A visible light communication method based on optical complementary code CDMA using Rake receiving technology

Abstract

This invention discloses a visible light communication method based on optical complementary codes (CDMA) employing Rake reception technology, belonging to the field of visible light communication technology. This method leverages the characteristic that each group of optical complementary codes contains multiple sub-codes. At the transmitting end of the VLC-CDMA system, a single user's data is divided into multiple data streams and transmitted as optical signals by spreading each stream with a sub-code. At the receiving end, the multiple data streams of a single user are merged, and Rake reception technology is used to fully utilize the received multipath energy, thereby improving the ISI problem caused by multipath transmission of optical signals and effectively enhancing the system's communication performance. The VLC-CDMA system structure includes a transmitting end with K light sources (i.e., K user transmitters), a transmission channel, and a receiving end with one Rake receiver. The optical complementary codes used in this invention overcome the limitations of traditional address codes, such as poor correlation and insufficient number of users, providing the system with better anti-interference capability and bit error rate performance; they can enhance the received signal energy, improve the signal-to-noise ratio, and enhance the system's communication performance.

Description

Technical Field

[0001] This invention belongs to the field of visible light communication technology, and relates to Rake receiving technology, and particularly to a visible light communication method based on optical complementary code CDMA using Rake receiving technology. Background Technology

[0002] Visible Light Communication (VLC), a novel wireless communication technology, is based on the widely used indoor light-emitting diodes (LEDs) and integrates lighting and communication functions. With the rapid development of VLC technology, multi-user scenarios are inevitable. Using Code Division Multiple Access (CDMA) as the multiple access method for VLC systems can fully leverage the advantages of CDMA technology, enabling multiple light sources to transmit data simultaneously and meeting the needs of multiple users accessing the network simultaneously.

[0003] However, the performance of practical multi-source VLC-CDMA systems is affected by many factors. On the one hand, VLC-CDMA systems require unipolarity in the transmitted signal, and the correlation of the selected address code will seriously affect the system's anti-interference capability against multipath interference and its ability to suppress multiple access interference. On the other hand, in the transmission scenario of multi-source VLC, the indoor scattering environment will cause the optical signal generated at the transmitter to undergo multiple reflections before reaching the receiver, resulting in multipath transmission of the transmission optical path and causing inter-symbol interference (ISI), which seriously affects the communication performance of the system. Summary of the Invention

[0004] The technical problem to be solved by this invention is to select a unipolar code with ideal relevant characteristics and that meets the requirements of multi-user transmission as the address code, and at the same time, to solve the problem of ISI caused by multi-source signals affecting the system communication performance during multi-path transmission.

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

[0006] A visible light communication method based on Optical Complementary Code (OCC) CDMA using Rake receiver technology is disclosed. This method leverages the characteristic that each code group in an Optical Complementary Code (OCC) contains multiple sub-codes. At the transmitting end of the VLC-CDMA system, a single user's data is divided into multiple data streams and transmitted as optical signals by spreading each stream with a sub-code. At the receiving end, the multiple data streams of a single user are merged, and Rake receiver technology is used to fully utilize the received multipath energy, thereby improving the ISI problem caused by multipath transmission of optical signals and effectively enhancing the system's communication performance. The VLC-CDMA system of this invention consists of three parts: a transmitting end with K light sources (K user transmitters), a transmission channel, and a receiving end with one Rake receiver. The specific steps of the visible light communication method of this invention are as follows:

[0007] Part 1: Transmitter Section

[0008] Step 1: Subcode allocation for user data stream

[0009] The family of optical complementary codes allocated to K users is represented as OCC(N,ω,M,λ). a ,λ c ), where N represents the subcode length, ω represents the code group weight, i.e., the number of "1"s in each subcode, M represents the number of subcodes contained in each code group, and λ a This represents the maximum value of the sidelobe of the autocorrelation function and satisfies λ. a =0,λ c The maximum value of the cross-correlation function that satisfies λ c =1. Let b (k) Let be the data signal of the k-th user. Divide the data transmitted by each user into M data streams. Let m be the data stream of the k-th user. Where m ∈ {1, 2, ..., M}, k ∈ {1, 2, ..., K}. Therefore, the optical complementary code assigned to the k-th user can be represented as: in, Let m be the m-th subcode of user k, and Then the spread spectrum waveform of the m-th subcode of the k-th user It can be represented as:

[0010]

[0011] Where t represents the time variable, T c Let q(t) be the chip time, and q(t) be the waveform of the chip transmission, which can be assumed to be a rectangular pulse, and its expression is:

[0012]

[0013] Step 2: Spread spectrum modulation of user data stream

[0014] From the m-th sub-code of the k-th user in step one Each user's M data streams are spread with M subcodes, and then the i-th data sequence of the m-th data stream sent by the k-th user is obtained. AND subcode Spread spectrum signal The expression is:

[0015]

[0016] Among them, P t For transmission power, T b The duration of one bit, and T b =NT c , where I represents the length of the data being sent.

[0017] Step 3: Transmission of user optical signals

[0018] Each user's data stream is assigned a separate LED, meaning each user's sub-code uses an LED of a different wavelength to transmit optical signals, avoiding interference between sub-codes of the same user. Since the gain of the filters at the receiver and transmitter corresponding to the wavelengths is F... m The response sensitivity of a photoelectric detector (PD) is γ. m Therefore, a compensation circuit needs to be added to the LED at the transmitting end to achieve equal gain combining during the despreading process of the optical signal at the receiving end, with a gain of 1 / (F). m ×γ m The signal obtained in step two. The spread spectrum signal is amplified by an amplifier, and the amplified signal is then fed onto each LED after passing through a compensation circuit. M groups of optical signals are transmitted using OOK modulation. The transmitted signal s of the k-th user after combining the M groups of optical signals is then calculated. (k) The expression for (t) is:

[0019]

[0020] Where λ is the wavelength, S m (λ) is the spectral function of the m-th LED at the transmitter.

[0021] Part Two: Transmission Channel Section

[0022] Since VLC systems typically employ Intensity Modulation / Direct Detection (IM / DD) for modulation and demodulation, the transmission channel can be approximated as a linear time-invariant system. The channel model can be represented by the impulse response, and the expression for the impulse response h(t) of the q-th LED is:

[0023]

[0024] Among them, Q LED h represents the total number of LEDs. (p) (t) represents the channel impulse response after the p-th reflection.

[0025] Part Three: Receiver Section

[0026] Step 1: Receiving K user signals

[0027] The receiving end recovers the data transmitted by each user through a Rake receiver. The transmitted signal s in equation (4) is used to... (k) Given the channel impulse response h(t) in equation (5), the expression for the received signal r(t) of the Rake receiver for K users is:

[0028]

[0029] Where L represents the total number of paths the signal takes after reflection, h (k) (t) represents the channel impulse response of the k-th user, h l(k) (t) represents the channel impulse response of the l-th path for the k-th user, s l(k) (t) represents the signal after the k-th user passes through the l-th path with a time delay, and s l(k) (t)=s (k) (t-τ l ), τ l Let represent the time delay of the signal as it travels through the l-th path, and n(t) represent the noise.

[0030] Step 2: Time Delay Alignment of L Path Signals

[0031] Each path signal in the received signal r(t) needs to be time-delay aligned before demodulation. Therefore, the received signal r of the l'-th path after time-delay alignment... l' The expression for (t) is:

[0032] r l' (t)=r[t-(τ L -τ l' (7)

[0033] Where, τ Lτ represents the time delay of the signal as it travels along the Lth path. l' This represents the time delay of the signal as it travels through the l'-th path.

[0034] Step 3: Despread and merge the M groups of data streams containing the j-th data from the g-th user.

[0035] The time-delayed aligned signal r obtained from step two l' (t) demodulates the signals of each user and each path after delay alignment. The demodulation process is the same for each user and each path. Taking the demodulation of the signal of the g-th user as an example, the received signal of the m-th data stream of the g-th user on the l'-th path is... The expression is:

[0036]

[0037] in, Let m represent the data stream signal of the k-th user after the time delay of traversing the l-th path, and assume that the channel impulse response of each subcode is the same, which is h. l(k) , τ k Let n represent the propagation delay for the k-th user. m (t) represents the noise of the m-th data stream. Optical signals carrying different sub-codes are filtered out by a filter and converted into electrical signals by a PD. The user data is despread using complementary codes consisting of M sub-codes allocated to the g-th user. Assuming the receiver and the g-th user's signals satisfy the synchronization condition, the received signal is determined by equation (8). The expression for the despreading result of the j-th data of the m-th subcode of the g-th user on the l'-th path is:

[0038]

[0039] in, τ represents the m-th sub-code of user g. g h represents the propagation delay for the g-th user. l'(g) The first term of equation (9) represents the channel impulse response of the l'th path of the g-th user. The second term represents the j-th data after despreading the m-th subcode on the l'th path of user g. This indicates that user g's data stream in the m-th group on the l'-th path is interfered with by other users, the third term. This indicates the multipath interference experienced by user g on the m-th data stream along the l'-th path; the last term Let m represent the noise of the m-th data stream on the l'-th path, which is Gaussian white noise. Equation (9) is used to despread all M data streams of the j-th data of the g-th user, and these M data streams are then merged with equal gain to obtain the merged result of the l'-th path for user g. This allows us to obtain the energy of all L paths for the j-th data of the g-th user.

[0040] Step 4: Merging the energy of L paths

[0041] The merging results of each path are obtained from step three. The system employs three Rake receiver combining methods—selective, maximum ratio, and equal gain—to combine the output results of the L paths for the g-th user. When the system uses selective combining, the weighting coefficient ζ on the selected path is 1. In visible light communication, the path with the highest energy is usually the first path, i.e., l' = 1, ζ1 = 1. When the system uses maximum ratio combining, the weighting coefficient ζ on the path... l' The ratio of the current path energy to all energies is expressed as: Among them, E l' Let h be the energy of the signal from the l'th path, and let h be the path coefficients normalized. 1 +h 2 +…+h l' +…+h L =1, then the merging coefficient ζ l' =h l' When the system uses an equal-gain combining method, its combining coefficient ζ l' All are equal, and are the reciprocal of the total number of paths L, i.e., ζ1=ζ2=ζ3=…=ζ L = 1 / L. Therefore, combining the path coefficients of each merging method, the energy of the L paths for the g-th user and the j-th data has the following three merging results: and The expressions are as follows:

[0042]

[0043]

[0044]

[0045] In equations (10), (11), and (12), the first term represents the j-th bit of data from user g that needs to be recovered. The second term in equation (10) is I... 1(g) The first path of user g is interfered with by other users, and the third term J 1(g) The fourth term V represents the multipath interference experienced by user g's first path. 1 The noise of the first path is Gaussian white noise. The second term I in equations (11) and (12) l'(g) The l'th path of user g is interfered with by other users and The third item J l'(g) The multipath interference experienced by user g's l'th path and Fourth item V l' The noise of the l'th path of user g and Where V l' Distribution and They are the same, both being Gaussian white noise.

[0046] Step 5: Recover data through judgment

[0047] According to steps three and four, each user uses the same optical complementary code as during spread spectrum to despread user data. Based on the combined results of equations (10), (11), and (12), and assuming normalized transmit power, the j-th data result of user g is obtained by setting a decision variable, usually set to half of the detection peak value, thereby recovering all data of user g.

[0048] Repeat steps three, four, and five above to finally recover all transmitted data from K users, thus realizing visible light communication data transmission for K users within the system.

[0049] The effects and benefits of this invention are as follows:

[0050] Compared to VLC-CDMA systems using traditional unipolar codes, the optical complementary codes used in this invention overcome limitations such as poor correlation of traditional address codes and insufficient user numbers, providing the system with better anti-interference capabilities and bit error rate performance. Furthermore, addressing the ISI problem caused by multipath transmission in multi-source VLC transmission scenarios, this invention leverages the characteristic of optical complementary codes containing multiple subcodes to divide the data of a single user into multiple data stream optical signals. At the receiving end, Rake reception technology is used to merge the data streams and fully utilize the energy gain from multipath transmission, superimposing the energy from multiple paths to enhance the received signal energy, improve the signal-to-noise ratio, and enhance the system's communication performance. Attached Figure Description

[0051] Figure 1 This is a flowchart illustrating the specific process of transmitting optical signals at the transmitting end of the visible light communication method of the present invention. In the diagram: 1 represents the four data streams divided into the data transmitted by the k-th user; 2 represents the four sub-codes assigned to the four data streams; 3 represents the spreading operation performed on the four data streams and the four sub-codes respectively; and 4 represents the user's spreading signal being loaded onto each LED through a compensation circuit and transmitted as an optical signal using OOK modulation.

[0052] Figure 2This is a flowchart illustrating the demodulation of multipath signals by a Rake receiver in the receiving end of the visible light communication method of this invention. In the diagram: 1 represents the combined signals from the four users received by the receiver; 2 represents the four path signals after time delay alignment; 3 represents the despreading and merging of the signals after passing through filters and PDs with optical complementary codes into four data streams; 4 represents the merging of the energy of the four paths based on path coefficients; and 5 represents the data recovery through decision processing. Detailed Implementation

[0053] The specific embodiments of the present invention are described in detail below with reference to the technical solution (and accompanying drawings).

[0054] A visible light communication method based on optical complementary code CDMA using Rake receiver technology is disclosed. The VLC-CDMA system consists of three parts: a transmitter section with four light sources (i.e., four user transmitters), a transmission channel section, and a receiver section with one Rake receiver. The specific steps for visible light communication between the four users are as follows:

[0055] Part 1: Transmitter Section

[0056] Step 1: Subcode allocation for user data stream

[0057] Let b (k) Let be the data signal of the k-th user, where k∈{1,2,3,4}. Assume that each user's data is divided into 4 data streams. As attached Figure 1 As shown in section 1, the first four user codes C of the family of optical complementary codes OCC(16,1,4,0,1) assigned to four users. (1) C (2) C (3) and C (4) They are respectively:

[0058]

[0059]

[0060]

[0061]

[0062] In this system, the subcode length N = 16, each subcode contains only one "1", the number of subcodes M = 4, meaning the detection peak value is also 4, and the maximum value of the autocorrelation function sidelobe λ is... a =0, the maximum value of the cross-correlation function λ c =1. Therefore, the optical complementary code assigned to the k-th user can be represented as: in, Let m be the m-th subcode of user k, and The four sub-codes assigned to each user are as follows: Figure 1 As shown in section 2. From equations (1) and (2), the spread spectrum waveforms of the 16 subcodes for the 4 users are obtained as follows.

[0063] Step 2: Spread spectrum modulation of user data stream

[0064] Equation (3) combines the four user data b (1) b (2) b (3) b (4) Each of the four data streams is associated with user code C. (1) C (2) C (3) C (4) Each set of four subcodes is spread spectrum modulated, as shown in the attached diagram. Figure 1 As shown in point 3.

[0065] Obtain the spread spectrum signal

[0066] Step 3: Transmission of user optical signals

[0067] Each user's four data streams are assigned a separate LED, meaning each subcode of each user uses an LED with a different wavelength to transmit the optical signal. The spread-spectrum signal is amplified by an amplifier, and the amplified signal is then compensated and applied to each LED. The combined optical signal s from the user's four data streams is transmitted using OOK modulation. (k) (t), then the transmitted signals s of the four users are obtained from equation (4). (1) (t), s (2) (t), s (3) (t) and s (4) (t), as shown in the appendix Figure 1 As shown in point 4.

[0068] Part Two: Transmission Channel Section

[0069] By modulating and demodulating the information using IM / DD, and approximating the transmission channel as a linear time-invariant system, the channel impulse response of the four LED light sources is obtained from equation (5) as h(t).

[0070] Part Three: Receiver Section

[0071] Step 1: Receiving 4 User Signals

[0072] The receiving end recovers the data signals from each user using a Rake receiver. This is based on the transmitted signals from the four users.(1) (t), s (2) (t), s (3) (t), s (4) (t) and the channel impulse response h(t) of 4 LED light sources, assuming the total number of reflected paths L = 4, then the combined received signal of the receiver for the 4 users is obtained from equation (6) as r(t), as shown in the appendix. Figure 2 As shown at point 1 in the middle.

[0073] Step 2: Time Delay Alignment of the 4 Path Signals

[0074] Equation (7) is used to perform time delay alignment on the four path signals of the received signal r(t) obtained in step one. The four path signals that need to be demodulated after time delay alignment are r(t) and r(t). 1 (t), r 2 (t), r 3 (t) and r 4 (t), as shown in the appendix Figure 2 As shown in point 2.

[0075] Step 3: Despread and merge the four data streams of the g-th user and the j-th data.

[0076] For the time-delay aligned signal r 1 (t), r 2 (t), r 3 (t) and r 4 (t) Demodulation is performed, where the demodulation process is the same for each user and each path signal. Taking the demodulation of the g-th user's signal as an example, and assuming that the channel impulse response of each subcode is the same, which is h. l(k) , where g∈{1,2,3,4}. The received signal from equation (8) Where l'∈{1,2,3,4}, the received signal is filtered through a filter to extract optical signals carried by different subcodes, and then converted into electrical signals by a PD. The optical complementary code, consisting of 4 subcodes, allocated to the g-th user is used to despread the user data. Assuming that the receiver and the signal of the g-th user satisfy the synchronization condition, the four data streams of the j-th data of the g-th user on the l'-th path are despread by equation (9). The four data streams are then combined with equal gain to obtain the merged result b of the l'th path for user g. l'(g) (j), and thus obtain the energy b of all 4 paths of the j-th data of the g-th user. 1(g) (j), b 2(g) (j), b 3(g) (j), b 4(g) (j) The process of despreading and merging the four data streams of a single user is shown in the appendix. Figure 2 As shown in point 3.

[0077] Step 4: Merging the energy of the 4 paths

[0078] The merging results of the four paths obtained in step three are then combined using three Rake receiver merging methods: selective, maximum ratio, and equal gain, to merge the energy outputs of the four paths for the g-th user. When the system uses selective merging, l' = 1 and ζ1 = 1; when the system uses maximum ratio merging, through power normalization, it is assumed that the channel gain values ​​of the four paths are h... 1 =0.529, h 2 =0.243, h 3 =0.139 and h 4 =0.09, occurring at t=15 (7.5ns), t=19 (9.5ns), t=21 (10.5ns), and t=24 (12ns), respectively. Then the merging coefficient ζ is... l' =h l' When the system uses an equal-gain combining method, its combining coefficient ζ l' All are equal, i.e., ζ1=ζ2=ζ3=ζ4=1 / 4. Therefore, combining the path coefficients of the three merging methods, from equations (10), (11) and (12), based on the energy of the four paths obtained in step three, the three merging results of the energy of the L paths of the j-th data of the g-th user are as follows: and The process of merging the four paths based on the path coefficients assigned to each path is shown in the appendix. Figure 2 As shown in point 4.

[0079] Step 5: Recover data through judgment

[0080] Based on steps three and four, and the combined results of equations (10), (11), and (12) and Based on the assumption of normalized transmit power, the j-th data result of user g is obtained by setting the decision variable to half of the detected peak value, as shown in the appendix. Figure 2 As shown in section 5. Then, all data for the g-th user is recovered.

[0081] Repeat steps three, four, and five above to finally recover all sent data from the four users. (1) ,b (2) ,b (3) ,b (4) This enables visible light communication data transmission between four users within the system.

[0082] 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 visible light communication method based on optical complementary code CDMA using Rake receiving technology, characterized in that, The method described above combines the characteristic that each group of codes in Optical Complementary Code (OCC) contains multiple subcodes. At the transmitting end of the VLC-CDMA system, a single user's data is divided into multiple data streams and transmitted as optical signals by spreading each stream with subcodes. At the receiving end, the multiple data streams of a single user are merged, and Rake reception technology is used to fully utilize the received multipath energy, thus improving the ISI problem caused by multipath transmission of optical signals and enhancing the system's communication performance. The structure of the VLC-CDMA system consists of three parts, namely containing... One light source The visible light communication method comprises a transmitter section, a transmission channel section, and a receiver section containing a Rake receiver; the specific steps of the method are as follows: Part 1: Transmitter Section Step 1: Subcode allocation for user data stream will be assigned to The family of optical complementary codes for each user is represented as follows: ,in, Indicates the subcode length. This represents the weight of the code group, that is, the number of "1"s in each subcode. This indicates the number of subcodes contained in each code group. This represents the maximum value of the sidelobe of the autocorrelation function and satisfies , Denotes the maximum value of the cross-correlation function and satisfies ; set up It is the first The data signals of each user are divided into the data sent by each user. Group data stream, then For the first The first user's Group data stream; among which, , Therefore, the first The optical complementary code assigned to each user is represented as follows: ;in, For users The Number of codes, and , ; Then the first The user Spread spectrum waveform of individual code Represented as: (1) in, Representing the independent variable of time, For chip time, The waveform for chip transmission can be assumed to be a rectangular pulse, and its expression is: (2) Step 2: Spread spectrum modulation of user data stream From step one The user Subcode Each user Group data streams respectively with If the sub-code is used for spreading operation, then the first sub-code... The first user sent the The first group of data streams Data sequences AND subcode Spread spectrum signal The expression is: (3) in, For transmission power, The duration of one bit, and , Indicates the length of the data sent; Step 3: Transmission of user optical signals Each user's data stream is assigned a separate LED, meaning each user's sub-code uses an LED of a different wavelength to transmit optical signals, avoiding interference between sub-codes of the same user; since the gain of the filters at the receiver and transmitter corresponding to the wavelengths is... The response sensitivity of the photodetector PD is Therefore, a compensation circuit needs to be added to the LED at the transmitting end to achieve equal-gain combining during the despreading process of the optical signal at the receiving end, with a gain of [value missing]. The signal obtained in step two The spread spectrum signal is amplified by an amplifier, and the amplified signal is then fed onto each LED after passing through a compensation circuit and transmitted using OOK modulation. Group of optical signals, then the first Merge individual users Transmitted signal after group optical signal The expression is: (4) in, For wavelength, For the first transmitter The spectral function of an LED; Part Two: Transmission Channel Section If the channel model is represented by the impulse response, then the first... The impulse response of an LED The expression is: (5) in, The total number of LEDs For the first Channel impulse response after the second reflection; Part Three: Receiver Section Step 1: Reception of user signals The receiving end recovers the data transmitted by each user through a Rake receiver; the transmitted signal in formula (4) The channel impulse response in formula (5) Then the Rake receiver for Received signal for each user The expression is: (6) in, This represents the total number of paths the signal takes after reflection. For the first Channel impulse response of individual users For the first The first user's Channel impulse response of each path Indicates the first The user went through the first The signal after the path delay, and , Indicates that the signal has passed through the first The delay of the path, Indicates noise; Step Two: Delay alignment of path signals Received signal Each path signal in the signal needs to be time-delay aligned before demodulation can be performed. Therefore, after time-delay alignment, the [missing information - likely a specific path or function]... Received signal along the path The expression is: (7) in, Indicates that the signal has passed through the first The delay of the path, Indicates that the signal has passed through the first The delay of the path; Step 3: De-expand and merge the first The user Data Group data stream The time-delayed aligned signal obtained from step two Demodulate the signals after time delay alignment for each user and each path; the demodulation process is the same for each user and each path signal, with the demodulation of the first... Taking the signal of the first user as an example, then the first user's signal... The user in the first The first on the path Group data stream received signal The expression is: (8) in, Indicates the first The user went through the first The first path delay The data stream signal is grouped, and it is assumed that the channel impulse response of each subcode is the same, and all are... , Indicates the first Propagation delay per user, For the first Noise in the group data stream; the optical signals carried by different subcodes are filtered out by the optical filter, and then converted into electrical signals by the PD, which are then used to allocate the signal to the first... Individual users include The complementary code of the sub-code is used to despread the user data; assuming the receiver and the... The signals of each user satisfy the synchronization condition, and the received signal is obtained from equation (8). Then the first The user in the first The first path The first of the sub-codes The expression for the despreading result of the data is: (9) in, Indicates user The Individual code, Indicates the first Propagation delay per user, Indicates the first The user The channel impulse response of the path, the first term of equation (9) represents the user's The The first path The descaling of the first subcode One data point, the second item Indicates user In the The first path The group data stream is interfered with by other users, the third item Indicates user In the The first path Multipath interference affecting the group data stream; the last item Indicates the first The first path The noise in the group of data streams is Gaussian white noise; the first result is obtained by solving equation (9). The user All data Group data stream, and Group data stream gain merging to obtain user No. The result of merging the paths And thus obtain the first The user All data Path energy; Step Four: Merging of path energy The merging results of each path are obtained from step three. Three Rake receiver combining methods—selective, maximum ratio, and equal gain—were applied to the first Rake receiver. users The output results of the energy of each path are merged; Step 5: Recover data through judgment Based on steps three and four, each user uses the same optical complementary code as during spread spectrum to despread user data; from the merging result of step four, assuming normalized transmit power, the user data is obtained by setting a decision variable to half of the detection peak value. The The data result is used to recover the first data result. All data of each user; Repeat steps three, four, and five above to finally restore. All data sent by each user, realizing the system's internal... Visible light communication data transmission for individual users.

2. The visible light communication method based on optical complementary code CDMA using Rake receiving technology according to claim 1, characterized in that, Step Four of Part Three During the merging of path energies: When the system uses a selective merging method, the weighting coefficients on the selected paths In visible light communication, the path with the highest path energy is the first path, i.e. , When the system uses the maximum ratio merging method, the path weighting coefficients... The ratio of the current path energy to all energies is expressed as: ;in, For the first The energy of each path signal, and the path coefficients are normalized, i.e. Then the merging coefficient ; When the system adopts an equal-gain combining method, its combining coefficient is... All are equal, representing the total number of paths. The reciprocal of, that is ; Therefore, combining the path coefficients of each merging method, the first... The user Data Three merging results of path energy , and The expressions are as follows: (10) (11) (12) In equations (10), (11), and (12), the first term represents the user who needs to be restored. The Bit data; The second term in equation (10) For users The first path is interfered with by other users, the third path For users The first path is subject to multipath interference, the fourth item The noise of the first path is Gaussian white noise; the second term in equations (11) and (12) For users The The path is interfered with by other users and The third item For users The The path is subject to multipath interference and , fourth item For users The Noise along the path and ,in Distribution and They are the same, both being Gaussian white noise.

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