JP2002044030A - Optical wireless communication apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress variation in d-c level of a received signal when a signal is transmitted, received and filtered with a high-pass filter after a LED emits in a binary burst only in a transmit section for transmitting data, while the LED is stopped from emission in a no-signal section in which no data is transmitted. SOLUTION: The communication apparatus has a photo detector 1 for receiving optical signals transmitted from other optical wireless communication apparatus, and a high-pass filter 7 for removing disturbance optical components from the received signal by the detector 1. It comprises a carrier sensing unit 6 for detecting a receiving section having burst signals and a no-signal section having no burst signal from the received signal, a holder 5 for inserting at least a d-c signal corresponding to the center level of the receiving section into the no-signal section, and a changeover switch 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wireless communication apparatus suitable for an optical wireless communication system for transmitting and receiving signals by optical wireless, and more particularly, to an optical wireless communication apparatus for receiving burst transmission light.

[0002]

2. Description of the Related Art Conventionally, a plurality of information processing devices such as personal computers are interconnected to each other to form a LAN (Local Arrangement).
ea Network), these information processing devices
For example, they are often connected by a wire such as a coaxial cable or an optical cable. Wired connection is advantageous in that there are few data errors due to extraneous noise because a mechanically secure connection is possible, but the wiring work is complicated and requires work for each layout change. There is a point.

In recent years, there has been an increasing demand for data transmission by interconnecting portable information processing apparatuses such as personal computers such as laptops, books and palmtops, and electronic notebooks. On the other hand, these portable information processing devices are devices originally intended to be moved and used, and it is extremely rare that they are moved while being connected by wire. For this reason, when data transmission is performed by connecting these portable information processing devices to each other, a connector must be connected and disconnected each time the device is moved, and such a connection operation is very troublesome. In addition, if the connector is repeatedly inserted and removed, there is a possibility that mechanical damage of a connection portion such as the connector may occur.

[0004] For these reasons, when data is transmitted and received between various types of information processing equipment, not limited to the stationary type and the portable type, all or a part of the transmission path is made wireless to reduce wired connections. There is a request to want.

[0005] As the wireless transmission method, there are a method using radio waves as a transmission medium and a method using light as a transmission medium.
High-speed data transmission can be realized by using any of these radio wave and light transmission media. However, radio waves are subject to legal regulations, and wireless transmission using light without any legal restrictions is not possible. It is advantageous.

An optical wireless communication device that performs wireless transmission using such light as a transmission medium generally includes a light emitting unit for transmitting signal light to a partner optical wireless communication device and a light emitting unit for transmitting signal light from the partner optical wireless communication device. And a receiving unit that receives the signal light and converts the received signal light into a reception signal. As a light emitting element of the light emitting section, it is common to use an LED (light emitting diode) from the viewpoint of safety. On the other hand, the light receiving element provided in the receiving unit is a PD (photodiode).
It is common to use In addition, as a light receiving element, a high-sensitivity optical sensor having a self-multiplication function is used.
A PD (avalanche photodiode) may be used.

Further, in the optical wireless communication device, as described above, an LED is used as a light emitting element, and L is set according to a transmission signal.
Signals are transmitted by causing the ED to emit light.However, when causing the LED to emit light, a constant DC current is supplied, and the drive current is increased or decreased at a constant amplitude around the DC current. A signal is transmitted by changing the light emission amount of the LED. That is, as shown in FIG. 6A, the LED light emission at the time of signal transmission emits light at a constant level L corresponding to the constant DC current in a non-signal section NS in which data transmission is not performed. In the transmission section TS, the light is emitted (BWa) in a binary burst of “0” or “1” according to the constant level L and the transmission signal.

On the other hand, in the optical wireless communication apparatus on the receiving side, the above-mentioned burst transmission light BWa is received by the PD. However, in the case where the optical wireless communication device on the receiving side receives the transmission light, there is a possibility that, in addition to the transmission light, environmental light emitted from a fluorescent lamp, an incandescent lamp, or the like may also enter the PD. In particular, the spectrum of ambient light from a fluorescent lamp using an inverter that converts the frequency of a household power supply is 1M.
Hz or higher (harmonic components around 40 kHz to 50 kHz)
It has been extended to. For this reason, the receiving unit cuts disturbance due to ambient light by passing a signal received from the PD through a high-pass filter. That is, FIG.
The signal waveform when the transmission light shown in (a) is received by the PD and the received signal is passed through a high-pass filter is shown in FIG.
As shown in (b), in a no-signal section NS in which data transmission is not performed, the constant value corresponds to the constant level L,
In the transmission section TS (reception section RS), a binary reception signal waveform (BWb) of “0” or “1” according to the constant level L and the transmission signal is obtained, and a signal that is not affected by ambient light is obtained. The received signal after passing through this high-pass filter is
After that, a binarization process or the like based on comparison with a predetermined threshold is performed.

Meanwhile, in the optical wireless communication apparatus on the transmitting side, as shown in FIG.
If a constant DC current is caused to flow through the ED, the DC current continues to flow through the LED even during non-data transmission without transmitting a signal, and extra power is consumed.

On the other hand, for example, in a non-signal section NS in which no data is transmitted, the DC current to the LED is cut to stop the light emission, so that the power consumption of the LED can be reduced. it is conceivable that. That is, as shown in FIG. 6C, the light emission of the LED is stopped in the no-signal section where no data transmission is performed, and the LED is set to “0” or “0” corresponding to the transmission signal only in the transmission section TS where the data transmission is performed. If the light is emitted (BWc) in a binary burst of “1”, the power consumption of the LED can be reduced.

[0011]

However, FIG.
As shown in (c), when the optical level of the non-signal section NS is set to “0” and the burst light (BWc) is transmitted only in the transmission section TS in which data transmission is performed, the receiving side The signal waveform that has passed through the high-pass filter in the receiving unit of the optical wireless communication device has a waveform (BWd) as shown in FIG.

That is, when the signal shown in FIG. 6C is passed through a high-pass filter, a signal response output such that the upper and lower integral values of the burst signal BWd become equal at the center value of the received signal level in the receiving section RS, for example. Become
As a result, as shown in FIG. 6 (d), the signal after passing through the high-pass filter has its waveform largely shifted to the positive side at the beginning of the burst signal BWd in the reception section RS, and then has the high-pass filter. Changes to a signal whose upper and lower amplitude levels are equal in a time proportional to the time constant of
After the end of the burst signal BWd of S, the signal returns to the AC midpoint level from the negative side in accordance with the time constant of the high-pass filter.

Further, as described above, if the DC level of the received signal fluctuates greatly as shown in FIG. 6D, there is a possibility that correct data cannot be taken out in the subsequent binarization processing. In other words, it is very difficult to set a threshold value in the binarization process so that correct data can be extracted from the received signal.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problem, and stops the light emission of an LED in a non-signal section in which no data is transmitted, and only in a transmission section in which data is transmitted.
When a signal is transmitted by emitting light in the form of a binary burst of “0” or “1”, and the transmitted light is received and passed through a high-pass filter, fluctuations in the DC level of the received signal are suppressed. Accordingly, it is an object of the present invention to provide an optical wireless communication device capable of extracting correct data from a received signal without specially setting a threshold value in a subsequent binarization process.

[0015]

According to the present invention, there is provided an optical wireless communication apparatus according to the present invention, comprising: a light receiving element for receiving an optical signal transmitted from another optical wireless communication device; An optical wireless communication device comprising a high-pass filter for removing a disturbance light component from a received signal, wherein a signal section having a burst signal and a burst signal section are provided as means for solving the above-mentioned problem. Detecting means for detecting a no-signal section where no signal is present, and at least a center level inserting means for inserting a DC signal corresponding to the center level of the signal in the signaled section into the no-signal section of the received signal. Have.

According to a second aspect of the present invention, as a means for solving the above-mentioned problems, when the detection by the detection means has a delay of a predetermined time, the reception signal is A delay unit that delays by a time corresponding to the predetermined time.

In the optical wireless communication apparatus according to a third aspect of the present invention, as a means for solving the above-mentioned problem, the center level inserting means corresponds to at least a center level of a signal in the signal section. DC signal generating means for generating a DC signal, and when a signal section is detected by the detection means, the signal of the signal section of the received signal is selected, and when a non-signal section is detected by the detection means, Switching selection means for selecting the DC signal generated by the DC signal generation means.

According to a fourth aspect of the present invention, as a means for solving the above-mentioned problem, the center level inserting means corresponds to at least a center level of a signal in the signal section. DC signal generating means for generating a DC signal, and light emitting means for emitting light having an intensity corresponding to the DC signal generated by the DC signal generating means when at least a no-signal section is detected by the detecting means The light emitting means is arranged near a light receiving surface of the light receiving element.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the configuration of a main part of an optical wireless communication apparatus on the receiving side as a first embodiment according to the present invention.

In FIG. 1, a transmission light transmitted from a light emitting section of an optical wireless communication device on the transmission side and other environmental light enter a light receiving element 1 composed of a photodiode. The received light (transmitted light from the transmitting-side optical wireless communication device) received by the optical wireless communication device according to the present embodiment performs data transmission in the same manner as that shown in FIG. A non-signal section NS due to no data transmission (the LED is not emitting light) and a binary burst reception section RS due to data transmission being performed (the LED is driven to emit light according to the transmission signal). (Transmission section TS).

The light receiving element 1 photoelectrically converts incident light containing ambient light in the received light. The light-receiving signal obtained by the photoelectric conversion in the light-receiving element 1 is amplified by the amplifier unit 2, and then is delayed by the delay unit 3 and the carrier sense (Career Sens
e) Input to section 6. Note that the light-receiving signal waveform output from the amplifier unit 2 (the signal waveform at the point A in FIG. 1 subsequent to the amplifier unit 2) is, as shown in FIG. Become.

As shown in FIG. 2B, the carrier sense section 6 is at H level (high level) when the reception section RS is detected from the received light signal, and is at L level (low level) when the non-signal section NS is detected. ) Is output. Note that both the H-level output timing when the reception section RS is detected and the L-level output timing due to detection of the no-signal section NS include a time lag TL for the detection processing. The carrier sense signal CS output from the carrier sense unit 6 is sent to the hold unit 5 as a hold control signal and is also sent to the changeover switch unit 4 as a switch changeover control signal.

The output signal from the changeover switch 4 is input to the hold unit 5, and when the carrier sense signal CS is at the H level, a signal that changes according to the output signal level from the changeover switch 4 is output. On the other hand, when the carrier sense signal CS is at the L level, the signal DC component level at the previous reception is held, that is, the carrier sense signal CS
Holds the DC component level of the signal when is at the H level. The output signal of the hold unit 5 is sent to the switched terminal 4a of the switch unit 4.

On the other hand, the delay unit 3 delays the received light signal supplied from the amplifier unit 2 by a time corresponding to the detection processing time (time lag TL) in the carrier sense unit 6, and switches the received light signal after the delay. The signal is sent to the switched terminal 4b of the switch unit 4. That is, the output signal waveform of this delay unit 3 (B in FIG. 1)
As shown in FIG. 2C, the signal waveform at the point is delayed from the signal at point A in FIG. 1 by a delay time DL (= TL).

Next, the switch unit 4 is switched to the switched terminal 4b when the carrier sense signal CS is at the H level, and is switched to the switched terminal 4a when the carrier sense signal CS is at the L level. That is, the output signal of the hold unit 5 is supplied to the switched terminal 4a of the changeover switch unit 4, the output signal of the delay unit 3 is supplied to the switched terminal 4b, and the switched terminals 4a and 4b are
The switching is controlled by the carrier sense signal CS shown in FIG. Thereby, the changeover switch unit 4
The output signal waveform (signal waveform at point C in FIG. 1) is shown in FIG.
As shown in (d), a signal waveform in which the signal level in the no-signal section is the DC level in the reception section (a signal waveform in which the level in the no-signal section and the DC level in the reception section are constant) is obtained. The output signal from the common terminal of the changeover switch unit 4 is sent to the high-pass filter 7.

The high-pass filter 7 outputs a received signal from which a disturbance noise component caused by environmental light has been removed from the received light signal, and sends the signal to a binarization processing unit (not shown) having a configuration at a later stage.

As described above, according to the optical wireless communication apparatus of the first embodiment of the present invention, the presence or absence of a signal (no signal section NS and reception section RS) is detected from a received signal, and a certain delay is detected. Carrier sense section 6 which outputs the detection signal as carrier sense signal CS after a time (time lag TL).
A delay unit 3 for delaying a received signal by a time DL corresponding to a time lag TL of the carrier sense unit 6;
The holding unit 5 detects the center level based on the reception signal delayed by the above, holds the center level in the non-signal section NS, and re-detects the center level in the reception section RS, and the pseudo center level (DC Level), and a changeover switch unit 4 for inserting a signal into the no-signal section NS, and maintaining the center level of the no-signal section NS and the receiving section RS constant, thereby enabling the center of the signal after passing through the high-pass filter 7 to be maintained. The potential change does not occur, so that the binarization processing unit at the subsequent stage does not need to set a special threshold value and can easily extract correct data.

Next, a description will be given of a second embodiment of the present invention. A capacitor is provided immediately after the light-receiving element, and after the DC component is cut by this capacitor, only the signal component is extracted and amplified, eliminating the DC component of the signal and environmental light in the background, etc., and efficiently only the signal component. Can be amplified. However, in this case, since the capacitor provided immediately after the light receiving element functions as a high-pass filter, the reception of the burst signal causes a change in the DC level. Further, since the signal current immediately after the light receiving element is very small, it is difficult to insert a DC component using a switch or the like as in the example of FIG. Therefore, in the second embodiment, functions similar to those of the above-described first embodiment are realized as follows.

First, FIGS. 3A and 3B are block diagrams of main parts of a receiving optical wireless communication apparatus according to the second embodiment. FIG. 3A shows a signal receiving state. FIG. 3B shows a signal non-receiving state. This figure 3
As can be seen from (a) and (b), the optical wireless communication device according to the second embodiment includes a pseudo DC level insertion light emitting element 10 that emits a pseudo DC level signal that is a sine wave signal having a constant frequency fd. A light receiving element 11 that receives a transmission signal when receiving a signal and receives a pseudo DC level signal from the pseudo DC level insertion light emitting element 10 when no signal is received.

Further, this optical wireless communication apparatus has a light receiving element 1
A first high-pass filter 12 for extracting only a signal component by removing a DC component superimposed on the received light signal from No. 1 and an influence of background environmental light, and a signal component extracted by the first high-pass filter 12 And an amplifier 13 that amplifies the signal with a predetermined gain and outputs the amplified signal.

In the optical wireless communication apparatus, when receiving a signal, the light receiving signal from the amplifier unit 13 is transmitted as it is, and when no signal is received, the light receiving element 11 passes through the first high-pass filter 12 and the amplifier unit 13 without receiving the signal. Second high-pass filter 1 for removing the supplied pseudo DC level signal
8, a carrier sense 16 which becomes a high level (H) when a light receiving signal output from the second high-pass filter 18 is detected (receiving section RS), and a second signal when receiving a signal.
And a hold circuit 15 for detecting the center potential of the light reception signal output from the high-pass filter 18 and holding and outputting the center potential when no signal is received.

Further, the optical wireless communication apparatus has a light emission level adjusting circuit for outputting a pseudo DC level signal which is a sine wave signal of the constant frequency fd based on the central potential held by the hold circuit 15 when no signal is received. 14 and
A switch 17 that is turned on when no signal is received, and supplies a pseudo DC level signal from the light emission level adjustment circuit 14 to the pseudo DC level insertion light emitting element 10 to drive the light emission.

Next, the operation of the optical wireless communication apparatus according to the second embodiment having such a configuration will be described.

First, in the case of "at the time of signal reception", FIG.
As shown in (1), the switch 17 is turned off because the output from the carrier sense 16 described below is at a low level (L), and the light emitting element 10 for inserting a pseudo DC level is stopped. In this state, the light receiving element 11 transmits the transmission signal f
s and receives the received light signal as a first high-pass filter 12.
To supply.

The first high-pass filter 12 removes a DC component from the received light signal and a component such as background environmental light, extracts only a signal component, and supplies the extracted signal component to the amplifier unit 13. The amplifier unit 13 amplifies the received light signal with a predetermined gain, and outputs the amplified signal via the second high-pass filter 18. Thereby, only the signal component can be output.

On the other hand, when the carrier sense 16 detects the light receiving signal from the second high-pass filter 18, it forms a high-level carrier sense signal (CS = H). And switch 17.

The hold circuit detects the center potential of the light receiving signal from the second high pass filter while the high level carrier sense signal is being supplied. Further, the light emission level adjustment circuit 14 and the switch 17 are controlled to be off while the high level carrier sense signal is being supplied.

Next, in the case of "when no signal is received", the pseudo high DC level signal is cut by the second high-pass filter 18 as described below, so that the low level carrier sense signal is output from the carrier sense 16. Will be output. When the low-level carrier sense signal is supplied, the hold circuit 15 holds the central potential of the light-receiving signal detected at the time of signal reception, and supplies this to the light-emission level adjusting circuit 14. The light emission level adjustment circuit 14 is activated when a low level carrier sense signal is supplied from the carrier sense 16, the central potential held by the hold circuit 15, and the amplifier 1 described below.
3 based on the pseudo DC level signal from
Is supplied to the pseudo DC level insertion light emitting element 10 from the carrier sense 16 via the switch 17 which is turned on by the low level carrier sense signal. Thus, the pseudo DC level insertion light emitting element 10 emits a pseudo DC level signal that is a sine wave signal having a constant frequency fd.

Next, the pseudo DC level signal is received by the light receiving element 11 and supplied to the first high-pass filter 12. The cutoff frequency of the first high-pass filter 12 is set higher than the frequency fd of the pseudo DC level signal. Therefore, the first high-pass filter 12
The pseudo DC level signal supplied to the
The light is supplied to the light emission level adjusting circuit 14 and the second high-pass filter 18 through the third light-emitting element 3.

The cut-off frequency of the second high-pass filter 18 is set lower than the frequency fd of the pseudo DC level signal. For this reason, the pseudo DC level signal supplied to the second high-pass filter 18 is cut by the second high-pass filter 18. Therefore, when this signal is not received, the signal supplied to the carrier sense 16 is cut off, so that the carrier sense signal becomes low level and the hold circuit 15
Performs the hold operation of the central potential, and the light emission level adjustment circuit 1
4 is turned on, the switch 17 is turned on, and the pseudo DC level insertion light emitting element 10 is driven to emit light.

Next, the operation of the optical wireless communication apparatus according to the second embodiment will be described in detail with reference to FIG.

As shown in FIG. 4A, the waveform of the received light signal output from the light receiving element 11 includes a non-signal section NS and a receiving section RS.
As shown in FIG. 4D, the non-signal section NS is at the “0” level, and the reception section RS is at the midpoint level of the intra-section signal. Further, as shown in FIG. 4C, the carrier sense signal CS is such that the reception signal is changed from the no-signal section NS to the reception section RS
Is changed from L level to H level after a certain time lag TL. On the other hand, when the carrier sense signal CS is at the L level, the light emitting element 10 for pseudo DC level insertion outputs the output signal potential of the hold circuit 15 (the midpoint level corresponding to the central potential of the reception section RS). ) And the light emitting element 10 for inserting a pseudo DC level
As shown in FIG. 4B, light is emitted with a light intensity such that the potential generated by the light emission (the output signal potential of the amplifier unit 13) matches.

Therefore, as can be seen from FIGS. 4B and 4D, as shown in FIG. 4E, the DC component level of the light receiving signal of the light receiving element 11 changes from the non-signal section NS to the point where the receiving signal is no signal. After the change to the reception section RS, a rectangular wave is formed only for a certain time lag TL until the carrier sense signal CS changes from the L level to the H level (that is, a period during which the light emission of the light emitting element 10 overlaps with the reception section RS). Will increase.

As shown in FIG. 4E, when a signal including a portion where the DC component level changes in a rectangular wave shape passes through the first high-pass filter 12, the DC component level of the signal is changed to the level shown in FIG. f).

That is, the DC component level of the signal after passing through the first high-pass filter 12 gradually decreases in the rectangular wave portion of FIG. 4F, while after the rectangular wave portion, Since the light emission of the pseudo DC level insertion light-emitting element 10 stops, after swinging to the negative side, the DC component level gradually returns to the original level and changes so as to be stabilized.

Here, the decrease in the DC level in the rectangular wave portion shown in FIG. 4F depends on the time constant of the first high-pass filter 12 and the time of the time lag TL of the carrier sense signal CS. C
When the time lag TL of the S signal is short or when the time constant of the first high-pass filter 12 is large, the fluctuation amount of the DC component level is small. The time required for the DC component level of the signal after passing through the first high-pass filter 12 to be stabilized is 2T, where T is the time of the time lag TL of the carrier sense signal CS.

As described above, in the case of the second embodiment, the time lag T from the transition from the no-signal section NS to the reception section RS until the carrier sense signal CS goes to the H level is set.
In the period of time T of L, the DC component level of the signal after passing through the first high-pass filter 12 changes in a rectangular wave shape. Thereafter, the time from T to 2T until the DC component level is stabilized is equal to the high-pass filter 12. , The DC component level slightly fluctuates depending on the time constant. Therefore, the non-signal section NS
During the period of 2T after the transition from to the reception section RS, there is a possibility that the reproduction of the reception signal is disturbed as shown in FIG. However, when transmitting and receiving a burst signal of a high frequency, a PLL (Phas
e Locked Loop) Since a preamble for synchronization is added, even if the head of the preamble part is slightly missing by passing through the first high-pass filter 12, the reproduction of the original signal part after the preamble part is not performed. There is no problem at all.

As described above, according to the optical wireless communication apparatus of the second embodiment of the present invention, the pseudo direct current level insertion light emitting element 10 is arranged near the light receiving surface of the light receiving element 11,
Under the control by the carrier sense signal from the carrier sense 16, the light emitting element 10 emits light during the no-signal section NS, and a pseudo DC level corresponding to the central potential of the reception section RS is inserted into the no-signal section NS. In addition, a DC component equivalent to that of the reception section RS can be given to the no-signal section NS, and the fluctuation of the center level between the no-signal section NS and the reception section RS can be kept short. For this reason, correct data can be easily extracted based on the received signal from the second high-pass filter 18 without setting a special threshold value in the subsequent binarization processing unit.

Further, according to the second embodiment of the present invention, the hold section 15 is provided with a filter having a large delay or a large time constant at the input stage, so that the hold section 15 can receive the signal for a certain period of time when the non-signal section NS occurs. It is possible to hold the signal.

Next, FIG. 5 shows an example of an optical wireless communication system to which the optical wireless communication device having the configuration of the first or second embodiment of the present invention can be applied.

In FIG. 5, the optical wireless communication system is a system connected to a trunk network such as, for example, Ethernet (registered trademark) for transmitting and receiving data by packet transmission. Between the network trunk line 31 and the terminal 42 (the terminals 42a and 42b each including a personal computer in the example of FIG. 1) as an optical wireless communication device (hereinafter, referred to as a parent device 32) as a parent device and a child device. Optical wireless communication device (hereinafter referred to as slave unit 41 (41a, 41a)
b)) using half-duplex optical communication.

The optical wireless communication device as the master unit 32 is provided with a diffusion type optical wireless communication unit 32 capable of outputting light L1 over a wide range and capable of receiving light from a wide range. The optical wireless communication device as 41b includes narrow directional optical wireless communication units 44a and 44b capable of receiving signal light at a narrow angle and outputting a light beam L2 at a narrow angle. In the example of FIG. 5, each of the slave units 41 is connected to the terminal 42 via a predetermined cable, and the master unit 32 is attached to, for example, a ceiling, and connected to the network trunk 31 spanning the ceiling. Assume that they are connected.

In the optical wireless communication system shown in FIG.
If the optical wireless communication device according to the first or second embodiment of the present invention described above is applied, light emission of the LED is stopped in the no-signal section in the optical wireless communication device on the transmission side to reduce power consumption, In a case where a high-pass filter is provided in the optical wireless communication device on the receiving side in order to remove the influence of disturbance due to environmental light, the optical wireless communication device on the receiving side detects the center potential of the signal after passing through the high-pass filter. It is possible to easily extract correct data without any fluctuation and without having to set a special threshold value in the subsequent binarization processing unit.

Finally, the description of the above embodiment is an example of the present invention. For this reason, the present invention is not limited to the above embodiments, and various changes can be made according to the design and the like as long as the technical idea according to the present invention is not deviated. It is.

[0056]

According to the optical wireless communication apparatus of the present invention, a signal section having a burst signal and a non-signal section having no burst signal are detected from a received signal. Detecting means, and a central level inserting means for inserting at least a DC signal corresponding to the central level of the signal in the signaled section into the non-signal section of the received signal, for example, In the section, the LED is stopped from emitting light, and a signal is transmitted such that the LED is caused to emit a binary burst of “0” or “1” only in the transmission section for transmitting data. When performing processing that passes through a filter, fluctuations in the DC level of the received signal can be suppressed, and as a result, for example, a threshold value in the subsequent binarization processing is not particularly set. , It is possible to retrieve the correct data from the received signal.

According to the optical wireless communication apparatus of the present invention, when there is a delay of a predetermined time in detection of a signal section and a non-signal section from a reception signal, the reception signal is delayed for the predetermined time. The provision of the delay means for delaying by a corresponding time makes it possible to simultaneously start the reception of the received signal and start the detection.

According to the third aspect of the present invention, the center level inserting means generates a DC signal corresponding to the center level of the signal in the signaled section, and the signaled section is detected. Switching selection means for selecting the signal of the signaled section of the received signal when the signal is received, and selecting the DC signal when the non-signaled section is detected, so that the signal of the signaled section is signaled in the signaled section. Output can be performed, and a DC signal can be output in a non-signal section, so that when a process of passing the output signal through a high-pass filter is performed, a change in the DC level of the signal can be suppressed.

According to the fourth aspect of the present invention, the center level inserting means includes a DC signal generating means for generating a DC signal corresponding to at least a center level of a signal in a signaled section; A light emitting unit that emits light having an intensity corresponding to the DC signal when at least the no-signal section is detected, and a DC signal is inserted into the no-signal section by disposing the light emitting unit near the light receiving surface of the light receiving element. Thus, when a process of passing the output signal through a high-pass filter is performed, a change in the DC level of the signal can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram illustrating a configuration of a main part of an optical wireless communication device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram used for describing the operation of each unit of the optical wireless communication apparatus according to the first embodiment shown in FIG.

FIG. 3 is a block circuit diagram illustrating a configuration of a main part of an optical wireless communication device according to a second embodiment of the present invention.

FIG. 4 is a waveform chart used to describe the operation of each unit of the optical wireless communication apparatus according to the second embodiment shown in FIG.

FIG. 5 is a diagram illustrating an example of an optical wireless communication system to which the optical wireless communication device having the configuration according to the first or second embodiment of the present invention can be applied;

FIG. 6 is a waveform diagram used to explain the relationship between an optical signal and a waveform after passing through a high-pass filter in a conventional optical wireless communication device.

[Explanation of symbols]

1, 11: light receiving element, 2, 13: amplifier section, 3: delay section, 4: switch section, 5, 15: hold section, 6,
16 carrier sense section, 10 light emitting element, 17 switch section

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/04 H04L 12/28

Claims (4)

[Claims] 1. An optical wireless communication device comprising: a light receiving element for receiving an optical signal transmitted from another optical wireless communication device; and a high-pass filter for removing a disturbance light component from a signal received by the light receiving element. Detecting means for detecting, from the received signal, a signal section in which a burst signal is present and a non-signal section in which no burst signal is present; and at least a DC signal corresponding to the center level of the signal in the signal section And a center level inserting unit for inserting the received signal into the no-signal section of the received signal. 2. The optical device according to claim 1, further comprising a delay unit that delays the reception signal by a time corresponding to the predetermined time when the detection by the detection unit is delayed by a predetermined time. Wireless communication device. 3. The central level inserting means includes: a DC signal generating means for generating a DC signal corresponding to at least a central level of a signal in the signaled section; Switching selecting means for selecting a signal of the signaled section of the received signal, and selecting the DC signal generated by the DC signal generating means when a non-signal section is detected by the detecting means. The optical wireless communication device according to claim 1 or 2, wherein: 4. A DC signal generating means for generating a DC signal corresponding to at least a central level of a signal in the signaled section; a central level inserting means provided near a light receiving surface of the light receiving element; 2. The optical wireless communication apparatus according to claim 1, further comprising: a light emitting unit that emits light having an intensity corresponding to the DC signal generated by the DC signal generating unit when a no-signal section is detected by the unit. .