JP2003283433A - Optical radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical radio communication system in which mis-recognition of an inverter light is prevented, and the reliability of searching is enhanced. <P>SOLUTION: The optical radio communication system comprises an optical radio collection and delivery apparatus and optical radio communication terminals. The optical radio collection and delivery apparatus is provided with: an optical transmission reception means for transceiving data with the optical radio communication terminal by using an optical radio signal; and a pilot light emitting means for emitting a pilot light used by the optical radio terminal to align the optical axis of the optical radio signal. The optical radio terminals are each provided with: an optical transmission/ reception means for transceiving data with the optical radio collection and delivery apparatus by using the optical radio signal; a pilot light reception means for receiving the pilot light from the pilot light emitting means; a pilot light extracting means for extracting the components of the pilot light from the optical signal received by the pilot light emitting means; an inverter light extracting means for extracting the components of the inverter light from the optical signal received by the pilot light reception means; and a search means for searching in response to an output from the pilot light extracting means and the inverter light extracting means. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wireless communication system for transmitting a signal through optical wireless, and more particularly to an optical communication system for properly aligning the optical axis of pilot light. The present invention relates to a wireless communication system. 2. Description of the Related Art Generally, when a signal is transmitted via optical wireless communication, an LED (light emitting diode) or a laser diode is used as a light emitting element on the light emitting side. Since it does not spread even if it is transmitted over long distances, it is used for transmission between buildings or across rivers. However, since the beam diameter is extremely small, if the beam enters the human body, especially to the eyes, the eyes may be damaged. Therefore, the beam cannot be used in premises such as offices. On the other hand, an LED is not suitable for long-distance transmission because an LED has a wide directivity and a light beam spreads with distance.
By integrally forming the ED and the focusing lens, the transmission distance can be extended. Since optical noise generated by illumination light or the like mainly has a low-frequency spectrum, data is generally converted to a broadband signal by modulation such as FM and PM. Japanese Patent Application Laid-Open No. Hei 6-224858 describes a transmitting terminal having a transmitting device for transmitting the light emitted from the LED, which is the above-mentioned light emitting element, in parallel by a parabolic reflector. Such an optical wireless terminal is connected to a station such as a personal computer or the like, and the optical axis alignment is automatically performed by servo means for an optical wireless collection and distribution device mounted on a ceiling, relying on pilot light coming from the collection and distribution device. And established a link for optical wireless communication. [0005] However, in the optical axis alignment method in the optical wireless communication system described above, the signal frequency (several tens of kHz) used in the pilot light is used.
Since the flicker frequency of the indoor fluorescent lamp is close to that of the indoor fluorescent lamp, there is a problem that the optical wireless terminal erroneously recognizes the light of the inverter fluorescent lamp as the pilot light when searching for the optical wireless collection and distribution device. 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 has turned to the inverter light, the level of the means for extracting the inverter light can be confirmed by the pilot. The purpose is to prevent misidentification of light. [0006] In order to solve the above-mentioned problems, an optical wireless collection and distribution device for collecting and delivering data by an optical wireless signal, and an optical wireless collection and delivery device for transmitting and receiving data by the optical wireless signal. An optical wireless communication system having a plurality of optical wireless communication terminals performed between the optical wireless communication terminal, wherein the optical wireless collection and delivery device, optical receiving means for receiving data from the optical wireless communication terminal by the optical wireless signal, Optical transmission means for transmitting data to the optical wireless communication terminal by the optical wireless signal, pilot light emitting means for emitting pilot light used by the optical wireless communication terminal to adjust the optical axis of the optical wireless signal, and the data And a light communication procedure means for controlling communication with the optical wireless communication terminal, wherein the optical wireless communication terminal is Optical receiving means for receiving data by an optical wireless signal;
An optical transmission unit for transmitting data to the optical wireless collection / delivery device using the optical wireless signal, a data processing unit for processing the data, an optical communication procedure unit for controlling communication with the optical wireless collection / delivery device, and the optical wireless A pilot light receiving unit for receiving pilot light from a pilot light emitting unit of the collection and distribution device, a pilot light extracting unit for extracting a pilot light component from an optical signal received by the pilot light receiving unit, and the pilot light Inverter light extracting means for extracting the component of the inverter light from the optical signal received by the receiving means, and transmitting the optical wireless signal to the optical receiving means according to the outputs from the pilot light extracting means and the inverter light extracting means. And a search means for directing the optical transmission means in the direction of the optical transmission means. An embodiment of the optical wireless communication system according to the present invention will be described below 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 collection and delivery device 8 attached to a ceiling, a wall, or the like and a plurality of communication terminals (first communication terminal 4, second communication terminal 2,
Form a star topology with the communication terminal 5 and the third communication terminal 6), and each of the communication terminals 4 to
6 and other communication devices on the trunk line 7 (communication devices other than the communication devices 1 to 3). In a network environment composed of a collection and delivery device 8 and a plurality of communication terminals 4 to 6 as shown in FIG. 5, if there is data to be transmitted to the third communication terminal 6, it is determined that the transmission path is not occupied. After confirmation, a transmission request signal is transmitted to the collection and delivery device 8. When recognizing the transmission request from the third communication terminal 6, the collection and delivery device 8 confirms that the transmission path can be used, and transmits a response signal indicating permission for transmission to the third communication terminal 6 within the network. A reply is sent to each of the communication terminals 4 to 6. The transmission permission signal from the collection / delivery device 8 is received by all communicable communication terminals in the network, but the content of the transmission permission includes an ID for specifying the third communication terminal 6 to which transmission is permitted. The third communication terminal 6 having an ID that matches this acquires the transmission right. Then, when the ID included in the transmission permission signal matches the ID of the own device, the third communication terminal 6 starts transmitting data to the collection and distribution device 8 (the collection and distribution device 8 transmits the data from the third communication terminal 6 to the third communication terminal 6). After the data transmission is completed, the connection is terminated and the transmission path is released. While the third communication terminal 6 is transmitting data, the transmission path is occupied and transmission from other communication terminals cannot be performed. However, after the transmission path is released, all communication terminals 4 To 6 can be transmitted. In addition, a communication terminal in which the transmission permission is not replied or the communication terminal whose ID included in the transmission permission signal does not match its own ID cannot transmit the data because the transmission right cannot be acquired. At this time, the communication terminal having the data to be transmitted transmits a transmission request to the collection and delivery device 8 again after a predetermined time interval. Next, a configuration example of the collection and delivery device 8 according to the present invention will be described with reference to FIG. The collection / delivery device 8 includes an optical transmission unit 8e using infrared rays such as an LED and an optical reception unit 8d using a PD (photodetector) for performing optical wireless communication with each communication terminal. A main line transmitting unit 8a and a main line receiving unit 8b for communicating with the main line 7 to which the communication device is connected. The control block 8c includes a data processing unit that receives data from the trunk line 7 and the communication terminal and sends the data to an appropriate destination (the trunk line 7 and the communication terminal), and an optical communication procedure unit that performs a communication procedure with the communication terminal. There is. The collection and distribution device 8 also includes pilot light generating means 8f for allowing the communication terminal to align the optical axis with the collection and distribution device 8. FIG. 3 is a diagram showing an example of a communication terminal according to the present invention. Here, the structure of a first communication terminal is shown. In order to perform optical wireless communication with the collection / delivery device 8, the first communication terminal 4 has an optical transmission unit 4 a using an infrared ray such as an LED.
And a light receiving means 4b such as a PD.
And a transmission unit 4e and a reception unit 4d for communicating with the communication device 1. Further, a pilot light receiving means 4f for receiving the pilot light transmitted from the collection and distribution device 8 for aligning the optical axis with the collection and distribution device 8, and a pilot light component is extracted from the optical signal received by the pilot light reception means 4f. Based on pilot light extracting means 4g, inverter light extracting means 4h for extracting an inverter light component from the optical signal received by pilot light receiving means 4f, and light receiving levels from pilot light extracting means 4g and inverter light extracting means 4h. Search control means 4i for controlling optical axis alignment to collection and delivery device 8
And search means 4j for rotating (panning, tilting, etc.) the direction of the first communication terminal 4 by a servo mechanism or the like. FIG. 4 is a flowchart showing the operation of the communication terminal in the optical wireless communication system according to the present invention. In this embodiment, the first communication terminal 4 is used as a communication terminal. First, when the power of the first communication terminal 4 is turned on or when the optical axis shift of the first communication terminal 4 is detected (Y in step S1), the search by the 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 terminates 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 (Y in step S4), the search is terminated assuming that the pilot light has been correctly detected (step S4). S
5). If the reception level of the inverter light detected by the inverter light extraction unit 4h is equal to or higher than a preset threshold, it is determined that the inverter light extraction unit 4h has searched for the inverter light, and the search is performed again (step N at S4). At this time, the location searched last time may be stored so that the same inverter light is searched to avoid an infinite loop, and the search may be performed so as to exclude this location. FIG. 5 shows an electric signal spectrum of a commercially available inverter fluorescent lamp. As can be seen from this figure, this electric signal spectrum has a fundamental spectrum of 40 to 60 kHz, and a high-order spectrum extends to almost 1 MHz. As the inverter light extraction means of the communication terminal according to the present invention, an electric signal spectrum unique to the inverter fluorescent lamp is used, and either the fundamental wave or the higher-order component is filtered to extract only the inverter component. This may be used for discriminating the pilot light. As described above, in the optical wireless communication system according to the present invention, when searching for pilot light, light such as an inverter fluorescent light is erroneously recognized as pilot light, and the search does not end normally. However, by providing an inverter light extracting means for extracting a signal unique to the inverter light from the received signal of the pilot light, it is possible to prevent the mistaken recognition of the inverter light and improve the search reliability. It is.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing one 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 an 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. [Description of Signs] 1, 2, 3 Communication devices 4, 5, 6 Communication terminal 7 Trunk line 8 Collection / delivery device

Claims (1)

Claims: 1. An optical wireless collection / delivery device for collecting and delivering data by an optical wireless signal, and a plurality of optical wireless communication devices for transmitting / receiving data by the optical wireless signal to / from the optical wireless collection / delivery device. An optical wireless communication system having a terminal, wherein the optical wireless collection / delivery device is configured to receive data from the optical wireless communication terminal by the optical wireless signal, Optical transmission means for transmitting data, pilot light emission means for emitting pilot light used by the optical wireless communication terminal to align the optical axis of an optical wireless signal, data processing means for processing the data, Optical communication procedure means for controlling communication with a wireless communication terminal, wherein the optical wireless communication terminal receives data from the optical wireless collection and distribution device using the optical wireless signal. Stage, optical transmission means for transmitting data to the optical wireless collection and distribution device by the optical wireless signal, data processing means for processing the data, optical communication procedure means for performing communication control with the optical wireless collection and distribution device, Pilot light receiving means for receiving pilot light from the pilot light emitting means of the optical wireless concentrator, pilot light extracting means for extracting a component of the pilot light from the optical signal received by the pilot light receiving means, An inverter light extracting means for extracting a component of the inverter light from the optical signal received by the pilot light receiving means; and the optical receiving means according to an output from the pilot light extracting means and the inverter light extracting means. An optical wireless communication system comprising: a search unit for directing a signal to the optical transmission unit.