JP2013183395A - Optical space communication system and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical wireless LAN system enabling efficient access between devices, without causing an interference problem if optical transmission/reception directivity between a base station device B and a plurality of terminal devices T is widely set, and enabling application to a mobile.SOLUTION: Bidirectional communication between the base station device B and each terminal device T is performed through space communication using light as a medium. Data transmission from the base station device to the terminal device T is performed through baseband transmission, whereas data transmission from the terminal device T to the base station device is performed through broadband transmission including a carrier wave having a higher frequency than a signal occupation band in the baseband transmission. Multi-channel access from the base station device to the plurality of terminal devices T is performed using the TDMA system, whereas multi-channel access from the plurality of terminal devices T to the base station device B is performed using the FDMA system. The base station device includes a visible light transmitter 13 and an infrared receiver. Each terminal device T includes a visible light receiver 34 and an infrared transmitter 42.

Description

  The present invention relates to an optical space communication system and apparatus for connecting devices such as portable personal computers and portable terminals over a wireless network using light as a medium, and in particular, a plurality of terminal apparatuses and base station apparatuses can be connected to each other without interference. The present invention relates to a communication method and apparatus for enabling connection.

  In recent years, an optical wireless network (LAN) using infrared rays, as shown in Patent Document 1, has been proposed. Further, as shown in Patent Document 2, an optical wireless LAN system using visible light communication as a downlink and infrared communication as an uplink has been proposed.

  In these optical wireless networks, a broadband transmission system or a baseband transmission system is adopted as a transmission system. The baseband transmission system has a simpler circuit configuration than the broadband transmission system and can be used even in fields with high transmission speeds. The broadband transmission system is a method for the optical noise generated from fluorescent lamps and monitors. There is a merit that it is not easily affected and is relatively resistant to long-distance transmission.

  Therefore, in the conventional optical wireless network, any one of the above transmission methods is adopted according to the purpose of use. Also, as shown in Patent Document 3, an optical space communication device has been proposed in which a single device is used by switching between a baseband transmission method and a broadband transmission method.

JP 2003-304205 A JP 2009-225196 A JP-A-11-239103

  The transmission mode of optical wireless communication can be classified into a direct-light system that secures a line-of-sight propagation path between transmitters and receivers and a diffuse reflection system that enables communication even outside the line-of-sight using diffusely reflected light on walls and ceiling surfaces. In addition, for each, there are a directional system that performs directional control of both transmitters and receivers, a non-directional system that does not perform directional control, and a hybrid system in which only one of the transceivers performs directional control.

  As described above, the direct-hybrid system is used in an indoor optical LAN system in which a terminal device is fixed or a moving range is narrow because a direct hybrid method can realize relatively high-speed data transmission with power saving. However, this direct-light hybrid system is not suitable for transmission between a portable information device and a base station apparatus that are supposed to move.

  On the other hand, the direct non-directional method performs medium-sharing one-to-n communication called multi-channel access using the TDMA method or the FDMA method between a base station apparatus having wide directivity and a plurality of terminals. Therefore, when constructing a LAN, a complicated access procedure between the base station apparatus and the terminal apparatus is necessary so that interference between the terminal apparatuses does not occur.

  In particular, when the terminal device is mounted on a portable information device such as a tablet PC, the terminal device transmits and receives data to and from the base station device while moving. Widening is desired. However, if the directivity of optical transmission / reception is widened in the direct-light omnidirectional method, the possibility of interference between devices increases.

  For example, when the downlink and uplink multichannel access is a TDMA system, there are the following problems. First, in the TDMA system, the downlink is performed by baseband transmission, the uplink is performed by broadband transmission, the frequency band used by the downlink and the uplink is divided, and both the downlink and uplink access procedures are the TDMA system. Although the transmission rate is higher than when the uplink is an FDMA system, the transmission rate is reduced because the uplink transmission rate is high. In addition, the TDMA system requires an inter-packet gap and requires packet overhead, which deteriorates transmission efficiency. Further, since the transmission light of the slave unit is received by itself, the base station device returns the signal from the slave unit and is received by the slave unit. The slave unit receives the return signal from the base station device simultaneously with the self-transmission. Comparison is made, and if it matches, the transmission is continued, if it does not match, the transmission is stopped, and transmission is performed again after a time, and access control based on the carrier sense multi-channel access / collision detect (CAMA / CD) method is performed. Since it cannot be performed, there is a problem that transmission efficiency deteriorates.

  On the other hand, when the downlink and uplink are performed by baseband transmission of the same band and both access control is performed by the TDMA method, for example, a terminal device that performs uplink transmission needs to suppress transmission power with a battery-driven portable device, If the transmission rate is set to be reduced at a trade-off relationship in order to secure the transmission distance, the time rate of the uplink will increase and the room for the downlink to be interrupted will be drastically reduced, and the speed of the down will be greatly reduced. There is.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and its purpose is to adopt a direct-light non-directional method between a base station device and a terminal device provided on a mobile unit. Provided is an optical space communication method and apparatus that enables efficient access without causing interference between terminal apparatuses even when the directivity of optical transmission / reception of a plurality of terminal apparatuses is set widely. There is.

  In order to achieve the above object, an optical space communication system and apparatus of the present invention performs data transmission from a base station apparatus to a terminal apparatus by baseband transmission, and performs data transmission from the terminal apparatus to the base station apparatus. The transmission is performed by broadband transmission having a carrier having a frequency higher than the occupied band of the baseband transmission signal. In this case, TDMA is used for multichannel access from a base station apparatus to a plurality of terminal apparatuses, and FDMA is used for multichannel access from a plurality of terminals to a base station apparatus.

  In the present invention, the base station device may be built in the lighting device, and data transmission may be performed by a light emitting element of the lighting device. Further, a base station device or a single terminal device used in the optical space communication system as described above is also an aspect of the present invention.

  According to the present invention, by attaching a terminal device provided with a wide-directional light transmitting / receiving unit to a portable information device such as a tablet PC, wireless LAN access using a moving light as a medium becomes possible. Even if there are a plurality of information terminals, information terminals provided in each portable information device can simultaneously perform wireless LAN access.

The network figure which shows the whole structure of the optical space communication system of this invention. The top view which shows the external shape of the terminal device and portable information device in embodiment of this invention. The block diagram which shows embodiment of the base station apparatus in this invention. The block diagram which shows embodiment of the terminal device in this invention. The graph which shows the frequency band which an uplink and a downlink in embodiment of this invention use.

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

[1. Overall configuration: FIGS. 1 to 3]
As shown in FIG. 1, the system of the present embodiment includes a base station device B provided in a lighting fixture having an optical communication function, and a terminal device T provided in each portable information device M such as a tablet personal computer. ing.

  The base station device B is connected to a server device or the Internet N by a network cable, and the terminal device T is attached to the portable information device M by means such as USB connection. As a result, a one-to-n LAN system configured by connecting the portable information device M to the Internet N or a server via the base station device B provided in the lighting fixture is configured.

  FIG. 2 is a perspective view showing an example of the portable information device M and a terminal device T attached to the portable information device M. The terminal device T is provided with a transmitting LED 2 and a light receiving photodiode (hereinafter referred to as PD) 3 on the upper surface of the case 1, and a USB terminal 4 on the side surface of the case 1. By inserting the USB terminal 4 into the USB connector 5 provided in the portable information device M, the terminal device T is connected integrally with the portable information device M, and exchanges data and supplies power between the two.

  In this embodiment, the downlink for transmitting data from the base station apparatus B to the terminal apparatus T is performed by visible light communication using the baseband transmission method, and the uplink for transmitting data from the terminal apparatus T to the base station apparatus B is broadband. This is done by infrared communication using the transmission method.

  In this case, the occupied bandwidth of the uplink broadband transmission signal is performed by a carrier having a frequency higher than the occupied bandwidth of the downlink baseband transmission signal, and TDMA is used for downlink multi-channel access (multiplexing method). The FDMA method is used for uplink multi-channel access. As the modulation method, the downlink performs 4-level PPM modulation (pulse-position modulation), and the uplink performs 4-channel ASK modulation (amplitude shift keying).

  FIG. 3 is a graph showing the frequency bands of the downlink and the uplink. In this embodiment, the downlink uses a TDMA scheme in a frequency band of 10 MHz or less, and the uplink uses an FDMA scheme having four transmission frequency bands in a frequency band from 10 MHz to 20 MHz.

  Furthermore, this embodiment, which employs the direct-light non-directional method, reduces the transmission speed that has a trade-off relationship with the transmission distance in order to secure the transmission distance because the amount of light reaching the receiving end decreases because the transmission light is diffused over a wide range. Therefore, the transmission efficiency must be set lower than that of the direct hybrid system, so the downlink transmission rate is set to 4 Mbps and the uplink transmission rate is set to 156.25 kbps.

  In this case, the downlink 4 Mbps is slower in speed than the conventionally proposed direct-light hybrid system, but corresponds to wide directivity by the direct-light omni-directional system. Moreover, it is suitable when not using a special LED for transmission of the base station apparatus B but using a phosphor use type LED with a relatively slow response speed generally used in illumination.

  On the other hand, the uplink 156.25 kbps has a trade-off relationship in order to secure transmission distance in the terminal device T supplied with power from the portable information device M, and has a trade-off relationship. This is a result of limiting. Therefore, this embodiment is an unbalanced system in which the uplink is considerably slower than the downlink, but it is assumed that the amount of uplink transmission is small, such as recent cloud computing and usage as a remote PC. This is a highly usable wireless solution.

[2. Configuration of base station apparatus B ... FIG. 4]
In order to employ the two transmission methods as described above, the base station apparatus B and the terminal apparatus T are each provided with a visible light communication unit and an infrared communication unit. FIG. 4 is a block diagram showing a configuration of base station apparatus B.

  In FIG. 4, reference numeral 10 denotes a network interface unit for connecting the base station apparatus B to the network N, which includes a RJ-45 standard connection terminal 11 and a 10 / 100BASE-TX Ethernet (registered trademark, the same applies hereinafter) interface. Has a function to convert to MII (Media Independent Interface).

  The network interface unit 10 is connected to a signal processing unit 12 constituted by a CPLD (Complex Programmable Logic Device). The signal processing unit 12 is a block that performs digital processing, adds information such as a frame length to the Ethernet frame received from the MII, performs four-value PPM modulation, and transmits the serial information. The signal processing unit 12 deletes the frame length information and the like from the frame received from the 4-channel infrared receiving unit to form an Ethernet frame, and then multiplexes the 4 channels and sends them to the network interface unit 10 side.

Therefore, the signal processing unit 12 has the following configuration and functions as an example.
(a) A receive buffer that stores information frames.
(b) A transfer arbiter that transmits data after adding a preamble and SFD to the information frame stored in the corresponding reception buffer.
(c) During transmission of the information frame, the receiving unit of the network interface unit 10 is monitored to check that no collision has occurred in the information frame being transmitted.
(d) The information frame in the reception buffer is erased after transmission of all contents of the information frame being transmitted is completed.
(e) When a collision is confirmed during transmission, transmission is immediately stopped, an information frame is secured, and transmission is attempted again after the back-off timer expires.

  The signal processor 12 is connected with a visible light transmitter 13 for downlink and an infrared receiver 16 for uplink. The visible light transmitter 13 is provided with an LED drive circuit 14 that causes the LED 15 for transmission to emit light at a period corresponding to data transmission based on the four-value PPM signal received from the signal processor 12. In the present embodiment, the LED 15 has a luminescent color such as white or daytime that can also be used as a lighting device.

  The infrared receiving unit 16 is provided with a light receiving element (hereinafter referred to as PD) 17 that receives infrared rays used for the uplink. Since PD17 is a direct omnidirectional system as PD17, the thing of the large diameter which can ensure the viewing angle of full width at half maximum of 120 degree | times is preferable as directivity. An optical-electrical signal (O / E) conversion circuit 18 is connected to the output side of the PD 17, and a band-pass filter 19 for four channels is connected to the output side of the optical-electrical signal conversion circuit 18.

  An amplifier 20 is connected to the output side of the band-pass filter 19 for each channel, and an ASK demodulator circuit 21 for demodulating received transmission data and a carrier sense circuit 22 for detecting a collision between the channels on the output side of the amplifier 20. Is connected. The output sides of the ASK demodulation circuit 21 and the carrier sense circuit 22 are connected to the signal processing unit 12.

[3. Configuration of Terminal Device T ... FIG. 4]
The terminal device T includes a device-side interface unit 30 for connecting to the portable information device M. As an example, the device-side interface unit 30 is provided with a USB connection terminal 31. A visible light receiving unit 33 and an infrared transmitting unit 38 are connected to the device side interface unit 30 via a signal processing unit 32.

  The visible light receiving unit 33 is provided with a PD 34 that receives downlink visible light, and a binarization circuit 37 is connected to the output side of the PD 34 via an optical-electrical signal conversion circuit 35 and an amplification circuit 36. Has been. The output of the binarization circuit 37 is input to the signal processing unit 32.

  The infrared transmitter 38 is provided with an ASK modulation circuit 39 including a carrier frequency changeover switch 40. The changeover switch 40 is used to select which frequency of the infrared rays the terminal device T uses to uplink data. As a selection method, an infrared frequency used by another terminal device T is detected via the base station device B, and a channel having a frequency other than that is used. And a method in which the user manually switches each time can be used.

  A transmission signal from the portable information device T supplied via the device-side interface unit 30 is input to the ASK modulation circuit 39. The output side of the ASK modulation circuit 39 is connected to an LED 42 for infrared light emission via an LED drive circuit 41.

[4. Downlink processing]
The downlink processing is performed in the following procedure.
(1) When a signal for transmission is input from the network N or the server device to the base station device B, the signal processing unit 12 causes the network interface unit 10 to detect a significant information frame from the input signal. This is modulated into a 4-value PPM and sent to the visible light transmitter 13. In the 4-value PPM modulation processing, bit information in a data frame is identified by the positions of four bit flags prepared as 2-bit units.

(2) The visible light transmission unit 13 transmits a signal by visible light from the LED 15 toward the plurality of terminal devices T by blinking the LED 15 by the LED driving circuit 14 based on the 4-value PMM signal. In this case, transmission data transmitted from the LED 15 is performed using the TDMA method in a frequency band of 10 MHz or less.

(3) When the terminal device T receives the visible light signal from the base station device B by the PD 34 of the visible light receiving unit 33, the terminal device T converts the signal into an electrical signal by the optical-electrical signal conversion circuit 35, and then amplifies it. After being amplified by the circuit 36, it is converted into a digital signal by the binarization circuit 27 and sent to the signal processing unit 32.

(4) The signal processing unit 32 converts this input signal into a signal in a format that can be used by the portable information device M, and sends it to the portable information device M via the USB terminal 31 of the device-side interface unit 30.

  As described above, in the present embodiment, the downlink from the LED 15 uses the baseband transmission based on the TDMA method in the frequency band of 10 MHz or less, and therefore, the high-speed data is transmitted using the entire frequency band. Transmission is possible. Moreover, although LED which emits visible light has the characteristic that the responsiveness in a high frequency is inferior, in this embodiment, since the visible light part uses a low frequency band, such a problem does not arise. Furthermore, in the present embodiment, the frequency bands of the uplink and the downlink are divided, so even if the TDMA scheme is adopted, there is no interference between the uplink and the downlink, and the downlink can be performed at a high speed.

[5. Uplink processing]
Uplink processing is performed in the following procedure.

(1) Data input from the portable information device M to the device-side interface unit 30 via the USB terminal 31 is converted into a signal capable of ASK modulation by the signal processing unit 32.

(2) The ASK modulation circuit 39 modulates a signal supplied from the device-side interface unit 30 using any of the frequencies of the four channels in FIG. Output to 40.

(3) The LED driving circuit 40 blinks the infrared light emitting LED 41 based on the signal from the ASK modulation circuit 39 and transmits data to the base station apparatus B.

(4) After the signal from the terminal device T detected by the PD 17 of the infrared receiver 16 of the base station device B is separated by the band-pass filter 19 based on a total of four carriers and distributed to each channel The signal is sent to the signal processing unit 12 via the ASK demodulation circuit 21 and the carrier sense circuit 22.

(5) When the signal processing unit 12 detects the SFD that is the head of the information frame for each channel, the signal processing unit 12 extracts the frame length information stored following the SFD, and the information has a size according to the content. The frame is stored in a reception buffer (not shown) prepared individually for each channel.

(6) When the transfer arbiter provided in the signal processing unit 12 confirms the presence of the reception buffer storing the information frame to be relayed by period monitoring, the transfer arbiter confirms the status of the network interface unit 10 and transmits the information frame. When it is determined that the data frame can be transmitted, the network interface unit 10 transmits data to the network N after adding a preamble and SFD to the information frame stored in the corresponding reception buffer.

(7) The transfer arbiter monitors the receiving unit of the network interface unit 10 during transmission of the information frame, and monitors whether a collision has occurred in the information frame being transmitted.

(8) The signal processing unit 12 deletes the information frame in the reception buffer after the transmission of all the contents of the information frame being transmitted is completed. In this case, if a collision is confirmed during transmission, transmission is immediately stopped, an information frame is secured, and transmission is attempted again after the back-off timer expires.

[6. Effects of the embodiment]
According to the present embodiment, full-duplex communication is possible by using a band above the download band, and even if access from a plurality of terminal apparatuses T to the base station apparatus B occurs simultaneously, the downlink speed Will not be affected.

  Further, in the present embodiment, the transmission speed can be increased by performing download in visible light communication with a high frequency limit by baseband modulation with high frequency utilization efficiency. On the other hand, since the uplink is performed by broadband modulation, the transmission distance can be secured by reducing the transmission speed according to the power supply capability of the terminal.

[7. Other Embodiments]
The present invention is not limited to the above-described embodiment, and includes other embodiments as follows.

(1) Although only one base station apparatus 1 is shown in the illustrated embodiment, server devices and the Internet can be connected by cascading a plurality of base station apparatuses 1 arranged at predetermined intervals. It is also possible to connect to N.

(2) In the illustrated embodiment, the terminal device T is detachable from the portable information device M by USB connection, but may be connected by another interface, and the terminal device T is integrated in the portable information device M. It can also be incorporated.

(3) Instead of incorporating the base station apparatus B into the lighting apparatus, the base station apparatus can be used by an apparatus having only LEDs dedicated for optical communication.

(4) The present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

B ... Base station device T ... Terminal device M ... Portable information device N ... Network 10 ... Network interface unit 12, 32 ... Signal processing unit 13 ... Visible light transmission unit 15, 41 ... LED
16 ... Infrared receiver 17, 34 ... PD
30 ... Device side interface unit 33 ... Visible light receiving unit 34 ... Infrared transmitting unit

Claims (5)

Data transmission from the base station apparatus to the terminal apparatus is performed by baseband transmission, and data transmission from the terminal apparatus to the base station apparatus is performed by broadband transmission having a carrier having a frequency higher than the occupied band of the baseband transmission signal. In optical space communication system,
An optical space communication system using TDMA for multichannel access from the base station apparatus to a plurality of terminal apparatuses and FDMA for multichannel access from a plurality of terminals to the base station apparatus.   The optical space communication system according to claim 1, wherein the base station device is built in a lighting device, and data transmission is performed by a light emitting element of the lighting device.   The optical space according to claim 1 or 2, wherein data transmission from the base station device to the terminal device is performed by visible light communication, and data transmission from the terminal device to the base station device is performed by infrared communication. Communication method. Light having a transmitter and a receiver that perform data transmission to the terminal device by baseband transmission, and perform data transmission from the terminal device by broadband transmission having a carrier having a frequency higher than the occupied band of the baseband transmission signal In a base station device for spatial communication,
A base station apparatus for optical space communication, wherein TDMA is used for multichannel access to a plurality of terminal apparatuses, and FDMA is used for multichannel access from a plurality of terminals. A transmission unit and a reception unit that perform data transmission from the base station device by baseband transmission, and perform data transmission to the base station device by broadband transmission having a carrier having a frequency higher than the occupied band of the baseband transmission signal. In a terminal device for optical space communication,
A terminal apparatus for optical space communication, wherein TDMA is used for multichannel access from a base station apparatus, and FDMA is used for multichannel access to the base station apparatus.

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