JPH09233026A - Optical radio transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent interference without changing a carrier frequency of each system where a service area is divided into plural areas and one system covers each division area. SOLUTION: The directivity of light transmission and that of light reception of a light transmitter and a light receiver of a center 1 are made both omnidirectional in the horizontal direction. A 1st light transmitter and a 1st light receiver of the center 1 have respectively sharp light emitting and sharp light receiving directivity to make full duplex communication with the transmitter and receiver, and a 2nd light transmitter and a 2nd light receiver of the center 1 have respectively comparatively wide light emitting and light receiving directivity to make full duplex communication with a data terminal 4. The light transmitter and the light receiver of the data terminal 4 have respectively light emitting and light receiving directivity upward with prescribed spread to make full duplex communication with one repeater 3 or over.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wireless transmission system in which a center and a data terminal communicate with each other via a repeater by optical wireless communication.

[0002]

2. Description of the Related Art In general, when a center and a data terminal communicate with each other by optical wireless communication, the communication area is expanded. A method of performing communication via a device is known.

In this method, as shown in FIG. 12, a non-directional transmitter / receiver in the repeater 3 or a transmitter / receiver having directivity with respect to both the center and data terminal transmitters / receivers 2, 4 is used. When used, there is an advantage that the installation location of the repeater 3 can be very easily selected and the number of repeaters 3 can be small if it is an open space where there is no shield in the communication area. However, it is general that there is a shield in the actual communication area, and a corresponding number of repeaters 3 are required to prevent the incommunicable area.

In the conventional system, when one space is divided into a plurality of areas such as areas "1" and "2" as shown in FIG. 13 and each divided area is configured by one system, Repeaters 3 in adjacent areas "1" and "2"
When the light emitting areas of are too large to interfere with each other, the interference can be prevented by changing the carrier frequency of each system. Note that other conventional optical wireless transmission systems include those disclosed in, for example, Japanese Patent Application Laid-Open Nos. 4-98913 and 4-299628.

[0005]

However, in the method of changing the carrier frequency of the repeater 3 of each adjacent system, four carrier frequencies are required for one system in order to realize full-duplex communication. However, it is difficult to allocate frequencies so that they do not interfere with each other. Furthermore, if the transfer rate is increased, the required band becomes wider, and it becomes more difficult to allocate frequencies.

In view of the above conventional problems, the present invention prevents interference without changing the carrier frequency of each system when the service area is divided into a plurality of areas and each divided area is configured by one system. It is an object of the present invention to provide an optical wireless transmission system capable of performing the above.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention divides a service area into a plurality of areas, and when each divided area is configured by one system, optical signals are mutually transmitted between the systems. In order to prevent interference, the directivity of the light transmitter and the light receiver of the repeater that performs optical communication with the light transmitter and the light receiver of the center is sharpened (in this specification, the directivity is narrow and wide). And refers to the breadth of the half-value angle). Therefore, according to the present invention, in an optical wireless transmission system in which a center and a data terminal communicate by optical wireless communication via a repeater, the center has a light-transmitting directivity and a light-receiving directivity with one or more repeaters. The transmitter has a transmitter and a receiver that perform optical communication with light having a wide range of characteristics, and the repeater is a light source having a sharp light-transmitting directivity and a light-receiving directivity between the center transmitter and the light receiver. A first light transmitter and a light receiver for optical communication, and a second light transmitter and a light receiver for optical communication with light having wide light-transmitting directivity and light-receiving directivity between the data terminal, The data terminal includes a light transmitter and a light receiver that perform optical communication with the second light transmitter and the light receiver of the repeater using light having a wide light transmission directivity and a wide light reception directivity, respectively. An optical wireless transmission system is provided. Also, the transmitter and receiver of the center and the first and second transmitters and receivers of the repeater are arranged on substantially the same horizontal plane and higher than the transmitter and receiver of the data terminal. The center transmitter and receiver are omnidirectional in the horizontal direction and have narrow directivity in the vertical direction, and the second transmitter and receiver of the repeater are The data transmitter and the light receiver of the data terminal have a wide directivity below the horizontal plane of the installation position, and a wide directivity above the horizontal plane of the installation position. Further, the light transmitter of the center and the second light transmitter of the repeater transmit light at a first carrier frequency, and the light transmitter of the data terminal and the first light transmitter of the repeater Light is transmitted at a carrier frequency of 2. Further, the repeater is characterized by having a manual movable part and an indicator for directing the first light transmitter and the light receiver toward the light transmitter and the light receiver of the center. In addition, the repeater,
It is characterized by having an automatic adjusting means for automatically orienting the first light transmitter and the light receiver toward the light transmitter and the light receiver of the center.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing the overall configuration of an embodiment of an optical wireless transmission system according to the present invention, and FIG. 2 is an explanatory diagram showing the transmitter / receiver of the center of FIG. 1 and its directivity.
3 is a configuration diagram showing the transmitter / receiver of the repeater of FIG. 1, FIG. 4 is an explanatory diagram showing the directivity of the transmitter / receiver of the repeater of FIG. 1, and FIG. 5 is a transmitter / receiver of the data terminal of FIG. FIG. 6 is an explanatory diagram showing directivity, FIG. 6 is an explanatory diagram showing carrier frequencies of the center, the repeater, and each of the transmitter / receivers of the data terminal, and FIG. 7 is an explanatory diagram showing carrier frequency bands of FIG. Is an explanatory diagram showing other carrier frequencies, FIG. 9 is an explanatory diagram showing the directivity of the repeater with respect to the transmitter / receiver at the center when the area is divided, and FIGS. 10 and 11 are diagrams showing the center when the area is divided into four. It is explanatory drawing which shows the installation position of a light transmitter / receiver.

As an example, the system shown in FIG. 1 divides one space into three areas, one center 1, three repeaters 3 covering each area, and a plurality of units installed in each area. The data terminal 4 of FIG. The data terminal 4 is installed on a desk or the like and performs optical communication with the repeater 3, and the transmitter / receiver (hereinafter, center transmitter / receiver) 2 and the repeater 3 of the center 1 are, for example, a wall shelf or a ceiling. And the like, which are relatively higher than the data terminal 4 and are installed on the same horizontal plane to perform optical communication with each other.

The center light transmitter / receiver 2 has a light transmitter 2a and a light receiver 2b as shown in FIG. 2, and the light transmitter 2a and the light receiver 2b transmit to all the repeaters 3 so as to be capable of optical communication. Both the light directivity and the light receiving directivity are non-directional in the horizontal direction. In addition, the directivity in the vertical direction is reduced by using a lens, and
a emits light only in the substantially horizontal direction, and the light receiver 2b also receives only light in the substantially horizontal direction. Thereby, the light from the data terminal 4 installed at a low position and the light to the data terminal 4, which is a noise source, can be reduced to the minimum.

As shown in FIG. 3, the repeater 3 has a first light transmitter 3a and a first light transmitter 3a having sharp light emitting directivity and light receiving directivity for performing full-duplex communication with the center light transmitter / receiver 2. In order to perform full-duplex communication between the first light receiver 3b and the data terminal 4, the second light transmitter 3c and the second light receiver 3d each having a relatively wide light emitting directivity and light receiving directivity. Have. Although not shown in the figure, the repeater 3 converts the frequency of the light received by the first light receiver 3b from the center light transmitter / receiver 2 and transmits it from the second light transmitter 3c to the data terminal 4, It has a frequency conversion function for converting the frequency of the light received by the second light receiver 3d from the data terminal 4 and transmitting it from the first light transmitter 3a to the center light transmitter / receiver 2.

As shown in FIG. 4, the first light transmitter 3a (and the first light receiver 3b) has a light emitting directivity (and a light receiving directivity) horizontally narrowed by a lens or a parabolic reflector. In response to this, the second light transmitter 3c (and the second light transmitter 3c
3d) has an omnidirectionality in the horizontal direction (uniform over 360 °), and has a light emission directivity (and light reception directivity) directed downward with a certain spread in the vertical direction. As shown in FIG. 5, the data terminal 4 is a light transmitter having a light emitting directivity and a light receiving directivity that are upwardly spread with a certain spread as shown in FIG. 5 so that full-duplex communication with one or more repeaters 3 is possible. 4a and the light receiver 4b.

The first light transmitter 3a and the first light receiver 3b of the repeater 3 are also rotated in the horizontal direction so as to face the center light transmitter / receiver 2 as shown in FIG. 3 (a). Yes, it is possible and the operator can make manual adjustments while looking at the indicator. Where center 1
Since the light transmitter / receiver 2 and the repeater 3 are installed on the same horizontal plane, the optical axes can be aligned only by rotating in the horizontal direction. A motor may be used instead of manual operation, and the microcomputer may search for a position having the highest reception level and automatically perform optical axis alignment.

Next, with reference to FIGS. 6 and 7, the carrier frequencies of the transmitter / receivers of the center 1, the repeater 3 and the data terminal 4 will be described. The light transmitter 2a of the center 1 modulates the optical signal modulated at the carrier frequency f1 with the frequency f0 (<f
The light of (1) is mixed and transmitted, and the repeater 3 transmits this light (f
When 1 + f0) is received by the first light receiver 3b, it is converted to frequency f2 (= f1 + f0) by the frequency f0, and the second
The light is transmitted from the light transmitter 3c. As a result, since all the repeaters 3 perform frequency conversion with the synchronized frequency f0, the light receiver 4b of the data terminal 4 can receive light without interference between the repeaters 3.

Similarly, the light transmitter 4a of the data terminal 4 transmits the optical signal modulated at the frequency f3 (> f2), and the repeater 3
When this light f3 is received by the second light receiver 3d, the frequency f0 is received by the frequency f0 received from the center 1 side.
4 (= f3 + f0) and transmitted from the first light transmitter 3a. As a result, since all the repeaters 3 perform frequency conversion with the synchronized frequency f0, light can be received by the light receiver 2b on the center 1 side without interference between the repeaters 3.

Here, the frequencies f1 to f4 must be assigned so as not to interfere with each other. In this embodiment, by performing frequency conversion, 1. Transmitter 2a of center 1 → repeater 3 → terminal 4 2. Although the interference due to the phase shift of the two systems of the light transmitter 2a of the center 1 to the terminal 4 is avoided, in the present embodiment, the center light transmitter / receiver 2 and the terminal 4 are provided by optical isolation as shown in FIG. Communication between the two does not occur. Therefore, the repeater 3 can avoid the interference without converting the carrier frequency as shown in FIGS. 6 and 7.

Referring to FIG. 8, the light transmitter 2a of the center 1 transmits an optical signal modulated at the carrier frequency f1, and the repeater 3 receives this light f1 by the first light receiver 3b. 2nd frequency f1 without frequency conversion
The light is transmitted from the light transmitter 3c. Further, the light transmitter 4a of the data terminal 4 transmits an optical signal modulated at the frequency f3, and the repeater 3 receives this light f3 by the second light receiver 3d,
The first light transmitter 3a at the frequency f3 without frequency conversion
Send from As a result, in all the repeaters 3, the signals become synchronized without performing frequency conversion, and the light receiver 2b on the center terminal 1 side and the light receiver 4 on the data terminal 4 side.
b can be received without interfering with the light from the light transmitters 3a and 3c of the repeater 3.

Next, a case of dividing an area will be described with reference to FIGS. In the present invention, the first light transmitter 3 of the repeater 3 for optical communication with the center light transmitter / receiver 2
Since the directivity of a and the light receiver 3b is sharpened, one space is divided into a plurality of areas such as areas "1" and "2" as shown in FIG. 9, and each divided area is configured by one system. In this case, it is possible to deal with the problem by only considering the installation position of the light transmitter / receiver 2 of the center 1 instead of dividing the area by the carrier frequency as in the conventional example.

10 and 11 show four areas "1"-
An example of division into “4” is shown, and in FIG. 10, the center transmitters / receivers 2-1 to 2-4 are installed at the centers of the areas “1” to “4”. In this case, for example, from the first light transmitter 3a of the repeater 3-1 in the area "1" to the center light transmitter / receiver 2-
Light directed to 1 is a center transmitter / receiver 2-2 in area "2"
It may not reach the proper location because it may reach the station and cause interference. Therefore, as shown in FIG. 11, the center transmitters / receivers 2-1 to 2-4 are installed in the areas "1" to "4" farthest from the other areas to prevent interference. .

Further, according to the present invention, the directivity of the first light transmitter 3a of the repeater 3 with respect to the center light transmitter / receiver 2 is narrowed, and the second light transmitter 3c of the repeater 3 with respect to the data terminal 4 is narrowed down.
Covers a relatively small area, so that efficient light emission can reduce power consumption.

[0021]

As described above, according to the present invention, when the service area is divided into a plurality of areas and each divided area is configured by one system, optical signals do not interfere with each other between the systems. Since the directivity of the light transmitter and the light receiver of the repeater for optical communication with the light transmitter and the light receiver of the center is sharpened, it is possible to prevent the interference without changing the carrier frequency of each system. Also, the transmitter and receiver of the center and the first and second transmitters and receivers of the repeater are arranged on substantially the same horizontal plane, and are installed at a higher position than the transmitter and receiver of the data terminal, The center transmitter and receiver have a horizontal directivity of 360 ° and a vertical directivity, and the second transmitter and receiver of the repeater are below the horizontal plane of the installation position. Has a wide directivity, and the transmitter and the receiver of the data terminal have a wide directivity above the horizontal plane of the installation position, so that the center transmitter and the second transmitter of the repeater are provided. The optical device is the first
Since it is possible to transmit light at the carrier frequency of 2 and the first transmitter of the data terminal and the first transmitter of the repeater can transmit at the second carrier frequency, it is possible to configure the system with two channels.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of an embodiment of an optical wireless transmission system according to the present invention.

FIG. 2 is an explanatory diagram showing a transmitter / receiver at the center of FIG. 1 and its directivity.

FIG. 3 is a configuration diagram showing a transmitter / receiver of the repeater of FIG.

FIG. 4 is an explanatory diagram showing the directivity of the transmitter / receiver of the repeater of FIG.

5A and 5B are explanatory views showing a light transmitter / receiver and directivity of the data terminal of FIG.

6 is an explanatory diagram showing carrier frequencies of respective transmitters / receivers of a center, a repeater, and a data terminal of FIG. 1. FIG.

FIG. 7 is an explanatory diagram showing bands of the carrier frequency of FIG.

FIG. 8 is an explanatory diagram showing another carrier frequency.

FIG. 9 is an explanatory diagram showing the directivity of the repeater with respect to the central transmitter / receiver when the area is divided.

FIG. 10 is an explanatory diagram showing the installation positions of the light-transmitting and receiving devices at the center when the area is divided into four.

FIG. 11 is an explanatory diagram showing a preferable installation position of the light transmitter / receiver at the center when the area is divided into four.

FIG. 12 is an explanatory diagram showing a system configuration when an area is divided into four.

FIG. 13 is an explanatory diagram showing the directivity of the conventional transmitter / receiver of the repeater with respect to the center transmitter / receiver when the area is divided.

[Explanation of symbols]

 1 center 2 center transmitter / receiver 3 repeater 4 data terminal 2a, 3a, 3c, 4a transmitter 2b, 3b, 3d, 4b receiver

Front page continued (72) Inventor Manabu Sakane 3-12 Moriya-cho, Kanagawa-ku, Yokohama, Japan Victor Company of Japan, Ltd. (72) Toshiaki Okumura 3--12 Moriya-cho, Kanagawa-ku, Yokohama Japan Victor Co., Ltd. (72) Inventor Hideki Hasegawa, 3-12 Moriya-cho, Kanagawa-ku, Yokohama, Kanagawa Japan Victor Co., Ltd. (72) Inventor Masanobu Tamura 3--12, Moriya-cho, Kanagawa-ku, Yokohama Japan Victor Co., Ltd. (72) Inventor Takaaki Takeda 3-3-3 Toyosu, Koto-ku, Tokyo NTT Data Communications Co., Ltd. (72) Inventor Ken Nomoto 3-3-3 Toyosu, Koto-ku, Tokyo NTT DATA Communications Co., Ltd.

Claims (3)

[Claims] 1. An optical wireless transmission system in which a center and a data terminal communicate with each other via a repeater by optical wireless, wherein the center has a light transmission directivity with one or more repeaters,
It has a light transmitter and a light receiver that perform optical communication with light having a wide light reception directivity, and the repeater has sharp light transmission directivity and light reception directivity between the center light transmitter and the light receiver. A first light transmitter and a light receiver that perform optical communication with light, and a second light transmitter and a light receiver that perform optical communication with light having wide light-transmitting directivity and light-receiving directivity between the data terminal are provided. However, the data terminal may include a light transmitter and a light receiver that perform optical communication with the second light transmitter and the light receiver of the repeater by using light having wide light transmission directivity and light reception directivity, respectively. Characteristic optical wireless transmission system. 2. The transmitter and receiver of the center and the first and second transmitters and receivers of the repeater are arranged on substantially the same horizontal plane, and the transmitter and receiver of the data terminal are arranged. It is installed at a position higher than the transmitter, and the transmitter and receiver of the center have omnidirectionality in the horizontal direction and narrow directivity in the vertical direction. The device has a wide directivity below the horizontal plane of its installation position, and the transmitter and the receiver of the data terminal have a wide directivity above the horizontal plane of its installation position. 1. The optical wireless transmission system according to 1. 3. The optical transmitter of the center and the second optical transmitter of the repeater transmit at a first carrier frequency, and the optical transmitter of the data terminal and the first optical transmitter of the repeater. The vessel is second
3. The light is transmitted at the carrier frequency of 2.
The optical wireless transmission system described.