Illumination and communication integrated luminous flux optimization method based on photoelectric and thermal characteristics of LED array

Abstract

The invention relates to an illumination and communication integrated luminous flux optimization method based on the photoelectric and thermal characteristics of an LED array, and the method comprises the steps: building a dynamic photoelectric and thermal model of the LED array, considering the influence of a modulation mode, modulation depth, power, temperature and the number of arrays on the luminous flux output characteristics, and building a design criterion which can be used for evaluating the illumination capability and communication capability of the LED on the basis, according to application requirements of indoor illumination communication, the visible light communication optimization method without losing illumination capability is designed, the optimal modulation depth and bias combination of the LED array is obtained, the optimization target of maximizing signal components on the basis of meeting the illumination requirements is achieved, and the method has high engineering application value.

Description

Technical Field

[0001] The present invention relates to the technical field of visible light communication, and in particular to a method for optimizing the integrated light flux based on the photoelectric and thermal characteristics of an LED array. Background Art

[0002] In recent years, in order to solve the problem of insufficient spectrum resources for wireless communication and the rapidly growing data demand, higher frequency band communication methods are urgently needed. Visible light communication makes full use of 380nm-780nm optical carriers to achieve communication. While expanding spectrum resources, it also has natural advantages such as security, deep coverage, anti-electromagnetic interference, and compatibility with basic lighting facilities. It has now become an important alternative technology for the sixth generation of mobile communications.

[0003] In visible light communication systems, light-emitting diodes (LEDs) are usually used as lighting sources and communication base stations. In practical applications, it is necessary to couple a modulated signal to the forward current of the LED to output a light flux with varying strengths to provide lighting and transmit digital information; the lighting capacity of the LED is usually represented by the average value of the light flux, and the fluctuation of the light flux can be used for information transmission. However, the electro-optical response of the LED is severely nonlinear, and additional signal modulation may cause a loss in lighting performance and communication performance.

[0004] In order to study the effect of modulation on LED performance, it is necessary to build a reasonable LED model. On the one hand, the bias current of the LED has a convex function relationship with the power consumption, and on the other hand, the bias current of the LED has a concave function relationship with the luminous flux. In early literature analysis, the analysis was usually based on a linearized LED electrical model, and the dependence of the LED array on temperature was ignored, making this method of limited value in practical applications.

[0005] In practical applications, LEDs are usually present in the form of arrays to provide stronger lighting and communication capabilities. Multiple LED lamp beads are integrated on a heat sink with limited area, which makes the impact of temperature on LED performance more serious. To study the impact of temperature on LED performance, a common approach is to construct a photoelectric thermal model of the LED array and analyze the relationship between current, temperature, and luminous flux.

[0006] At present, researchers have carried out comprehensive modeling of the mutual influence of LED photoelectric and thermal mechanisms. Some scholars have derived the characteristic equation of LED electro-optical response from the perspective of microscopic carrier recombination mechanism and considered the influence of temperature on the recombination mechanism. However, this model is a physical theoretical model with serious nonlinearity and is difficult to be directly applied to communication design. Other scholars have established a static photoelectric and thermal model of LED, but have not considered the influence of modulation on LED performance. Some scholars have analyzed the average luminosity and instantaneous luminosity of different modulation modes. However, this study assumes that the temperature of the LED is constant and ignores the power and temperature changes caused by the modulation signal. The results obtained are only accurate when the modulation depth is small. Therefore, the existing technology lacks a reasonable model to characterize the dynamic relationship between the current, temperature, and luminous flux of the LED array, and thus cannot effectively optimize the LED array.

[0007] In addition, the optimization of LED arrays must also be designed in conjunction with the target application of VLC (Visible Light Communication). In indoor applications, LIFI (Light-Fidelity) applications need to meet lighting standards, while communication design needs to avoid possible flickering and more obvious illumination loss, and on this basis, increase the signal component as much as possible. How to maximize the signal component while meeting lighting requirements is a problem that needs to be solved. Summary of the invention

[0008] In view of the defects of the prior art, the present invention provides a lighting and communication integrated luminous flux optimization method based on the photoelectric and thermal characteristics of LED arrays. Taking the dynamic electro-photothermal array model as a benchmark, the dynamic influence of modulation mode and modulation depth on the instantaneous luminous flux output by the LED array is considered in real time. Combined with the number of LED arrays, indoor lighting needs and communication needs as constraints, a comprehensive inductive design is carried out to realize an LED array lighting and communication integrated design method with practical engineering application value.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array, comprising the following steps:

[0011] S1. Establish a dynamic photoelectric thermal model of LED array;

[0012] S2. Establishing design criteria for evaluating LED lighting and communication capabilities based on the characteristics of the modulated LED output luminous flux;

[0013] S3. Under the premise of not losing the lighting capability, the optimal combination design of LED bias current and modulation mode is carried out with the optimization goal of maximizing the communication luminous flux of the LED array to achieve the optimization goal.

[0014] Furthermore, in step S1, a static photoelectric thermal model of the LED array is established without considering communication modulation; then, based on the static photoelectric thermal model, the influence of communication modulation on luminous flux is considered to establish a dynamic photoelectric thermal model of the LED array.

[0015] Furthermore, the established dynamic photoelectric thermal model of the LED array can describe the relationship between the number of LEDs, junction temperature, bias current, power, and modulation scheme and the dynamic instantaneous luminous flux of the LED array.

[0016] Furthermore, when constructing the dynamic photoelectric thermal model, a linear model of the equivalent resistance of an ideal diode in series with an LED is used for modeling.

[0017] Furthermore, in the process of constructing the dynamic photoelectric thermal model, a modulation signal is coupled to the DC bias of the LED, and the modulation signal adopts a stably ergodic random modulation signal.

[0018] Furthermore, in the dynamic photoelectric thermal model of the LED array, the instantaneous luminous flux output of the LED array is determined by the mean square value of the modulation current and the instantaneous value of the modulation current.

[0019] Furthermore, in step S2, the design criterion is that the expected value of the dynamic instantaneous luminous flux of the LED array is used to represent the illumination luminous flux of the LED array, and the root mean square value of the dynamic instantaneous luminous flux of the LED array is used to represent the signal flux of the LED array.

[0020] Furthermore, step S3 is specifically to optimize the LED array based on the dynamic electro-thermal model of the LED array according to indoor lighting requirements, communication requirements, array quantity, LED electro-thermal characteristics and modulation methods under the calibrated lighting flux with the goal of maximizing the signal flux of the LED array.

[0021] Furthermore, during optimization, the minimum and maximum values ​​of the temperature of the LED array, as well as the maximum and minimum values ​​of the current of the LEDs, are limited.

[0022] Furthermore, in step S3, the result of the optimized design can obtain the optimal bias current of the LED array, and modulation of the bias current can maintain the lighting performance of the LED array and obtain the maximum communication luminous flux.

[0023] Beneficial effects:

[0024] (1) The present invention fully considers the influence of array scale and temperature on the lighting communication performance of LED arrays, and considers the influence of modulation on the output luminous flux of LED arrays, and establishes a dynamic photoelectric thermal model of LED arrays. The model can describe the relationship between the number of LEDs, junction temperature, bias current, power, modulation scheme and luminous flux, and cracks the functional relationship between temperature, electricity and luminosity, which has high accuracy and engineering application value.

[0025] (2) According to the lighting characteristics and communication characteristics of the LED array, the present invention constructs an expression method that can characterize the LED lighting flux and the communication flux. The expected value of the changing flux is used to represent the lighting capability of the LED array, and the root mean square value of the dynamic fluctuation of the LED array flux is used to represent the communication capability of the LED array. On this basis, according to the lighting requirements of the indoor LED array, a design method for the maximum communication flux under the calibrated lighting flux is proposed.

[0026] (3) The present invention designs a visible light communication application solution without sacrificing lighting capability based on the application requirements of indoor lighting communication. The optimal bias current of the LED array is obtained based on the indoor lighting requirements, communication requirements, array quantity, LED electrothermal characteristics and modulation method. By modulating at this bias current, the maximum communication luminous flux can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The relationship between the electrothermal effect of LED and the luminous flux of lighting and communication;

[0028] Figure 2 LED modulation mode and electrothermal equivalent circuit;

[0029] Figure 3 The relationship between bias current and LED luminous flux;

[0030] Figure 4 The volt-ampere characteristic curve of LED;

[0031] Figure 5 Schematic diagram of visible light communication application solution taking into account lighting communication scenarios;

[0032] Figure 6 The maximum illumination flux and communication flux allowed by different array sizes (I b =0.35A, R jc =1℃ / W and R hs =0.3°C / W);

[0033] Figure 7 The maximum illumination flux and communication flux allowed by different array sizes (I b =0.35A, R jc =1℃ / W and Rhs =1.5℃ / W)

[0034] Figure 8 Maximum lighting flux and communication flux allowed by different bias currents (N=24, R jc =1℃ / W and R hs =0.3°C / W);

[0035] Fig. 9 Maximum lighting flux and communication flux allowed by different bias currents (N=24, R jc =1℃ / W and R hs =1.5℃ / W);

[0036] Fig.10 Bit error rate performance of PAM signal under different bias currents (N=24, R jc =1℃ / W and R hs =0.5℃ / W, Bw=10Mbps);

[0037] Fig.11 Bit error rate performance of PAM signal under different bias currents (N=24, R jc =1℃ / W and R hs =0.3℃ / W, Bw=10Mbps);

[0038] Fig.12 BER performance of OFDM signal under different bias currents (N=24, R jc =1℃ / W and R hs =0.5℃ / W, Bw=10Mbps);

[0039] Fig.13 Bit error rate performance of OFDM signal under different bias currents (N=24, R jc =1℃ / W and R hs =0.3℃ / W, Bw=10Mbps). DETAILED DESCRIPTION

[0040] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] The present invention is aimed at indoor visible light communication application scenarios that take into account both lighting and communication. Based on the intrinsic photoelectric and thermal characteristics of the LED array, the coupling signal characteristics, the array scale and other factors, the luminous flux correlation optimization design of the integrated lighting and communication is carried out. The design mainly includes the following three steps:

[0042] Firstly, a dynamic photoelectric thermal model of LED array is established, which can describe the relationship between the number of LEDs, junction temperature, bias current, power, and modulation scheme and the dynamic instantaneous luminous flux of LED array.

[0043] Secondly, according to the characteristics of the modulated LED output luminous flux, a design criterion that can be used to evaluate the LED lighting and communication capabilities is established;

[0044] Finally, without losing lighting capability, the optimal combination of LED bias current and modulation mode is designed with the optimization goal of maximizing LED communication luminous flux to achieve the optimization goal.

[0045] The electrical, thermal, and optical properties of LED arrays interact with each other. Figure 1 The relationship between the various physical mechanisms of LED is given in the figure. The electrical characteristics of LED are determined by the modulation current I(t), which depends on the bias current I b and modulation scheme s(t); the thermal characteristics of the LED are determined by the junction temperature T j OK, but the junction temperature T j Depends on power dissipation, heat sink temperature coefficient R ja and ambient temperature T a , bias current I b The increase in temperature not only increases the lighting flux, but also increases the power consumption and temperature of the LED. However, the increase in temperature may reduce the bias voltage (typically -2mv / ℃ to -3mv / ℃) and aggravate the nonlinearity of power current-luminous flux.

[0046] Therefore, when establishing the dynamic photoelectric thermal model of the LED array, the present invention takes into account the electrical characteristics, temperature characteristics, and optical characteristics of the LED array, and models the LED array in combination with a typical modulation mode. The modeling process is divided into two steps. The first step is to establish a static photoelectric thermal model of the LED array. The model is designed without considering the communication modulation. The second step is to consider the influence of modulation and establish a dynamic photoelectric thermal model of the LED array. The detailed process is as follows.

[0047] Step 1: Modeling the static response characteristics of LED arrays

[0048] The output luminous flux of an LED is closely related to the forward current and junction temperature. Figure 2 (A) shows the modulation circuit of LED. Figure 2 (B) shows the electrothermal equivalent circuit of the LED. In the electrical domain, the electrical characteristics of the LED are described using the model of the diode series equivalent resistance; in the thermal domain, the temperature characteristics of the LED are characterized using a similar node voltage method. The thermal radiation power P of the LED heat is the main heat source, T hs 、T j and T a Refers to heat sink temperature, junction temperature and ambient temperature respectively, R hs and R jc They refer to the thermal resistance from the heat sink to the environment and the thermal resistance from the PN junction to the heat sink casing respectively.

[0049] according to Figure 2 LED system model and electrothermal equivalent circuit, for unmodulated LED, with bias current I b As the independent variable, the functional relationship between LED luminous flux and bias current is constructed. According to the electrothermal equivalent model of LED, the bias voltage of LED can be calculated as:

[0050]

[0051] Where n is an ideal factor with a value of 1 to 2, K is the Boltzmann constant, T is the Kelvin temperature, q is the electron charge, and I s is the saturation current of the LED, R L is the equivalent load, K V is the rate at which the voltage changes with junction temperature (in V / °C), T j is the junction temperature, T0 is the reference temperature.

[0052] According to the electrothermal characteristics of LEDs, the junction temperature is affected by the power, quantity and ambient temperature of the LEDs. ja Indicates the change in thermal resistance from the junction to the environment. The junction temperature T j It can be calculated as:

[0053] T j =T a +(N·R hs +R jc )·V b I b ·K h (2)

[0054] Where N is the number of LEDs, R hs and R jc They represent the thermal resistance from heat sink to ambient and from junction to case, T a Indicates the ambient temperature, K h It represents the occupancy rate of the converted thermal radiation power to the LED power (typical value is between 0.8-0.9). According to equations (1) and (2), considering the influence of temperature on the LED, the bias voltage of the LED can be expressed as:

[0055]

[0056] The junction temperature and bias current of the LED are the main factors in the luminous flux modeling. This application uses a first-order linear relationship to characterize the temperature and luminous flux, current and luminous flux of the LED. The relationship between the junction temperature and luminous flux of the LED can be approximately expressed as:

[0057] F T (Tj )=K0-K1×T j ·(I b / I0) (4)

[0058] Among them, F T It is obtained under a constant reference current I0, K0 and K1 are linear fitting coefficients. The luminous flux and bias current of the LED can also be approximately characterized by a first-order linear relationship:

[0059] F I (I b )=d0+d1·(I b / I0), (5)

[0060] Obtain F at a constant reference temperature I (T0 is 25°C), d0 is the dependence coefficient of lighting flux and bias current, and its typical value is 0; d1 is the angular coefficient, and F0 is the standard luminous flux obtained under I0 and T0; considering the influence of junction temperature and bias current, according to the electrothermal characteristics, the output luminous flux of the LED can be calculated as:

[0061] The modeling of equation (6) is based on the temperature and electrical behavior of the LED array, and assuming thermal steady-state operation, a static model describing the luminous flux of the LED array can be obtained; Figure 3 As shown in the figure, it can be clearly seen that with the increase of bias current, the nonlinearity between LED current and luminous flux increases significantly.

[0062] Step 2: Establishment of dynamic photoelectric thermal model of LED array

[0063] The luminous flux expression obtained by the above equation (6) cannot be used to analyze the luminous flux under the bias current I b The luminous flux of the coupled modulated signal s(t). Since the result of equation (6) is the result of the comprehensive optics, electricity and heat, but does not consider the impact of communication modulation on LED performance, it is necessary to consider the impact of signal modulation on the static photoelectric thermal model and construct a dynamic photoelectric thermal model. In the following section, considering the impact of the modulation signal on the luminous flux, a dynamic PET (Photoelectrothermal, photoelectric thermal) array model is proposed to analyze the instantaneous luminous flux of the modulated LED.

[0064] From the volt-ampere model mentioned in formula (1), it can be seen that there is a convex relationship between voltage and current, and both the modulation mode and the modulation signal will affect the additional power consumption. In this application, the modulation mainly occurs in the linear region of the LED, and avoids the inflection point of the volt-ampere curve as much as possible; when constructing the dynamic model, the ideal diode and the equivalent resistance of the LED are connected in series to model the model. This model is a linear approximation of the LED theoretical model. This approximation can fit the linear part of the LED well. Taking the TW3535 model LED as an example, the fitted volt-ampere curve is as follows Figure 4 As shown, Figure 4 (A), V0 = 2.63 V, R L =3.67Ω, Figure 4 (B), V0 = 2.66 V, R L =3.96Ω. After adopting the approximate model, the relationship between the bias current and bias voltage of the LED is as follows:

[0065]

[0066] Wherein, V0 is the threshold voltage of the LED device.

[0067] When the modulation signal s(t) is coupled to the DC bias, the modulation current I(t) can be expressed as:

[0068] I(t)=(1+s(t))·I b (8)

[0069] Among them, the modulation signal s(t)I b Can be normalized to DC bias I b function, and -1≤s(t)≤1. When the LED is loaded with a modulation signal, the modulation voltage V(t) of the LED can be calculated as:

[0070]

[0071] Where s(t) is the shape of the modulated signal sample, and the modulation index is defined as the mean square value of the modulated signal. The modulation index can be calculated as:

[0072]

[0073] If a stable ergodic random modulation signal is used, the LED power consumption P dyn The expectation of can be calculated as:

[0074]

[0075] Wherein, P(I) is the probability density function (PDF) of the modulation current I(t).

[0076] The present invention mainly takes two typical modulation modes as examples, namely, discrete unbiased PAM signal and continuous zero-mean OFDM signal. Based on these two modulation modes, equation (11) can be simplified as:

[0077]

[0078] In equation (12), the power of the LED is determined by the expected value of the modulation current E[I(t)]. For a stationary ergodic signal, E[s(t)] = 0 and To simplify the integral function. By biasing the current I b and modulation index s rms Calculate the power of the LED.

[0079] For a discrete M-PAM signal with equidistant signal levels, the modulation current I(t) can be expressed as: Where speak is the peak value of the modulation depth. The mean square value of the modulation current I(t) is:

[0080] For a 2-PAM signal with M=2, the mean square value of the modulation current can be calculated as: I rms =(1+s peak )I b .

[0081] For OFDM signals with a large number of subcarriers, according to the central limit theorem, s(t) can be approximated as a Gaussian random signal If the modulation current has no obvious clipping distortion, the modulation current of the OFDM signal can be approximately expressed as

[0082] Within the -3dB bandwidth of the LED, it can be considered that the instantaneous value of the illumination flux depends on the modulation current I(t). The electrical effect in the dynamic luminous flux of the LED is directly related to the instantaneous current I(t), while the thermal effect is directly related to the mean square value of the modulation current I rms Considering the influence of modulation on LED, the dynamic instantaneous luminous flux of LED can be calculated as:

[0083] The result of equation (14) can be used to characterize the instantaneous luminous intensity of the LED array considering the electrothermal effect; the instantaneous luminous flux output of the LED array is determined by the mean square value of the modulation current and the instantaneous value of the modulation current.

[0084] like Figure 5As shown in the figure, in JIC (Joint Illumination and Communication) applications, the radiation area of ​​the LED needs to cover the room, which requires the LED to output sufficient lighting flux, and the receiving user can be at any location in the room area. Therefore, on the basis of satisfying the lighting flux, it is also necessary to output as much communication flux as possible to achieve data transmission; however, the nonlinearity of the electro-optical response and the additional modulation will lead to the loss of LED lighting capacity. Therefore, for JIC applications, on the one hand, it is necessary to avoid the loss of lighting flux caused by modulation, and on this premise, maximize the communication capacity of the LED.

[0085] LED array communication characteristics expression form

[0086] After establishing the dynamic photoelectric thermal model of the LED array, it is necessary to determine the expression form of the LED array lighting characteristics and communication characteristics; first of all, the main performance indicators of the VLC system must be clarified: lighting flux F DC and signal flux F AC Luminous flux is usually used to indicate the lighting capacity of LED. In this application, the expected value of instantaneous luminous flux is used for calculation. DC It can be calculated as:

[0087] F DC =N·E[F0·F T ·(T j (I rms ))·F I (I(t))]=N·F0·F T ·(T j (I rms ))·E[F I (I(t))] (15)

[0088] Take 2-PAM and DC-OFDM modulation schemes as examples. For 2-PAM signal, the modulation current I(t) can be expressed as I(t) = [[1-s peak ].I b ,[1+s peak ].I b ], when 2-PAM modulation is used, the DC luminous flux of the LED can be expressed as:

[0089] For OFDM signals, the modulation current can be approximately expressed as At this time, the luminous flux of the LED array can be approximately calculated as:

[0090] The light and dark flashing of LED can be used for data transmission, so we use signal flux to describe the intensity of the LED transmission signal. In this application, signal flux is expressed by the RMS value of LED luminous flux:

[0091]

[0092] Among them, t0 and t f Respectively represent the start and end time of the signal sample s(t). For a 2-PAM signal, the signal flux of the LED can be calculated as:

[0093]

[0094] For OFDM signals, the modulation current obeys Distribution, the signal flux of the LED can be calculated as:

[0095]

[0096] LED array lighting joint optimization design

[0097] Through equations (15) and (20), the lighting flux and signal flux of the LED can be calculated. Depending on the application scenario of the LED, the optimization scheme is also different. In the JIC scenario, our optimization goal is to maximize the communication performance of the LED without sacrificing the lighting performance. This optimization problem can be expressed as:

[0098] Among them, F lm is the calibrated illumination flux, I min and I max They represent the minimum current and maximum current allowed by the LED, T jmin and T jmax Indicates the maximum and minimum allowed junction temperature.

[0099] In formula (21), the optimization goal is to maximize the communication luminous flux of the LED array, constraint 1 is that the LED array does not lose the lighting luminous flux, that is, the lighting luminous flux takes the calibrated value, constraint 2 is that the temperature of the LED array must be between the maximum and minimum values ​​allowed, and constraint 3 is that the current of the LED must be between the maximum and minimum values ​​allowed.

[0100] Typically, the temperature of the LED array is 25-105 degrees Celsius and the current of the LEDs is between 0 and 1.05A.

[0101] To solve the signal light flux F AC The maximum value depends on the maximum modulation index s rms When the luminous flux F DCWhen constant, the optimum bias current can be used to obtain the maximum modulation index.

[0102] According to equation (15), P AC With P DC The relationship can be expressed as:

[0103]

[0104] DC power P DC It can be calculated as:

[0105]

[0106] AC power P AC It can be calculated as:

[0107]

[0108] Among them, P AC is the modulation current s rms I b The generated AC signal power, P DC is the bias current I b The generated lighting power. Substituting equations (23) and (24) into equation (22) to solve the expression for the modulation index, it can be calculated as:

[0109] Thus, the bias current that allows the maximum signal flux can be calculated as:

[0110] The result obtained is I b That is, the optimal bias point of the LED array when taking lighting into consideration, at which the dynamic optimization of the LED array can be achieved.

[0111] Simulation results and analysis of LED arrays

[0112] Through the above optimization process, it can be known that there is a bias point in the LED array that does not lose lighting capability and maximizes communication capability. The key results involved in the present invention will be verified by experiments and simulations below, including the influence of the LED array scale, the temperature coefficient of the heat sink, and the bias current of the LED array on the maximum lighting flux and communication flux provided by the LED.

[0113] (1) Impact of LED array size on performance

[0114] In this section, we analyze the impact of different array sizes on the communication performance of LED lighting. To fully illustrate the results, we selected two heat dissipation modules with different temperature coefficients as the experimental control group, namely R jc=1℃ / W and R hs =1.5℃ / W heat dissipation module and R jc =1℃ / W and R hs =0.3℃ / W heat dissipation module. The experimental results are as follows Figure 6 and Figure 7 As shown, the horizontal axis represents the lighting flux, and the vertical axis represents the communication flux.

[0115] exist Figure 6 middle, I b =0.35A, R jc =1℃ / W, R hs =0.3℃ / W. Due to the use of a better heat dissipation module, the temperature coefficient of the LED array is small, and the impact of temperature on LED lighting and communication is small. When the LED array scale N=8, the LED can achieve a lighting flux of 1512lm and a communication flux of 1439lm. As the array scale increases, when N=16, the lighting flux of the LED array is about 2959lm, and the communication flux is about 2713lm; and when N=24, the lighting flux of the LED array is about 4334lm, and the communication flux is about 3825lm. Obviously, when the array size is doubled, the lighting and communication flux of the LED array with N=16 does not reach twice the effect of N=8. If the results are normalized, the lighting flux when N=16 and N=24 is only 97.8% and 95.5% of that when N=8, while the communication flux is normalized to be approximately 94.2% and 88.6% of that when N=8. Therefore, it can be seen that when the temperature effect is low, as the array size increases, the system is more affected by temperature, and there is a certain loss in both lighting flux and communication flux.

[0116] exist Figure 7 middle, I b =0.35A, R jc =1℃ / W and R hs=1.5℃ / W. When the LED array uses a module with poor heat dissipation performance, the LED is more seriously affected by temperature, and the temperature of the LED array has a more serious impact on the lighting flux and communication flux. When N=8, the lighting flux of the LED is about 1383lm, and the communication flux is about 1115lm. When the array scale N=16, the lighting flux of the LED is about 2456lm, and the communication flux is about 1471lm. When the array scale N=24, the lighting flux of the LED is about 3235lm, and the communication flux is about 1291lm. If the results are normalized for comparison, the lighting flux when N=16 and N=24 is only 88.7% and 77.9% of that when N=8, while the communication flux is about 65.9% and 38.6% of that when N=8 after normalization. Obviously, with the increase of the array scale, the temperature of the LED array rises, which significantly reduces the lighting and communication fluxes of the LED array, especially the communication flux. When N=24, the communication flux of the LED array is even lower than that when N=16. The poor heat dissipation performance leads to a significant increase in the temperature of the LED array and a significant decrease in the performance of the LED. In addition, compared with the control group with better heat dissipation performance, the performance of the LED array with a larger temperature coefficient will significantly decrease as the array size increases. When N = 8, the performance of the LED array with R jc =1℃ / W and R hs =1.5℃ / W LED array, its lighting flux and communication flux are about R jc =1℃ / W and R hs = 0.3℃ / W LED array 91.5% and 77.5%, and as the array size increases, the performance of the LED decreases more significantly. When N = 16, R jc =1℃ / W and R hs =1.5℃ / W LED array, its lighting flux and communication flux are about 83% and 54.2% of the control group; when the array size increases to N=24, R jc =1℃ / W and R hs =1.5℃ / W, the lighting flux and communication flux of the LED array are about 74.6% and 31.9% of the control group. Obviously, as the array size increases, the lighting and communication functions of the LED array decrease.

[0117] (2) The influence of LED array bias current on lighting flux and communication flux

[0118] In this section, we analyze the illumination flux and signal flux allowed by different bias points. Figure 8 The results show that the selected temperature coefficient is smaller (N = 24, R jc =1℃ / W and R hs=0.3℃ / W) of the LED array. Obviously, when the temperature coefficient is lower, the heat dissipation effect of the LED is better, and the influence of temperature on the LED array is smaller. At this time, the bias current is positively correlated with the lighting and communication performance of the LED. As the bias current of the LED increases, the lighting flux and signal flux output by the LED array increase, and the lighting and communication capabilities of the LED array are stronger.

[0119] When we choose a larger temperature coefficient (N = 24, R jc =1℃ / W and R hs =1.5℃ / W) heat dissipation module, the heat dissipation performance of the LED array decreases, and the influence of temperature on the LED increases, such as Fig. 9 As shown in the figure, although monotonically increasing the bias current of the LED will increase the lighting flux of the LED, the communication flux of the LED does not increase monotonically. When the bias current increases from 0.3A to 0.5A, the maximum communication component of the LED is 1529lm, 1471lm, 1309lm, 1132lm and 974lm, and the communication flux of the LED decreases in turn. This result is consistent with Figure 8 The result is completely opposite. The main reason is that the increase of bias current leads to the increase of temperature of LED array. When the temperature coefficient is large, the higher the temperature of LED array, the more serious the performance of LED is affected by temperature, thus the performance is reduced.

[0120] (3) Bit error rate experimental verification

[0121] In the optimization design part, an optimal bias current or bias point can be obtained according to formula (26). Modulation at this bias point can ensure that the lighting performance of the LED array is not lost and the communication performance is maximized.

[0122] This section verifies the performance of the LED array by conducting a bit error rate experiment. Assuming an indoor scene, the bit error rate experiment is performed with different bias currents; first, the calibrated lighting flux is selected according to the illumination requirements, and on this basis, the effect of changing the bias current on the bit error rate of the VLC system is observed. In order to meet the indoor lighting requirements, the LED array used indoors usually selects a lighting flux of more than 4000lm. Therefore, this experiment selects the array scale N=24, and fixes the lighting flux to 4000lm to 7000lm. On this basis, the bias current I is observed. b Impact on the communication luminous flux of LED array.

[0123] To ensure the universality of the results, we use discrete PAM signals and continuous OFDM signals as examples to conduct experimental verification. The results are as follows: Fig.10 , Fig.11 , Fig.12 , Fig.13As shown in the figure, the horizontal axis is the bias current and the vertical axis is the bit error rate. Fig.10 (N=24, R jc =1℃ / W and R hs =0.5℃ / W, Bw=10Mbps) and Fig.11 (N=24, R jc =1℃ / W and R hs =0.3℃ / W, Bw=10Mbps) is the experimental result of PAM signal. Fig.12 (N=24, R jc =1℃ / W and R hs =0.5℃ / W, Bw=10Mbps) and Fig.13 (N=24, R jc =1℃ / W and R hs =0.3℃ / W, Bw=10Mbps) is the experimental result of OFDM signal; it can be clearly seen from the figure that there is an optimal bias current for the bit error rate performance of the LED array, that is, the optimal bias current obtained by formula (26).

[0124] The experimental results show that there is an optimal bias point for the LED array, which is the bias current point corresponding to the lowest bit error rate in the figure. Modulating at this point can achieve the lowest communication bit error rate, that is, the lighting performance of the LED array is not lost and the communication performance is maximized.

[0125] In summary, the present invention is aimed at the application scenario of indoor visible light communication with integrated illumination and communication, and optimizes the correlation of the luminous flux of integrated illumination and communication based on the intrinsic characteristics of photoelectricity and heat of LED array, the characteristics of coupled signals, and the scale of array. The innovation is mainly reflected in:

[0126] 1) A dynamic photoelectric thermal model of the LED array was established, and the effect of modulation on the output luminous flux of the LED array was considered.

[0127] 2) According to the lighting characteristics and communication characteristics of the LED array, an expression method that can characterize the LED lighting flux and communication flux is constructed. On this basis, according to the lighting requirements of the indoor LED array, the design method of the maximum communication flux under the calibrated lighting flux is studied.

[0128] 3) This method fully considers the impact of array scale and temperature on the lighting and communication performance of LED arrays, deciphers the functional relationship among temperature, electricity and luminosity, designs a design method integrating modulation mode, lighting and communication, and verifies the effectiveness of this method.

[0129] Aiming at the luminous flux output demand of indoor lighting and communication, the present invention constructs a photoelectric thermal model of the LED array and considers the influence of the modulation mode, modulation depth, power, temperature and array quantity on the luminous flux output characteristics, and constructs a photoelectric thermal dynamic response model of the LED array. On this basis, the influence of the signal characteristics of high-order PAM and OFDM on the lighting and communication performance is considered, and the lighting performance and communication performance after the LED is coupled with the dynamic signal are established. Finally, the influence of the modulation index, bias current, array scale and other factors is considered to construct a luminous flux optimization design criterion for both lighting and communication. On the basis of meeting the lighting luminous flux, the communication luminous flux is maximized to obtain the optimal bias point.

[0130] The performance of LED is affected by many factors, and the existing solutions have not fully explored the dynamic photoelectric thermal relationship of LED arrays, and have not studied the lighting and communication boundaries of LEDs from the aspects of LED array scale, temperature coefficient, modulation mode, etc. The present invention takes the actual indoor lighting needs as the starting point, studies the optimal modulation point of the LED array under the premise of indoor lighting, further optimizes the performance of the LED array, fully considers the correlation between the four disciplines of temperature, electricity, optics, and communication, and designs the LED array based on this. By fully exploring the multi-dimensional correlation factors, the optimal performance results are obtained, the accuracy is high, and it has practical guiding significance for engineering applications.

[0131] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of LED arrays, characterized in that: The following steps are involved: S1. Establish a dynamic photoelectric thermal model of LED array; S2. Establishing design criteria for evaluating LED lighting and communication capabilities based on the characteristics of the modulated LED output luminous flux; S3. Under the premise of not losing the lighting capability, the optimal combination design of LED bias current and modulation mode is carried out with the optimization goal of maximizing the communication luminous flux of the LED array to achieve the optimization goal.

2. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 1, characterized in that: In step S1, a static photoelectric thermal model of the LED array is established without considering communication modulation; then, based on the static photoelectric thermal model, the influence of communication modulation on luminous flux is considered to establish a dynamic photoelectric thermal model of the LED array.

3. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 2, characterized in that: The established dynamic photoelectric thermal model of the LED array can describe the relationship between the number of LEDs, junction temperature, bias current, power, and modulation scheme and the dynamic instantaneous luminous flux of the LED array.

4. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 2, characterized in that: When constructing the dynamic photoelectric thermal model, a linear model of the equivalent resistance of an ideal diode in series with an LED is used for modeling.

5. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 4, characterized in that: In the process of constructing the dynamic photoelectric thermal model, a modulation signal is coupled to the DC bias of the LED, and the modulation signal adopts a stably ergodic random modulation signal.

6. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 4, characterized in that: In the dynamic photoelectric thermal model of the LED array, the instantaneous luminous flux output of the LED array is determined by the mean square value of the modulation current and the instantaneous value of the modulation current.

7. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 3, characterized in that: In step S2, the design criterion is that the expected value of the dynamic instantaneous luminous flux of the LED array is used to represent the illumination luminous flux of the LED array, and the root mean square value of the dynamic instantaneous luminous flux of the LED array is used to represent the signal flux of the LED array.

8. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 7, characterized in that: Specifically, step S3 is to optimize the LED array based on the dynamic electro-thermal model of the LED array, according to indoor lighting requirements, communication requirements, array quantity, LED electro-thermal characteristics and modulation methods, with the goal of maximizing the signal flux of the LED array under the calibrated lighting flux.

9. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 8, characterized in that: During optimization, the minimum and maximum values ​​of the temperature of the LED array and the maximum and minimum values ​​of the LED current are limited.

10. The method for optimizing the integrated luminous flux based on the photoelectric and thermal characteristics of an LED array according to claim 8, characterized in that: In step S3, the result of the optimized design can obtain the optimal bias current of the LED array. Modulation at the bias current can maintain the lighting performance of the LED array and obtain the maximum communication luminous flux.

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