JP7748010B2 - Optical wireless communication system, optical wireless communication device, and optical wireless communication control method - Google Patents

Description

The present invention relates to an optical wireless communication system, an optical wireless communication device, and an optical wireless communication control method.

With the depletion of radio frequency resources, optical wireless communication systems are being considered, which achieve wireless communication using a method different from conventional wireless communication using radio waves. Optical wireless communication systems are communication systems that use electromagnetic waves (light) with wavelengths ranging from infrared to visible light to achieve wireless communication that does not interfere with conventional wireless communication using a specific frequency band. Furthermore, optical wireless communication systems are resistant to eavesdropping because light does not penetrate through obstructions such as building walls, and are therefore attracting attention from the perspective of high security (see, for example, non-patent document 1).

The following describes the configuration of a typical optical wireless communication system when visible light is used to transmit downstream signals. Figure 10 is a diagram showing an example of the configuration of a typical optical wireless communication system. The optical wireless communication system 8 shown in Figure 10 is composed of 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 an indoor ceiling, and functions as a wireless 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.

As shown in FIG. 10 , the optical wireless communication device 810 includes a light source 811, an infrared receiving unit 812, and an optical signal processing unit 813. The light source 811 includes, for example, an LED (Light Emitting Diode) and emits visible light VL. The light source 811 may be a light source provided in a general lighting fixture, etc. The light source 811 is connected to the optical signal processing unit 813. The optical signal processing unit 813 controls the light source 811 and can change the lighting period and lighting intensity of the visible light VL emitted from the light source 811. The optical signal processing unit 813 converts desired information to be transmitted to the optical wireless communication device 820 into an optical signal represented by changes in the visible light VL. As a result, an optical signal (downstream signal) using the visible light VL is transmitted from the optical wireless communication device 810 to the optical wireless communication device 820. The optical signal processing unit 813 may be connected to a higher-level communication network, such as the Internet or an intranet.

As shown in FIG. 10 , the optical wireless communication device 820 is configured to include a visible light receiving unit 821 and an infrared transmitting unit 822. The visible light receiving unit 821 receives visible light VL emitted from the light source 811. The visible light receiving unit 821 reads out an optical signal (downstream signal) contained 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. In addition, infrared rays are used for the optical signal (upstream signal) transmitted from the optical wireless communication device 820 to the optical wireless communication device 810. The infrared transmitting unit 822 transmits an optical signal using infrared rays to the optical wireless communication device 810.

The infrared rays sent from the infrared transmitter 822 are received by the infrared receiver 812 of the optical wireless communication device 810. The infrared receiver 812 reads out the optical signal (upstream signal) contained in the infrared rays. The infrared receiver 812 is connected to the optical signal processor 813. The optical signal processor 813 performs various processes, such as reception processing and data conversion, on the optical signal read out by the infrared receiver 812. The optical signal processor 813 may also transfer the optical signal that has undergone various processes to a higher-level communication network. In this way, a general optical wireless communication system using visible light and infrared rays is realized.

Note that the optical wireless communication system 8 shown in FIG. 10 is configured to transmit downstream signals using visible light VL, for example, using existing lighting equipment such as indoor LED lighting. However, infrared light may also be used for downstream signal transmission. FIG. 11 is a diagram showing an example of the configuration of an optical wireless communication system that uses infrared light for both upstream and downstream signal transmission. The optical wireless communication system 9 shown in FIG. 11 includes an optical wireless communication device 910 and an optical wireless communication device 920. The optical wireless communication device 910 includes an infrared transmitter 911, an infrared receiver 912, and an optical signal processor 913. The infrared transmitter 911 is connected to the optical signal processor 913. The optical signal processor 913 controls the infrared transmitter 911 to blink the infrared light transmitted from the infrared transmitter 911. The optical signal processor 913 converts desired information to be transmitted to the optical wireless communication device 920 into an optical signal represented, for example, by infrared light being on or off. As a result, an optical signal (downstream signal) using infrared rays is transmitted from the optical wireless communication device 910 to the optical wireless communication device 820 .

As shown in FIG. 11, the optical wireless communication device 920 is configured to include an infrared receiving unit 921 and an infrared transmitting unit 922. The infrared receiving unit 921 receives infrared light transmitted from the infrared transmitting unit 911. The infrared receiving unit 921 reads out the optical signal (downstream signal) contained 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 out by the infrared receiving unit 921. In addition, the optical signal (upstream signal) transmitted from the optical wireless communication device 920 to the optical wireless communication device 910 uses infrared light, as in the optical wireless communication system 8 shown in FIG. 10 above. The configurations of the infrared transmitting unit 922 and the infrared receiving unit 912 are similar to the configurations of the infrared transmitting unit 822 and the infrared receiving unit 812 shown in FIG. 10 above.

The infrared receiving unit 912 of the optical wireless communication device 910 is connected to the 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 receiving unit 912. In this way, a general optical wireless communication system using infrared rays for both upstream and downstream signal transmission is realized.

Note that the optical wireless communication system 8 illustrated in Figure 10 is configured to perform wireless communication between an optical wireless communication device 810, which is a wireless base station, and an optical wireless communication device 820, which is a wireless communication terminal, and the optical wireless communication system 9 illustrated in Figure 11 is configured to perform wireless communication between an optical wireless communication device 910, which is a wireless base station, and an optical wireless communication device 920, which is a wireless communication terminal, but is not limited to such configurations. For example, the optical wireless communication system may be a communication system for performing wireless communication using visible light, infrared light, etc. between multiple optical wireless communication devices having the same configuration, such as multiple wireless relay stations in a relay wireless system. In this way, the optical wireless communication system can have any system configuration depending on the purpose.

S. Wu, H. Wang and C. Youn, "Visible Light Communications for 5G Wireless Networking Systems: From Fixed to Mobile Communications," IEEE Network, vol. 28, no. 6, pp. 41-45, November-December, 2014 Isao Yoda, "Optics and Applications of Polarizing Plates," Journal of the Illuminating Engineering Institute of Japan, Vol. 42, No. 1, pp. 7-14, 1958

The transmission frequency (transmission wavelength and equivalent) of signal light in an optical wireless communication system is determined by the elements used in the light source, such as LEDs. When multiple optical signals are transmitted simultaneously using multiple light sources of the same type installed close to each other, interference may occur between these optical signals, degrading transmission characteristics.

Figure 12 is a diagram showing an example of the configuration of an optical wireless communication system that simultaneously transmits multiple optical signals using multiple light sources of the same type. The optical wireless communication system 8' shown in Figure 12 is configured with two sets of optical wireless communication devices 810 and 820 of the optical wireless communication system 8 shown in Figure 10, installed close to each other. As shown in Figure 12, optical wireless communication device 810-1 and optical wireless communication device 820-1 are a combination of optical wireless communication devices that communicate with each other, and optical wireless communication device 810-2 and optical wireless communication device 820-2 are a combination of optical wireless communication devices that communicate with each other.

In the optical wireless communication system 8' shown in Figure 12, in which multiple light sources 811 of the same type are installed close to each other, a downstream signal is transmitted from each of these multiple light sources 811 to the opposing optical wireless communication device 820. In the past, in such cases, there was a problem that interference occurred between the two downstream signals, degrading the transmission characteristics. Furthermore, similar problems existed not only in the transmission of downstream signals, but also in the transmission of upstream signals.

In light of the above circumstances, the present invention aims to provide technology that enables optical wireless communication without interference between optical signals, even when multiple light sources of the same type are used to transmit optical signals.

One aspect of the present invention is an optical wireless communication system having a plurality of first optical wireless communication devices, a plurality of second optical wireless communication devices, and a control unit, and forming a communication link for each combination of the first optical wireless communication device and the second optical wireless communication device, wherein the first optical wireless communication device is equipped with a first polarizing filter that transmits or absorbs an optical signal transmitted between the first optical wireless communication device and the second optical wireless communication device, and the second optical wireless communication device is equipped with a second polarizing filter that transmits or absorbs an optical signal transmitted between the first optical wireless communication device and the second optical wireless communication device, and a reference information transmitter that transmits reference information to the control unit, the reference information being information related to the orientation of the transmission axis of the second polarizing filter, and wherein the control unit estimates an index value related to the communication quality when the communication link is formed between the first optical wireless communication device and each of the second optical wireless communication devices that are candidates for allocation of the communication opportunity, based on the reference information acquired from each of the second optical wireless communication devices that are candidates for allocation of the communication opportunity and the orientation of the transmission axis of the first polarizing filter, and determines the second optical wireless communication device to which the communication opportunity with the first optical wireless communication device is allocated based on the estimated index value.

Another aspect of the present invention is an optical wireless communication device comprising: a first polarizing filter that transmits or absorbs an optical signal transmitted between the optical wireless communication device and another optical wireless communication device; and a control unit that acquires reference information from each of the other optical wireless communication devices that are candidates for allocation of a communication opportunity, the reference information being information regarding the orientation of the transmission axis of a second polarizing filter provided in the other optical wireless communication device that transmits or absorbs the optical signal; estimates an index value related to communication quality when a communication link is formed between the optical wireless communication device and each of the other optical wireless communication devices that are candidates for allocation of the communication opportunity based on the acquired reference information and the orientation of the transmission axis of the first polarizing filter; and determines the other optical wireless communication device to which the communication opportunity is allocated based on the estimated index value.

Another aspect of the present invention is an optical wireless communication control method having a plurality of first optical wireless communication devices, a plurality of second optical wireless communication devices, and a control unit, and forming a communication link for each combination of the first optical wireless communication device and the second optical wireless communication device, the method comprising: a first polarization step in which the first optical wireless communication device transmits or absorbs an optical signal transmitted between the first optical wireless communication device and the second optical wireless communication device using a first polarizing filter; a second polarization step in which the second optical wireless communication device transmits or absorbs an optical signal transmitted between the first optical wireless communication device and the second optical wireless communication device using a second polarizing filter; and a determination step of the control unit estimating an index value relating to communication quality when the communication link is formed between the first optical wireless communication device and each of the second optical wireless communication devices that are candidates for allocation of a communication opportunity based on the reference information and the orientation of the transmission axis of the first polarizing filter acquired from each of the second optical wireless communication devices that are candidates for allocation of a communication opportunity, and determining the second optical wireless communication device to which the communication opportunity with the first optical wireless communication device is to be allocated based on the estimated index value.

Another aspect of the present invention is an optical wireless communication control method comprising: a first polarization step of transmitting or absorbing an optical signal transmitted between the optical wireless communication device and another optical wireless communication device using a first polarization filter; and a control step of acquiring reference information, which is information regarding the orientation of the transmission axis of a second polarization filter provided in the other optical wireless communication device that transmits or absorbs the optical signal, from each of the other optical wireless communication devices that are candidates for allocation of a communication opportunity; estimating an index value related to communication quality when a communication link is formed between the optical wireless communication device and each of the other optical wireless communication devices that are candidates for allocation of the communication opportunity based on the acquired reference information and the orientation of the transmission axis of the first polarization filter; and determining the other optical wireless communication device to which the communication opportunity is to be allocated based on the estimated index value.

This invention makes it possible to perform optical wireless communication without interference between optical signals, even when multiple light sources of the same type are used to transmit optical signals.

1 is a diagram showing a configuration of an optical wireless communication system 1 according to an embodiment of the present invention. 2 is a schematic diagram showing the configuration of a polarizing filter 115 and a polarizing filter 125 according to an embodiment of the present invention. FIG. 3A and 3B are diagrams illustrating light blocking by a polarizing filter 115 and a polarizing filter 125 according to an embodiment of the present invention. 3A and 3B are diagrams illustrating the transmission of light by a polarizing filter 115 and a polarizing filter 125 according to an embodiment of the present invention. 1 is a diagram illustrating the configuration of a rotation mechanism 127 for a polarization filter 125 included in an optical wireless communication device 120 according to an embodiment of the present invention. 1 is a diagram illustrating the configuration of a rotation mechanism 127 for a polarization filter 125 included in an optical wireless communication device 120 according to an embodiment of the present invention. 1 is a diagram for explaining a communication opportunity allocation process performed by the optical wireless communication system 1 according to an embodiment of the present invention. 1 is a block diagram showing a configuration of an optical wireless communication system 1 according to an embodiment of the present invention. 10 is a flowchart illustrating an operation of the optical wireless communication device 120 according to the embodiment of the present invention. FIG. 1 is a diagram illustrating an example of the configuration of a general optical wireless communication system. 1 is a diagram illustrating an example of the configuration of an optical wireless communication system that uses infrared rays for both upstream and downstream signal transmission. FIG. 1 is a diagram illustrating an example of the configuration of an optical wireless communication system that simultaneously transmits multiple optical signals using multiple light sources of the same type.

The optical wireless communication system, optical wireless communication device, and optical wireless communication control method of the present invention will be described below with reference to the drawings. The present invention relates to an optical wireless communication system, optical wireless communication device, and optical wireless communication control method that realizes optical wireless communication using visible light, infrared light, etc. Note that the embodiment described below is merely one form, and embodiments to which the present invention can be applied are not limited to the embodiment described below.

[Configuration of optical wireless communication system]
The configuration of an optical wireless communication system 1 according to an embodiment will be described below. Fig. 1 is a diagram showing the configuration of the optical wireless communication system 1 according to an 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.

In the following description, when there is no need to distinguish between optical wireless communication device 110-1 and optical wireless communication device 110-2, they may simply be referred to as "optical wireless communication device 110."In the following description, when there is no need to distinguish between optical wireless communication device 120-1 and optical wireless communication device 120-2, they may simply be referred to as "optical wireless communication device 120."

Optical wireless communication device 110-1 is a communication device installed, for example, on an indoor ceiling, and functions as a wireless base station accommodating optical wireless communication device 120-1. Similarly, optical wireless communication device 110-2 is a communication device installed, for example, on an indoor ceiling, and functions as a wireless base station accommodating optical wireless communication device 120-2.

Optical wireless communication device 120-1 is, for example, a small terminal device, and communicates with optical wireless communication device 110-1. Similarly, optical wireless communication device 120-2 is, for example, a small terminal device, and communicates with optical wireless communication device 110-2.

As shown in FIG. 1, the optical wireless communication device 110-1 includes a light source 111, an infrared receiving unit 112, an optical signal processing unit 113, and two polarizing filters 115. The light source 111 includes, for example, an LED, and emits visible light VL. The light source 111 may also be a light source provided in a general lighting fixture, etc. The light source 111 is connected to the optical signal processing unit 113.

The optical signal processing unit 113 controls the light source 111 and can change the lighting period and lighting intensity 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 changes in the visible light VL. As a result, an optical signal (downstream signal) using the visible light VL is transmitted from the optical wireless communication device 110-1 to the optical wireless communication device 120-1.

Visible light VL emitted from the light source 111 is transmitted through a polarizing filter 115. The configuration of the polarizing filter 115 will be described later.

In addition, the optical signal processing unit 113 may be connected to a higher-level communication network such as the Internet or an intranet.

As shown in FIG. 1, the optical wireless communication device 120-1 is configured to include a visible light receiving unit 121, an infrared transmitting unit 122, and two polarizing filters 125. The visible light receiving unit 121 receives visible light VL emitted from the light source 111. The visible light receiving unit 121 receives the visible light VL through the polarizing filter 125. The configuration of the polarizing filter 125 will be described later.

The visible light receiving unit 121 reads out the optical signal (downstream signal) contained 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 out by the visible light receiving unit 121. For example, the visible light receiving unit 121 converts the downstream signal from an optical signal to an electrical signal.

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, for example, by turning the infrared light on and off. The infrared transmitting unit 122 transmits infrared rays including an optical signal toward the optical wireless communication device 110-1 by flashing the infrared light. As a result, 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.

The infrared transmitter 122 transmits the infrared light through a polarizing filter 125. The configuration of the polarizing filter 125 will be described later.

The infrared light transmitted from the infrared transmitting unit 122 through the polarizing filter 125 is received by the infrared receiving unit 112 of the optical wireless communication device 110-1. The infrared receiving unit 112 receives the infrared light through the polarizing filter 115. The configuration of the polarizing filter 115 will be described later.

The infrared receiving unit 112 reads out the optical signal (upstream signal) contained in the infrared light. The infrared 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 receiving unit 112. For example, the optical signal processing unit 113 converts the downstream signal from an optical signal to an electrical signal. The optical signal processing unit 113 may also transfer the optical signal that has undergone various processes to a higher-level communication network. In this way, optical wireless communication using visible light and infrared light is realized.

Note that the configuration of optical wireless communication device 110-2 is similar to the configuration of optical wireless communication device 110-1 described above, and the configuration of optical wireless communication device 120-2 is similar to the configuration of optical wireless communication device 120-1 described above, so descriptions of the configurations of optical wireless communication device 110-2 and optical wireless communication device 120-2 will be omitted.

[Polarizing filter configuration]
The following describes the configurations of the polarizing filter 115 and the polarizing filter 125. Note that the function of the polarizing filter 125 is basically the same as the function of the polarizing filter 115, so the polarizing filter 115 will be used as an example for the description here.

The polarizing filter 115 is, for example, a colorless, transparent film approximately 0.1 mm thick made of polyvinyl alcohol or its derivatives, which is stretched three to five times its original size using thermoelasticity or swelling elasticity and then fixed, causing polymer micelles to be aligned in a specific direction.

Figure 2 is a schematic diagram showing the configurations of polarizing filter 115 and polarizing filter 125 in an embodiment of the present invention. As mentioned above, the configuration of polarizing filter 125 is similar to the configuration of polarizing filter 115. Polarizing filter 115 is a filter that transmits only light of a specific transmission axis, such as a linear polarizing filter. Polarizing filter 115 may also be a filter other than a linear polarizing filter, such as a circular polarizing filter.

As shown in Figure 2, polarizing filter 115 is a linear polarizing filter that has a transmission axis that is the axis in the fiber direction and an absorption axis that is the axis perpendicular to the transmission axis. For example, when light that oscillates randomly through 360 degrees passes through polarizing filter 115, the extremely fine slit-like structure of polarizing filter 115 allows waves that oscillate along the transmission axis to pass through, while waves that oscillate along the absorption axis are absorbed and not transmitted. Furthermore, of waves that oscillate obliquely, the component that corresponds to the transmission axis is transmitted, and the component that corresponds to the absorption axis is absorbed.

By installing the polarizing filters 115 and 125 facing in a specific direction, the light transmitted between the optical wireless communication device 110 and the optical wireless communication device 120 can be blocked or transmitted by the polarizing filter on the receiving side.

Figure 3 is a diagram illustrating the blocking of light by polarizing filter 115 and polarizing filter 125 in an embodiment of the present invention. When polarizing filter 115 and polarizing filter 125 are linear polarizing filters, light is blocked by placing polarizing filter 115 and polarizing filter 125 so that their transmission axes are perpendicular to each other. In Figure 3, polarizing filter 115 is placed so that its transmission axis is vertical, and polarizing filter 125 is placed so that its transmission axis is horizontal, so that their transmission axes are perpendicular to each other. Therefore, in Figure 3, the area where polarizing filter 115 and polarizing filter 125 overlap is the area where light is blocked.

Figure 4 is a diagram illustrating the transmission of light through polarizing filter 115 and polarizing filter 125 in an embodiment of the present invention. When polarizing filter 115 and polarizing filter 125 are linear polarizing filters, light is transmitted by placing polarizing filter 115 and polarizing filter 125 so that their transmission axes are parallel. In Figure 4, polarizing filter 115 is placed so that its transmission axis is vertical, and polarizing filter 125 is similarly placed so that its transmission axis is vertical, so that their transmission axes are parallel. Therefore, in Figure 4, light is transmitted throughout the entire range, including the area where polarizing filter 115 and polarizing filter 125 overlap.

The optical wireless communication system 1 of the embodiment shown in Figure 1 utilizes the properties of the polarizing filters 115 and 125 described above, so that even when multiple light sources 111 of the same type are placed in close proximity and optical signals are transmitted simultaneously, optical wireless communication can be performed without interference between the optical signals transmitted from each light source 111.

As shown in FIG. 1, optical wireless communication device 110-1 and optical wireless communication device 110-2 each have a polarizing filter 115 with a transmission axis in a specific direction outside the light source 111 and outside the infrared receiving unit 112. Furthermore, optical wireless communication device 120-1 and optical wireless communication device 120-2 each have a polarizing filter 115 with a transmission axis in a specific direction outside the visible light receiving unit 121 and outside the infrared transmitting unit 122.

As shown in Figure 1, optical wireless communication is possible when optical wireless communication device 110 and optical wireless communication device 120 are combined such that the transmission axis of polarizing filter 115 and the transmission axis of polarizing filter 125 are aligned. This is because the direction of the transmission axis of polarizing filter 115 and the direction of the transmission axis of polarizing filter 125 are the same, so light that passes through polarizing filter 115 also passes through polarizing filter 125. Similarly, light that passes through polarizing filter 125 also passes through polarizing filter 125.

In FIG. 1, the direction of the transmission axis of the polarizing filter 115 of the optical wireless communication device 110-1 matches the direction of the transmission axis of the polarizing filter 125 of the optical wireless communication device 120-1 (in FIG. 1, both transmission axes are vertical). Therefore, optical wireless communication can be performed between the optical wireless communication device 110-1 and the optical wireless communication device 120-1. Also, in FIG. 1, the direction of the transmission axis of the polarizing filter 115 of the optical wireless communication device 110-2 matches the direction of the transmission axis of the polarizing filter 125 of the optical wireless communication device 120-2 (in FIG. 1, both transmission axes are horizontal). Therefore, optical wireless communication can be performed between the optical wireless communication device 110-2 and the optical wireless communication device 120-2.

On the other hand, in Figure 1, the transmission axis of the polarizing filter 115 of the optical wireless communication device 110-1 is oriented vertically, and the transmission axis of the polarizing filter 125 of the optical wireless communication device 120-2 is oriented horizontally, with both transmission axes oriented perpendicular to each other. Therefore, the optical wireless communication devices 110-1 and 120-2 cannot perform optical wireless communication. Also, in Figure 1, the transmission axis of the polarizing filter 115 of the optical wireless communication device 110-2 is oriented horizontally, and the transmission axis of the polarizing filter 125 of the optical wireless communication device 120-1 is oriented vertically, with both transmission axes oriented perpendicular to each other. Therefore, the optical wireless communication devices 110-2 and 120-1 cannot perform optical wireless communication.

This is because the direction of the transmission axis of polarizing filter 115 and the direction of the transmission axis of polarizing filter 125 are perpendicular to each other, so light that passes through polarizing filter 115 does not pass through polarizing filter 125. Similarly, light that passes through polarizing filter 125 does not pass through polarizing filter 115.

By having such a configuration, according to the optical wireless communication system 1 of the embodiment, the multiple visible light beams VL emitted from the multiple nearby light sources 111 and transmitted through the polarizing filter 115 or the polarizing filter 125 do not interfere with each other on the receiving side. Similarly, according to the optical wireless communication system 1 of the embodiment, the multiple infrared beams transmitted through the polarizing filter 115 or the polarizing filter 125 and received by the multiple nearby infrared receiving units 112 do not interfere with each other on the receiving side. This allows the optical wireless communication system 1 to prevent deterioration of transmission quality due to interference.

Specifically, as shown in Figure 1, the polarizing filters (polarizing filter 115 and polarizing filter 125) of optical wireless communication devices that perform optical wireless communication with each other are installed so that the transmission axes thereof are oriented in the same direction, and the polarizing filters of optical wireless communication devices that do not perform optical wireless communication with each other are installed so that the transmission axes thereof are oriented in different directions (e.g., perpendicular directions), thereby making it possible to prevent interference between optical signals in multiple optical wireless communication devices.

As mentioned above, polarizing filter 115 and polarizing filter 125 do not necessarily have to be compatible with linearly polarized light, and may be, for example, circularly polarized light. The optical wireless communication system is not limited to the configuration of the optical wireless communication system 1 described above, as long as it is capable of simultaneous spatial multiplexing transmission by combining polarizing filters with different (e.g., orthogonal) transmission axes.

It is also possible for the polarizing filter 115 to be provided only in the light source 111 of the optical wireless communication device 110, and the polarizing filter 125 to be provided only in the visible light receiving unit 121 of the optical wireless communication device 120. In other words, the polarizing filter 115 and the polarizing filter 125 may be used only for downstream signals, so that interference between optical signals in the transmission of downstream signals can be prevented. Conversely, the polarizing filter 115 may be provided only in the infrared receiving unit 112 of the optical wireless communication device 110, and the polarizing filter 125 may be provided only in the infrared transmitting unit 122 of the optical wireless communication device 120. In other words, the polarizing filter 115 and the polarizing filter 125 may be used only for upstream signals, so that interference between optical signals in the transmission of upstream signals can be prevented.

In the optical wireless communication system 1 illustrated in FIG. 1, the optical wireless communication device 110 is configured to include one light source 111 and one infrared receiving unit 112, but may also include multiple light sources 111 and multiple infrared receiving units 112. For example, one optical wireless communication device 110 may be configured to perform optical wireless communication with both optical wireless communication device 120-1 and optical wireless communication device 120-2, using polarizing filters 115 that are installed in different orientations.

The type and transmission axis direction of the polarizing filters 115 provided in the light source 111 and the infrared receiving unit 112 may be the same or different. Similarly, the type and transmission axis direction of the polarizing filters 125 provided in the visible light receiving unit 121 and the infrared transmitting unit 122 may be the same or different. In other words, the type and transmission axis direction of the polarizing filters 115 and 125 can be selected arbitrarily as long as the same light is transmitted between optical wireless communication devices that perform optical wireless communication with each other (e.g., optical wireless communication device 110-1 and optical wireless communication device 120-1, and optical wireless communication device 110-2 and optical wireless communication device 120-2) and the same light is not transmitted between optical wireless communication devices that do not perform optical wireless communication with each other (e.g., optical wireless communication device 110-1 and optical wireless communication device 120-2, and optical wireless communication device 110-2 and optical wireless communication device 120-1).

[Correction process for the direction of the transmission axis of the polarizing filter]
The process of correcting the direction of the transmission axis of the polarizing filter 125 by the optical wireless communication device 120 of the optical wireless communication system 1 according to the embodiment will be described below.

If at least one of the optical wireless communication devices 110 and 120 is a device that may perform an operation involving, for example, rotation, the orientation of the transmission axis of the polarizing filter may change in response to that operation. That is, if the positional relationship between the optical wireless communication devices 110 and 120 or the orientation of at least one of the optical wireless communication devices 110 and 120 changes, a misalignment (deviation) may occur between the orientation of the transmission axis of the polarizing filter 115 of the optical wireless communication device 110 and the orientation of the transmission axis of the polarizing filter 125 of the optical wireless communication device 120. If a misalignment occurs in the orientation of the transmission axis of the polarizing filter between the optical wireless communication devices 110 and 120, the optical signal will be blocked by the polarizing filter of the receiving optical wireless communication device, resulting in degradation of transmission characteristics.

The optical wireless communication device 120 of the optical wireless communication system 1 in the embodiment may be provided with a rotation mechanism that rotates the polarizing filter 125 so as to correct any misalignment between the direction of the transmission axis of the polarizing filter 115 of the optical wireless communication device 110 and the direction of the transmission axis of the polarizing filter 125 of the optical wireless communication device 120. Note that, as an example, a case where the above rotation mechanism is provided only in the optical wireless communication device 120 will be described here, but this configuration is not limited to this. The above rotation mechanism may be provided in both the optical wireless communication device 110 and the optical wireless communication device 120, or may be provided only in the optical wireless communication device 110.

Figures 5 and 6 are diagrams for explaining the configuration of the rotation mechanism 127 of the polarizing filter 125 provided in the optical wireless communication device 120 in an embodiment of the present invention. Figure 5 is a side view of the area around the rotation mechanism 127 of the optical wireless communication device 120, and Figure 6 is a plan view of the area around the rotation mechanism 127 of the optical wireless communication device 120.

As shown in FIG. 5, the rotation mechanism 127 is provided between the visible light receiving unit 121 and the infrared transmitting unit 122, and the polarizing filter 125. When infrared light is used to transmit downstream signals, the rotation mechanism 127 is provided between the infrared receiving unit (not shown) and the polarizing filter 125. The polarizing filter 125 is fixedly installed relative to the rotation mechanism 127. The rotation mechanism 127 is installed so as to be movable relative to the visible light receiving unit 121 and the infrared transmitting unit 122 (i.e., so that the rotation mechanism 127 can rotate).

Also, as shown in FIG. 6, a polarizing filter rotation mechanism drive unit 126 is provided in contact with the rotation mechanism 127. The polarizing filter rotation mechanism drive unit 126 rotates the rotation mechanism 127. For example, the polarizing filter rotation mechanism drive unit 126 may be configured to rotate by power from a power source (not shown) such as a motor, causing the rotation mechanism 127 in contact with the polarizing filter rotation mechanism drive unit 126 to rotate in the opposite direction in tandem. This changes the installation direction of the polarizing filter 125 fixedly installed on the rotation mechanism 127, and changes the direction of the transmission axis of the polarizing filter 125.

[Communication Opportunity Allocation Processing]
The process of allocating communication opportunities by the optical wireless communication system 1 according to the embodiment will be described below.

For example, in cases where the number of optical wireless communication devices 120, which are terminal devices, is greater than the number of optical wireless communication devices 110, which are wireless base stations, it is expected that multiple optical wireless communication devices 120 will simultaneously request the allocation of communication opportunities to the same optical wireless communication device 110. In such cases, the optical wireless communication system 1 of the embodiment selects an optical wireless communication device 120 with a higher priority based on predetermined rules and allocates communication opportunities to the selected optical wireless communication device 120.

Figure 7 is a diagram for explaining the communication opportunity allocation process by the optical wireless communication system 1 in an embodiment of the present invention. As shown in Figure 7, the optical wireless communication system 1 is configured to include optical wireless communication device 110-1, optical wireless communication device 110-2, optical wireless communication device 120-1, optical wireless communication device 120-2, optical wireless communication device 120-3, and optical wireless communication device 120-4. Note that compared to Figure 1 described above, optical wireless communication device 120-3 and optical wireless communication device 120-4 have been added in Figure 7, but the configurations of optical wireless communication device 120-3 and optical wireless communication device 120-4 are similar to the configuration of optical wireless communication device 120-1 (and optical wireless communication device 120-2).

For example, as shown in Figure 7, the positional relationship between each of the optical wireless communication devices 110 and each of the optical wireless communication devices 120 is different. Also, as shown in Figure 7, for example, each of the optical wireless communication devices 120, which are terminal devices, can face in various directions. In such a situation, the communication situation between the optical wireless communication devices 110 and 120 will differ depending on the positional relationship between the optical wireless communication devices 110 and 120, the direction in which the optical wireless communication devices 120 are facing, etc.

As shown in Figure 7, in the optical wireless communication system 1 of this embodiment, multiple optical wireless communication devices 120 each transmit reference information to the optical wireless communication device 110 to be used in the communication opportunity allocation process by the optical wireless communication device 110. The communication opportunity allocation process here refers to a process in which the optical wireless communication device 110 determines the optical wireless communication device 120 to which the communication opportunity is to be connected (i.e., the optical wireless communication device 120 to which the communication opportunity is to be allocated) in response to a communication opportunity allocation request in which the optical wireless communication device 120 requests a communication connection to the optical wireless communication device 110.

The reference information is information used by the optical wireless communication device 110 to determine the optical wireless communication device 120 to which a communication opportunity should be allocated. Based on the reference information, the optical wireless communication device 110 estimates the SINR (Signal to Interference plus Noise Ratio) that will be obtained when communicating with each of the optical wireless communication devices 120. Then, based on the estimation results, the optical wireless communication device 110 allocates a communication opportunity to the optical wireless communication device 120 (e.g., the optical wireless communication device 110 that is estimated to have the highest SINR).

In addition, if the maximum estimated SINR value is lower than a predetermined threshold (i.e., if there is no communication link estimated to have an SINR exceeding the threshold), the optical wireless communication device 110 may not allocate communication opportunities to any of the optical wireless communication devices 120. This makes it possible to prevent interference between communication links.

Generally, the SINR can be calculated based on the values of the desired power and interference power. However, in the configuration of the optical wireless communication system 1 in this embodiment, the desired power and interference power are highly dependent on the orientation of the transmission axis of the polarizing filter. Therefore, the optical wireless communication device 110 identifies the orientation of the transmission axis of the polarizing filter 125 of each optical wireless communication device 120, for example, based on the orientation (posture) of each optical wireless communication device 120 identified based on the reference information and the positional relationship between the optical wireless communication device 110 and the optical wireless communication device 120. The optical wireless communication device 110 then estimates the SINR based on the orientation of the transmission axis of the polarizing filter 125 of the identified optical wireless communication device 120 and the orientation of the transmission axis of its own polarizing filter 115.

In this case, the reference information includes sensor information that enables identification of the orientation (posture) of the optical wireless communication device 120 and the orientation of the transmission axis of the polarizing filter 125 based on the positional relationship between the optical wireless communication device 110 and the optical wireless communication device 120. The sensor information referred to here is, for example, sensor information acquired by a gyro sensor, magnetic sensor, acceleration sensor, or the like. Alternatively, the sensor information referred to here may be, for example, the received power of the downlink signal at the optical wireless communication device 120, information indicating the position or orientation of the optical wireless communication device 120, or information indicating the distance from the optical wireless communication device 110. Alternatively, the sensor information referred to here may be a combination of the above types of sensor information. Furthermore, the reference information may include, for example, information indicating the azimuth difference between the orientation of the light source 111 (transmitter) and the orientation of the visible light receiving unit 121 (receiver).

The reference information may be transmitted from the optical wireless communication device 120 to the optical wireless communication device 110 using an infrared upstream signal from the infrared transmitting unit 122 and the infrared receiving unit 112, or may be transmitted using wireless communication at a different frequency. For example, the reference information may be transmitted from the optical wireless communication device 120 to the optical wireless communication device 110, or to another device equipped with a control unit 114 that performs communication opportunity allocation processing, 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 communication method.

In addition, the optical wireless communication device 110 may take into consideration not only the SINR but also other factors related to the communication situation, such as fairness of communication opportunities and traffic volume, in order to determine the optical wireless communication device 120 to which a communication opportunity should be allocated. In other words, the optical wireless communication device 110 may be configured to determine the optical wireless communication device 120 to which a communication opportunity should be allocated, taking into account at least information based on the direction of the transmission axis of the polarizing filter 115 of its own device and the direction of the transmission axis of the polarizing filter 125 of the optical wireless communication device 120.

[Functional configuration of optical wireless communication device]
The following describes the functional configuration of the optical wireless communication device 110 and the optical wireless communication device 120. Fig. 8 is a block diagram showing the functional configuration of the optical wireless communication device 110 and the optical wireless communication device 120 according to an embodiment of the present invention.

Note that the optical wireless communication device 110 and the optical wireless communication device 120 shown in Figure 8 have a functional configuration that mimics the configuration of the optical wireless communication system 1 shown in Figure 1. Therefore, as an example, it is assumed here that a downstream signal is transmitted using visible light VL and an upstream signal is transmitted using infrared light between the optical wireless communication device 110, which is a base station device, and the optical wireless communication device 120, which is a terminal device. However, this configuration is not limited to this, and for example, infrared light may be used for both the transmission of the downstream signal and the transmission of the upstream signal.

As shown in Figure 8, the optical wireless communication device 110 is composed of a light source 111 (transmitter), an infrared receiver 112, an optical signal processor 113, a controller 114, two polarizing filters 115, and a transmitter 116. As mentioned above, the optical wireless communication device 110 is a communication device installed, for example, on an indoor ceiling, and functions as a wireless base station that houses the optical wireless communication device 120.

The light source 111 emits visible light VL through a polarizing filter 115. The optical signal processing unit 113 controls the light source 111 and can change the lighting period and lighting intensity 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 changes in the visible light VL. As a result, an optical signal (downstream signal) using the visible light VL is transmitted from the optical wireless communication device 110-1 to the optical wireless communication device 120-1.

The infrared receiving unit 112 receives the infrared light transmitted from the optical wireless communication device 120 through the polarizing filter 115. The infrared receiving unit 112 reads out the optical signal (downstream signal) contained in the received infrared light. Note that the configuration of the polarizing filter 115 is similar to that of the polarizing filter 115 shown in Figures 2 to 4 described above, and therefore a description thereof will be omitted.

The optical signal processing unit 113 performs various processes, such as reception processing and data conversion, on the optical signal read by the infrared receiving unit 112. For example, the optical signal processing unit 113 converts the downstream signal from an optical signal to an electrical signal. The optical signal processing unit 113 may also forward the optical signal that has undergone various processes to a higher-level communication network.

The control unit 114 performs a communication opportunity allocation process using reference information acquired from each optical wireless communication device 120. As mentioned above, the communication opportunity allocation process here refers to the process of determining the optical wireless communication device 120 to which a communication opportunity will be allocated. The control unit 114 is configured to include a processor, such as a CPU (Central Processing Unit).

In this embodiment, the control unit 114 is provided in the optical wireless communication device 110, but this configuration is not limited to this. The control unit 114 may also be provided in a separate device provided outside the optical wireless communication device 110. In this case, the control unit 114 may be configured to collectively perform the process of allocating communication opportunities that is performed for each of the multiple optical wireless communication devices 110.

The transmission unit 116 transmits signals between a higher-level network or other optical wireless communication devices 110.

As shown in FIG. 8, the optical wireless communication device 120 is composed of a visible light receiving unit 121, an infrared transmitting unit 122, an optical signal processing unit 123, an information acquisition and processing unit 124, and two polarizing filters 125. As mentioned above, the optical wireless communication device 120 is a small terminal device whose orientation may change due to, for example, rotation. The optical wireless communication device 120 functions as a wireless communication terminal housed in the opposing optical wireless communication device 110.

The visible light receiving unit 121 receives visible light VL transmitted from the opposing optical wireless communication device 110. The visible light receiving unit 121 receives the visible light VL through a polarizing filter 125. The configuration of the polarizing filter 125 is as described above with reference to Figures 2 to 4.

The visible light receiving unit 121 reads out an optical signal (downstream signal) from the received visible light VL. The visible light receiving unit 121 performs various processes on the read out optical signal, such as reception processing and data conversion. For example, the visible light receiving unit 121 converts the downstream signal from an optical signal to an electrical signal. The visible light receiving unit 121 is connected to the optical signal processing unit 123. The visible light receiving unit 121 outputs the signal that has undergone various processes to the optical signal processing unit 123.

Infrared rays are used for the optical signal (upstream signal) transmitted from the optical wireless communication device 120 to the optical wireless communication device 110. An electrical signal indicating the desired information to be transmitted to the optical wireless communication device 110 is converted by the infrared transmitting unit 122 into an optical signal represented, for example, by turning infrared rays on and off. The infrared transmitting unit 122 transmits infrared rays including an optical signal toward the optical wireless communication device 110 by flashing the infrared rays. As a result, an optical signal (upstream signal) using infrared rays is transmitted from the optical wireless communication device 120 to the optical wireless communication device 110.

The infrared transmitter 122 transmits the infrared light through a polarizing filter 125. The configuration of the polarizing filter 125 is the same as the configuration of the polarizing filter 125 described above with reference to Figures 2 to 4.

The information acquisition and processing unit 124 acquires sensor information related to the orientation of the transmission axis of the polarizing filter 125 of the device itself. The information acquisition and processing unit 124 then performs processing to transmit reference information including the sensor information to the optical wireless communication device 110, for example, via the infrared transmission unit 122.

As mentioned above, the sensor information here refers to information that enables the orientation of the transmission axis of the polarizing filter 125 to be determined based on the position and orientation of the optical wireless communication device 120. For example, the sensor information may be sensor information acquired by a gyro sensor, magnetic sensor, acceleration sensor, etc., or the received power of the downlink signal at the visible light receiving unit 121, information indicating the position or orientation of the device itself, or information indicating the distance from the optical wireless communication device 110. Note that the sensor information may be a combination of multiple types of information described above. Furthermore, the reference information may include, for example, information indicating the azimuth difference between the orientation of the light source 111 and the orientation of the visible light receiving unit 121.

[Operation of control unit]
An example of the operation of the control unit 114 in the process of allocating communication opportunities will be described below. Note that, as an example, a case will be described in which the control unit 114 is provided in a device other than the optical wireless communication device 110 and the optical wireless communication device 120, and the control unit 114 collectively controls the process of allocating communication opportunities to the multiple optical wireless communication devices 110, but the present invention is not necessarily limited to such a configuration. Each of the multiple optical wireless communication devices 110 may individually allocate communication opportunities to the optical wireless communication device 120.

Figure 9 is a flowchart showing the operation of the control unit 114 in an embodiment of the present invention. The operation of the control unit 114 shown in the flowchart of Figure 9 is initiated, for example, when the control unit 114 acquires reference information from each of the multiple optical wireless communication devices 120.

First, the control unit 114 detects whether there are any unassigned optical wireless communication devices 110 (i.e., optical wireless communication devices 110 for which an optical wireless communication device 120 with which to communicate has not been determined) (step S01).

If there are no unallocated optical wireless communication devices 110 (step S01, NO), the operation of the control unit 114 shown in the flowchart of Figure 9 ends. On the other hand, if there are unallocated optical wireless communication devices 110 (step S01, YES), the control unit 114 selects one optical wireless communication device 110 from the unallocated optical wireless communication devices 110 to be the target of the communication opportunity allocation process (step S02).

Next, the control unit 114 extracts candidates for the optical wireless communication device 120 to which the communication opportunity is to be allocated. For example, the control unit 114 extracts, from all the optical wireless communication devices 120, the optical wireless communication device 120 that has received a request for allocation of a communication opportunity (step S03). The control unit 114 detects whether at least one candidate for the optical wireless communication device 120 to which the communication opportunity is to be allocated has been extracted (step S04).

If no candidate optical wireless communication device 120 to which a communication opportunity is to be allocated is extracted (step S04, NO), the process returns to step S01 above, and the control unit 114 detects whether there is an unallocated optical wireless communication device 110 (i.e., an optical wireless communication device 110 for which an optical wireless communication device 120 to communicate with has not been determined) and whether there is an optical wireless communication device 110 that has not yet been selected as a target for the communication opportunity allocation process.

On the other hand, if one or more optical wireless communication devices 120 are extracted as candidates for allocation of communication opportunities (step S04, YES), the control unit 114 estimates the SINR for each of the extracted optical wireless communication devices 120 based on reference information obtained from each of the extracted optical wireless communication devices 120 (step S05).

Next, the control unit 114 detects whether the maximum SINR among the estimated SINRs is higher than a predetermined threshold value (step S06). If the maximum SINR is equal to or lower than the predetermined threshold value (step S06, NO), the process returns to step S01 above, and the control unit 114 detects whether there is an unassigned optical wireless communication device 110 (i.e., an optical wireless communication device 110 for which the communication partner optical wireless communication device 120 has not been determined) and has not yet been selected as a target for the communication opportunity allocation process.

On the other hand, if the maximum SINR is higher than the predetermined threshold (step S06, YES), the control unit 114 allocates a communication opportunity to the optical wireless communication device 120 with the highest estimated SINR (step S07). Then, returning to the processing of step S01 above, the control unit 114 detects whether there is an optical wireless communication device 110 that has not yet been determined as the optical wireless communication device 110 to be allocated and is still unallocated (i.e., an optical wireless communication device 110 for which the optical wireless communication device 120 with which it will communicate has not yet been determined).

The control unit 114 may be configured to be able to determine the instantaneous received power of the downlink signal at each of the optical wireless communication devices 120 from the reference information acquired from each of the optical wireless communication devices 120. In this case, the control unit 114 may also determine the average received power of the downlink signal at each of the optical wireless communication devices 120 from the instantaneous received power obtained from the reference information previously acquired. In this case, the control unit 114 may calculate the ratio of the instantaneous received power to the average received power for each of the optical wireless communication devices 120 that are candidates for allocation of a communication opportunity, and allocate the communication opportunity to the optical wireless communication device 120 with the highest power ratio.

The communication opportunity allocation process by the control unit 114 shown in the flowchart of Figure 9 is configured so that when there is a combination of an optical wireless communication device 110 and a candidate optical wireless communication device 120 to which a communication opportunity has not been allocated, the control unit 114 determines whether to further allocate a communication opportunity by applying multiplexed transmission using a polarized filter.

Specifically, as in the processes of steps S05 to S07 shown in Figure 9 described above, the control unit 114 estimates the SINR that would result if a communication opportunity were allocated to each of the optical wireless communication devices 120 that are candidates for allocation of a communication opportunity, based on the acquired reference information. If the highest SINR exceeds a preset threshold, the control unit 114 allocates the communication opportunity to the optical wireless communication device 120 that is estimated to have the highest SINR. The threshold may be set to, for example, a value that satisfies the desired communication quality or a value required to expand communication capacity.

The control unit 114 performs the above series of processes until there are no candidate combinations of optical wireless communication devices 110 and 120 to which communication opportunities have not been allocated, or until the maximum estimated SINR value no longer exceeds the threshold value, and then terminates the process of allocating communication opportunities for that time slot.

The optical wireless communication system 1 in the embodiment described above enables optical wireless communication without interference between the communication links, even when optical wireless transmission is performed using light sources of the same type installed in close proximity. This is expected to increase communication capacity and throughput.

Furthermore, in the optical wireless communication system 1 in the embodiment described above, the two opposing optical wireless communication devices each have a polarizing filter that is installed so that the transmission axis is oriented in the same direction, or a polarizing filter that is controlled so that the transmission axis is oriented in the same direction. This allows optical wireless communication to be established only between communication links formed via polarizing filters with the same transmission axis orientation, thereby preventing interference between communication links.

The optical wireless communication system 1 may be configured to have a control station (not shown) that collectively controls the allocation of communication opportunities to the multiple optical wireless communication devices 120 and the rotation of the polarizing filters 125 of the multiple optical wireless communication devices 120. Furthermore, the multiple optical wireless communication devices 120 may be configured to exchange information related to such control with each other, so that each of the multiple optical wireless communication devices 110 and each of the multiple optical wireless communication devices 120 can recognize the status of allocation of communication opportunities, the appropriate orientation of the transmission axis of the polarizing filter, etc.

In addition, the reference information transmitted from each optical wireless communication device 120 to the optical wireless communication device 110 may be configured to be shared among multiple optical wireless communication devices 110.

In this embodiment, we have described a case where the orientation of the transmission axis of the transmitting polarizing filter 115 or polarizing filter 125 of the optical wireless communication device 110 and the optical wireless communication device 120 is the same as the orientation of the transmission axis of the receiving polarizing filter 115 or polarizing filter 125, but this configuration is not limited to this and the orientations may be different from each other.

Note that, while this embodiment describes an optical wireless communication system that uses visible light and infrared light, the present invention is not limited to this configuration. The present invention can be applied to any optical wireless communication system that uses a polarizing filter, including so-called free-space optical communication (FSO), such as lasers, that performs such communication.

According to the above-described embodiment, the optical wireless communication system has a plurality of first optical wireless communication devices, a plurality of second optical wireless communication devices, and a control unit, and forms a communication link for each combination of the first optical wireless communication device and the second optical wireless communication device. For example, the optical wireless communication system is the optical wireless communication system in the embodiment, the first optical wireless communication device is the optical wireless communication device 110 in the embodiment, the second optical wireless communication device is the optical wireless communication device 120 in the embodiment, and the control unit is the control unit 114 in the embodiment.

The first optical wireless communication device is equipped with a first polarizing filter. For example, the first polarizing filter is polarizing filter 115. The first polarizing filter transmits or absorbs optical signals transmitted between the first optical wireless communication device and the second optical wireless communication device. For example, the optical signals are downstream signals and upstream signals in the embodiment.

The second optical wireless communication device described above includes a second polarizing filter and a reference information transmission unit. For example, the second polarizing filter is polarizing filter 125 in the embodiment, and the reference information transmission unit is infrared transmission unit 122 in the embodiment. The second polarizing filter transmits or absorbs optical signals transmitted between the first optical wireless communication device and the second optical wireless communication device. For example, the optical signals are downstream signals and upstream signals in the embodiment. The reference information transmission unit transmits reference information, which is information regarding the orientation of the transmission axis of the second polarizing filter, to the control unit.

The control unit estimates an index value related to the communication quality when a communication link is formed between the first optical wireless communication device and each of the second optical wireless communication devices that are candidates for allocation of a communication opportunity, based on the reference information acquired from each of the second optical wireless communication devices that are candidates for allocation of a communication opportunity and the direction of the transmission axis of the first polarizing filter, and determines the second optical wireless communication device to which a communication opportunity with the first optical wireless communication device will be allocated based on the estimated index value. For example, the second optical wireless communication device that is a candidate for allocation of a communication opportunity is optical wireless communication device 120 that sent a request for allocation of a communication opportunity to optical wireless communication device 110 in the embodiment.

In addition, in the above-mentioned optical wireless communication system, the index value related to communication quality may be SINR (signal-to-interference-plus-noise ratio).

In addition, in the above-mentioned optical wireless communication system, the control unit may determine a second optical wireless communication device to which a communication opportunity with the first optical wireless communication device is assigned when the maximum value of the estimated signal-to-interference-plus-noise power ratio is higher than a predetermined threshold.

In addition, in the above-mentioned optical wireless communication system, the optical signal may be visible light or infrared light.

In the above-mentioned optical wireless communication system, the reference information may include at least one of sensor information acquired by a gyro sensor, a magnetic sensor, or an acceleration sensor, information indicating the received power of the optical signal, information indicating the position or orientation of the second optical wireless communication device, information indicating the distance between the first optical wireless communication device and the second optical wireless communication device, and information indicating the azimuth difference between the orientation of the optical signal transmitter of the first optical wireless communication device and the orientation of the optical signal receiver of the second optical wireless communication device.

Furthermore, according to the above-described embodiment, the optical wireless communication device includes a first polarizing filter and a control unit. For example, the optical wireless communication device is optical wireless communication device 110 in the embodiment, the first polarizing filter is polarizing filter 115 in the embodiment, and the control unit is control unit 114 in the embodiment. The first polarizing filter transmits or absorbs optical signals transmitted between the other optical wireless communication device. For example, the other optical wireless communication device is optical wireless communication device 120 in the embodiment, and the optical signals are downstream signals and upstream signals in the embodiment.

The control unit acquires reference information, which is information relating to the orientation of the transmission axis of the second polarizing filter provided in the other optical wireless communication devices that transmit or absorb optical signals, from each of the other optical wireless communication devices that are candidates for allocation of communication opportunities, estimates an index value related to communication quality when a communication link is formed between the control unit and each of the other optical wireless communication devices that are candidates for allocation of communication opportunities based on the acquired reference information and the orientation of the transmission axis of the first polarizing filter, and determines the other optical wireless communication device to which the communication opportunity is allocated based on the estimated index value. For example, the second polarizing filter is polarizing filter 125 in the embodiment, and the index value related to communication quality is SINR (signal-to-interference-plus-noise ratio) in the embodiment.

In the above-described embodiments, part of the optical wireless communication device 110, part of the optical wireless communication device 120, and part or all of the control unit 114 may be implemented by a computer. In this 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 loaded into a computer system and executed to implement the function. Note that the term "computer system" here includes hardware such as an OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, CD-ROMs, and storage devices such as hard disks built into a computer system.

Furthermore, "computer-readable recording medium" may include a medium that dynamically stores a program for a short period of 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, or a medium that stores a program for a fixed period of time, such as volatile memory within a computer system that serves as a server or client in such cases. Furthermore, the program may be one that realizes some of the functions described above, or one that can realize the functions described above in combination with a program already stored in the computer system, or one that can be realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

The above describes in detail an embodiment of the present invention with reference to the drawings, but the specific configuration is not limited to this embodiment and also includes designs that do not deviate from the gist of the present invention.

1, 8, 8', 9...Optical wireless communication system, 110, 110-1, 110-2...Optical wireless communication device, 111...Light source, 112...Infrared receiving unit, 113...Optical signal processing unit, 114...Control unit, 115...Polarizing filter, 116...Transmission unit, 120, 120-1, 120-2, 120-3, 120-4...Optical wireless communication device, 121...Visible light receiving unit, 122...Infrared transmitting unit, 123...Optical signal processing unit, 124...Information acquisition/processing unit, 125...Polarizing filter, 126...Polarizing Filter rotation mechanism drive unit, 127... rotation mechanism, 810, 810-1, 810-2... optical wireless communication device, 811... light source, 812... infrared receiving unit, 813... optical signal processing unit, 820, 820-1, 820-2... optical wireless communication device, 821... visible light receiving unit, 822... infrared transmitting unit, 910... optical wireless communication device, 911... infrared transmitting unit, 912... infrared receiving unit, 913... optical signal processing unit, 920... optical wireless communication device, 921... infrared receiving unit, 922... infrared transmitting unit

Claims (8)

An optical wireless communication system including a plurality of first optical wireless communication devices, a plurality of second optical wireless communication devices, and a control unit, wherein a communication link is formed for each combination of the first optical wireless communication devices and the second optical wireless communication devices,
the first optical wireless communication device,
a first polarization filter that transmits or absorbs an optical signal transmitted between the first optical wireless communication device and the second optical wireless communication device;
the second optical wireless communication device,
a second polarizing filter that transmits or absorbs an optical signal transmitted between the first optical wireless communication device and the second optical wireless communication device;
a reference information transmitting unit configured to transmit reference information, which is information relating to the orientation of the transmission axis of the second polarizing filter, to the control unit;
Equipped with
The control unit
an index value relating to communication quality when the communication link is formed between the first optical wireless communication device and each of the second optical wireless communication devices that are candidates for allocation of communication opportunities, based on the reference information acquired from each of the second optical wireless communication devices that are candidates for allocation of communication opportunities and the direction of the transmission axis of the first polarizing filter, and a second optical wireless communication device to which the communication opportunity with the first optical wireless communication device is allocated is determined based on the estimated index value. The optical wireless communication system according to claim 1 , wherein the index value relating to the communication quality is a signal-to-interference-plus-noise power ratio. The optical wireless communication system according to claim 2, wherein the control unit determines the second optical wireless communication device to which the communication opportunity with the first optical wireless communication device is assigned when the maximum value of the estimated signal-to-interference-plus-noise power ratio is higher than a predetermined threshold. The optical wireless communication system according to claim 1 or 2, wherein the optical signal is visible light or infrared light. 3. The optical wireless communication system according to claim 1, wherein the reference information includes at least one of sensor information acquired by a gyro sensor, a magnetic sensor, or an acceleration sensor, information indicating a received power of the optical signal, information indicating a position or orientation of the second optical wireless communication device, information indicating a distance between the first optical wireless communication device and the second optical wireless communication device, and information indicating an azimuth difference between an orientation of a transmitter of the optical signal of the first optical wireless communication device and an orientation of a receiver of the optical signal of the second optical wireless communication device. a first polarizing filter that transmits or absorbs an optical signal transmitted between the first polarizing filter and another optical wireless communication device;
a control unit that acquires, from each of the other optical wireless communication devices that are candidates for allocation of a communication opportunity, reference information that is information regarding the orientation of a transmission axis of a second polarizing filter provided in the other optical wireless communication devices that transmit or absorb the optical signal, estimates an index value related to communication quality when a communication link is formed between the optical wireless communication device itself and each of the other optical wireless communication devices that are candidates for allocation of the communication opportunity based on the acquired reference information and the orientation of the transmission axis of the first polarizing filter, and determines the other optical wireless communication devices to which the communication opportunity is to be allocated based on the estimated index value;
An optical wireless communication device comprising: 1. An optical wireless communication control method comprising: a plurality of first optical wireless communication devices; a plurality of second optical wireless communication devices; and a control unit; and forming a communication link for each combination of the first optical wireless communication devices and the second optical wireless communication devices,
a first polarization step in which the first optical wireless communication device transmits or absorbs an optical signal transmitted between the first optical wireless communication device and the second optical wireless communication device using a first polarization filter;
a second polarization step in which the second optical wireless communication device transmits or absorbs an optical signal transmitted between the first optical wireless communication device and the second optical wireless communication device using a second polarization filter;
a reference information transmitting step in which the second optical wireless communication device transmits reference information, which is information regarding the orientation of the transmission axis of the second polarization filter, to the control unit;
a determination step in which the control unit estimates an index value related to communication quality when the communication link is formed between the first optical wireless communication device and each of the second optical wireless communication devices that are candidates for allocation of communication opportunities, based on the reference information and the direction of the transmission axis of the first polarization filter acquired from each of the second optical wireless communication devices that are candidates for allocation of communication opportunities, and determines the second optical wireless communication device to which the communication opportunity with the first optical wireless communication device is to be allocated, based on the estimated index value;
An optical wireless communication control method comprising: a first polarization step of transmitting or absorbing an optical signal transmitted between the optical fiber and another optical wireless communication device by a first polarization filter;
a control step of acquiring reference information, which is information relating to the orientation of a transmission axis of a second polarizing filter provided in the other optical wireless communication devices that transmit or absorb the optical signal, from each of the other optical wireless communication devices that are candidates for allocation of a communication opportunity, estimating an index value relating to communication quality when a communication link is formed between the optical wireless communication device itself and each of the other optical wireless communication devices that are candidates for allocation of the communication opportunity based on the acquired reference information and the orientation of the transmission axis of the first polarizing filter, and determining the other optical wireless communication device to which the communication opportunity is to be allocated based on the estimated index value;
An optical wireless communication control method comprising: