Pilot-assisted visible light communication light source waveform design method

Abstract

The application discloses a pilot-assisted visible light communication light source waveform design method, and belongs to the technical field of visible light communication. By minimizing the cross-correlation interference generated when demodulating each light source signal, a light source transmission waveform combination of "orthogonal code + non-orthogonal code" is designed for the transmission end of a multi-light source VLC-CDMA system, and a demodulation algorithm is provided for the transmitted light source waveform at the receiving end, so that the demand of more users for simultaneous data transmission can be met under the condition that the hardware condition of the image sensor is limited. The design method of the light source waveform comprises a transmission end part and a receiving end part. The application can effectively reduce the cross-correlation interference generated when demodulating each light source superposition signal, can realize data communication of the multi-user VLC-CDMA system by using a shorter code length of the spread spectrum sequence, and can meet the demand of more users for simultaneous data transmission under the condition that the hardware condition of the image sensor is limited.

Description

Technical Field

[0001] This invention belongs to the field of visible light communication technology and relates to the design of light source emission waveforms, particularly to a pilot-assisted visible light communication light source waveform design method for image sensors. Background Technology

[0002] Visible Light Communication (VLC) technology, as a novel wireless communication technology, transmits information by emitting high-speed, imperceptible on / off signals from light-emitting diodes (LEDs), achieving the dual functions of lighting and communication. Furthermore, for multi-user scenarios, Code Division Multiple Access (CDMA) is used as the multiple access method for VLC systems, fully leveraging the advantages of CDMA technology to enable simultaneous data transmission from multiple light sources.

[0003] However, in multi-source VLC-CDMA systems, meeting the data transmission needs of multiple users is limited by several factors. Firstly, because the spreading codes used by users are typically not perfectly orthogonal, demodulating a single user's signal is subject to cross-correlation interference from other users, severely impacting the demodulation of their transmitted data. Secondly, considering the current mainstream trend of using image sensors as VLC receivers, and the complexity of resolving cross-correlation interference, increasing the spreading code length to improve multiple access capability is difficult due to the limitations of image sensor hardware, which cannot accommodate excessive bright and dark stripes. Furthermore, an excessively long code length significantly increases the computational load of the demodulated signal at the receiver, thus affecting the communication performance of the VLC-CDMA system. Summary of the Invention

[0004] The technical problem this invention aims to solve is that in current multi-source VLC-CDMA systems, the spreading code used causes severe cross-correlation interference when the receiver demodulates a single user's data during data transmission by multiple users, failing to meet the needs of simultaneous data transmission by too many users. Furthermore, due to the limitations of current image sensor hardware, it is difficult to improve the access capability of multiple users by increasing the spreading code length.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A pilot-assisted visible light communication light source waveform design method is proposed. This method minimizes the cross-correlation interference generated when demodulating the signals of each light source. It designs a combination of "orthogonal code + non-orthogonal code" light source transmission waveforms at the transmitter of a multi-light source VLC-CDMA system and provides a demodulation algorithm for the transmitted light source waveforms at the receiver. This allows the method to meet the needs of more users to transmit data simultaneously under the current limitations of image sensor hardware.

[0007] Assume a multi-source VLC-CDMA system has K+1 light sources. K light sources act as communication signal transmitters, enabling data communication for K users; one light source acts as a pilot signal transmitter, enabling synchronous communication for the same K users; and a CMOS image sensor receiver receives the superimposed signals from the pilot and communication signals from the K+1 VLC-CDMA sources, demodulates the transmitted data from the K users, and realizes the communication transmission from the K light sources. The design method for the light source waveforms consists of two parts:

[0008] Part 1: Transmitter Section

[0009] Step 1: Determine the spreading sequence of the communication light source

[0010] Let the spreading sequences of K communication light sources be Walsh sequences, where the code length of the Walsh sequence is L. W Must meet:

[0011] L W -1≥K (1)

[0012] Among them, L W -1 represents the number of sequences after removing a sequence of all 1s from the Walsh sequence, then equation (1) represents the remaining L W One Walsh sequence is sufficient to be allocated to K users, thus determining that the spreading sequence for the K communication light sources has a code length of L. W s1,s2,...,s K .

[0013] Step 2: Determine the spreading sequence of the pilot light source.

[0014] Let the spreading sequence of one pilot light source be M-sequence. The pilot light source provides synchronization for the signals transmitted by K communication light sources, where the code length L of the M-sequence is... M With code length L W Must meet:

[0015] L M =NL W (2)

[0016] Where N is a multiple of the code length and N≥1, i.e., L M With LW The relationship is always an integer multiple, and the code length is L. W The M-sequence must satisfy the condition that its autocorrelation function has a sidelobe value of less than or equal to 4, thereby reducing cross-correlation interference generated during demodulation. Finally, the spreading sequence of the pilot light source that satisfies the above conditions is determined to be of code length L. M s M .

[0017] Step 3: Transmission of communication signals and pilot signals

[0018] Let the data transmitted by K communication light sources be d1, d2, ... d K Where d1, d2, ... d K ∈{-1,+1}. Based on the spreading sequence s1,s2,...,s of the communication light source determined in step one. K If the transmitted data from K users are spread spectrum modulated with their corresponding spreading sequences, then the baseband signal T of the k-th user after spreading is... k for:

[0019] T k =d k s k (3)

[0020] Where k∈{1,2,...,K}. The baseband signals T1,T2,...,T... K After unipolar conversion, the signals are modulated using OOK and applied to K communication light sources respectively, thereby transmitting the VLC-CDMA signals y1, y2, ..., y from the K communication light sources. K The VLC-CDMA signal y transmitted by the kth communication light source k for:

[0021]

[0022] Among them, A k r represents the amplitude value of the optical power of the signal transmitted by the light source. k This represents the baseband signal of the communication light source after unipolar conversion, and r k ∈{0,1}, meaning "1" represents the light source being on and "0" represents the light source being off. Let the transmitted data of the pilot light source be d. M , where d M ∈{+1}, based on the spreading sequence s of the pilot light source determined in step two. M Similarly to equations (3) and (4), the data d to be sent will be... M With pilot light source spread spectrum sequence s M Spread spectrum modulation is performed to obtain the spread spectrum baseband signal T. MAfter undergoing unipolar conversion, the signal is modulated by OOK and applied to the pilot light source to obtain the VLC-CDMA signal y transmitted by the pilot light source. M .

[0023] Part Two: Receiver Section

[0024] Step 1: Bipolar transformation of unipolar superimposed grayscale value sequences

[0025] Using a CMOS image sensor as the receiver in a VLC-CDMA system, K+1 superimposed VLC-CDMA signals from the pilot and communication light sources are received via a rolling shutter exposure mode. After grayscale processing of the CMOS sensor's image, the unipolar superimposed grayscale value sequence representing the K+1 superimposed VLC-CDMA signals is y. G(uni) Its sequence length is L, and its expression is:

[0026]

[0027] Among them, y GM y represents the unipolar grayscale value sequence of the pilot light source. Gk Let r represent the unipolar grayscale value sequence of the k-th communication light source. M This represents the baseband signal of the pilot light source after unipolar conversion, and r M ∈{0,1}, G M G represents the grayscale value of the bright stripes on the image from which the pilot light source is located. k G represents the grayscale value of the k-th communication light source. M and G k All are related to the optical power amplitude value A of the pilot light source M Amplitude value A of the communication light source k The relationship is linear. Therefore, the unipolar superimposed gray value sequence y... G(uni) Transformed into a bipolar sequence y G(bi) The expression is:

[0028] y G(bi) =2y G(uni) -y G(uni)max (6)

[0029] Among them, y G(uni)max Represents the sequence y G(uni) The maximum value in y can be obtained by statistical analysis. G(uni) The sequence value is output.

[0030] Step 2: Determine the start and end points of demodulation.

[0031] Based on the determined pilot light source spreading sequence s M code length L M The sequence y after bipolar transformationG(bi) The front L M Position and after L M The positions are respectively related to s M Perform cross-correlation calculations, and then perform peak detection on the results of the two correlation calculations, recording the positions A1 and A2 of the maximum peaks respectively. Then, for a bipolar sequence y... G(bi) The demodulation begins at position A. begin for:

[0032] A begin =A1 (7)

[0033] Demodulation ends at position A end for:

[0034] A end =L-(L M -A2)-1 (8)

[0035] Based on the start and end demodulation positions, the bipolar sequence y G(bi) The first to the A1-1th and the L-(L)th positions M -A2) is used to truncate the left and right ends of the sequence up to the Lth position, resulting in the truncated sequence y. cut Its sequence length is L cut .

[0036] Step 3: Amplitude estimation of pilot light source signal

[0037] First, calculate the spread spectrum sequence s of the pilot light source. M (n-1)L W +1 to nL W Sum of M within the range n Where n∈{1,2,...,N}, if the result of a certain sum is 0, then discard the result of that sum and record the order of the sums with 0 values ​​n, thus obtaining the sum sequence D after removing the order of the sums with 0 values ​​n. M D M ={M1,M2,...,M k-1 M k+1 ,...M N}

[0038] Secondly, based on the sequence y extracted in step two... cut By moving a length of L W The summation window, every L W bit pair sequence y cut Calculate L W The summation within M units i until the window moves to sequence y cut The sum ends with the last digit, where W iThis represents the summation result of the i-th summation, where the summation count i = (m-1)N+n, and m ∈ {1,2,...,L}. cut / L M If the sum is discarded, the final result is the discarded sum W. i The summation sequence D y .

[0039] Finally, sequence D y The elements in the sequence D M The sequence lengths are respectively related to D M Divide the elements in the table, take the absolute value of the result, and then calculate the average value using all the results to obtain the grayscale estimate G of the pilot light source. M '.

[0040] Step 4: Reconstruct the pilot light source signal and remove...

[0041] Based on the grayscale estimate G obtained in step three M ', the spreading sequence s of the pilot light source determined by the transmitting end portion M and sending data d M Remodulate the pilot light source signal y GM ', its expression is:

[0042] y GM '=G M 'd M s M (9)

[0043] And superimposed sequence y GM 'From sequence y cut After removal, a new superimposed sequence y is obtained. cut ', its expression is:

[0044] y cut '=y cut -y GM (10)

[0045] Step 5: Demodulate the communication light source signal

[0046] The new superposition sequence y obtained from step four cut ', based on the spreading sequence s1,s2,...,s of the communication light source determined at the transmitting end. K Despreading is performed simultaneously on K communication light sources to recover the transmission sequences d1', d2', ... d of each light source. K This enables data transmission between K communication light sources in a multi-light source VLC-CDMA system.

[0047] The beneficial effects of this invention are as follows:

[0048] Compared to VLC-CDMA systems that use traditional pseudo-random sequences for spread spectrum, this invention designs the system's transmitter light source as a combination of "orthogonal code + non-orthogonal code" transmitted waveforms. Specifically, a pilot light source with a non-orthogonal code spread spectrum provides pilot synchronization for each communication light source with an orthogonal code spread spectrum. This effectively reduces cross-correlation interference generated when demodulating the superimposed signals from each light source. Simultaneously, at the receiver, a targeted demodulation method is provided to recover the data transmitted by each communication light source from the designed light source waveforms. This enables data communication in multi-user VLC-CDMA systems using shorter code-length spread spectrum sequences, thus meeting the need for more users to transmit data simultaneously under current limitations in image sensor hardware. Attached Figure Description

[0049] Figure 1 This is a flowchart illustrating the specific process of transmitting optical signals at the transmitting end of the visible light communication light source waveform design method of the present invention. In the figure: 1 is the spreading sequence of four communication light sources, 2 is the spreading sequence of the pilot light source, 3 is the transmission data of the four communication light sources and the transmission data of one pilot light source, and 4 is the process of spreading the communication light source and the pilot light source, converting to unipolarity, and transmitting VLC-CDMA optical signals via LEDs.

[0050] Figure 2 This is a flowchart illustrating the receiving end portion of the visible light communication light source waveform design method of the present invention, which receives and demodulates the superimposed signal. In the figure: 1 is the bipolar superimposed sequence after conversion; 2 is the demodulated sequence obtained by truncating the left and right ends of the sequence; 3 is the amplitude estimation process of the pilot light source signal; 4 is the process of reconstructing the pilot light source signal and removing it from the superimposed sequence; 5 is the transmitted data of the four communication light sources recovered by demodulation. Detailed Implementation

[0051] The specific embodiments of the present invention are described in detail below with reference to the technical solutions (and accompanying drawings).

[0052] Assume a multi-source VLC-CDMA system has 4+1 light sources. Four light sources serve as communication light sources, responsible for data communication between the four users; one light source serves as a pilot light source, responsible for synchronous communication between the four users; and a CMOS image sensor receiver is responsible for receiving the superimposed signals from the pilot and communication light sources (4+1 VLC-CDMA signals), demodulating the transmitted data from the four users, and realizing communication transmission between the four light sources. The light source waveform design method consists of two parts:

[0053] Part 1: Transmitter Section

[0054] Step 1: Determine the spreading sequence of the communication light source

[0055] Let the spreading sequences of the four communication light sources be Walsh sequences. The code length L can be determined by equation (1). W If the code length is 16, then the spreading sequences of the four communication light sources are s1, s2, s3, and s4 with a code length of 16, as shown in the attached diagram. Figure 1 As shown in section 1, s1, s2, s3, and s4 are respectively:

[0056] s1=[-1,-1,-1,-1,-1,-1,-1,-1,+1,+1,+1,+1,+1,+1,+1,+1] (11)

[0057] s2=[-1,-1,-1,-1,+1,+1,+1,+1,+1,+1,+1,+1,-1,-1,-1,-1] (12)

[0058] s3=[-1,-1,-1,-1,+1,+1,+1,+1,-1,-1,-1,-1,+1,+1,+1,+1] (13)

[0059] s4=[-1,-1,+1,+1,+1,+1,-1,-1,-1,-1,+1,+1,+1,+1,-1,-1] (14)

[0060] Step 2: Determine the spreading sequence of the pilot light source.

[0061] Let the spreading sequence of one pilot light source be the M-sequence. The pilot light source provides synchronization for the signals transmitted by the four communication light sources. Let the code length multiple N = 4. The code length L is obtained from equation (2). M =64, then select the M sequence s with a code length of 64 and an autocorrelation sidelobe value less than or equal to 4. M As attached Figure 1 As shown in section 2, it is represented as follows:

[0062]

[0063] Step 3: Transmission of communication signals and pilot signals

[0064] Let the transmitted data of the four communication light sources be d1, d2, d3, d4, where d1, d2, d3, d4 ∈ {-1, +1}. Using the spreading sequences s1, s2, s3, s4 of the communication light sources, spread spectrum modulation is performed on the transmitted data of the four users with their corresponding spreading sequences according to equation (3), resulting in four spread baseband signals T1, T2, T3, T4. Then, according to equation (4), the four baseband signals are unipolar converted and loaded onto the communication light sources through OOK modulation, transmitting the VLC-CDMA signals y1, y2, y3, y4 of the four communication light sources. Let the transmitted data of the pilot light source be d... M , where d M∈{+1}, based on the spreading sequence s of the pilot light source M Similarly to equations (3) and (4), the data d to be sent will be... M With spread spectrum sequence s M After spread spectrum modulation, the baseband signal T is obtained. M and the signal T M After undergoing unipolar conversion, the signal is modulated by OOK and applied to the pilot light source to obtain the VLC-CDMA signal y transmitted by the pilot light source. M The transmitted data d1, d2, d3, d4 from the four communication light sources and the transmitted data d from the pilot light source. M As attached Figure 1 As shown in section 3, the process of spreading the communication light source and pilot light source, converting their unipolarity, and then loading the light signal onto the LED via OOK modulation is as follows: Figure 1 As shown in point 4.

[0065] Part Two: Receiver Section

[0066] Step 1: Bipolar transformation of unipolar superimposed grayscale value sequences

[0067] Using a CMOS image sensor as the receiver of the VLC-CDMA system, the system receives 4+1 superimposed VLC-CDMA signals from the pilot light source and the communication light source through a rolling shutter exposure mode. After grayscale processing of the image from the CMOS sensor, according to equation (5), the unipolar superimposed grayscale value sequence of the 4+1 superimposed VLC-CDMA signals is y. G(uni) , where y G(uni) =y GM +y G1 +y G2 +y G3 +y G4 y G(uni) The sequence length is L. Simultaneously, according to equation (6), the statistical sequence y... G(uni) The maximum value in the unipolar superposition of gray value sequences y G(uni) Transformed into a bipolar sequence y G(bi) As attached Figure 2 As shown in section 1.

[0068] Step 2: Determine the start and end points of demodulation.

[0069] Based on the determined pilot light source spreading sequence s M code length L M The sequence y after bipolar transformation G(bi) The front L M Position and after L M The positions are respectively related to s MPerform cross-correlation calculations and peak detection on the results of the two correlation calculations. If the positions of the maximum peaks are A1 and A2 respectively, then according to equations (7) and (8), the sequence y G(bi) The start demodulation position A begin and the end demodulation position A end They are A1 and L-(64-A2)-1 respectively, and the sequence y G(bi) The left and right ends of the sequence are truncated from the 1st to the A1-1th position and from the L-(64-A2)th to the Lth position to obtain the truncated sequence y. cut Its sequence length is L cut The extracted sequence y cut As attached Figure 1 As shown in point 2.

[0070] Step 3: Amplitude estimation of pilot light source signal

[0071] First, calculate the spread spectrum sequence s of the pilot light source respectively. M The sums of bits 1 to 16, 17 to 32, 33 to 48, and 49 to 64 are obtained as follows: 2, 2, 0, and -4 respectively. Since the sum of the third bit is 0, the order of the 0-values ​​is recorded as 3, resulting in the sum sequence D after removing the 0-values. M D M ={2,2,-4}.

[0072] Secondly, based on the sequence y extracted in step two... cut By shifting a summing window of length 16, the sequence y is paired every 16 bits. cut Calculate the sum M within 16 bits. i until the window moves to sequence y cut The summation ends when the number of summations is 16(m-1)+3, where m∈{1,2,...,L}. cut If the sum is 64, then discard the sum result, and finally obtain the sum sequence D containing the discarded sum results. y .

[0073] Finally, sequence D y The elements in the sequence D M The sequence length 3 is sequentially related to D M Divide the elements in the matrix by M1 / 2, M2 / 2, M4 / -4, ..., and take the absolute value of all results. Then, calculate the average value of all results to obtain the grayscale estimate G of the pilot light source. M The amplitude estimation process for the pilot light source signal is shown in the attached figure. Figure 2 As shown in point 3.

[0074] Step 4: Reconstruct the pilot light source signal and remove...

[0075] Based on the grayscale estimate G obtained in step three M ', the spreading sequence s of the pilot light source determined by the transmitting end portion M and sending data d M The remodulated pilot light source signal y is obtained according to equation (9). GM ', and by equation (10) the superimposed sequence y GM 'From sequence y cut After removal, a new superimposed sequence y is obtained. cut The process for reconstructing and removing the pilot light source signal is shown in the attached figure. Figure 2 As shown in point 4.

[0076] Step 5: Demodulate the communication light source signal

[0077] The new superposition sequence y obtained from step four cut Based on the spreading sequences s1, s2, s3, s4 of the communication light sources determined by the transmitting end, the four communication light sources are simultaneously despread to recover the transmitted data d1', d2', d3', d4' of each communication light source, as shown in the attached figure. Figure 2 As shown in section 5, the data transmission of four communication light sources in the multi-light source VLC-CDMA system is finally realized.

[0078] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A pilot-assisted visible light communication source waveform design method, characterized in that, The design method described above reduces cross-correlation interference generated during demodulation of signals from various light sources. It designs an "orthogonal code + non-orthogonal code" combination of transmitted waveforms for the transmitter of a multi-source VLC-CDMA system and provides a demodulation algorithm for the transmitted waveforms at the receiver. This allows for simultaneous data transmission by more users despite current limitations in image sensor hardware. The visible light communication waveform design method includes a transmitter section and a receiver section, as detailed below: Part 1: Transmitter Section Step 1: Determine the spreading sequence of the communication light source; Step 2: Determine the spreading sequence of the pilot light source; Step 3: Transmission of communication signals and pilot signals; Part Two: Receiver Section Step 1: Bipolar conversion of unipolar superimposed grayscale value sequences; Step 2: Determine the start and end points of demodulation; Step 3: Amplitude estimation of the pilot light source signal; Step 4: Reconstruct and remove the pilot light source signal; Step 5: Demodulate the communication light source signal; Assuming there is a multi-source VLC-CDMA system One light source, among which... Each light source serves as a communication signal transmitter, realizing... The system provides data communication functionality for each user, using a single light source as a pilot signal transmitter. Synchronous communication functionality for individual users; and a CMOS image sensor receiver for receiving pilot signals and communication signals. The signals superimposed by VLC-CDMA are demodulated. Sending data to individual users, achieving Communication transmission of a single light source; the transmitting end and receiving end are specifically as follows: Part 1: Transmitter Section Step 1: Determine the spreading sequence of the communication light source make The spreading sequence of the communication light source is a Walsh sequence, where the code length of the Walsh sequence is... Must meet: （1） in, Let represent the number of sequences after removing a sequence of all 1s from the Walsh sequence. Then, equation (1) represents the remaining sequence. A number of Walsh sequences are sufficient to allocate Individual users, thereby determining The spreading sequence of the communication light source is a code length of of ; Step 2: Determine the spreading sequence of the pilot light source. Let the spreading sequence of a pilot light source be the M-sequence, and the pilot light source be... The signals transmitted by the communication light source provide synchronization functionality, wherein the code length of the M sequence is... With code length Must meet: （2） in, Multiples of code length and ,Right now and Always an integer multiple, and the code length is The M-sequence must satisfy the condition that its autocorrelation function has a sidelobe value less than or equal to 4, thereby reducing cross-correlation interference generated during demodulation. Finally, the spreading sequence of the pilot light source that satisfies the above conditions is determined to have a code length of... of ; Step 3: Transmission of communication signals and pilot signals make The data transmitted by each communication light source is ,in, Based on the spreading sequence of the communication light source determined in step one. ,Will The transmitted data from each user is spread spectrum modulated with its corresponding spreading sequence, then the data transmitted by the first user is spread spectrum modulated with the first user's corresponding spreading sequence. The baseband signal spread by individual users for: （3） in, ; baseband signal After unipolar conversion, the signal is loaded separately into OOK modulation. On a communication light source, thereby sending VLC-CDMA signal of a communication light source , of which VLC-CDMA signals transmitted by a communication light source for: （4） in, This represents the amplitude value of the optical power of the signal transmitted by the light source. This represents the baseband signal of the communication light source after unipolar conversion, and That is, "1" represents the light source being on, and "0" represents the light source being off; let the pilot light source transmit data as... ,in, Based on the spread spectrum sequence of the pilot light source determined in step two. Similarly to equations (3) and (4), the data to be sent will be... With spread spectrum sequence Spread spectrum modulation is performed to obtain the spread spectrum baseband signal. After undergoing unipolar conversion, the signal is modulated by OOK and applied to the pilot light source to obtain the VLC-CDMA signal transmitted by the pilot light source. ; Part Two: Receiver Section Step 1: Bipolar transformation of unipolar superimposed grayscale value sequences A CMOS image sensor is used as the receiver in the VLC-CDMA system, and the pilot light source and communication light source are received through a rolling shutter exposure mode. The signals superimposed by VLC-CDMA, after grayscale processing of the CMOS sensor's image, represent... The unipolar superimposed grayscale value sequence of a VLC-CDMA superimposed signal is as follows: Its sequence length is Its expression is: （5） in, This represents the unipolar grayscale value sequence of the pilot light source. Indicates the first A unipolar grayscale value sequence of a communication light source. This represents the baseband signal of the pilot light source after unipolar conversion, and , This indicates the grayscale value of the bright stripes on the image caused by the pilot light source. Indicates the first The grayscale value of each communication light source, and All are related to the optical power amplitude value of the pilot light source Amplitude value of communication light source If the relationship is linear, then the unipolar superimposed gray value sequence Transformed into a bipolar sequence The expression is: （6） in, Represents a sequence The maximum value in can be obtained through statistics. The sequence value is output; Step 2: Determine the start and end points of demodulation. Based on the determined pilot light source spreading sequence code length The sequence after bipolar conversion The former Position and after The positions are respectively with Perform cross-correlation calculations, perform peak detection on the results of the two correlation calculations, and record the location of the maximum peak value. and For bipolar sequences The position where demodulation begins for: （7） The position where demodulation ends for: （8） The bipolar sequence is determined based on the start and end demodulation positions. The 1st to the 1st The position and the first To the The left and right ends of the sequence are truncated to obtain the truncated sequence. Its sequence length is ; Step 3: Amplitude estimation of pilot light source signal First, calculate the spread spectrum sequence of the pilot light source. middle to Sum within the range ,in If the sum of any additions is 0, discard the sum and record the order in which the sums with 0 values ​​were added. The order of summation after removing zero values ​​is obtained. The summation sequence of , ; Secondly, based on the sequence extracted in step two... By moving a length of The summation window, every bit pair sequence calculate Sum of digits until the window moves to the sequence The sum ends with the last digit, where Indicates the first The summation result of the summation, when the summation number is... At that time, among them If the sum is not found, then discard the sum and finally obtain the discarded sum. The summation sequence of ; Finally, the sequence The elements in the sequence The sequence lengths are respectively with Divide the elements in the table, take the absolute value of the result, and then calculate the average value using all the results to obtain the grayscale estimate of the pilot light source. ; Step 4: Reconstruct the pilot light source signal and remove... Based on the grayscale estimate obtained in step three The spread spectrum sequence of the pilot light source determined by the transmitting end. and sending data Remodulate the pilot light source signal Its expression is: （9） and superimposed sequence From sequence Remove the excess material to obtain a new superimposed sequence. Its expression is: （10） Step 5: Demodulate the communication light source signal The new superposition sequence obtained from step four Based on the spreading sequence of the communication light source determined at the transmitting end. ,right Each communication light source is despread simultaneously to recover the transmission sequence of each communication light source. Realizing multi-source VLC-CDMA systems Data transmission of a communication light source.

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