a single polarization obtained by the equalization unit 2051. The demapping unit 206 then synthesizes the signals in units of multiple wavelengths.

[0042] Furthermore, Figure 5 shows an example of the configuration of the detection unit 204 and demodulation unit 205 when the modulation method is intensity modulation, that is, when the optical signal obtained by the optical modulation unit 104 is an intensity-modulated signal. In Figure 5, the detection unit 204 has a local light source 2041 and a polarization-multiplexed coherent detection unit 2042, and the demodulation unit 205 has an equalization unit 2051 and an intensity conversion unit 2053.

[0043] The local light source 2041 and the polarization-multiplexed coherent detection unit 2042 are the same as described above.

[0044] The equalization unit 2051 compensates for waveform distortion caused by the frequency characteristics of analog components, etc., in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042, and extracts electrical signals with two polarizations, namely right-hand circular polarization and left-hand circular polarization.

[0045] There are two intensity conversion units 2053, one for each polarization. These intensity conversion units 2053 convert the electrical signals of the corresponding polarizations extracted by the equalization unit 2051 into an intensity signal which is a combination of the I component and the Q component signals.

[0046] Here, when the number of parallelizations is 2 × N, the equalization unit 2051 compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042 and extracts the electrical signals of the two polarizations. Then, each intensity conversion unit 2053 converts each of the two polarization electrical signals obtained by the equalization unit 2051 into an intensity signal.

[0047] Furthermore, when the number of parallelizations is N, the parallelization unit 103 parallelizes the data on a wavelength basis. That is, the parallelization unit 103 inputs the same data to two optical modulation units 104 for each wavelength. The equalization unit 2051 then compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042 and extracts the electrical signals of the two polarizations. Then, each intensity conversion unit 2053 converts each of the two polarization electrical signals obtained by the equalization unit 2051 into an intensity signal. Finally, the demapping unit 206 synthesizes the signals on a wavelength basis.

[0048] Furthermore, if the number of parallelizations is N / 2 or less, the parallelization unit 103 parallelizes the data in units of multiple wavelengths. That is, the parallelization unit 103 inputs the same data to the optical modulation unit 104 corresponding to the multiple wavelengths. The equalization unit 2051 then compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042 and extracts the electrical signals of the two polarizations. The intensity conversion unit 2053 then converts each of the two polarization electrical signals obtained by the equalization unit 2051 into an intensity signal. The demapping unit 206 then synthesizes the signals in units of multiple wavelengths.

[0049] Furthermore, Figure 6 shows another configuration example of the detection unit 204 and demodulation unit 205 when the modulation method is intensity modulation, that is, when the optical signal obtained by the optical modulation unit 104 is an intensity-modulated signal. In Figure 6, the detection unit 204 has a polarization separation unit (PBS) 2043 and a direct detection unit 2044, and the demodulation unit 205 has an equalization unit 2051.

[0050] The polarization separation unit 2043 separates the optical signal of the corresponding wavelength obtained by the wavelength demultiplexer unit 203 into two optical signals with different polarizations, namely right-hand circular polarization and left-hand circular polarization.

[0051] There are two direct detection units 2044, one for each polarization. These direct detection units 2044 obtain the light intensity as an electrical signal by directly detecting the optical signal of the corresponding polarization after it has been separated by the polarization separation unit 2043.

[0052] There are two equalization units 2051, one for each polarization. These equalization units 2051 compensate for waveform distortion caused by the frequency characteristics of analog components and the like in the electrical signal obtained by the corresponding direct detection unit 2044.

[0053] In this case, when the number of parallelizations is 2 × N, each equalization unit 2051 compensates for waveform distortion for each of the two polarized electrical signals obtained by the direct detection unit 2044.

[0054] Furthermore, when the number of parallelizations is N, the parallelization unit 103 parallelizes the data on a wavelength basis. That is, the parallelization unit 103 inputs the same data to two optical modulation units 104 for each wavelength. Then, each equalization unit 2051 compensates for waveform distortion for each of the two polarization electrical signals obtained by the direct detection unit 2044. The demapping unit 206 then synthesizes the signals on a wavelength basis.

[0055] Furthermore, if the number of parallelizations is N / 2 or less, the parallelization unit 103 parallelizes the data in units of multiple wavelengths. That is, the parallelization unit 103 inputs the same data to the optical modulation unit 104 corresponding to the multiple wavelengths. Then, each equalization unit 2051 compensates for waveform distortion for each of the two polarization electrical signals obtained by the direct detection unit 2044. The demapping unit 206 then synthesizes the signals in units of multiple wavelengths.

[0056] When intensity modulation is used as the modulation method, the optical modulation unit 104 in the transmitting terminal 1 has a simple configuration by using a directly modulable laser or EML (electric field absorption modulated laser). On the other hand, when QAM is used as the modulation method, frequency utilization efficiency can be increased. Furthermore, when the modulation method is intensity modulation, the use of a polarization-multiplexed coherent detection unit 2042 in the receiving terminal 2 enables higher receiving sensitivity compared to when a direct detection unit 2044 is used.

[0057] While there are no problems when communication is established with the above functions and configuration, in some cases, depending on the ground station, the antenna gain of the optical system may be small or the spatial propagation loss may be large due to the optical system or geographical conditions, resulting in a small amount of optical power input to the optical amplification unit 202 at the receiving terminal 2, and the communication power budget may not be sufficient. In such cases, it is possible to compensate for the decrease in antenna gain and the increase in spatial propagation loss by changing the signal transmitted from the transmitting terminal 1 from a signal corresponding to 8-parallel data to a signal corresponding to 4-parallel, 2-parallel, or non-parallel data.

[0058] Figure 7 shows an example of the configuration of the parallelization unit 103 in Embodiment 1. The parallelization unit 103 shown in Figure 7 has an 8-parallelization unit 1031, a 4-parallelization unit 1032, a 2-parallelization unit 1033, and a switch unit 1034. In the example in Figure 7, eight switch units 1034 are provided.

[0059] The 8-parallelization unit 1031 divides the data after error correction coding by the error correction coding unit 102 into eight distinct data sets. Each of these divided data sets from the 8-parallelization unit 1031 is input to the corresponding switch unit 1034.

[0060] The 4-parallelization unit 1032 divides the data after error correction coding by the error correction coding unit 102 into four distinct data sets. These divided data sets from the 4-parallelization unit 1032 are input to the corresponding switch units 1034, each corresponding to a wavelength. In other words, the same data is input to the switch unit 1034 corresponding to the same wavelength.

[0061] The parallelization unit 1033 divides the data after error correction coding by the error correction coding unit 102 into two distinct data sets. The data divided by the parallelization unit 1033 is input to the corresponding switch unit 1034, group by group. That is, the same data is input to the switch unit 1034 corresponding to the same group.

[0062] Furthermore, the data after error correction coding by the error correction coding unit 102 is input to each switch unit 1034. In other words, the same data is input to each optical modulation unit 104.

[0063] The switch unit 1034 selects the output of the input signal according to the number of parallelizations selected by the control unit 101. Specifically, each switch unit 1034 outputs the data output by the 8-parallelization unit 1031 to the corresponding optical modulation unit 104 when the control unit 101 selects 8-parallelization; outputs the data output by the 4-parallelization unit 1032 to the corresponding optical modulation unit 104 when the control unit 101 selects 4-parallelization; outputs the data output by the 2-parallelization unit 1033 to the corresponding optical modulation unit 104 when the control unit 101 selects 2-parallelization; and outputs the data from the error correction coding unit 102 to the corresponding optical modulation unit 104 when the control unit 101 selects same data transmission.

[0064] Next, we will describe an example of the operation of the transmitting terminal 1 and the receiving terminal 2 when communication is performed using signals corresponding to four parallel data. In this case, in the transmitting terminal 1 shown in Figure 2, the parallelization unit 103 parallelizes the data into four according to the control unit 101 and inputs the same data to the two optical modulation units 104 for each wavelength.

[0065] If the modulation scheme is QAM, the two optical modulation units 104 at the transmitting terminal 1, one for each wavelength, either modulate light from the same light source or modulate light from two phase-locked light sources. In this case, the optical signal transmitted from the optical modulation unit 104 is a single-polarization signal.

[0066] Furthermore, the receiving terminal 2 collects the optical signal transmitted by the transmitting terminal 1 through the optical system 201, amplifies it in the optical amplification unit 202, and then converts it to four wavelengths (λ). １ ~λ ４ The optical signal is then split into two wavelengths. The split optical signal is converted into an electrical signal by the detection unit 204 of the corresponding wavelength, demodulated into symbols by the demodulation unit 205, and converted back into data by the decoding unit 207.

[0067] In this case, if the modulation method is QAM, the operating detector unit 204 and demodulation unit 205 are as shown in FIG. 8, for example. The signal input to the demodulation unit 205 is compensated for waveform distortion in the equalization unit 2051, and a single polarization wave is extracted. Subsequently, in the phase compensation unit 2052, phase fluctuations depending on the phase noise of the light sources on the transmission side and the reception side are compensated. Also, in the demapping unit 206, demapping of the symbols of the signal of the extracted single polarization wave is performed.

[0068] When the modulation method is intensity modulation, the operating detector unit 204 and demodulation unit 205 are the same as in the case of 8 parallel. Note that in the demapping unit 206, demapping is performed after synthesizing by overlapping the signals corresponding to two polarization waves.

[0069] Here, when comparing the case of performing communication in 8 parallel and the case of performing communication in 4 parallel, if the modulation method and symbol rate are the same, in the case of performing communication in 4 parallel, the communication capacity becomes 1 / 2 times that in the case of performing communication in 8 parallel. Also, in the case of performing communication in 4 parallel, even if the optical power loss caused by the optical system 109 and spatial propagation is twice as large as that in the case of performing communication in 8 parallel, the same SNR can be achieved. This is because when coherent detection is performed, the signals of two polarization waves are synthesized by the MISO process of the demodulation unit 205, and when direct detection is performed, the signals of two polarization waves are synthesized when overlapping in the demapping unit 206.

[0070] Next, an operation example of the transmission terminal 1 and the reception terminal 2 in the case of performing communication using a signal corresponding to 2 - parallel data will be described. In this case, in the transmission terminal 1 shown in FIG. 2, according to the control by the control unit 101, the parallelization unit 103 parallelizes the data into two, and for example, the same data is input to the optical modulation units 104 of λ １ , λ ２ , and different same data is input to the optical modulation units 104 of λ ３ , λ ４ .

[0071] Also, in the reception terminal 2, the operating detector unit 204 and demodulation unit 205 are the same as in the case of 4 - parallelization.

[0072] Furthermore, if the modulation scheme is QAM, the demapping unit 206 will have λ １ and λ ２ The signals are combined, and λ ３ and λ ４ The signals are combined and demapping is performed on each. The combination can be achieved by superposition. Also, when the modulation method is intensity modulation, the demapping unit 206 performs λ １ and λ ２ The four signals are combined, and λ ３ and λ ４ The four signals are combined, and each is demapped. This allows the same SNR to be achieved even with four times the loss compared to communication using eight parallel connections.

[0073] Next, we will describe an example of the operation of the transmitting terminal 1 and the receiving terminal 2 when communication is performed using signals corresponding to data that is not parallelized. In this case, in the transmitting terminal 1 shown in Figure 2, the parallelization unit 103 inputs the same data to all optical modulation units 104 without parallelizing the data, in accordance with the control unit 101.

[0074] Furthermore, the receiving terminal 2 performs demodulation in the same way as in the case of 4 parallel connections, and the demapping unit 206 synthesizes the signals corresponding to all wavelengths and performs demapping. As a result, the same SNR can be achieved even with eight times the loss compared to when communication is performed with 8 parallel connections.

[0075] As described above, by reducing the number of parallelizations, even when the optical power input to the optical amplification unit 202 in the receiving terminal 2 is small due to a small antenna gain in the optical system or a large spatial propagation loss, the SNR can be maintained and communication can be established. For example, when the transmitting terminal 1 is mounted on a satellite and communicates with multiple ground stations at different times, the optical power input to the optical amplification unit 202 will differ depending on the optical system 201 of the ground station or geographical conditions. In such cases, the number of parallelizations required for communication to be established is calculated in advance, and the control unit 101 in the transmitting terminal 1 switches the processing of the parallelization unit 103 to change the number of parallelizations according to the ground station it is communicating with, and the receiving terminal 2 with the corresponding number of parallelizations is installed at the ground station. This makes it possible to achieve the maximum communication capacity according to the ground station and maximize the amount of data that can be transmitted from the satellite to the ground.

[0076] In this example, a transmitting terminal 1 consisting of eight optical modulation units 104 and a corresponding receiving terminal 2 are shown, but the number of optical modulation units 104 can be any number. Also, in this example, a transmitting terminal 1 that combines two wavelengths and transmits from a single optical system 109 is shown, but any number of wavelengths can be combined, or wavelength combination may not be performed at all. In other words, the wavelength combining unit 107 in the transmitting terminal 1 and the wavelength demultiplexing unit 203 in the receiving terminal 2 are not essential components.

[0077] Furthermore, in the synthesis in the demapping unit 206, simple superposition may be performed, or maximum ratio synthesis may be performed considering the SNR of each symbol input from the demodulation unit 205.

[0078] As described above, according to this embodiment 1, the satellite optical communication system comprises a transmitting terminal 1 and a plurality of receiving terminals 2, the transmitting terminal 1 includes a control unit 101 that selects the number of parallelizations, an error correction coding unit 102 that performs error correction coding of data, a parallelization unit 103 that parallelizes the data after error correction coding by the error correction coding unit 102 according to the number of parallelizations selected by the control unit 101, an optical modulation unit 104 provided one set per wavelength that converts the corresponding data parallelized by the parallelization unit 103 into an optical signal of the corresponding wavelength, a polarization conversion unit 105 provided for each wavelength that converts the polarization of the optical signal obtained by one of the corresponding optical modulation units 104 into orthogonal polarizations, a polarization combining unit 106 provided for each wavelength that polarizes and combines the optical signal obtained by the other corresponding optical modulation unit 104 and the optical signal converted by the corresponding polarization conversion unit 105, and a number less than the number of wavelengths The system includes an optical amplification unit 108 provided for each number of groups, which amplifies the signal based on the signal after polarization multiplexing by the corresponding polarization multiplexing unit 106, and an optical system 109 provided for each group, which transmits the amplified signal from the corresponding optical amplification unit 108 to the receiving terminal 2. The receiving terminal 2 includes an optical system 201 that collects the optical signal transmitted by the transmitting terminal 1, an optical amplification unit 202 that amplifies the optical signal collected by the optical system 201, a detection unit 204 provided for each wavelength, which converts the optical signal based on the optical signal after optical amplification by the optical amplification unit 202 into an electrical signal, a demodulation unit 205 provided for each wavelength, which demodulates the electrical signal obtained by the corresponding detection unit 204 according to the number of parallelizations, a demapping unit 206 that demmaps the demodulated signal from the multiple demodulation units 205 according to the number of parallelizations, and a decoding unit 207 that decodes the signal after demapping by the demapping unit 206. As a result, the satellite optical communication system according to Embodiment 1 can avoid a situation in which communication is not possible due to insufficient power budget.

[0079] Furthermore, according to this embodiment 1, the optical signal obtained by the optical modulation unit 104 is a QAM signal, the detection unit 204 has a polarization-multiplexed coherent detection unit 2042 that converts the optical signal based on the optical signal after optical amplification by the optical amplification unit 202 into an electrical signal by interfering it with local light, and the demodulation unit 205 has an equalization unit 2051 that compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042 and extracts an electrical signal of a specific polarization, and a corresponding polarization extracted by the equalization unit 2051 is provided for each polarization The system includes a phase compensation unit 2052 that compensates for phase fluctuations in the electrical signals. When the number of parallelizations is twice the number of wavelengths, the equalization unit 2051 extracts electrical signals of two polarizations. When the number of parallelizations is the number of wavelengths, the parallelization unit 103 parallelizes the data on a wavelength basis, and the equalization unit 2051 extracts the electrical signal of one polarization. When the number of parallelizations is 1 / 2 or less the number of wavelengths, the parallelization unit 103 parallelizes the data on multiple wavelength units, and the equalization unit 2051 extracts the electrical signal of one polarization. The demapping unit 206 synthesizes the signals on these multiple wavelength units. As a result, in the satellite optical communication system according to Embodiment 1, when the modulation scheme is QAM, it is possible to avoid a situation where the power budget is not met and communication is not possible.

[0080] Furthermore, according to this embodiment 1, the optical signal obtained by the optical modulation unit 104 is an intensity-modulated signal, the detection unit 204 has a polarization-multiplexed coherent detection unit 2042 that converts an optical signal based on the optical signal after optical amplification by the optical amplification unit 202 into an electrical signal by interfering it with local light, the demodulation unit 205 has an equalization unit 2051 that compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042 and extracts electrical signals of two polarizations, and an intensity conversion unit 2053 provided for each polarization that converts the electrical signal of the corresponding polarization extracted by the equalization unit 2051 into an intensity signal, and when the number of parallelizations is the number of wavelengths, the parallelization unit 103 parallelizes the data in units of wavelengths and the demapping unit 206 synthesizes the signals in units of those wavelengths, and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit 103 parallelizes the data in units of multiple wavelengths and the demapping unit 206 synthesizes the signals in units of those multiple wavelengths. As a result, in the satellite optical communication system according to Embodiment 1, when the modulation method is intensity modulation, it is possible to avoid a situation where the power budget is not met and communication is not possible.

[0081] Furthermore, according to this embodiment 1, the optical signal obtained by the optical modulation unit 104 is an intensity-modulated signal, the detection unit 204 has a polarization separation unit 2043 that separates the optical signal based on the optical signal after optical amplification by the optical amplification unit 202 into two polarization optical signals, and a direct detection unit 2044 provided for each polarization that converts the optical signal of the corresponding polarization after separation by the polarization separation unit 2043 into an electrical signal, the demodulation unit 205 has an equalization unit 2051 provided for each polarization that compensates for waveform distortion in the electrical signal obtained by the corresponding direct detection unit 2044, and when the number of parallelizations is the number of wavelengths, the parallelization unit 103 parallelizes the data in wavelength units and the demapping unit 206 synthesizes the signals in wavelength units, and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit 103 parallelizes the data in multiple wavelength units and the demapping unit 206 synthesizes the signals in multiple wavelength units. As a result, in the satellite optical communication system according to Embodiment 1, when the modulation method is intensity modulation, it is possible to avoid a situation where the power budget is not met and communication is not possible.

[0082] Embodiment 2. Embodiment 2 describes a case in which polarization multiplexing is not used compared to Embodiment 1. In Embodiment 2, the frequency utilization efficiency is lower compared to Embodiment 1, but the configuration of the transmitting terminal 1 can be simplified.

[0083] Figure 9 shows an example of the configuration of the transmitting terminal 1 according to Embodiment 2. The transmitting terminal 1 includes, for example, a control unit 101, an error correction coding unit 102, a parallelization unit 103, an optical modulation unit 104, a wavelength multiplexing unit 107, an optical amplification unit 108, and an optical system 109, as shown in Figure 9.

[0084] The control unit 101 selects the number of parallelizations in the parallelization unit 103. Here, the number of parallelizations that can be received by the receiving terminal 2 differs for each receiving terminal 2. Therefore, the control unit 101 selects the number of parallelizations in the parallelization unit 103 to match the number of parallelizations that can be received by the receiving terminal 2 that is the target of communication. In this case, for example, the control unit 101 selects the number of parallelizations specified by the user.

[0085] The error correction coding unit 102 performs error correction coding on the data to be transmitted. In this process, for example, the error correction coding unit 102 performs forward error correction coding (FEC).

[0086] The parallelization unit 103 parallelizes the data after error correction coding by the error correction coding unit 102. In this case, the parallelization unit 103 performs parallelization using the number of parallelizations selected by the control unit 101. In the example in Figure 9, the parallelization unit 103 shows a case where 4 parallelizations are possible.

[0087] Here, we assume that the satellite optical communication system handles four wavelengths and that there are two groups to which the wavelengths are grouped. In this case, if the control unit 101 selects four-parallel processing, the parallel processing unit 103 divides the error-corrected encoded data into four distinct data sets and outputs each of the divided data sets to the corresponding optical modulation unit 104. If the control unit 101 selects two-parallel processing, the parallel processing unit 103 divides the error-corrected encoded data into two distinct data sets and outputs each of the divided data sets to the corresponding optical modulation unit 104 in group units. In this case, the same data is input to the optical modulation unit 104 corresponding to the same group. Furthermore, if the control unit 101 selects same data transmission, the parallel processing unit 103 does not divide the error-corrected encoded data and outputs the data to each optical modulation unit 104. In this case, the same data is input to each optical modulation unit 104.

[0088] There are N optical modulation units 104, one for each wavelength. These optical modulation units 104 convert the corresponding data, parallelized by the parallelization unit 103, into an optical signal of the corresponding wavelength. In this process, the optical modulation unit 104 maps the data to symbols such as QPSK or OOK, shapes the waveform, and then modulates the light of the corresponding wavelength to generate the optical signal. In the example in Figure 9, the wavelength is λ １ ~λ ４ These are the four points.

[0089] There is one wavelength multiplexing unit 107 for each group, i.e., M units in total. Each wavelength multiplexing unit 107 combines the optical signals obtained by the corresponding optical modulation units 104. In the example in Figure 9, there are two groups.

[0090] There is one optical amplification unit 108 for each of the above groups, i.e., M units in total. Each optical amplification unit 108 amplifies the signal after it has been combined by the corresponding wavelength multiplexing unit 107.

[0091] There is one optical system 109 for each of the above groups, i.e., M systems in total. This optical system 109 transmits the signal amplified by the corresponding optical amplification unit 108 to the receiving terminal 2.

[0092] Next, an example of the configuration of the detection unit 204 and the demodulation unit 205 in Embodiment 2 will be described. First, Figure 10 shows an example of the configuration of the detection unit 204 and the demodulation unit 205 when the modulation scheme is QAM such as QPSK, that is, when the optical signal obtained by the optical modulation unit 104 is a QAM signal. In Figure 10, the detection unit 204 has a local light source 2041 and a polarization-multiplexed coherent detection unit 2042, and the demodulation unit 205 has an equalization unit 2051 and a phase compensation unit 2052.

[0093] The local light source 2041 inputs local light of the same wavelength as the optical signal input to the polarization-multiplexed coherent detection unit 2042 to the polarization-multiplexed coherent detection unit 2042.

[0094] In Figure 10, the local light source 2041 is shown as being located inside the detection unit 204. However, the local light source 2041 is not limited to this configuration and may be located outside the detection unit 204.

[0095] The polarization-multiplexed coherent detection unit 2042 interferes the optical signals of the corresponding wavelengths obtained by the wavelength demultiplexer unit 203 with local light input by the local light source 2041, thereby converting them into electrical signals of the I and Q components of two orthogonal polarizations.

[0096] The equalization unit 2051 compensates for waveform distortion caused by the frequency characteristics of analog components and the like in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042.

[0097] The phase compensation unit 2052 compensates for phase fluctuations, i.e., phase differences, that which depend on the phase noise of the light sources on the transmitting and receiving sides, for the electrical signals extracted by the equalization unit 2051.

[0098] Here, if the number of parallelizations is N, the equalization unit 2051 compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042. Then, the phase compensation unit 2052 compensates for phase fluctuations in the electrical signal obtained by the equalization unit 2051.

[0099] Furthermore, if the number of parallelizations is N / 2 or less, the parallelization unit 103 parallelizes the data in units of multiple wavelengths. That is, the parallelization unit 103 inputs the same data to the optical modulation unit 104 of the multiple wavelengths. The equalization unit 2051 then compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042. The phase compensation unit 2052 then compensates for phase fluctuations in the electrical signal obtained by the equalization unit 2051. The demapping unit 206 then synthesizes the signals in units of the multiple wavelengths.

[0100] Furthermore, Figure 11 shows an example of the configuration of the detection unit 204 and demodulation unit 205 when the modulation method is intensity modulation, that is, when the optical signal obtained by the optical modulation unit 104 is an intensity-modulated signal. In Figure 11, the detection unit 204 has a local light source 2041 and a polarization-multiplexed coherent detection unit 2042, and the demodulation unit 205 has an equalization unit 2051 and an intensity conversion unit 2053.

[0101] The local light source 2041, the polarization-multiplexed coherent detection unit 2042, and the equalization unit 2051 are the same as described above.

[0102] The intensity conversion unit 2053 converts the electrical signal extracted by the equalization unit 2051 into an intensity signal which is a combination of the I component and the Q component signals.

[0103] Here, if the number of parallelizations is N, the equalization unit 2051 compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042. Then, the intensity conversion unit 2053 converts the electrical signal obtained by the equalization unit 2051 into an intensity signal.

[0104] Furthermore, if the number of parallelizations is N / 2 or less, the parallelization unit 103 parallelizes the data in units of multiple wavelengths. That is, the parallelization unit 103 inputs the same data to the optical modulation unit 104 of the multiple wavelengths. The equalization unit 2051 then compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042. The intensity conversion unit 2053 then converts the electrical signal obtained by the equalization unit 2051 into an intensity signal. The demapping unit 206 then synthesizes the signals in units of the multiple wavelengths.

[0105] Furthermore, Figure 12 shows another example of the configuration of the detection unit 204 and demodulation unit 205 when the modulation method is intensity modulation, that is, when the optical signal obtained by the optical modulation unit 104 is an intensity-modulated signal. In Figure 12, the detection unit 204 has a direct detection unit 2044, and the demodulation unit 205 has an equalization unit 2051.

[0106] The direct detection unit 2044 obtains the light intensity as an electrical signal by directly detecting the optical signal of the corresponding wavelength obtained by the wavelength demultiplexer unit 203.

[0107] The equalization unit 2051 compensates for waveform distortion caused by the frequency characteristics of analog components and the like in the electrical signal obtained by the corresponding direct detection unit 2044.

[0108] Here, if the number of parallelizations is N, the equalization unit 2051 compensates for waveform distortion in the electrical signal obtained by the corresponding direct detection unit 2044.

[0109] Furthermore, if the number of parallelizations is N / 2 or less, the parallelization unit 103 parallelizes the data in units of multiple wavelengths. That is, the parallelization unit 103 inputs the same data to the optical modulation units 104 of the multiple wavelengths. The equalization unit 2051 then compensates for waveform distortion in the electrical signals obtained by the corresponding direct detection units 2044. The demapping unit 206 then synthesizes the signals in units of the multiple wavelengths.

[0110] Here, we have shown an example of a transmitting terminal 1 consisting of four optical modulation units 104 and a corresponding receiving terminal 2, but the number of optical modulation units 104 can be any number. Also, here we have shown an example of a transmitting terminal 1 that combines two wavelengths and transmits from a single optical system 109, but any number of wavelengths can be combined, or wavelength combination may not be performed at all. In other words, the wavelength combining unit 107 in the transmitting terminal 1 and the wavelength demultiplexing unit 203 in the receiving terminal 2 are not essential components.

[0111] As described above, according to this embodiment 2, the satellite optical communication system comprises a transmitting terminal 1 and a plurality of receiving terminals 2. The transmitting terminal 1 includes a control unit 101 that selects the number of parallelizations, an error correction coding unit 102 that performs error correction coding of data, a parallelization unit 103 that parallelizes the data after error correction coding by the error correction coding unit 102 according to the number of parallelizations selected by the control unit 101, an optical modulation unit 104 provided for each wavelength and converting the data parallelized by the parallelization unit 103 into an optical signal of the corresponding wavelength, an optical amplification unit 108 provided for each group less than the number of wavelengths and amplifying the optical signal based on the optical signal obtained by the corresponding optical modulation unit 104, and a corresponding The system includes an optical system 109 that transmits the amplified signal from the optical amplification unit 108 to the receiving terminal 2. The receiving terminal 2 includes an optical system 201 that collects the optical signal transmitted by the transmitting terminal 1, an optical amplification unit 202 that amplifies the optical signal collected by the optical system 201, a detection unit 204 provided for each wavelength that converts the signal based on the optical signal amplified by the optical amplification unit 202 into an electrical signal, a demodulation unit 205 provided for each wavelength that demodulates the electrical signal obtained by the corresponding detection unit 204 according to the number of parallelizations, a demapping unit 206 that demmaps the demodulated signal from the multiple demodulation units 205 according to the number of parallelizations, and a decoding unit 207 that decodes the signal after demapping by the demapping unit 206. As a result, the satellite optical communication system according to Embodiment 2 can avoid a situation in which communication is not possible due to a power budget not being met.

[0112] Furthermore, according to this second embodiment, the optical signal obtained by the optical modulation unit 104 is a QAM signal, the detection unit 204 has a polarization-multiplexed coherent detection unit 2042 that converts the optical signal based on the optical signal after optical amplification by the optical amplification unit 202 into an electrical signal by interfering it with local light, the demodulation unit 205 has an equalization unit 2051 that compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042, and a phase compensation unit 2052 that compensates for phase fluctuations in the electrical signal extracted by the equalization unit 2051, and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit 103 parallelizes the data in multiple wavelength units, and the demapping unit 206 synthesizes the signals in the multiple wavelength units. As a result, in the satellite optical communication system according to the second embodiment, when the modulation method is QAM, it is possible to avoid a situation in which the power budget is not met and communication is not possible.

[0113] Furthermore, according to this second embodiment, the optical signal obtained by the optical modulation unit 104 is an intensity-modulated signal, the detection unit 204 has a polarization-multiplexed coherent detection unit 2042 that converts the optical signal based on the optical signal after optical amplification by the optical amplification unit 202 into an electrical signal by interfering it with local light, the demodulation unit 205 has an equalization unit 2051 that compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit 2042, and an intensity conversion unit 2053 that converts the electrical signal extracted by the equalization unit 2051 into an intensity signal, and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit 103 parallelizes the data in multiple wavelength units, and the demapping unit 206 synthesizes the signals in the multiple wavelength units. As a result, the satellite optical communication system according to the second embodiment can avoid a situation in which communication is not possible because the power budget is not met when the modulation method is intensity modulation.

[0114] Furthermore, according to this second embodiment, the optical signal obtained by the optical modulation unit 104 is an intensity-modulated signal, the detection unit 204 has a direct detection unit 2044 that converts the optical signal based on the optical signal after optical amplification by the optical amplification unit 202 into an electrical signal, the demodulation unit 205 has an equalization unit 2051 that compensates for waveform distortion in the electrical signal obtained by the corresponding direct detection unit 2044, and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit 103 parallelizes the data in multiple wavelength units, and the demapping unit 206 synthesizes the signals in the multiple wavelength units. As a result, the satellite optical communication system according to the second embodiment can avoid a situation in which communication is not possible because the power budget is not met when the modulation method is intensity modulation.

[0115] Embodiment 3. Embodiment 3 describes a case in which, compared to Embodiments 1 and 2, the receiving terminal 2 can also select the number of parallelizations based on the number of error corrections in the decoding unit 207.

[0116] Figure 13 shows an example of the configuration of the transmitting terminal 1 according to Embodiment 3. In the transmitting terminal 1 according to Embodiment 3 shown in Figure 13, the control unit 101 is changed to a control unit 101b compared to the transmitting terminal 1 according to Embodiment 1 shown in Figure 2, and an antenna 110 and a command receiving unit 111 are added. Other configuration examples of the transmitting terminal 1 according to Embodiment 3 shown in Figure 13 are the same as the configuration example of the transmitting terminal 1 according to Embodiment 1 shown in Figure 2, and only the different parts will be described using the same reference numerals.

[0117] Figure 14 shows an example of the configuration of the receiving terminal 2 according to Embodiment 3. In the receiving terminal 2 according to Embodiment 3 shown in Figure 14, a control unit (second control unit) 208, a command transmission unit 209, and an antenna (second antenna) 210 are added compared to the receiving terminal 2 according to Embodiment 1 shown in Figure 3. Other configuration examples of the receiving terminal 2 according to Embodiment 3 shown in Figure 14 are the same as the configuration example of the receiving terminal 2 according to Embodiment 1 shown in Figure 3, and only the different parts will be described using the same reference numerals.

[0118] Antenna 110 converts electromagnetic waves transmitted by receiving terminal 2 into electrical signals.

[0119] The command receiving unit 111 performs command reception (command identification) processing, which detects a signal indicating the number of parallelizations from the electrical signal (RF signal) obtained by the antenna 110.

[0120] The control unit 101b differs from the control unit 101 in that it selects the number of parallel processes in response to a signal indicating the number of parallel processes detected by the command receiving unit 111.

[0121] The control unit 208 selects the number of parallelizations based on the number of error corrections in the decoding unit 207. In this case, the control unit 208 estimates the BER from the number of error corrections in the decoding unit 207, and if the BER approaches the error correction limit by a threshold, it selects to reduce the number of parallelizations. If the BER is below the BER equivalent to more than twice the SNR of the error correction limit, it selects to increase the number of parallelizations.

[0122] The command transmission unit 209 performs command transmission processing to send a signal to the antenna 210 indicating the number of parallelizations selected by the control unit 208.

[0123] The antenna 210 transmits a signal (electrical signal) indicating the number of parallelizations transmitted by the command transmission unit 209 to the transmission terminal 1 as a spatial RF signal (electromagnetic wave).

[0124] In Embodiment 3, the demodulation unit 205 performs demodulation processing according to the number of parallelizations selected by the control unit 208. Also, in Embodiment 3, the demapping unit 206 performs synthesis and demapping according to the number of parallelizations selected by the control unit 208.

[0125] The receiving terminal 2 changes the number of parallel processes according to the state transition diagram shown in Figure 15, for example. Here, B1 to B3 are BER values ​​that have a margin over the error correction limit. B4 to B6 are set to values ​​where the BER has a margin of at least twice the SNR over the error correction limit, and are set to values ​​that allow a BER below the error correction limit to be achieved when the number of parallel processes is doubled.

[0126] In this manner, the receiving terminal 2 determines the number of parallelized communications by comparing the BER estimated from the number of error corrections in the decoding unit 207 with thresholds B1 to B6, and notifies the transmitting terminal 1. The transmitting terminal 1 then changes the number of parallelized signals to be transmitted according to the notified number of parallelized communications.

[0127] In the receiving terminal 2, the processing of the detection unit 204 does not depend on the number of parallel processes, but the processing of the demodulation unit 205 and the demapping unit 206 differs depending on the number of parallel processes. Therefore, the demodulation unit 205 and the demapping unit 206 perform processing according to the number of parallel processes selected by the control unit 208.

[0128] As a result, in the satellite optical communication system according to Embodiment 3, even if the loss due to optical propagation fluctuates due to factors such as atmospheric conditions or weather, the number of parallelizations can be adaptively controlled to prevent communication interruptions and maximize communication capacity.

[0129] In the above, we have shown a case in which, compared to the transmitting terminal 1 according to Embodiment 1, the control unit 101 is changed to a control unit 101b, and an antenna 110 and a command receiving unit 111 are added, and a control unit 208, a command transmitting unit 209, and an antenna 210 are added to the receiving terminal 2 according to Embodiment 1. However, we are not limited to this, and in the transmitting terminal 1 according to Embodiment 2, the control unit 101 is changed to a control unit 101b, and an antenna 110 and a command receiving unit 111 are added, and in the receiving terminal 2 according to Embodiment 2, a control unit 208, a command transmitting unit 209, and an antenna 210 are added, and the same effects as above can be obtained.

[0130] As described above, according to this embodiment 3, the transmitting terminal 1 includes an antenna 110 that converts electromagnetic waves transmitted by the receiving terminal 2 into electrical signals, and a command receiving unit 111 that detects a signal indicating the number of parallelizations from the electrical signals obtained by the antenna 110. The control unit 101b selects the number of parallelizations according to the signal indicating the number of parallelizations detected by the command receiving unit 111. The receiving terminal 2 includes a control unit 208 that estimates the BER from the number of error corrections based on the number of error corrections in the decoding unit 207, and selects to reduce the number of parallelizations if the BER approaches the error correction limit by a threshold, and selects to increase the number of parallelizations if the BER is below a BER that corresponds to more than twice the SNR of the error correction limit. The receiving terminal 2 includes a command transmitting unit 209 that transmits a signal indicating the number of parallelizations selected by the control unit 208, and an antenna 210 that transmits the signal indicating the number of parallelizations transmitted by the command transmitting unit 209 to the transmitting terminal 1 as an electromagnetic wave. The demodulation unit 205 and the demapping unit 206 perform processing according to the number of parallelizations selected by the control unit 208. As a result, the satellite optical communication system according to Embodiment 3 allows the receiving terminal 2 to select the number of parallel connections.

[0131] Embodiment 4. Embodiment 4 describes a case in which, compared to Embodiment 3, the receiving terminal 2 can also select the number of parallelizations based on the input power input to the optical amplification unit 108.

[0132] Figure 16 shows an example of the configuration of a receiving terminal 2 according to Embodiment 4. In the transmitting terminal 1 according to Embodiment 4 shown in Figure 16, the control unit 208 is changed to a control unit (second control unit) 208b compared to the receiving terminal 2 according to Embodiment 3 shown in Figure 14. Other configuration examples of the receiving terminal 2 according to Embodiment 4 shown in Figure 16 are the same as the configuration example of the receiving terminal 2 according to Embodiment 3 shown in Figure 14, and only the different parts will be described using the same reference numerals.

[0133] The control unit 208b selects the number of parallel circuits based on the optical power input to the optical amplification unit 108. In this case, the control unit 208b selects to decrease the number of parallel circuits if the optical power input to the optical amplification unit 108 approaches a threshold value of the received power that is the error correction limit, and selects to increase the number of parallel circuits if the optical power exceeds the received power that corresponds to more than twice the SNR of the error correction limit.

[0134] In the fourth embodiment, the command transmission unit 209 performs command transmission processing to transmit a signal to the antenna 210 indicating the number of parallelizations selected by the control unit 208b.

[0135] Furthermore, in Embodiment 4, the demodulation unit 205 performs demodulation processing according to the number of parallelizations selected by the control unit 208b. Also, in Embodiment 4, the demapping unit 206 performs synthesis and demapping according to the number of parallelizations selected by the control unit 208b.

[0136] The receiving terminal 2 changes the number of parallel connections according to the state transition diagram shown in Figure 17, for example. Here, P1 to P3 are the input power required for communication in 8 parallel, 4 parallel, and 2 parallel configurations. Also, P4 is the same as P1, P5 is the same as P2, and P6 is the same as P3.

[0137] As a result, in the satellite optical communication system according to Embodiment 4, even if the loss due to optical propagation fluctuates due to factors such as atmospheric conditions or weather, the number of parallelizations can be adaptively controlled to prevent communication interruptions and maximize communication capacity.

[0138] Furthermore, regarding the values ​​of P4-P6 and P1-P3, in order to avoid frequent switching of the number of parallel processes near the switching threshold, the values ​​of P1-P3 may be made slightly larger or smaller than the values ​​of P4-P6.

[0139] As described above, according to this embodiment 4, the transmitting terminal 1 includes an antenna 110 that converts electromagnetic waves transmitted by the receiving terminal 2 into electrical signals, and a command receiving unit 111 that detects a signal indicating the number of parallelizations from the electrical signals obtained by the antenna 110. The control unit 101b selects the number of parallelizations according to the signal indicating the number of parallelizations detected by the command receiving unit 111. The receiving terminal 2 includes a control unit 208b that, based on the optical power input to the optical amplification unit 202, selects to decrease the number of parallelizations if the optical power approaches the receiving power which is the error correction limit by a threshold, and selects to increase the number of parallelizations if the optical power exceeds the receiving power which is equivalent to more than twice the SNR of the error correction limit. A command transmitting unit 209 transmits a signal indicating the number of parallelizations selected by the control unit 208b. An antenna 210 transmits the signal indicating the number of parallelizations transmitted by the command transmitting unit 209 to the transmitting terminal 1 as an electromagnetic wave. The demodulation unit 205 and the demapping unit 206 perform processing according to the number of parallelizations selected by the control unit 208b. As a result, the satellite optical communication system according to Embodiment 4 allows the receiving terminal 2 to select the number of parallel connections.

[0140] Embodiment 5. Embodiment 5 describes a case in which, compared to Embodiment 3, the receiving terminal 2 can also select the number of parallelizations based on the elevation angle of the satellite monitored by the satellite tracking optical system 201.

[0141] Figure 18 shows an example of the configuration of a receiving terminal 2 according to Embodiment 5. In the transmitting terminal 1 according to Embodiment 5 shown in Figure 18, the control unit 208 is changed to a control unit (second control unit) 208c compared to the receiving terminal 2 according to Embodiment 3 shown in Figure 14. Other configuration examples of the receiving terminal 2 according to Embodiment 5 shown in Figure 18 are the same as the configuration example of the receiving terminal 2 according to Embodiment 3 shown in Figure 14, and only the different parts will be described using the same reference numerals.

[0142] The control unit 208c selects the number of parallel processes based on the elevation angle of the satellite in the optical system 201. In this case, the control unit 208c selects to decrease the number of parallel processes if the elevation angle approaches the elevation angle at which the error correction limit is reached by a threshold, and selects to increase the number of parallel processes if the elevation angle exceeds the elevation angle at which the SNR is twice or more relative to the error correction limit.

[0143] In the fifth embodiment, the command transmission unit 209 performs command transmission processing to transmit a signal to the antenna 210 indicating the number of parallelizations selected by the control unit 208c.

[0144] Furthermore, in Embodiment 5, the demodulation unit 205 performs demodulation processing according to the number of parallelizations selected by the control unit 208c. Also, in Embodiment 5, the demapping unit 206 performs synthesis and demapping according to the number of parallelizations selected by the control unit 208c.

[0145] The receiving terminal 2 changes the number of parallel connections according to the state transition diagram shown in Figure 19, for example. Here, E1 to E3 are the minimum elevation angles at which communication is possible with 8 parallel connections, 4 parallel connections, and 2 parallel connections, respectively. Also, E4 is the same as E1, E5 is the same as E2, and E6 is the same as E3. As the elevation angle decreases, the loss due to light propagation increases, so it is necessary to reduce the number of parallel connections.

[0146] As a result, in the satellite optical communication system according to Embodiment 5, by adaptively controlling the number of parallelizations, it is possible to prevent communication interruptions and maximize communication capacity.

[0147] Furthermore, regarding the values ​​of E4-E6 and E1-E3, if there is a difference in the tracking performance of the ground station and satellite when the elevation angle increases versus decreases, different values ​​may be used to provide a larger margin for the worse tracking performance.

[0148] As described above, according to this embodiment 5, the transmitting terminal 1 is mounted on a satellite and the receiving terminal 2 is installed on the ground. The transmitting terminal 1 includes an antenna 110 that converts electromagnetic waves transmitted by the receiving terminal 2 into electrical signals, and a command receiving unit 111 that detects a signal indicating the number of parallelizations from the electrical signals obtained by the antenna 110. The control unit 101b selects the number of parallelizations according to the signal indicating the number of parallelizations detected by the command receiving unit 111, and the receiving terminal 2, based on the elevation angle of the satellite in the optical system 201, determines if the elevation angle is incorrect. The satellite optical communication system according to Embodiment 5 includes a control unit 208c that selects to reduce the number of parallelizations when the elevation angle approaches the correction limit by a threshold, and selects to increase the number of parallelizations when the elevation angle exceeds an elevation angle that corresponds to more than twice the SNR of the error correction limit; a command transmission unit 209 that transmits a signal indicating the number of parallelizations selected by the control unit 208c; and an antenna 210 that transmits the signal indicating the number of parallelizations transmitted by the command transmission unit 209 as an electromagnetic wave to the transmitting terminal 1. The demodulation unit 205 and the demapping unit 206 perform processing according to the number of parallelizations selected by the control unit 208c.

[0149] Figure 20 shows an example of the hardware configuration of the transmission terminal 1 according to Embodiments 1 and 2. The processing circuit 120 provides the signal processing functions of the control unit 101, the error correction coding unit 102, the parallelization unit 103, and the optical modulation unit 104. The function of the optical modulation unit 104 is provided by the DAC 121 and the optical modulator 122 in addition to the processing circuit 120. The signal generated by the processing circuit 120 is converted into an analog signal by the DAC 121, and an optical signal is generated by optical modulation in the optical modulator 122.

[0150] Figure 21 shows an example of the hardware configuration of the receiving terminal 2 according to Embodiments 1 and 2. The functions of the demodulation unit 205 are provided by the processing circuit 220 and the ADC 221. The analog signal from the detection unit 204 is converted into a digital signal by the ADC 221 and processed by the processing circuit 220. The functions of the control unit 101, the demapping unit 206, and the decoding unit 207 are also provided by the processing circuit 220.

[0151] Figure 22 shows another hardware configuration example of the transmission terminal 1 according to Embodiments 1 and 2. The hardware configuration example shown in Figure 22 is a hardware configuration example in which the processing circuit 120 shown in Figure 20 is provided by a processor 123 and memory 124.

[0152] Figure 23 is a diagram showing another hardware configuration example of the receiving terminal 2 according to Embodiments 1 and 2. The hardware configuration example shown in Figure 23 is a hardware configuration example in which the processing circuit 220 shown in Figure 21 is provided by a processor 222 and memory 223.

[0153] The generation of the transmission signal, the functions of the control unit 101, and demodulation processing may be implemented by dedicated hardware as shown in Figures 20 and 21, or by a CPU (Central Processing Unit, also known as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP) that executes programs stored in memories 124 and 223, as shown in Figures 22 and 23.

[0154] Furthermore, if the processing circuits 120 and 220 are dedicated hardware, they may include, for example, single circuits, composite circuits, programmed processors, parallel programmed processors, ASICs (AppliCatIon SpecIfIc Integrated Circuits), FPGAs (Field Programmable Gate Arrays), or combinations thereof.

[0155] Furthermore, when processing circuits 120 and 220 are CPUs, the functions of selecting the number of parallel processes, error correction coding, parallelization, mapping, waveform shaping, demodulation, demapping, and decoding are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in memories 124 and 223. Processing circuits 120 and 220 realize their functions by reading and executing the programs stored in memories 124 and 223. In other words, they are provided with memories 124 and 223 for storing programs in which the processing steps of selecting the number of parallel processes, error correction coding, parallelization, mapping, waveform shaping, demodulation, demapping, and decoding will be executed as a result. These programs can also be said to cause the computer to execute procedures or methods of digital signal processing. Here, memory 124,223 refers to non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), or EEPROM (Electronically EPROM), or magnetic disks, flexible disks, optical disks, compact disks, minidiscs, or DVDs (Digital Versatile Discs).

[0156] Furthermore, the functions of the processing circuits 120 and 220 may be partially implemented by dedicated hardware and partially by software or firmware.

[0157] Thus, the processing circuits 120 and 220 can realize the above-mentioned functions through hardware, software, firmware, or a combination thereof.

[0158] Figure 24 is a flowchart showing an example of the operation of the processing circuit 120 in Embodiments 1 and 2. In the example of the operation of the processing circuit 120 in Embodiments 1 and 2, as shown in Figure 24, for example, first the processing circuit 120 selects the number of parallelizations (step ST101). Next, the processing circuit 120 performs error correction coding (step ST102). Next, the processing circuit 120 performs parallelization (step ST103). Next, the processing circuit 120 performs mapping (step ST104). Next, the processing circuit 120 performs waveform shaping (step ST105). After that, the sequence returns to step ST101 and the above process is repeated.

[0159] Figure 25 is a flowchart showing an example of the operation of the processing circuit 220 in Embodiments 1 and 2. In the example of the operation of the processing circuit 220 in Embodiments 1 and 2, as shown in Figure 25, for example, first the processing circuit 220 performs demodulation (step ST201). Next, the processing circuit 220 performs demapping (step ST202). Next, the processing circuit 220 performs decoding (step ST203). After that, the sequence returns to step ST201 and the above process is repeated.

[0160] Figure 26 is a diagram showing an example of the hardware configuration of the transmitting terminal 1 according to embodiments 3 to 5. Figure 27 is a diagram showing an example of the hardware configuration of the receiving terminal 2 according to embodiments 3 to 5. Figure 28 is a diagram showing another example of the hardware configuration of the transmitting terminal 1 according to embodiments 3 to 5. The hardware configuration example shown in Figure 28 is a hardware configuration example in which the processing circuit 120 shown in Figure 26 is provided by a processor 123 and memory 124. Figure 29 is a diagram showing another example of the hardware configuration of the receiving terminal 2 according to embodiments 3 to 5. The hardware configuration example shown in Figure 29 is a hardware configuration example in which the processing circuit 220 shown in Figure 27 is provided by a processor 222 and memory 223.

[0161] Figure 30 is a flowchart showing an example of the operation of the processing circuit 120 in Embodiments 3 to 5. In the example of the operation of the processing circuit 120 in Embodiments 3 to 5, for example as shown in Figure 30, first the processing circuit 120 demodulates the RF signal (step ST301). Next, the processing circuit 120 performs command identification (step ST302). Next, the processing circuit 120 selects the number of parallelizations (step ST303). Next, the processing circuit 120 performs error correction coding (step ST304). Next, the processing circuit 120 performs parallelization (step ST305). Next, the processing circuit 120 performs mapping (step ST306). Next, the processing circuit 120 performs waveform shaping (step ST307). After that, the sequence returns to step ST301 and the above processing is repeated.

[0162] Figure 31 is a flowchart showing an example of the operation of the processing circuit 220 in embodiments 3 to 5. In the example of the operation of the processing circuit 220 in embodiments 3 to 5, for example as shown in Figure 31, first the processing circuit 220 performs demodulation (step ST401). Next, the processing circuit 220 performs demapping (step ST402). Next, the processing circuit 220 performs decoding (step ST403). Next, the processing circuit 120 performs parallelization number selection (step ST404). Next, the processing circuit 120 performs command selection (step ST405). Next, the processing circuit 120 generates an RF signal (step ST406). After that, the sequence returns to step ST401 and the above process is repeated.

[0163] Furthermore, it is possible to freely combine the embodiments, modify any component of each embodiment, or omit any component in each embodiment.

[0164] The satellite optical communication system described herein can avoid situations where communication is impossible due to insufficient power budget, and is therefore suitable for use in satellite optical communication systems and the like.

[0165] 1 Transmitting terminal, 2 Receiving terminal, 101, 101b Control unit, 102 Error correction coding unit, 103 Parallelization unit, 104 Optical modulation unit, 105 Polarization conversion unit, 106 Polarization multiplexing unit, 107 Wavelength multiplexing unit, 108 Optical amplification unit, 109 Optical system, 110 Antenna, 111 Command receiving unit, 120 Processing circuit, 121 DAC, 122 Optical modulator, 123 Processor, 124 Memory, 201 Optical system (second optical system), 202 Optical amplification unit (second optical amplification unit), 203 Wavelength demultiplexing unit, 204 Detection unit, 205 Demodulation unit, 206 Demapping unit, 207 Decoding unit, 208, 208b, 208c Control unit (second control unit), 209 Command transmission unit, 210 Antenna (second antenna), 220 Processing circuit, 221 ADC, 222 Processor, 223 Memory, 1031 8-parallelization unit, 1032 4-parallelization unit, 1033 2-parallelization unit, 1034 Switching unit, 2041 Local light source, 2042 Polarization multiplexed coherent detection unit, 2043 Polarization separation unit, 2044 Direct detection unit, 2051 Equalization unit, 2052 Phase compensation unit, 2053 Intensity conversion unit.

Claims

1. A transmitting terminal and a plurality of receiving terminals, the transmitting terminal comprises: a control unit for selecting the number of parallelizations; an error correction coding unit for error-correcting and coding the data; a parallelization unit for parallelizing the data after error-correction coding by the error correction coding unit according to the number of parallelizations selected by the control unit; an optical modulation unit provided one set per wavelength, which converts the corresponding data parallelized by the parallelization unit into an optical signal of the corresponding wavelength; a polarization conversion unit provided for each wavelength, which converts the polarization of the optical signal obtained by one of the corresponding optical modulation units into orthogonal polarizations; a polarization combining unit provided for each wavelength, which polarizes and combines the optical signal obtained by the other corresponding optical modulation unit and the optical signal converted by the corresponding polarization conversion unit; an optical amplification unit provided for each group less than the number of wavelengths, which amplifies the signal based on the signal after polarization combining by the corresponding polarization combining unit; and an optical system provided for each group, which transmits the amplified signal by the corresponding optical amplification unit to the receiving terminal, the receiving terminal comprises: a second optical system for collecting the optical signal transmitted by the transmitting terminal, A satellite optical communication system comprising: a second optical amplification unit that amplifies an optical signal focused by the second optical system; a detection unit provided for each wavelength that converts an optical signal based on the optical signal amplified by the second optical amplification unit into an electrical signal; a demodulation unit provided for each wavelength that demodulates the electrical signal obtained by the corresponding detection unit according to the number of parallel units; a demapping unit that demmaps the demodulated signal from a plurality of demodulation units according to the number of parallel units; and a decoding unit that decodes the signal after demapping by the demapping unit.

2. The optical signal obtained by the optical modulation unit is a QAM signal, the detection unit has a polarization-multiplexed coherent detection unit that converts an optical signal based on the optical signal after optical amplification by the second optical amplification unit into an electrical signal by interfering it with local light, the demodulation unit has an equalization unit that compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit and extracts an electrical signal of a specific polarization, and a phase compensation unit provided for each polarization that compensates for phase fluctuations in the electrical signal of the corresponding polarization extracted by the equalization unit, when the number of parallelizations is twice the number of wavelengths, the equalization unit extracts electrical signals of two polarizations, when the number of parallelizations is the number of wavelengths, the parallelization unit parallelizes the data on a wavelength basis and the equalization unit extracts an electrical signal of one polarization, The satellite optical communication system according to claim 1, characterized in that, when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit parallelizes the data in units of multiple wavelengths, the equalization unit extracts the electrical signal of one polarization, and the demapping unit synthesizes the signals in units of the multiple wavelengths.

3. The optical signal obtained by the optical modulation unit is an intensity-modulated signal; the detection unit has a polarization-multiplexed coherent detection unit that converts an optical signal based on the optical signal after optical amplification by the second optical amplification unit into an electrical signal by interfering it with local light; the demodulation unit has an equalization unit that compensates for waveform distortion in the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit and extracts electrical signals of two polarizations; and an intensity conversion unit provided for each polarization that converts the electrical signal of the corresponding polarization extracted by the equalization unit into an intensity signal; and when the number of parallelizations is the number of wavelengths, the parallelization unit parallelizes the data in wavelength units and the demapping unit synthesizes the signals in wavelength units; and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit parallelizes the data in multiple wavelength units and the demapping unit synthesizes the signals in multiple wavelength units, characterized in that the satellite optical communication system according to claim 1.

4. The optical signal obtained by the optical modulation unit is an intensity-modulated signal; the detection unit includes a polarization separation unit that separates the optical signal based on the optical signal after optical amplification by the second optical amplification unit into two polarization optical signals; a direct detection unit provided for each polarization that converts the optical signal of the corresponding polarization after separation by the polarization separation unit into an electrical signal; the demodulation unit includes an equalization unit provided for each polarization that compensates for waveform distortion in the electrical signal obtained by the corresponding direct detection unit; when the number of parallelizations is the number of wavelengths, the parallelization unit parallelizes the data in wavelength units and the demapping unit synthesizes the signals in wavelength units; and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit parallelizes the data in multiple wavelength units and the demapping unit synthesizes the signals in multiple wavelength units, characterized in that the satellite optical communication system according to claim 1.

5. A transmitting terminal and a plurality of receiving terminals, wherein the transmitting terminal comprises: a control unit for selecting the number of parallelizations; an error correction coding unit for error-correcting and coding the data; a parallelization unit for parallelizing the data after error-correction coding by the error correction coding unit according to the number of parallelizations selected by the control unit; an optical modulation unit provided for each wavelength and converting the data parallelized by the parallelization unit into an optical signal of the corresponding wavelength; an optical amplification unit provided for each group less than the number of wavelengths and amplifying the optical signal based on the optical signal obtained by the corresponding optical modulation unit; and an optical system provided for each group and transmitting the amplified signal from the corresponding optical amplification unit to the receiving terminal, wherein the receiving terminal comprises: a second optical system for collecting the optical signal transmitted by the transmitting terminal; a second optical amplification unit for amplifying the optical signal collected by the second optical system; a detection unit provided for each wavelength and converting the signal based on the optical signal after optical amplification by the second optical amplification unit into an electrical signal; and a demodulation unit provided for each wavelength and demodulating the electrical signal obtained by the corresponding detection unit according to the number of parallelizations, A satellite optical communication system characterized by comprising a demapping unit that demapplications the demodulated signals from a plurality of demodulation units according to the number of parallelization units, and a decoding unit that decodes the signals from the demapping units.

6. The satellite optical communication system according to claim 5, wherein the optical signal obtained by the optical modulation unit is a QAM signal, the detection unit has a polarization-multiplexed coherent detection unit that converts an optical signal based on the optical signal after optical amplification by the second optical amplification unit into an electrical signal by interfering it with local light, the demodulation unit has an equalization unit that compensates for waveform distortion of the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit, and a phase compensation unit that compensates for phase fluctuations of the electrical signal extracted by the equalization unit, and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit parallelizes the data in multiple wavelength units, and the demapping unit synthesizes the signals in the multiple wavelength units.

7. The satellite optical communication system according to claim 5, wherein the optical signal obtained by the optical modulation unit is an intensity-modulated signal, the detection unit has a polarization-multiplexed coherent detection unit that converts an optical signal based on the optical signal after optical amplification by the second optical amplification unit into an electrical signal by interfering it with local light, the demodulation unit has an equalization unit that compensates for waveform distortion with respect to the electrical signal obtained by the corresponding polarization-multiplexed coherent detection unit, and an intensity conversion unit that converts the electrical signal extracted by the equalization unit into an intensity signal, and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit parallelizes the data in multiple wavelength units, and the demapping unit synthesizes the signals in the multiple wavelength units.

8. The satellite optical communication system according to claim 5, characterized in that the optical signal obtained by the optical modulation unit is an intensity-modulated signal, the detection unit has a direct detection unit that converts an optical signal based on the optical signal after optical amplification by the second optical amplification unit into an electrical signal, the demodulation unit has an equalization unit that compensates for waveform distortion with respect to the electrical signal obtained by the corresponding direct detection unit, and when the number of parallelizations is 1 / 2 or less of the number of wavelengths, the parallelization unit parallelizes the data in multiple wavelength units, and the demapping unit synthesizes the signals in the multiple wavelength units.

9. The satellite optical communication system according to any one of claims 1 to 8, wherein the transmitting terminal comprises an antenna that converts electromagnetic waves transmitted by the receiving terminal into electrical signals, and a command receiving unit that detects a signal indicating the number of parallelizations from the electrical signals obtained by the antenna, the control unit selects the number of parallelizations according to the signal indicating the number of parallelizations detected by the command receiving unit, the receiving terminal comprises a second control unit that estimates the BER from the number of error corrections based on the number of error corrections in the decoding unit, and selects to reduce the number of parallelizations if the BER approaches the error correction limit by a threshold, and selects to increase the number of parallelizations if the BER is less than a BER that corresponds to more than twice the SNR of the error correction limit, a command transmitting unit that transmits a signal indicating the number of parallelizations selected by the second control unit, and a second antenna that transmits the signal indicating the number of parallelizations transmitted by the command transmitting unit to the transmitting terminal as electromagnetic waves, and the demodulation unit and the demapping unit perform processing according to the number of parallelizations selected by the second control unit.

10. The satellite optical communication system according to any one of claims 1 to 8, wherein the transmitting terminal comprises an antenna that converts electromagnetic waves transmitted by the receiving terminal into electrical signals, and a command receiving unit that detects a signal indicating the number of parallelizations from the electrical signals obtained by the antenna, the control unit selects the number of parallelizations according to the signal indicating the number of parallelizations detected by the command receiving unit, the receiving terminal comprises a second control unit that, based on the optical power input to the second optical amplification unit, selects to reduce the number of parallelizations if the optical power approaches the receiving power which is the error correction limit by a threshold, and selects to increase the number of parallelizations if the optical power exceeds the receiving power which is equivalent to more than twice the SNR of the error correction limit, a command transmitting unit that transmits a signal indicating the number of parallelizations selected by the second control unit, and a second antenna that transmits the signal indicating the number of parallelizations transmitted by the command transmitting unit as electromagnetic waves to the transmitting terminal, and the demodulation unit and the demapping unit perform processing according to the number of parallelizations selected by the second control unit.

11. The satellite optical communication system according to any one of claims 1 to 8, wherein the transmitting terminal is mounted on a satellite, and the receiving terminal is installed on the ground, the transmitting terminal comprises an antenna that converts electromagnetic waves transmitted by the receiving terminal into electrical signals, and a command receiving unit that detects a signal indicating the number of parallelizations from the electrical signals obtained by the antenna, the control unit selects the number of parallelizations according to the signal indicating the number of parallelizations detected by the command receiving unit, the receiving terminal comprises a second control unit that, based on the elevation angle of the satellite in the second optical system, selects to reduce the number of parallelizations if the elevation angle approaches the elevation angle that is the error correction limit by a threshold, and selects to increase the number of parallelizations if the elevation angle exceeds an elevation angle that corresponds to more than twice the SNR of the error correction limit, a command transmitting unit that transmits a signal indicating the number of parallelizations selected by the second control unit, and a second antenna that transmits the signal indicating the number of parallelizations transmitted by the command transmitting unit to the transmitting terminal as electromagnetic waves, and the demodulation unit and the demapping unit perform processing according to the number of parallelizations selected by the second control unit.

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