JP4373855B2 - Optical wireless transmission system and apparatus - Google Patents

Description

The present invention relates to an optical wireless transmission system and a device, an optical wireless transmission system and a device for the optical signal radio transmission.

  In recent years, with the widespread use of ADSL (Asymmetric Digital Subscriber Lines) and optical fibers, an environment in which high-speed Internet of Mbps class and Gbps class is used in homes and offices is being prepared. Thereby, multimedia information including image transmission such as HDTV (high definition television) can be easily viewed at home or office through various distribution services.

  High-speed lines between Internet service providers and communication companies and homes and offices are provided by wire. The high-speed line is fixed, and a wired connection is desired because it needs to be connected stably. On the other hand, in homes and offices, the cable installation environment becomes a problem as the number of terminals increases.

  Therefore, network connection using a wireless LAN (IEEE standard 802.11a / b / g) that does not require a radio station license is becoming widespread in homes and offices. Transmission technology is attracting attention. Connecting terminals wirelessly facilitates the installation of terminals, increases the degree of freedom of installation, and eliminates cables that crawl on the floor and the like, contributing to the safety of the indoor environment.

  However, considering real-time transmission of HDTV signals, it is difficult to ensure a sufficient transmission speed in a wireless LAN using radio waves. Even after waiting for the introduction of a future wireless LAN (IEEE standard 802.11e, 802.11n, etc.) that is currently under study, it is finally possible to transmit a single channel HDTV signal to one terminal.

  In wire transmission, transmission using optical fibers promises high-speed transmission of Gbps. Light waves can transmit information over a wide band exceeding GHz against a background of an overly high carrier frequency compared to radio waves. In addition, since the use of light waves is not restricted by the Radio Law or the like, it is also a transmission medium that can be used freely. Therefore, wireless transmission using optical waves and optical wireless transmission (or optical space transmission) have been studied, and several transmission apparatuses have been put into practical use so far.

  However, when a light wave is used for wireless transmission, a problem of line margin arises. In the case of wired optical fiber transmission, the broadband transmission is supported by an extremely low loss optical fiber. In the case of optical wireless transmission, the longer the transmission distance is due to the diffusion of the light wave, the more the power of the light wave is attenuated, and the light detector receives the square wave detection. Therefore, in the environment where the reception noise is thermal noise, Loss is attenuated by 20 dB at the receiving end.

  Therefore, it is necessary to transmit the light wave with a very narrow directivity characteristic and to suppress the attenuation amount. For this purpose, a technique for accurately adjusting the optical axis of the light source of the terminal is required. For example, as described in Patent Document 1, it is necessary to provide a means for detecting the arrival direction of a light wave from a communication partner (master) and a mechanical turning mechanism, and adjust the optical axis.

  In addition, in order to relax the optical axis adjustment, a method for enabling transmission even at a low S / N ratio has been studied. Patent Document 2 discloses a technique for transmitting a digital signal capable of error correction and ensuring a line margin so that the light source has a relatively wide directivity and omits optical axis adjustment between the transceivers. ing.

  In addition, it is conceivable to prepare a plurality of light waves to increase the transmission speed of the information signal without changing the line design and to perform division multiplexing using some means. As a typical means, it is conceivable to perform division multiplexing (wavelength division multiplexing transmission) with different wavelengths (or frequencies) utilizing the characteristics of a broadband light wave. The wavelength division multiplex transmission technique has become a natural technique for wired optical fiber transmission.

However, it is difficult to use an optical fiber demultiplexer for separating optical waves multiplexed at high density as they are for optical wireless transmission. A technique for coping with this is disclosed in Patent Document 3. Here, wavelength filtering suitable for optical wireless transmission can be performed by using a rotatable interference filter or diffraction grating.
Japanese Patent Laid-Open No. 11-74844 JP-A-9-46296 JP 10-327129 A

  In the technique described in Patent Document 1, in order to irradiate a predetermined light receiver with a light wave with a narrow directivity, the direction-of-arrival detection means that relies on the light wave from the communication partner and a turn that turns the optical axis in a predetermined direction A mechanism is provided. The light wave of the communication partner is irradiated so as to cover a wide area. Since this method is provided with a tracking mechanism, it naturally moves mechanically in a complicated manner. If the control is not optimized, jitter due to the tracking mechanism may affect signal transmission. Another problem is that if the communication partner is lost in some way, it will not function.

  On the other hand, the technique described in Patent Document 2 is intended to secure a line margin by applying an error correction technique, but only by reducing the condition of the SN ratio of a received signal that enables signal transmission, This is effective for wireless transmission at a constant transmission speed. However, if the transmission speed is newly increased, the directivity of the light wave must be adjusted in the direction to reduce the directivity so as to meet the line design again. The same as the previous system.

  Although the technique described in Patent Document 3 can contribute to an increase in transmission speed in terms of circuit design, it is necessary to mechanically configure an optical filter (or an optical demultiplexer), which lacks the mechanical stability of the system and transmits. There was a problem that it was necessary to strictly control the wavelength of the light wave.

The present invention has been made in view of the above points, and provides an optical wireless transmission system and apparatus that can wirelessly transmit a wide-band, large-capacity digital signal as an optical signal, have a simple mechanical configuration, and can be easily installed. For the purpose.

The invention according to claim 1 is an optical wireless transmission transmitter that wirelessly transmits a digital signal by an optical wave.
Bit stream division encoding means for performing error correction encoding by dividing the digital signal into a plurality of sets of bit streams;
Pilot signal multiplexing means for identifying a plurality of sets of bitstreams and generating a plurality of sets of pilot signals for performing propagation path estimation and multiplexing each of the plurality of sets of bitstreams;
By having a light wave transmitting means for modulating a plurality of sets of light waves with a bit stream in which the plurality of sets of pilot signals are multiplexed, and transmitting the modulated plurality of sets of light waves from a point spatially separated at a transmission position, A wide-band, large-capacity digital signal can be wirelessly transmitted as an optical signal, and the mechanical configuration is simple and installation is easy.

The invention according to claim 2 is the transmission apparatus according to claim 1 ,
By having directivity adjusting means for adjusting the directivity of the plurality of sets of light waves transmitted from the light wave transmitting means, the interval at which the plurality of sets of light waves are separated can be made independent of the transmission distance.

The invention according to claim 3 is an optical wireless transmission receiver that wirelessly transmits a digital signal by an optical wave.
Condensing means for condensing the plurality of sets of light waves transmitted from the transmission device according to claim 1 or 2 at a plurality of focal points spatially separated at a reception point;
A light wave receiving means for receiving light waves collected at the plurality of focal points at a plurality of points equal to or more than the plurality of focal points;
Pilot signal separating means for separating the plurality of sets of pilot signals from received signals of light waves received at the plurality of points;
Channel estimation means for performing channel estimation by obtaining a blending ratio of each pilot signal at the plurality of points from the plurality of sets of separated pilot signals;
Based on the propagation path estimation result obtained by the propagation path estimation means, the plurality of sets of bit streams separated by separating the plurality of bit streams from which interference has been removed from the received signals of the light waves received at the plurality of points, and the separated sets of bits Bitstream separation and decoding means for performing error correction decoding of the stream;
By having a bitstream multiplexing means for decoding the digital signal by multiplexing the plurality of sets of bitstreams output from the bitstream separation and decoding means , a wideband and large-capacity digital signal can be wirelessly transmitted as an optical signal, Simple mechanical configuration and easy installation.

A fourth aspect of the present invention is the receiving apparatus according to the third aspect ,
Based on the plurality of sets of pilot signals separated by the pilot signal separation means, the light wave reception means switches and selects light wave reception signals received at the plurality of points, and supplies them to the bitstream separation and decoding means. By having the switching selection means, useless signal processing can be omitted.

The invention according to claim 5 is the transmission apparatus according to claim 1 or 2 ,
The pilot signal multiplexing means outputs a plurality of sets of OFDM signal multiplexed with each of the plurality of sets of pilot signals mapping the plurality of sets of bit stream into a modulation signal,
The invention described in claim 6 is the receiving device according to claim 3 or 4 ,
The pilot signal separation means separates pilot signals multiplexed into a plurality of sets of OFDM signals from light wave reception signals received at the plurality of points,
The bit stream separating decoding means, by demodulating the plurality of sets of bit stream by performing demapping with separating a plurality of sets of OFDM signals from the received signal of the light wave received by the plurality of points, waveform equalization It is possible to incorporate a function that realizes

  According to the present invention, a broadband and large-capacity digital signal can be wirelessly transmitted as an optical signal, the mechanical configuration is simple, and installation is easy.

  In order to enable transmission while ensuring a line margin while having a wide light wave directivity that is easy to optically adjust, the present invention has a noise bandwidth that increases with a wide signal band and optical attenuation. Pay attention to light detection by square detection, which is emphasized in the electrical stage, and secure the power of the light wave by using multiple light sources while suppressing the increase of noise bandwidth by dividing the digital signal into multiple digital signals Considering that, focusing on the fact that it is possible to receive by defocusing if wireless transmission is performed in a state where the plurality of light sources are spatially separated, by using optical space division multiplex transmission without using an optical filter, A wide-band, large-capacity digital signal can be transmitted wirelessly.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the principle of the present invention will be described. Usually, in a photodiode used as a photodetector, a light wave is converted into electricity by square detection. The current flowing through the photodiode is proportional to the power of the light wave received by the photodiode. Therefore, in optical transmission, it is common to send a signal by changing the intensity (power) of the light wave.

  Therefore, when the light wave transmitted from the transmitter with a sufficient signal-to-noise ratio (signal-to-noise ratio) is received by the photodiode after being transmitted for a certain distance, the light wave attenuates to some extent, and the thermal noise is reduced. In an environment where the noise due to is dominant, the equation (1) is obtained.

SN ratio = R _L (ηP _r ) ² / n _T B (1)
Here, _Pr is the received light power (power of the light wave received by the photodiode), η is the radiation sensitivity (conversion coefficient between the power of the light wave and the current), _RL is the load resistance, and n _T is the thermal noise per unit frequency. Power, B is the noise bandwidth.

From this relationship, SN ratio is proportional to the square of the light-receiving power P _r, seen to be inversely proportional to the noise bandwidth B. That is, ratio SN when receiving power _{P r} is 10dB attenuation is 20dB degradation, SN ratio if it 10 times noise bandwidth B it can be seen that 10dB degradation.

  For example, in the case of a baseband signal, the noise bandwidth B increases as the signal bandwidth increases, such as ½ of the signal bandwidth. Even when a signal with a transmission rate of 100 Mbps and a signal with 10 Mbps have the same received power, a difference of 10 dB occurs in the SN ratio between the two.

  In the case of optical wireless transmission, in order to fill this 10 dB, the directivity of the light wave is narrowed, for example, what was sent with a beam width of 5 degrees is narrowed to a beam width of 2.5 degrees, and the received power is improved by 5 dB. In many cases. This narrows the range in which the light wave can be received, making it difficult to adjust the optical axis.

  Therefore, the transmission speed is not changed to 10 Mbps for each light wave, and the number of light waves is set to 10, for example, so that 100 Mbps is achieved as a whole, the directivity of the light wave is not changed, and the line design is maintained. In the background, even if the number of light waves increases, when the semiconductor laser or light emitting diode is used as the light source and the photodiode is used as the photodetector, the physical size of the light source or the photodetector itself is small. There may be no significant impact on the scale of the transmission device.

  In the present invention, a transmission speed for optical wireless transmission by spatially multiplexing and transmitting a light wave between a spatially separated light source and a spatially separated photodetector. Secure.

  As shown in FIG. 1A, when there is a pair of lenses 1 having a focal length f in space, on the optical axis of the lens 1 (a line connecting the centers of curvature of the refraction or reflection curved surfaces constituting the optical system). If a light wave light source is located at a point A away from the lens 1 by a distance L and is ri-offset from the optical axis, the light wave output from the light source passes through the lens 1 and passes through the lens 1. An image is formed with B as a focal point. The point B is a point separated from the lens by a distance do on the plane to which the optical axis of the lens 1 and the point A belongs, and is a point offset by ro from the optical axis. L, ri, do, and ro have the relationship of equation (2).

L / do = (L + f) / f = ri / ro (2)
Note that L is processed by substituting a negative value.

  From the equation (2), when the light wave output from the optical axis of the lens 1 at the offset ri is focused by the lens 1, the offset ro from the optical axis of the lens 1 at the focal point has a magnitude opposite to that of ri. It can be seen that is proportional. That is, the light wave transmitted from the point A having the different finite offsets ri and ri ′ and the point A ′ as the light source passes through the lens 1 of the receiving apparatus and has the point B having the different finite offsets ro and ro ′. And B ′, respectively.

  For example, assuming that the offsets ri and ri ′ are 5 cm and 3 cm, respectively, and the distance L is 10 m, when receiving using the lens 1 having a focal length f of 5 cm, an image is formed at a distance do of about 5 cm. The offsets ro and ro ′ take values of about −0.25 mm and about −0.15 mm, respectively.

  Further, as shown in FIG. 1B, when a pair of lenses 3 at the focal point f ′ is set with a common optical axis at a distance di on the optical axis from the light source at the point A, the relationship between the offset ri and the offset ro. Can be made irrelevant to the distance L between the lenses 2 and 3, as shown in equation (3).

di / do = −f ′ / f = ri / ro (3)
However, di shall be processed by substituting a negative value.

  Similarly to the case of the equation (2), the light wave transmitted from the point A having the different finite offsets ri and ri ′ and the point A ′ as the light source passes through the lenses 2 and 3 of the transmission device and the reception device, Images are respectively formed at points B and B ′ having different finite offsets ro and ro ′. For example, when ri and ri ′ are 5 cm and 3 cm, respectively, transmission is performed using the lens 3 having a focal distance f ′ of 5 cm, and reception is performed using the lens 2 having a focal distance f of 5 cm, and the distance di is 5 cm. The distance do is also 5 cm, and the offsets ro and ro ′ are −5 cm and −3 cm, respectively.

  The above principle means that light waves transmitted from two different points can be separated and received via a pair of lenses at the time of reception.

  Therefore, in the present invention, a wide-band, large-capacity digital signal is divided into a plurality of sets of bit streams, and the divided sets of bit streams are transmitted on a plurality of light waves together with a plurality of pilot signals for identifying them. The plurality of light waves are collected at a reception point at a plurality of spatially separated focal points through at least one pair of lenses, and received at the plurality of focal points, respectively, and based on information of the detected pilot signals. The plurality of sets of bit streams are demodulated from a plurality of received signals obtained by receiving light, and the transmitted digital signals are decoded.

  In addition, the pilot signal has an optical defect of the lens used, the light wave is received with a certain intensity distribution, there is a certain amount of overlap of the light wave, the transmission is received with the position switched, etc. Is used for identifying received signals, recognizing the degree of interference of multiplexed light waves, and removing interference to make it easier to separate individual signals.

  An optical wireless transmission apparatus that realizes spatial multiplexing transmission of light waves based on the above optical wireless transmission method will be described.

  2A and 2B are block diagrams of a first embodiment of an optical wireless transmission device and a reception device that realize space division multiplexing transmission of light waves according to the principle of FIG. 1A. In this embodiment, the digital signal is divided into four.

In the transmission apparatus shown in FIG. 2A, the serial-parallel conversion circuit 10 inputs digital signals and converts them into four sets of bit streams. The four error correction coding circuits 12 _{1 to} 12 ₄ each perform error correction coding on the four sets of bit streams divided by the serial-parallel conversion circuit 10. The pilot signal generation circuit 14 generates four sets of pilot signals to be inserted for identifying the four sets of bit streams at the receiving device. The four-circuit pilot signal multiplexing circuits 16 _{1 to} 16 ₄ include four sets of bit streams generated by the pilot signal generation circuit 14 into four sets of bit streams encoded by the four-circuit error correction encoding circuits 12 _{1 to} 12 ₄ . Each pilot signal is multiplexed.

The four drive circuits 18 ₁ to 18 ₄ are light waves output from the light sources of the four subsequent circuits by four sets of bit streams in which the pilot signals are multiplexed by the four pilot signal multiplexing circuits 16 _{1 to} 16 _4. In order to modulate the intensity of each, the currents flowing to the light sources are varied. The light sources 20 _{1 to} 20 ₄ are driven by currents supplied from the _four drive circuits 18 ₁ to 18 ₄ , respectively, and output light waves whose intensity is modulated. The four lenses ₂₂ 1 to 22 ₄ outputs to the space 4 of the lightwave output from the light source ₂₀ 1 to 20 ₄ of the four circuits in a predetermined directivity.

Here, the light sources 20 _{1 to} 20 ₄ are assumed to be semiconductor lasers or light emitting diodes, and output light waves having a wavelength of 0.8 μm band, 1.3 μm band, or 1.55 μm band. The 0.8 μm band is used when it is realized at a low price, and the 1.3 μm band or the 1.55 μm band is used when the reflection of light waves is a concern for video transmission. The offsets ri from the optical axes of the light sources 20 _{1 to} 20 ₄ are different from each other.

The intensity modulation of the light sources 20 _{1 to} 20 ₄ may directly change the current for driving the light source, but the circuit for driving the light source simply outputs the light wave and supplies the output of the light wave to the external modulator. Alternatively, a modulation signal based on a bit stream may be input to the driving circuit of the external modulator. When an external modulator is used, the size of the light source does not need to be increased by using a semiconductor laser and an external modulator that have been created on the same device in advance or those that have been built in the same package.

In the receiving apparatus shown in FIG. 2B, a lens 24 (corresponding to the lens 1 in FIG. 1A) receives four light waves transmitted from the transmitting apparatus, separates them into four focal points, and outputs them. The four-circuit photodetectors 26 _{1 to} 26 ₄ each receive four light waves separated into four focal points by the lens 24 and output four sets of electrical signals. 4 circuit pilot signal separating circuit ₂₈ 1 to 28 _4, respectively extracts the four sets of pilot signals from the four sets of electric signals output from the photodetector ₂₆ 1-26 ₄ 4 circuit.

The propagation path estimation circuit 30 identifies each of four sets of bit streams mixed in each electric signal by the four sets of pilot signals extracted from the _four pilot signal separation circuits 28 _{1 to} 28 ₄ , and 4 The mixing (blending) ratio of a set of bitstreams is determined. The interference cancellation circuit 32 separates and outputs the four sets of bit streams obtained by removing the interference from the four sets of electrical signals based on the information output from the propagation path estimation circuit 30. The four error correction decoding circuits 34 _{1 to} 34 ₄ respectively correct the four sets of bit streams separated by the interference cancellation circuit 32 and decode the original four sets of bit streams transmitted. The parallel-serial conversion circuit 36 multiplexes the four sets of bit streams decoded by the _four error correction decoding circuits 34 _{1 to} 34 ₄ to decode and output the transmitted digital signal.

Here, the photodetector ₂₆ 1-26 _4, such as an avalanche photodiode or a PIN photodiode is used. In the propagation path estimation circuit 30, the four sets of transmitted pilot signals are P1, P2, P3, and P4, which are known signals that can be reproduced by the receiving apparatus, but the pilot signals P1 to P4 and the received four sets pilot signals P1 ', P2', P3 ' , P4' by taking the cross-correlation out with, obtains the blending ratio of each pilot signal P1~P4 at each photodetector ₂₆ 1-26 _4, channel matrix H ( In this case, a 4 × 4 matrix is output.

Further, the interference cancellation circuit 32 uses the propagation path matrix H supplied from the propagation path estimation circuit 30, for example, to receive the four sets of electric signals Y1, Y2, Y3, Y4 (the vector obtained by combining these is Y and 4 sets of bit streams X1, X2, X3, and X4 (the vector obtained by combining them) is taken out as X. As the background, the relationship of Y = HX is used, and decoding of X can be realized by ^obtaining an inverse matrix H ⁻¹ of H.

Note that since the operation for ^obtaining the inverse matrix H ⁻¹ has a large amount of calculation, a circuit with some contrivances is used in an actual circuit. As an example, there is a method based on a minimum mean square error (MMSE) standard. Multiplied by the weighting coefficient W to the output Y from the photodetector ₂₆ 1-26 ₄ Consider the determination of the X and. At this time, the pilot signals P1, P2, P3, and P4 are used as reference signals P, the coefficient W is corrected so that the mean square error between the reference signals P and WY is minimized, and X is calculated based on the obtained W. Decoding method.

Another example is a method of demodulating against a background of a high DU ratio (a power ratio between a desired signal and an undesired signal) according to the principle of the present invention. That is, in accordance with the principles of the present invention, through a set of lenses of the receiving apparatus, four light wave transmitted are respectively received in separate optical detectors 26 ₁ to 26 ₄ at a high rate. The received electrical signal Y1 includes, for example, a high ratio of X4 in the transmitted light waves, similarly, Y2 includes a high ratio of X3, Y3 includes a high ratio of X2, and Y4 includes Is included at a high ratio of X1. Therefore, a replica is made using these signals as temporary signals, and X is decoded by removing it from Y with the combination shown by the previous propagation path matrix H. In this case, if this operation is repeated as necessary, the accuracy improves.

  By the way, pilot signal multiplexing methods include a method of inserting by time division multiplexing as shown in FIG. 3 and a method of inserting by frequency division multiplexing as shown in FIG.

  In the time division multiplexing of FIG. 3, for example, each of four sets of bit streams divided by serial-parallel conversion is divided into, for example, every 188 bits, and for example, a 16-bit synchronization identifier and, for example, a 32-bit pilot signal are divided into Each is inserted and transmitted before the bit stream of the data signal. The synchronization identifier is common to the four sets of bit streams, and the pilot signal is set to a different value for the four sets of bit streams. Thereby, since it is known that the pilot signal follows the synchronization identifier in the receiving apparatus, the pilot signal can be obtained by extracting 32 bits appearing after the synchronization identifier is detected.

  At this point, it is assumed that the pilot signal is subject to interference from other signal components, and a level change is detected with a gradation of 8 bits or more even when processing is performed via an analog-digital conversion circuit. It shall be possible. By performing a cross-correlation operation with known pilot signals P1 to P4 on this signal, the previous channel matrix H can be obtained. When P1 is 1, P2, P3, and P4 are 0 (null), and when P2 is 1, P1, P3, and P4 are 0, and the pilot signal is intermittently transmitted at different timings for each light wave. May be.

  The pilot signal multiplexing method by frequency division multiplexing shown in FIG. 4 can be used as a method for detecting a pilot signal relatively easily when the frequency characteristic in the band of the received signal is relatively flat. For example, the pilot signal P1 is a sine wave of frequency f1, P2 is a sine wave of frequency f2 (≠ f1), P3 is a sine wave of frequency f3 (≠ f1, f2), and similarly, P4 is a frequency f4 (≠ f1, f2 , F3) and sine waves for transmission, in order to obtain the propagation path matrix H in the receiving apparatus, it is only necessary to extract and detect with a filter of each frequency, so that the pilot signal can be realized relatively easily. It is also possible to remove this by simply passing it through a low-pass filter. Further, only the synchronization identifier is required to change the transmission rate of the bit stream by being added to each bit stream.

  Numerical examples when optical signal transmission is performed using the optical wireless transmission device and the reception device of FIGS. Consider transmitting signals by transmitting light waves from four light sources that can transmit at a transmission rate of 100 Mbps. Assuming that the signal-to-noise ratio that can be transmitted error-free in consideration of error correction is 5 dB, each light wave is output with a directivity of 10 mW and a beam width of 30 degrees, and is received by a lens having an effective aperture of 3 cm and a PIN photodiode. When an NF (Noise Figure) built in the detector is received via a 6 dB preamplifier, the distance that can be transmitted with a 10 dB line margin in the electrical stage is 10 m. If the pilot signal insertion method is frequency division multiplexing and the mixing ratio of the synchronization identifier is not changed, transmission at a transmission rate of 400 Mbps is possible as a whole.

  Here, if transmission with the same transmission rate of 400 Mbps is realized with one light source, the signal band is quadrupled, resulting in a line loss of 6 dB. As a result, when transmitting with the same beam width, the transmission distance is reduced to 7 m. Alternatively, in order to set the transmission distance to 10 m, it is necessary to narrow the beam width to 20 degrees.

  On the other hand, when considering the spatial separation distance, if the transmission light sources of 4 circuits are arranged in a line in an array, and 5 cm, 3 cm, −3 cm, and −5 cm are assigned as the values of ri in FIG. In the receiving apparatus, ro in FIG. 1A is about −0.25 mm, about −0.15 mm, about 0.15 mm, and about 0.25 mm, respectively, at a transmission distance of 10 m. This corresponds to receiving four PIN photodiodes with a diameter of about 80 μm arranged in a row at intervals of about 0.2 mm.

  Considering the practical use of the optical wireless transmission device, the optical axes of the transmitting lens and the receiving lens do not exactly match. Further, the focal point does not necessarily become one point due to the aberration of the lens, but has a certain spread. Furthermore, as shown in FIG. 1A, in the case of receiving with a lens shared only on the receiving side, the interval at which the focus is separated depends on the transmission distance (distance L in FIG. 1A). Change. FIG. 5 shows an embodiment in which the receiving apparatus in FIG.

The receiving apparatus shown in FIG. 5 is a block diagram of a second embodiment of the receiving apparatus corresponding to FIG. In the figure, a lens 44 receives four light waves transmitted from a transmission device, separates them into four focal points, and outputs them. The N-circuit photodetectors 46 _{1 to} 46 _N each receive one or a combination of the four light waves separated into four focal points by the lens 44 (there may not be received at all) and receive N (N Is an integer greater than 4) sets of electrical signals.

N circuit pilot signal separation circuits 48 _{1 to} 48 _N are configured to output N sets of pilot signals (four sets of transmitted pilot signals) from N sets of electrical signals output from N circuit photodetectors 46 _{1 to} 46 _N. Each of them is extracted according to the separation situation of light waves). The propagation path estimation circuit 50 includes four sets of transmitted bit streams mixed in the N circuit electrical signals by the N sets of pilot signals extracted from the N circuit pilot signal separation circuits 48 _{1 to} 48 _N. The identification and blending ratio are determined.

The interference cancellation circuit 52 separates and outputs four sets of bit streams from the electrical signal of the N circuit based on the information output from the propagation path estimation circuit 50. The four error correction decoding circuits 54 _{1 to} 54 ₄ respectively decode the four sets of bit streams transmitted by error correction of the four sets of bit streams separated by the interference cancellation circuit 52. The parallel-serial conversion circuit 56 multiplexes four sets of bit streams decoded by the _four error correction decoding circuits 54 _{1 to} 54 ₄ to decode and output the transmitted digital signal.

That is, in order to receive a light wave with a shifted focal position or a light wave with a spread beam spot, the photodetectors 46 _{1 to} 46 _N of N circuits are used instead of adjusting and receiving the position of the photodetector. It aims to achieve its purpose by receiving light in a wide range.

  In order to receive light waves transmitted by assigning 5 cm, 3 cm, −3 cm, and −5 cm, respectively, as the values of ri in FIG. In addition, in the receiving apparatus, eight PIN photodiodes having a diameter of about 80 μm are arranged in a row at intervals of about 0.1 mm in a range of about −0.35 mm to about 0.35 mm at a transmission distance of 10 m, or 2 This corresponds to receiving 16 columns and 24 columns.

  Although the case where four light waves are arranged and transmitted in one row has been described, in an actual apparatus, a light source is arranged and transmitted on a two-dimensional plane instead of one row. Therefore, for example, an arrangement image in the case of using a light source of 8 circuits is as shown in FIG. In the transmitting apparatus, four points every 90 degrees on the circumference of the radius ri_1, and further four points every 90 degrees on the circumference of the radius ri_2 (> ri_1) by shifting 45 degrees, a total of eight points. Eight circuit light sources, for example, semiconductor lasers, are installed at each separated point.

  The receiving device separates and receives the eight light waves output from the light sources of the eight circuits, and uses a pair of lenses. Further, a 40-circuit photodetector, for example, a PIN photodiode is placed on the plane. Place and receive. For this demodulation, the receiving apparatus shown in FIG. 5 is used with N circuits expanded to 40 circuits and 4 sets of bit stream outputs expanded to 8 sets.

  For example, the arrangement of 40 photodiodes of PIN photodiodes is as shown in FIG. First, similarly to the arrangement of the transmission light source, 4 points every 90 degrees on the circumference of the radius ro_1, and further, 4 points every 90 degrees on the circumference of the radius ro_2 (> ro_1) by shifting 45 degrees, a total of 8 points. Eight circuits of PIN photodiodes are arranged at each spatially separated point. These positional relationships conform to the arrangement of the transmission light sources. Furthermore, a total of 32 PIN photodiodes are arranged in 8 circuits at positions offset by dr in the four directions, up, down, left, and right, of each of the 8 points in FIG. 6B. As a result of the above, a total of 40 PIN photodiodes are arranged on the plane, which corresponds to a focus shift due to a change in transmission distance, a focus position shift due to an optical axis shift, and the like. At this time, if the offset do in FIG. 1A is made slightly smaller than the original position, the effect is great.

  Confirm the above using numerical values. When the arrangement radii ri_1 and ri_2 of the transmission light source are 3 cm and 6 cm, respectively, the arrangement radii ro_1 and ro_2 of the reception photodetector are about 0.15 mm and 0.3 mm, respectively, for a transmission distance of 10 m. When the aperture of the PIN photodiode is set to 80 μm, an offset dr is set to 0.1 mm, thereby realizing a system that allows a beam spot change of ± 0.07 mm. This means that the transmission distance can be allowed to change within a range of about 7 m to 15 m, and that the optical axis can be allowed to shift by about 3 degrees.

  Further, FIG. 7 shows an embodiment in which a larger number of photodetectors are arranged more redundantly to increase the reliability. In FIG. 7, photodetectors are arranged in a two-dimensional array with an interval dr within an area of 2ro × 2ro.

  As can be said for FIG. 6B, in particular, when the photodetector having the configuration shown in FIG. 7 is used, there are actually some photodetectors that do not receive the light wave. FIG. 8 shows a third embodiment of a receiving apparatus applied when such a photodetector is used. At this time, the receiving apparatus will be described as a receiving apparatus corresponding to FIG. In FIG. 8, the same parts as those in FIG.

In FIG. 8, a lens 44 receives four light waves transmitted from a transmission device, separates them into four focal points, and outputs them. The photodetectors 46 _{1 to} 46 _N of the N (N is an integer greater than 4) circuit are any one or a combination of four light waves separated into four focal points by the lens 44 (there may not be received at all). Are received and N sets of electrical signals are output. N circuit pilot signal separation circuits 48 _{1 to} 48 _N are configured to output N sets of pilot signals (four sets of transmitted pilot signals) from N sets of electrical signals output from N circuit photodetectors 46 _{1 to} 46 _N. Each of them is extracted according to the separation situation of light waves).

The signal level determination circuit 58 determines the level of each electric signal of the N circuit based on the N sets of pilot signals extracted from the pilot signal separation circuits 48 _{1 to} 48 _N of the N circuit, and M (M is 4 or more). And a control signal for selecting a set of electrical signals is generated and transmitted to the signal selection circuit 57, and a pilot signal related to the selected M sets of electrical signals is transmitted to the propagation path estimation circuit 59. Send to. The signal selection circuit 57 selects and outputs M sets of electrical signals from the N sets of electrical signals input based on the control signal transmitted by the signal level determination circuit 58.

  The propagation path estimation circuit 59 includes four sets of transmitted bit streams mixed in the M sets of electrical signals selected based on the pilot signals related to the M sets of electrical signals transmitted from the signal level determination circuit 58. Each identification and blending ratio are determined. The interference cancellation circuit 60 separates and outputs four sets of bit streams from M sets of electrical signals based on information output from the propagation path estimation circuit 59.

The four error correction decoding circuits 54 _{1 to} 54 ₄ each correct the four sets of bit streams separated by the interference cancellation circuit 60 by error correction and decode the original four sets of bit streams transmitted. The parallel-serial conversion circuit 56 multiplexes four sets of bit streams decoded by the _four error correction decoding circuits 54 _{1 to} 54 ₄ to decode and output the transmitted digital signal.

  This receiving apparatus is provided with a mechanism for ignoring a photodetector that does not receive a light wave based on the power level and SN ratio of a pilot signal input to the signal level determination circuit 58 or that has a small received light power. . Thereby, useless signal processing can be omitted.

  In recent years, digital signal processing is often performed using a digital circuit as a main circuit of a transmission / reception apparatus. In that case, in the case where the receiving apparatus has the signal selection circuit 57 as shown in FIG. 8, an analog-digital conversion circuit is inserted in the subsequent stage of the signal selection circuit 57 and the subsequent processing can be performed by the digital circuit. Conceivable. At this time, it is conceivable that after the analog signal is converted to digital, the pilot signal is separated again to estimate the propagation path. FIG. 9 shows a fourth embodiment of a receiving apparatus applied in that case.

The difference between FIG. 9 and FIG. 8 is that in the receiving apparatus of FIG. 8, N sets of pilot signals (four sets of transmitted signals) are generated from N circuit electrical signals output from N circuit photodetectors 46 _{1 to} 46 _N. N pilot signal separation circuits 48 _{1 to} 48 _N that respectively extract pilot signals mixed in accordance with light wave separation conditions) and N circuit pilot signal separation circuits 48 _{1 to} 48 _N Based on the N sets of pilot signals, the level of each electric signal in the N circuit is determined, and a control signal for selecting the M sets of electric signals is generated and transmitted to the signal selection circuit 57. The selected M sets of electric signals A signal level determination circuit 58 that transmits a pilot signal related to the transmission path estimation circuit 59, and M sets of electrical signals from N sets of electrical signals that are input based on the control signal transmitted by the signal level determination circuit 58. And four sets of transmissions mixed in the M sets of electrical signals selected based on the pilot signals related to the M sets of electrical signals transmitted from the signal selection circuit 57 and the signal level determination circuit 58. In the receiving apparatus shown in FIG. 9, the portion that has been used as the propagation path estimation circuit 59 that determines the identification and combination ratio of each of the bitstreams is set to N sets of electricity output from the photodetectors 46 _{1 to} 46 _N of the N circuit. N circuit pilot signal detection circuits 62 _{1 to} 62 _N that respectively extract N sets of pilot signals (4 transmitted pilot signals are combined in accordance with the light wave separation state) from the signals; signal selection to create a control signal for selecting the extracted N sets of M sets of electrical signal level determined by the respective electric signals of the N sets based on the pilot signal from the pilot signal detecting circuit 62 ₁ through 62 _N A signal level determination circuit 63 for transmitting to the circuit, a signal selection circuit 64 for selecting and outputting M sets of electrical signals from the N sets of electrical signals input based on the control signal transmitted by the signal level determination circuit 63, M circuit pilot signal separation circuits 65 _{1 to} 65 _M for extracting M sets of pilot signals from signals obtained by analog-digital conversion of M sets of electrical signals selected by the signal selection circuit 64, and M circuit pilot signal separation Propagation path estimation for determining the identification and mixing ratio of each of the four sets of transmitted bit streams mixed in the M sets of electrical signals based on the M sets of pilot signals respectively extracted from the circuits 65 _{1 to} 65 _M The circuit 66 is used.

  In the optical wireless transmitter and receiver shown in FIGS. 2A and 2B realized in accordance with the principle shown in FIG. 1A, the interval at which the light waves are separated in the receiver depends on the transmission distance. I decided. Therefore, in this device, the longer the transmission distance, the larger the transmission device and the smaller the reception device.

  Therefore, the fifth embodiment which can be used without worrying about the transmission distance is the optical wireless transmission device and the reception device shown in FIGS. 10A and 10B, which are the principle of FIG. based on. 10A and 10B, the same parts as those in FIGS. 2A and 2B are denoted by the same reference numerals.

In the transmission apparatus illustrated in FIG. 10A, the serial-parallel conversion circuit 10 inputs digital signals and converts them into four sets of bit streams. The four error correction coding circuits 12 _{1 to} 12 ₄ each perform error correction coding on the four sets of bit streams divided by the serial-parallel conversion circuit 10. The pilot signal generation circuit 14 generates four sets of pilot signals to be inserted for identifying the four sets of bit streams at the receiving device. The four-circuit pilot signal multiplexing circuits 16 _{1 to} 16 ₄ include four sets of bit streams generated by the pilot signal generation circuit 14 into four sets of bit streams encoded by the four-circuit error correction encoding circuits 12 _{1 to} 12 ₄ . Each pilot signal is multiplexed.

The four drive circuits 18 ₁ to 18 ₄ are light waves output from the light sources of the four subsequent circuits by four sets of bit streams in which the pilot signals are multiplexed by the four pilot signal multiplexing circuits 16 _{1 to} 16 _4. In order to modulate the intensity of each, the currents flowing to the light sources are varied. The light sources 20 _{1 to} 20 ₄ are driven by currents supplied from the _four drive circuits 18 ₁ to 18 ₄ , respectively, and output light waves whose intensity is modulated. The lens 23 (corresponding to the lens 3 in FIG. 1B) collectively outputs the four light waves output from the four circuit light sources 20 _{1 to} 20 ₄ to the space with a predetermined directivity.

In the receiving apparatus shown in FIG. 10B, the lens 24 (corresponding to the lens 2 in FIG. 2A) receives four light waves transmitted from the transmitting apparatus, separates them into four focal points, and outputs them. To do. The four-circuit photodetectors 26 _{1 to} 26 ₄ each receive four light waves separated into four focal points by the lens 24 and output four sets of electrical signals. 4 circuit pilot signal separating circuit ₂₈ 1 to 28 _4, respectively extracts the four sets of pilot signals from the four sets of electric signals output from the photodetector ₂₆ 1-26 ₄ 4 circuit.

The propagation path estimation circuit 30 identifies each of four sets of bit streams mixed in each electric signal by the four sets of pilot signals extracted from the _four pilot signal separation circuits 28 _{1 to} 28 ₄ , and 4 The mixing (blending) ratio of a set of bitstreams is determined. The interference cancellation circuit 32 separates and outputs the four sets of bit streams obtained by removing the interference from the four sets of electrical signals based on the information output from the propagation path estimation circuit 30.

The four error correction decoding circuits 34 _{1 to} 34 ₄ respectively correct the four sets of bit streams separated by the interference cancellation circuit 32 and decode the original four sets of bit streams transmitted. The parallel-serial conversion circuit 36 multiplexes the four sets of bit streams decoded by the _four error correction decoding circuits 34 _{1 to} 34 ₄ to decode and output the transmitted digital signal.

  The configuration of the reception device illustrated in FIG. 10B is basically the same as the configuration of the reception device illustrated in FIG. However, as described in the explanation of the principle, the installation interval of the photodetectors in the receiving apparatus is different from the case of FIG. Therefore, by using lenses having the same focal length, the light source arrangement in the transmission device and the photodetector arrangement in the reception device can be made symmetrical.

  Even in this apparatus, the optical axes of the transmitting lens and the receiving lens do not exactly match. Further, the focal point does not necessarily become one point due to the aberration of the lens, but has a certain spread. Therefore, the receiving device having the configuration shown in FIGS. 5 to 9 having the number of photodetectors equal to or greater than the number of light waves to be transmitted is applied to the reception of the light wave transmitted from the transmitting device shown in FIG. Is meaningful.

  The modulation of each light wave in the above embodiment has been described mainly assuming a baseband digital signal. Depending on the propagation environment of the light wave, especially when a relatively wide directional light wave is transmitted indoors, the frequency characteristics within the signal band transmitted by multipath fluctuate, as in the case of wireless transmission using radio waves. May have. In such a case, the baseband signal is converted to an orthogonal frequency division multiplexing (OFDM) transmission format used in terrestrial digital broadcasting, wireless LAN, etc., and then transmitted over an optical wave. Can be considered.

  In OFDM signal transmission, it is possible to incorporate a function of transmitting a pilot carrier and realizing waveform equalization for the purpose of equalizing a signal waveform distorted due to characteristics of a transmission path. Therefore, FIGS. 11A and 11B show a sixth embodiment to which the OFDM system is applied in the present invention.

  The optical wireless transmission apparatus shown in FIG. 11 is obtained by replacing the baseband signal of the optical wireless transmission apparatus shown in FIG. 10 with an OFDM signal (OFDM signal).

In the transmission apparatus shown in FIG. 11A, a serial-parallel conversion circuit 70 inputs a digital signal and converts it into four sets of bit streams. The four error correction encoding circuits 72 _{1 to} 72 ₄ each perform error correction encoding on the four sets of bit streams divided through the serial-parallel conversion circuit 70. The pilot signal generation circuit 74 generates four sets of pilot signals to be inserted for identifying the four sets of bit streams at the receiving device.

The four OFDM signal modulation circuits 76 _{1 to} 76 ₄ map the four sets of bit streams that have been error correction encoded by the _four error correction encoding circuits 72 _{1 to} 724 to modulated signals such as QPSK and 16QAM. Thereafter, each of the four sets of pilot signals generated by the pilot signal generation circuit is multiplexed together to generate four sets of OFDM signals. The four circuit driving circuits 78 _{1 to} 78 ₄ respectively change the intensity of the light wave output from the four light sources by the four sets of OFDM signals generated by the four circuit OFDM signal modulation circuits 76 _{1 to} 76 _4. The current flowing through the light source is varied for modulation. The light sources 80 ₁ to 80 ₄ are each driven by a current supplied from four drive circuits, and output light waves whose intensity is modulated. Lens 83 together four of the lightwave output from the light source 80 ₁ to 80 ₄ of 4 circuit outputs to the space with a predetermined directivity.

In the receiving device shown in FIG. 11B, the lens 84 receives four light waves transmitted from the transmitting device, separates them into four focal points, and outputs them. The four-circuit photodetectors 86 _{1 to} 86 ₄ each receive the four light waves separated into four focal points by the lens 84 and output four sets of electrical signals.

4 OFDM signal demodulation circuit ₈₈ 1 to 88 ₄ of the circuit, the four sets of electric signals output from the fourth circuit photodetector ₈₆ 1-86 ₄ demodulates the OFDM signal, four sets of pilot signals transmitted Four sets of pilot signals in a state of interference and four sets of electrical signals in a state of interference of four sets of bit streams transmitted as modulated signals mapped to QPSK, 16QAM, and the like are extracted.

The propagation path estimation circuit 90 includes four sets of electric signals in a state in which the transmitted four sets of bit streams are interfered with the four sets of pilot signals extracted from the _four OFDM signal demodulation circuits 88 _{1 to} 88 ₄ . The identification and blending ratio of each of the four sets of transmitted bitstreams mixed in are determined. The interference cancellation circuit 92 separates the four sets of bit streams from the four sets of electric signals in a state where the four sets of bit streams transmitted based on the information output from the propagation path estimation circuit 90 interfere with each other, and QPSK, 16QAM, etc. Demap from and output.

The four error correction decoding circuits 94 _{1 to} 94 ₄ respectively decode the four sets of bitstreams transmitted by error-correcting the four sets of bitstreams separated by the interference cancellation circuit 92. The parallel-serial conversion circuit 96 multiplexes the four sets of bit streams decoded by the _four error correction decoding circuits 94 _{1 to} 94 ₄ to decode and output the transmitted digital signal.

  Here, the pilot signal is multiplexed at the time of OFDM signal modulation using both the pilot signal for waveform equalization in the OFDM signal and the pilot signal for identification for each light wave in the present invention. However, depending on the system configuration, these pilot signals may be created separately and multiplexed.

  As the OFDM signal, a signal created in accordance with the format of the OFDM signal defined in IEEE standard 802.11a or 802.11g used in the wireless LAN can be used. Moreover, what was produced according to the format of the OFDM signal prescribed | regulated to ARIB specification STD-B33 etc. can also be utilized.

  The optical wireless transmission apparatus using the OFDM signal shown in FIGS. 11A and 11B has a waveform equalizing function even when the signal waveform is distorted due to the multipath of the optical wave, Wireless transmission using optical waves of a large-capacity digital signal with a wide bandwidth suitable for the purpose can be realized.

  When transmitting an OFDM signal, a multilevel modulation signal such as QPSK or 16QAM is often used, so that a required SN ratio is required to be higher than when a baseband signal is transmitted. Therefore, in order to increase the directivity of the light wave to be transmitted, it is necessary to narrow the usable band and increase the number of light waves to be transmitted.

  FIG. 12 shows a seventh example in which the receiving apparatus shown in FIG. 9 with increased redundancy and the receiving capability is applied to the transmission of an OFDM signal for receiving the light wave transmitted by the transmitting apparatus shown in FIG. An embodiment is shown.

In the receiving apparatus shown in FIG. 12, the lens 104 receives four light waves transmitted from the transmitting apparatus, separates them into four focal points, and outputs them. The N circuit photodetectors 106 _{1 to} 106 _N each receive one or a combination of the four light waves separated into four focal points by the lens 104 (which may not receive light at all) and receive N sets of light waves. Outputs electrical signals. N circuit pilot signal detection circuits 108 _{1 to} 108 _N are configured to output N sets of pilot signals (four sets of pilot signals transmitted from N sets of electrical signals output from N circuit photodetectors 106 _{1 to} 106 _N). Each of them is extracted according to the separation situation of light waves).

The signal level determination circuit 110 determines the level of each of the N sets of electric signals based on the N sets of pilot signals extracted from the N sets of pilot signal detection circuits 108 _{1 to} 108 _N, and outputs M sets of electric signals. A control signal to be selected is created and transmitted to the signal selection circuit 112. The signal selection circuit 112 selects and outputs M sets of electrical signals from the N sets of electrical signals input based on the control signal transmitted by the signal level determination circuit 110.

OFDM signal demodulation circuit ₁₁₄ 1 to 114 _M of the M circuit, the selected M sets of electrical signals and demodulated as an OFDM signal by the signal selection circuit 112, the transmitted four sets of the state where the pilot signal has interference M sets of The M sets of electrical signals in a state where the pilot signals and the four sets of bit streams transmitted as modulated signals mapped to QPSK, 16QAM, etc. are mixed are extracted.

The propagation path estimation circuit 116 includes M sets of electric signals in a state in which four sets of bit streams are interfered with M sets of pilot signals extracted from the M circuit OFDM signal demodulation circuits 114 _{1 to} 114 _M. The identification and blending ratio of each of the four sets of transmitted bitstreams mixed in are determined. Based on the information output from the propagation path estimation circuit 116, the interference cancellation circuit 118 separates the four sets of bit streams from the M sets of electric signals in a state in which the transmitted four sets of bit streams are mixed with each other, and QPSK and 16QAM. Demap and output from.

The four error correction decoding circuits 120 _{1 to} 120 ₄ each decode the original four sets of bit streams transmitted by error correcting the four sets of bit streams separated by the interference cancellation circuit 118. The parallel-serial conversion circuit 122 multiplexes the four sets of bit streams decoded by the _four error correction decoding circuits 120 _{1 to} 120 ₄ to decode and output the transmitted digital signal.

  With this receiving device, an optical wireless transmission device with enhanced signal transmission is realized by using more photodetectors than the number of transmitted light waves.

  In the above description, the light waves to be transmitted are 4 waves or 8 waves. However, when assembling an actual device, a system in which more light waves such as 16 waves and 32 waves are multiplexed is more effective. is there.

  By using the present invention, a wide-band and large-capacity digital signal such as an HDTV video signal can be transmitted wirelessly, but a simple mechanical configuration and installation without using a complicated optical adjustment mechanism or an optical filter are possible. An easy optical wireless transmission device can be realized.

  As a result, it is easy to install devices required in homes and offices, the degree of freedom of installation is high, and there is no cable that crawls on the floor, enabling wireless connection between terminals that can contribute to the safety of the indoor environment. However, higher-speed wireless transmission can be realized. Also, if you want to use high-speed wireless transmission for temporary purposes such as exhibitions and conferences, it is very convenient because it uses a light wave that does not require a license and can be used without worrying about the interference of others. It can be a transmission means.

Incidentally, the serial-parallel conversion circuit 10 and 70, error correction encoding circuit ₁₂ 1 _{to 12 4,} 72 1 to 72 ₄ corresponds to a bit stream dividing coding means according to claim, the pilot signal generating circuit 14,74, pilot signal multiplexing circuit ₁₆ 1 _{~ 16} 4, OFDM signal modulation circuit ₇₆ 1 to 76 ₄ correspond to the pilot signal multiplexing means, driving circuit _{18 1-18 4,} 78 1 to 78 _4, the light source ₂₀ 1 _{to 20} 4, 80 ₁ 80 ₄ corresponds to the light wave transmission means, lens 23,83 corresponds to the directivity adjustment unit, the lens 24,44,84,104 corresponds to the condensing unit, the photodetector _{26 1-26} 4, 46 _{1 ~46 N, 86 1 ~86 4} , 106 1 ~106 N corresponds to the lightwave receiver, a pilot signal separating circuit _{28 1 ~28 4, 48 1 ~48} N, 65 1 ~65 , OFDM signal demodulating circuit _{88 1 ~88 4, 114 1 ~114} M corresponds to the pilot signal separating means, channel estimation circuit 30,50,59,66,90,116 corresponds to the propagation path estimation unit, interference removal circuit 32,52,60,92,118, corresponding to the error correction decoding circuit ₃₄ 1 _{to 34 4,} 54 ₁ to 54 _{4, 94} 1 to 94 _4, 120 1 to 120 ₄ bit stream separating decoding means, parallel Serial conversion circuits 36, 56, 96, 122 correspond to bit stream multiplexing means, and signal selection circuits 57, 64, 112, signal level determination circuits 58, 63, 110, pilot signal detection circuits 62 _{1 to} 62 _N , 108 ₁ ˜108 _N corresponds to the switching selection means.

It is a figure for demonstrating the principle of this invention. 1 is a block diagram of a first embodiment of an optical wireless transmitter and receiver according to the present invention. It is a figure for demonstrating the multiplexing method of a pilot signal. It is a figure for demonstrating the multiplexing method of a pilot signal. It is a block diagram of 2nd Embodiment of the receiver of this invention. It is a figure which shows embodiment of arrangement | positioning of a light source and a photodetector. It is a figure which shows embodiment of arrangement | positioning of a photodetector. It is a block diagram of 3rd Embodiment of the receiver of this invention. It is a block diagram of 4th Embodiment of the receiver of this invention. It is a block diagram of 5th Embodiment of the optical wireless transmitter and receiver of this invention. It is a block diagram of 6th Embodiment of the receiver of this invention. It is a block diagram of 7th Embodiment of the receiver of this invention.

Explanation of symbols

10, 70 P converter 12 ₁ to 12 _{4, 72} 1 to 72 ₄ error correction encoding circuit 14,74 a pilot signal generating circuit _161-164 pilot signal multiplexing circuit 18 _{1-18 4, 78} 1 to 78 ₄ Drive circuits 20 _{1 to} 20 ₄ , 80 ₁ to 80 ₄ Light sources _{1, 2} , ₃ , 22 _{1 to} 22 ₄ , 23, 24, 44, 83, 84, 104 Lenses 26 _{1 to} 26 ₄ , 46 _{1 to} 46 _N , 86 _{1 to} 86 ₄ , 106 _{1 to} 106 _N photodetectors 28 _{1 to} 28 ₄ , 48 _{1 to} 48 _N , 65 _{1 to} 65 _M pilot signal separation circuit 30, 50, 59, 66, 90, 116 propagation path estimation circuit 32,52,60,92,118 interference canceller 34 _{1-34 4 54 1-54} 4 _{94 1-94 4,} 120 1 to 120 ₄ error correction decoding circuit 36, 56 96,122 serializer circuit 57,64,112 signal selecting circuit 58,63,110 signal level judging circuit _{62 1 ~62 N, 108 1 ~108} N pilot signal detecting circuit 76 ₁ to 76 ₄ OFDM signal modulation circuit 88 ₁ .About.88 ₄ , 114 _{1 to} 114 _M OFDM signal demodulation circuit

Claims (7)

In a transmission device for optical wireless transmission that wirelessly transmits digital signals by light waves,
Bit stream division encoding means for performing error correction encoding by dividing the digital signal into a plurality of sets of bit streams;
Pilot signal multiplexing means for identifying a plurality of sets of bitstreams and generating a plurality of sets of pilot signals for performing propagation path estimation and multiplexing each of the plurality of sets of bitstreams;
A plurality of sets of light waves, each modulated with a bit stream in which the plurality of sets of pilot signals are multiplexed, and a plurality of sets of modulated light waves are transmitted from a point spatially separated at a transmission position. A transmitting device. The transmission device according to claim 1 , wherein
A transmitting apparatus comprising directivity adjusting means for adjusting directivity of the plurality of sets of light waves transmitted from the light wave transmitting means. In a receiver for optical wireless transmission that wirelessly transmits a digital signal by light waves,
Condensing means for condensing the plurality of sets of light waves transmitted from the transmission device according to claim 1 or 2 at a plurality of focal points spatially separated at a reception point;
A light wave receiving means for receiving light waves collected at the plurality of focal points at a plurality of points equal to or more than the plurality of focal points;
Pilot signal separating means for separating the plurality of sets of pilot signals from received signals of light waves received at the plurality of points;
Channel estimation means for performing channel estimation by obtaining a blending ratio of each pilot signal at the plurality of points from the plurality of sets of separated pilot signals;
Based on the propagation path estimation result obtained by the propagation path estimation means, the plurality of sets of bit streams separated by separating the plurality of bit streams from which interference has been removed from the received signals of the light waves received at the plurality of points, and the separated sets of bits Bitstream separation and decoding means for performing error correction decoding of the stream;
A receiving apparatus comprising: a bitstream multiplexing unit that multiplexes the plurality of sets of bitstreams output from the bitstream separation / decoding unit and decodes the digital signal. The receiving device according to claim 3 ,
Based on the plurality of sets of pilot signals separated by the pilot signal separation means, the light wave reception means switches and selects light wave reception signals received at the plurality of points, and supplies them to the bitstream separation and decoding means. A receiving apparatus comprising switching selection means. The transmission apparatus according to claim 1 or 2 ,
The pilot signal multiplexing means, transmitting apparatus and outputs a plurality of sets of OFDM signal by mapping the plurality of sets of bit stream into a modulated signal multiplexed with each of the plurality of sets of pilot signals. The receiving apparatus according to claim 3 or 4 ,
The pilot signal separation means separates pilot signals multiplexed into a plurality of sets of OFDM signals from light wave reception signals received at the plurality of points,
The bitstream separation / decoding means separates the plurality of sets of bitstreams by separating a plurality of sets of OFDM signals from the received signals of the lightwaves received at the plurality of points and performing demapping. apparatus. In an optical wireless transmission system that wirelessly transmits a digital signal from a transmitting device to a receiving device by light waves,
  The transmitter is
  Bit stream division encoding means for performing error correction encoding by dividing the digital signal into a plurality of sets of bit streams;
  Pilot signal multiplexing means for identifying a plurality of sets of bitstreams and generating a plurality of sets of pilot signals for performing propagation path estimation and multiplexing each of the plurality of sets of bitstreams;
  A plurality of sets of light waves, each modulated with a bit stream in which the plurality of sets of pilot signals are multiplexed, and a plurality of sets of modulated light waves are transmitted from a point spatially separated at a transmission position;
  The receiving device is:
  Condensing means for condensing the plurality of sets of light waves transmitted from the transmission device at a plurality of focal points spatially separated at a reception point;
  A light wave receiving means for receiving light waves collected at the plurality of focal points at a plurality of points equal to or more than the plurality of focal points;
  Pilot signal separating means for separating the plurality of sets of pilot signals from received signals of light waves received at the plurality of points;
  Channel estimation means for performing channel estimation by obtaining a blending ratio of each pilot signal at the plurality of points from the plurality of sets of separated pilot signals;
  Based on the propagation path estimation result obtained by the propagation path estimation means, the plurality of sets of bit streams separated by separating the plurality of bit streams from which interference has been removed from the received signals of the light waves received at the plurality of points, and the separated sets of bits Bitstream separation and decoding means for performing error correction decoding of the stream;
  Bit stream multiplexing means for decoding the digital signal by multiplexing the plurality of sets of bit streams output from the bit stream separation and decoding means
An optical wireless transmission system characterized by the above.

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