A channel estimation error correction method for visible light communication system

Abstract

The present invention proposes a channel estimation error correction method for a visible light communication system. The method first performs spectrum spreading at the transmitting end, then performs subcarrier conjugate symmetry operation, and obtains an LED driving signal after IFFT and zero-value limiting; the receiving end performs channel estimation after FFT operation, and then extracts effective subcarriers for spectrum despreading; according to the linear minimum mean square error criterion, the mean of the mean square error with respect to the channel estimation error is calculated, and the mean is minimized to obtain a filter matrix of a linear filter, and linear filtering is performed. The method of the present invention can effectively reduce the interference caused by the channel estimation error, and under the same signal-to-noise ratio conditions, a lower bit error rate performance can be obtained.

Description

Technical Field

[0001] The invention relates to a visible light communication system channel estimation error correction method, belonging to the technical field of visible light communication. Background Art

[0002] Visible light communication (VLC) has become one of the candidate solutions for 6G indoor coverage because it does not require spectrum licenses, can take into account lighting, has good confidentiality and high system speed. In order to increase the transmission rate, VLC usually adopts a modified orthogonal frequency division multiplexing (OFDM) modulation scheme. In order to further improve the spectrum efficiency, some people have proposed to transplant the multi-carrier MC-CDMA modulation that combines OFDM and code division multiple access (CDMA) modulation technologies into the VLC system. Channel estimation is an indispensable step in this process. When there are errors in channel estimation, the orthogonality of the user identity code will be destroyed, causing interference. Therefore, finding a method to linearly correct the existing channel estimation errors is crucial to improving system performance. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention proposes a channel estimation error correction method for a visible light communication system, applies MC-CDMA modulation technology to visible light communication, establishes an asymmetric tailored light ACO-MC-CDMA system model, and studies the channel estimation error correction problem.

[0004] In order to solve the above problems, the technical solution adopted by the present invention is:

[0005] A visible light communication system channel estimation error correction method, characterized in that the system is composed of a transmitting end and a receiving end, and the specific steps of the transmitting end are as follows:

[0006] Step A: Spread the QAM symbol, the expression is:

[0007] k=sc

[0008] Where k is the symbol matrix after spread spectrum, the dimension is n×M, n is the length of the transmitted QAM symbol, M=N / 4 is the length of the spread spectrum sequence, N is the number of FFT points, k=(k0,k1,…,k i ,…,k n-1 ), k i is the i-th symbol vector after spread spectrum, k i =(k 0,i ,k 1,i ,…,k m,i ,…,k M-1,i ) T , m is the frequency domain number, k m,iis the value of the ith symbol vector on the mth subcarrier after spread spectrum; s is the QAM symbol matrix with dimension n×U, where U is the number of users, s=(s0,s1,…,s u ,…,s U-1 ), s u is the QAM symbol vector sent by user u, s u =(s 0,u ,s 1,u ,…s i,u ,…,s n-1,u ) T ,s i,u is the i-th QAM symbol sent by user u; c is the orthogonal spreading matrix with dimension U×M, c=(c0,c1,…,c u ,…,c U-1 ) T , c u =(c 0,u ,c 1,u ,…,c m,u ,…,c M-1,u ), c u is any non-repeating row in an orthogonal spread spectrum matrix such as the Walsh matrix, c m,u The value of is 0 or 1; (·) T Represents the transpose of a vector or matrix;

[0009] Step B: For the symbol vector k i Perform subcarrier conjugate symmetry operation and map it to N subcarriers to obtain D i , the D i for:

[0010] D i =(D 0,i ,D 1,i ,…,D m,i …,D N-1,i ) T

[0011] Among them, D m,i for:

[0012]

[0013] in,(·) * It means taking conjugate;

[0014] Step C: D i Perform N-point IFFT operation and get the output d i ;

[0015] Step D: i Perform zero-value limiting, that is, set the signal less than 0 to 0, and obtain the driving signal of the LED;

[0016] The error correction method of the system receiving end comprises the following steps:

[0017] Step E: Convert the serial received signal on the PD into parallel data r i , length is n;

[0018] Step F: i Perform N-point FFT operation and get the output Said for:

[0019]

[0020] in, Represents the data of the i-th symbol vector on the m-th subcarrier after FFT operation;

[0021] Step G: Perform channel estimation to obtain B i , B i =(B 0,i ,B 1,i ,…,B m,i ,…,B M-1,i ) T , where B m,i The expression is:

[0022]

[0023] H m is the channel estimation value on the mth subcarrier; is the exact value of the channel on the mth subcarrier, is the channel estimation error on the mth subcarrier, ε0,…,ε m ,…,ε M-1 Independent and identically distributed, all have mean 0 and variance σ 2 Normal distribution of

[0024] Step H: From B i Extracted from Said for:

[0025]

[0026] The extraction method is:

[0027]

[0028] in, Represents the value of the i-th symbol vector on the m-th subcarrier after data extraction;

[0029] Step I: Perform despreading to obtain the received symbol E i , wherein E i for:

[0030] E i =(E 0,i ,E 1,i ,…,E m,i ,…,E M-1,i ) T

[0031] The despreading method is:

[0032]

[0033] Among them, E i The receiving symbol is c u and The inner product of

[0034] Step J: E i Perform linear filtering to reduce the interference caused by channel estimation error, let E i After the linear filter matrix L, the linear filter matrix L is:

[0035]

[0036] Among them, c m =(c 0,m ,c 1,m ,…,c U-1,m ), is the variance of the channel noise, and I is the identity matrix.

[0037] Beneficial effects: The present invention proposes a channel estimation error correction method for a visible light communication system. The method first performs spectrum spread at the transmitting end, then performs subcarrier conjugate symmetry operation, and obtains the LED driving signal after IFFT and zero-value limiting; the receiving end performs channel estimation after FFT operation, and then extracts the effective subcarrier for despreading; according to the linear minimum mean square error criterion, the mean of the mean square error with respect to the channel estimation error is calculated, and the mean is minimized to obtain the filter matrix of the linear filter, and linear filtering is performed. The use of this method can effectively reduce the interference caused by the channel estimation error, and under the same signal-to-noise ratio conditions, a lower bit error rate performance can be obtained. DETAILED DESCRIPTION

[0038] The present invention proposes a channel estimation error correction method for a visible light communication system. The method first performs spectrum spread at the transmitting end, and then performs a subcarrier conjugate symmetric operation, and obtains an LED drive signal after IFFT and zero-value limiting; the receiving end performs channel estimation after FFT operation, and then extracts the effective subcarrier for despreading; according to the linear minimum mean square error criterion, the mean of the mean square error with respect to the channel estimation error is calculated, and the mean is minimized to obtain a filter matrix of the linear filter, and linear filtering is performed. The use of this method can effectively reduce the interference caused by the channel estimation error, and under the same signal-to-noise ratio conditions, a lower bit error rate performance can be obtained. In order to better illustrate the method of the present invention, the present invention is described below in conjunction with specific embodiments:

[0039] In a visible light ACO-MC-CDMA system, the number of effective subcarriers M=32, the total number of subcarriers N=128, and the number of users U=8.

[0040] Sending Side

[0041] The first step is to spread the QAM symbol, which is expressed as:

[0042] k=sc

[0043] Where k is the symbol matrix after spread spectrum, the dimension is n×M, n is the length of the transmitted QAM symbol, M=N / 4 is the length of the spread spectrum sequence, N is the number of FFT points, k=(k0,k1,…,k i ,…,k n-1 ), k i is the i-th symbol vector after spread spectrum, k i =(k 0,i ,k 1,i ,…,k m,i ,…,k M-1,i ) T , m is the frequency domain number, k m,i is the value of the ith symbol vector on the mth subcarrier after spread spectrum; s is the QAM symbol matrix with dimension n×U, where U is the number of users, s=(s0,s1,…,s u ,…,s U-1 ), s u is the QAM symbol vector sent by user u, s u =(s 0,u ,s 1,u ,…s i,u ,…,s n-1,u ) T ,s i,u is the i-th QAM symbol sent by user u; c is the orthogonal spreading matrix with dimension U×M, c=(c0,c1,…,c u ,…,c U-1 )T , c u =(c 0,u ,c 1,u ,…,c m,u ,…,c M-1,u ), c u is any non-repeating row in an orthogonal spread spectrum matrix such as the Walsh matrix, c m,u The value of is 0 or 1; (·) T Represents the transpose of a vector or matrix.

[0044] The second step is to transform the symbol vector k i Perform subcarrier conjugate symmetry operation and map it to N subcarriers to obtain D i , the D i for:

[0045] D i =(D 0,i ,D 1,i ,…,D m,i …,D N-1,i ) T

[0046] Among them, D m,i for:

[0047]

[0048] in,(·) * Indicates conjugation.

[0049] Step 3: D i Perform N-point IFFT operation and get the output d i .

[0050] Step 4: d i Perform zero-value limiting, that is, set the signal less than 0 to 0, and obtain the driving signal of the LED.

[0051] Receiver

[0052] The fifth step is to convert the serial received signal on the PD into parallel data r i , with a length of n.

[0053] Step 6: i Perform N-point FFT operation and get the output Said for:

[0054]

[0055] in, Represents the data of the i-th symbol vector on the m-th subcarrier after FFT operation.

[0056] Step 7: Perform channel estimation to obtain B i , B i =(B 0,i ,B 1,i ,…,B m,i ,…,B M-1,i ) T , where B m,i The expression is:

[0057]

[0058] H m is the channel estimation value on the mth subcarrier; is the exact value of the channel on the mth subcarrier, is the channel estimation error on the mth subcarrier, ε0,…,ε m ,…,ε M-1 Independent and identically distributed, all have mean 0 and variance σ 2 The normal distribution of .

[0059] Step 8. From B i Extracted from Said for:

[0060]

[0061] The extraction method is:

[0062]

[0063] in, Represents the value of the i-th symbol vector on the m-th subcarrier after data extraction.

[0064] Step 9, yes Perform despreading to obtain the received symbol E i , wherein E i for:

[0065] E i =(E 0,i ,E 1,i ,…,E m,i ,…,E M-1,i ) T

[0066] The despreading method is:

[0067]

[0068] Among them, E i The receiving symbol is c u and The inner product of .

[0069] Step 10, for E i Perform linear filtering to reduce the interference caused by channel estimation error, let E i After the linear filter matrix L, the linear filter matrix L is:

[0070]

[0071] Among them, c m =(c 0,m ,c 1,m ,…,c U-1,m ), is the variance of the channel noise, and I is the identity matrix.

Claims

1. A method for correcting channel estimation errors in a visible light communication system, wherein the visible light communication system is composed of a transmitting end and a receiving end, characterized in that: The error correction method of the transmitting end comprises the following steps: Step A: Spread the QAM symbol, the expression is: k=sc Where k is the symbol matrix after spread spectrum, the dimension is n×M, n is the length of the transmitted QAM symbol, M=N / 4 is the length of the spread spectrum sequence, N is the number of FFT points, k=(k0,k1,…,k i ,…,k n-1 ), k i is the i-th symbol vector after spread spectrum, k i =(k 0,i ,k 1,i ,...,k m,i ,...,k M-1,i ) T , m is the frequency domain number, k m,i is the value of the ith symbol vector after spread on the mth subcarrier; s is the QAM symbol matrix with dimension n×U, where U is the number of users, s=(s0,s1,...,s u ,...,s U-1 ), s u is the QAM symbol vector sent by user u, s u =(s 0,u ,s 1,u ,...s i,u ,...,s n-1,u ) T ,s i,u is the i-th QAM symbol sent by user u; c is the orthogonal spreading matrix with dimension U×M, c=(c0,c1,…,c u ,…,c U-1 ) T , c u =(c 0,u ,c 1,u ,…,c m,u ,…,c M-1,u ), c u is any non-repeating row in an orthogonal spread spectrum matrix such as the Walsh matrix, c m,u The value of is 0 or 1; (·) T Represents the transpose of a vector or matrix; Step B: For the symbol vector k i Perform subcarrier conjugate symmetry operation and map it to N subcarriers to obtain D i , the D i for: D i =(D 0,i ,D 1,i ,…,D m,i …,D N-1,i ) T Among them, D m,i for: in,(·) * It means taking conjugate; Step C: D i Perform N-point IFFT operation and get the output d i ; Step D: i Perform zero-value limiting, that is, set the signal less than 0 to 0, and obtain the driving signal of the LED; The error correction method of the receiving end comprises the following steps: Step E: Convert the serial received signal on the PD into parallel data r i , length is n; Step F: i Perform N-point FFT operation and get the output Said for: in, Represents the data of the i-th symbol vector on the m-th subcarrier after FFT operation; Step G: Perform channel estimation to obtain B i , B i =(B 0,i ,B 1,i ,…,B m,i ,…,B M-1,i ) T , where B m,i The expression is: H m is the channel estimation value on the mth subcarrier; is the exact value of the channel on the mth subcarrier, is the channel estimation error on the mth subcarrier, ε0,…,ε m ,…,ε M-1 Independent and identically distributed, all have mean 0 and variance σ 2 Normal distribution of Step H: From B i Extracted from Said for: The extraction method is: in, Represents the value of the i-th symbol vector on the m-th subcarrier after data extraction; Step I: Perform despreading to obtain the received symbol E i , wherein E i for: AND i =(And 0,i ,AND 1,i ,…,AND m,i ,…,AND M-1,i ) T The despreading method is: Among them, E i The receiving symbol is c u and The inner product of Step J: E i Perform linear filtering to reduce the interference caused by channel estimation error; let E i After the linear filter matrix L, the linear filter matrix L is: Among them, c m =(c 0,m ,c 1,m ,…,c U-1,m ), is the variance of the channel noise, and I is the identity matrix.

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