JP4379160B2 - Optical wireless transmission device - Google Patents

Description

  The present invention relates to an optical wireless transmission apparatus in which an optical reception unit receives an optical signal transmitted by an optical transmission unit of an optical transmission unit.

  Conventionally, there is an optical wireless transmission technology that performs spatial transmission of information using light. In general, infrared light is used for the optical wireless transmission, and a semiconductor light emitting element such as a light emitting diode or a laser diode is used as the light emitting element. In such optical wireless transmission, when it is desired to provide a sufficient distance between transmission and reception, it is necessary to narrow the output angle of the light beam emitted from the transmission device sharply, that is, to narrow it so that a signal with a sufficient light level is incident on the reception device side. Therefore, the optical axes of the transmission device and the reception device must be aligned. Therefore, alignment of the optical axis of the optical wireless transmission apparatus is a very troublesome operation because a light beam having a narrow emission angle is used or infrared light whose light beam is invisible is used. Therefore, conventionally, there has been proposed an optical wireless transmission apparatus that can easily perform this optical axis alignment.

As an example, Patent Document 1 below discloses that the visible light from the transmission device is focused on the same optical axis as the signal transmission infrared light or parallel optical axis and sent together to the reception device side. An optical wireless transmission device is disclosed in which an operator adjusts the optical axis of a transmission device while observing the visible light reflected by the visible light reflection means and being applied to the provided visible light reflection means. As another technique, an optical sight transmission device that installs a sighting device in the transmission device and aligns the optical axis while looking at the sighting device, or a measuring device for detecting the received light level is connected to the receiving device side. However, there is also an optical wireless transmission device that performs optical axis alignment with a pair of two persons. Also, as disclosed in Patent Document 2 below, there is a type that uses a light source for adjusting the optical axis on the receiver side to fold back the reception level information of the transmission light from the transmitter and adjust the optical axis accordingly. .
JP-A-62-110339 (FIGS. 1 and 2) JP-A-7-131422 (abstract)

  However, the optical wireless transmission device as disclosed in the above-described Patent Document 1 requires a configuration that causes the transmission device to generate visible light used for purposes other than optical wireless transmission. In addition, when it is desired to keep a sufficient distance between the transmitting and receiving devices, the visible light emission output must be made sufficiently large, and it is necessary to add the configuration, thereby increasing the cost of the transmitting device. In addition, the device becomes large. This is the same when a sighting machine is installed in the transmission device.

  Further, it is necessary to precisely match the optical axis of visible light, the aim of the sighting device, and the optical axis of infrared light for signal transmission, which causes a cost increase. In addition, even when a measuring device for detecting the received light level is connected to the receiving device and the operation is performed by one set of two people, there are disadvantages such as the need to prepare the measuring device for detecting the received light level and the need for manpower. . As described above, if the conventional optical wireless transmission device tries to simplify the optical axis alignment, it leads to an increase in the cost and size of the transmission / reception device, and conversely, an attempt to reduce the cost and size of the transmission / reception device. As a result, there is a drawback that it takes time and effort to align the optical axis.

  Further, Patent Document 2 attempts to solve the above-described problem, but a single light receiving element in which transmission light is mounted on the transmitter as a pilot signal from an optical axis adjusting optical transmission element attached to the receiver. The optical axis is adjusted based only on the received light level and the reception level at the receiver of the transmission light for signal transmission from the transmitter. For this reason, when a person adjusts the optical axis using a level display device or the like based on this information, the effort can be simplified sufficiently, but when the optical axis is adjusted automatically, unnecessary operations increase. End up.

  The reason is that it is impossible to determine whether the receiver is located on the top, bottom, left, or right only by the level of the transmission light for adjusting the optical axis obtained by a single light receiving element. Therefore, in order to automatically adjust the optical axis, it must always move once and it must be judged whether the direction of its movement is correct compared to the light reception level, and it must be judged after moving. . In this case, there is a problem in that unnecessary movement increases, and considering the time required for mechanical driving, it becomes a drag on high-speed automatic optical axis alignment. Furthermore, during automatic optical axis adjustment, the transmitter will transmit the transmitted light in an unspecified direction, which may adversely affect other peripheral optical systems, etc., or if a laser is used as the light source, I'm worried about the impact on people.

  In consideration of the above, the transmitter is provided with a plurality of receiving elements for receiving position notification light from the receiver, or the reception level on the receiver side of the transmission light from the transmitter is set. It is conceivable to align the optical axis based on the base. However, matching the optical axis at the reception level of the transmitted light on the receiver side does not necessarily guarantee the optical axis as an optimum condition. That is, in the optical wireless transmission system, the reception level is expected to vary greatly depending on the distance between the transmitter and the receiver, and it is not easy to determine and adjust the optical axis at a certain level. In addition, what is actually required for optical axis adjustment is not the magnitude of the received light level, but the purpose is to send the transmitted data without error. Aligning the axes is not the best way.

  Therefore, the present invention has been made paying attention to the above points, and it is possible to easily direct the optical axis of an optical signal having a relatively narrow emission angle transmitted by a transmitter to a receiver, and more reliably. An object of the present invention is to provide an optical wireless transmission apparatus that can guarantee a data transmission path.

The present invention in order to achieve the above object, the optical signal optical transmission means of the optical transmission unit to transmit, to an optical wireless transmission device which makes received by the optical receiving unit of the optical receiving unit,
The optical receiving unit is:
Error rate calculating means for calculating an error rate of an optical signal received by the optical receiving means ;
A pilot light transmitting means for transmitting a pilot light modulating the error rate calculated by the error rate calculating means,
With
The optical transmission unit includes:
Pilot light receiving means for receiving the pilot light transmitted from the pilot light transmitting means by a light receiving unit including a plurality of light receiving elements ;
A light receiving level detecting means for detecting each light receiving level of the plurality of light receiving elements received by the pilot light receiving means;
Demodulation means for demodulating the pilot light received by the pilot light receiving means to obtain an error rate;
Holding means for holding integrally said light transmitting means and before Kipa pilots light receiving means,
First direction changing means for changing the direction of the holding means with respect to the pilot light so that the light receiving levels of the plurality of light receiving elements detected by the light receiving level detecting means are equal ;
The light receiving axis of the pilot light receiving means at the position where the direction of the holding means has been changed by the first direction changing means is directed outward so that the error rate obtained by the demodulating means is below a predetermined value. Second direction changing means for changing the direction of the holding means in a spiral shape ;
It was set as the structure provided with .

Further, the present invention in order to achieve the above object, the optical signal optical transmission means of the optical transmission unit to transmit, to an optical wireless transmission device which makes received by the optical receiving unit of the optical receiving unit,
The optical receiving unit is:
Error rate calculating means for calculating an error rate of an optical signal received by the optical receiving means ;
Pilot light transmitting means for transmitting pilot light obtained by modulating the error rate calculated by the error rate calculating means ;
With
The optical transmission unit includes:
Pilot light receiving means for receiving the pilot light transmitted from the pilot light transmitting means by a light receiving unit including a plurality of light receiving elements ;
A light receiving level detecting means for detecting each light receiving level of the plurality of light receiving elements received by the pilot light receiving means;
Demodulation means for demodulating the pilot light received by the pilot light receiving means to obtain an error rate;
Holding means for holding integrally said light transmitting means and before Kipa pilots light receiving means,
First direction changing means for changing the direction of the holding means with respect to the pilot light so that the light receiving levels of the plurality of light receiving elements detected by the light receiving level detecting means are equal ;
Storage means for storing a correction amount for the deviation amount of the optical axis of said light transmitting means and the front Kipa pilots light receiving means which is integrally held by the holding means,
Based on the correction amount stored in the storage means, a second direction changing means for changing the direction of said holding means modified by the first direction changing means,
The light receiving axis of the pilot light receiving means at the position where the direction of the holding means has been changed by the second direction changing means so that the error rate obtained by the demodulating means is a predetermined value or less. A third direction changing means for changing the direction of the holding means in a spiral shape ;
It was set as the structure provided with .

  According to the present invention, after the transmitter quickly finds the approximate position of the receiver while minimizing unnecessary operations, the error is reduced based on the error rate information sent from the receiver. The optical axis is aligned with a relatively large step width when the error is relatively large, and with a relatively small step width when the error is relatively small. The optical axis of a narrow optical signal can be easily directed to the receiver, and a reliable data transmission path can be guaranteed.

<First Embodiment>
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of a system configuration in a first embodiment of an optical wireless communication system according to an optical wireless transmission apparatus of the present invention. This system transmits an image signal from an image reproducing apparatus 1 such as a video or DVD player to a display 2 such as a television, a projector, or a PDP using an optical wireless communication system. The transmission unit 100 is provided on the apparatus 1 side, and the reception unit 200 is provided on the display 2 side.

  FIG. 2 is a block diagram showing the main part of the transmission unit 100 of the present invention. The transmission unit 100 receives the image data from the image reproduction apparatus 1, the reception unit 200 shown in FIG. And an optical transmission means 103 using infrared or eye-safe LD such as LED for communication.

  The transmission unit 100 also receives a pilot signal from the reception unit 200 and an error packet signal in the pilot signal in order to align the optical axis of the optical transmission unit 103 with the optical reception unit 201 (see FIG. 3) of the reception unit 200. Pilot light receiving means 104, reception level detecting means 105 for detecting the reception level of pilot light receiving means 104, demodulation means 106 for demodulating an error packet signal from receiving unit 200, and analyzing the demodulated error packet The error packet analysis means 107, the control means 101 for controlling the optical axis alignment of the optical transmission means 103 with respect to the reception unit 200 using the reception level and error information of the pilot light, the optical transmission means 103 and the pilot light by a servo mechanism, etc. The receiving means 104 is integrated with bread and chill. A search unit 109 for, and a drive control means 108 for driving the search means 109.

  FIG. 3 is a block diagram showing the main part of the receiving unit 200 of the present invention. The receiving unit 200 causes the display 2 to display the optical receiving means 201 such as a PD (photo detector) for receiving the optical signal from the optical transmitting means 103 of the transmitting unit 100 and the image data transmitted by the optical signal. An image display means 202 is provided.

  The reception unit 200 also includes a signal level detection unit 203 that detects the signal level of the optical signal received by the optical reception unit 201, an error detection unit 204 that detects an error in the received data, a signal level detection unit 203, and an error detection unit. A control unit 205 that controls to determine the signal from 204 and notify the transmission unit 100 of the current error amount, an error packet generation unit 206 that packetizes the error information, and the generated error packet A modulation means 207 for modulating the signal to be put on the signal, and a pilot optical transmission means 208 for transmitting the modulated signal or a single carrier pilot signal in space are provided.

  Next, referring to FIG. 4, as an example of the light receiving element used as the pilot light receiving means 104 of the transmission unit 100, a light receiving element in which four (= left and right x 2 up and down) PD elements are enclosed by one lens ( A case where 4-division PD) is used will be described. The principle of this quadrant PD will be briefly described. As shown in FIG. 4, the 4-split PD is one in which four PDs (light receiving elements: PD1, PD2, PD3, PD4) are housed in one optical lens 10. In this element, the light receiving level of each light receiving element (PD1, PD2, PD3, PD4) varies depending on the incident direction of light. Here, the principle is shown in FIGS. 4 (a), 4 (b), and 4 (c). Three patterns are shown as examples.

  In the case of FIG. 4A, the light source 29 is located on the left side (PD1, PD3 side) with respect to the four-divided PD. In this case, incident light is transmitted by the optical lens 10 in which each PD is enclosed. The light is condensed toward the PD2 and PD4, and as a result, the relationship of PD1 <PD2 and PD3 <PD4 is obtained for each light receiving level. In the case of FIG. 4B, the light source 29 is located in front of the 4-split PD. In this case, since the light is condensed at the center where each PD is located, the relationship between the reception levels is PD1 = PD2. PD3 = PD4. In the case of FIG. 4C, the light source 29 is located on the right side (PD2, PD4 side) with respect to the four-divided PD. In this case, incident light is transmitted by the optical lens 10 in which each PD is enclosed. The light is condensed toward the PD1 and PD3 sides, and as a result, the relationship between PD1> PD2 and PD3> PD4 is obtained for each light receiving level.

  Based on such a principle, the quadrant PD can know the direction in which the light source 29 is located by comparing the reception levels of the light receiving elements. An example of the operation will be described with reference to FIGS. FIG. 5 shows a state in which the pilot light receiving means 104 mounted on the transmission unit 100 is composed of four light receiving elements (PD1, PD2, PD3, PD4) arranged in two left and right and two above and below, and this pilot light receiving means. It shows where the receiving unit 200 is as viewed from 104 (in FIG. 5, the position of the receiving unit 200 is shown as the light source 29).

  Here, when the receiving unit 200 is located in the direction of the position A of the light source 29 shown in FIG. 5 when viewed from the transmitting unit 100, the receiving level of the pilot light receiving means 104 is set to the receiving level of SL1 and PD2. Assuming that the reception levels of SL2 and PD3 are SL3 and the reception level of PD4 is SL4, the relationship is approximately SL1 = SL2 <SL3 = SL4 as shown in FIG. From this, the control means 101 compares the reception levels obtained from these, and if the relationship SL1 = SL2 <SL3 = SL4 is obtained, it is determined that the reception unit 200 is in the upward direction, and the drive control means A control signal is sent to 108 (and search means 109) so that optical transmission means 103 and pilot optical reception means 104 face upward. Similarly, when there is a receiving unit 200 at each of the positions A to H, a relationship as shown in FIG. 6 occurs approximately between SL1, SL2, SL3, and SL4, and the control unit 101 checks this relationship while checking FIG. The optical transmission means 103 and the pilot light reception means 104 are controlled so as to face each direction shown in FIG.

  By repeating such control several times, the pilot light receiving means 104 is moved to a position where the reception levels SL1 to SL4 of the pilot light receiving means 104 of the transmission unit 100 all have the same value. In such a state, the transmission unit 100 roughly grasps the position of the reception unit 200.

  Here, if the optical transmission angle (directivity) of the optical transmission unit 103 of the transmission unit 100 is sufficiently wide, the transmission unit 100 can transmit a signal to the reception unit 200 using the optical transmission unit 103 in this state. Is possible. However, if the emission angle of the light transmitting means 103 is widened, the optical power (light quantity) decreases, and it often happens that a sufficient transmission distance cannot be obtained. It is required to narrow the emission angle of the transmission means 103. However, in the method of searching for the position of the pilot light from the receiving unit 200 using the pilot light receiving unit 104 described above, the optical transmission signal emitted from the light transmitting unit 103 having a narrow emission angle by this method is received by the receiving unit. In order to accurately capture the 200 light receiving means 201, the light emitting axis of the light transmitting means 103 and the light receiving axis of the light receiving means 201 must be parallel. This will be described with reference to FIG.

  FIG. 7A shows the light emitting element 9 as the light transmitting means 103 and the light emitting axis 51 of the light receiving element 17 as the light receiving means 201, the light source 29 as the pilot light transmitting means 208, and the optical lens as the pilot light receiving means 104. 10 shows an ideal case in which the light receiving axis 50 of the quadrant PD enclosed in 10 is in a parallel state. In such a case, the first optical signal emitted from the optical transmission unit 103 can be applied to the optical reception unit 201 placed adjacent to the light source 29 by finding the position of the light source 29 with the 4-split PD. . However, in the actual manufacturing process, there may occur a case where the light emitting shaft 51 and the light receiving shaft 50 are not necessarily parallel when the components are dispersed or assembled / attached. Rather, it seems that there are more cases where the optical axes are not parallel.

  FIG. 7B shows a case where the light emitting shaft 51 and the light receiving shaft 50 are not in a parallel state but in an off-axis state. In such a case, even if the position of the light source 29 is found by the 4-split PD, the optical signal emitted from the optical transmission unit 103 cannot be accurately applied to the optical reception unit 201 adjacent to the light source 29. Data transmission cannot be realized.

  Therefore, in the present invention, after the pilot light receiving means 104 of the transmission unit 100 finds the position of the pilot light transmission means 208 of the reception unit 200, the reception error rate information detected by the error detection means 204 is received from the reception unit 200 as pilot light. Based on this information, the transmission unit 100 realizes more accurate automatic optical axis alignment by aligning the optical axis so that the error indicated by the error rate information is reduced as much as possible. Yes.

  Next, in the present invention, error rate information packetized with pilot light is transmitted from the receiving unit 200. An example of the packet configuration is introduced in FIG. As shown in FIG. 8, a command header 40 for identifying data for transmitting error rate information, a data length 41 to be transmitted, error rate data (information) 42, and a data end 43 are included. The packet is transmitted with a pilot optical signal.

  In the present invention, the amount of search movement steps is varied according to the amount of reception error rate. That is, when the error is large, the optical axis is moved roughly, and when the error is small, the optical axis is aligned at higher speed and with higher reliability. FIG. 9 is an explanatory diagram showing an example of a search operation using error information. The transmission unit 100 performs a search operation based on error information from the reception unit 200 after the search based on the pilot light level from the reception unit 200 is completed. In this search operation, the point where the error is smaller than the error rate of the start point is searched for while spirally moving the position aligned with the optical axis by the 4-split PD from the center to the outside. Furthermore, when a point with fewer errors is found, a new spiral search operation is performed using that point as a start point. When the error rate falls below a certain threshold (for example, 10 −9), the search is terminated. To do.

  FIGS. 10A and 10B show the difference in search operation depending on the error amount. If there are many errors at the start point, there is a high possibility that it is far away from the original optical axis. Therefore, by increasing the step width that moves at one time (rough) as shown in FIG. It is designed to be close to the axis with a small number of operations. FIG. 10B shows a case where it is assumed that there are few errors at the start point and that it is close to the original optical axis. The amount of movement at one time is reduced (finely) so that the optimum point is not removed. I have to.

<Second Embodiment>
FIG. 11 shows a light emitting shaft 51 and a light receiving shaft 50 by an exterior (cover) 60 provided on the front surface of a quadrant PD enclosed in the light emitting element 9 as the light transmitting means 103 and the optical lens 10 as the pilot light receiving means 104. The state of the optical axis deviation is shown. Even when the light emitting axis 51 and the light receiving axis 50 are parallel as shown in FIG. 7A, the optical axis shift occurs due to the difference in refractive index due to the exterior (cover) 60. Even if the position of the light source 29 is found by the divided PD, the optical signal emitted from the light transmitting means 103 to the light receiving element 17 that is the light receiving means 201 placed adjacent to the light source 29 that is the pilot light transmitting means 208 is accurately detected. It cannot be applied and data transmission cannot be realized.

  FIG. 12 shows a transmission unit 100a constituting an optical wireless communication system according to the optical wireless transmission apparatus of the second embodiment of the present invention, and a correction amount storage means 110 is added to the structure shown in FIG. . Since the other configuration of the transmission unit 100a and the configuration of the reception unit 200 (see FIG. 3) constituting the optical wireless communication system of the second embodiment are the same, detailed description thereof is omitted. In the second embodiment, these optical axis misalignment factors (cover and manufacturing process variations) are measured in advance, and the optical axis misalignment correction amount is stored in the correction amount storage means 110 as a map, and the transmission unit. After finding the position of the pilot light transmitting means 208 of the receiving unit 200 by the pilot light receiving means 104 of 100a, the optical axis deviation correction amount at that position is read from the correction amount storage means 110, and the optical axis is corrected. Realizes more accurate optical axis alignment.

  FIG. 13 shows an example of an optical axis correction amount map stored in the correction amount storage means 110. When the movable range of the search is ± 15 degrees for both pan and tilt, the correction amount is stored every 5 degrees. When the pan position is −10 degrees and the tilt position is 5 degrees, the correction amounts are 2 degrees pan and 1 degree tilt. In this example, the correction amount is every 5 degrees, but of course, this may be taken finely, for example, every 1 degree to increase the accuracy.

  Further, in the second embodiment, as in the first embodiment, after the optical axis deviation correction described above, the reception error rate information detected by the error detection means 204 from the reception unit 200 is converted to the pilot light transmission means 208. Based on this information, the transmission unit 100a performs more accurate searching by the method shown in FIGS. 9 and 10 so that the error indicated by the error rate information is reduced as much as possible. Automatic optical axis alignment is realized.

1 is a configuration diagram illustrating a first embodiment of an optical wireless communication system according to the present invention. FIG. It is a block diagram which shows the principal part of the transmission unit of FIG. It is a block diagram which shows the principal part of the receiving unit of FIG. It is explanatory drawing which shows the relationship between a light source position and the reception level of 4 division | segmentation PD. It is explanatory drawing which shows the 1st optical axis alignment method in this invention. It is explanatory drawing which shows the 1st optical axis alignment method in this invention in detail. It is explanatory drawing which shows an optical axis shift. It is explanatory drawing which shows the structural example of an error information transmission packet. It is explanatory drawing which shows an example of the search operation | movement using error information. It is explanatory drawing which shows the difference in the search operation by the amount of errors. It is explanatory drawing which shows another optical axis shift. It is a block diagram which shows the principal part of the transmission unit of 2nd Embodiment. It is explanatory drawing which shows the example of a map of the optical axis correction amount memorize | stored in the correction amount memory | storage means of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image reproducing apparatus 2 Display 9 Light emitting element 10 Optical lens 17 Light receiving element 29 Light source 40 Command header 41 Data length 42 Error rate data 43 Data end 50 Light receiving axis 51 Light emitting axis 60 Exterior (cover)
100, 100a Transmission unit 101, 205 Control means 102 Image reception means 103 Optical transmission means 104 Pilot light reception means 105 Reception level detection means 106 Demodulation means 107 Error packet analysis means 108 Drive control means 109 Search means (pan, tilt)
110 Correction amount storage means 200 Reception unit 201 Optical reception means 202 Image display means 203 Signal level detection means 204 Error detection means 205 Control means 206 Error packet generation means 207 Modulation means 208 Pilot light transmission means

Claims (2)

The optical signal optical transmission means of the optical transmission unit to transmit, to an optical wireless transmission device which makes received by the optical receiving unit of the optical receiving unit,
The optical receiving unit is:
Error rate calculating means for calculating an error rate of an optical signal received by the optical receiving means ;
A pilot light transmitting means for transmitting a pilot light modulating the error rate calculated by the error rate calculating means,
With
The optical transmission unit includes:
Pilot light receiving means for receiving the pilot light transmitted from the pilot light transmitting means by a light receiving unit including a plurality of light receiving elements ;
A light receiving level detecting means for detecting each light receiving level of the plurality of light receiving elements received by the pilot light receiving means;
Demodulation means for demodulating the pilot light received by the pilot light receiving means to obtain an error rate;
Holding means for holding integrally said light transmitting means and before Kipa pilots light receiving means,
First direction changing means for changing the direction of the holding means with respect to the pilot light so that the light receiving levels of the plurality of light receiving elements detected by the light receiving level detecting means are equal ;
The light receiving axis of the pilot light receiving means at the position where the direction of the holding means has been changed by the first direction changing means is directed outward so that the error rate obtained by the demodulating means is below a predetermined value. Second direction changing means for changing the direction of the holding means in a spiral shape ;
An optical wireless transmission device comprising: The optical signal optical transmission means of the optical transmission unit to transmit, to an optical wireless transmission device which makes received by the optical receiving unit of the optical receiving unit,
The optical receiving unit is:
Error rate calculating means for calculating an error rate of an optical signal received by the optical receiving means ;
Pilot light transmitting means for transmitting pilot light obtained by modulating the error rate calculated by the error rate calculating means ;
With
The optical transmission unit includes:
Pilot light receiving means for receiving the pilot light transmitted from the pilot light transmitting means by a light receiving unit including a plurality of light receiving elements ;
A light receiving level detecting means for detecting each light receiving level of the plurality of light receiving elements received by the pilot light receiving means;
Demodulation means for demodulating the pilot light received by the pilot light receiving means to obtain an error rate;
Holding means for holding integrally said light transmitting means and before Kipa pilots light receiving means,
First direction changing means for changing the direction of the holding means with respect to the pilot light so that the light receiving levels of the plurality of light receiving elements detected by the light receiving level detecting means are equal ;
Storage means for storing a correction amount for the deviation amount of the optical axis of said light transmitting means and the front Kipa pilots light receiving means which is integrally held by the holding means,
Based on the correction amount stored in the storage means, a second direction changing means for changing the direction of said holding means modified by the first direction changing means,
The light receiving axis of the pilot light receiving means at the position where the direction of the holding means has been changed by the second direction changing means is directed outward so that the error rate obtained by the demodulating means is below a predetermined value. A third direction changing means for changing the direction of the holding means in a spiral shape ;
An optical wireless transmission device comprising:

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