Cdma encoding and decoding method based on wireless ultraviolet light communication

Abstract

The application discloses a CDMA encoding and decoding method based on wireless ultraviolet light communication, and comprises the following steps: 1, constructing an address code code set according to the number of wireless ultraviolet light communication users; 2, selecting different address codes in the constructed code set to perform spread spectrum processing on the source signals of each user, and simultaneously sending the spread spectrum processed signals of each user through an ultraviolet light source; 3, converting the ultraviolet light signals sent in step 2 into electric signals through a photomultiplier at a receiving end, and performing address code decoding processing on the electric signals to recover original data signals. The application solves the problems that time division multiplexing needs to uniformly schedule the sending end, and the sending end can only send information in the allocated time slot; solves the problem that space division multiplexing limits the spatial position of the sending end; and simultaneously solves the problems that the existing prime code and optical orthogonal code of ultraviolet light CDMA communication have poor anti-code interference ability and high bit error rate.

Description

CDMA Encoding and Decoding Methods Based on Wireless Ultraviolet Communication Technical Field

[0001] This invention belongs to the field of ultraviolet light communication technology, specifically relating to a CDMA encoding and decoding method based on wireless ultraviolet light communication. Background Technology

[0002] Ultraviolet (UV) communication uses the "solar-blind" band (200-280nm) of UV light as the information transmission carrier and the atmospheric channel as the transmission medium. Solar radiation in the "solar-blind" band is strongly absorbed by ozone molecules in the stratosphere, and this UV band is almost non-existent in the near-Earth solar spectrum; therefore, it is commonly referred to as the "solar-blind zone." UV communication has advantages such as strong anti-interference capability, high security, low resolution, non-line-of-sight communication, and all-weather operation. It can achieve both line-of-sight and non-line-of-sight communication, solving the problem of high alignment requirements between the transmitting and receiving ends in traditional communication methods, and has gradually become a research hotspot.

[0003] Multiplexing techniques in wireless ultraviolet (UV) communication significantly impact system communication quality. Time-division multiplexing (TDM), space-division multiplexing (SDM), and code-division multiple access (CDMA) effectively address inter-link interference in UV communication, improving overall system quality. However, TDM suffers from limitations, such as users only being able to transmit information in specific time slots, and SDM faces restrictions on the locations of multiple transmitters and receivers. CDMA, on the other hand, distinguishes different users by using different address codes. Each transmitter is assigned a unique address code, and upon receiving, only by knowing the specific address code assigned to a particular user can the information be correctly decoded. This allows different users to communicate simultaneously on the same channel without interference. Therefore, using CDMA is of significant importance in addressing special cases where multiple links are simultaneously located in the same area or where the distance between transmitters is small.

[0004] Currently, the CDMA coding methods used in ultraviolet light communication systems include primitive digital codes and optical orthogonal codes. However, these two coding methods are prone to inter-code interference due to the scattering effect of ultraviolet light. Summary of the Invention

[0005] The purpose of this invention is to provide a CDMA encoding and decoding method based on wireless ultraviolet light communication, which solves the problems of inter-link interference and inter-code interference when multiple ultraviolet light links communicate simultaneously in the same location or when the distance between transmitters is small.

[0006] The technical solution adopted in this invention is a CDMA encoding and decoding method based on wireless ultraviolet light communication, which is implemented according to the following steps:

[0007] Step 1: Construct an address code set based on the number of wireless ultraviolet light communication users;

[0008] Step 2: Select different address codes in the constructed code set to spread the source signal of each user, and transmit the spread signal of each user simultaneously through an ultraviolet LED.

[0009] Step 3: The receiving end converts the received ultraviolet light signal into an electrical signal through a photomultiplier tube, and performs address code decoding on the electrical signal to recover the original data signal.

[0010] The invention is further characterized by:

[0011] Step 1 is as follows:

[0012] Step 1.1: Set the initial matrix as...

[0013] Step 1.2: Add a zero sequence after each column to construct a code set with K=2 wireless ultraviolet light communication users and w=1 code weight.

[0014]

[0015] Where A1 = [1 0], B1 = [0 0], C1 = [0 0], D1 = [1 0];

[0016] Step 1.3: If the code weight w remains constant, as the number of wireless ultraviolet communication users K increases, the iterative formula for the code set is:

[0017]

[0018] Where X is a diagonal matrix Y is an inverse diagonal matrix The code length of the newly constructed code set C is L = 2K = 2 n+1 The maximum number of users available is K = 2 n ;

[0019] Step 1.4: If the number of users K remains constant, and the code weight w increases, the iterative formula for the code set is:

[0020]

[0021] After construction, the new code set C has a code length of L = 2Kw = w2. n+1 The number of available users is K = 2 n .

[0022] Step 2 involves selecting different address codes from the constructed code set to perform spread spectrum processing on the source signal of each user. Specifically, each row of the address code set in Step 1 corresponds to an address code. Any row is selected as the address code of the user. Each bit of the original data signal is multiplied by its corresponding address code, which expands one bit to the corresponding number of bits of the address code.

[0023] The specific process in step 2 is as follows:

[0024] Step 2.1: Let X be the N-bit binary sequence of user k's data. k ={x k,0 ,x k,1 ,…,x k,i ,…,x k,N-1 The time-domain expression of the signal transmitted by the k-th user is:

[0025]

[0026] in

[0027] Step 2.2: The address code sequence of user k is the code set. Let d be a row of elements. k ={d k,0 ,d k,1 ,…,d k,j ,…,d k,L-1 The time-domain expression of user k's data after encoding and spreading is:

[0028]

[0029] in,

[0030] Step 2.3: After spreading and coding, the K user data are simultaneously transmitted via an ultraviolet light source as follows:

[0031]

[0032] Step 2: The ultraviolet wavelength emitted by the ultraviolet LED is 200nm-400nm.

[0033] Step 3 is as follows:

[0034] Step 3.1: The photomultiplier tube at the receiving end uses a photomultiplier tube with a wavelength coverage of 200nm-400nm to receive ultraviolet light signals and convert the ultraviolet light signals into electrical signals;

[0035] Step 3.2: When decoding the electrical signal, the same address code as the sending end is used to multiply the electrical signal, and then a decision is made to recover the required user signal.

[0036] Step 3.2 The specific process is as follows:

[0037] The signal expression received by the receiver is:

[0038] R(t) = S(t) + n(t)

[0039] Where n(t) is the additive white Gaussian noise (AWGN) signal;

[0040] Let R be the matrix of the received signal amplitude value sequence over the time interval [i, i+T). i ={R i,0 ,R i,1 ,…R i,j ,…,R i,L-1},and

[0041]

[0042] After decoding using the same address code as user k at the receiving end, the data for the time period [i, i+T) is calculated as follows:

[0043] Th i =d k ·R i T

[0044] Among them, R i T For R i Transpose of;

[0045] The original data signal r of user k in the time period [i, i+T) was recovered through the judgment. k (i), whose decision expression is:

[0046]

[0047] The required user signals are recovered based on the decision expression.

[0048] The beneficial effects of this invention are:

[0049] This invention presents a CDMA encoding and decoding method for wireless ultraviolet (UV) communication, solving the problems of inter-link interference, high bit error rate, and poor communication quality in UV communication when multiple links communicate simultaneously in the same location. The encoding method of this invention generates a code set where no two consecutive 1s exist in a single codeword, and no identical or adjacent bits are 1 between different codewords. Furthermore, it can construct codewords with different weights to accommodate different numbers of users, avoiding pulse superposition caused by scattering at the UV communication receiver and solving the problem of inter-symbol interference in UV communication. The overall principle is simple and easy to implement; information transmission is ultimately completed through photoelectric conversion, encoding / decoding, and modulation / demodulation. The principle and method are simple, and the communication quality is improved. Attached Figure Description

[0050] Figure 1 is a diagram of the application scenarios solved by the wireless ultraviolet CDMA communication of the present invention.

[0051] Figure 2 is a schematic diagram of the spread spectrum of the wireless ultraviolet CDMA communication of the present invention, which satisfies two transmitting end codes;

[0052] Figure 3 is a schematic diagram of the working principle of wireless ultraviolet CDMA communication of the present invention;

[0053] In Figure 1, T1 and T2 are the transmitting ends, and R1 and R2 are the receiving ends. Detailed Implementation

[0054] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0055] Example

[0056] This invention relates to a CDMA encoding and decoding method based on wireless ultraviolet light communication. The application scenario is shown in Figure 1, and the method is implemented according to the following steps:

[0057] Step 1: Construct an address code set based on the number of wireless ultraviolet light communication users; to construct an address code with a code weight w of 2 that satisfies the needs of 4-bit users, the construction steps are as follows:

[0058] Step 1.1: Set the initial matrix as...

[0059] Step 1.2: Construct a code set with K = 2 users and w = 1 code weight.

[0060]

[0061] Where A1 = [1 0], B1 = [0 0], C1 = [0 0], and D1 = [1 0].

[0062] Step 1.3, when the code weight w remains constant and the number of users K = 4,

[0063]

[0064] The new code set C after construction has a code length of L = 2K = 2 3 =8, number of available users K=2 2 =4.

[0065] Step 1.4, keeping the number of users K constant, when the code weight w = w + 1 = 2, the code set for:

[0066]

[0067] The new code set C after construction has a code length of L = 2Kw = w2 n+1 =2×2 3 =16, number of available users K=2 2 =4.

[0068] Step 2: Select different address codes in the constructed code set to spread the source signal of each user, and transmit the spread signal of each user simultaneously through an ultraviolet LED.

[0069] Different address codes are selected from the constructed code set to spread the source signal of each user. The specific process is as follows: the rows of the address code set are encoded, with each row corresponding to an address code. Each bit of the original data signal is multiplied by its corresponding address code, that is, one bit is expanded to the corresponding number of bits of the address code.

[0070] As shown in Figure 2, the specific process is as follows:

[0071] Step 2.1: Let the N-bit binary sequence of user 1's data be X1 = {1, 0, 1, 0}, and its function expression be:

[0072]

[0073] Let the N-bit binary sequence of user 2's data be X2 = {1, 1, 0, 0}, and its function expression be:

[0074]

[0075] in,

[0076] Step 2.2: Set the code The row elements are assigned to users 1 and 2 as address codes. Assume that the address code sequence of user 1 is d1 = {1,0,0,0} and the address code sequence of user 2 is d2 = {0,0,1,0}.

[0077] The function of User 1's data after encoding and spreading is:

[0078]

[0079] The function of User 2's data after encoding and spreading is:

[0080]

[0081] in,

[0082] Step 2.3: After spreading and coding, the two user data signals are simultaneously transmitted via an ultraviolet light source as follows:

[0083]

[0084] The time interval for each pulse is T. c .

[0085] The ultraviolet wavelength emitted by ultraviolet LEDs is 200nm-400nm.

[0086] Step 3: The receiving end converts the received ultraviolet light signal into an electrical signal using a photomultiplier tube, and then performs address code decoding on the electrical signal to recover the original data signal. The specific process is as follows:

[0087] Step 3.1: The photomultiplier tube at the receiving end uses a photomultiplier tube with a wavelength coverage of 200nm-400nm to receive ultraviolet light signals and convert the ultraviolet light signals into electrical signals;

[0088] Step 3.2: When decoding the electrical signal, the same address code as the transmitting end is used to multiply the electrical signal, and then a decision is made to recover the required user signal. The specific steps for decoding the received signal and making a decision to recover the original data of user 1 in this example are as follows:

[0089] The matrix of the signal amplitude value sequence received by the receiving end in the time period [0, 0+T) is R0 = {R 0,0 ,R 0,1 ,R 0,2 ,R 0,3},in

[0090]

[0091] Similarly, we can obtain R 0,1 =|n(t)|, R 0,2 =1+|n(t)|, R 0,3=|n(t)|.

[0092] After decoding at the receiving end using the same address code as User 1, the time interval [0, 0 + T) is used to determine the data Th0 = d1·R0. T =1+|n(t)|. The original data signal r1(0)=1 of user 1 in the time period [0,0+T) is recovered by the decision.

[0093] Similarly, we can obtain r1(1) = 0, r1(2) = 1, r1(3) = 0; then the recovered binary sequence of user 1 signal is r1 = {1, 0, 1, 0}.

[0094] The initial matrix given in the encoding construction and the addition of a column of 0s after each column are to avoid the inter-symbol interference caused by the occurrence of continuous light pulses to the communication system. In the subsequent construction process, it is always ensured that a single codeword cannot have two adjacent 1s and that different codewords cannot have the same bit or adjacent bits as 1. This is to avoid the occurrence of continuous light pulses causing inter-symbol interference to the communication system even after multiple signals are superimposed.

[0095] As shown in Figure 3, the principle of the CDMA encoding and decoding method based on wireless ultraviolet light communication in this invention is that multiple transmitters are located at the same position and transmit information simultaneously. After the source information is spread by modulation and coding information, the transmitter emits ultraviolet light signals at a certain frequency and power. After the photomultiplier tube of the receiver detects the ultraviolet light signal, the required original signal is obtained through photoelectric conversion, decoding and threshold judgment.

[0096] The present invention provides a simple principle and structure for CDMA encoding and decoding methods based on wireless ultraviolet light communication. It solves the problem that time-division multiplexing transmitters cannot communicate at random times, thus improving channel utilization. It also solves the problem of spatial location limitations of space-division multiplexing transmitters. Furthermore, it addresses the problems of poor inter-symbol interference resistance and high bit error rate of existing atom codes and optical orthogonal codes in ultraviolet CDMA communication.

Claims

1. A CDMA encoding and decoding method based on wireless ultraviolet light communication, characterized in that, The specific implementation is as follows: Step 1: Construct an address code set based on the number of wireless ultraviolet light communication users; Step 2: Select different address codes from the constructed code set to spread the source signal of each user, and simultaneously transmit the spread signal of each user through an ultraviolet LED; Step 3: The receiving end converts the received ultraviolet light signal into an electrical signal through a photomultiplier tube, and performs address code decoding on the electrical signal to recover the original data signal; The specific process of Step 1 is as follows: Step 1.1: Set the initial matrix as... ； Step 1.2: Add a zero sequence after each column to construct a code set with K=2 wireless ultraviolet light communication users and w=1 code weight. ： Where A1=[10], B1=[00], C1=[00], D1=[10]; Step 1.3: If the code weight w remains unchanged, when the number of wireless ultraviolet communication users K increases, the iterative formula of the code set is: Where X is a diagonal matrix Y is an inverse diagonal matrix After construction, the code length of the new code set C is L=2K=2 n+1 The maximum number of users available is K=2 n Step 1.4: If the number of users K remains constant, and the code weight w increases, the iterative formula for the code set is: After construction, the new code set C has a code length of L=2Kw=w2. n+1 The number of available users is K=2 n .

2. The CDMA encoding and decoding method based on wireless ultraviolet light communication according to claim 1, characterized in that, Step 2 describes selecting different address codes from the constructed code set to perform spread spectrum processing on the source signal of each user. The specific process is as follows: each row of the address code set in Step 1 corresponds to an address code. Select any row as the address code of the user, and multiply each bit of the original data signal with its corresponding address code, that is, expand one bit to the corresponding number of bits of the address code.

3. The CDMA encoding and decoding method based on wireless ultraviolet light communication according to claim 1, characterized in that, The specific process in step 2 is as follows: Step 2.1, let the N-bit binary sequence of user k's data be... The time-domain expression of the signal transmitted by the k-th user is: in ； Step 2.2: The address code sequence of user k is the code set. A certain row of elements, denoted as The time-domain expression of user k's data after encoding and spreading is: in, And T c =T / L; Step 2.3, after spreading and coding, the K user data are simultaneously transmitted as signals through an ultraviolet light source: 。 4. The CDMA encoding and decoding method based on wireless ultraviolet light communication according to claim 1, characterized in that, The ultraviolet wavelength emitted by the ultraviolet LED in step 2 is 200nm-400nm.

5. The CDMA encoding and decoding method based on wireless ultraviolet light communication according to claim 1, characterized in that, Step 3 is as follows: Step 3.1: The photomultiplier tube at the receiving end uses a photomultiplier tube with a wavelength coverage of 200nm-400nm to receive ultraviolet light signals and convert the ultraviolet light signals into electrical signals; Step 3.2: When decoding the electrical signals, the same address code as the transmitting end is used to multiply the electrical signals, and then a decision is made to recover the required user signals.

6. The CDMA encoding and decoding method based on wireless ultraviolet light communication according to claim 5, characterized in that, Step 3.2 The specific process is as follows: The signal expression received by the receiving end is: Where n(t) is the additive white Gaussian noise (AWGN) signal; let the matrix of the received signal amplitude value sequence over the time interval [i, i+T) be: ,and After decoding using the same address code as user k at the receiving end, the data for the time period [i, i+T) is calculated as follows: in, for The transpose of; the address code sequence of user k is the code set. A certain row of elements, denoted as The original data signal of user k in the time period [i, i+T) is recovered through the judgment. Its decision expression is: The required user signals are recovered based on the decision expression.

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