Hub optical communication device and control method

Abstract

Provided is a line concentrating optical communication device that communicates with a plurality of optical communication devices through free space optical communication, the line concentrating optical communication device comprising: an optical device control unit that, on the basis of angle information that is information indicating an angle at which the optical communication devices and a spatial optical device that can control the angle can communicate, and a time slot that represents the time at which communication is possible assigned to each optical communication device, controls the angle of the spatial optical device for each time slot; and an optical communication unit that communicates with each of the optical communication devices via the spatial optical device.

Description

Technical Field

[0001] The present invention relates to a concentrator optical communication device and a control method.

Background Art

[0002] In current free space optical communication systems, data communication between an optical transmitter and an optical receiver is performed in a P2P (point-to-point) topology. FIG. 4 is a diagram showing the configuration of a conventional free space optical communication system 100. The free space optical communication system 100 includes one optical communication device 110 and one optical communication device 210. The optical communication device 110 and the optical communication device 210 perform wireless communication using light. The optical communication device 110 includes a spatial optical device 111, a modulator 112, a light source 113, a photodetector 114, and a demodulator 115.

[0003] The spatial optical device 111 forms a transmission optical beam using, for example, the light output from the light source 113. The spatial optical device 111 receives, for example, the light transmitted from the optical communication device 210. The modulator 112 modulates data to be transmitted (hereinafter referred to as "transmission data"). The light source 113 generates an optical signal using the modulated transmission data. The photodetector 114 converts the optical signal received by the spatial optical device 111 into an electrical signal. The demodulator 115 demodulates the electrical signal converted by the photodetector 114.

[0004] The optical communication device 210 includes a spatial optical device 211, a modulator 212, a light source 213, a photodetector 214, and a demodulator 215. Since each functional unit included in the optical communication device 210 performs the same processing as each function included in the optical communication device 110, the description thereof is omitted. As described above, in the P2P communication shown in the conventional free space optical communication system 100, intensity modulation or demodulation (OOK: On-Off Keying) is performed in a binary on-off value, and since the optical communication device 110 and the optical communication device 210 are always connected, data communication is performed using a continuous signal.

Prior Art Documents

Non-Patent Documents

[0005] [Non-Patent Document 1] Dong-Yiel Song, Yoon-Suk Hurh, Jin-Woo Cho, Jung-Hwan Lim, Dong-Woo Lee, Jae-Seung Lee and Youngchul Chung, “4×10 Gb / s terrestrial optical free space transmission over 1.2 km using an EDFA preamplifier with 100 GHz channel spacing”, Optics Express vol. 7, no. 8, pp. 280-284, Oct. 2000. Summary of the Invention [Problem to be solved by the invention]

[0006] In free-space optical communication systems, it is possible to connect them using a point-to-multipoint (P2MP) topology to make communication more efficient. The P2MP topology has the advantage that a large number of optical communication devices can be accommodated more economically by placing a single optical concentrator. On the other hand, to realize free-space optical communication in a P2MP topology, multiple optical communication devices must be connected to a single optical concentrator. It is possible to use an optical splitter to connect multiple optical communication devices to a single optical concentrator, but the use of an optical splitter results in large optical loss. Therefore, in order to suppress optical loss, a technology is desired that allows communication in a P2MP topology without using an optical splitter.

[0007] In view of the above circumstances, an object of the present invention is to provide a technique that enables communication in a point-to-multipoint topology without using an optical splitter in a free space optical communication system. [Means for solving the problem]

[0008] One aspect of the present invention is a hub optical communication device that communicates with a plurality of optical communication devices by free-space optical communication, and includes angle information indicating an angle at which a spatial optical device capable of controlling the angle with each optical communication device can communicate, and an optical device control unit that controls the angle of the spatial optical device for each time slot based on a time slot representing the communicable time assigned to each optical communication device, and an optical communication unit that communicates with each optical communication device via the spatial optical device.

[0009] One aspect of the present invention is a control method performed by a hub optical communication device that communicates with a plurality of optical communication devices by free-space optical communication, and controls the angle of the spatial optical device for each time slot based on angle information indicating an angle at which a spatial optical device capable of controlling the angle with each optical communication device can communicate, and a time slot representing the communicable time assigned to each optical communication device, and communicates with each optical communication device via the spatial optical device.

Advantages of the Invention

[0010] According to the present invention, in a free-space optical communication system, it is possible to communicate in a point-to-multipoint topology without using an optical splitter.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a diagram showing a configuration of a free space optical communication system 1 according to the present invention. The free space optical communication system 1 includes a plurality of optical communication devices 10-1 to 10-n (n is an integer equal to or greater than 2) and one optical communication concentrator 20. The optical communication concentrator 20 is connected to a free space optical device 40 via an optical fiber 30. Hereinafter, when there is no need to distinguish between the optical communication devices 10-1 to 10-n, they will simply be referred to as optical communication device 10.

[0013] The spatial optical device 40 is an optical device capable of controlling the radiation angle and reception angle of the light beam at high speed, for example, a high-speed mechanical mirror actuator or an optical SLM (spatial light modulator). The optical concentrator 20 uses the spatial optical device 40 to control the radiation angle and reception angle of the light beam at high speed, so that the optical concentrator 20 connects the optical communication devices 10 to the optical communication device 20. A free space transmission path is formed between the optical communication devices 10-1 to 10-n and the spatial optical device 40, and the optical beam is transmitted. Since the optical concentrator 20 in this embodiment needs to control the angle of the spatial optical device 40 based on the time slot, it is preferable that the spatial optical device 40 is an optical device capable of operating at high speed.

[0014] The optical communication device 10 is a device that performs communication with the optical communication concentrator 20. For example, the optical communication device 10 is a satellite located in outer space or an optical communication device installed on the ground.

[0015] The concentrating optical communication device 20 communicates with a plurality of optical communication devices 10-1 to 10-n. For example, communication between the plurality of optical communication devices 10-1 to 10-n and the concentrating optical communication device 20 is performed by TDM (Time Division Multiplexing). The concentrating optical communication device 20 assigns time slots so that the optical communication devices 10 do not overlap, and switches the emission angle and the reception angle of the spatial optical device 40 according to the assigned time slots to connect to and communicate data with each optical communication device 10.

[0016] Next, each functional unit of the optical communication device 10 and the aggregated optical communication device 20 will be described. Since the functional units provided in the optical communication devices 10-1 to 10-n are the same, they will be described without particular distinction. The optical communication device 10 includes a spatial optical device 11, a modulator 12, a light source 13, a photodetector 14, and a demodulator 15.

[0017] The spatial optical device 11 forms an optical beam for transmission using, for example, the light output from the light source 13. The spatial optical device 11 receives, for example, the light transmitted from the spatial optical device 40. The spatial optical device 11 is, for example, an optical device capable of controlling the emission angle and the reception angle of the optical beam. For example, the spatial optical device 11 may be a mechanical mirror actuator or an optical SLM. Note that the spatial optical device 11 is not limited to the above, and may be a conventionally used spatial optical device 111. The spatial optical device 11 is provided facing the direction of the spatial optical device 40. On the other hand, the spatial optical device 40 is controlled to switch the emission angle and the reception angle according to the control of the aggregated optical communication device 20. Therefore, when the directions of the emission angle and the reception angle of the spatial optical device 40, which can be switched at high speed, match the directions of the emission angle and the reception angle of the spatial optical device 11, the optical communication device 10 can communicate with the aggregated optical communication device 20 via the spatial optical device 11 and the spatial optical device 40.

[0018] The modulator 12 modulates the transmission data. The light source 13 generates an optical signal using the modulated transmission data. The photodetector 14 converts the optical signal received by the spatial optical device 11 into an electrical signal. The photodetector 14 is, for example, a PD (Photo Diode). The demodulator 15 demodulates the electrical signal converted by the photodetector 14.

[0019] The multiplexed optical communication device 20 includes a front-end unit 21 (optical communication unit), a modulation / demodulation unit 22, and an optical device control unit 23. The front-end unit 21 is composed of a burst transmission circuit 24, a light source 25, a photodetector 26, and a burst reception circuit 27. The burst transmission circuit 24 generates a burst signal. The light source 25 generates an optical signal using the burst signal generated by the burst transmission circuit 24. The burst transmission circuit 24 and the light source 25 correspond to an optical transmission unit that transmits an optical signal.

[0020] The photodetector 26 converts the optical signal received by the optical fiber 30 into an electrical signal. The photodetector 26 is, for example, a PD. The burst reception circuit 27 compensates for the power difference of the received burst frame generated by different space transmission paths from the optical communication device 10 to the multiplexed optical communication device 20. The photodetector 26 and the burst reception circuit 27 correspond to an optical reception unit that receives an optical signal.

[0021] The modulation / demodulation unit 22 is composed of a modulator 28 and a demodulator 29. The modulator 28 modulates the transmission data. The demodulator 29 demodulates the electrical signal output from the burst reception circuit 27. Note that the modulation / demodulation unit 22 may perform either intensity modulation direct detection or multi-value modulation coherent detection.

[0022] The optical device control unit 23 determines a time slot to be assigned to each optical communication device 10 based on the identification information of each optical communication device 10 and the information on the arrival time. Then, the optical device control unit 23 controls the emission angle and the light reception angle of the spatial optical device 40 based on the information on the determined time slot and the angle information.

[0023] The angle information is information indicating an angle for directing an optical beam to each optical communication device 10. If the orientations of the spatial optical device 11 and the spatial optical device 40 provided in each optical communication device 10 do not match, communication cannot be performed. In order to enable communication with each optical communication device 10, the angle information includes information indicating an angle for directing an optical beam to the optical communication device 10 in association with the identification information of each optical communication device 10. The angle information is stored in advance in the optical concentrator 20. The identification information of each optical communication device 10 is stored in advance in the optical concentrator 20.

[0024] The arrival time indicates the arrival time of the burst frame generated by each optical communication device 10 to the optical concentrator 20. The optical device control unit 23 estimates the arrival time of each burst frame based on distance information between each optical communication device 10 and the optical concentrator 20 and refractive index information of the spatial transmission path. The distance information between each optical communication device 10 and the optical concentrator 20 may be acquired using position information obtained by a GPS (Global Positioning System). Furthermore, the optical device control unit 23 acquires refractive index information of the outer space and the atmosphere using measurement information obtained from a meteorological observation device, a space satellite, or the like. The refractive index information indicates the refractive index occurring in the space between each optical communication device 10 and the optical concentrator 20. The refractive index information differs for each spatial communication path between each optical communication device 10 and the optical concentrator 20.

[0025] 2 is a diagram showing an example of burst frames transmitted and received between the optical communication device 10 and the optical concentrator 20 in the embodiment. Each frame 50 shown in FIG. 2 represents a burst frame transmitted from each optical communication device 10 to the optical concentrator 20, or a burst frame transmitted from the optical concentrator 20 to each optical communication device 10.

[0026] FIG. 3 is a flowchart showing a process flow of the optical concentrator 20 in the embodiment. The optical device control unit 23 acquires distance information indicating the distance between each optical communication device 10 and the optical communication concentrator 20 using the position information obtained by the GPS (step S101). Next, the optical device control unit 23 acquires refractive index information of outer space and the atmosphere using measurement information obtained from meteorological observation equipment, space satellites, etc. (step S102).

[0027] The optical device control unit 23 estimates the arrival time of the burst frame generated by each optical communication device 10 at the concentrating optical communication device 20 using the acquired multiple pieces of distance information and the refractive index information (step S103). Specifically, the optical device control unit 23 estimates the arrival time for each optical communication device 10 based on the following formula (1). Note that the refractive index indicated by the refractive index information differs for each spatial communication path between each optical communication device 10 and the concentrating optical communication device 20. Therefore, the optical device control unit 23 estimates the arrival time for each optical communication device 10 using the refractive index information of the spatial communication path between the optical communication device 10 for which the arrival time is to be obtained and the concentrating optical communication device 20.

[0028] Arrival time = (distance × refractive index) / speed of light in vacuum Equation (1)

[0029] The optical device control unit 23 assigns time slots to each optical communication device 10 based on the estimated arrival time for each optical communication device 10 so that the optical communication devices 10 do not overlap (step S104). For example, the optical device control unit 23 may assign time slots in ascending order of arrival time. The optical device control unit 23 notifies each optical communication device 10 of information on the time slots assigned to the optical communication devices 10. After that, the optical device control unit 23 controls switching of the angle of the spatial optical device 40 according to the time slot (step S105).

[0030] Specifically, when it is time corresponding to the time slot assigned to the optical communication device 10-1, the optical device control unit 23 generates a control signal for controlling the angle of the spatial optical device 40 so that the angle indicated by the angle information corresponding to the optical communication device 10-1 is obtained. The optical device control unit 23 outputs the generated control signal to the spatial optical device 40. The spatial optical device 40 changes the emission angle and the light reception angle to the angle included in the control signal according to the control signal. In this way, the optical device control unit 23 generates a control signal including information for setting the angle of the spatial optical device 40 to a desired angle, and outputs the generated control signal to the spatial optical device 40 to control the angle of the spatial optical device 40. As a result, burst frames can be transmitted and received between the optical communication device 10-1 and the hub optical communication device 20.

[0031] For example, the hub optical communication device 20 transmits an optical signal, which is a burst frame output from the front-end unit 21, to the optical communication device 10-1 via the spatial optical device 40. For example, the hub optical communication device 20 receives an optical signal, which is a burst frame transmitted from the optical communication device 10-1, via the spatial optical device 40.

[0032] Thereafter, the optical device control unit 23 repeatedly performs the above control according to the time slot to control communication between each optical communication device 10 and the hub optical communication device 20.

[0033] According to the free space optical communication system 100 configured as described above, in the free space optical communication system, it becomes possible to perform communication in a point-to-multipoint topology without using an optical splitter. Specifically, the concentrator optical communication device 20 includes an optical device control unit 23 that controls the angle of the spatial optical device 40 for each time slot based on the angle information and the time slot, and a front-end unit 21 that communicates with each optical communication device 10 via the spatial optical device 40. In this way, the concentrator optical communication device 20 controls the angle of the spatial optical device 40 according to the time slot and connects to each optical communication device 10. As a result, in the free space optical communication system, it becomes possible to perform communication in a point-to-multipoint topology without using an optical splitter.

[0034] Furthermore, the concentrator optical communication device 20 estimates the arrival time of the signals transmitted from each optical communication device 10 based on the distance information and the refractive index information, and assigns time slots so that each optical communication device 10 does not overlap according to the arrival time. In this way, the concentrator optical communication device 20 estimates the arrival time taking into account the refractive index generated in the space between each optical communication device 10. Therefore, it becomes possible to reduce the influence of the arrival time according to the weather conditions and realize communication in a point-to-multipoint topology.

[0035] Furthermore, the concentrator optical communication device 20 generates a control signal including information for setting the angle of the spatial optical device 40 to a desired angle, and controls the angle of the spatial optical device 40 by outputting the generated control signal to the spatial optical device 40. As a result, it becomes possible to freely switch the angle of the spatial optical device 40 according to the time slot.

[0036] Hereinafter, a modification example of the free space optical communication system 100 will be described. The spatial optical device 40 may be provided in the concentrator optical communication device 20.

[0037] Some functions of the above-described optical concentration communication device 20 (for example, the optical device control unit 23) may be implemented by a computer. In that case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed to implement it. Here, the "computer system" shall include hardware such as an OS and peripheral devices. Further, the "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, etc., and a storage device such as a hard disk incorporated in a computer system.

[0038] Furthermore, the "computer-readable recording medium" also includes those that dynamically hold a program for a short time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, and those that hold a program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or a client in that case. Also, the above program may be for implementing a part of the aforementioned functions, and may further be capable of being implemented in combination with a program already recorded in the computer system for implementing the aforementioned functions, or may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0039] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and designs and the like within the scope not departing from the gist of the present invention are also included.

Industrial Applicability

[0040] The present invention can be applied to free space optical communication system technology for performing point-to-multipoint communication.

Explanation of Signs

[0041] 10-1 to 10-n... optical communication device, 11... spatial optical device, 12... modulator, 13... light source, 14... photodetector, 15... demodulator, 20... hub optical communication device, 21... front-end unit, 22... modulation / demodulation unit, 23... optical device control unit, 24... burst transmission circuit, 25... light source, 26... photodetector, 27... burst reception circuit, 28... modulator, 29... demodulator, 30... optical fiber, 40... spatial optical device

Claims

1. A hub optical communication device that communicates with a plurality of optical communication devices by free space optical communication, an optical device control unit that controls the angle of the spatial optical device for each time slot based on angle information indicating an angle at which communication with each optical communication device is possible with a spatial optical device whose angle can be controlled, and a time slot representing communicable time assigned to each optical communication device; an optical communication unit that communicates with each optical communication device via the spatial optical device; comprising: The optical device control unit estimates the arrival time of a signal transmitted from each optical communication device based on distance information between the hub optical communication device and each optical communication device and refractive index information representing a refractive index generated in the space between the hub optical communication device and each optical communication device, and assigns the time slot so that the communicable times of the respective optical communication devices do not overlap according to the arrival time. A hub optical communication device.

2. The optical device control unit generates a control signal including information for setting the angle of the spatial optical device to a desired angle, and outputs the generated control signal to the spatial optical device to control the angle of the spatial optical device. The hub optical communication device according to claim 1.

3. The optical communication unit communicates with each optical communication device by means of a burst frame. The hub optical communication device according to claim 1 or 2.

4. A control method performed by a hub optical communication device that communicates with a plurality of optical communication devices by free space optical communication, controlling the angle of the spatial optical device for each time slot based on angle information indicating an angle at which communication with each optical communication device is possible with a spatial optical device whose angle can be controlled, and a time slot representing communicable time assigned to each optical communication device; communicating with each optical communication device via the spatial optical device; estimating the arrival time of a signal transmitted from each optical communication device based on distance information between the hub optical communication device and each optical communication device and refractive index information representing a refractive index generated in the space between the hub optical communication device and each optical communication device; A control method for assigning the time slot so that the communicable times of the respective optical communication devices do not overlap according to the arrival time.

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