A method for finding the extreme value of correlation between visible light communication and positioning system based on CDMA

Abstract

The present invention discloses a method for finding extreme values ​​of correlation values ​​in a visible light communication and positioning system based on CDMA. Based on CDMA technology, in an indoor visible light communication and positioning system, the method assigns a highly correlated optical address code to the reserved undefined portion of the VLC frame to be transmitted by each LED light. At the receiving end, the local address code is used to continuously perform correlation operations on the received signal using a sliding window method to obtain a number of correlation values. The extreme values ​​and extreme value points of the correlation values ​​are then used for synchronous detection to determine the position of the address code in the VLC frame, and these extreme values ​​are used for positioning. The present invention can be used to separate positioning and communication signals in a combined visible light positioning and communication system, achieving simultaneous communication and positioning, and performing synchronous detection on signals with asynchronous arrival times.

Description

Technical Field

[0001] The present invention belongs to the technical field of visible light positioning, and in particular relates to a method for finding extreme values ​​of correlation between visible light communication and a positioning system based on CDMA. Background Art

[0002] With the development of wireless communication technology, the demand for positioning services has increased dramatically. GPS has advantages such as relatively high accuracy and ease of use, making it the most widely used positioning and navigation system. However, GPS can only be used in outdoor environments where there is a direct connection between the target device and the satellite, and NLOS (Non-Line-of-Sight) can cause the GPS signal to weaken and be interrupted. In addition, indoor positioning systems often require higher positioning accuracy, which GPS cannot meet. In traditional indoor positioning systems, such as RFID (Radio Frequency Identification), Wi-Fi, Bluetooth and UWB (Ultra Wide Band) systems, high-precision positioning is usually not achieved, and these systems are also affected by electromagnetic interference and multipath propagation.

[0003] VLC (Visible Light Communications) and the VLP (Visible Light Positioning) technology developed based on VLC have received increasing attention in recent years. VLP systems offer advantages such as high positioning accuracy, strong resistance to electromagnetic interference, compatibility with building lighting systems, low energy consumption, and low cost. They utilize RSS (Received Signal Strength), AOA (Angle-of-Arrival), TOA (Time-of-Arrival), TDOA (Time Delay of Arrival), and PDOA (Phase Difference of Arrival) to obtain positioning information. RSS uses a light attenuation model to estimate the distance between an LED light and a photodetector, and then uses a triangulation algorithm to calculate the coordinates of the target device. The RSS algorithm has the advantages of low complexity and ease of implementation, making it the most widely studied algorithm in VLP systems.

[0004] VLP systems usually require three optical signals to complete the positioning process. These three optical signals are transmitted in the channel separately, and then the photodetector receives the mixed signals of the three channels. Therefore, multiplexing technology is needed to prevent the three signals from interfering with each other. Traditional multiplexing technologies include FDM (Frequency Division Multiplexing), TDM (Time Division Multiplexing) and CDM (Code Division Multiplexing). FDM distinguishes signals based on the different frequencies loaded on the LED. FDM requires the design of an ideal filter at the receiving end, so it is difficult to implement in practical applications. TDM distinguishes multiple signals based on the different time slots occupied by different signals in the time domain. This technology has high synchronization requirements and is therefore difficult to implement. CDMA (Code Division Multiplexing Access) is used to distinguish different signals. When applied to visible light positioning systems, it has the advantages of strong anti-interference ability and high positioning accuracy. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a method for finding the extreme values ​​of the correlation values ​​between visible light communication and positioning systems based on CDMA. The method uses the principle that the address codes in CDMA technology are mutually orthogonal to distinguish different signals to determine the start and end time of the reception of VLC frames. The method is suitable for determining the arrival start and end time of data frames when sending data.

[0006] In order to achieve the above functions, the present invention adopts the following technical solutions:

[0007] The method for finding the extreme value of the correlation between visible light communication and positioning system based on CDMA includes:

[0008] S1. Select a CDMA address code and assign an address code to each LED light according to the number of LED lights used in the room, denoted as a i , i=1,2,3,…,n; the receiving end address code used for correlation operation at the receiving end is recorded as a i _R, length is L1.

[0009] S2, the address code a i Insert it into the undefined portion of the VLC data frame with a length of L2 to be sent, and generate the data frame T to be sent. i (t); the data frame T i (t) is modulated, and the modulated signal is S i (t).

[0010] S3, S i(t) are respectively sent to the corresponding driving circuit to drive the LED lamp. The LED lamp sends the signal by flashing on and off, where bright represents 1 and dark represents 0. After passing through the channel, the receiver receives the superimposed mixed signal, and after photoelectric conversion and demodulation, the mixed received signal r(t) is obtained.

[0011] S4, using the characteristics of CDMA technology, use the corresponding receiving end address code a i _R performs sliding correlation operation on r(t) to obtain several correlation values, which are recorded as λ; λ is continuously compared with the correlation value μ in another strictly synchronized visible light positioning system that only sends address codes. i Compare and find the one that satisfies λ maxi =μ i Correlation value of ±0.001.

[0012] S5. Using λ maxi Perform positioning and infer the distance D between the receiver and the transmitter i ,According to the indoor visible light positioning algorithm, the positioning result is obtained.

[0013] Furthermore, the address code in step S1 is an optical address code, and the specific requirements are as follows:

[0014] (1) The optical address code at the transmitting end is positive polarity because the optical channel can only transmit positive polarity signals.

[0015] (2) Address code a of the receiving end i _R is composed of the transmitter address code a i The purpose of mapping is to achieve the ideal cross-correlation effect.

[0016] (3) The optical address code has the ideal correlation in CDMA technology, that is, the autocorrelation and cross-correlation characteristics meet the characteristics of small multiple access interference and the ability to separate different address codes.

[0017] Furthermore, in step S4, the address code is mixed with the received signal and correlation operation is performed every 1 bit from right to left to obtain the correlation value λ. The specific calculation formula is:

[0018]

[0019] Wherein, r(x) represents the mixed received signal, and a(x) represents the address code.

[0020] After shifting a(x) by x' code elements, the result is integrated and accumulated with r(x), and the result is the correlation value.

[0021] Furthermore, when only the address code is sent, the mixed signal at the receiving end and the local address code a i _R correlation value μ obtained after correlation operationi , the specific calculation formula is:

[0022]

[0023] Furthermore, the specific formula for obtaining the positioning result in step S5 is:

[0024]

[0025]

[0026] Among them, P ri is the received optical power of the i-th LED light received by the receiver; P ti is the emitted light power of the i-th LED lamp; θ i Is the sending and receiving address code, that is, a i with a i _R correlation value; P NLOS is the total reflected power; m is the Lambertian index; A r is the effective receiving area of ​​the photodetector PD; T s is the gain of the optical filter; g is the gain of light focusing; h i is the vertical distance between the receiver and the i-th LED light.

[0027] Using the trilateration algorithm based on the received signal strength, the positioning result D i Perform the conversion to obtain the coordinate position of the receiver. The specific formula is:

[0028] (x-xi)²+(y-yi)²+(z-zi)²=Di²

[0029] Among them, the coordinates of the i-th LED light are (x i ,y i ,z i ), the receiver coordinates are (x, y, z), where the LED light is the transmitter and its position is known; the receiver coordinates are unknown and are the target to be located.

[0030] Furthermore, the present invention also proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the computer program, the steps of the method for finding the extreme values ​​of the correlation between visible light communication and positioning systems based on CDMA as described above are implemented.

[0031] Furthermore, the present invention also proposes a computer-readable storage medium, which stores a computer program. When the computer program is run by a processor, it executes the method for finding the extreme value of the correlation value between visible light communication and positioning system based on CDMA as described above.

[0032] The present invention adopts the above technical solution, and compared with the prior art, its significant technical effects are as follows:

[0033] This paper proposes a CDMA-based method for finding the extreme value of the correlation between visible light communication and positioning systems. This method can separate positioning and communication signals and use this extreme value for positioning. Furthermore, based on the sliding position of the extreme value found, the address code's position in the VLC frame can be determined, thereby determining the start and end times of the received signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the overall steps of the present invention.

[0035] Figure 2 It is a schematic diagram of the size of the correlation value obtained by the sliding window method of the present invention. DETAILED DESCRIPTION

[0036] The specific technical solutions for implementing the present invention will be further described below with reference to the accompanying drawings:

[0037] The present invention proposes a method for finding the extreme value of the correlation between visible light communication and positioning system based on CDMA, such as Figure 1 The specific contents include:

[0038] S1. Select an OZCZ (Optical Zero Correlation Zone) address code with a length of 32. For a room with 3 LED lights, assign an OZCZ code to each LED light, denoted as a1, a2, and a3. At the receiving end, the address codes a1_R, a2_R, and a3_R are obtained by mapping 0 to -1 and 1 to remain unchanged. Each address code has a length of 32. The specific contents are shown in Table 1.

[0039] Table 1 LED light OZCZ code and the address code of the receiving end

[0040] <![CDATA[a1]]> 1 1 1 0 1 0 0 1 0 0 0 1 0 1 1 0 0 0 0 0 1 1 0 1 1 1 1 1 0 0 1 0 <![CDATA[a2]]> 1 1 1 0 1 0 0 1 1 1 1 0 1 0 0 1 0 0 0 0 1 1 0 1 0 0 0 0 1 1 0 1 <![CDATA[a3]]> 1 0 1 1 1 1 0 0 1 0 1 1 1 1 0 0 0 1 0 1 1 0 0 0 0 1 0 1 1 0 0 0 <![CDATA[a1_R]]> -1 -1 -1 1 -1 1 1 -1 1 1 1 -1 1 -1 -1 1 1 1 1 1 -1 -1 1 -1 -1 -1 -1 -1 1 1 -1 1 <![CDATA[a2_R]]> -1 -1 -1 1 -1 1 1 -1 -1 -1 -1 1 -1 1 1 -1 1 1 1 1 -1 -1 1 -1 1 1 1 1 -1 -1 1 -1 <![CDATA[a3_R]]> -1 1 -1 -1 -1 -1 1 1 -1 1 -1 -1 -1 -1 1 1 1 -1 1 -1 -1 1 1 1 1 -1 1 -1 -1 1 1 1

[0041] The address code used is an optical address code that meets the following conditions:

[0042] (1) The optical address code at the transmitting end is positive polarity because the optical channel can only transmit positive polarity signals.

[0043] (2) Address code a of the receiving end i _R is composed of the transmitter address code a i The purpose of mapping is to achieve the ideal cross-correlation effect.

[0044] (3) The optical address code has the ideal correlation in CDMA technology, that is, the autocorrelation and cross-correlation characteristics meet the characteristics of small multiple access interference and the ability to separate different address codes.

[0045] S2. Generate a random binary VLC data frame of length 256 and insert the address code into bits 101 to 132 of the VLC data frame to generate data frames T1(t), T2(t), and T3(t) to be sent. The length of the data frame is the length of the VLC data frame plus the length of the address code, that is, 288. Data frames T1(t), T2(t), and T3(t) are OOK modulated, and the modulated signals are S1(t), S2(t), and S3(t).

[0046] S3, S1(t), S2(t), and S3(t) are fed into corresponding driver circuits to drive LED lights. The LED lights transmit signals by flashing on and off, with bright representing 1 and dark representing 0. After passing through the channel, the receiver receives the superimposed mixed signal, which undergoes optoelectronic conversion and OOK demodulation to obtain the mixed received signal r(t). The length of r(t) is 288.

[0047] S4. For r(t) in step S3, use the corresponding receiving end address code a i _R performs sliding correlation operation on it to obtain several correlation values, recorded as λ, the number of λ is related to the VLC data frame and address code a i The specific formula is:

[0048]

[0049] Where r(x) represents the mixed received signal and a(x) represents the address code. After a(x) is shifted by x' code elements, the result of integrating it with r(x) and then accumulating it is the correlation value. The length of the VLC data frame is 256, and the address code a i If the length of _R is 32, 225 correlation values ​​λ can be obtained.

[0050] λ is continuously compared with the related value μ in another visible light positioning system i Compare until you find one that matches μ i λ of similar size maxi , that is, λ maxi =μ i ±0.001. i The calculation formula is:

[0051]

[0052] Calculate μ i =0.0047. The λ obtained under this system maxi=0.0048, and the obtained λ maxi It is obtained by the 101th correlation operation, which can determine the position of the address code in the received signal and determine the start and end time of the received signal. Figure 2 As shown, after the sliding operation, several correlation values ​​can be obtained, and the 101th correlation value is the largest. Therefore, when the extreme value point is found at the 101th position, it can be determined that the data frame is between 101 and 132, and this correlation value can be used to calculate the coordinate position.

[0053] S5. Using λ maxi Perform positioning and infer the distance D between the receiver and the transmitter i , and then according to the indoor visible light positioning algorithm, the positioning results are obtained. The specific content is:

[0054]

[0055]

[0056] Among them, P ri is the received optical power of the i-th LED light received by the receiver; P ti is the emitted light power of the i-th LED lamp; θ i Is the sending and receiving address code, that is, a i with a i _R correlation value; P NLOS is the total reflected power; m is the Lambertian index; A r is the effective receiving area of ​​the photodetector PD; T s is the gain of the optical filter; g is the gain of light focusing; h i is the vertical distance between the receiver and the i-th LED light.

[0057] Using the trilateration algorithm based on the received signal strength, the positioning result D i Perform the conversion to obtain the coordinate position of the receiver. The specific formula is:

[0058] (x-xi)²+(y-yi)²+(z-zi)²=Di²

[0059] Among them, the coordinates of the i-th LED light are (x i ,y i ,z i ), the receiver coordinates are (x, y, z), where the LED light is the transmitter and its position is known; the receiver coordinates are unknown and are the target to be located.

[0060] In this example, a three-lamp model is used. The room size is 5m*5m*3m, and the three LEDs are positioned at (2.5, 1.25), (1.25, 3.75), and (3.75, 3.75). Taking the center point (2.3, 2.3) of the plane as an example, the estimated distances from the three LEDs to point (0, 0) are D1 = 4.2811, D2 = 2.6129, and D3 = 4.7450, resulting in an estimated horizontal coordinate of (2.32825, 2.41657).

[0061] An embodiment of the present invention further provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. It should be noted that each module in the aforementioned system corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the method. For technical details not fully described in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0062] The present invention also provides a computer-readable storage medium storing a computer program. It should be noted that each module in the above system corresponds to the specific steps of the method provided in the present invention, and has corresponding functional modules and beneficial effects for executing the method. For technical details not fully described in this embodiment, please refer to the method provided in the present invention.

[0063] The above embodiments are only for illustrating the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for finding the extreme value of correlation between visible light communication and positioning system based on CDMA, characterized in that: include: S1. Select a CDMA address code and assign an address code to each LED light used, recorded as a i , i=1,2,3,…,n; the receiving end address code used for correlation operation at the receiving end is recorded as a i _R, length L1; S2, the address code a i Insert it into the undefined portion of the VLC data frame with a length of L2 to be sent, and generate the data frame T to be sent. i (t); for data frame T i (t) is modulated, and the modulated signal is S i (t); S3, S i (t) are respectively fed into corresponding driving circuits for driving LED lights, and the LED lights send signals by flashing on and off; After passing through the channel, the receiver receives the superimposed mixed signal, and after optical-to-electrical conversion and demodulation, obtains the mixed received signal r(t); S4, using CDMA technology, the corresponding receiving end address code a i _R performs sliding correlation operation on r(t) to obtain several correlation values, which are recorded as λ; λ is continuously compared with the correlation value μ in another strictly synchronized visible light positioning system that only sends address codes. i Compare and find the one that satisfies λ maxi =μ i Correlation value of ±0.001; S5. Using λ maxi Perform positioning, infer the distance between the receiver and the transmitter, and obtain the positioning result based on the indoor visible light positioning algorithm.

2. The method for finding the extreme value of correlation between visible light communication and positioning system based on CDMA according to claim 1, characterized in that: The address code in step S1 is an optical address code, and the specific requirements are as follows: (1) The optical address code at the transmitting end is positive polarity; (2) Address code a of the receiving end i _R is composed of the transmitter address code a i Mapping (3) The optical address code has the ideal correlation in CDMA technology, that is, the autocorrelation and cross-correlation characteristics meet the characteristics of small multiple access interference and the ability to separate different address codes.

3. The method for finding the extreme value of correlation between visible light communication and positioning system based on CDMA according to claim 1, characterized in that: In step S4, the address code is mixed with the received signal and correlation operation is performed every 1 bit from right to left to obtain the correlation value λ. The specific calculation formula is: Where r(x) represents the mixed received signal, and a(x) represents the address code; After shifting a(x) by x' code elements, the result is integrated and accumulated with r(x), and the result is the correlation value.

4. The method for finding the extreme value of correlation between visible light communication and positioning system based on CDMA according to claim 3, characterized in that: When only the address code is sent, the mixed signal at the receiving end is the same as the local address code a i _R performs correlation operation to obtain the correlation value μ i , the specific calculation formula is:

5. The method for finding the extreme value of correlation between visible light communication and positioning system based on CDMA according to claim 1, characterized in that: The specific formula for obtaining the positioning result in step S5 is: Among them, P ri is the received optical power of the i-th LED light received by the receiver; P ti is the emitted light power of the i-th LED lamp; θ i Is the sending and receiving address code, that is, a i with a i _R correlation value; P NLOS is the total reflected power; m is the Lambertian index; A r is the effective receiving area of ​​the photodetector PD; T s is the gain of the optical filter; g is the gain of light focusing; h i is the vertical distance between the receiver and the i-th LED light; The positioning result D is obtained by the trilateration algorithm based on the received signal strength. i Perform the conversion to obtain the coordinate position of the receiver. The specific formula is: Among them, the coordinates of the i-th LED light are (x i ,y i ,z i ), the receiver coordinates are (x, y, z), where the LED light is the transmitter and its position is known; the receiver coordinates are unknown and are the target to be located.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 5 is performed.

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