Design method of two-input two-output visible light communication system model between vehicles

Abstract

The application relates to a design method of a two-input two-output visible light communication system model between vehicles, and belongs to the technical field of visible light communication, which comprises the following steps: step 1, establishment of a vehicle headlamp model; step 2, analysis of a line-of-sight link; step 3, analysis of a non-line-of-sight link; step 4, analysis of system noise; and step 5, analysis of a signal received by a photodetector. The application improves the reliability of the two-input two-output visible light communication system model between vehicles, and further improves the accuracy of the two-input two-output visible light communication simulation result between vehicles, thereby providing a reliable theoretical basis and experimental guidance for future technical research.

Description

TECHNICAL FIELD

[0001] The application relates to a design method of a two-input two-output visible light communication system model between vehicles, and belongs to the technical field of visible light communication. BACKGROUND

[0002] Visible light communication uses visible light emitted by a light-emitting diode as a carrier of wireless communication, has advantages of unlicensed spectrum, no electromagnetic interference, high bandwidth, strong privacy, etc., and is therefore considered as a very promising complementary technology of short-distance radio frequency wireless communication technology between vehicles, and has been widely concerned by the academic and industrial circles in recent years.

[0003] Since experimental equipment for visible light communication between vehicles is relatively expensive, scheme verification and performance testing of visible light communication between vehicles are mostly realized by establishing a simulation model. However, in the two-input two-output visible light communication system model used by current researchers, the description of the illumination intensity distribution of the automobile headlamp and the reflection characteristics of the road surface is based on the ideal Lambertian model commonly used for indoor visible light communication system modeling. However, the ideal Lambertian model is inaccurate for simulating the illumination intensity distribution of the automobile headlamp and the reflection characteristics of the real road surface.

[0004] Therefore, how to model the two-input two-output visible light communication system between vehicles to make it more reliable is an important basis for the further development of visible light communication technology between vehicles. SUMMARY

[0005] The purpose of the application is to provide a design method of a two-input two-output visible light communication system model between vehicles, so as to change the current situation that the two-input two-output model between vehicles is too idealized and has a large difference from the actual communication state between vehicles.

[0006] In order to achieve the above purpose, the technical scheme adopted by the application is:

[0007] A design method of a two-input two-output visible light communication system model between vehicles, comprising the following steps:

[0008] Step 1: establishment of an automobile headlamp model;

[0009] Step 2: line-of-sight link analysis;

[0010] Step 3: non-line-of-sight link analysis;

[0011] Step 4: system noise analysis;

[0012] Step 5: analysis of the received signal of the photodetector.

[0013] Further improvement of the technical scheme of the present application is that the expression of the light intensity of the headlamp in step 1 is:

[0014] I T (a,b) (1)

[0015] Wherein, a and b are the horizontal and vertical angles between the light direction of the headlamp and the lamp axis direction of the headlamp;

[0016] The illumination formula of any position of the irradiated road surface or the photodetector surface is:

[0017]

[0018] Wherein, φ is the luminous flux; S is the corresponding area of the irradiated road surface or the photodetector surface; ω is the solid angle of the light; r is the straight line distance between the light exit point and the point in the irradiated road surface or the photodetector surface; and c is the angle between the light direction of the headlamp and the normal of the irradiated road surface or the normal of the photodetector surface.

[0019] Further improvement of the technical scheme of the present application is that the line-of-sight link in step 2 is the light that does not pass through the road surface reflection and directly enters the photodetector I and the photodetector II when the headlamp I and the headlamp II of the two-input two-output visible light communication system model communicate with each other, and the received line-of-sight link power of the photodetector I and the photodetector II is:

[0020]

[0021] Wherein, P j LOS is the total power received by the photodetector j from the system line-of-sight link; a ij and b ij are the horizontal and vertical angles between the line-of-sight link formed by the headlamp i and the photodetector j and the lamp axis direction of the headlamp i; c ij is the angle between the line-of-sight link formed by the headlamp i and the photodetector j and the normal of the photodetector surface; r ij is the straight line distance between the headlamp i and the photodetector j; and ψ is the half angle of the field of view received by the photodetector I3 and the photodetector II4.

[0022] Further improvement of the technical scheme of the present application is that the specific steps of step 3 are:

[0023] Step 3.1: When the light of the headlamp I causes the road surface reflection, the brightness of the reflection point A on the road surface is:

[0024]

[0025] Wherein, cA is the angle between the back extension of the incident light ray of the reflection point A on the road surface and the projection of the reflected light ray on the road surface; d A is the light incidence angle, i.e. the angle between the incident light ray of point A and the normal of the road surface; r A , tand A are the brightness coefficients of the asphalt or cement road surface at point A; h TX is the vertical height of the automobile headlamp I from the road surface;

[0026] Step 3.2: the illumination intensity of the headlamp I (1) at the road surface reflection point A is:

[0027]

[0028] wherein S A is the reflection area at the reflection point A;

[0029] Step 3.3: the emitted light of the headlamp I at the reflection point A is taken as a secondary light source with the luminous intensity of , and the light power received by the photodetector I and the photodetector II from the unit reflection area A is:

[0030]

[0031] wherein, is the produced illumination of the headlamp I at point A within the reflection area on the road surface; r A-RX-j is the straight-line distance from the reflection point A to the photodetector j; θ A-j is the angle between the non-line-of-sight link formed by the reflection point A and the photodetector j and the normal direction of the photodetector surface; LER is the luminous efficacy of the automobile headlamp I; A r is the surface area of the photodetector.

[0032] Step 3.4: the reflection areas of the headlamp I and the headlamp II on the road surface are respectively denoted as S1 and S2, and A and A' are the reflection points within S1 and S2, so the non-line-of-sight link power received by the photodetector I and the photodetector II from the reflection range of the headlamp I and the headlamp II on the road surface is:

[0033]

[0034] wherein S1 and S2 are the reflection areas on the road surface corresponding to the headlamp I and the headlamp II respectively, and A and A' are the reflection points within the areas S1 and S2; is the non-line-of-sight light power received by the photodetector j.

[0035] Further improvement of the technical scheme of the present application is that the system noise of step 4 includes shot noise, inter-symbol interference noise and thermal noise represented by additive white Gaussian noise, and the specific steps are as follows:

[0036] Step 4.1: the interference of shot noise to the two-input two-output visible light communication system model between vehicles is:

[0037]

[0038] wherein, is the variance of the shot noise of the photodetector j; q is the electronic charge quantity; R is the response rate of the photodetector; B is the system bandwidth; I bg is the received background noise current; I2 is the noise bandwidth factor of the background noise;

[0039] Step 4.2: the inter-symbol interference noise caused by the multipath effect is:

[0040]

[0041] wherein, is the variance of the inter-symbol interference noise of the photodetector j;

[0042] Step 4.3: the thermal noise represented by the additive white Gaussian noise is:

[0043]

[0044] wherein, is the variance of the thermal noise; k is the Boltzmann constant; T k is the absolute temperature; Γ is the transistor channel noise factor; G is the open-loop voltage gain; g m is the transistor inverse transconductance; η is the fixed capacitance of the photodetector per unit area; I3 is the transistor channel noise current of the thermal noise.

[0045] Further improvement of the technical scheme of the present application is that the specific steps of step 5 are as follows:

[0046] Step 5.1: the two-input two-output visible light communication system model between vehicles adopts binary amplitude shift keying modulation technology and photodetector direct detection calculation to modulate and receive information, so the signal-to-noise ratio of the collected signal is defined as:

[0047]

[0048] wherein, SNR j is the signal-to-noise ratio of the photodetector j;

[0049] Step 5.2: Maximum ratio combining is performed on the signal-to-noise ratio of the signals collected by the photodetector I and the photodetector II, and the final signal-to-noise ratio of the system is obtained, and the calculation formula is as follows:

[0050]

[0051] Step 5.3: The system bit error rate is calculated according to the signal-to-noise ratio of the two-input two-output visible light communication system between the workshops:

[0052]

[0053] Wherein, Q(x) is a function for calculating the tail probability of the standard Gaussian distribution.

[0054] Thanks to the above technical solutions, the application has the following technical effects:

[0055] The application improves the reliability of the two-input two-output visible light communication system model between vehicles, and further improves the accuracy of the simulation results of the two-input two-output visible light communication between vehicles, thereby providing a reliable theoretical basis and experimental guidance for future technical research.

[0056] The two-input two-output visible light communication model between vehicles designed by the application considers the real automobile headlamp light intensity distribution model and the reflection of the road surface of different materials, thereby providing a theoretical basis and practical value for the visible light communication between vehicles. DETAILED DESCRIPTION

[0057] Figure 1 is a schematic diagram for calculating the light intensity and illumination of the automobile headlamp;

[0058] Figure 2 is a schematic diagram of two-input two-output visible light communication between two vehicles on a straight road section;

[0059] Figure 3 is a schematic diagram of the actual road surface reflection;

[0060] Figure 4 is the relationship between the received optical power of the photodetector and the distance between vehicles,

[0061] Wherein: (a) photodetector height = 0.2m; (b) photodetector height = 0.4m;

[0062] (c) photodetector height = 0.6m; (d) photodetector height = 0.8m;

[0063] Figure 5 is the relationship between the communication distance and the bit error rate under different photodetector heights when the road surface is asphalt;

[0064] Wherein, 1, headlamp I, 2, headlamp II, 3, photodetector I, 4, photodetector II, 5, incident light, 6, emergent light. DETAILED DESCRIPTION

[0065] The application will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0066] A design method of a two-input two-output visible light communication system model between vehicles, specifically comprising the following steps:

[0067] Step 1: Establishment of a car headlamp model

[0068] In the first 90% of vehicles sold on the market, 25 experimental samples are randomly selected for photometric measurement, and the measurement results are weighted according to the current sales proportion of the corresponding vehicle model, and finally the light intensity data conforming to the mainstream vehicle headlamp light intensity distribution on the market are obtained. As shown in the accompanying Figure 1 The light intensity of the headlamp I1 and the headlamp II2 market weighted beam model is represented as:

[0069] I T (a,b) (1)

[0070] Wherein, a and b are the horizontal and vertical angles of the emergent light of the car headlamp and the lamp axis direction.

[0071] The illumination formula of any position of the irradiated road surface or photodetector surface is:

[0072]

[0073] Wherein, φ is the luminous flux (lm); S is the corresponding area of the irradiated road surface or photodetector surface (m 2 ); ω is the solid angle of the light (sr); r is the straight line distance between the light exit point and the point in the irradiated road surface or the photodetector surface (m), and c is the angle between the direction of the emergent light of the car headlamp and the normal of the irradiated road surface or the normal of the photodetector surface.

[0074] Step 2: Processing of the line-of-sight link

[0075] The straight road communication situation of the two-input two-output visible light communication system model between vehicles is shown in the accompanying Figure 2 , but is not limited to straight road communication. The light rays of the headlamp I1 and the headlamp II2 of the left vehicle that do not pass through the road surface reflection and directly enter the photodetector I3 and the photodetector II4 of the right vehicle are the line-of-sight link. The line-of-sight link power received by the photodetector I3 and the photodetector II4 is:

[0076]

[0077] where P j LOS is the total power received by the photodetector j from the LoS link; a ij and b ij are the horizontal and vertical angles between the LoS link formed by the headlamp i and the photodetector j and the headlamp i's optical axis; c ij is the angle between the LoS link formed by the headlamp i and the photodetector j and the surface normal of the photodetector; r ij is the straight-line distance between the headlamp i and the photodetector j; A r is the photodetector surface area; and ψ is the half-angle of the field of view received by the photodetector I3 and the photodetector II4.

[0078] Step 3: NLoS link processing

[0079] The light rays emitted by the headlamp Ii and the headlamp II2 of the left vehicle and reflected by the road surface into the photodetector I3 and the photodetector II4 of the right vehicle are the NLoS link of the two-input and two-output VLC system model between vehicles. The embodiment selects the cement and asphalt road surfaces for the NLoS link reflection surface, but is not limited to the cement and asphalt road surfaces. The road surface reflection caused by the left vehicle headlamp Ii at the corresponding reflection point on the road is shown in FIG. 5, where the incident light ray 5 is reflected by the road surface to produce the outgoing light ray 6. Figure 3

[0080] Step 3.1: When the light rays of the headlamp Ii cause the road surface reflection, the brightness of the reflection point A on the road surface is:

[0081]

[0082] where c A is the angle between the reverse extension line of the incident light ray of the reflection point A on the road surface and the projection of the reflected light ray on the road surface; d A is the light ray incidence angle, i.e., the angle between the incident light ray of point A and the road surface normal; r(c A , tand A ) is the brightness coefficient of the asphalt or cement road surface at point A; h TX is the vertical height of the headlamp Ii from the road surface.

[0083] Step 3.2: The illumination intensity of the headlamp Ii at the road surface reflection point A is:

[0084]

[0085] where S A is the reflection area at the reflection point A. ​

[0086] Step 3.3: The emitted light of headlamp I1 at reflection point A is taken as a secondary light source with luminous intensity of The light power received by photodetector I3 and photodetector II 4 from unit reflection area A is:

[0087]

[0088] wherein, is the produced illuminance of headlamp I1 at point A in the area where reflection can occur on the road surface; r A-RX-j is the straight-line distance from reflection point A to photodetector j; θ A-j is the included angle between the non-line-of-sight link formed by reflection point A and photodetector j and the normal direction of the photodetector surface; LER is the luminous efficacy of the automobile headlamp I1.

[0089] Step 3.4: The areas on the road surface where headlamp I1 and headlamp II 2 can reflect are respectively denoted as S1 and S2, and A and A' are respectively reflection points in S1 and S2, so the non-line-of-sight link power received by photodetector I3 and photodetector II 4 from the reflection range of headlamp I1 and headlamp II 2 on the road surface is:

[0090]

[0091] wherein, S1 and S2 are respectively the reflection areas of headlamp I1 and headlamp II 2 on the road surface, and A and A' are respectively reflection points in areas S1 and S2; is the non-line-of-sight light power received by photodetector j.

[0092] Step 4: System noise processing

[0093] The two-input two-output visible light communication system model between the vehicles is used for analysis of the performance of the two-input two-output visible light communication system between the vehicles in the daytime, so the ambient light will have a greater impact on the transmission of the signal. In the presence of ambient light, shot noise, inter-symbol interference noise, and thermal noise represented by additive white Gaussian noise will have a greater impact on the transmission of the signal.

[0094] Step 4.1: The interference of shot noise on the system model is:

[0095]

[0096] wherein, is the variance of the shot noise of photodetector j; q is the electronic charge quantity; R is the response rate of the photodetector; B is the system bandwidth; I bg is the received background noise current; I2 is the noise bandwidth factor of the background noise.

[0097] Step 4.2: The inter-symbol interference noise caused by the multipath effect is as follows:

[0098]

[0099] in, The variance of inter-symbol interference noise of photodetector j.

[0100] Step 4.3: The thermal noise represented by additive Gaussian white noise is:

[0101]

[0102] in, Let g be the variance of thermal noise; k is the glass transition temperature. m Philosopher's constant; T k Γ is the absolute temperature; G is the transistor channel noise factor; I3 is the open-loop voltage gain; η is the transistor back conductivity; I3 is the fixed capacitance per unit area of ​​the photodetector; and I4 is the thermal noise transistor channel noise current.

[0103] Step 5: Processing the signals received by the photodetector

[0104] Step 5.1: The model uses binary amplitude shift keying (BSK) modulation technology and direct detection calculation by photodetectors to modulate and receive information. Therefore, the signal-to-noise ratio of the acquired signal is defined as:

[0105]

[0106] Among them, SNR j Let j be the signal-to-noise ratio of the photodetector.

[0107] Step 5.2: Perform maximum ratio combining on the signal-to-noise ratios of the signals acquired by photodetector 3 and photodetector 4 to obtain the final signal-to-noise ratio of the system. The calculation formula is as follows:

[0108]

[0109] Step 5.3: Calculate the system bit error rate based on the signal-to-noise ratio of the workshop's two-input two-output visible light communication system:

[0110]

[0111] Where Q(x) is a function used to calculate the tail probability of the standard Gaussian distribution.

[0112] Step 6: System Simulation

[0113] Step 6.1: The two-input two-output VLC system model between two vehicles is configured as follows: low beam (50% intensity) in the daytime, the distance between headlamp I1 and headlamp II2 is 1.2 m, the distance from the road surface is 0.66 m, the distance between photodetector I3 and photodetector II4 is 1.2 m, and the two vehicles are in the same lane with the lateral distance of the center line of the vehicles being 0 m. Table 1 shows the key parameters of the system modeling.

[0114] Table 1 System model parameter table

[0115]

[0116] Step 6.2: The headlamp I1 and headlamp II2 emit light with a certain intensity, and the received visual and non-visual light powers of the photodetectors I3 and I4 are calculated according to the formulas (3) and (7). When the road surface is asphalt and cement respectively, the visual and non-visual powers received by different photodetectors are shown in Figs. 6 and 7, respectively. Figure 4 It can be seen that the road surface material has a greater impact on the received non-visual light power and a smaller impact on the received visual light power. Figure 4

[0117] Step 6.3: The relationship between the height of different photodetectors and the system bit error rate is calculated according to the formula (13), as shown in Fig. 8. According to Fig. 9, it can be seen that the optimal receiving height of the photodetector is 0.2 m. Figure 5 Figure 5 It can be seen that the road surface material has a greater impact on the received non-visual light power and a smaller impact on the received visual light power.

[0118] In the specific embodiments, the road surface type and the height of the photodetector are analyzed to analyze the received power of the photodetector in the visual link and the non-visual link, and the height of the photodetector is analyzed to analyze the system bit error rate performance, but the present application is not limited to the above performance analysis of the two-input two-output VLC between two vehicles.

[0119] The above-described embodiments are only to describe the working modes of the present application, and not to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application. The unmentioned part of the present application is applicable to the prior art.​​

Claims

1. A method for designing a two-input two-output visible light communication system model between vehicles, characterized in that, The method comprises the following steps: Step 1: establishment of a car headlamp model; The arbitrary headlamp light intensity expression in step 1 is: I T (a,b)(1) Wherein, a and b are the horizontal and vertical angles between the headlamp light direction and the headlamp axis direction; The illumination expression of any position on the irradiated road surface or the photodetector surface is: Wherein, φ is the luminous flux; S is the corresponding area of the irradiated road surface or the photodetector surface; ω is the light solid angle; r is the straight-line distance between the light exit point and the point in the irradiated road surface or the photodetector surface; and c is the angle between the car headlamp light direction and the normal of the irradiated road surface or the normal of the photodetector surface; Step 2: line-of-sight link analysis; The line-of-sight link in step 2 is the light directly incident on the photodetector I (3) and the photodetector II (4) without being reflected on the road surface when the car-to-car two-input two-output visible light communication system model communicates using the headlamp I (1) and the headlamp II (2); and the line-of-sight link power received by the photodetector I (3) and the photodetector II (4) is: where P j LOS is the total power received by the photodetector j from the system LIDAR link; a ij and b ij are the horizontal and vertical angles of the LIDAR link formed by the automobile headlamp i and the photodetector j with respect to the headlamp i's optical axis; c ij is the angle of the LIDAR link formed by the automobile headlamp i and the photodetector j with respect to the photodetector's surface normal; r ij is the straight-line distance between the automobile headlamp i and the photodetector j; ψ is the half-angle of the field of view received by the photodetector I3 and the photodetector IV; A r is the photodetector surface area; LER is the luminous efficacy of the automobile headlamp II. Step 3: Non-line-of-sight link analysis; the emitted light of headlamp I (1) at reflection point A is considered as a secondary light source with luminous intensity of The light power received by photodetector I (3) and photodetector II (4) from unit reflection area A is: wherein, I (1) is the generated illuminance at point A within the area where the headlamp I (1) can occur reflection on the road surface; r A-RX-j is the straight-line distance from the reflection point A to the photodetector j; θ A-j is the angle between the non-line-of-sight link formed by the reflection point A and the photodetector j and the surface normal direction of the photodetector; LER is the luminous efficacy of the automobile headlamp I (1); A r is the surface area of the photodetector; The areas where the headlamp I (1) and the headlamp II (2) are reflected on the road surface are denoted as S1 and S2, respectively; and A and A' are the reflection points in S1 and S2, respectively; therefore, the non-line-of-sight link power received by the photodetector I (3) and the photodetector II (4) from the reflection range of the headlamp I (1) and the headlamp II (2) on the road surface is: Wherein, S1 and S2 are the corresponding reflection areas of the headlamp I (1) and the headlamp II (2) on the road surface, A and A' are the reflection points in the areas S1 and S2 respectively; Pnonlos is the non-line-of-sight optical power received by the photodetector j; Step 4: system noise analysis; Step 5: analysis of the photodetector received signal.

2. The method of claim 1, wherein the method is characterized by: The specific steps of step 3 are: Step 3.1: when the light of the headlamp I (1) causes road surface reflection, the brightness of the reflection point A on the road surface is: wherein c A is the angle between the back extension of the projection of the incident light ray at the reflection point A on the road surface and the projection of the reflected light ray on the road surface;d A is the angle of incidence of the light ray, i.e. the angle between the incident light ray at point A and the normal to the road surface;r(c A ,tand A ) is the luminance factor of the asphalt or concrete road surface at point A;h TX is the vertical height of the car headlight I(1) from the road surface; Step 3.2: the light intensity of the headlamp I (1) at the road surface reflection point A is: where S A is the reflection area at the reflection point A.

3. The method of claim 1, wherein the method is characterized by: The system noise of step 4 includes shot noise, inter-symbol interference noise, and thermal noise represented by additive white Gaussian noise, and the specific steps are: Step 4.1: the interference of shot noise on the car-to-car two-input two-output visible light communication system model is: wherein is the variance of the shot noise of the photodetector j; q is the electronic charge; R is the responsivity of the photodetector; B is the system bandwidth; I bg is the received background noise current; I2is the noise bandwidth factor of the background noise; Step 4.2: the inter-symbol interference noise caused by the multipath effect is: wherein, a variance of inter-symbol interference noise of the photodetector j; Step 4.3: the thermal noise represented by additive white Gaussian noise is: wherein, is the variance of thermal noise; k is the Boltzmann constant; T k is the absolute temperature; Γ is the transistor channel noise factor; G is the open loop voltage gain; g m is the transistor transconductance; η is the fixed capacitance per area of the photodetector; I3is the transistor channel noise current of thermal noise.

4. The method of claim 1, wherein the method is characterized by: The specific steps of step 5 are: Step 5.1: the car-to-car two-input two-output visible light communication system model uses binary amplitude shift keying modulation technology and photodetector direct detection calculation to modulate and receive information, so the signal-to-noise ratio of the collected signal is defined as: wherein SNR j is the signal-to-noise ratio of the photodetector j; Step 5.2: the signal-to-noise ratios of the photodetector I (3) and the photodetector II (4) collected signals are combined by maximum ratio combining, and the final signal-to-noise ratio of the system is obtained, and the calculation formula is as follows: Step 5.3: the system bit error rate is calculated according to the signal-to-noise ratio of the car-to-car two-input two-output visible light communication system: Wherein, Q(x) is a function for calculating the tail probability of the standard Gaussian distribution.

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