Optical space communication device, optical space communication system, optical space communication method, and program

Abstract

To provide an optical space communication technique that effectively reduces the occurrence of burst errors caused by packet attenuation and loss.SOLUTION: An optical space communication device (1) includes a light transmitting / receiving unit (10) that transmits and receives communication light, and a communication control unit (11) that controls packet communication. The communication control unit (11) causes the light transmitting / receiving unit (10) to transmit either an arbitrary packet (Pi-j) or first encoded information, and then causes the light transmitting / receiving unit (10) to transmit second encoded information (Pi') that includes the arbitrary packet (Pi-j) and a packet (Pi) received at the time a first predetermined time (TLoss) has elapsed by the light transmitting / receiving unit (10).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical space communications device, an optical space communications system, an optical space communications method, and a program. [Background technology]

[0002] In recent years, traffic on the Internet and mobile networks has increased significantly, at an annual rate of 20 to 40%. For this reason, there are high hopes for the practical application of networks using free-space optical communications (FSOC). Free-space optical communications is high-speed wireless communication through free space, using laser light with wavelengths ranging from visible light to infrared light as the transmission medium for communication signals, and in recent years has achieved wireless communication speeds approaching those of fiber optic communications.

[0003] In optical free space communications, communication signals are attenuated or lost due to natural phenomena such as atmospheric turbulence, rainfall, strong winds, and earthquakes, causing burst errors. Burst errors are a major factor that reduces the reliability of optical free space communications. Therefore, various technologies have been researched and developed to achieve high reliability in optical free space communications. For example, Patent Document 1 shows an example of a technology for achieving high reliability in optical free space communications. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-135909 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology disclosed in Patent Document 1 is useful as a technology to deal with the interruption of laser light caused by the presence of obstacles, etc. However, this technology does not deal with the attenuation or loss of communication signals, and is not necessarily sufficient in terms of reducing the occurrence of burst errors caused by the attenuation or loss of communication signals.

[0006] An object of one aspect of the present invention is to provide an optical space communication technology that effectively reduces the occurrence of burst errors due to attenuation or loss of a communication signal. [Means for solving the problem]

[0007] An optical space communications device according to one embodiment of the present invention comprises a light transmitting and receiving means for transmitting and receiving communication light, and a communication control means for controlling packet communication via the light transmitting and receiving means, wherein the communication control means causes the light transmitting and receiving means to transmit either a first packet received by the light transmitting and receiving means or first encoded information generated by network coding and including the first packet, and then causes the light transmitting and receiving means to transmit second encoded information generated by network coding and including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed since the transmission of either the first packet or the first encoded information.

[0008] An optical space communication system according to one embodiment of the present invention is an optical space communication system including a plurality of optical space communication devices, at least any two or more of the plurality of optical space communication devices are equipped with a light transmitting and receiving means for transmitting and receiving communication light, and a communication control means for controlling packet communication via the light transmitting and receiving means, and the communication control means causes the light transmitting and receiving means to transmit either a first packet or first encoded information generated by network coding and including the first packet, and then causes the light transmitting and receiving means to transmit second encoded information generated by network coding and including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed since the transmission of either the first packet or the first encoded information.

[0009] An optical space communication method according to one embodiment of the present invention is an optical space communication method including packet communication control via a light transmitting and receiving means that transmits and receives communication light, wherein the packet communication control includes causing the light transmitting and receiving means to transmit either a first packet or first encoded information generated by network coding and including the first packet, and then causing the light transmitting and receiving means to transmit second encoded information generated by network coding and including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed since the time of transmission of either the first packet or the first encoded information.

[0010] One aspect of the present invention includes a program for causing a computer to operate as the optical space communications device. Effect of the Invention

[0011] According to one aspect of the present invention, it is possible to provide an optical space communication technology that effectively reduces the occurrence of burst errors caused by attenuation and loss of packets. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a configuration of an optical space communications system including an optical space communications device according to a first exemplary embodiment of the present invention. [Diagram 2] 1 is a flow chart showing a flow of an optical space communication method according to the first exemplary embodiment of the present invention. [Diagram 3] FIG. 1 is a block diagram showing a configuration of an optical space communications system including optical space communications devices according to second and third exemplary embodiments of the present invention. [Figure 4] 11 is a block diagram showing a configuration of a light transmitting and receiving unit provided in an optical space communications device according to an exemplary embodiment 2 of the present invention. FIG. [Diagram 5] FIG. 11 is a diagram showing an example of a setting process of a first predetermined time period executed by a communication control unit of an optical space communications device according to an exemplary embodiment 2 of the present invention. [Figure 6]FIG. 11 is a diagram illustrating the principle of packet communication performed by an optical space communication system according to an exemplary embodiment 2 of the present invention. [Figure 7] FIG. 2 is a diagram illustrating an example of an encoded information transmission process executed by the communication control unit described above. [Figure 8] 11 is a flow chart showing the flow of an optical space communication method according to an exemplary embodiment 2 of the present invention. [Figure 9] FIG. 11 is a diagram illustrating a modified example of the encoded information transmission process executed by the communication control unit described above. [Figure 10] FIG. 11 is a diagram showing an example of characteristic processing executed by a communication control unit of an optical space communications device according to an exemplary embodiment 3 of the present invention. [Figure 11] FIG. 2 is a flow chart showing the flow of the characteristic processing described above. [Figure 12] FIG. 2 is a block diagram showing a hardware configuration of a computer that is an example of implementing an optical space communications device according to each exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Example Embodiment 1 A first exemplary embodiment of the present invention will be described in detail with reference to the drawings. This exemplary embodiment is a basic form of the exemplary embodiments described later.

[0014] <Configuration of the optical free space communication system 100> The configuration of an optical space communication system including an optical space communication device according to this exemplary embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the configuration of an optical space communication system 100. The optical space communication system 100 is composed of two optical space communication devices 1 and 2 and another optical space communication device (not shown), and realizes spatial multiplexing transmission by simultaneous connection of multiple communication lights. The optical space communication system 100 employs packet communication as a communication method for optical space communication. Fig. 1 shows an example in which the optical space communication system 100 is composed of two optical space communication devices 1 and 2, but the number of optical space communication devices constituting the optical space communication system 100 is not limited to the example of Fig. 1.

[0015] In the following, the optical space communications device 1 will be mainly described, and the optical space communications device 2 and other optical space communications devices will be described as optical space communications devices that are communication partners of the optical space communications device 1. However, the optical space communications device 2 and other optical space communications devices can have the same configuration as the optical space communications device 1.

[0016] <Configuration of the optical space communications device 1> The optical space communication device 1 according to this exemplary embodiment is a communication device that performs optical space communication. Optical space communication is communication using light propagating through space. Light used in optical space communication may include millimeter waves, submillimeter waves, infrared light, visible light, ultraviolet light, and the like.

[0017] 1, the optical space communications device 1 includes a light transmitting / receiving unit 10 and a communication control unit 11. The light transmitting / receiving unit 10 is an example of a light transmitting / receiving means in the claims, and the communication control unit 11 is an example of a communication control means in the claims.

[0018] (Light transmitting / receiving unit 10) The light transmitting / receiving unit 10 transmits and receives communication light. That is, the light transmitting / receiving unit 10 is composed of a light transmitting unit (light transmitting means) that transmits the communication light, and a light receiving unit (light receiving means) that receives the communication light. The communication light is light used for optical space communication, and is continuous light on which digital information (communication signal) including the communication content is superimposed. The communication light is, for example, laser light. The light transmitting / receiving unit 10 superimposes packets as digital information on the communication light. Furthermore, the light transmitting / receiving unit 10 includes a light emitting element in the light transmitting unit, and may also include a lens, etc. The configuration of the light transmitting / receiving unit 10 will be described in detail later.

[0019] The communication light transmitted from the light transmitting / receiving unit 10 is received by the light transmitting / receiving unit 20 of the communication partner optical space communications device 2 and the light transmitting / receiving unit of the other optical space communications device. Conversely, the communication light transmitted from the light transmitting / receiving unit 20 of the communication partner optical space communications device 2 and the light transmitting / receiving unit of the other optical space communications device is received by the light transmitting / receiving unit 10 of the optical space communications device 1.

[0020] (Communication control unit 11) The communication control unit 11 controls communication via the light transmitting and receiving unit 10. Specifically, the communication control unit 11 causes the light transmitting and receiving unit 10 to transmit either a first packet or first encoded information for a plurality of packets received by the light transmitting and receiving unit 10. The first packet is any one of the plurality of packets received by the light transmitting and receiving unit 10. The first encoded information is information including the first packet generated by network coding by the communication control unit 11. The first packet is transmitted from the light transmitting and receiving unit of another optical space communication device. In addition, the first packet and the first encoded information are transmitted to the light transmitting and receiving unit 20 of the optical space communication device 2.

[0021] After transmitting either the first packet or the first encoded information, the communication control unit 11 causes the light transmitting / receiving unit 10 to transmit second encoded information. The second encoded information is information including the first packet and the second packet, which is generated by the network coding by the communication control unit 11. The second packet is transmitted after a first predetermined time T from the transmission of either the first packet or the first encoded information. Loss The second encoded information is a packet received by the light transmitting / receiving unit 10 at the time when the first predetermined time T Loss Details will be given later.

[0022] <Effects of the optical space communications system 100 and the optical space communications device 1> As described above, the optical space communication device 1 according to this exemplary embodiment, and the optical space communication system 100 including the optical space communication device 1, are equipped with a light transmitting and receiving means for transmitting and receiving communication light, and a communication control means for controlling communication via the light transmitting and receiving means, and the communication control means is configured to cause the light transmitting and receiving means to transmit either a first packet or first encoded information generated by network coding and including the first packet for a plurality of packets received by the light transmitting and receiving means, and then cause the light transmitting and receiving means to transmit second encoded information including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed since the transmission of either the first packet or the first encoded information.

[0023] Therefore, according to this exemplary embodiment, even if fading or the like occurs during data transmission from the light transmitting / receiving unit 10, the packets that have been attenuated or lost can be restored by decoding the second encoded information. This makes it possible to effectively reduce the occurrence of burst errors due to packet attenuation or loss. In addition, since the second encoded information is obtained by performing network coding on the first packet or the like, packet communication is possible without increasing the total communication data size even if the amount of information or number of packets increases, and communication failures such as network delays can be avoided. From the above, the optical space communication device 1 and the optical space communication system 100 including the optical space communication device 1 can be said to be highly reliable optical space communication technology.

[0024] <Flow of optical space communication method S1> The flow of the optical free space communication method S1 according to this exemplary embodiment will be described with reference to Fig. 2. Fig. 2 is a flow diagram showing the flow of the optical free space communication method S1 by the optical free space communication system 100 according to this exemplary embodiment.

[0025] 2, the optical space communication method S1 includes a communication control step (step S10) of controlling communication via the light transmitting and receiving unit 10. This communication control step (S10) includes a first transmission step (S11) of causing the light transmitting and receiving unit 10 to transmit either a first packet or first encoded information for a plurality of packets received by the light transmitting and receiving unit 10. The communication control step (S10) also includes a second transmission step (S12) of causing the light transmitting and receiving unit 10 to transmit second encoded information after the first transmission step (S11) is completed.

[0026] <Effects of the optical space communication method S1> As described above, the optical space communication method S1 according to this exemplary embodiment can effectively reduce the occurrence of burst errors due to packet attenuation and loss, while realizing smooth optical space communication. For this reason, the optical space communication method S1 can be said to be a highly reliable optical space communication method.

[0027] Exemplary embodiment 2 A second exemplary embodiment of the present invention will be described in detail with reference to the drawings. Note that components having the same functions as those described in the first exemplary embodiment are given the same reference numerals, and the description thereof will be omitted as appropriate.

[0028] <Configuration of the optical space communication system 200> The configuration of an optical space communication system including an optical space communication device according to this exemplary embodiment will be described with reference to Fig. 3. Fig. 3 is a block diagram showing the configuration of an optical space communication system 200. The optical space communication system 200 is composed of a first optical space communication device 3, a second optical space communication device 4, and another optical space communication device (not shown), and realizes spatial multiplexing transmission by simultaneous connection of multiple communication lights. The communication method of the optical space communication system 200 is packet communication similar to that of the optical space communication system 100. Fig. 3 shows an example in which the optical space communication system 200 is composed of two optical space communication devices, but the number of optical space communication devices constituting the optical space communication system 200 is not limited to the example of Fig. 3.

[0029] In the following, the first optical space communications device 3 will be mainly described, and the second optical space communications device 4 and the other optical space communications device will be described as optical space communications devices that are communication partners of the first optical space communications device 3. That is, the other optical space communications device will be the source of the first packet transmitted to the first optical space communications device 3. Also, the second optical space communications device 4 will be the destination of the second encoded information transmitted from the first optical space communications device 3. In the example of FIG. 3, the first optical space communications device 3, the second optical space communications device 4, and the other optical space communications devices have the same configuration.

[0030] <Configuration of the first space optical communications device 3> 3, the first optical space communications device 3 according to this exemplary embodiment includes a light transmitting / receiving unit 10, a control unit 31, and a storage unit 32. The storage unit 32 stores various data such as predetermined parameters indicating a light receiving state, such as a light receiving level and a packet loss. The storage unit 32 also stores packets transmitted and received by the light transmitting / receiving unit 10, and first and second encoded information generated by the communication control unit 312.

[0031] (Light transmitting / receiving unit 10) The optical communication medium that the light transmitting and receiving unit 10 transmits and receives, i.e., communication light, has already been described, and therefore will not be described in this exemplary embodiment. The light transmitting and receiving unit 10 may be a well-known light transmitting and receiving unit that can be used for optical space communication. In this exemplary embodiment, the light transmitting and receiving unit 10 will be described by taking as an example a well-known light transmitting and receiving unit having the configuration shown in FIG. 4.

[0032] In the example of Fig. 4, a light transmitting unit 10t for transmitting an optical communication medium and a light receiving unit 10r for receiving the optical communication medium are configured separately. The light transmitting unit 10t is configured to receive a signal from an electrical-optical conversion unit 10ta and transmit a laser light (optical communication medium) emitted from a laser light source 10tb to the outside via a collimator lens 10tc. On the other hand, the light receiving unit 10r is configured to collect the laser light from the outside with a lens 10ra, receive the light with a light receiving element 10rb, and convert the light into an electrical signal by an electrical-optical conversion unit 10rc.

[0033] (Control unit 31) The control unit 31 comprehensively controls each unit included in the first optical space communications device 3. The detailed configuration of the control unit 31 will be described below. The control unit 31 includes an estimation unit 311, a communication control unit 312, and a decoding unit 313. Note that the decoding unit 313 has the same configuration and function as a decoding unit 413 (to be described later) included in the second optical space communications device 4, and therefore a description thereof will be omitted.

[0034] (Estimation Department 311) The estimation unit 311 estimates the duration of fading that occurs during packet communication by measuring the signal strength of multiple packets received by the light transmitting / receiving unit 10. The estimation unit 311 is an example of an estimation means in the claims. Here, fading is a phenomenon in which the reception level of radio waves fluctuates during communication in wireless communication such as optical space communication. Fading is one of the main causes of burst errors in optical space communication.

[0035] In the following, fading will be taken as an example of a burst error that occurs in the free space optical communication system 200. However, the effect of the free space optical communication system 200 is not limited to fading, but is effective against all burst errors. In addition, the duration of fading estimated by the estimation unit 311 is referred to as an "estimated duration T Optic " It is called.

[0036] In this exemplary embodiment, the estimation process executed by the estimation unit 311 will be described with reference to an example shown in Fig. 5. First, the estimation unit 311 measures the signal strengths of a plurality of packets received by the light transmitting / receiving unit 10 within a predetermined period (hereinafter, "received signal strength") to obtain a time series change in the received signal strength as shown in Fig. 5.

[0037] The above-mentioned predetermined period can be set arbitrarily as long as it is long enough to include the time series change in the received signal strength indicating the occurrence of fading. In other words, the number of packets required for the estimation unit 311 to obtain the time series change in the received signal strength is not limited in any way as long as it is a number that can identify the time series change in the received signal strength indicating the occurrence of fading.

[0038] Next, the estimation unit 311 identifies the time when the received signal strength became the lowest from the time series change of the received signal strength. Then, the estimation unit 311 specifies a certain time period extending before and after the time when the received signal strength became the lowest, and performs FFT (Fast Fourier Transform) using the certain time period and the minimum value of the received signal strength as parameters. Using this FFT, the estimation unit 311 calculates the frequency of the maximum amplitude of the received signal strength in the aforementioned period. Finally, the estimation unit 311 calculates "1 / calculated frequency" for the estimated duration T Optic Let us assume that.

[0039] In this exemplary embodiment, before the free space optical communication system 200 performs packet communication (hereinafter, abbreviated as "before the start of packet communication"), the estimation unit 311 estimates the estimated duration T Optic Then, the estimation unit 311 calculates the calculated estimated duration T Optic to the communication control unit 312.

[0040] It should be noted that the first optical space communications device 3 may estimate the estimated duration T Optic For example, the first optical space communications device 3 can obtain the estimated duration T Optic The light transmitting / receiving unit 10 receives the estimated duration T Optic may be obtained.

[0041] The first optical space communications device 3 receives the estimated duration T Optic , the estimation unit 411 performs an estimation process as in this exemplary embodiment to obtain an estimated duration T Optic may be calculated.

[0042] Alternatively, the estimation unit 411 measures a plurality of actual durations, which are durations of fading that actually occurred during packet communication, and calculates the maximum value of the plurality of actual durations as the estimated duration T OpticIn this case, the estimation unit 411 measures the signal strength of a plurality of packets received by the light transmitting / receiving unit 20 of the second optical space communications device 4 within a predetermined period, thereby identifying the plurality of actual durations. However, the estimation unit 411 may determine the estimated duration T by using an average value of the plurality of actual durations instead of the maximum value described above. Optic Alternatively, the top few percent of the actual durations may be extracted and their average value may be calculated as the estimated duration T Optic Furthermore, the estimation unit 311 may estimate the estimated duration T based on the measurements of multiple actual durations. Optic It is also preferable that this series of processing steps be executed before the start of packet communication.

[0043] (Communication control unit 312) The communication control unit 312 has a function equivalent to that of the communication control unit 11 described in the first exemplary embodiment, and is an example of a realization of a communication control means in the claims. In this exemplary embodiment, the communication control unit 312 has a function equivalent to that of the communication control unit 11, and further has a function of controlling the estimated duration T Optic The first predetermined time T Loss It has the function to set the

[0044] Specifically, the communication control unit 312 calculates the estimated duration T Optic and adjustment time T Point and the synchronization time T Rink The total time of at least one of the above is set to a first predetermined time T Loss The adjustment time T Point is the time required to adjust the angle of the antenna (not shown) in the light transmitting / receiving unit 10 again in order to reduce further occurrence of fading. Link is the time required to resynchronize (specifically, clock synchronize) the communication signals of the packet communication by the optical space communication system 200 and establish a link. More specifically, the synchronization time T Link is the delay time from when the clock synchronization of the communication signal of the packet communication by the optical space communication system 200 is lost to when the signal is input and the clock is synchronized again. Linkdiffers for each optical space communications device, and a value of 1 [ms], for example, is observed.

[0045] In this exemplary embodiment, the communication control unit 312 sets the adjustment time T Point and the synchronization time T Rink Both are estimated for duration T Optic to obtain the first predetermined time T Loss In the example of FIG. 5, the communication control unit 312 calculates the adjustment time T Point However, other calculation formulas may be used.

[0046] T Point =S(L)=0.01+0.0001×L…Formula (1) S(L): Function showing the degree of antenna axis misalignment according to communication distance, L: Communication distance In this exemplary embodiment, the adjustment time T Point and the synchronization time T Rink Then, the communication control unit 312 temporarily stores the first predetermined time T Loss When calculating the adjustment time T Point and the synchronization time T Rink Read out.

[0047] The communication control unit 312 determines the estimated duration T Optic Depending on the length of the signal or the time series change in the received signal strength, the adjustment time T Point and the synchronization time T Rink The communication control unit 312 may set the adjustment time T Point and the estimated duration T Optic The total time is set as a first predetermined time T Loss Alternatively, the synchronization time T Rink and the estimated duration T Optic The total time is set as a first predetermined time T Loss The communication control unit 312 may set the adjustment time T Point and the synchronization time T Rink Without using both, the estimated duration T Optic The first predetermined time TLoss It may be set as

[0048] Furthermore, the communication control unit 312 determines whether the first predetermined time T Loss When setting the adjustment time T Point , synchronous time T Rink and the estimated duration T Optic In this case, the estimation unit 311 is not necessary, and the first predetermined time T Loss can be set arbitrarily. In this case, the first predetermined time T Loss may be stored in advance in the storage unit 32, or may be input by the user via an operation input unit (not shown) included in the first space optical communications device 3.

[0049] In this exemplary embodiment, the estimated duration T Optic Calculation of the first predetermined time T Loss The setting is performed before the start of packet communication, but may be performed after the start of packet communication. In this case, the communication control unit 312 sets the first predetermined time T Loss Until the first predetermined time T Loss After setting the above, the communication control unit 312 may execute the encoded information transmission process described below.

[0050] The communication control unit 312 determines whether the first predetermined time T Loss After setting, the coded information transmission process is executed. The principle of the coded information transmission process will be described below with reference to FIG. 6 as an example. The communication control unit 312 performs coded information transmission process for packets received by the light transmitting / receiving unit 10 for each round. In the example of FIG. 6, 10 packets are included per round. That is, the value of "N" in FIG. 6 is 10. FIG. 6 illustrates an example in which 10 packets P100 to P109 are included in a specific round. Also, in the example of FIG. 6, the amount of information in one packet is 1500 [Bytes], so the amount of information per round is 1500×N (N=10).

[0051] Specifically, the communication control unit 312 detects an arbitrary packet P i-j The communication control unit 312 causes the light transmitting / receiving unit 10 to transmit the (first packet) as is. i-j is stored in the storage unit 32.

[0052] Any packet P i-j After causing the light transmitting / receiving unit 10 to transmit the packet P i-j Then, the communication control unit 312 reads out an arbitrary packet P i-j and packet P i (second packet) and performing network coding on the second coded information P i ´(=P i +P i-j ) is generated. i is any packet P i-j A first predetermined time T Loss The packet is received by the light transmitting / receiving unit 10 at the time when the time has elapsed. Then, the communication control unit 312 generates the second encoded information P i The communication control unit 312 repeatedly executes the above series of processes as the encoded information transmission process.

[0053] In the example of FIG. 6, the packet transfer rate is B, and the first predetermined time T Loss When F is used, the second encoded information P i The amount of information per round of the ' is 1500 × (N + B × F) [Bytes]. For example, the packet transfer rate is 83,333 [pkt / s], and the first predetermined time T Loss When the time is 2 [ms], the second encoded information P i The amount of information per round of ´ is 1500 × (10 + 83,333 × 0.002) ≒ 2,514 [KByte].

[0054] Here, the above-mentioned second encoded information P iThe process of generating the ' will be described by applying it to a specific round shown in FIG. 6. Note that, Loss It is assumed that one round received by the light transmitting and receiving unit 10 at the time when the time has elapsed includes ten packets P90 to P99.

[0055] For example, any packet P i-j If "packet P90", packet P i becomes "packet P100", and the second encoded information P i ´ is "packet P100 + packet P90". Here, the symbol "+" represents network coding. For example, any packet P i-j If "packet P99", packet P i becomes "packet P109", and the second encoded information P i ´ becomes "packet P109 + packet P99".

[0056] Although not shown, the communication control unit 312 may also be configured to, when the light transmitting / receiving unit 10 receives a specific packet, i-j In this case, the communication control unit 312 may transmit the first encoded information instead of the arbitrary packet P i and the arbitrary packet P i The communication control unit 312 performs network coding on the packet immediately preceding the current packet (see FIG. 7) to generate first encoded information. Then, the communication control unit 312 causes the light transmitting and receiving unit 10 to transmit the generated first encoded information. The communication control unit 312 also causes the storage unit 32 to store the first encoded information.

[0057] After causing the light transmitting / receiving unit 10 to transmit the first encoded information, the communication control unit 312 reads out the first encoded information from the storage unit 32. Then, the communication control unit 312 outputs the first encoded information and the packet P i and perform network coding on the second encoded information P i Then, the communication control unit 312 generates the generated second coded information P i ' is transmitted to the light transmitting / receiving unit 10.

[0058] Next, a specific example of the encoded information transmission process by the communication control unit 312 will be described with reference to Fig. 7. Here, the numbers "1" to "28" in Fig. 7 are numbers assigned to packets and represent the order in which the light transmitting and receiving unit 10 received the packets.

[0059] In the following description, the nth packet received by the light transmitting / receiving unit 10 is denoted as "packet P(n)". For example, the first (first) packet received by the light transmitting / receiving unit 10 is "packet P(1)". Furthermore, the first encoded information when the light transmitting / receiving unit 10 receives packet P(n) is denoted as "first encoded information P((n-1)+n)", and the second encoded information is denoted as "second encoded information P'((nm)+n)" or "second encoded information P'((nm)+(n-1)+n)". "m" is the number of transmission data per round.

[0060] In the following description, the transmission time of the packet P(1) is set to "0", and thereafter, the light transmitting / receiving unit 10 transmits and receives at intervals of 0.0001 [s]. Furthermore, the communication control unit 312 transmits and receives the packet P(1) at a first predetermined time T Loss is set to 0.001[s].

[0061] In the specific example of FIG. 7, since it is unclear whether or not there is a subsequent packet at the time when the light transmitting / receiving unit 10 receives the packet P(1), the communication control unit 312 transmits the packet P(1) to the light transmitting / receiving unit 10 as is. This makes it possible to prevent the communication control unit 312 from needlessly waiting to transmit the packet P(1) in order to generate the first encoded information even when there is no subsequent packet. Furthermore, if there is a subsequent packet, the communication control unit 312 can immediately generate the first encoded information using the packet P(1). Therefore, smooth packet transmission to the second optical space communications device 4 can be realized regardless of whether or not there is a subsequent packet.

[0062] Here, it is not essential that the communication control unit 312 transmits the packet P(1) as is to the light transmitting / receiving unit 10. For example, the communication control unit 312 may cause the light transmitting / receiving unit 10 to wait for the transmission of the packet P(1), and upon receiving a subsequent packet, transmit the first encoded information obtained by performing network coding on the packet P(1) and the subsequent packet to the light transmitting / receiving unit 10.

[0063] After transmitting packet P(1), when the light transmitting / receiving unit 10 receives packet P(2), the communication control unit 312 performs network coding on packet P(1) and packet P(2) to generate first encoded information P(1+2). Then, the communication control unit 312 causes the light transmitting / receiving unit 10 to transmit the generated first encoded information P(1+2). After that, the communication control unit 312 repeats this series of processes until the light transmitting / receiving unit 10 transmits the first encoded information P(9+10).

[0064] Here, it is not essential that the communication control unit 312 causes the light transmitting / receiving unit 10 to transmit the first encoded information P(1+2) to P(9+10). For example, the communication control unit 312 may cause the light transmitting / receiving unit 10 to transmit all of the packets P(1) to P(10) as they are, without generating the first encoded information P(1+2) to P(9+10). However, generating the first encoded information P(1+2) to P(9+10) as in the specific example of FIG. 7 increases the possibility of decoding the packets P(1) to P(10) when fading occurs, compared to not generating the first encoded information. Therefore, it is preferable that the communication control unit 312 generates the first encoded information P(1+2) to P(9+10).

[0065] After transmitting the first encoded information P(9+10), the communication control unit 312 reads out the packet P(10) again from the storage unit 32 and causes the light transmitting / receiving unit 10 to transmit the packet P(10) as is. The series of packet communications up to this point constitutes one round.

[0066] As described above, it is not essential to transmit the single packet transmitted one time before at the end of one round as is, and for example, this transmission process may be omitted. However, transmitting one packet as is at the end of one round increases the possibility of decoding the single packet when fading occurs, compared to not transmitting the single packet. Moreover, since this transmission process is executed only once at the end of one round, it does not hinder smooth packet transmission to the second free space optical communications device 4. Therefore, it is preferable to transmit one packet as is at the end of one round.

[0067] After the packet P(10) is transmitted, the light transmitting / receiving unit 10 receives the packet P(11), and the first predetermined time T Loss has elapsed. The communication control unit 312 reads out packet P(1) again from the storage unit 32, and performs network coding on packet P(1) and packet P(11) to generate second encoded information P'(1+11). Then, the communication control unit 312 causes the light transmitting and receiving unit 10 to transmit the generated second encoded information P'(1+11). When the light transmitting and receiving unit 10 transmits the second encoded information P'(1+11), the next round begins.

[0068] After transmitting the second encoded information P'(1+11), when the light transmitting / receiving unit 10 receives the packet P(12), the communication control unit 312 reads the packet P(11) from the storage unit 32 and reads the packet P(2) again. Then, the communication control unit 312 performs network coding on the packets P(2), P(11), and P(12) to generate the second encoded information P'(2+11+12). Then, the communication control unit 312 causes the light transmitting / receiving unit 10 to transmit the generated second encoded information P'(2+11+12). After that, the communication control unit 312 repeats this series of processes until the light transmitting / receiving unit 10 transmits the second encoded information P'(10+19+20).

[0069] After transmitting the second encoded information P'(10+19+20), the communication control unit 312 reads out the packet P(20) again from the storage unit 32 and causes the light transmitting / receiving unit 10 to transmit the packet P(20) as is. When the light transmitting / receiving unit 10 transmits the packet P(20) as is, the next round ends.

[0070] After the light transmitting / receiving unit 10 receives the packet P(21), the same series of processes as those from when the light transmitting / receiving unit 10 receives the packet P(11) to when it transmits the packet P(20) as is are repeated.

[0071] In other words, the communication control unit 312 of the first optical space communications device 3 transmits the unprocessed packet, the first encoded information, and the second encoded information to the light transmitting / receiving unit 10. The unprocessed packet is a packet that has not been subjected to network coding by the communication control unit 312. In the example of FIG. 7, the unprocessed packets are packet P(1) at time 0 [s], packet P(10) at time 0.001 [s], packet P(20) at time 0.0021 [s], and packet P(30) at time 0.0032 [s]. That is, the first optical space communications device 3 is an example of the realization of another optical space communications device in the claims.

[0072] 7, if fading occurs during the period from time 0.0015 to time 0.0018, packets P(15) to P(17) will have been lost or otherwise lost at the time when the light transmitting / receiving unit 10 receives packet P(20). However, the communication control unit 312 will later generate second encoded information P'(15+24+25) to P'(17+26+27). Therefore, the decoding unit 413 described below can decode this second encoded information to restore each piece of information in packets P(15) to P(17).

[0073] <Configuration of second space optical communications device 4> As shown in Fig. 3, the second optical space communications device 4 according to this exemplary embodiment includes a light transmitting / receiving unit 20, a control unit 41, and a storage unit 42. The optical communications medium that the light transmitting / receiving unit 20 transmits and receives, i.e., communication light, has already been described, and therefore will not be described in this exemplary embodiment. Similarly to the light transmitting / receiving unit 10, the light transmitting / receiving unit 20 may be a well-known light transmitting / receiving unit having the configuration shown in Fig. 4.

[0074] The control unit 41 has the same configuration as the control unit 31 provided in the first optical space communications device 3. The control unit 41 includes an estimation unit 411, a communication control unit 412, and a decoding unit 413. The estimation unit 411 has been described in detail above, so a description thereof will be omitted here. The communication control unit 412 has the same configuration as the communication control unit 312 provided in the first optical space communications device 3. In other words, the communication control unit 412 is one example of the realization of a communication control means in the claims.

[0075] (Decoding unit 413) The decoding unit 413 is a unit capable of decoding the unprocessed packet, the first encoded information, and the second encoded information. In this exemplary embodiment, the decoding unit 413 decodes the unprocessed packet, the first encoded information, and the second encoded information transmitted from the light transmitting / receiving unit 10 of the first optical space communications device 3. That is, the decoding unit 413 is an example of the implementation of the decoding means in the claims.

[0076] In the example of FIG. 6, for example, the light transmitting / receiving unit 20 receives the second encoded information P i If the light transmitting / receiving unit 20 receives "packet P100+packet P90" as the second encoded information P', the decoding unit 413 has already decoded the packet P90 unless fading or the like occurs. Therefore, the decoding unit 413 decodes "packet P100+packet P90" to restore the information of the packet P100. i When "packet P109+packet P99" is received as the received signal, the decoder 413 has already decoded packet P99 unless fading or the like occurs. Therefore, the decoder 413 decodes "packet P109+packet P99" to restore the information of packet P109.

[0077] 7, the decoding unit 413 decodes the first coded information P((n-1)+n) in the first round of packets P(1) to P(10) to restore the information of packet P(n). Next, the decoding unit 413 decodes the second coded information P'((nm)+n) or P'((nm)+(n-1)+n) in the first round of packets P(1) to P(20) and thereafter to restore the information of packet P(n).

[0078] Here, the decoding unit 413 decodes the second coded information P'(15+24+25) to P'(17+26+27) in one round of the second coded information P'(11+21) to packets P(30). Therefore, even if fading occurs during the period from time 0.0015 to 0.0018, the decoding unit 413 can restore the information of packets P(15) to P(17) that were lost or otherwise lost in the previous round.

[0079] <Effects of the optical space communications system 200 and the optical space communications devices 3 and 4> The optical space communications device (first optical space communications device 3 and second optical space communications device 4) according to this exemplary embodiment, and the optical space communications system 200 including each of these optical space communications devices, further includes an estimation means for estimating the duration of fading occurring during the packet communications by measuring the signal strength of a plurality of packets received by the light transmitting / receiving means, and the communication control means is configured to set the estimated duration, which is the duration of the fading estimated by the estimation means, as the first predetermined time.

[0080] This makes it possible to reduce the situation where the total communication data size increases more than necessary because the second encoded information is generated too early. It also makes it possible to reduce the situation where attenuated or lost packets cannot be restored because the second encoded information is generated too late. This makes it possible to efficiently generate the second encoded information, and to achieve smoother free-space optical communication.

[0081] In addition, the optical space communication device and optical space communication system 200 according to this exemplary embodiment further includes an estimation means for estimating the duration of fading occurring during the packet communication by measuring the signal strength of multiple packets received by the light transmitting and receiving means, and the communication control means is configured to set the first predetermined time to the sum of the estimated duration estimated by the estimation means and at least one of the adjustment time required to adjust the angle of the antenna of the light transmitting and receiving means and the synchronization time required to synchronize the communication signal of the packet communication.

[0082] As described above, according to the present exemplary embodiment, at least one of the adjustment time and the synchronization time is taken into consideration when setting the first predetermined time. Therefore, the second encoded information can be generated at a more appropriate timing than when these times are not taken into consideration. This allows the second encoded information to be generated more efficiently, and enables smoother optical space communication to be realized.

[0083] Furthermore, in the optical space communications device and optical space communications system 200 according to this exemplary embodiment, at least any two or more of the optical space communications devices further include a decoding means capable of decoding an unprocessed packet, which is a packet that has not been network coded by the communication control means, the first encoded information, and the second encoded information, and a configuration is adopted in which the decoding means of one optical space communications device decodes the unprocessed packet, the first encoded information, and the second encoded information transmitted from the light transmitting and receiving means of another optical space communications device.

[0084] As described above, according to this exemplary embodiment, the decoding means of one optical space communications device decodes all types of information transmitted from another optical space communications device. This eliminates decoding omissions and ensures the restoration of packets that have been attenuated or lost due to fading or the like. This makes it possible to more effectively reduce the occurrence of burst errors and further increase the reliability of optical space communications.

[0085] <Flow of optical space communication method S2> The flow of the optical free space communication method S2 according to this exemplary embodiment will be described with reference to Fig. 8. Fig. 8 is a flow diagram showing the flow of the optical free space communication method S1 by the optical free space communication system 200 according to this exemplary embodiment.

[0086] As shown in Fig. 8, the optical space communication method S2 includes an estimation step (S20), a communication control step (S21), and a decoding step (S22). S20 is a step of measuring the signal strength of a plurality of packets to estimate the duration of fading occurring during packet communication. S21 is a step of executing packet communication control via the light transmitting and receiving means. S22 is a step of decoding the unprocessed packet, the first encoded information, and the second encoded information received by the light transmitting and receiving means.

[0087] The communication control step (S21) includes a time setting step (S211), a first transmission step (S212), and a second transmission step (S213). S211 is a step of setting a first predetermined time. S212 is a step of executing the same process as S111 shown in FIG. 2. S213 is a step of executing the same process as S112 shown in FIG. 2.

[0088] (S20) In S20, the estimation unit 311 of the control unit 31 estimates the duration of fading that occurs during packet communication and sets the estimated duration T Optic The details of the acquisition have been described above, so the description will be omitted.

[0089] (S211) In S211, the communication control unit 312 of the control unit 31 sets the adjustment time T Point and the synchronization time T Rink Both are estimated for duration T Optic The first predetermined time T Loss The details of the settings have been described above, so a detailed description thereof will be omitted.

[0090] (S212) In S212, the communication control unit 312 of the control unit 31 causes the light transmitting and receiving unit 10 to transmit the unprocessed packet (for example, "packet P(1)" in FIG. 7) as is. Thereafter, the communication control unit 312 of the control unit 31 causes the light transmitting and receiving unit 10 to transmit the first encoded information (for example, "first encoded information P((n-1)+n)" in FIG. 7). The details of these transmission processes have been described above, and therefore will not be described again.

[0091] (S213) In S213, the communication control unit 312 of the control unit 31 performs a first predetermined time T Loss At the time when the time has elapsed, the second coded information (for example, “second coded information P i The light transmitting / receiving unit 10 transmits the signal "P" from the light transmitting / receiving unit 10. The details of this transmission process have been described above, and therefore will not be described here.

[0092] (S22) In S22, the decoding unit 413 of the control unit 41 decodes the unprocessed packet received by the light transmitting and receiving unit 20. After decoding the unprocessed packet, the decoding unit 413 of the control unit 41 decodes the first encoded information received by the light transmitting and receiving unit 20. After decoding the first encoded information, the decoding unit 413 of the control unit 41 decodes the second encoded information received by the light transmitting and receiving unit 20. The details of this decoding process have been described above, and therefore will not be described again.

[0093] <Modification> The communication control units (communication control units 312 and 412) of the optical space communications device according to this exemplary embodiment may increase the data length of the transmission data to be transmitted by the light transmitting / receiving unit 10 in the encoded information transmission process. Hereinafter, an explanation will be given with reference to FIG. 9. In the example of FIG. 9, the first predetermined time T Loss It is assumed that the time t1 is 0.0004 [s]. It is also assumed that the light transmitting / receiving unit 10 transmits packets P(1) to P(4) in the first round.

[0094] 7, the communication control unit 312 causes the light transmitting / receiving unit 10 to transmit packet P(4) as is at the time of 0.0004 [s]. On the other hand, the communication control unit 312 according to this modification reads out not only packet P(4) but also packet P(2) from the storage unit 32 at the time of 0.0004 [s]. Then, the communication control unit 312 according to this modification performs network coding on packet P(2) and packet P(4) to generate first encoded information P(2+4), and causes the light transmitting / receiving unit 10 to transmit it. As a result, the data length of the transmission data of the light transmitting / receiving unit 10 at the time of 0.0004 [s] is increased by the amount of packet P(2).

[0095] According to the specific example of FIG. 7, the communication control unit 312 causes the light transmitting / receiving unit 10 to transmit the second encoded information P'(1+5) at the time of 0.0005 [s]. Meanwhile, the communication control unit 312 according to this modification reads out not only the packet P(1) but also the packets P(3) and P(4) from the storage unit 32 at the time of 0.0005 [s]. Then, the communication control unit 312 according to this modification performs network coding on the packets P(1), P(3), P(4), and P(5) to generate the second encoded information P'(1+3+4+5), and causes the light transmitting / receiving unit 10 to transmit it. As a result, the data length of the transmission data of the light transmitting / receiving unit 10 at the time of 0.0005 [s] is increased by the amount of the packets P(3) and P(4).

[0096] Increasing the redundancy of the data transmitted by the light transmitting / receiving unit 10 as described above increases the number of times that information of a packet that has been lost or otherwise processed can be restored. This makes it possible to more effectively deal with packet loss or the like caused by fading.

[0097] Exemplary embodiment 3 The above-described exemplary embodiments 1 and 2 are premised on the premise that the light transmitting / receiving unit 10 performs the transmission process reliably. However, this premise is not essential, and a configuration may be adopted in which the communication control unit 312 can handle the case where the light transmitting / receiving unit 10 does not perform the transmission process at a certain timing due to some factor.

[0098] For example, when specific information is not transmitted from the light transmitting / receiving unit 10, the communication control unit 312 may cause the light transmitting / receiving unit 10 to transmit the specific information after a second predetermined time has elapsed from the time of non-transmission. The specific information is either the first packet or the first encoded information, or the second encoded information, which was not transmitted from the light transmitting / receiving unit 10. The time of non-transmission is the time when the specific information should have been transmitted. The second predetermined time is a time that can be set arbitrarily, and may be stored in advance in the storage unit 32, or may be input by the user via an operation input unit provided in the first optical space communications device 3.

[0099] Hereinafter, the characteristic process executed by the communication control unit 312 (abbreviated as "communication control unit 312") according to this exemplary embodiment will be described with reference to FIG. 10. In the example of FIG. 10, the communication control unit 312 does not generate the first encoded information, but instead causes the light transmitting / receiving unit 10 to transmit the first packet as is. In addition, the first predetermined time T Loss The second predetermined time T o is preset as 0.0005 [s] and stored in the storage unit 32.

[0100] As a premise, the communication control unit 312 sets a forced transmission time for all transmission data transmitted from the light transmitting / receiving unit 10. The forced transmission time is the time at which the target transmission data is transmitted if the target transmission data has not been transmitted from the light transmitting / receiving unit 10. Specifically, the forced transmission time is set to the time at which the target transmission data should have been transmitted originally, after a second predetermined time T o This is the time added.

[0101] For example, if the packet P(1) is not included in the second coded information P'(1+6) to be transmitted when the time reaches 0.0005 [s], the communication control unit 312 o= 0.001 [s], packet P(1) is read out from storage unit 32. Then, communication control unit 312 causes light transmitting / receiving unit 10 to transmit packet P(1). In this case, packet P(1) becomes specific information, and the forced transmission time becomes 0.001 [s].

[0102] In the example of FIG. 10, packets P(8) to P(12) that should be transmitted in sequence have not been transmitted when the time reaches 0.0012 to 0.0016 [s]. In other words, packets P(8) to P(12) become specific information. Therefore, the communication control unit 312 determines that, for example, when the time reaches 0.0012+T o = 0.0017 [s], packet P(8) is read out from storage unit 32. Then, communications control unit 312 causes light transmitting / receiving unit 10 to transmit packet P(8). Thereafter, packets P(9) to P(12) are transmitted in sequence when the time reaches 0.0018 to 0.0021 [s]. In other words, 0.0017 to 0.0021 [s] become the forced transmission time. Note that, although in the example of FIG. 10, specific information is transmitted when the forced transmission time is reached, specific information may be transmitted at any time after the forced transmission time.

[0103] <Flow of Characteristic Processing Executed by the Communication Control Unit 312 According to the Present Exemplary Embodiment> The flow of the characteristic process S3 executed by the communication control unit 312 will be described with reference to Fig. 11. Fig. 11 is a flow diagram showing the flow of the characteristic process S3. Note that the example of Fig. 11 is an example in which the communication control unit 312 executes the encoded information transmission process of the specific example shown in Fig. 7.

[0104] (S30) In S30, the communication control unit 312 detects that the light transmitting / receiving unit 10 has received the packet P i The light transmitting / receiving unit 10 determines whether or not the packet P i If the light transmitting / receiving unit 10 has not received the packet P (No in S30), the communication control unit 312 proceeds to the process of S31. i If it has been received (Yes in S30), the communication control unit 312 proceeds to the process of S33.

[0105] (S31) In S31, the communication control unit 312 determines whether the time t now is packet P i Forced transmission time t i Determine whether the forced transmission time t i If the forced transmission time t i If it has passed (Yes in S31), the communication control unit 312 proceeds to the process of S32.

[0106] (S32) In S32, the communication control unit 312 reads the packet P i and transmits the packet P i In addition, the communication control unit 312 transmits the forced transmission time t i After the process of S32 ends, the communication control unit 312 executes the process of S30 again.

[0107] (S33) In S33, the communication control unit 312 determines whether the receiving order i of the packet Px is "1" or not, or whether the receiving order i satisfies "i mod 10=0". If the receiving order i satisfies either of these two conditions (Yes in S33), the communication control unit 312 proceeds to processing of S34. On the other hand, if the receiving order i does not satisfy either of these two conditions (No in S33), the communication control unit 312 proceeds to processing of S35.

[0108] (S34) In S34, the communication control unit 312 transmits the packet P i This prevents the time until the information of the lost or other packet is restored by the decoder 413 from becoming too long, and ensures reliable and smooth space optical communication. In addition, the communication controller 312 adds the packet P to the second encoded information to be transmitted thereafter. i Assuming that the forced transmission time t i In this case, the forced transmission time t i is the time tnow , packet P i A first predetermined time T corresponding to the second encoded information including Loss and a second predetermined time T o After the process of S34 ends, the communication control unit 312 executes the process of S30 again.

[0109] (S35) In S35, the communications control unit 312 determines whether or not the condition "ik<0" is satisfied. Here, "k" is the number of packets included in one round, and in the example of FIG. 11, k=11. If the condition "ik<0" is satisfied (Yes in S35), the communications control unit 312 proceeds to processing of S36. On the other hand, if the condition "ik<0" is not satisfied (No in S35), the communications control unit 312 proceeds to processing of S37.

[0110] (S36) In S36, the communication control unit 312 i and the packet P i The packet P received by the light transmitting / receiving unit 10 one time before i-1 and perform network coding on the first coded information packet P i +Packet P i-1 In addition, the communication control unit 312 generates the forced transmission time t i In this case, the forced transmission time t i is the time t now , packet P i A first predetermined time T corresponding to the second encoded information including Loss and a second predetermined time T o After the process of S36 ends, the communication control unit 312 executes the process of S30 again.

[0111] (S37) In S37, the communication control unit 312 reads the packet P i-k Packet P i-k The packet P i-k and the first encoded information packet Pi +Packet P i-1 As a result, the communication control unit 312 generates a packet P i-k +Packet P i +Packet P i-1 Generate.

[0112] In addition, the communication control unit 312 determines the forced transmission time t i-k After canceling the setting, a new forced transmission time t i-k+1 Set the forced transmission time t i-k is the second coding information P i-k +Packet P i +Packet P i-1 is the forced transmission time when the message was not sent at the time it should have been sent. i-k+1 is the time t now , packet P i-k A first predetermined time T corresponding to the second encoded information including Loss and a second predetermined time T o The time is the time added.

[0113] After completing the process of S37, the communication control unit 312 executes the process of S30 again. After that, the communication control unit 312 repeatedly executes each of the processes of S30 to S37.

[0114] <Effects of the optical space communications system 200 and the optical space communications devices 3 and 4> In the optical space communication devices (first optical space communication device 3 and second optical space communication device 4) according to this exemplary embodiment, and in the optical space communication system 200 including each of these optical space communication devices, the communication control means is configured to, when the first packet, the first encoded information, or the second encoded information is not transmitted from the light transmitting and receiving means, cause the light transmitting and receiving means to transmit the not transmitted information after a second predetermined time has elapsed from the time when the not transmitted information should have been transmitted.

[0115] This eliminates the risk of missing transmissions from the light transmitting and receiving means, and the decoding means can reliably restore packets that have been attenuated or lost due to fading, etc. This makes it possible to more effectively reduce the occurrence of burst errors and further increase the reliability of free space optical communications.

[0116] [Software implementation example] A part or all of the functions of the optical space communications devices 1 and 2 may be realized by hardware such as an integrated circuit (IC chip), or may be realized by software.

[0117] In the latter case, the optical free space communications devices 1 and 2 are realized, for example, by a computer that executes instructions of a program, which is software that realizes each function. An example of such a computer (hereinafter, referred to as computer C) is shown in FIG. 12. The computer C includes at least one processor C1 and at least one memory C2. The memory C2 stores a program P for operating the computer C as the optical free space communications devices 1 and 2. In the computer C, the processor C1 reads and executes the program P from the memory C2, thereby realizing each function of the optical free space communications devices 1 and 2.

[0118] The processor C1 may be, for example, a central processing unit (CPU), a graphic processing unit (GPU), a digital signal processor (DSP), a micro processing unit (MPU), a floating point number processing unit (FPU), a physics processing unit (PPU), a microcontroller, or a combination of these. The memory C2 may be, for example, a flash memory, a hard disk drive (HDD), a solid state drive (SSD), or a combination of these.

[0119] The computer C may further include a RAM (Random Access Memory) for expanding the program P during execution and for temporarily storing various data. The computer C may further include a communication interface for transmitting and receiving data to and from other devices. The computer C may further include an input / output interface for connecting input / output devices such as a keyboard, a mouse, a display, and a printer.

[0120] Furthermore, the program P can be recorded on a non-transitory tangible recording medium M that can be read by the computer C. Such a recording medium M can be, for example, a tape, a disk, a card, a semiconductor memory, or a programmable logic circuit. The computer C can obtain the program P via such a recording medium M. Furthermore, the program P can be transmitted via a transmission medium. Such a transmission medium can be, for example, a communication network or broadcast waves. The computer C can also obtain the program P via such a transmission medium.

[0121] [Additional Note 1] The present invention is not limited to the above-described embodiments and modifications, and various modifications are possible within the scope of the claims. For example, embodiments obtained by appropriately combining the technical means disclosed in the above-described embodiments and modifications are also included in the technical scope of the present invention.

[0122] [Additional Note 2] Some or all of the above-described embodiments and modified examples can be described as follows. However, the present invention is not limited to the following described aspects.

[0123] (Appendix 1) A light transmitting / receiving means for transmitting and receiving communication light; A communication control means for controlling packet communication via the light transmitting and receiving means, The communication control means After transmitting, to the light transmitting / receiving means, either a first packet received by the light transmitting / receiving means or first encoded information including the first packet and generated by network coding, an optical space communications device that causes the light transmitting and receiving means to transmit second encoded information generated by network coding, the second encoded information including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed since the transmission of either the first packet or the first encoded information.

[0124] (Appendix 2) The present invention further includes an estimation unit that estimates a duration of fading occurring during the packet communication by measuring a signal strength of a plurality of packets received by the light transmitting / receiving unit, 2. The optical space communications device according to claim 1, wherein the communication control means sets an estimated duration, which is the duration of the fading estimated by the estimation means, as the first predetermined time.

[0125] (Appendix 3) The present invention further includes an estimation unit that estimates a duration of fading occurring during the packet communication by measuring a signal strength of a plurality of packets received by the light transmitting / receiving unit, The optical space communications device according to claim 1, wherein the communication control means sets the first predetermined time to the sum of the estimated duration estimated by the estimation means and at least one of an adjustment time required to adjust the angle of the antenna of the light transmitting and receiving means and a synchronization time required to synchronize the communication signal of the packet communication.

[0126] (Appendix 4) The optical space communications device according to claim 1, wherein, when either the first packet or the first encoded information, or the second encoded information is not transmitted, the communication control means causes the light transmitting / receiving means to transmit the not-transmitted information after a second predetermined time has elapsed from the time when the not-transmitted information should have been transmitted.

[0127] (Appendix 5) An optical space communication system including a plurality of optical space communication devices, Among the plurality of optical space communications devices, at least two or more optical space communications devices are A light transmitting / receiving means for transmitting and receiving communication light; A communication control means for controlling packet communication via the light transmitting and receiving means, The communication control means After transmitting, to the light transmitting / receiving means, either a first packet or first coded information including the first packet and generated by network coding, an optical space communication system that causes the light transmitting and receiving means to transmit second encoded information generated by network coding, the second encoded information including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed since the transmission of either the first packet or the first encoded information.

[0128] (Appendix 6) At least two or more of the optical space communications devices, The method further includes a decoding unit capable of decoding an unprocessed packet that is a packet that has not been network-coded by the communication control unit, the first coded information, and the second coded information, An optical space communication system as described in Appendix 5, wherein the decoding means of one optical space communication device decodes the unprocessed packet, the first encoded information, and the second encoded information transmitted from the light transmitting and receiving means of another optical space communication device.

[0129] (Appendix 7) An optical space communication method including packet communication control via a light transmitting / receiving means for transmitting and receiving communication light, The packet communication control includes: After transmitting, to the light transmitting / receiving means, either a first packet or first coded information including the first packet and generated by network coding, a second encoded information generated by network coding and including the first packet and a second packet received by the light transmitting / receiving means at a time when a first predetermined time has elapsed since the transmission of either the first packet or the first encoded information, the second encoded information being generated by the light transmitting / receiving means;

[0130] (Appendix 8) A program for causing a computer to operate as the optical space communications device according to any one of claims 1 to 4, the program causing the computer to function as each of the means.

[0131] (Appendix 9) An optical space communications device having at least one processor, The processor, A communication process for performing packet communication; A communication control process for controlling the packet communication is executed; The optical space communications device executes the communication control process.

[0132] The optical space communications device may further include a memory, and the memory may store a program for causing the processor to execute each of the processes. The program may be recorded in a computer-readable, non-transitory, tangible recording medium. [Explanation of symbols]

[0133] 1, 2 Optical space communication equipment 3. First free space optical communications device (another free space optical communications device) 4 Fourth free space optical communications device (one free space optical communications device) 10, 20 Light transmitting / receiving unit (light transmitting / receiving means) 11, 312, 412 Communication control unit (communication control means) 311, 411 Estimation unit (estimation means) 313, 413 Decoding unit (decoding means) 100, 200 Optical space communication system Pi-j Any packet (first packet) P i Packet (second packet) P i ´ Second coding information T Link Synchronization Time T Loss First predetermined time T Point Adjustment Time T Optic Estimated duration T o Second Predetermined Time

Claims

1. A light transmitting / receiving means for transmitting and receiving communication light; a communication control means for controlling packet communication via the light transmitting and receiving means, The communication control means After transmitting, to the light transmitting / receiving means, either a first packet received by the light transmitting / receiving means or first encoded information including the first packet and generated by network coding, An optical space communications device that causes the light transmitting and receiving means to transmit second encoded information generated by network coding, the second encoded information including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed since the transmission of either the first packet or the first encoded information.

2. The present invention further includes an estimation unit that estimates a duration of fading occurring during the packet communication by measuring a signal strength of a plurality of packets received by the light transmitting / receiving unit, The optical space communications device according to claim 1 , wherein the communication control means sets an estimated duration, which is the duration of the fading estimated by the estimation means, as the first predetermined time.

3. The present invention further includes an estimation unit that estimates a duration of fading occurring during the packet communication by measuring a signal strength of a plurality of packets received by the light transmitting / receiving unit, 2. The optical space communications device according to claim 1, wherein the communication control means sets the first predetermined time to the sum of the estimated duration estimated by the estimation means and at least one of an adjustment time required to adjust the angle of the antenna of the light transmitting and receiving means and a synchronization time required to synchronize the communication signal of the packet communication.

4. The optical space communications device according to claim 1, wherein, when the first packet, the first encoded information, or the second encoded information is not transmitted from the light transmitting / receiving means, the communication control means causes the light transmitting / receiving means to transmit the not-transmitted information after a second predetermined time has elapsed from the time when the not-transmitted information should have been transmitted.

5. An optical space communication system including a plurality of optical space communication devices, Among the plurality of optical space communications devices, at least two or more optical space communications devices are A light transmitting / receiving means for transmitting and receiving communication light; A communication control means for controlling packet communication via the light transmitting and receiving means, The communication control means After transmitting, to the light transmitting / receiving means, either a first packet or first coded information including the first packet and generated by network coding, An optical space communication system that causes the light transmitting and receiving means to transmit second encoded information generated by network coding, the second encoded information including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed from the time of transmission of either the first packet or the first encoded information.

6. At least two or more of the optical space communications devices, a decoding unit capable of decoding an unprocessed packet that is a packet that has not been network-coded by the communication control unit, the first coded information, and the second coded information; The optical space system according to claim 5, wherein the decoding means of one optical space communication device decodes the unprocessed packet, the first encoded information, and the second encoded information transmitted from the transmitting and receiving means of another optical space communication device.

7. An optical space communication method including packet communication control via a light transmitting / receiving means for transmitting and receiving communication light, The packet communication control includes: After transmitting, to the light transmitting / receiving means, either a first packet or first coded information including the first packet and generated by network coding, A method for optical space communication, comprising causing the light transmitting and receiving means to transmit second encoded information generated by network coding, the second encoded information including the first packet and a second packet received by the light transmitting and receiving means at a time when a first predetermined time has elapsed since the transmission of either the first packet or the first encoded information.

8. A program for causing a computer to operate as the optical free space communications device according to any one of claims 1 to 4, the program causing the computer to function as each of the means.

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