Method, device and system for visible light communication using field sequential color LCD

Abstract

The application provides a method, device and system for visible light communication by using a field sequential color LCD, which uses a direct backlight partition field sequential color liquid crystal display as a medium for visible light communication, and uses RGB three-color LEDs in each backlight partition as signal sources. The three-color LEDs are turned on at the same time in a sub-frame, and can be modulated with three high-frequency signals respectively. Each single-color LED constitutes a single signal source, and the communication capacity obtained by the system is three times that of a space-mixing type LCD used as a transmitting end. The backlight partition and a receiving end jointly constitute a multiple-input multiple-output (MIMO) visible light communication system. Independent modulation of the RGB three-color LEDs of the backlight partition realizes effective simultaneous improvement of the communication capacity and reliability of the system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of visible light communication, and particularly relates to a method, device and system for visible light communication using a field sequential color LCD. BACKGROUND

[0002] Visible light communication can be a powerful supplement to modern communication due to its rich spectrum resources, no need for authorization, strong anti-interference ability, high security, and no electromagnetic radiation interference problem. The characteristic of visible light communication using visible light as an information transmission carrier determines that the transmitter of the visible light communication system can not only be limited to an LED, but also can be any device that can emit light.

[0003] Liquid crystal display (LCD) is one of the most common light-emitting devices, and its application scenarios are wide. It is an important development trend to use LCD for visible light communication. Using LCD as a transmitter of visible light communication aims to realize the integration of display and communication without affecting the normal display of the LCD.

[0004] Traditional technical solutions for implementing visible light communication based on LCD mainly fall into two categories. One category encodes the pixel array displayed by the LCD in the spatial and temporal dimensions at the transmitting end, receives the display content at the receiving end using a receiving device, and uses a computer to decode the information. This solution cannot realize the integration of display and communication, and the communication signal capacity that can be transmitted is low after the pixel information is encoded using pattern information. The other category uses a modulator to control the backlight flicker to transmit information based on the backlight of the LCD, and uses a photodiode or a camera as a receiver to receive the backlight flicker signal. This solution has limited communication capacity and high error rate of the signal received at the receiving end because it only uses one backlight of the LCD as a transmitter of visible light signal.

[0005] Chinese patent application CN114221705A takes advantage of the large number of backlight partitions of Mini-LED backlight and proposes that each backlight partition can independently modulate as a transmitter of a visible light communication system. However, because a conventional spatial color mixing type LCD uses a white LED backlight and a color filter to realize color, only one white LED in each backlight partition can be independently modulated within one frame of time in this solution. The communication capacity of visible light communication using the LCD still has room for improvement. SUMMARY

[0006] Therefore, the present application proposes a method, device and system for visible light communication using a field sequential color LCD, which improves the communication capacity of visible light communication and enhances the reliability of communication by using the field sequential color display principle.

[0007] In a first aspect, the present application provides a method for visible light communication using field sequential color LCD, which is applied to a transmitting end and comprises the following steps:

[0008] encoding and modulating the original data to obtain digital signals;

[0009] sending the digital signals through a plurality of signal sources;

[0010] The plurality of signal sources are composed of RGB LEDs in each backlight partition of the direct backlight partitioned field sequential color LCD, the RGB LEDs in each backlight partition are turned on at the same time in each sub-frame, and the RGB LEDs in each backlight partition send digital signals with independent content.

[0011] Preferably, the relative brightness levels of the RGB LEDs in each backlight partition are determined before the original data is encoded and modulated, and the determination specifically comprises the following steps:

[0012] dividing an input image into a plurality of dimming blocks, each dimming block corresponding to a backlight partition;

[0013] determining the brightness level ratio of the RGB channels of the image content corresponding to the dimming block using a local dimming algorithm;

[0014] determining the relative brightness levels of the RGB LEDs in the backlight partition corresponding to the dimming block in each sub-frame using a local primary color desaturation algorithm according to the brightness level ratio.

[0015] Preferably, the brightness level ratio of the RGB channels of the image content corresponding to the dimming block is determined using a local dimming algorithm, and the determination specifically comprises the following steps:

[0016] determining the brightness level maximum value of the RGB channels of the image content corresponding to the dimming block using a maximum value algorithm, and the brightness level maximum value of each channel is represented as I1 = max(R i,j ) / 255, I2 = max(G i,j ) / 255, I3 = max(B i,j ) / 255, R i,j , G i,j , and B i,j represent the R, G, and B pixel gray scale values corresponding to pixel (i, j), respectively.

[0017] Preferably, the relative brightness levels of the RGB LEDs in the backlight partition corresponding to the dimming block in each sub-frame are determined using a local primary color desaturation algorithm, and the determination specifically comprises the following steps:

[0018] determining the X, Y, and Z stimulus values that the dimming block should reach according to the brightness level ratio;

[0019] obtaining the required three stimulus values when the RGB LEDs are turned on.

[0020] The relative luminance levels of the RGB three-color LEDs in each sub-frame are determined according to the following matrix calculation formula:

[0021]

[0022] Xi represents the relative luminance level of the RGB three-color LEDs in the i-th sub-frame, each row of the matrix represents the tristimulus values when the RGB three-color LEDs are all turned on, Xi represents the X, Y, Z tristimulus values that the backlight block should reach when the RGB three-color LEDs are simultaneously turned on and mixed in the i-th sub-frame.

[0023] Preferably, the process of encoding the original data comprises:

[0024] The original data is encoded using the Manchester encoding method.

[0025] Preferably, the process of modulating the original data comprises:

[0026] A bit sequence corresponding to the original data is generated;

[0027] The bit sequence is converted from serial to parallel and transmitted to each backlight block, and the bit sequence entering each backlight block is converted from serial to parallel to obtain the bit sequence to be transmitted by the RGB three-color LEDs in the same sub-frame, respectively;

[0028] The light pulses corresponding to the RGB three-color LEDs are obtained by using MPPM modulation and OOK modulation.

[0029] In a second aspect, the present application provides a method for visible light communication using a field sequential color LCD, which is applied to a receiving end and used for processing digital signals transmitted by the method of the first aspect, comprising:

[0030] Receiving a plurality of digital signals transmitted by a plurality of signal sources;

[0031] The plurality of signal sources are composed of RGB three-color LEDs of each backlight block in a field sequential color liquid crystal display with direct backlighting, and the RGB three-color LEDs in each backlight block are turned on simultaneously in each sub-frame, and the RGB three-color LEDs in each backlight block transmit digital signals with independent content, respectively;

[0032] Photoelectrically converting the plurality of digital signals to obtain modulation signals to be transmitted by the RGB three-color LEDs, respectively;

[0033] Demodulating the modulation signals to obtain the communication content.

[0034] Preferably, when the photodiode is used as the receiving end, a maximum likelihood detector is used to demodulate the modulated signal.

[0035] In a third aspect, the present application provides a device for visible light communication using a field sequential color LCD, which is applied to a transmitting end and used to implement the method for visible light communication in the first aspect, and comprises:

[0036] a modulation unit configured to encode and modulate the original data to obtain a digital signal;

[0037] a signal transmitting unit configured to transmit the digital signal to a plurality of signal sources, and send the plurality of digital signals through the plurality of signal sources;

[0038] The plurality of signal sources are composed of RGB three-color LEDs of each backlight partition in the field sequential color LCD with direct backlight partitioning, the RGB three-color LEDs in each backlight partition are turned on at the same time in each sub-frame, and the RGB three-color LEDs in each backlight partition send digital signals with independent contents respectively.

[0039] In a fourth aspect, the present application provides a device for visible light communication using a field sequential color LCD, which is applied to a receiving end and used to implement the method for visible light communication in the second aspect, and comprises:

[0040] a receiving unit configured to receive the plurality of digital signals transmitted by the plurality of signal sources;

[0041] The plurality of signal sources are composed of RGB three-color LEDs of each backlight partition in the field sequential color LCD with direct backlight partitioning, the RGB three-color LEDs in each backlight partition are turned on at the same time in each sub-frame, and the RGB three-color LEDs in each backlight partition send digital signals with independent contents respectively.

[0042] a photoelectric conversion unit configured to photoelectrically convert the plurality of digital signals to obtain modulated signals to be transmitted by the RGB three-color LEDs respectively;

[0043] a demodulation unit configured to demodulate the modulated signals to obtain the communication content.

[0044] In a fifth aspect, the present application provides a system for visible light communication using a field sequential color LCD, which comprises a transmitting end, a receiving end and a field sequential color LCD with direct backlight partitioning.

[0045] The transmitting end transmits the digital signals to the field sequential color LCD for communication signal transmission by using the method in the first aspect;

[0046] The receiving end receives the digital signals by using the method in the second aspect;

[0047] The RGB three-color LEDs of each backlight partition of the direct backlight partitioned field sequential color liquid crystal display constitute a plurality of signal sources for emitting a plurality of digital signals transmitted by the emission end, the RGB three-color LEDs in each backlight partition are opened at the same time in each subframe, and the RGB three-color LEDs in the backlight partition respectively send digital signals of independent content.

[0048] From the above technical solutions, the present application has the following beneficial effects:

[0049] The present application uses the direct backlight partitioned field sequential color liquid crystal display as a visible light communication medium, the RGB three-color LEDs in each backlight partition as a signal source, the three-color LEDs are opened at the same time in a subframe, and can be respectively modulated to embed three high-frequency signals, each single-color LED constitutes a single signal source, and the communication capacity obtained by the system is three times that of the mixed color type LCD used as the emission end; the backlight partition and the receiving end jointly constitute a multiple-input multiple-output (MIMO) visible light communication system, and the independent modulation of the RGB three-color LEDs of the backlight partition realizes the effective simultaneous improvement of the communication capacity and reliability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only the embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0051] Figure 1 is a flow chart of the method for visible light communication using the field sequential color LCD according to the embodiment of the present application;

[0052] Figure 2 is a comparison diagram of the backlight state of the single-color field and the mixed color field in a subframe according to the embodiment of the present application;

[0053] Figure 3 is a diagram for determining the brightness level of the RGB three-color LEDs according to the embodiment of the present application;

[0054] Figure 4 is a light pulse diagram obtained by using the MPPM modulation and the OOK modulation according to the embodiment of the present application;

[0055] Figure 5 is a flow diagram of the modulation of the original data according to the embodiment of the present application;

[0056] Figure 6 is a diagram for receiving the bit information transmitted by the emission end using a camera according to the embodiment of the present application;

[0057] Figure 7 is a schematic diagram of transmitting end transmitting bit information received by photodiode array according to an embodiment of the present application;

[0058] Figure 8 is a schematic diagram of visible light communication device applied to transmitting end according to an embodiment of the present application;

[0059] Figure 9 is a schematic diagram of visible light communication device applied to receiving end according to an embodiment of the present application;

[0060] Figure 10 is a system architecture diagram of visible light communication using field sequential color liquid crystal display according to an embodiment of the present application. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0062] The definitions mentioned in the following embodiments of the present application are explained as follows:

[0063] Luminance level: the luminance level output by the dimming block corresponding to the backlight partition is divided into 0-255 levels like the pixel gray scale value. According to the output luminance level of the dimming block, the physical driving level of each LED in the backlight partition can be determined. The commonly used method is to adjust the duty cycle of the pulse driving power supply.

[0064] The color display principle of liquid crystal display mainly includes two types, one is spatial color mixing type color display, and the other is field color sequence (time color mixing) type color display. The traditional spatial color mixing type color display mainly utilizes the limit of spatial resolution of human eye vision. Each liquid crystal pixel on the display panel is composed of three sub-pixels. A red, green and blue filter is respectively placed in front of each sub-pixel. Since the distance between the sub-pixels is very small, the effect observed by the human eye is the mixed effect of the three sub-pixels. In this type of liquid crystal display, the filtering effect of the color filter will cause at least two-thirds of the light to be lost, which will reduce the actual light energy utilization rate of the liquid crystal display. In addition, the sub-pixel structure makes the original resolution of the liquid crystal display become one-third of the original. If the spatial color mixing type LCD is used as the transmitter of the visible light communication system, in the technical solution of adjusting the backlight flicker to transmit visible light communication signal, even if a direct backlight LCD with backlight partitions is used, for each backlight partition, only one white backlight source can be controlled, and the communication rate is not high.

[0065] The field sequential color LCD does not need color filter, and uses time color mixing method to achieve color display effect by using the visual persistence of human eyes. The backlight of the field sequential color LCD does not use single white light source, but uses color backlight source, usually R, G and B three independent light sources, and the backlight of different colors is refreshed in each sub-frame time to achieve color display effect. In the case that the RGB three-color light sources are turned on to form multiple color mixing sub-frames in each sub-frame time, the R, G and B light sources can be independently controlled and modulated, and different high-frequency communication signals are embedded in each sub-frame time, and visible light communication is independently carried out. Compared with the traditional spatial color mixing type LCD, the field sequential color LCD can obtain three times of communication capacity of the spatial color mixing type LCD in the same time under the same number of backlight partitions; at the same time, the field sequential color LCD reduces the absorption of light energy by the color filter, can improve the light efficiency of the LCD, can obtain three times of resolution under the same process, and has the advantages of energy saving.

[0066] Therefore, the application aims to provide a visible light communication method based on the field sequential color LCD, for each backlight partition of the LCD, the color display principle of the field sequential color is used, the RGB three LEDs are turned on in each sub-frame, and the high-frequency signals to be transmitted by the respective LEDs are embedded; the receiving end can separate the three wavelength bearing communication signals sent by the transmitting end at the same time, and demodulate the signals to restore the original bit sequence.

[0067] Specifically, the RGB three-color LEDs of the backlight partition of the field sequential color LCD are used as the transmitting end of the visible light communication, the three-color LEDs are turned on in each sub-frame, and the RGB three-color LEDs in each backlight partition are used to send digital signals of independent content. The receiving end can use the CMOS sensor of the camera or the photodiode array (PD array), and the three-color LEDs of multiple backlight partitions and the camera CMOS sensor or the PD array jointly constitute a multiple-input multiple-output (MIMO) system.

[0068] For the MIMO system constructed above, the spatial multiplexing technology is used at the transmitting end to improve the system bandwidth, and the diversity technology is used to improve the reliability of communication and reduce the bit error rate.

[0069] Referring to Figure 1 This embodiment introduces the method for visible light communication using the field sequential color LCD from the perspective of the transmitting end.

[0070] Different from the principle of traditional spatial color mixing method for color display, the field sequential color liquid crystal display no longer has color filters, but through independent R, G and B color backlight systems, different colors of backlight are refreshed in turn within a frame of time, and the transmittance of liquid crystal molecules in each time slice is adjusted at the same time, so as to achieve the purpose of color display by using the visual persistence characteristics of the human eye. The simplest field sequential color LCD divides a frame of image into three sub-frames of R, G and B, each frame is a single-color LED, and when the total brightness value is determined, only one color of LED can transmit a visible light communication signal in each sub-frame, and the communication capacity cannot be improved by using the characteristics of field sequential color. When R, G and B three-color LEDs are turned on in each sub-frame, i.e. RGB three-color mixing in each sub-frame, R, G and B three LEDs can independently embed high-frequency communication signals in each sub-frame, and complete visible light communication, and at this time, the communication capacity can be theoretically increased by 3 times. Figure 2 The RGB backlight states when opening a single-color field and mixing colors in three fields when composing a white light image are respectively shown.

[0071] From the perspective of the transmitting end, the method of the embodiment comprises:

[0072] The original data is encoded and modulated to obtain a digital signal.

[0073] The multiple digital signals are transmitted by multiple signal sources.

[0074] The multiple signal sources are composed of RGB three-color LEDs of each backlight partition in the direct backlight partitioned field sequential color liquid crystal display, the RGB three-color LEDs in each backlight partition are turned on at the same time in each sub-frame, and the RGB three-color LEDs in the backlight partition respectively transmit digital signals of independent content.

[0075] For example, for a direct backlight field sequential color liquid crystal display with 4*4 backlight partitions, 4*4*3 independent signal sources can be formed, the RGB three-color LEDs in each backlight partition independently modulate and transmit signals, the communication capacity is expanded to 48 times, and the effect of spatial multiplexing is achieved.

[0076] Color separation is a relatively serious negative effect in time sequential color display, and in a further embodiment, in order to improve the display quality, a local dimming algorithm and a local primary color desaturation algorithm can be used to reduce the effect.

[0077] Specifically in an example aspect, for an input image, the image is divided according to backlight partitions of the LCD to obtain dimming blocks corresponding to the backlight partitions, the dimming blocks represent local content of the input image, and for the backlight partition corresponding to each dimming block, a local dimming algorithm and a local primary color desaturation algorithm are used to determine the brightness level of the RGB three-color LEDs in each sub-frame.

[0078] Generally, the RGB luminance level of each pixel in the display image finally presented by the field sequential LCD is the superposition of the liquid crystal transmittance in the three sub-frames and the luminance level of the backlight of the R, G and B channels, as shown below:

[0079]

[0080] wherein represents the R, G and B gray scale values of the output image, [T1 T2 T3] represents the liquid crystal transmittance in each sub-frame, represents the luminance level of the RGB three-color LED in each sub-frame.

[0081] Suppose there are m x n backlight partitions, when an input image is inputted, the input image is first equally divided according to the number of backlight partitions to obtain m x n dimming blocks, each dimming block corresponds to a backlight partition, and finally a complete image is displayed on the LCD. As shown in the schematic diagram, a single dimming block is taken as an example to illustrate the determination of the luminance level of the RGB three-color LED in each sub-frame by using the local dimming algorithm and the local primary color desaturation algorithm. Figure 3

[0082] According to the principle of the local dimming algorithm, the maximum value method is used to determine the maximum value of the luminance level of all channels of the corresponding image in the dimming block, to obtain the ratio I1, I2 and I3 of the maximum value to the luminance level when the three-color channel is fully opened, which correspond to the R, G and B channels respectively. A color pixel is composed of the pixel gray scale values of the R, G and B three sub-channels, and R i,j , G i,j , B i,j represent the R, G and B pixel gray scale values corresponding to the pixel (i, j). Taking the R channel as an example, it is represented as I1 = max(R i,j ) / 255, and the range of R i,j is limited in the dimming block. Similarly, the luminance level ratios of the G channel and the B channel are I2 = max(G i,j ) / 255 and I3 = max(B i,j ) / 255 respectively.

[0083] ​According to the principle of the local color desaturation algorithm, the color coordinates of all pixel points in the dimming block are found on the color gamut diagram. The color coordinates of the pixel points in each dimming block are different from the color coordinates of the pixel points of the whole image on the whole color gamut diagram, and the color coordinates of the pixel points in each dimming block are concentrated in a smaller new color gamut range. Usually, for all pixel points in each dimming block, a smaller new color gamut triangle with P1, P2, and P3 as the vertices can be found. If the three vertex color coordinates P1, P2, and P3 replace the original R, G, and B color coordinates as the backlight primary colors of the three subframes in the corresponding backlight partition (for example, a new color gamut triangle P1, P2, and P3 is determined for a certain backlight partition, and at this time, the color of the first subframe is the color corresponding to the P1 coordinate, the color of the second subframe is the color corresponding to the P2 coordinate, and the color of the third subframe is the color corresponding to the P3 coordinate), the color separation phenomenon can be effectively reduced, and at the same time, in each subframe, the R, G, and B LEDs can flash simultaneously and embed high-frequency communication signals.

[0084] For a backlight partition, when the RGB three-color LEDs are turned on and mixed, the determination of the X, Y, and Z three stimulus values that the corresponding dimming block (i.e., the local content of the image) should reach has the following process:

[0085]

[0086] B d Each of B represents the X, Y, and Z three stimulus values that the backlight partition reaches when the RGB three-color LEDs are turned on and mixed in a subframe, Each of B represents the three stimulus values that the corresponding new primary colors P1, P2, and P3 should reach when the RGB three-color LEDs are turned on and mixed in each subframe. I1, I2, and I3 represent the brightness level matrix, and I1, I2, and I3 respectively correspond to the ratio of the maximum brightness level of all pixels in the dimming block calculated by the maximum value method to the brightness level when each color LED is turned on, which is determined by the calculation process of the above maximum value method.

[0087] The above B d The matrix determines the relationship between the X, Y, and Z three stimulus values that the dimming block should reach and the LED brightness level. Taking the first subframe as an example, to reach the corresponding three stimulus values, the ratio of the corresponding brightness level when the RGB three-color LEDs are turned on and mixed to the brightness level when the RGB is turned on is I R1 ,I G1 ,I B1 , which should satisfy:

[0088]

[0089] wherein, Each of B represents the three stimulus values when the RGB is turned on.

[0090] Thus, the relative luminance levels of the RGB tri-color LEDs in the first sub-frame can be calculated as follows:

[0091]

[0092] Similarly, the relative luminance levels of the other two sub-frames can be calculated, and the relative luminance levels of the RGB in a frame time (with three sub-frames) can be expressed as follows, where subscript i represents the sub-frame number.

[0093]

[0094] After determining the relative luminance levels of R, G, and B in each sub-frame in each backlight partition, in order to transmit the communication signal while maintaining the stability of the light source luminance, embodiments of the present application adopt pulse width modulation (MPPM modulation).

[0095] The original data is encoded before modulation, and specifically, Manchester encoding can be adopted to obtain an encoded signal, and then the encoded signal is modulated for transmission through the backlight partitions of the LCD.

[0096] Generally, for the luminance adjustment of LEDs, pulse width modulation (PWM) waves are adopted, that is, the on-time of the LEDs is changed by changing the duty cycle of the high level in a period. When the frequency of the PWM wave is much greater than the flicker frequency threshold value that can be distinguished by the human eye, the luminance that can be perceived by the human eye is the time average value of the LED luminance. However, the PWM wave can only adjust the luminance level of the LED and cannot embed communication bits to transmit communication signals. If a multi-pulse position modulation (MPPM) mode is adopted, the bit information can be embedded while meeting the luminance adjustment requirement and ensuring the stability of the corresponding backlight source luminance.

[0097] MPPM modulation refers to mapping n-bit information bits into modulation symbols with M time slots. For the determined R, G, and B luminance levels I Ri , I Gi , I Bi in each backlight partition in each sub-frame, the dimming level a (0-1) is determined according to the ratio of I Ri , I Gi , I Bi to the luminance levels (represented by I Rif , I Gif , I Bif ) of the R, G, and B tri-color LEDs when fully on in a sub-frame: (taking R as an example).

[0098] In the embodiment, the number of time slots of each modulation symbol is set to 10, and 11 dimming levels are set, i.e., a is limited from 0 to 1, and the interval between two adjacent dimming levels is 0.1. Taking the dimming level a = 0.4 as an example, the modulation principle is explained as follows:

[0099] When the dimming level a = 0.4, in the modulation symbol with the number of time slots being 10, in order to meet the brightness requirement, four time slots are selected to emit light pulse signals, and there are a total of

[0100]

[0101] Different selection modes are selected, so there are 210 different modulation symbols, and the number of bits that can be transmitted by each MPPM modulation symbol is:

[0102] n = [log2C] = 7

[0103] If the time slot frequency is f, the bit rate that can be obtained is:

[0104]

[0105] When a = 0.4, the corresponding code word table relationship between the modulation symbol and the transmission bit group can be defined as shown in the following table:

[0106]

[0107] For the symbol obtained after MPPM modulation, the light pulse can be emitted in the OOK modulation mode. As shown in Figure 4 , a light pulse signal emission diagram when the dimming level a = 0.4 is shown, and the high level represents the emission of light pulse, and the low level represents no light pulse emission.

[0108] Therefore, for each dimming level, a corresponding bit group-modulation symbol mapping table can be set, and after demodulation at the receiving end, the original bit information can be restored according to the corresponding mapping table. The process of modulating the original data by using the MPPM modulation and the OOK modulation is as follows:

[0109] At the transmitting end, the coded bit sequence to be transmitted is transmitted to each backlight partition through serial-parallel conversion;

[0110] The bit sequence entering each backlight partition is subjected to serial-parallel conversion to obtain the bit sequence to be transmitted by R, G and B respectively at the same time;

[0111] For each RGB three-color LED in the backlight partition, MPPM modulation is adopted, and the mapping symbol is obtained according to the corresponding code word table according to the corresponding dimming level;

[0112] After obtaining the continuous mapping symbol, the light pulse is transmitted in the OOK mode.

[0113] The above process is shown by Figure 5 .

[0114] The visible light communication method provided by the application is introduced from the perspective of the receiving end.

[0115] Specifically, in the example aspect, a camera is used as the receiving end, the camera uses a CMOS as an image sensor, and each pixel point on the image sensor can convert the light signal into an electrical signal corresponding thereto. The COMS sensor has the advantages of low cost and fast imaging speed, and therefore most of the cameras of mobile devices on the market are COMS sensors, which are based on a rolling shutter for exposure. The rolling shutter is used for visible light communication, which can solve the problem that the data rate of VLC is limited by the frame rate of the image sensor. At the same time, a color camera can be used as a natural wavelength division multiplexing receiver to separate the R, G, and B signals transmitted by the transmitting end at the same time, thereby achieving a three-fold communication capacity effect.

[0116] The principle of acquiring a color image by most modern color cameras is to add a set of Bayer filter arrays (Bayer array) in front of the CMOS array, and to acquire color information through color filters. In the Bayer filter array, each photosensitive point corresponds to a single-color filter, and simultaneously corresponds to one pixel point below, that is, each pixel point only senses one color component. For each pixel, the surrounding color information is considered to restore the lost two color information. The data obtained directly through the Bayer array is called raw data, also known as a raw image. After various interpolation methods, a complete RGB three-channel image can be obtained. In this embodiment, the camera is used as the receiver of the visible light communication system. For the visible light communication signal transmitted by the field sequential LCD of the transmitting end, the three color channels in the color image received by the camera contain the bit information respectively transmitted by the R, G, and B LEDs of the transmitting end. Figure 6 .

[0117] The rolling shutter operation means that each row of pixels in the CMOS sensor is activated sequentially, and the whole image is not captured at one time. The appearance of the rolling shutter effect makes the communication rate of the visible light communication system with the camera as the receiver no longer limited by the frame rate of the camera. In the case of a single backlight LCD as the transmitter, bits 0 and 1 can be represented by the light and dark of a row of pixels. In the case of a backlight partitioned LCD as the transmitter, bits 0 and 1 can be represented by the light and dark of each pixel block detected by the camera. At this time, for the backlight partitioned LCD, the communication rate in the row direction has reached the upper limit determined by the rolling shutter effect of the camera. Only the net communication rate of the system can be increased in the column direction. If a field sequential color LCD is further combined, the net communication rate can be theoretically three times the above communication rate.

[0118] In addition to using the camera as the receiver, a photodiode array can also be used. Specifically, as shown in Figure 7 three photodiodes are placed in each group, and a red, green, and blue filter is placed in front of each photodiode in each group. Each group of photodiodes corresponds to each backlight partition of the LCD through an imaging lens (or lens group). Each group has three photodiodes, and a red, green, and blue color filter is placed in front of each photodiode to receive the signals emitted by the corresponding backlight partition R, G, and B LEDs, respectively. At the same time, the photoelectric conversion performance of the photodiode is used, that is, the modulation signal sent by the transmitter can be obtained.

[0119] After obtaining the modulation signal sent by the transmitter by using the photoelectric conversion performance of the photodiode, the embodiment adopts an ML detector based on the ML criterion to demodulate the MPPM, while assuming that at any time, the channel model of the LED in the corresponding backlight partition of the transmitter and the PD corresponding to it in the receiver is a Gaussian white noise channel:

[0120] Y = Hx + n

[0121] where Y represents the signal received by the receiver; x represents the visible light signal (a vector, also in bold) transmitted by the transmitter; n represents additive Gaussian white noise, which is mainly caused by circuit noise introduced by the preamplifier circuit of the receiver and shot noise caused by current; H represents the direct current channel gain in the visible light communication link. At this time, the probability density function of the signal Y received by the receiver with x as the condition is:

[0122]

[0123] where N represents the number of bits in each modulation symbol, and σ 2is the variance of the Gaussian white noise. According to the principle of the ML detector, the maximum of the conditional probability function is obtained, i.e. the minimum of the Euclidean distance in the above formula is obtained, i.e.

[0124]

[0125] Also has:

[0126]

[0127] In each sub-frame time, when the value of the dimming level a is determined, the number of the transmitted pulses in each modulation symbol is determined, at this time the inner product value of the corresponding modulation symbol in the code word table is determined, i.e.

[0128]

[0129] For each received signal sequence Y, the inner product value is also determined. In order to reduce the calculation complexity, the objective function of the ML detector can be transformed into:

[0130]

[0131] For each received symbol, the corresponding code word table is traversed (for different dimming levels, there are different modulation symbol mapping tables, i.e. code word tables), and the code word satisfying the above formula is the code word obtained by demodulating using the ML detector, and the corresponding bit group is obtained by mapping through the code word table.

[0132] Referring to Figure 8 , a visible light communication device applied to a transmitting end and using a field sequential color LCD is provided, comprising:

[0133] A modulation unit 11 is configured to encode and modulate original data to obtain a digital signal.

[0134] A signal transmission unit 12 is configured to transmit the digital signal to a plurality of signal sources, and the plurality of signal sources are configured to send the plurality of digital signals.

[0135] The plurality of signal sources are composed of RGB three-color LEDs of each backlight partition in a direct backlight partitioned field sequential color LCD, the RGB three-color LEDs in each backlight partition are turned on at the same time in each sub-frame, and the RGB three-color LEDs in the backlight partition send independent content digital signals.

[0136] Referring to Figure 9 , a visible light communication device applied to a receiving end and using a field sequential color LCD is provided, comprising:

[0137] A receiving unit 21 is configured to receive a plurality of digital signals transmitted by a plurality of signal sources.

[0138] The multiple signal sources are composed of RGB three-color LEDs of each backlight partition of the direct backlight partitioned field sequential color type LCD, the RGB three-color LEDs in each backlight partition are opened at the same time in each sub-frame, and the RGB three-color LEDs in the backlight partition respectively send digital signals of independent content;

[0139] The photoelectric conversion unit 22 is used for photoelectrically converting the multiple digital signals to obtain modulation signals to be transmitted by the RGB three-color LEDs respectively;

[0140] The demodulation unit 23 is used for demodulating the modulation signals to obtain communication content.

[0141] Referring to Figure 10 , a system for visible light communication by using a field sequential color type LCD is provided, which comprises a transmitting end 31, a receiving end 32 and a direct backlight partitioned field sequential color type LCD 33;

[0142] The transmitting end 31 transmits digital signals to the field sequential color type LCD 33 for transmitting communication signals by using the visible light communication method for the transmitting end in the foregoing embodiment;

[0143] The receiving end 32 receives digital signals by using the visible light communication method for the receiving end in the foregoing embodiment;

[0144] The RGB three-color LEDs of each backlight partition of the direct backlight partitioned field sequential color type LCD 33 constitute multiple signal sources, which are used for transmitting multiple digital signals transmitted by the transmitting end 31, the RGB three-color LEDs in each backlight partition are opened at the same time in each sub-frame, and the RGB three-color LEDs in the backlight partition respectively send digital signals of independent content.

[0145] The foregoing embodiments are only used to illustrate the technical solutions of the present application, but not limit the same; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of visible light communication using a field sequential color LCD, characterized by, The method is applied to a transmitting end and comprises: The field sequential color liquid crystal display is divided into at least one backlight partition, the relative brightness levels of the RGB three-color LEDs in each backlight partition are determined according to an input image, and the method comprises: dividing the input image into a plurality of dimming blocks, each dimming block corresponding to a backlight partition; determining the brightness level ratio of the RGB channels of the image content corresponding to the dimming block by using a local dimming algorithm; determining the relative brightness levels of the RGB three-color LEDs in the backlight partition corresponding to the dimming block in each sub-frame by using a local primary color desaturation algorithm according to the brightness level ratio; encoding and modulating the original data to obtain digital signals; transmitting the digital signals by a plurality of signal sources; the plurality of signal sources are composed of the RGB three-color LEDs of each backlight partition in the field sequential color liquid crystal display with direct backlight partitioning, one monochromatic LED being one independent signal source, the RGB three-color LEDs in each backlight partition being turned on at the same time and reaching the relative brightness levels in each sub-frame, and the RGB three-color LEDs in the backlight partition transmitting digital signals of independent content, so that each sub-frame is a mixture of RGB three colors, and the R, G and B monochromatic LEDs all flash at the same time and independently embed high-frequency communication signals within the time of each sub-frame. 2.The method of visible light communication using a field sequential color LCD according to claim 1, wherein, The method of determining the brightness level ratio of the RGB channels of the image content corresponding to the dimming block by using a local dimming algorithm comprises: The maximum value algorithm is used to determine the ratio of the maximum brightness level of the RGB channels of the image content corresponding to the dimming block to the brightness level when each channel is fully open, which is expressed as follows: , , , , , Representing pixels The corresponding R, G, and B pixel grayscale values.

3. The method of visible light communication using field sequential color type LCD according to claim 2, wherein, The method of determining the relative brightness levels of the RGB three-color LEDs in the backlight partition corresponding to the dimming block in each sub-frame by using a local primary color desaturation algorithm comprises: determining the X, Y and Z three stimulus values that the dimming block should reach according to the brightness level ratio; obtaining the three stimulus values required when the RGB three-color LEDs are fully turned on; determining the relative brightness levels of the RGB three-color LEDs in the backlight partition in each sub-frame according to the following matrix calculation formula: ； Indicates the first The relative brightness levels of the RGB three-color LEDs in each subframe Each column represents the tristimulus values ​​when RGB is fully enabled. Indicates the dimming block at the 1st The X, Y, and Z tristimulus values ​​that should be achieved when the RGB three-color LEDs are turned on simultaneously for color mixing in a subframe. 4.The method of visible light communication using a field sequential color LCD according to claim 1, wherein, The process of encoding the original data comprises: encoding the original data by using a Manchester encoding mode. 5.The method of visible light communication using a field sequential color LCD according to claim 1, wherein, The process of modulating the original data comprises: generating a bit sequence corresponding to the original data; performing serial-parallel conversion on the bit sequence and transmitting the bit sequence to each backlight partition, and performing serial-parallel conversion on the bit sequence entering each backlight partition to obtain the bit sequences to be transmitted by the RGB three-color LEDs in the same sub-frame; adopting MPPM modulation and OOK modulation to obtain the light pulses corresponding to the RGB three-color LEDs.

6. A method of visible light communication using a field sequential color LCD, characterized by, The method is applied to a receiving end and is used for processing the digital signals transmitted by the method of any one of claims 1 to 5, and the method comprises: receiving the digital signals transmitted by the plurality of signal sources; the plurality of signal sources are composed of the RGB three-color LEDs of each backlight partition in the field sequential color liquid crystal display with direct backlight partitioning, one monochromatic LED being one independent signal source, the RGB three-color LEDs in each backlight partition being turned on at the same time and reaching the relative brightness levels in each sub-frame, and the RGB three-color LEDs in each backlight partition being used for transmitting digital signals of independent content, so that each sub-frame is a mixture of RGB three colors, and the R, G and B monochromatic LEDs all flash at the same time and independently embed high-frequency communication signals within the time of each sub-frame. The relative brightness level of the RGB three-color LEDs in each backlight partition in each sub-frame is determined according to the input image; The multiple digital signals are photoelectrically converted to obtain modulation signals to be transmitted by the RGB three-color LEDs respectively; The modulation signals are demodulated to obtain the communication content.

7. The method of visible light communication using field sequential color type LCD according to claim 6, wherein, When the photodiode is used as the receiving end, a maximum likelihood detector is used to demodulate the modulation signals.

8. A device for visible light communication using a field-sequence LCD, characterized in that, The device is applied to the transmitting end and is used to implement the method for visible light communication using the field sequential LCD according to any one of claims 1-5, and comprises: a modulation unit configured to encode and modulate the original data to obtain digital signals; a signal transmission unit configured to transmit the digital signals to multiple signal sources and send the multiple digital signals through the multiple signal sources; The multiple signal sources are composed of RGB three-color LEDs in each backlight partition of the direct-lit backlight partition field sequential LCD, the RGB three-color LEDs in each backlight partition are turned on at the same time in each sub-frame, and the RGB three-color LEDs in each backlight partition are used to send digital signals of independent content.

9. A device for visible light communication using a field-sequence LCD, characterized in that, The device is applied to the receiving end and is used to implement the method for visible light communication using the field sequential LCD according to any one of claims 6-7, and comprises: a receiving unit configured to receive the multiple digital signals transmitted by the multiple signal sources; The multiple signal sources are composed of RGB three-color LEDs in each backlight partition of the direct-lit backlight partition field sequential LCD, the RGB three-color LEDs in each backlight partition are turned on at the same time in each sub-frame, and the RGB three-color LEDs in each backlight partition are used to send digital signals of independent content. a photoelectric conversion unit configured to photoelectrically convert the multiple digital signals to obtain modulation signals to be transmitted by the RGB three-color LEDs respectively; a demodulation unit configured to demodulate the modulation signals to obtain the communication content.

10. A system for visible light communication using a field sequential color LCD, characterized by The device comprises a transmitting end, a receiving end, and a direct-lit backlight partition field sequential LCD; The transmitting end transmits the digital signals to the field sequential LCD to perform communication signal transmission by using the method for visible light communication using the field sequential LCD according to any one of claims 1-5; The receiving end receives the digital signals by using the method for visible light communication using the field sequential LCD according to any one of claims 6-7; The RGB three-color LEDs in each backlight partition of the direct-lit backlight partition field sequential LCD constitute the multiple signal sources, one monochromatic LED is one independent signal source, and the multiple digital signals transmitted by the transmitting end are emitted, the RGB three-color LEDs in each backlight partition are turned on at the same time in each sub-frame and reach a relative brightness level, and the RGB three-color LEDs in each backlight partition send digital signals of independent content, so that each sub-frame is a mixture of RGB three colors, and in each sub-frame, the R, G, and B monochromatic LEDs are turned on at the same time and independently embedded with high-frequency communication signals. The relative brightness level of the RGB three-color LEDs in each backlight partition in each sub-frame is determined according to the input image.

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