Visible light communication system based on angular diversity reception and PD inclination angle optimization method

Abstract

The invention discloses a visible light communication system based on angular diversity reception and a PD inclination angle optimization method, the PD is a photoelectric detector with an adjustable inclination angle, and the optimization method comprises the following steps: S1, pre-defining N grid points covering an indoor space; initializing a population in the inclination angle boundary based on a genetic algorithm, wherein the population comprises P candidate inclination angle individuals; s2, enabling each candidate inclination angle individual in the population to traverse all grid points, carrying out M times of Monte Carlo random sampling at each grid point, and dynamically generating sampling points; calculating an average bit error rate and a space average signal to interference plus noise ratio at all grid points under the same inclination angle individual through the instantaneous signal to interference plus noise ratio of each sampling point; according to the optimization method, the optimal inclination angle of the photoelectric detector in the corresponding angle diversity receiver can be quickly found while the mobility of the user is considered, and in an indoor visible light mobile communication system in which the receiver is arranged by adopting the photoelectric detector configured with the optimal inclination angle, the communication performance of the user in a mobile environment is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of visible light communication, in particular to a visible light communication system based on angle diversity reception and a PD tilt angle optimization method. BACKGROUND

[0002] With the wide application and rapid development of wireless technology in various industries, the next generation of mobile communication technology is changing from "Internet of Things" to "Internet of Intelligence", which makes the number of indoor devices and terminals increase rapidly. At the same time, the demand for high-speed, large-capacity multi-user communication also puts forward higher requirements. However, in the further development process of radio frequency-based wireless communication technology, it faces multiple challenges such as limited spectrum resources, security threats and electromagnetic interference, which will restrict the widespread application of emerging businesses. As a new wireless communication method, visible light communication (VLC) technology based on light-emitting diode (LED) has become an effective supplement or alternative solution to solve the limitations of existing mobile communication technology, with its significant advantages of wideband high-speed, green energy-saving, ubiquitous coverage, no electromagnetic interference, etc., especially in small indoor mobile scenarios, it can provide reliable support for information access.

[0003] In actual indoor VLC applications, multiple light sources are usually used in the indoor to meet the lighting needs of users, and the layout of the light sources is usually for lighting purposes. For communication design, multiple overlapping light cells can cause the lack of rank of the channel matrix of visible light communication, and the inter-cell interference (ICI) problem becomes more serious, the decoding error increases, the BER rises, the SINR received by the user decreases significantly, and the user is difficult to achieve robust and reliable data reception.

[0004] To improve the receiving performance of users in indoor multi-light source scenes and reduce the ICI problem, an angular diversity technique is usually used at the receiving end to reduce the correlation of the communication channel. The structure is usually composed of multiple photodetectors (PDs) pointing in different directions. In VLC-MIMO systems, relevant scholars have proposed several different ADR structures. Xue et al. use a cubic structure receiver to improve the transmission performance at the light cell overlap, but this method only considers a linear industry scene with 2 light cells, and has limited value in indoor applications. Harada et al. studied the Square pyramid (SP), Square frustum (SF), Hexagonal pyramid (HP) and Hexagonal frustum (HF) four kinds of ADR angular diversity receivers in indoor uniform mobile scenes. Studies have shown that angular diversity receivers with appropriate PD tilt angles can effectively improve communication coverage and communication performance, but it is difficult to find the optimal PD tilt angle for angular diversity receivers with different PD numbers and different PD tilt angles. At the same time, user mobility can affect the performance of the receiver, especially the impact of PD tilt angle changes on channel characteristics in dynamic scenarios, so it is necessary to propose a visible light communication system based on angular diversity reception and a PD tilt angle optimization method. SUMMARY

[0005] The purpose of the present application is to propose a visible light communication system based on angular diversity reception and a PD tilt angle optimization method. The optimization method can quickly find the optimal tilt angle of the photodetector in the corresponding angular diversity receiver while considering user mobility. An indoor visible light mobile communication system with photodetectors arranged with optimal tilt angles is adopted, and the communication performance of users in a mobile environment is greatly improved.

[0006] The technical solution adopted by the present application is: a PD tilt angle optimization method based on angular diversity reception, the PD is a tilt angle adjustable photodetector, and the optimization method comprises the following steps:

[0007] S1, predefine N grid points covering the indoor space;

[0008] Initialize the population within the tilt angle boundary based on the genetic algorithm, and the population contains P candidate tilt angle individuals;

[0009] S2, make each candidate tilt angle individual in the population traverse all grid points, perform M times of Monte Carlo random sampling at each grid point, and dynamically generate sampling points; calculate the average bit error rate of all grid points under the same tilt angle individual and the spatial average signal-to-interference-and-noise ratio through the instantaneous signal-to-interference-and-noise ratio of each sampling point; construct fitness with the goal of maximizing the spatial average signal-to-interference-and-noise ratio and minimizing the average bit error rate;

[0010] S3, updating the local optimal solution and the global optimal solution according to the fitness, and driving the genetic operation to update the population;

[0011] S4, repeating steps S2-S3 until the maximum iteration number is reached, and outputting the current global optimal solution corresponding to the photoelectric detector tilt angle.

[0012] As a preferred solution, the average bit error rate at all grids under the same tilt angle individual and the spatial average signal-to-noise ratio are calculated as follows:

[0013] Based on the selected merging method, the instantaneous signal-to-noise ratio of each sampling point is calculated, the bit error rate under each sampling is calculated, and the average bit error rate of all sampling points at each grid point is compared. The maximum average bit error rate after traversing the N grid points in the room is taken as the effective average bit error rate under the same tilt angle.

[0014] The average signal-to-noise ratio is obtained by averaging the instantaneous signal-to-noise ratio of all sampling points at each grid point, and the average signal-to-noise ratio of all grid points under the same tilt angle individual is taken as the spatial average signal-to-noise ratio.

[0015] As a preferred solution, updating the local optimal solution includes obtaining the local optimal solution and updating the local optimal solution:

[0016] Obtaining the local optimal solution: comparing the spatial average signal-to-noise ratio and the average bit error rate of each tilt angle individual in the population The tilt angle individual with the maximum spatial average signal-to-noise ratio and the minimum average bit error rate is taken as the local optimal solution And record the spatial average signal-to-noise ratio and the average bit error rate corresponding to the local optimal solution

[0017] Updating the local optimal solution: if the spatial average signal-to-noise ratio of a tilt angle individual in the current population is greater than the spatial average signal-to-noise ratio corresponding to the local optimal solution , then update the local optimal solution If the difference between the spatial average signal-to-noise ratio corresponding to the local optimal solution and the spatial average signal-to-noise ratio corresponding to a tilt angle individual is less than or equal to the performance tolerance threshold τ, and the average bit error rate corresponding to the local optimal solution is greater than the average bit error rate corresponding to the tilt angle individual, then update the local optimal solution

[0018] As a preferred solution, the updating of the global optimum solution comprises the obtaining of the global optimum solution and the updating of the global optimum solution:

[0019] The obtaining of the global optimum solution: obtaining the local optimum solution of the initial generation of populations As the initial global optimum solution

[0020] The updating of the global optimum solution: calculating the local optimum solution of the current generation and comparing it with the global optimum solution of the previous generation; if the difference between the local optimum solution of the current generation and the global optimum solution is less than the threshold value ε of the stopping criterion, the current global optimum solution is maintained if the difference between the local optimum solution of the current generation and the global optimum solution is greater than or equal to the threshold value ε of the stopping criterion, the current global optimum solution is updated As a preferred solution, the genetic operation comprises the following steps:

[0021] Screening the parent population according to the fitness;

[0022] Selecting the parent individuals using the tournament selection method;

[0023] Generating the offspring by performing binary crossover through the selected parent individuals;

[0024] Controlling the generated offspring within the tilt angle boundary.

[0025] As a preferred solution, the formula for calculating the instantaneous signal-to-interference-and-noise ratio based on the selection merging method is:

[0026]

[0027]

[0028] wherein, is the instantaneous signal-to-interference-and-noise ratio, SINR, obtained after merging; ij is the signal-to-interference-and-noise ratio received by each PD; P0 is the average optical power transmitted by the LED j ; h ij is the channel gain between the LED j and the PD i ; I is the sum of the interference power from other LEDs in the interfering cell; is the gain of the line-of-sight, LOS, channel; is the responsivity of the PD; is the sum of the interference power from other LEDs in the interfering cell; i ​​noise variance.

[0029] As a preferred solution, the line of sight (LOS) channel gain is calculated as follows:

[0030]

[0031] where m is the Lambertian order, m = -ln2 / ln cos Φ 1 / 2 , Φ 1 / 2 is the half-power angle, A is the effective receiving area of the PD; Ψ is the radiation half-field angle of the LED; d ij is the distance between the LED j and the PD i , is the radiation angle formed by the vector from the LED j to the PD i and the normal vector n j of the LED j , θ ij is the incidence angle formed by the vector from the LED j to the PD i and the normal vector n i of the PD i , the normal vector n j of the LED j points to the negative direction of the Z axis, n j = [0, 0, -1].

[0032] As a preferred solution, the normal vector n i of the PD j in the three-dimensional space is expressed as:

[0033]

[0034] where, is the azimuth angle of the PD i , is the inclination angle of the PD, and δ R is the random rotation angle generated by the uniform distribution pseudo-random integer of the receiver in the X-Y plane from 0° to 360°.

[0035] As a preferred solution, the formula for calculating the bit error rate is as follows:

[0036]

[0037] where, t is the probability of the threshold falling into the error judgment due to the Gaussian signal noise offset; BER OOK is the bit error rate based on the OOK modulation scheme, and Q is the Gaussian function.

[0038] The visible light communication system based on angle diversity reception comprises a plurality of LEDs capable of emitting optical signals on the top of a room and an angle diversity receiver movable on the ground of the room, the angle diversity receiver is provided with a plurality of photodetectors for receiving the optical signals, and the photodetectors are configured with optimal tilt angles obtained by an optimization method.

[0039] Compared with the prior art, the present application has the beneficial effects that:

[0040] The PD tilt angle optimization method based on angle diversity reception in the present application takes the genetic algorithm as a model, and constructs the fitness standard according to the spatial average signal-to-interference-and-noise ratio and the average error code, so that the optimal tilt angles of the photodetectors in the angle diversity receiver can be quickly found; the Monte Carlo random sampling is integrated into the genetic algorithm, so that the movement characteristics of the user can be effectively simulated, the performance influence in the dynamic scene is reduced, and the optimal tilt angles obtained have the characteristics of high accuracy and strong applicability.

[0041] The visible light communication system based on angle diversity reception in the present application adopts the indoor visible light mobile communication system arranged by the photodetector receiver with the optimal tilt angles, and the communication performance of the user in the mobile environment is greatly improved. DETAILED DESCRIPTION

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0043] Figure 1 The model diagram and the actual diagram of the application scenario;

[0044] Figure 2 The geometric relationship between the LED j and the PD i ;

[0045] Figure 3 The schematic diagram of five ADR configurations;

[0046] Figure 4 The top view and the front view of the ADR;

[0047] Figure 5 The schematic diagram of the indoor four light cell layout;

[0048] Figure 6 The SINR three-dimensional distribution and the top view distribution diagram of the SFA DR;

[0049] Figure 7 The BER distribution plot for SF ADR;

[0050] Figure 8 The three-dimensional and top-view distributions of SINR for HF ADR are shown.

[0051] Figure 9 This is a BER distribution plot for HF ADR. Detailed Implementation

[0052] The present invention will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0053] It should be noted that, unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "a," "an," or "the," etc., used in the specification and claims of this patent application do not express a limitation on quantity, but rather indicate the presence of at least one; the terms "first," "second," and "third," as used herein, should not be considered as a limitation on the order of components, but are merely for distinguishing different components; the terms "comprising," "including," etc., indicate that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including" and their equivalents, but do not exclude other elements or objects having the same function.

[0054] To more clearly describe the specific components of this visible light communication system based on angle diversity reception and the PD tilt angle optimization method, in conjunction with the appendix... Figures 1-9 Describing this embodiment: We will consider a VLC-MIMO unit with four light-emitting diodes (LEDs), such as Figure 1 As shown in (a), this spatial structure and light source distribution are quite common in LIFI applications and have a certain degree of universality. Here, we first construct a system model.

[0055] System Model:

[0056] System models for indoor applications, such as Figure 1 As shown in (b), the indoor scene uses a 4m×4m×3m house structure, and the ceiling of the room is decorated with N. t There are N LEDs, and the receiving system consists of N... r The system consists of several digital detectors (PDs), and the receiving system uses a planar diversity or angle diversity structure. The receiver is approximately 1 meter above the ground and can be moved randomly. For the entire VLC system, we use IM / DD modulation and output an OOK signal with varying intensity. The vector representation of the electrical signal is: X = [x1, x2, ..., x...].Nt ] T , here [.] T This represents the transpose operation. The signal emitted by the LED is received by the ADR via a VLC-MIMO channel. Therefore, the signal vector received by the PD can be written as:

[0057]

[0058] In the formula, The response of the PD is expressed in A / W; N is a vector with a mean of zero and a variance of . The real-valued additive white Gaussian noise (AWGN) N r A ×1 vector matrix; and H is an N ... r ×N t The channel matrix can be written as:

[0059]

[0060] Where h ij Represents the i-th PD (PD) i ) from the j-th LED (LED j (channel gain)

[0061] The link geometry between PD and LED is as follows Figure 2 As shown. In reality, channel gain typically includes both line-of-sight (LOS) and non-line-of-sight (NLOS) components. Considering that the primary and secondary reflections of NLOS have a relatively small impact on received power, they will not be discussed in this paper. Therefore, this study only considers the LOS channel, where the line-of-sight (LOS) channel gain... By:

[0062]

[0063] In the formula, m = -ln2 / lncosΦ 1 / 2 This is the formula for calculating the Lambertian order in the Lambertian light source model, used to describe the radiation intensity distribution characteristics of an LED light source. The larger the value of m, the more concentrated the radiation; conversely, the smaller the value, the more diffuse the radiation. Where Φ... 1 / 2 θ is the half-power angle. A refers to the effective receiving area of ​​the PD. Ψ is the radiation half-field of view (FOV) of the LED, when θ ij When the signal is greater than Ψ, the receiver is outside the radiation range of the light source, and the channel gain is 0. ij It refers to LED j With PD i The distance between them, such as Figure 3 As shown, using LEDs j and PD i Calculation of geometric relationships between positions:

[0064] is the radiation angle formed by the vector from the LED j to the PD i and the normal vector n j of the LED j ; θ ij is the incidence angle formed by the vector from the LED j to the PD i and the normal vector n i of the PD i . Thus, the radiation angle and the incidence angle can be expressed in vector form as:

[0065]

[0066] where the normal vector n j of the LED j points to the negative direction of the Z-axis, so n j = [0, 0, -1]. <,> represents the dot product operation between two vectors; |||| represents the norm operation, which calculates the length of a vector. The normal vector of the PD i in three-dimensional space can be expressed using the azimuth angle and the inclination angle of the PD i :

[0067]

[0068] Receiver models:

[0069] Referring to Figure 3 , for the receiving system, five receiver structures, planar diversity and angular diversity structures, are defined in a three-dimensional coordinate system. The planar diversity structure is a general planar structure with 5 PDs, which distributes all the PDs in the same plane without additional vertical or inclination angles (i.e., the PD inclination angle is 0°), wherein 1 PD is located at the positive center position in the plane, and the remaining 4 PDs are symmetrically arranged at the four azimuthal axial positions of the central PD. The angular diversity structure is a three-dimensional structure angular diversity receiver based on different PD quantities and spatial azimuth distribution, including square pyramid (SP), square frustum (SF), hexagonal pyramid (HP), and hexagonal frustum (HF). The square pyramid (SP) contains 4 PDs, which are arranged on four sides to form a three-dimensional structure with a vertex; the square frustum (SF) contains 5 PDs, which adds a PD at the top center position compared to SP to form a frustum; the hexagonal pyramid (HP) adds 2 PDs on the side compared to SP to form a hexagonal pyramid; and the hexagonal frustum (HF) adds 1 PD at the top hexagonal plane center position compared to HP to form a hexagonal frustum structure, as shown in Figure 3 Fig. 1. From the perspective of the top viewFigure 4 The coordinates of the top PD and side PDs of the ADR are shown. The side PDs are placed at r = 3 cm from the center of the X-Y plane, with a height of r / 2, on each side of the ADR. For the planar structure, all PDs are in one plane, with 1 PD in the center of the plane and 4 PDs in the center of the axis in four orientations. For the truncated cone ADR with one top PD, the coordinate position of the PD only needs to be positioned upward from the center of the ADR. The coordinates of the PDs can be expressed as: i

[0070]

[0071] where is the azimuth angle of the PD i is given by:

[0072]

[0073] where δ R is the random rotation angle generated by a uniformly distributed pseudo-random integer from 0° to 360° for the receiver in the X-Y plane.

[0074] The signal-to-interference-and-noise ratio (SINR) is given by:

[0075] As shown in Figure 1 , multiple optical cells are used in the indoor VLC-MIMO scenario, and all LEDs transmit the same information to the user. However, when the radiation ranges of the light sources in one optical cell and adjacent optical cells overlap with each other, the VLC system is severely affected by ICI, and thus the SINR from the LED j to the PD i is calculated as:

[0076]

[0077] where P0 is the average optical power transmitted by the LED j , is the sum of the interference powers from other LEDs in the interfering cell, is the noise variance at the PD i , which includes the shot noise variance and the thermal noise variance is given by:

[0078]

[0079] where q is the number of electronic charges, is the total received optical power from all LED transmitters, I bg is the background current, I2 is the noise bandwidth coefficient, and κ B ​Where η is Boltzmann constant, T is absolute temperature, η is the fixed capacitance per unit area of ​​PD, G is open-loop gain, Γ is the channel noise figure of FET (Field-Effect Transistor), and g is the open-loop gain. m For FET transconductance, a symbol duration Ts of 1 μs and an equivalent noise bandwidth Bn of 1 MHz were used in this paper. In this analysis, these thermal noise parameters were set as follows: q = 1.6e-19C, I... bg =5100μA, I2=0.562, I3=0.0868, T=298K, eta=112pF / cm2, G=10, Γ=1.5, g m =30ms.

[0080] Receiver Channel Performance Modeling and Optimization Method

[0081] Analysis of factors affecting receiver performance:

[0082] Within a 4m × 4m area, grid points are constructed at 0.1m intervals. The user starts from the origin at a speed of 1.2m / s and sequentially evaluates the channel characteristics at each location to simulate the dynamic characteristics of the channel changing with the user's position during movement. Figure 5 As shown.

[0083] In this visible light mobile communication system (VLC), the channel gain response is modeled based on Lambertian radiation and reception, and its channel gain... The expression is shown in formula (3). According to formulas (5) and (6), the initial azimuth and tilt angle of each PD determine its spatial orientation on the receiving surface, thus determining the PD. i The normal vector n of the receiving surface i The normal vector is from the LED j To PD i The vector forms the incident angle θ ij Its magnitude directly affects the angle-related factor in the channel gain, thus making the channel gain exhibit a complex nonlinear relationship with angle changes.

[0084] Furthermore, as can be seen from formula (4), PD i Fine-tuning the tilt angle will also change the LED. j With PD i The distance d between ij In terms of channel gain In expression (3), the form is squared. When a term appears in the denominator, even a small change in it can be amplified, thus having a significant impact on received power and system channel quality.

[0085] Therefore, the initial tilt angle of the PD not only affects the incident angle response through the angle change, but also indirectly affects the channel attenuation through the geometric position offset, and is a key design parameter for improving the communication performance of the VLC system.

[0086] The application provides a PD tilt angle optimization method based on angle diversity reception, the PD being a tilt angle adjustable photoelectric detector, and the optimization method comprising the following steps:

[0087] S1, predefining N grid points covering an indoor space;

[0088] initializing a population within a tilt angle boundary based on a genetic algorithm, the population comprising P candidate tilt angle individuals;

[0089] S2, making each candidate tilt angle individual in the population traverse all the grid points, performing M times of Monte Carlo random sampling at each grid point to dynamically generate sampling points; calculating the average bit error rate at all the grid points under the same tilt angle individual and the spatial average signal-to-interference-and-noise ratio (SINR) through the instantaneous SINR of each sampling point; and constructing fitness for the purpose of maximizing the spatial average SINR and minimizing the average bit error rate;

[0090] S3, updating the local optimal solution and the global optimal solution according to the fitness, and driving genetic operation to update the population;

[0091] S4, repeating steps S2-S3 until the maximum iteration number is reached, and outputting the tilt angle of the photoelectric detector corresponding to the current global optimal solution.

[0092] In one specific technical solution, the calculation steps of the average bit error rate at all the grid points under the same tilt angle individual and the spatial average SINR are as follows:

[0093] The instantaneous SINR of each sampling point is calculated based on a selection merging method, the bit error rate under each sampling is calculated, and then the average of the bit error rates of all the sampling points at each grid point is compared, and the maximum average bit error rate after traversing the N grid points in the room is taken as the effective average bit error rate under the same tilt angle;

[0094] The average SINR is obtained by averaging the instantaneous SINRs of all the sampling points at each grid point, and the average of the average SINRs of all the grid points under the same tilt angle individual is taken as the spatial average SINR.

[0095] Specifically, the calculation formula of the bit error rate is as follows:

[0096]

[0097] wherein, t is the probability of the Gaussian signal noise offset falling into the threshold of error judgment; BER OOK is the bit error rate based on the OOK modulation scheme, and Q is a Gaussian function.

[0098] To evaluate the receiving performance of the system in the moving state, the following optimization problem is constructed:

[0099]

[0100] where N is the total number of indoor grid points, M is the number of Monte Carlo sampling times for each grid point, is the instantaneous signal-to-interference-and-noise ratio obtained after combination;

[0101] Specifically, the formula for calculating the instantaneous signal-to-interference-and-noise ratio based on the selection combination method is:

[0102]

[0103] where SINR ij is the signal-to-interference-and-noise ratio received by each PD; P0 is the average optical power transmitted by the LED j ; h ij is the channel gain between the LED j and the PD i , is the gain of the line-of-sight (LOS) channel; is the responsivity of the PD; is the sum of interference powers from other LEDs in the interfering cell; is the noise variance of the PD i .

[0104] In one specific embodiment, updating the local optimal solution includes obtaining the local optimal solution and updating the local optimal solution:

[0105] Obtaining the local optimal solution: compare the spatial average signal-to-interference-and-noise ratio and the average bit error rate of each tilt individual in the population The tilt individual with the maximum spatial average signal-to-interference-and-noise ratio and the minimum average bit error rate is taken as the local optimal solution and the spatial average signal-to-interference-and-noise ratio and the average bit error rate corresponding to the local optimal solution

[0106] Updating the local optimal solution: if the spatial average signal-to-interference-and-noise ratio of a tilt individual in the current population is greater than the spatial average signal-to-interference-and-noise ratio corresponding to the local optimal solution , the local optimal solution is updated If the spatial average signal-to-interference-and-noise ratio corresponding to the local optimal solution in the current population is the difference between the spatial average SINR of the current local optimal solution and the spatial average SINR of the global optimal solution is less than or equal to a performance tolerance threshold τ, and the current local optimal solution is updated corresponding average BER is greater than the average BER corresponding to the current local optimal solution the current local optimal solution is updated

[0107] wherein the performance tolerance threshold τ is a preset value in dB, τ is close to zero but greater than zero, and τ is exemplarily 5 dB. In a specific embodiment, updating the global optimal solution comprises obtaining the global optimal solution and updating the global optimal solution:

[0108] obtaining the global optimal solution: taking the local optimal solution of the initial population as the initial global optimal solution

[0109] updating the global optimal solution: calculating the local optimal solution of the current generation and comparing it with the global optimal solution of the previous generation; if the difference between the spatial average SINR of the local optimal solution of the current generation and the spatial average SINR of the global optimal solution is less than a stop criterion threshold ε, the current global optimal solution is maintained if the difference between the spatial average SINR of the local optimal solution of the current generation and the spatial average SINR of the global optimal solution is greater than or equal to the stop criterion threshold ε, the current global optimal solution is updated

[0110] wherein the stop criterion threshold ε is a preset value in dB, ε is close to zero but greater than zero, and ε is exemplarily 1 dB.

[0111] In a specific embodiment, the genetic operation comprises the following steps:

[0112] selecting the parent population according to the fitness;

[0113] selecting the parent individuals by tournament selection;

[0114] generating the offspring by performing binary crossover through the selected parent individuals;

[0115] controlling the generated offspring tilt angle within the tilt angle boundary.

[0116] ​​​​​​​​The application also provides a visible light communication system based on angle diversity reception, comprising a plurality of LEDs capable of emitting optical signals on the top of a room and an angle diversity receiver movable on the ground of the room, the angle diversity receiver having a plurality of photodetectors for receiving the optical signals, and the photodetectors are configured at the optimal inclination angle obtained by the above optimization method.

[0117] The pseudo code constructed based on the above PD inclination optimization method is as follows:

[0118] First, the local optimal solution is obtained according to Algorithm 1, and the code is as follows:

[0119]

[0120]

[0121] Then, the global optimal solution is updated according to the local optimal solution, and the specific process is shown in Algorithm 2:

[0122]

[0123] Simulation verification:

[0124] In order to verify the adaptability of the proposed PD tilt angle optimization method based on the three-dimensional diversity receiver (PTAO-SDR) in the dynamic scene, the PD tilt angle of the receiver is optimized and analyzed based on the link geometry relationship and user movement characteristics of the VLC-MIMO system. Under the system parameter setting shown in Table I, the simulation environment is constructed.

[0125] TABLE I: SIMULATION PARAMETERS

[0126]

[0127] Performance analysis of optimal PD tilt angle of different ADRs in mobile state:

[0128] Based on the PD inclination optimization calculation method constructed in the foregoing, the SF and HF two three-dimensional receiving structures are selected to carry out tilt angle search, and the optimal PD tilt angle solutions thereof are finally calculated as 22.93° and 24.06° respectively. In view of the limitation of angle adjustment precision in engineering practice, and in order to ensure that the simulation verification has good implementability and repeatability, the integer angle closest to the optimal solution is selected as a representative configuration for performance evaluation.

[0129] Based on the optimization method proposed in the foregoing, the optimal tilt angle under the SF structure is about 23°. In order to further verify the effectiveness and stability of the result in its neighborhood, three groups of angles of 22°, 23° and 24° are selected for local simulation comparison, as shown inFigure 6 and Figure 7 In Figure 6 , the contrast relationship of SF ADR's SINR three-dimensional distribution and overhead distribution diagram is: (a) 22° and SINR, (b) 23° and SINR, (c) 24° and SINR. The SINR of three groups of angles maintains about 45 dB in most areas of the room, all showing good signal reception performance. However, 22° and 24° have large fluctuations in the center of the room, and the SINR at the edge of the room drops to about 12 dB, especially 24°, which drops more significantly and the signal attenuation is more serious. At the same time, the SINR overhead distribution diagrams under three tilt angles are further demonstrated, and the results show that the high SINR area in the center of the room under 22° and 24° is significantly weakened, and the SINR at the edge of the four corners decreases more significantly. In contrast, the SINR distribution under 23° is more uniform, the central area is stable, and the attenuation at the edge of the room is relatively small. The spatial average of the average SINR of all grid points is 44.8517 dB, 44.8618 dB and 44.6747 dB respectively. Among them, 23° performs best, balancing signal coverage and system stability.

[0130] In Figure 7 , the contrast relationship of SF ADR's BER distribution is: (a) 22° and BER, (b) 23° and BER, (c) 24° and BER. The BER of three angles is stable at 0 in most areas of the room, indicating good communication quality. However, at the edge of the room, the BER is as high as 10 -5 orders of magnitude, reaching maximum values of 4.5×10 -5 , 3.2×10 -5 and 6.6×10 -5 respectively. Among them, the BER of 23° is the lowest, further verifying the effectiveness of the optimal tilt angle solution calculated in this paper.

[0131] Based on the optimization method proposed in the foregoing, the optimal tilt angle under the HF structure is calculated to be about 24°. To further verify the effectiveness and stability of the result in its neighborhood, this paper selects three groups of angles of 23°, 24° and 25° for local simulation comparison, Figure 8 In Figure 8 and Figure 9 , the contrast relationship of simulation diagrams and PD tilt angles is: (a) 23° and SINR, (b) 24° and SINR, (c) 25° and SINR, as shown in Figure 8It is shown that the SINR of most areas in the three groups of angle rooms is maintained at about 45 dB. The top view of SINR at three angles is also shown, and the distribution of SINR changes little, but when the tilt angle is 23° and 24°, the range of SINR decline at the edge of the room is smaller, and the coverage is more uniform, while the edge attenuation at 25° is more significant. The spatial average of the average SINR of all grid points at the three angles is 45.0699 dB, 45.0513 dB and 44.9813 dB respectively, which is very small, but the spatial average at 23° is slightly higher than that at 24°, which is the best.

[0132] Figure 9 The BER distribution changes when the tilt angle is 23°, 24° and 25° are shown. The simulation graph and the control relationship of PD angle are as follows: (a) 23° and BER, (b) 24° and BER, (c) 25° and BER. At the three angles, the BER of most areas in the room is stable at 0, but the BER at the edge of the room fluctuates, with the maximum values being 7×10 -6 , 4×10 -6 and 2.7×10 -5 , respectively, of which the BER at 24° is the lowest. Therefore, the comprehensive analysis results show that the tilt angle of 24° realizes the lowest BER on the basis of ensuring that the spatial average SINR meets the tolerance requirements, further verifying the correctness and practicability of its optimal solution as the HF receiving structure.

[0133] From the above simulation comparison, it can be seen that after optimizing the tilt angle of the PD by the optimization method, the uniformity of the SINR spatial distribution of the SF and HF structures can be significantly improved, and the BER level of the edge area can be reduced. Among them, the average BER of the HF structure under the optimal tilt angle is reduced by about 8 times compared with the SF, showing stronger robustness and performance potential.

[0134] The parts not described in detail in the above embodiments are prior art.

[0135] It should be noted that although the present application has been described by the above embodiments, the present application can have other various embodiments. Those skilled in the art can obviously make various corresponding changes and modifications to the present application without departing from the spirit and scope of the present application, but these changes and modifications should belong to the scope of protection of the appended claims and their equivalents of the present application.

Claims

1. A PD tilt angle optimization method based on angular diversity reception, the PD being a tilt angle adjustable photodetector, characterized in that, The optimization method comprises the following steps: S1, predefining N grid points covering the indoor space; S2, initializing a population within the tilt angle boundary based on a genetic algorithm, the population comprising P candidate tilt angle individuals; S3, updating a local optimal solution and a global optimal solution according to the fitness, and driving a genetic operation to update the population; S4, repeating steps S2-S3 until the maximum iteration number is reached, and outputting the photodetector tilt angle corresponding to the current global optimal solution. The steps of calculating the average bit error rate and the spatial average signal-to-interference-and-noise ratio of all grid points under the same tilt angle individual are as follows:

2. The PD dip angle optimization method based on angular diversity reception according to claim 1, characterized in that: The instantaneous signal-to-interference-and-noise ratio of each sampling point is calculated based on the selection merging method, the bit error rate under each sampling is calculated, and then the average bit error rate of all sampling points at each grid point is compared, and the maximum average bit error rate after traversing the N grid points in the room is taken as the effective average bit error rate under the same tilt angle; The average signal-to-interference-and-noise ratio is obtained by averaging the instantaneous signal-to-interference-and-noise ratio of all sampling points at each grid point, and the average signal-to-interference-and-noise ratio of all grid points under the same tilt angle individual is taken as the spatial average signal-to-interference-and-noise ratio. The updating of the local optimal solution comprises obtaining the local optimal solution and updating the local optimal solution:

3. The PD tilt angle optimization method based on angular diversity reception according to claim 1, characterized in that, The updating of the global optimal solution comprises obtaining the global optimal solution and updating the global optimal solution: Obtaining local optimal solution: comparing the spatial average signal-to-interference-and-noise ratio corresponding to each tilt individual in the population and average bit error rate the spatial average signal-to-interference-and-noise ratio maximum and average bit error rate the tilt individual with the minimum as the local optimal solution and recording the spatial average signal-to-interference-and-noise ratio corresponding to the local optimal solution and average bit error rate Update of local optimum: If the spatial average signal-to-interference-plus-noise ratio corresponds to an individual at a certain tilt angle in the current population Greater than the local optimum Corresponding spatial average signal-to-interference-plus-noise ratio Then update the local optimal solution. If the current population has a local optimum Corresponding spatial average signal-to-interference-plus-noise ratio Spatial average signal-to-interference-plus-noise ratio corresponding to an individual at a certain tilt angle The difference is less than or equal to the performance tolerance threshold τ, and the local optimum is... Corresponding average bit error rate The average bit error rate corresponding to individuals with a tilt angle greater than this Then update the local optimal solution.

4. The PD tilt angle optimization method based on angular diversity reception according to claim 1, characterized in that, The genetic operation comprises the following steps: obtaining a global optimum solution: obtaining a local optimum solution of the initial population as an initial global optimum solution Update of the global optimum solution: Compute the contemporary local optimum solution and compare it with the global optimum solution of the previous generation If the difference in spatially averaged SINR between the contemporary local optimum solution and the global optimum solution is less than the stopping criterion threshold ε, maintain the current global optimum solution If the difference in spatially averaged SINR between the contemporary local optimum solution and the global optimum solution is greater than or equal to the stopping criterion threshold ε, update the current global optimum solution 5. The PD tilt angle optimization method based on angular diversity reception according to claim 1, characterized in that: Screening the parent population according to the fitness; Selecting the parent individuals by using the tournament selection method; Generating offspring by performing binary crossover through the selected parent individuals; Controlling the generated offspring tilt angle within the tilt angle boundary. The formula for calculating the instantaneous signal-to-interference-and-noise ratio based on the selection merging method is as follows:

6. The PD tilt angle optimization method based on angular diversity reception according to claim 1, characterized in that: The formula for calculating the bit error rate is as follows: in, SINR is the instantaneous signal-to-interference-plus-noise ratio obtained after merging. ij P0 represents the signal-to-interference-plus-noise ratio received by each PD; P0 represents the LED. j Average transmitted optical power; h ij For LED j To PD i Channel gain between Gain for the line-of-sight (LOS) channel; The responsiveness of the PD; It is the sum of the interference power from other LEDs in the interfering cell; For PD i The noise variance.

7. The PD tilt angle optimization method based on angular diversity reception according to claim 6, characterized in that: Line of sight, LOS, channel gain The formula for calculating the LOS channel gain is as follows: Wherein, m is Lambert order number, m = -ln2 / lncosΦ 1 / 2 , Φ 1 / 2 is half power angle, A is effective receiving area of PD; Ψ is radiation half field angle of LED; d ij is distance between LED j and PD i , is radiation angle formed by vector from LED j to PD i and normal vector n j of LED j , θ ij is incidence angle formed by vector from LED j to PD i and normal vector n i of PD i , Normal vector n j of LED j points to Z axis negative direction, n j = [0, 0, -1].

8. The PD tilt angle optimization method based on angular diversity reception according to claim 7, characterized in that: PD in three-dimensional space i Normal vector n of PD j is expressed as: wherein is the PD i azimuth angle, is the PD inclination, δ R is a random rotation angle generated by a uniform distribution pseudo-random integer from 0° to 360° for the receiver in the X-Y plane.

9. The PD tilt angle optimization method based on angular diversity reception according to claim 1, characterized in that: The indoor top comprises a plurality of LEDs capable of emitting optical signals, and the indoor floor comprises an angular diversity receiver capable of moving, the angular diversity receiver having a plurality of photodetectors for receiving optical signals, and the photodetectors are arranged at the optimal tilt angle obtained by the optimization method of any one of claims 1-9. wherein, t is the probability of a Gaussian signal noise offset falling into the threshold of an error decision; BER OOK is the bit error rate based on the OOK modulation scheme, Q is a Gaussian function.

10. A visible light communication system based on angular diversity reception, characterized by: ​

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