JPS6016038A - Optical radio communication equipment - Google Patents

Abstract

PURPOSE:To take a required S/N sufficiently for transmission with a few number of light transmitters by providing a spread spectrum modulator to the pre- stage at an optical radio transmission station and providing a spread spectrum demodulator to the post-stage of an optical demodulator at a reception station. CONSTITUTION:A primary modulator 5 in a transmission station 1 applies primary modulation such as FM modulation to a signal from an information source 4 and its output signal is subjected to spread spectrum modulation by a spread spectrum modulator 6. The optical intensity modulation is applied to an output signal of the modulator 6 by a light irradiation driving circuit 7 and the signal is released in space as a beam light 3 from a light transmitter 8. A reception station 2 receives the beam light 3 by a photodetector 9, demodulates the light into an electric signal, which is amplified (10) and inputted to a spread spectrum demodulator 11. The demodulator 11 demodulates the input signal into a primary modulation signal by a processing gain GP, its output is demodulated into the original signal by a primary demodulation 12 and outputted to an output circuit 13. The gain GP is defined by the ratio of band with Ba of a spread spectrum signal/band width Bd of the original signal and the S/N is improved by the value of the gain GP.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical wireless communication device that uses space as a communication path for transmitting information.

[Background of the invention]

There are two types of optical wireless communication devices: The first device is installed in the moving space of the moving object and the moving space of the moving object in order to perform two-way transmission between the moving object and a console for collecting and processing information from the moving object and controlling the moving object. A facing method (opposing method) that secures a communication path by controlling the light transmitters and receivers placed around the satellite, which are placed and connected by wire as a communication path with the console, so that they always face each other in synchronization with the movement of the moving object. (See Japanese Patent Application No. 57-194515). The second device diffuses light containing an information signal into the room where the terminal equipment is located in order to perform bidirectional transmission between the host computer and the terminal equipment located in a different room from the host computer. It uses a spreading method to secure communication channels. However, in order to obtain the signal-to-noise (8/N) ratio necessary for transmission, in the facing method, it is necessary to narrow down the transmission beam output from the transmitter, which consists of a light emitting element, lens, etc. The disadvantage is that it becomes difficult for the light receiver, which is composed of elements, lenses, etc., to capture the transmitted light from the light transmitter, making it difficult to secure a communication path. On the other hand, in the spreading method, υ is even more severe than in the opposing method, and it is particularly difficult to transmit video signals with a wide bandwidth.

Even if transmission is performed using the wave number method, the coverage area of one light emitting element or light emitter is narrow, and there are disadvantages in that a large number of light emitting elements or light emitters must be installed on the ceiling, wall, etc.

[Purpose of the invention]

Therefore, it is an object of the present invention to solve the above-mentioned drawbacks of the prior art, and to eliminate the 8/8/20 required for transmission with a small number of light emitting elements or light transmitters.
It is an object of the present invention to provide an optical wireless communication device that has a sufficient N ratio and can stably secure a communication path.

[Summary of the invention]

The present invention improves the 8/N required for optical transmission by providing a spread spectrum modulator before an optical modulator at a transmitting station, and by providing a spread spectrum demodulator after an optical demodulator at a receiving station. It is characterized by:

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing an example of the basic configuration of the present invention. In FIG. 1, 1 is a transmitting station, 2 is a receiving station, and 3 is a light beam. At the transmitting station 1, an information source 4 (e.g. TV
An output signal from a signal generating means such as a camera, a computer, etc. is subjected to linear modulation by a primary modulator 5 using FM modulation or the like. - The output signal of the humanities modulator 5 is subjected to spread spectrum modulation by the spread spectrum modulator 6, then light intensity modulated by the light emitting element drive circuit 7, and an optical signal (
It becomes a beam of light 3) and is emitted into space. On the other hand, at the receiving station 2, the light beam 3 is input to the light receiver 9, where the light beam 3 is optically demodulated into an electrical signal. This electrical signal is transmitted to the spread spectrum demodulator 11 via the amplifier 10, and the spread spectrum demodulator 11 generates p processing gain G,
It is then demodulated into a humanistic signal. Thereafter, it is demodulated into the source signal by the post-modulator 12, and the signal is demodulated by the output device 13 (for example, T
V monitor, control circuit, etc.). Here, the processing gain G is defined by equation (1).

G p ” B − / B a ・・・・・・・・・・・・
(1) where Bm is the bandwidth of the spread spectrum signal, and Ba is the bandwidth of the source signal.

Therefore, since the signal-to-noise ratio (8/N) is improved by the processing gain Gp, the intensity of the emitted beam can be reduced to 1/G. Therefore, in the opposing method, the beam diameter can be expanded by a times, or by 1/G in the wave number method.

The number of light emitting elements or light transmitters 8 installed can be reduced.

FIG. 2 shows the embodiment of FIG. 1 for two-way communication between a mobile object 17 running in a room 14 such as a containment vessel or a feed water heater room of a nuclear power plant and a console located in a separate room 15. An example of the application is shown below.

The mobile station 20 on the mobile body 17 performs bidirectional communication with any one of the satellite stations 401 to 4ON mounted on the ceiling of the room 14.

The satellite stations are arranged such that at least one can communicate with the mobile station 20 of the mobile body 17. Each satellite station 4
0+~4ON is the central office 30 on the console and the wired 18
are tied together. The computer 16 is connected to the central station 30 and determines the position of the mobile body 17 based on the position information of the mobile body 17 from the mobile station 20 that is input from the central station 30. 40+ (i=1.2
...Select N). Hereinafter, detailed structures of the mobile station 20, satellite station 40, and central station 30 will be explained using figures. FIG. 3 shows an embodiment of the mobile station 20. The subscript t of the number in FIG. 3 indicates a mobile station, and the same number as in FIG. 1 has the same function as the structure with the same number as in FIG. In this embodiment, the information source 4t is an ITV camera 4tt.
, (toss the bandwidth of the video signal Bt, 1), the microphone (same (Btu) and the state signal of the mobile 17 4
t3 (same < Bts). The spread spectrum modulator (direct sequence method) 6t is a carrier wave generator (frequency f.

(sine wave output) 6L1 is subjected to spread spectrum modulation in balanced modulators 6L3 to 6t based on three different M-sequence signals from the pseudo-noise code generator at+ to obtain respective code-modulated carrier signals. . This carrier wave signal is then transmitted to the information source 41. by the 1M modulators 5ts to 5Ls. The output signals of 4ZS to 4ZS are FM-modulated with corresponding code-modulated carrier signals, and are emitted as optical signals into space by the light emitting element drive circuit 71z and the light transmitter 8t via the combiner 19z.

Assuming that the bandwidth of the transmission signal at this time is B, ① the processing gains Gpl, Gp, for the video signal of the TV camera, the acoustic signal of the microphone, and the state signal of the moving object;

Gp3 is Ba /Bz+ + Bs /Btt, respectively
t Bs /Bzs. On the other hand, the received signal at the satellite station 40 is passed through the amplifier 10 to the spread spectrum modulator 6t, and is then applied to the FM demodulator 12t using the code-modulated carrier signal of the balanced modulator IIt obtained by the spread spectrum demodulator lit. The signal is FM demodulated and output to an output device (such as a control circuit of the moving object) 13t of the moving object. Fourth
An embodiment of the satellite station 40 is shown in the figure. Each satellite station 40+ (1=1.2...M) has a transmitter 8m+ (
' = I + 2...M), photoreceiver 91 (i = 1.2
...M), satellite station 40. Turn off the power to 0N-OFF
Relay contact 42 + (' = 1 + 2...
M), and the relay 1 drive circuit and satellite station 40+
Satellite channel selection circuit 41+ (f=
1.2...M). Hypothetically, the computer 16 on the console calls the satellite station 40. Suppose that the channel is selected. The channel selection method will be explained later in the embodiment of the central station 30.

When the selection signal superimposed on the transmission signal to the moving body 17 is detected, the satellite station selection circuit 411 contacts the relay contact 42! to supply power to the light transmitter 8.1 and the light receiver 9.1. 183 is its power supply line. Therefore, the transmitter 8
．． 1, the downlink signal 182 to the mobile body 17 is emitted into space as an optical signal, and the light receiver 9.1 detects the upstream signal from the mobile body 17 to the central station 30 and transmits it to the central station 30. It becomes possible. In this way, by always receiving signals at only one satellite station, it is possible to improve the F)8/N ratio. 9. All receivers at all times. When the satellite station is in the light receiving state, the received signals of satellite stations other than the satellite station actually transmitting and receiving become noise.

Possible sources of noise include background light such as sunlight and indoor lighting. Noise N is expressed by equation (2).

However, j is the number of the selected satellite station M is the number of satellite stations N+ is noise due to background light at i satellite station and No is fixed noise other than background light.

Therefore, if the satellite stations other than the one actually transmitting and receiving are released from the receiving state, the noise in the second term of equation (2) can be eliminated and the 8/N ratio can be improved. Figure 5 shows the central office 30 and computer 1 on the console.
It is a figure showing Example 6. In FIG. 5, the number subscript C indicates the central office, and the same numbers as in FIG. 1 perform the same functions as those in FIG. Therefore, explanations of operations similar to those in FIG. 2 will be omitted. It is assumed that the carrier sine wave frequency of the carrier wave generator 11.1 of the central station 30 is the same as the carrier sine wave frequency of the carrier wave generator 611 of the mobile station.

Furthermore, the pseudo-noise force generator 11.2 of the central station 30 outputs exactly the same M-sequence signal part as the pseudo-noise force generator 612 of the mobile station 20. And spread spectrum demodulator 1
The pseudo-noise boosted M-sequence signal that is input to the balanced modulators 11.3 to 11.5 (9) of 1e is the pseudo-noise boosted M-sequence signal that is input to the balanced modulators 6t3 to 6t11 of the mobile station 20. Each signal shall have the same characteristics as the signal.

Similarly, the pseudo-noise-added M-sequence signals that are input to the balanced modulators 11t1 and 6.1 have the same properties. In this way, by making the pseudo-noise added M-sequence signals on the modulation side and the demodulation side have regular properties, it is possible to discriminate and multiplex the transmission signals.

11.6 is a synchronization detection circuit that synchronizes the pseudo-noise force generator 612 of the mobile station 20 and the central station 30 and 11.2. 19.1 is a distributor. Next, a method for selecting satellite stations will be explained. The computer 16 detects the position of the mobile body 17 based on the position information of the mobile body 17, and detects the position of the mobile body 17.
The satellite station 40t (i=1.2...M
). The satellite station selection frequency oscillation circuit 50 generates a frequency ft (1=1.2·
.

Satellite channel selection circuit 41+ (1(1
0) = 1, 2...M), it is possible to detect that the own station has been selected by determining the presence or absence of the frequency for selecting the own station. Finally, we will discuss the effects of using spread spectrum.

Let us consider the relationship between the processing gain of each transmission signal in the case of multiplex transmission, such as the upstream signal from the mobile station 20 to the central station 30, and the expansion of the pumping range in the opposing method or spreading method. The bandwidth of the transmission signal, −B, is determined by the M-sequence signal of the pseudo-noisy force generator.

Also, if the transmission strength required for the three information source signals when spread spectrum communication is not used is 81 g 82 H83, the required transmission strength when using spread spectrum communication is calculated using the processing gain of each. Sl/Gpt+St/Gp
2. Ss/Gps. Here, the bandwidth BzI of the video signal is the bandwidth BzI of the audio signal and the mobile state signal.
Compared to t**Bta, Bt+ >Btz *Bzt
>Ba Because of the relationship Gpl <Gpz + Gpt <Gpa...
......(3). On the other hand, 81 + 82
For +88, 81 >82. 8+ >Ss・
・・・・・・・・・・・・(4)(11) Since there is the following relationship, we obtain the relationship shown in equation (5).

S! /Gp+ > 82 /GP2, St /Gp
t>Ss/Gps (5) Therefore, even when the spread spectrum communication method is used, the required transmission strength of the video signal dominates the overall required transmission strength. As a result, considering the transmission range diameter R, the transmission range of the upstream signal is determined by the video signal processing gain G, l.
=! The formula (6) is obtained.

R1 = V'dL-・Ro River... Self... (6) However, R1 is the transmission range when spread spectrum communication is used, and Ro is the transmission range when spread spectrum communication is not used. be.

The video signal processing gain G,1 is the video signal bandwidth 4MH.
2. Considering the bandwidth of the light emitting element and light receiving element, 40 to 10
It is possible to take a value of about 0.

Therefore, it is possible to increase the transmission range diameter by 6 to 10 times, and it is also possible to use a spreading method as a communication method with the mobile object 17. On the other hand, even in the facing method, since the diameter of the emitted beam can be made large, the received light can be easily followed by #l, and stable communication can be ensured.

(12) The embodiments applied inside a room have been described above. 6th
FIG. 7 shows an embodiment in which the present invention is applied to outdoor optical wireless communication. FIG. 6 shows communication between a building and a mobile object, and FIG. 7 shows communication between ships. 6th
In the figure, video signals from a relay vehicle 85 are transmitted to a satellite station 8 on the roof of a building 80, for example during a marathon broadcast.
4 shows an example of transmission. FIG. 8 shows an embodiment in which information is transmitted between ships 82. In the case of outdoor use, since the transmission distance is long, a facing method is suitable because it can maintain the light intensity.

Furthermore, if spread spectrum is used in the optical communication system between the mobile unit and the central office, the S/N ratio can be improved from the following points as well. A control device such as a microcomputer for controlling the moving body may be mounted on the moving body 17. Further, even in the facing method, a control device is required to control the opposing light transmitting and receiving devices so that they always face each other directly. The high-frequency component of the oscillator in the control device enters the receiving signal (13
) is the noise Nt. However, when spread spectrum communication is used, this noise N1 is not modulated with the pseudo-noise code, so the spread spectrum demodulator 11 conversely
The signal becomes modulated by the pseudo-noise signal and is reduced to the relationship shown in equation (7).

Nt' = Nt/Gp...l1・
Group (7) where Nt is the noise when spread spectrum communication is used, Nt' is the noise when spread spectrum communication is used, and Gp is the processing gain.

〔Effect of the invention〕

As explained above, according to the present invention, at the transmitting station,
By providing a spread spectrum modulator before the optical modulator and by providing a spread spectrum demodulator after the optical demodulator at the power receiving station, the 8/N ratio required for optical transmission is improved. By making it possible to use a diffusion method in communication, and also in the facing method, by increasing the transmission beam diameter and making it easier to capture the p1 received light (14), stable communication can be ensured.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the spread spectrum optical wireless communication of the present invention, and FIG. 2 is a diagram showing the application of the present invention to two-way communication between a moving object 17 running in a room and a console located in a separate room. FIG. 3 is a detailed system diagram of the mobile station shown in FIG. 2, FIG. 4 is a detailed system diagram of the satellite station in FIG. 2, and FIG. 5 is a detailed system diagram of the mobile station shown in FIG. The detailed system diagram of the central station in the figure, Figure 6 is an explanatory diagram when the present invention is used for optical communication between mobile objects and buildings, and Figure 7 is an explanatory diagram when the present invention is used for optical wireless communication between ships. FIG. 1... Transmitting station, 2... Receiving station, 4... Information source, 5
...-Humanities modulator, 6... Spread spectrum modulator,
7... Light emitting element drive circuit, 8... Light transmitter, 9...
Light emitter, 11... Spread spectrum demodulator, 12...
・-person adjustment device, 17...mobile object, 20...mobile station,
30...Central station, 40...Satellite station. Agent Patent attorney Akio Takahashi (15)

Claims (1)

[Claims] 1. A transmitting station having a signal generating means, a modulator for inputting the output signal of the signal generating means, and a light transmitter for outputting the output signal of the modulator as an optical signal; a light receiver for manually inputting the optical signal; In an optical wireless communication device comprising a receiving station having a demodulator that inputs an output signal of a light receiver, the modulation modulator of the transmitting station and the light transmitter are connected via a spread spectrum modulator, An optical wireless communication device characterized in that the optical receiver and the demodulator of a receiving station are connected via a spread spectrum demodulator.