CN110649966B - Method for realizing near-distance optical communication based on visible light and mobile phone camera imaging characteristics - Google Patents
Method for realizing near-distance optical communication based on visible light and mobile phone camera imaging characteristics Download PDFInfo
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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- H—ELECTRICITY
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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Abstract
The invention discloses a method for realizing near field communication based on visible light and mobile phone camera imaging characteristics. The method is based on Color Shift Keying (CSK) and Code-Division Multiple Access (CDMA) technologies, and Light Emitting Diode (LED) and Android smart phones are respectively used as a sending end and a receiving end of data, and Reed-Solomon coding is adopted, so that reliable optical communication of receiving data by Multiple receiving ends simultaneously is finally realized. The invention combines the LED lamp and the smart phone which are popularized at present, and has wide application prospect in actual life.
Description
Technical Field
The invention belongs to the field of visible Light communication, and discloses a near field optical communication method for realizing reliable transmission of multi-receiving-end data by utilizing the imaging characteristics of a Light Emitting Diode (LED) and a mobile phone camera and based on Color Shift Keying (CSK), Code-Division Multiple Access (CDMA) and Android systems.
Background
The visible light communication technology is a communication technology for transmitting data by using a high-frequency flicker signal emitted by a fluorescent lamp, a light emitting diode or other equipment. The technology adds a microcontroller to the lighting device to add communication functionality thereto. This enables the lights in daily life to be used not only for normal lighting but also for the ability to transmit data. Therefore, the visible light communication technology can fully play the potential of the existing lighting infrastructure and has important significance for realizing intelligent life.
In general, the visible light communication technology uses LED lamps as light sources and data transmitting terminals. The LED lamp has the characteristics of green energy conservation, low construction cost, support of high-frequency on-off control and the like, and is widely applied to various scenes. This lays a good foundation for the actual deployment of visible light communication systems.
Unlike the conventional radio communication method, the visible light communication technology uses the visible light band as a carrier for communication. The spectrum resource of visible light is very abundant, can realize bigger bandwidth and higher speed, and still belong to the free frequency channel, need not the authorization and can use. The wavelength of visible light is shorter, and the barrier cannot be penetrated, so the transmission range is controllable, information is not easy to be intercepted by a third party, and the transmission process is safer and more reliable. In addition, the visible light communication technology can be used in electromagnetic sensitive environments such as medical aerospace and the like, so that the research on the visible light communication technology has great value.
Nowadays, smart phones are widely popularized and are very common in life like LED lamps. Most Shutter modes of the smart phone camera are Rolling shutters (Rolling shutters), namely pixels of the camera sensor are exposed line by line, and imaging can not be performed until all the pixels are exposed. The rolling shutter characteristic of the mobile phone camera provides possibility for capturing high-frequency optical signals, so that a single image can simultaneously contain a plurality of color stripes, and the data volume capable of being transmitted in unit time is increased.
Disclosure of Invention
The invention develops new exploration on the visible light communication technology and provides a near field optical communication method suitable for reliable data transmission of multiple receiving ends. The invention combines CSK and CDMA technologies, adopts Reed-Solomon Codes (Reed-Solomon Codes), and respectively uses a single RGBLED lamp and a smart phone as a transmitting end and a receiving end of optical communication, wherein the receiving end receives optical signals by utilizing the imaging characteristic of a camera of the smart phone. The method comprises the following specific steps:
step one, a transmitting end adopts Reed-Solomon codes to encode U pieces of data to be transmitted.
And step two, converting the U pieces of encoded data into binary data, and replacing 0 in the binary data with-1. The data set at this time is denoted by D, which includes U pieces of data consisting of-1 and 1.
Step three, carrying out Walsh transformation on the data set D by using an N (N ═ U) order Hadamard matrix H to obtain transformed data SmThe value range of each element is [ -N, N [ -N]。
Step four, data SmNormalizing the values of the elements to make the value range of the elements be { -1,0,1}, and mapping the valuesAnd emitting the RGB symbols to obtain a character string consisting of the RGB symbols.
And step five, partitioning the character string by taking the length of the 16 characters as a unit. A header and a trailer are added for each block to form a data frame. Finally, a plurality of data frames are transmitted consecutively by the LED lamp.
And step six, recording a section of video by the U receiving ends, calculating the RGB value of the pixel point of each frame of image, obtaining the color symbol contained by the pixel point, and converting the color symbol into a corresponding data frame. And removing the head and the tail of each data frame, sequentially splicing the data frames in a receiving sequence, restoring the RGB three color symbols to be +1, -1,0, and restoring the data of which the sending end is subjected to Walsh transform.
And step seven, each receiving end uses respective orthogonal codes, namely corresponding vectors in the Hadamard matrix H, and the data obtained in the step six are subjected to Walsh inverse transformation. And replacing-1 in the inverse transformed data with 0 to obtain binary data. And decoding the binary data by using the Reed-Solomon code, and obtaining respective original data by the U receiving ends.
The invention takes the currently popular RGB LED lamp as a data sending end and the smart phone as a data receiving end, has low practical application cost and has better market popularization prospect. The invention has the following specific advantages:
(1) based on CSK and CDMA, the data can be transmitted to a plurality of receiving ends at the same time, and the past one-to-one data transmission mode is broken through.
(2) And the data lost in the transmission process is recovered by using Reed-Solomon codes, so that the reliability of data transmission is ensured.
(3) CSK adopts the RGB of LED to express three kinds of states, can realize high-rate data transmission.
(4) LED lamps are widely used for everyday lighting, are becoming widely popular in many countries, and lay a good market for the arrangement of the system in practical applications.
(5) The intelligent mobile phone has high popularity and is universal and easy to obtain as a receiving end. And the data acquisition is conveniently and quickly carried out by using the application program developed based on the smart phone system.
Drawings
Fig. 1 is a diagram of a visible light communication system architecture based on CSK and CDMA.
Fig. 2 is a diagram illustrating a data frame structure according to the present invention.
Fig. 3 is a schematic diagram of communication between an RGB LED lamp and a receiving terminal according to the present invention.
Detailed Description
The present invention will now be described more fully hereinafter with reference to the accompanying drawing, in which fig. 1 is shown. The specific embodiment is as follows:
step one, assuming that there are U receiving ends, the transmitting end simultaneously transmits data for the U receiving ends. The U pieces of data are first encoded with reed-solomon codes. The optical signal is lost and distorted by the interference noise present in the actual channel, and the reliability of the transmission process can be ensured by applying reed-solomon codes.
And step two, converting the coded data into binary data, and replacing 0 in the binary data with-1. Let D be the data set sent to U receivers, D being denoted as { D1；D2；...；DUIn which D isu＝(d1，d2，...，dM)，u∈[1，U]，dm∈ { -1, +1}, M being the data length of each receiver.
And step three, giving an N (N ═ U) order Hadamard matrix H (each element is 1 or-1, and any two rows and two columns are orthogonal). Order SmThe sum of inner products of the mth bit data sent to each receiving terminal and the corresponding vector in the Hadamard matrix H is represented as follows:
wherein,
m ∈ [1, M ] representing the mth bit of data sent to the u-th sink]，huRepresenting the corresponding vector of the receiving end u in the hadamard matrix H. Since the Hadamard matrix H is an N-order square matrix, there is Sm＝[Sm，1，Sm，2，...，Sm，N]. Therefore it has the advantages of
Thereby obtaining:
wherein h isu，nIs huThe nth data. After the data is coded, the sending end signal S can be obtainedm。
Step four, Sm，nHas a value range of [ -N, N]. When the order number N of the adada code matrix is large, the LED lamp will no longer have a sufficient number of color symbols to represent data. In order to combine CDMA with CSK, the method of the invention proposes a normalization method, reducing Sm，nThe normalization factor is defined as:
by means of normalization, it is possible to obtain:
according to Sm，nValue of (5) can give S'm，nThe value of (A) is as follows:
the following can be obtained:
wherein S'm，n∈ { -1,0, +1}, so only three colors are needed to represent the encoding result S ″' modulated by CSKm，nComprises the following steps:
and step five, generating a character string consisting of RGB symbols by the U pieces of original data through the steps. The character string is divided into blocks of a predetermined length (16 characters). Each data block has 2 extra symbols added to the head and tail, the head is a WO symbol, and the tail is an OW symbol, where W denotes White light (White) and O denotes no light (Off). The overall data frame format is shown in fig. 2. When the transmitting end transmits the R symbol, the RGB value of the LED lamp is set to be (255, 0, 0), namely the LED emits red light; the RGB value when the G symbol is sent is (0, 255, 0), namely the LED emits green light; the RGB value when the B symbol is sent is (0, 0, 255), namely the LED emits blue light; when the W symbol is transmitted, the parameters of the R, G, B three-color component are all 255. The LED lamp expresses color symbols in the data frames by emitting light with different colors, and the data frames are sequentially sent according to the sequence. The data transmission frequency of the LED lamp is controlled between 1Hz and 8 Hz.
Step six, as shown in fig. 3, while the sending end sends data, the receiving end records a segment of video. And extracting a first line of pixel points of each frame of image in the video, and calculating the RGB value of each pixel point. And according to the values of the three components of RGB, obtaining the color symbols contained in the frame image, and converting the color symbols into corresponding data frames. For example, if the R component is the maximum value in an interval, it can be determined that there is a red stripe in the interval and the color sign is R. And obtaining all data frames after the video processing is finished. And splicing the data frames according to the receiving sequence, removing the head and the tail of each data frame, restoring the R, G, B symbols to +1, -1,0 according to the formula (a) in step four, and restoring the data subjected to Walsh transform at the transmitting end.
Let the signal received by the receiving end be R ═ S ″m+ e, where e represents noise during signal transmission. R 'is obtained after the RGB color symbols are reduced to corresponding numbers'm＝S′m+ e. The data transmitted to each receiver is then separated by an inverse walsh transform. The part operates as follows:
each receiving end hasThe respective orthogonal codes, i.e., the corresponding vectors H in the hadamard matrix H, may be used to obtain respective original data. The v th receiving end passes hvObtained data
Comprises the following steps:
wherein F is Nfm，nAnd F > 0, η is a constant obtained by Walsh transform of e when u ≠ v, since the orthogonality of the Hadamard matrix is known,
assuming η is small enough to be ignored, there are:
since F > 0, therefore
Will not change
The symbol of (2). Taking:
order to
Which indicates the m-th data of each receiving end after inverse walsh transform. If not taken into considerationThe influence of noise is as follows
dm is the m-th bit of original data at each receiving end. To this end, the data is reduced to a data form of-1, 1.
Step seven, the
Replacing the-1 in (A) with 0 (B), and obtaining the data in binary form. And decoding by using Reed-Solomon codes, and finally obtaining the original data of each sending end by U receiving ends.
Claims (1)
1. The method for realizing the near field optical communication based on the imaging characteristics of the visible light and the mobile phone camera comprises the following specific steps that a single RGB LED lamp and an android smart phone are respectively used as a sending end and a receiving end of communication, and reliable optical communication that the single sending end sends data and a plurality of receiving ends receive the data simultaneously can be realized:
the method comprises the following steps that firstly, a sending end uses Reed-Solomon codes to respectively encode U pieces of data;
step two, converting the U pieces of coded data into binary data, and replacing 0 in the binary data with-1; d represents the data set at the moment, and the D comprises U pieces of data consisting of-1 and 1;
step three, carrying out Walsh transformation on the data set D by using an N-order Hadamard matrix H to obtain transformed data SmThe value range of each element is [ -N, N [ -N]Wherein N ═ U;
step four, data SmNormalizing the values of the elements to ensure that the value range of the elements is { -1,0,1}, and then mapping the values into RGB symbols to obtain a character string consisting of the RGB symbols;
step five, taking the length of the 16 characters as a unit, and partitioning the character string; adding a head and a tail to each block to form a data frame; finally, the LED lamp continuously sends a plurality of data frames, namely the LED lamp represents color symbols in the data frames one by using light with different colors, and the plurality of data frames are sent in sequence;
step six, when the sending end sends data, U receiving ends record a section of video respectively; extracting a first line of pixel points of each frame of image in the video, and calculating the RGB value of each pixel point; according to the values of the three components of RGB, the color symbol contained in the frame image is obtained, and the frame image is converted into a corresponding data frame; sequentially splicing the data frames in a receiving sequence, removing the head and the tail of each data frame, restoring R, G, B three color symbols to +1, -1,0, and restoring the data of which the sending end is subjected to Walsh transform;
step seven, each receiving end uses respective orthogonal code, namely the corresponding vector in the Hadamard matrix H, and the data obtained in the step six are subjected to Walsh inverse transformation; replacing-1 in the inverse transformed data with 0 to obtain binary data; and decoding the binary data by using the Reed-Solomon code, and obtaining respective original data by the U receiving ends.
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