Optical wireless communication system and optical wireless communication method

Abstract

This optical wireless communication system comprises: a first transmission device which wirelessly transmits an optical signal to a first reception device via a polarization filter having a transmission axis oriented in a first direction; the first reception device which receives the optical signal transmitted from the first transmission device via the polarization filter having the transmission axis oriented in the first direction; a second transmission device which wirelessly transmits the optical signal to a second reception device via the polarization filter having the transmission axis oriented in a second direction different from the first direction; and the second reception device which receives the optical signal transmitted from the second transmission device via the polarization filter having the transmission axis oriented in the second direction.

Description

Technical Field

[0001] The present invention relates to an optical wireless communication system and optical wireless communication method in the law .

Background Art

[0002] With the depletion of radio frequency resources, an optical wireless communication system that realizes wireless communication in a different way from conventional radio communication using radio waves has been studied. An optical wireless communication system is a communication system that performs wireless communication using electromagnetic waves (light) with wavelengths between infrared rays and visible light. According to the optical wireless communication system, it is possible to realize wireless communication that does not interfere with conventional wireless communication using a predetermined frequency band. In addition, since the optical wireless communication system does not cause light transmission in a shielding object such as a building wall, it has immunity to interference and is attracting attention from the viewpoint of high security (see, for example, Non-Patent Document 1).

[0003] Hereinafter, the configuration of a general optical wireless communication system when visible light is used for downlink signal transmission will be described. FIG. 7 is a diagram showing an example of the configuration of a general optical wireless communication system. The optical wireless communication system 8 shown in FIG. 7 includes an optical wireless communication device 810 and an optical wireless communication device 820. The optical wireless communication device 810 is a communication device installed, for example, on the ceiling indoors and functions as a radio base station that houses the optical wireless communication device 820. The optical wireless communication device 820 is, for example, a small terminal device and communicates with the optical wireless communication device 810.

[0004] As shown in FIG. 7, the optical wireless communication device 810 includes a light source 811, an infrared light receiving unit 812, and an optical signal processing unit 813. The light source 811 is configured to include, for example, an LED (Light Emitting Diode), and transmits visible light VL. Note that the light source 811 may be provided in a general lighting fixture or the like. The light source 811 is connected to the optical signal processing unit 813. The optical signal processing unit 813 can control the light source 811 and change the lighting cycle, lighting intensity, etc. of the visible light VL transmitted from the light source 811. The optical signal processing unit 813 converts the desired information to be transmitted to the optical wireless communication device 820 into an optical signal represented by a change in the visible light VL. Thereby, an optical signal (downlink signal) using the visible light VL is transmitted from the optical wireless communication device 810 to the optical wireless communication device 820. Note that the optical signal processing unit 813 may be connected to a higher-level communication network such as the Internet or an intranet.

[0005] As shown in FIG. 7, the optical wireless communication device 820 includes a visible light receiving unit 821 and an infrared light transmitting unit 822. The visible light receiving unit 821 receives the visible light VL transmitted from the light source 811. The visible light receiving unit 821 reads out the optical signal (downlink signal) included in the visible light VL. The optical wireless communication device 820 performs various processes such as reception processing and data conversion on the optical signal read out by the visible light receiving unit 821. Further, infrared light is used for the optical signal (uplink signal) transmitted from the optical wireless communication device 820 to the optical wireless communication device 810. The infrared light transmitting unit 822 transmits an optical signal using infrared light to the optical wireless communication device 810.

[0006] The infrared rays emitted from the infrared transmitting unit 822 are received by the infrared light receiving unit 812 of the optical wireless communication device 810. The infrared light receiving unit 812 reads out the optical signal (uplink signal) contained in the infrared rays. The infrared light receiving unit 812 is connected to the optical signal processing unit 813. The optical signal processing unit 813 performs various processes such as reception processing and data conversion on the optical signal read out by the infrared light receiving unit 812. Note that the optical signal processing unit 813 may transfer the optical signal on which various processes have been performed to the upper communication network. In this way, a general optical wireless communication system using visible light and infrared rays is realized.

[0007] Note that the optical wireless communication system 8 shown in FIG. 7 is a system configuration assuming that the downlink signal is transmitted using existing lighting equipment such as LED lighting installed indoors, for example, but an infrared ray may also be used for the transmission of the downlink signal. FIG. 8 is a diagram showing an example of the configuration of an optical wireless communication system that uses infrared rays for both the transmission of the uplink signal and the transmission of the downlink signal. The optical wireless communication system 9 shown in FIG. 8 includes an optical wireless communication device 910 and an optical wireless communication device 920. The optical wireless communication device 910 includes an infrared transmitting unit 911, an infrared light receiving unit 912, and an optical signal processing unit 913. The infrared transmitting unit 911 is connected to the optical signal processing unit 913. The optical signal processing unit 913 can control the infrared transmitting unit 911 and blink the infrared rays emitted from the infrared transmitting unit 911. The optical signal processing unit 913 converts the desired information to be transmitted to the optical wireless communication device 920 into an optical signal represented by, for example, the on and off of infrared rays. Thereby, an optical signal (downlink signal) using infrared rays is transmitted from the optical wireless communication device 910 to the optical wireless communication device 820.

[0008] As shown in FIG. 8, the optical wireless communication device 920 includes an infrared light receiving unit 921 and an infrared light transmitting unit 922. The infrared light receiving unit 921 receives the infrared light transmitted from the infrared light transmitting unit 911. The infrared light receiving unit 921 reads out the optical signal (downlink signal) included in the infrared light. The optical wireless communication device 920 performs various processes such as reception processing and data conversion on the optical signal read by the infrared light receiving unit 921. Also, infrared light is used for the optical signal (uplink signal) transmitted from the optical wireless communication device 920 to the optical wireless communication device 910, similar to the optical wireless communication system 8 shown in FIG. 7 described above. The configurations of the infrared light transmitting unit 922 and the infrared light receiving unit 912 are the same as the configurations of the infrared light transmitting unit 822 and the infrared light receiving unit 812 shown in FIG. 7 described above.

[0009] The infrared light receiving unit 912 of the optical wireless communication device 910 is connected to an optical signal processing unit 913. The optical signal processing unit 913 performs various processes such as reception processing and data conversion on the optical signal read by the infrared light receiving unit 912. In this way, a general optical wireless communication system using infrared light is realized for both the transmission of the uplink signal and the transmission of the downlink signal.

[0010] Note that the optical wireless communication system 8 illustrated in FIG. 7 is configured to perform wireless communication between the optical wireless communication device 810, which is a radio base station, and the optical wireless communication device 820, which is a wireless communication terminal. The optical wireless communication system 9 illustrated in FIG. 8 is configured to perform wireless communication between the optical wireless communication device 910, which is a radio base station, and the optical wireless communication device 920, which is a wireless communication terminal. However, it is not limited to such a configuration. For example, it may be a communication system for performing wireless communication using visible light, infrared light, etc. between a plurality of optical wireless communication devices having the same configuration, such as a plurality of wireless relay stations in relay wireless. Thus, the optical wireless communication system can have an arbitrary system configuration according to the purpose.

Prior Art Documents

Non-Patent Documents

[0011]

Non-Patent Document 1

[0012] The transmission frequency (equivalent to the transmission wavelength) of the signal light in an optical wireless communication system is defined by the elements used in light sources such as LEDs. Here, when multiple optical signals are transmitted simultaneously using a plurality of light sources of the same type installed in close proximity to each other, interference may occur between these optical signals, and the transmission characteristics may deteriorate.

[0013] FIG. 9 is a diagram showing an example of the configuration of an optical wireless communication system that simultaneously transmits a plurality of optical signals using a plurality of light sources of the same type. The optical wireless communication system 8' shown in FIG. 9 has a configuration in which two sets of the optical wireless communication devices 810 and 820 of the optical wireless communication system 8 shown in FIG. 7 are installed in close proximity. As shown in FIG. 9, the optical wireless communication device 810-1 and the optical wireless communication device 820-1 form a set of optical wireless communication devices that communicate with each other, and the optical wireless communication device 810-2 and the optical wireless communication device 820-2 form a set of optical wireless communication devices that communicate with each other.

[0014] In an optical wireless communication system 8' in which a plurality of light sources 811 of the same type are installed in proximity to each other as shown in FIG. 9, downstream signals are transmitted from these plurality of light sources 811 to a plurality of optical wireless communication devices 820 respectively. In such a case, there has been a problem that interference may occur between two downstream signals, resulting in deterioration of transmission characteristics. Also, there have been similar problems not only in the transmission of downstream signals but also in the transmission of upstream signals.

[0015] In view of the above circumstances, an object of the present invention is to provide a technology capable of performing optical wireless communication without causing interference between optical signals even when transmitting optical signals respectively using a plurality of light sources of the same type.

Means for Solving the Problem

[0016] One aspect of the present invention is a first transmission device that wirelessly transmits an optical signal to a first reception device via a polarization filter whose transmission axis direction is a first direction, the first reception device that receives the optical signal transmitted from the first transmission device via the polarization filter whose transmission axis direction is the first direction, a second transmission device that wirelessly transmits the optical signal to a second reception device via a polarization filter whose transmission axis direction is a second direction different from the first direction, and the second reception device that receives the optical signal transmitted from the second transmission device via the polarization filter whose transmission axis direction is the second direction, and is an optical wireless communication system having the same.

[0017] Also, one aspect of the present invention is a reception unit that receives a signal including control information wirelessly transmitted from another wireless communication device facing it, and based on the control information, specifies the direction of the transmission axis of a first polarization filter through which the optical signal passes when transmitted from the other wireless communication device, and corrects the direction of the second polarization filter so that the specified direction matches the direction of the transmission axis of a second polarization filter through which the optical signal passes when the own device receives it, and is an optical wireless communication device provided with the same.

[0018] In addition, one aspect of the present invention includes a first transmission step in which a first transmission device wirelessly transmits an optical signal to a first reception device via a polarization filter whose transmission axis is oriented in a first direction; a first reception step in which the first reception device receives the optical signal transmitted from the first transmission device via the polarization filter whose transmission axis is oriented in the first direction; a second transmission step in which a second transmission device wirelessly transmits the optical signal to a second reception device via a polarization filter whose transmission axis is oriented in a second direction different from the first direction; and a second reception step in which the second reception device receives the optical signal transmitted from the second transmission device via the polarization filter whose transmission axis is oriented in the second direction. This is an optical wireless communication method.

[0019] In addition, one aspect of the present invention includes a reception step of receiving a signal including control information wirelessly transmitted from another wireless communication device facing it; a control step of specifying the orientation of the transmission axis of a first polarization filter through which the optical signal passes when transmitted from the other wireless communication device based on the control information, and correcting the orientation of the second polarization filter so that the specified orientation matches the orientation of the transmission axis of the second polarization filter through which the optical signal passes when the own device receives it. This is an optical wireless communication control method.

Advantages of the Invention

[0020] According to the present invention, even when optical signals are transmitted respectively using a plurality of light sources of the same type, it becomes possible to perform optical wireless communication without causing interference between the optical signals.

Brief Description of the Drawings

[0021]

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[0022] Hereinafter, the optical wireless communication system of the present invention and Optical wireless communication method the law , will be described with reference to the drawings. The present invention relates to an optical wireless communication system that realizes optical wireless communication using visible light, infrared rays, etc. and Optical wireless communication method in the law Note that the embodiments described below are merely one form, and the embodiments to which the present invention can be applied are not limited to the embodiments described below.

[0023] [First Embodiment] Hereinafter, the first embodiment of the present invention will be described.

[0024] [Configuration of Optical Wireless Communication System] Hereinafter, the configuration of the optical wireless communication system 1 in the first embodiment will be described. FIG. 1 is a diagram showing the configuration of the optical wireless communication system 1 in the first embodiment of the present invention. As shown in FIG. 1, the optical wireless communication system 1 includes an optical wireless communication device 110-1, an optical wireless communication device 110-2, an optical wireless communication device 120-1, and an optical wireless communication device 120-2.

[0025] In the following description, when it is not necessary to distinguish between the optical wireless communication device 110-1 and the optical wireless communication device 110-2, they may simply be referred to as "optical wireless communication device 110". Also, in the following description, when it is not necessary to distinguish between the optical wireless communication device 120-1 and the optical wireless communication device 120-2, they may simply be referred to as "optical wireless communication device 120".

[0026] The optical wireless communication device 110-1 is a communication device installed, for example, on the ceiling indoors and functions as a wireless base station that houses the optical wireless communication device 120-1. Similarly, the optical wireless communication device 110-2 is a communication device installed, for example, on the ceiling indoors and functions as a wireless base station that houses the optical wireless communication device 120-2.

[0027] The optical wireless communication device 120-1 is a small terminal device, for example, and communicates with the optical wireless communication device 110-1. Similarly, the optical wireless communication device 120-2 is a small terminal device, for example, and communicates with the optical wireless communication device 110-2.

[0028] As shown in FIG. 1, the optical wireless communication device 110-1 includes a light source 111, an infrared light receiving unit 112, an optical signal processing unit 113, and two polarization filters 115. The light source 111 is configured to include, for example, an LED and emits visible light VL. Note that the light source 111 may be provided in a general lighting fixture or the like. The light source 111 is connected to the optical signal processing unit 113.

[0029] The optical signal processing unit 113 controls the light source 111 and can change the lighting cycle, lighting intensity, etc. of the visible light VL emitted from the light source 111. The optical signal processing unit 113 converts the desired information to be transmitted to the optical wireless communication device 120-1 into an optical signal represented by the change in the visible light VL. Thereby, an optical signal (downlink signal) using the visible light VL is transmitted from the optical wireless communication device 110-1 to the optical wireless communication device 120-1.

[0030] The visible light VL emitted from the light source 111 is transmitted through the polarization filter 115. Note that the configuration of the polarization filter 115 will be described later.

[0031] Note that the optical signal processing unit 113 may be connected to a higher-level communication network such as the Internet or an intranet.

[0032] As shown in FIG. 1, the optical wireless communication device 120-1 includes a visible light receiving unit 121, an infrared transmitting unit 122, and two polarization filters 125. The visible light receiving unit 121 receives the visible light VL emitted from the light source 111. The visible light receiving unit 121 receives the visible light VL through the polarization filter 125. Note that the configuration of the polarization filter 125 will be described later.

[0033] The visible light receiving unit 121 reads out the optical signal (downlink signal) included in the visible light VL. The optical wireless communication device 120-1 performs various processes such as reception processing and data conversion on the optical signal read by the visible light receiving unit 121.

[0034] In addition, infrared rays are used for the optical signal (uplink signal) transmitted from the optical wireless communication device 120-1 to the optical wireless communication device 110-1. The desired information to be transmitted to the optical wireless communication device 110-1 is converted into an optical signal represented by, for example, the on and off of infrared rays. The infrared transmitting unit 122 transmits the infrared rays including the optical signal by blinking and emitting them toward the optical wireless communication device 110-1. Thereby, an optical signal (uplink signal) using infrared rays is transmitted from the optical wireless communication device 120-1 to the optical wireless communication device 110-1.

[0035] The infrared transmission unit 122 transmits infrared rays through the polarization filter 125. The configuration of the polarization filter 125 will be described later.

[0036] The infrared rays transmitted from the infrared transmission unit 122 through the polarization filter 125 are received by the infrared light receiving unit 112 of the optical wireless communication device 110-1. The infrared light receiving unit 112 receives infrared rays through the polarization filter 115. The configuration of the polarization filter 115 will be described later.

[0037] The infrared light receiving unit 112 reads out the optical signal (uplink signal) included in the infrared rays. The infrared light receiving unit 112 is connected to the optical signal processing unit 113. The optical signal processing unit 113 performs various processes such as reception processing and data conversion on the optical signal read out by the infrared light receiving unit 112. Note that the optical signal processing unit 113 may transfer the optical signal that has undergone various processes to the upper communication network. In this way, optical wireless communication using visible light and infrared rays is realized.

[0038] Note that the configuration of the optical wireless communication device 110-2 is the same as that of the optical wireless communication device 110-1 described above, and the configuration of the optical wireless communication device 120-2 is the same as that of the optical wireless communication device 120-1 described above, so the description is omitted.

[0039] [Configuration of Polarization Filter] Hereinafter, the configurations of the polarization filter 115 and the polarization filter 125 will be described. Note that the function of the polarization filter 125 is basically equivalent to the function of the polarization filter 115, so here, the polarization filter 115 will be described as an example.

[0040] The polarization filter 115 is, for example, a colorless and transparent film made of polyvinyl alcohol or its derivative with a thickness of about 0.1 [mm], which is stretched and fixed 3 to 5 times using thermoelasticity or swelling elasticity, so that the polymer micelles are arranged in a fixed direction.

[0041] FIG. 2 is a schematic diagram showing the configuration of the polarization filter 115 in the first embodiment of the present invention. As described above, the configuration of the polarization filter 125 is the same as that of the polarization filter 115. The polarization filter 115 is a filter that transmits only light with a specific transmission axis, for example, a linear polarization filter. Note that the polarization filter 115 may be a filter other than a linear polarization filter, such as a circular polarization filter.

[0042] As shown in FIG. 2, the polarization filter 115 is a linear polarization filter having a transmission axis that is the axis in the fiber direction and an absorption axis that is the axis in the direction orthogonal to the transmission axis. For example, when light vibrating randomly at 360 degrees passes through the polarization filter 115, due to the extremely fine slit-like structure of the polarization filter 115, the wave along the transmission axis is transmitted, and the wave along the absorption axis is absorbed and not transmitted. Also, among the waves vibrating obliquely, the component corresponding to the transmission axis is transmitted, and the component corresponding to the absorption axis is absorbed.

[0043] By installing the polarization filter 115 and the polarization filter 125 in predetermined directions respectively, the light transmitted between the optical wireless communication device 110 and the optical wireless communication device 120 can be blocked or transmitted by the polarization filter on the receiving side.

[0044] FIG. 3 is a diagram for explaining the light shielding by the polarization filter 115 and the polarization filter 125 in the first embodiment of the present invention. When the polarization filter 115 and the polarization filter 125 are linear polarization filters, the light is shielded by installing the polarization filter 115 and the polarization filter 125 with their transmission axes orthogonal to each other. In FIG. 3, the polarization filter 115 is installed such that the transmission axis is in the vertical direction, and the polarization filter 125 is installed such that the transmission axis is in the horizontal direction, and their transmission axes are orthogonal to each other. Therefore, in FIG. 3, the range where the polarization filter 115 and the polarization filter 125 overlap is the range that shields the light.

[0045] FIG. 4 is a diagram for explaining the transmission of light by the polarization filter 115 and the polarization filter 125 in the first embodiment of the present invention. When the polarization filter 115 and the polarization filter 125 are linear polarization filters, the light is transmitted by installing the polarization filter 115 and the polarization filter 125 in such a direction that their transmission axes are parallel to each other. In FIG. 4, the polarization filter 115 is installed so that its transmission axis is in the vertical direction, and the polarization filter 125 is also installed so that its transmission axis is in the vertical direction, and their transmission axes are parallel to each other. Therefore, in FIG. 4, the light is transmitted in all ranges including the range where the polarization filter 115 and the polarization filter 125 overlap.

[0046] The optical wireless communication system 1 of the first embodiment shown in FIG. 1 utilizes the properties of the polarization filter 115 and the polarization filter 125 as described above, so that even when a plurality of light sources 111 of the same type are brought close to each other and the transmission of optical signals is performed simultaneously, optical wireless communication can be performed without causing interference between the optical signals transmitted from the respective light sources 111.

[0047] As shown in FIG. 1, the optical wireless communication device 110-1 and the optical wireless communication device 110-2 each include a polarization filter 115 having a transmission axis in a specific direction outside the light source 111 and outside the infrared light receiving unit 112. Further, the optical wireless communication device 120-1 and the optical wireless communication device 120-2 each include a polarization filter 115 having a transmission axis in a specific direction outside the visible light receiving unit 121 and outside the infrared light transmitting unit 122.

[0048] As shown in FIG. 1, when it is a combination of the optical wireless communication device 110 and the optical wireless communication device 120 such that the transmission axis of the polarization filter 115 coincides with the transmission axis of the polarization filter 125, optical wireless communication becomes possible. This is because the direction of the transmission axis of the polarization filter 115 and the direction of the transmission axis of the polarization filter 125 are the same, so the light transmitted through the polarization filter 115 also passes through the polarization filter 125. Similarly, the light transmitted through the polarization filter 125 also passes through the polarization filter 125.

[0049] In FIG. 1, the direction of the transmission axis of the polarization filter 115 of the optical wireless communication device 110-1 matches the direction of the transmission axis of the polarization filter 125 of the optical wireless communication device 120-1 (in FIG. 1, the direction of the transmission axis is the vertical direction in both cases). Therefore, the optical wireless communication device 110-1 and the optical wireless communication device 120-1 can perform optical wireless communication. Also, in FIG. 1, the direction of the transmission axis of the polarization filter 115 of the optical wireless communication device 110-2 matches the direction of the transmission axis of the polarization filter 125 of the optical wireless communication device 120-2 (in FIG. 1, the direction of the transmission axis is the horizontal direction in both cases). Therefore, the optical wireless communication device 110-2 and the optical wireless communication device 120-2 can perform optical wireless communication.

[0050] In contrast, in FIG. 1, the direction of the transmission axis of the polarization filter 115 of the optical wireless communication device 110-1 is the vertical direction, and the direction of the transmission axis of the polarization filter 125 of the optical wireless communication device 120-2 is the horizontal direction, and the directions of both transmission axes are orthogonal to each other. Therefore, the optical wireless communication device 110-1 and the optical wireless communication device 120-2 cannot perform optical wireless communication. Also, in FIG. 1, the direction of the transmission axis of the polarization filter 115 of the optical wireless communication device 110-2 is the horizontal direction, and the direction of the transmission axis of the polarization filter 125 of the optical wireless communication device 120-1 is the vertical direction, and the directions of both transmission axes are orthogonal to each other. Therefore, the optical wireless communication device 110-2 and the optical wireless communication device 120-1 cannot perform optical wireless communication.

[0051] This is because the direction of the transmission axis of the polarization filter 115 and the direction of the transmission axis of the polarization filter 125 are orthogonal, so the light transmitted through the polarization filter 115 does not pass through the polarization filter 125. Similarly, the light transmitted through the polarization filter 125 does not pass through the polarization filter 115.

[0052] With such a configuration, according to the optical wireless communication system 1 in the first embodiment, the visible light VL transmitted from each of the plurality of adjacent light sources 111 and transmitted through the polarization filter 115 or the polarization filter 125 does not interfere with each other on the receiving side. As a result, the optical wireless communication system 1 can prevent the deterioration of the transmission quality due to interference.

[0053] Specifically, as shown in FIG. 1, the polarization filters (polarization filter 115 and polarization filter 125) of the optical wireless communication devices that perform optical wireless communication with each other are installed so that the directions of the transmission axes are the same, and the polarization filters of the optical wireless communication devices that do not perform optical wireless communication with each other are installed so that the directions of the transmission axes are different from each other (for example, perpendicular directions). By doing so, it becomes possible to prevent interference between optical signals in a plurality of optical wireless communications.

[0054] Note that, as described above, the polarization filters 115 and 125 do not necessarily have to correspond to linearly polarized light, and may be, for example, circularly polarized light or the like. As long as it is an optical wireless communication system that can perform spatial multiplex transmission simultaneously by combining polarization filters having different (for example, perpendicular) transmission axes, it is not limited to the configuration of the optical wireless communication system 1 described above.

[0055] Note that a configuration may be adopted in which the polarization filter 115 is provided only in the light source 111 of the optical wireless communication device 110, and the polarization filter 125 is provided only in the visible light receiving unit 121 of the optical wireless communication device 120. That is, a configuration may be adopted in which the polarization filters 115 and 125 are used only for the downlink signal, and only the interference between optical signals in the transmission of the downlink signal is prevented. Conversely, a configuration may be adopted in which the polarization filter 115 is provided only in the infrared light receiving unit 112 of the optical wireless communication device 110, and the polarization filter 125 is provided only in the infrared light transmitting unit 122 of the optical wireless communication device 120. That is, a configuration may be adopted in which the polarization filters 115 and 125 are used only for the uplink signal, and only the interference between optical signals in the transmission of the uplink signal is prevented.

[0056] In the optical wireless communication system 1 illustrated in FIG. 1, the optical wireless communication device 110 includes one light source 111 and one infrared light receiving unit 112 each, but may include a plurality of light sources 111 and a plurality of infrared light receiving units 112. For example, one optical wireless communication device 110 may be configured to perform optical wireless communication with both the optical wireless communication devices 120-1 and 120-2 using polarization filters 115 installed in different directions respectively.

[0057] The types and the directions of the transmission axes of the polarization filters 115 provided in the light source 111 and the infrared light receiving unit 112 may be the same or different. Similarly, the types and the directions of the transmission axes of the polarization filters 125 provided in the visible light receiving unit 121 and the infrared light transmitting unit 122 may be the same or different. That is, the types and the directions of the transmission axes of the polarization filters 115 and 125 can be arbitrarily selected as long as the same light passes between the optical wireless communication devices (for example, between the optical wireless communication device 110-1 and the optical wireless communication device 120-1, and between the optical wireless communication device 110-2 and the optical wireless communication device 120-2) that perform optical wireless communication with each other, and the same light does not pass between the optical wireless communication devices (for example, between the optical wireless communication device 110-1 and the optical wireless communication device 120-2, and between the optical wireless communication device 110-2 and the optical wireless communication device 120-1) that do not perform optical wireless communication with each other.

[0058] <Second Embodiment> Hereinafter, a second embodiment of the present invention will be described. The optical wireless communication system 1 in the foregoing first embodiment is a communication system assumed to be installed such that the directions of the transmission axes of the polarization filter 115 and the polarization filter 125 are predetermined directions in advance. That is, in the foregoing first embodiment, between the optical wireless communication device 110 and the optical wireless communication device 120 that perform optical wireless communication with each other, they must be installed in advance such that the direction of the transmission axis of the polarization filter 115 included in the optical wireless communication device 110 and the direction of the transmission axis of the polarization filter 125 included in the optical wireless communication device 120 are the same direction.

[0059] However, for example, when the optical wireless communication device 120 is a terminal device that may perform an operation involving rotation, the directions of the transmission axes of the polarization filters 115 and 125 change according to the operation. In this case, a deviation may occur between the direction of the transmission axis of the polarization filter 115 of the optical wireless communication device 110 and the direction of the transmission axis of the polarization filter 125 of the optical wireless communication device 120. When a deviation occurs in the direction of the transmission axis between the transmission side and the reception side, optical wireless communication between the optical wireless communication device 110 and the optical wireless communication device 120 becomes impossible.

[0060] On the other hand, the optical wireless communication device 120a of the optical wireless communication system in the second embodiment described below is configured to include a rotation mechanism that rotates the polarization filter 125 in accordance with the rotation of the own device in order to cope with the change in the direction of the transmission axis of the polarization filter 125 accompanying the rotation of the own device.

[0061] Note that in the present embodiment, the optical wireless communication device 120a is configured to include a rotation mechanism that rotates the polarization filter 125 in accordance with the rotation of the own device. However, the present invention is not limited to such a configuration. For example, the optical wireless communication device 120a may be configured to include a rotation mechanism that rotates the own device itself in accordance with the rotation of the own device.

[0062] [Configuration of Optical Wireless Communication Device] Hereinafter, the configuration of the optical wireless communication device 120a of the optical wireless communication system in the second embodiment will be described. The optical wireless communication device 120a is, for example, a small terminal device. The optical wireless communication device 120a functions as a wireless communication terminal housed in an opposing optical wireless communication device 110 (not shown).

[0063] FIG. 5 is a block diagram showing the configuration of the optical wireless communication device 120a in the second embodiment of the present invention. As shown in FIG. 5, the optical wireless communication device 120a includes a visible light light receiving unit 121, an infrared ray transmitting unit 122, a data processing unit 123, a polarization filter control unit 124, and two polarization filters 125.

[0064] Note that the optical wireless communication device 120a shown in FIG. 5 is a terminal device of an optical wireless communication system that transmits a downstream signal using visible light VL and transmits an upstream signal using infrared light, similar to the optical wireless communication system 1 in the aforementioned first embodiment. However, it is not limited to such a configuration. For example, a configuration in which infrared light is used for both the transmission of the downstream signal and the transmission of the upstream signal may also be possible.

[0065] The visible light receiving unit 121 receives the visible light VL transmitted from the opposing optical wireless communication device 110 (not shown). The visible light receiving unit 121 receives the visible light VL through the polarization filter 125. Since the configuration of the polarization filter 125 is the same as the configuration of the polarization filter 115 shown in FIGS. 2 to 4 described above, the description thereof is omitted.

[0066] The visible light receiving unit 121 reads out the optical signal (downstream signal) included in the visible light VL. The visible light receiving unit 121 performs various processes such as reception processing and data conversion on the read optical signal. The visible light receiving unit 121 is connected to the data processing unit 123. The visible light receiving unit 121 outputs the signal on which various processes have been performed to the data processing unit 123.

[0067] In addition, infrared light is used for the optical signal (upstream signal) transmitted from the optical wireless communication device 120a to the optical wireless communication device 110 (not shown). The desired information transmitted to the optical wireless communication device 110 (not shown) is converted into an optical signal represented by, for example, the on and off of infrared light. The infrared transmission unit 122 emits infrared light by blinking it, thereby emitting infrared light including the optical signal toward the optical wireless communication device 110 (not shown). As a result, an optical signal (upstream signal) using infrared light is transmitted from the optical wireless communication device 120a to the optical wireless communication device 110 (not shown).

[0068] The infrared transmission unit 122 transmits infrared light through the polarization filter 125. Since the configuration of the polarization filter 125 is the same as the configuration of the polarization filter 115 shown in FIGS. 2 to 4 described above, the description thereof is omitted.

[0069] Further, the data processing unit 123 reads control information from the signal acquired by the visible light receiving unit 121. The control information referred to here is information including information regarding the polarization angle of the optical signal transmitted and received by the opposing optical wireless communication device 110 (not shown). The polarization angle is an angle determined by the direction of the transmission axis of the polarization filter 115 (not shown) provided in the optical wireless communication device 110 (not shown).

[0070] Also, the data processing unit 123 uses sensors not shown, such as an azimuth sensor, a magnetic sensor, a gyro sensor, and an acceleration sensor, or a positioning system not shown, such as GPS (Global Positioning System), to recognize the direction in which the own optical wireless communication device 120a is facing. The data processing unit 123 outputs control information including information indicating the orientation of the own device (hereinafter referred to as "azimuth information") and the information regarding the above polarization angle to the polarization filter control unit 124.

[0071] The polarization filter control unit 124 calculates the deviation (error) between the direction of the transmission axis of the polarization filter 115 (not shown) of the opposing optical wireless communication device 110 (not shown) and the direction of the transmission axis of the polarization filter 125 of the own device based on the control information and azimuth information acquired from the data processing unit 123. As described above, the direction of the transmission axis of the polarization filter 115 (not shown) of the opposing optical wireless communication device 110 (not shown) is determined by the polarization angle included in the control information. The polarization filter control unit 124 rotates the two polarization filters 125 so as to correct the calculated deviation. Thereby, the optical wireless communication device in the second embodiment can control the direction of the transmission axis of the polarization filter 115 (not shown) of the optical wireless communication device 110 (not shown) and the direction of the transmission axis of the polarization filter 125 of the optical wireless communication device 120a to always match.

[0072] Incidentally, since the configuration of the opposing optical wireless communication device 110 (not shown) is basically the same as that of the optical wireless communication device 110 in the aforementioned first embodiment, the description thereof is omitted. The difference between the configuration of the optical wireless communication device 110 in the aforementioned first embodiment and the configuration of the optical wireless communication device 110 (not shown) in the second embodiment is that control information including information regarding the polarization angle of the optical signal transmitted and received by the optical wireless communication device 110 (not shown) is transmitted by the downstream signal. Incidentally, instead of the information regarding the polarization angle, a configuration may be adopted in which information indicating the direction of the transmission axis of the polarization filter 115 (not shown) provided in the optical wireless communication device 110 (not shown) itself is included in the control information.

[0073] [Operation of Optical Wireless Communication Device] Hereinafter, an example of the operation of the optical wireless communication device 120a will be described. FIG. 6 is a flowchart showing the operation of the optical wireless communication device 120a in the second embodiment of the present invention. The operation of the optical wireless communication device 120a shown in the flowchart of FIG. 6 starts when the visible light receiving unit 121 reads out an optical signal (downstream signal) included in the visible light VL transmitted from the opposing optical wireless communication device 110 (not shown) and outputs a signal subjected to various processes to the data processing unit 123.

[0074] The data processing unit 123 reads out control information from the signal acquired from the visible light receiving unit 121. Here, the control information is information including information regarding the polarization angle of the optical signal transmitted and received by the opposing optical wireless communication device 110 (not shown), as described above (step S01).

[0075] Next, the data processing unit 123 recognizes the direction in which its own optical wireless communication device 120a is facing by using sensors (not shown) such as an azimuth sensor, a magnetic sensor, a gyro sensor, and an acceleration sensor, or a positioning system (not shown) such as GPS (step S02). The data processing unit 123 outputs the control information and the azimuth information to the polarization filter control unit 124. Here, the azimuth information is information indicating the direction in which its own optical wireless communication device 120a is facing, as described above.

[0076] Next, based on the control information and the orientation information acquired from the data processing unit 123, the polarization filter control unit 124 calculates the deviation (misalignment) between the direction of the transmission axis of the polarization filter 115 (not shown) of the opposing optical wireless communication device 110 (not shown) and the direction of the transmission axis of the polarization filter 125 of its own device. The polarization filter control unit 124 rotationally controls the two polarization filters 125 so as to correct the calculated deviation. (Step S03).

[0077] Thus, the operation of the optical wireless communication device 120a shown in the flowchart of FIG. 6 ends.

[0078] By having the configuration as described above, the optical wireless communication system in the second embodiment can perform optical wireless communication without causing interference between optical signals even when transmitting optical signals using a plurality of light sources of the same type, similar to the optical wireless communication system 1 in the aforementioned first embodiment.

[0079] Furthermore, in the optical wireless communication system in the second embodiment, since the optical wireless communication device 120a is provided with a mechanism for rotationally controlling the polarization filter 125 in accordance with its own orientation, the deviation between the direction of the transmission axis of the polarization filter 115 (not shown) of the opposing optical wireless communication device 110 (not shown) and the direction of the transmission axis of the polarization filter 125 of the optical wireless communication device 120a can be corrected. As a result, the optical wireless communication system in the second embodiment can perform optical wireless communication without causing interference between optical signals even when the optical wireless communication device 120a may rotate.

[0080] Note that the control information does not necessarily have to be transmitted from the optical wireless communication device 110 to the optical wireless communication device 120a by an optical signal using visible light VL. For example, the instruction information may be transmitted from the optical wireless communication device 110 or a higher-level network or the like to the optical wireless communication device 120a by communication using a cellular system such as 5G (5th Generation Mobile Communication System), a wireless LAN (Local Area Network), a wired LAN, or any other arbitrary communication method.

[0081] Note that in order to perform rotation control of the polarization filter 125, the optical wireless communication system may be configured to include a control station (not shown) that aggregates the control of a plurality of optical wireless communication devices 120a. Also, a configuration may be adopted in which control information is exchanged between a plurality of optical wireless communication devices 120a so that each of the plurality of optical wireless communication devices 120a can recognize an appropriate polarization angle of an optical signal.

[0082] Furthermore, information indicating the polarization angle of an optical signal transmitted and received by an optical wireless communication device 110 (not shown) facing the optical wireless communication device 120a may be configured to be shareable among a plurality of optical wireless communication devices 110 (not shown). In this case, since the polarization angles of the respective optical wireless communication devices 110 (not shown) can be controlled so that the polarization angles do not match among a plurality of adjacent optical wireless communication devices 110 (not shown), it becomes possible to perform optical wireless communication without causing interference between optical signals.

[0083] Note that in the above-described first and second embodiments, the case where the polarization angle of the optical signal transmitted by the optical wireless communication device 110 is the same as the polarization angle of the optical signal received by the optical wireless communication device 110 has been described, but the configuration is not limited to this, and they may be different from each other.

[0084] In the above-described first and second embodiments, an optical wireless communication system using visible light and infrared light has been described. However, the present invention is not limited to this configuration. The present invention can be applied to any optical wireless communication belonging to so-called free-space optical communication (FSO), including, for example, a laser, as long as it is an optical wireless communication system using a polarization filter.

[0085] According to the optical wireless communication system 1 in the first embodiment and the optical wireless communication system in the second embodiment described above, even when optical wireless transmission is performed using adjacent light sources of the same type, optical wireless communication can be performed without causing interference between the respective communication links. As a result, an increase in communication capacity and throughput can be expected.

[0086] Also, in the optical wireless communication system 1 in the first embodiment and the wireless communication system in the second embodiment described above, two opposing optical wireless communication devices are each provided with a polarization filter installed so as to have the same transmission axis direction or controlled so as to have the same transmission axis direction. Thereby, since optical wireless communication can be established only between communication links formed through polarization filters having the same transmission axis direction, the occurrence of interference between communication links can be prevented.

[0087] According to the above-described embodiment, the optical wireless communication system includes a first transmission device, a first reception device, a second transmission device, and a second reception device. For example, the optical wireless communication system is the optical wireless communication system 1 in the embodiment, the first transmission device is the optical wireless communication device 110-1 in the embodiment, the first reception device is the optical wireless communication device 120-1 in the embodiment, the second transmission device is the optical wireless communication device 110-2 in the embodiment, and the second reception device is the optical wireless communication device 120-2 in the embodiment.

[0088] The above-described first transmitting device wirelessly transmits an optical signal to the first receiving device via a polarization filter whose transmission axis is in a first direction. For example, the first direction is the vertical direction in the embodiment, and the polarization filter is the polarization filter 115 in the embodiment. The above-described first receiving device receives the optical signal transmitted from the first transmitting device via a polarization filter whose transmission axis is in the first direction. For example, the polarization filter is the polarization filter 125 in the embodiment. The above-described second transmitting device wirelessly transmits an optical signal to the second receiving device via a polarization filter whose transmission axis is in a second direction different from the first direction. For example, the second direction is the horizontal direction in the embodiment, and the polarization filter is the polarization filter 115 in the embodiment. The above-described second receiving device receives the optical signal transmitted from the second transmitting device via a polarization filter whose transmission axis is in the second direction. For example, the polarization filter is the polarization filter 125 in the embodiment.

[0089] In the above optical wireless communication system, the first direction and the second direction may be orthogonal to each other.

[0090] In the above optical wireless communication system, at least one of the first receiving device and the second receiving device may include a receiving unit and a control unit. For example, the first receiving device and the second receiving device are the optical wireless communication device 120a in the embodiment, the receiving unit is the visible light receiving unit 121 in the embodiment, and the control unit is the polarization filter control unit 124 in the embodiment.

[0091] In this case, the receiving unit receives a signal including control information transmitted from the first transmission device or the second transmission device. Also, in this case, the control unit specifies the direction of the transmission axis of the first polarization filter through which the optical signal passes when transmitted from the first transmission device or the second transmission device based on the control information, and corrects the direction of the second polarization filter so as to match the specified direction with the direction of the transmission axis of the second polarization filter through which the optical signal passes when the first receiving device or the second receiving device receives the signal. For example, the signal including control information is the optical signal (downlink signal) in the embodiment, the first polarization filter is the polarization filter 115 in the embodiment, and the second polarization filter is the polarization filter 125 in the embodiment.

[0092] In the above optical wireless communication system, at least one of the first receiving device and the second receiving device may further include a rotation mechanism. In this case, the rotation mechanism enables the second polarization filter to rotate. Also, in this case, the control unit corrects the direction of the second polarization filter using the rotation mechanism.

[0093] In the above optical wireless communication system, the control unit may correct the direction of the second polarization filter by changing the direction of the first receiving device or the second receiving device.

[0094] Also, according to the above-described embodiment, the optical wireless communication device includes a receiving unit and a control unit. For example, the optical wireless communication device is the optical wireless communication device 120a in the embodiment, the receiving unit is the visible light receiving unit 121 in the embodiment, and the control unit is the polarization filter control unit 124 in the embodiment. The above receiving unit receives a signal including control information wirelessly transmitted from another wireless communication device facing it.

[0095] For example, the other wireless communication device facing it is the optical wireless communication device 110 in the embodiment. The above control unit specifies the direction of the transmission axis of the first polarization filter through which the optical signal passes when transmitted from the other wireless communication device based on the control information, and corrects the direction of the second polarization filter so that it matches the specified direction and the direction of the transmission axis of the second polarization filter through which the optical signal passes when the own device receives the signal. For example, the signal including the control information is the optical signal (downlink signal) in the embodiment, the first polarization filter is the polarization filter 115 in the embodiment, and the second polarization filter is the polarization filter 125 in the embodiment.

[0096] A part of the optical wireless communication device 110, a part of the optical wireless communication device 120, and a part of the optical wireless communication device 120a in the above-described embodiment may be realized by a computer. In that case, a program for realizing 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 realize it. Here, the "computer system" is assumed to 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, or a storage device such as a hard disk built into a computer system.

[0097] Furthermore, the "computer-readable recording medium" may include 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 serving as a server or client in that case. Also, the above program may be for realizing a part of the aforementioned functions, and may further be realizable in combination with a program already recorded in the computer system for realizing the aforementioned functions, or may be realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0098] 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.

Explanation of Reference Numerals

[0099] 1, 8, 8’, 9... optical wireless communication system, 110, 110-1, 110-2... optical wireless communication device, 111... light source, 112... infrared light receiving unit, 113... optical signal processing unit, 115... polarization filter, 120, 120-1, 120-2, 120a... optical wireless communication device, 121... visible light receiving unit, 122... infrared light transmitting unit, 123... data processing unit, 124... polarization filter control unit, 125... polarization filter, 810, 810-1, 810-2... optical wireless communication device, 811... light source, 812... infrared light receiving unit, 820, 820-1, 820-2... optical wireless communication device, 821... visible light receiving unit, 822... infrared light transmitting unit, 910... optical wireless communication device, 911... infrared light transmitting unit, 912... infrared light receiving unit, 913... optical signal processing unit, 920... optical wireless communication device, 921... infrared light receiving unit, 922... infrared light transmitting unit

Claims

1. A first transmission device that wirelessly transmits an optical signal to a first reception device through a polarization filter whose transmission axis direction is a first direction; The first reception device that receives the optical signal transmitted from the first transmission device through the polarization filter whose transmission axis direction is the first direction; A second transmission device that wirelessly transmits the optical signal to a second reception device through the polarization filter whose transmission axis direction is a second direction; The second reception device that receives the optical signal transmitted from the second transmission device through the polarization filter whose transmission axis direction is the second direction; When the first transmission device and the second transmission device are transmission devices close to each other, a control unit that controls so that the first direction and the second direction do not match; An optical wireless communication system having the above.

2. The first direction and the second direction are directions orthogonal to each other The optical wireless communication system according to claim 1.

3. At least one of the first reception device and the second reception device, A reception unit that receives a signal including control information transmitted from the first transmission device or the second transmission device; Based on the control information, identify the direction of the transmission axis of the first polarization filter through which the optical signal passes when transmitted from the first transmission device or the second transmission device, and the identified direction and the first reception device or A control unit that corrects the direction of the second polarization filter so as to match the direction of the transmission axis of the second polarization filter through which the optical signal passes when the second reception device receives the signal; Comprising The optical wireless communication system according to claim 1.

4. At least one of the first reception device and the second reception device, A rotation mechanism that makes the second polarization filter rotatable Further comprising, The control unit corrects the direction of the second polarization filter using the rotation mechanism The optical wireless communication system according to claim 3.

5. The control unit corrects the direction of the second polarization filter by changing the direction of the first reception device or the second reception device The optical wireless communication system according to claim 3.

6. A first transmission step in which a first transmission device wirelessly transmits an optical signal to a first reception device through a polarization filter whose transmission axis direction is a first direction; a first receiving step in which the first receiving device receives the optical signal transmitted from the first transmitting device through the polarization filter whose transmission axis is in the first direction; a second transmitting step in which a second transmitting device wirelessly transmits the optical signal to a second receiving device through the polarization filter whose transmission axis is in a second direction; a second receiving step in which the second receiving device receives the optical signal transmitted from the second transmitting device through the polarization filter whose transmission axis is in the second direction; a control step in which the control unit controls so that the first direction and the second direction do not coincide when the first transmitting device and the second transmitting device are transmitting devices close to each other; An optical wireless communication method comprising the above.

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