KR101258879B1 - Multi-Input Multi-Output Visible Light Communication System - Google Patents

Abstract

An object of the present invention is to provide a multiple input and output visible light communication system, which enables multiple input and output while transmitting a signal using the visible light.
According to the present invention, in the Visible Light Communication (VLC) system 100 capable of Multi-Input Multi-Output Visible Light (MIMO), a plurality of output units 111 respectively outputting visible signals are provided. A transmission unit (110) for distributing transmission signals to a plurality of the output units (111); A receiver 120 having a plurality of input units 121 each receiving a visible light signal, and combining the optical signals received by the plurality of input units 121 into received signals; Located on the optical path between the output unit 111 and the input unit 121, when the optical signals output from the plurality of output unit 111 is input to the plurality of input unit 121 at intervals that can be resolved with each other An optical system 130 for adjusting an optical path to be input; And a control unit.

Description

Multi-Input Multi-Output Visible Light Communication System

The present invention relates to a multiple input and output visible light communication system.

Visible light communication technology has emerged as a technology that can be used as a communication light source, such as light emitting diodes (LEDs) that emit light by semiconductors, as semiconductors are also being used as lightings after memory and processors. . In other words, the LED lighting communication convergence is a fusion technology capable of communicating at the same time while lighting through the LED, the lighting is also visible light wireless communication or visible light communication because visible light visible. Visible light communication technology is a communication technology that combines digital lighting and communication, there is a convenience that communication can be visually confirmed. In the visible light communication technology, as described above, LED lights emitting light by semiconductors are used. Since the LED lights can be digitally controlled, the technology development speed is higher than that of conventional analog lights, and various multimedia lights and It can provide a communication service.

Light used in visible light communication has a wavelength of 780nm to 380nm. Converting this wavelength to frequency corresponds to 385 THz to 789 THz (frequency band = speed of light (300,000,000 m) / wavelength (380 ㅧ 1000)), with the audible (audio) frequency band corresponding to 20 Hz to 20,000 Hz. , IrDA using infrared wavelengths, IEEE 802.11n at 2.4 Hz, UWB, 802.15.4 Zigbee, Bluetooth, IEEE802.15-3c at 60 GHz, and visible light communication is 800-900 nm among conventional communication methods. It uses the most similar wavelength to IrDA, but it can communicate with lighting at the same time.

In case of using visible light communication, it uses light used as lighting, so it is harmless to human body unlike the conventional communication method using various kinds of electromagnetic waves, does not need to obtain frequency permit, no interference with ISM, and physical security function. There are a number of advantages, including the ability to provide high precision positioning and use for ultra-precision positioning. In particular, fluorescent lamps, which are typical analog lights used in the related art, have a problem that emissions of environmentally destructive materials are generated during production or disposal, whereas LED lighting is more environmentally friendly, and saves more than 90% of power, Because of its longevity, the US, Europe, and Japan are enacting legislation that recommends changing existing lighting fixtures to LED lighting. According to this global trend, the LED lighting infrastructure is expected to be further expanded, and thus the utilization area of visible light communication as described above is expected to be further expanded.

On the other hand, MIMO (Multi-Input Multi-Output) system is widely used in the current communication field, and refers to an antenna system capable of multiple input and output. In other words, by increasing the number of antennas of the base station and the portable terminal to two or more, the data is transmitted in various paths, and the receiving end detects the signals received in each path.

The principle of the MIMO (multi-input / output) system will be described in more detail with reference to examples in the fields currently being applied. Existing wireless LAN uses only one antenna according to the direction of AP (Access Point) connecting the wired network to the wireless network even though there are two antennas, but MIMO allows two antennas to operate simultaneously for high-speed data exchange. To make it possible. An independent signal is transmitted to N transmit antennas using the same frequency at the same time. The transmitted signals undergo spatially different fading on the wireless channel (a phenomenon in which the intensity of the received radio waves fluctuates in response to changes in the medium through which the received radio waves pass), resulting in non-correlation between the signals received by each antenna. . In this way, by transmitting different signals for each transmitting antenna, more data can be transmitted by the number of transmitting antennas (N) than before.

Advantages of using this MIMO technology are as follows. First of all, the existing wireless LAN has a speed of 54Mbps with ieee802.11g standard, whereas wireless LAN products equipped with MIMO technology show transmission speed of 250 ~ 500Mbps. In other words, by using the MIMO technology, there is an advantage that can significantly increase the transmission speed. In addition, the use of MIMO technology improves the transmission speed as well as the reach by four times compared to the existing WLAN. As such, MIMO technology is one of very efficient technologies that can easily improve the transmission speed and the reach by simply improving the antenna structure.

However, there is a difficulty in applying such MIMO technology to a VLC (visible light communication) system as described above. In the case of radio waves, when several different signals are transmitted at the same time as described above, even if interference occurs or mixed with each other, it is relatively easy to separate the signals into respective original signals. There is no big crowd. However, in the case of VLC, the medium that transmits the signal is visible light, which is very difficult to separate when it interferes or mixes with each other. Therefore, it is well known that it is almost impossible to apply MIMO technology to VLC as it is.

Accordingly, the present invention has been made to solve the problems of the prior art as described above, an object of the present invention is to perform the transmission and reception of signals using visible light, but to enable multiple input and output data transmission and reception in the visible light communication system An object of the present invention is to provide a multiple input / output visible light communication system capable of increasing capacity and speed.

In order to achieve the above object, the multiple input / output visible light communication system of the present invention is a visible light communication (VLC) system 100 capable of multiple input / output (Multi-Input Multi-Output Visible Light, MIMO). A transmission unit (110) having a plurality of output units (111) each outputting a visible light signal, and distributing transmission signals to the plurality of output units (111); A receiver 120 having a plurality of input units 121 each receiving a visible light signal, and combining the optical signals received by the plurality of input units 121 into received signals; Located on the optical path between the output unit 111 and the input unit 121, when the optical signals output from the plurality of output unit 111 is input to the plurality of input unit 121 at intervals that can be resolved with each other An optical system 130 for adjusting an optical path to be input; And a control unit.

In this case, the optical system 130 may include a first lens 131 that refracts the optical signals output from the plurality of output units 111 in a converging direction, and optical signals passing through the first lens 131. And a second lens 132 refracted in the diffusion direction. In this case, the optical system 130 may be formed such that the second lens 132 is disposed inside the focal length of the first lens 131.

In addition, the multiple input / output visible light communication system 100 is characterized in that a plurality of the output unit 111 is arranged in a one-dimensional linear form consisting of a single row or column. Alternatively, the multiple input / output visible light communication system 100 is characterized in that a plurality of the output unit 111 is arranged in a two-dimensional matrix form consisting of a plurality of rows and columns.

In addition, the output unit 111 is characterized in that it is implemented as a light emitting diode (LED).

In addition, the input unit 121 may be implemented as a photodiode.

According to the present invention, by introducing multiple input / output technologies in a visible light communication system, there is a great effect that a large amount of data can be easily and accurately transmitted and received even in visible light communication at a higher transmission speed than in the prior art. More specifically, according to the present invention, multiple inputs and outputs of the signals in the visible light communication can be realized by transmitting the multiple output signals in the visible light communication using an appropriate optical system so that the multiple inputs can be made. There is an effect that makes it possible.

Of course, according to the present invention, there is an effect of greatly extending the limits of the amount of data and the transmission rate that can be transmitted in the visible light communication system, and thus, the effect of extending the scope of application of the visible light communication system is also obtained. Can be.

1 is a visible light communication system using a simple multiple input and output technology.
2 is a principle of Fraunhofer diffraction.
3 is a principle of Airy disc and Rayleigh reference.
4 is a multiple input and output visible light communication system of the present invention.
5 illustrates embodiments of a multiple input / output visible light communication system of the present invention.
Figure 6 is an embodiment of the multiple input and output visible light communication system output unit of the present invention.
7 and 8 illustrate a prototype of a multiple input / output visible light communication system of the present invention.

Hereinafter, a multiple input / output visible light communication system according to the present invention having the configuration as described above will be described in detail with reference to the accompanying drawings.

1 schematically illustrates a visible light communication system using a simple multiple input / output technique. The transmitter 110 separates a plurality of transmission signals TX data into a plurality of output signals 111, and outputs each of them through a plurality of output units 111. In the receiver 120, a plurality of input units 121 each of the output units ( 111 receives the output signal and combines it with the received signal (RX Data). In this case, in the case of the visible light communication system, the output unit 111 may be a device such as an LED that can output visible light, and the input unit 121 may also be a device capable of sensing visible light. For example, it may be a device such as a photodiode.

However, as can be seen from the line marked in bold in FIG. 1, the signals transmitted from the plurality of output units 111 are introduced into one input unit 121 at a time. In this case, in the case of radio waves that are not visible light, various techniques for separating even if several different signals come in at the same time (for example, a technique for allowing separate input at a later point in time when multiple transmission signals are outputted). In the case of visible light, since its characteristics are very different from those of general radio waves, it is difficult to apply the conventional techniques in the communication technology using general radio waves. That is, as shown in FIG. 1, when the visible light emitted from the plurality of outputs 111 is combined into a single input unit 121, each of the lights interferes with each other, making it impossible to separate them. Therefore, it becomes impossible to extract meaningful data from the signals.

In order to solve this problem, in the present invention, by placing a suitable optical system between the output unit 111 and the input unit 121, the visible light signal emitted from each output unit 111 is easily separated into the input unit 121. It can be input. Here, the optical theory related to the threshold of the interval at which each of the multiple visible light signals received by the input unit 121 can be sufficiently and stably separated will be described.

2 briefly illustrates the principle of Fraunhofer diffraction. As shown in Fig. 2 (A), when a wall is obstructed in the direction of wave propagation and there is a small gap in the wall, the wave bends to a certain range around it as well as a straight path through the gap. This phenomenon is called diffraction. Fraunhofer diffraction refers to diffraction occurring in a plane wave, and FIG. 2 shows the principle of Fraunhofer diffraction due to a circular gap. As shown in Fig. 2A, the distance from the center of the circular gap to any one point in the radial direction is y, and the point at which the diffracted light reaches the incident surface from any one point is P. If the position vector from any one point to the point P is r and the angle of the r vector is θ, a plane wave as shown in Equation 1 below is incident. The intensity is calculated as in Equation 2. (The principles and calculations of these Fraunhofer diffraction are well known in general optical theory.)

When calculated in this manner, the intensity of the diffracted light due to the circular gap is shown in the form as shown in Fig. 2 (B), when it is displayed three-dimensionally as shown in Fig. 2 (C).

3 illustrates the principle of Airy discs and Rayleigh criteria. In fact, the measurement result of the diffracted light due to the circular gap is shown in Fig. 3 (A), that is, the bright and dark rings centered on the bright spot in the center appear concentrically. (It is the brightness of these rings that is represented by the diffracted light intensity in FIG. 2 (B) or FIG. 2 (C).) At this point, the bright point in the center (ie, the diffracted light traveling from the central axis as seen in FIG. 2 (B)) The area where the intensity graph appears to the first zero point is called an airy disc. When the wavelength of light is λ and the diameter of the circular gap is D, the size of the airy disk is shown as shown in Fig. 3B.

From this Airy disk, Rayleigh's criterion emerges. The Rayleigh criterion is a decomposition criterion between two point sources, indicating that the two point sources can barely resolve when the center of one diffraction pattern coincides with the first minima of the other diffraction pattern.

2, 3 and related descriptions are only for explaining the basic principle of the diffraction of light, and when the square wave is used, the calculation must be performed using the Fresnel diffraction principle, Naturally, various optical principles should be applied, without being limited to FIGS. 2, 3 and related descriptions, such as considering other factors when applied. These optical principles correspond to general optical knowledge, and the description of the basic optical principles will be omitted here, and a detailed description thereof will be omitted.

By applying the optical principles as described above, in applying the multi-input / output technology in the visible light communication system, it is possible to predict the minimum resolution of each input and output signal resolution, and if the input signal is to be more than this minimum interval visible light communication In the system, it can be expected that the input signals can be resolved without being mixed with each other, as shown in FIG.

4 illustrates a multiple input / output visible light communication system of the present invention. As shown, the multi-input multi-output (MIMO) visible light communication (VLC) system 100 of the present invention, the transmitter 110, as shown in FIG. , Including the receiver 120 and the optical system 130.

As shown, the transmitter 110 includes a plurality of output units 111 for outputting visible light signals, respectively, to distribute the original transmit signal TX data to the plurality of output units 111. give. In this way, a plurality of divided transmission signals are output through each of the output units 111, so that multiple outputs of the optical signals by the transmitter 110 are performed. In this case, the output unit 111 is preferably implemented as a light emitting diode (LED), which is generally used as an output unit in a visible light communication system, so as to easily make an optical signal in which desired data is added to a visible light signal.

As shown in the drawing, the receiver 120 includes a plurality of input units 121 for receiving a visible light signal, respectively, to combine the optical signals respectively received by the plurality of input units 121 into a received signal RX data. Play a role. That is, multiple inputs of the optical signals are performed by receiving the optical signals with the plurality of input units 121 provided in the receiver 120. In this case, the input unit 121 may be implemented as a photodiode. At this time, it is shown in the drawing as if one input unit 121 corresponds to one output unit 111, but of course, the input unit 121 is not so formed, and for example, a plurality of photoelectric elements are planar. It can be implemented such as to be made in the form that is arranged in two dimensions.

In this case, when only the transmitter 110 and the receiver 120 exist, as described with reference to FIG. 1, optical signals transmitted from each output unit 111 of the transmitter 110 are mixed into the input unit 121. As a result, it is impossible to separate each optical signal, and thus, it is difficult to reconstruct the received signal. In the present invention, the optical system 130 positioned on the optical path between the output unit 111 and the input unit 121 as shown in FIG. 4 solves this problem and enables multiple input / output in a visible light communication system. Let's do it.

As described above, the optical system 130 is positioned on an optical path between the output unit 111 and the input unit 121, so that the optical signals output from the plurality of output units 111 are output to the plurality of input units 121. When inputting to), it controls the optical paths so that they are input at intervals that can be separated from each other. As described above, the point light sources may be separated from each other and sensed if they are arranged at intervals of more than a Rayleigh reference. In the present invention, using the same principle, the optical paths of the multiple output signals transmitted from the plurality of output units 111 are adjusted to be arranged at intervals of more than a Rayleigh reference through the optical system 130 to the input unit 121. By incidence, separate input of each optical signal is made possible.

Hereinafter, the configuration of the optical system 130 will be described in detail. As shown in FIG. 4, the optical system 130 includes a first lens 131 that refracts the optical signals output from the plurality of output units 111 in a convergent direction, and the first lens 131. And a second lens 132 that refracts the optical signals passing through the light signals in the diffusion direction. In the process of first passing the multiple output optical signal through the first lens 131, the optical path is refracted as shown in FIG. 4 and converges in the focal direction. When the converged optical signal is received as it is, the interval between the optical signals may be less than the Rayleigh reference. Therefore, the light signal passes through the second lens 132 so as to be diffused again so as to be spaced apart at appropriate intervals. Thereafter, the input unit 121 is disposed at a position separated by an appropriate distance from the second lens 132 to receive an optical signal, so that a well separated optical signal can be input to each input unit 121.

In this case, in order to minimize interference between the optical signals and more effectively separate the optical signals, the optical system 130 has the second lens 132 as shown in FIG. More preferably, it is formed to be disposed inside the focal length. In addition, as described above, the distance between the first lens 131 and the second lens 132 may also reduce the volume of the optical system 130.

As a specific example, the multiple input / output visible light communication system of the present invention will be described in more detail. FIG. 5 illustrates various embodiments of a multiple input / output visible light communication system according to an embodiment of the present invention. First, as shown in FIG. 5A, the multiple input / output visible light communication system 100 includes a plurality of output units 111 arranged in a single row. Or it may be arranged in a one-dimensional linear form consisting of columns. In FIG. 5A, a plurality of the output units 111 are arranged in a vertical direction to form a single column, but of course, this is only one example, and the plurality of the output units 111 are horizontal. It may be arranged in a direction to form a single row, or may be arranged to form a diagonal direction or a predetermined angle.

In addition, as illustrated in FIG. 5B, the multiple input / output visible light communication system 100 may be configured such that a plurality of the output units 111 are arranged in a two-dimensional matrix form having a plurality of rows and columns. . Although FIG. 5B depicts a 2 × 2 matrix for simplicity, of course, the number of rows and columns can be increased.

As shown in FIG. 5A and FIG. 5B, the multiple output signals transmitted from the plurality of output units 111 form the same arrangement as S1, and the first lens 131. As it passes through the refraction, the arrangement itself is maintained as in S2, but only the size is reduced. At this time, the optical signals are refracted in the direction in which the optical signals are diffused while passing through the second lens 132, such that the interval between the optical signals is sufficiently widened as in S3 to be equal to or greater than the Rayleigh reference. ), Each optical signal can be easily received separately.

In order to realize multiple inputs and outputs by the system of the present invention, when the multiple outputs of the optical signals are input to the input unit 121, it is only necessary to make a condition that the distance between the optical signals should be at least a Rayleigh reference. This can be easily achieved by appropriately adjusting the gap between the second lens 132 and the input unit 121 or the gap between the first lens 131 and the second lens 132. That is, since the plurality of output units 111 can be separated in any form on the two-dimensional plane through the optical system 130 according to the structure of the present invention, the arrangement of the output unit 111 is illustrated in FIG. It is not limited to 5 at all and may be freely configured according to the intention and purpose of the designer. For example, the outputs 111 may be arranged radially as shown in FIG. 6 (A), or may be arranged without special regularity as shown in FIG. 6 (B). It may be any shape as long as it is disposed on a two-dimensional plane.

7 and 8 illustrate one embodiment of a prototype of a multiple input / output visible light communication system of the present invention. As shown in the photograph of FIG. 7, the multi-input / output visible light communication system of the present invention outputs a plurality of optical signals from a transmission unit in which a plurality of LEDs are arranged on a plane, and passes through an optical system including a first lens and a second lens. A plurality of optoelectronic devices are arranged to form a plane, and each optical signal is separately incident to each other to allow multiple inputs.

8 is an illustration showing that the optical signal is actually separated by the optical system proposed in the present invention. When the optical system is removed (i.e. in the system as shown in FIG. 1) as shown in the upper photograph of FIG. It can be seen that they are mixed and spread inseparably from each other. At this time, when the optical system proposed in the present invention is introduced as shown in the upper photograph of FIG. It clearly shows that the call is received very well separated.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It goes without saying that various modifications can be made.

100: multiple input / output visible light communication system (of the present invention)
110: transmitting unit 111: output unit
120: receiving unit 121: input unit
130: optical system
131: first lens 132: second lens

Claims (7)

In the Visible Light Communication (VLC) system 100 capable of Multi-Input Multi-Output Visible Light (MIMO),
A transmitter 110 having a plurality of output units 111 for outputting visible light signals, respectively, for distributing transmission signals to the plurality of output units 111;
A receiver 120 having a plurality of input units 121 each receiving a visible light signal, and combining the optical signals received by the plurality of input units 121 into received signals;
Located on the optical path between the output unit 111 and the input unit 121, when the optical signals output from the plurality of output unit 111 is input to the plurality of input unit 121 at intervals that can be resolved with each other An optical system 130 for adjusting an optical path to be input;
And,
The optical system 130 may include a first lens 131 that refracts the optical signals output from the plurality of output units 111 in a converging direction, and diffuses the optical signals passing through the first lens 131. And a second lens (132) refracting in the direction.
delete The method of claim 1, wherein the optical system 130
And the second lens (132) is disposed inside a focal length of the first lens (131).
The method of claim 1, wherein the multiple input and output visible light communication system 100
A multiple input and output visible light communication system, characterized in that a plurality of the output unit 111 is arranged in a one-dimensional linear form consisting of a single row or column.
The method of claim 1, wherein the multiple input and output visible light communication system 100
A multiple input and output visible light communication system, characterized in that the plurality of output unit 111 is arranged in the form of a two-dimensional matrix consisting of a plurality of rows and columns.
The method of claim 1, wherein the output unit 111
Multiple input and output visible light communication system, characterized in that implemented by LED (Light Emitting Diode).
The method of claim 1, wherein the input unit 121 is
Multiple input and output visible light communication system, characterized in that implemented as a photodiode.

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