JP3832738B2 - Optical wireless communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical wireless communication system that transmits signals via optical wireless, and more particularly to an optical wireless communication system for appropriately aligning the optical axis of pilot light.
[0002]
[Prior art]
In general, when transmitting a signal via optical radio, an LED (light emitting diode) or a laser diode is used as a light emitting element on the light emitting side. However, a laser diode has a narrow beam of emitted light and can transmit a long distance. Since it does not spread, it is used for transmission between buildings and transmission across rivers. However, since the beam diameter is extremely thin, if it enters the human body, particularly the eyes, it may cause damage to the eyes, and thus it cannot be used in a premises such as an office.
[0003]
On the other hand, the LED has a wide directivity and the light beam spreads with distance, so it is not suitable for long-distance transmission, but the transmission distance can be extended by integrally forming the LED and the focusing lens. Since optical noise generated by illumination light or the like mainly has a low frequency spectrum, data is generally converted into a broadband signal by modulation such as FM or PM.
[0004]
Japanese Patent Laid-Open No. 6-224858 describes a transmission terminal having a transmission device that transmits light emitted from an LED, which is a light emitting element, in parallel by a parabolic reflector. The wireless terminal is connected to a station such as a personal computer, and the optical axis alignment is automatically performed by the servo means for the optical wireless collection and delivery device mounted on the ceiling, relying on the pilot light coming from the collection and delivery device, A wireless communication link was established.
[0005]
[Problems to be solved by the invention]
However, in the optical axis alignment method in the optical wireless communication system described above, since the signal frequency (several tens of kHz) used for the pilot light is close to the flicker frequency of the inverter fluorescent lamp in the room, the optical wireless terminal uses the optical wireless collection and distribution device. When searching, there was a problem that the light of the inverter fluorescent lamp was mistakenly recognized as pilot light. Therefore, the present invention provides a means for extracting only the inverter light of the inverter fluorescent lamp, so that even if the optical wireless terminal faces the inverter light, the pilot is confirmed by checking the level of the means for extracting the inverter light. The purpose is to prevent misperception of light.
[0006]
[Means for Solving the Problems]
To solve the problems described above, between the light transmitting and receiving means (8e, 8d, 4a, 4b) and the optical wireless pick-up device provided with respectively (8) and multiple optical wireless communication terminal (4,5,6) in, an optical wireless communication system for transmitting and receiving data light by optical wireless communication, the optical wireless pick-up device (8) comprises a pilot light emitting means you emit pilot light (8f), the respective optical wireless communication terminal (4) has a front Symbol optical wireless pick-up device wherein the pilot light emitting means (8f) the inverter light when inverter light other than the light-emitting pilot light and the pilot light is coming from (8) A light receiving means (4f) capable of receiving light, a light receiving level detecting means (4g) for detecting a light receiving level of light received by the light receiving means (4f), and the inverter light included in the received light The received light Extracting the component of al the inverter light, inverter light extraction means for comparing the level of the components of the extracted inverter light with a preset level threshold (4h), the optical wireless communication terminal (4) in a predetermined direction And a search means (4j) for turning to the right , the search means (4j) is controlled to start a turning operation from a predetermined position, and the light reception level detected by the light reception level detection means (4g) is maximum, and When the inverter light extraction means (4h) determines that the level of the component of the inverter light is equal to or lower than the level threshold value, the turning control of the search means (4j) is stopped, while the level of the component of the inverter light is Search control means for executing the turning control of the search means (4j) again from the predetermined position when it is determined that the value exceeds the level threshold. And (4i), to provide an optical wireless communication system configuration with.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an optical wireless communication system according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration example of an optical wireless communication system according to the present invention. In this system, a star topology is formed between a collection / delivery device 8 attached to a ceiling or a wall and a plurality of communication terminals (first communication terminal 4, second communication terminal 5, and third communication terminal 6). Then, communication is performed between the communication terminals 4 to 6 and other communication devices (communication devices other than the communication devices 1 to 3) on the trunk line 7 via the collection and delivery device 8. When there is data to be transmitted to the third communication terminal 6 in the network environment composed of the collection / delivery device 8 and the plurality of communication terminals 4 to 6 as shown in the figure, the transmission path is not occupied. After confirmation, a transmission request signal is transmitted to the collection / delivery device 8. When the collection / delivery device 8 recognizes the transmission request from the third communication terminal 6, it confirms that the transmission path can be used, and sends a response signal indicating transmission permission to the third communication terminal 6 in the network. It returns to each communication terminal 4-6. The transmission permission signal from the collection / delivery device 8 is received by all communication terminals capable of communication in the network, but the content of the transmission permission includes an ID for specifying the third communication terminal 6 permitted to transmit. The third communication terminal 6 having an ID that matches this acquires the transmission right. When the ID included in the transmission permission signal matches the ID of the own device, the third communication terminal 6 starts to transmit data to the collection / delivery device 8 (the collection / delivery device 8 starts from the third communication terminal 6). After data transmission is completed, the connection is terminated and the transmission path is released. While the transmission line is occupied while the third communication terminal 6 is transmitting data, transmission cannot be performed from other communication terminals. However, after the transmission line is released, all the communication terminals 4 can be transmitted. ~ 6 can be transmitted. In addition, when the transmission permission is not returned or the communication terminal whose ID included in the transmission permission signal does not match the ID of its own device cannot acquire the transmission right, it cannot transmit data. At this time, the communication terminal having the data to be transmitted transmits a transmission request to the collection / delivery device 8 again after a predetermined time interval.
[0008]
Next, a configuration example of the collection and delivery apparatus 8 according to the present invention will be described with reference to FIG. In order to perform optical wireless communication with each communication terminal, the collection / delivery device 8 has an optical transmission means 8e using infrared rays such as LEDs, and an optical reception means 8d such as a PD (photo detector). The main line transmission means 8a and the main line reception means 8b which communicate with the main line 7 to which the communication apparatus is connected are provided. Further, in the control block 8c, data processing means for receiving data from the trunk line 7 and the communication terminal and sending it to an appropriate destination (the trunk line 7 and the communication terminal), an optical communication procedure means for performing a communication procedure with the communication terminal, There is. In addition, the collection / delivery device 8 includes pilot light generation means 8f for the communication terminal to align the optical axis with the collection / delivery device 8.
[0009]
FIG. 3 is a diagram showing an example of a communication terminal according to the present invention. Here, the configuration of the first communication terminal is shown. The first communication terminal 4 includes optical transmission means 4a using infrared rays such as LEDs and optical reception means 4b such as PDs for optical wireless communication with the collection and delivery device 8, and the first communication A transmission unit 4e and a reception unit 4d with the apparatus 1 are provided. Further, pilot light receiving means 4f for receiving pilot light transmitted from the collecting / distributing apparatus 8 in order to align the optical axis with the collecting / distributing apparatus 8, and a pilot light component are extracted from the optical signal received by the pilot light receiving means 4f. Based on the pilot light extraction means 4g, the inverter light extraction means 4h for extracting the inverter light component from the optical signal received by the pilot light reception means 4f, and the light reception levels from the pilot light extraction means 4g and the inverter light extraction means 4h Search control means 4i for controlling the optical axis alignment to the collection and delivery device 8 and search means 4j for rotating the direction of the first communication terminal 4 (pan, tilt, etc.) by a servo mechanism or the like.
[0010]
FIG. 4 is a flowchart showing the operation of the communication terminal in the optical wireless communication system according to the present invention. In the present embodiment, the first communication terminal 4 is used as the communication terminal. First, when the power of the first communication terminal 4 is turned on or when a shift of the optical axis of the first communication terminal 4 is detected (Y in step S1), search using pilot light is started (step S2). ). The pilot light received by the pilot light receiving means 4f provided in the first communication terminal 4 finds its peak by the pilot light extracting means 4g and ends the search (Y in step S3). Then, the inverter light extraction means 4h detects the light reception level, and if the level is equal to or lower than a preset threshold value (Y in step S4), the search is terminated assuming that the pilot light is correctly detected (step S4). S5). If the inverter light reception level detected by the inverter light extraction means 4h is equal to or higher than a preset threshold value, it is determined that the inverter light extraction means 4h has searched for the inverter light, and the search is performed again (step). N at S4). At this time, the same inverter light may be searched and the previously searched place may be stored so as not to fall into an infinite loop, and the search may be performed so as to exclude it.
[0011]
FIG. 5 shows an electric signal spectrum of a commercially available inverter fluorescent lamp. As can be seen from the figure, this electrical signal spectrum has a higher order spectrum extending to nearly 1 MHz with 40-60 kHz as the fundamental wave. Further, as the inverter light extraction means of the communication terminal according to the present invention, only the inverter component is extracted by filtering either the fundamental wave or the higher order component using the electric signal spectrum peculiar to the inverter fluorescent lamp. Thus, it may be used for discrimination from pilot light.
[0012]
【The invention's effect】
As described above, in the optical wireless communication system according to the present invention, when searching for pilot light, light from an inverter fluorescent lamp or the like may be misidentified as pilot light, and the search may not end normally. By providing the inverter light extraction means for extracting the signal peculiar to the inverter light from the received signal, it is possible to prevent erroneous recognition of the inverter light and improve the search reliability.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an optical wireless communication system according to the present invention.
FIG. 2 is a block diagram showing an example of a collection and delivery device applied to the optical wireless communication system according to the present invention.
FIG. 3 is a block diagram showing an example of a communication terminal applied to the optical wireless communication system according to the present invention.
FIG. 4 is a flowchart showing the operation of the optical wireless communication system according to the present invention.
FIG. 5 is a graph showing an example of an electric signal spectrum of an inverter fluorescent lamp.
[Explanation of symbols]
1, 2, 3 Communication device 4, 5, 6 Communication terminal 7 Trunk line 8 Pick-up device

Claims (1)

Between the optical wireless pick-up device and the multiple optical wireless communication terminal having a light transmitting and receiving means, respectively, an optical wireless communication system for transmitting and receiving data light by optical wireless communication,
The optical wireless pickup and delivery device
Comprising a pilot light emitting means you emit pilot light,
Each optical wireless communication terminal is
And the inverter light and capable of receiving a light receiving means when the pilot light emitting pilot light emitted from the unit and the inverter light other than the pilot light is incoming before Symbol optical wireless pick-up device,
A light receiving level detecting means for detecting a light receiving level of light received by the light receiving means;
When the received light includes the inverter light, the inverter light component is extracted from the received light, and the level of the extracted inverter light component is compared with a preset level threshold value. Inverter light extraction means;
Search means for turning the optical wireless communication terminal in a predetermined direction ;
The search means is controlled to start a turning operation from a predetermined position, and the light reception level detected by the light reception level detection means is maximum, and the inverter light extraction means determines that the level of the component of the inverter light is the level. The turning control of the search means is stopped when it is determined that it is below the threshold value, while the turning control of the search means is controlled at the predetermined position when it is determined that the level of the component of the inverter light exceeds the level threshold value. Search control means to be executed again,
An optical wireless communication system having a configuration comprising:

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