An optimization method and an optimization system for a visible light communication system

Abstract

The present invention provides an optimization method and an optimization system for a visible light communication system. The visible light communication system includes a transmitting end device and a receiving end device. The transmitting end device includes a light emitting diode for emitting an optical signal, and the receiving end device includes a photodiode for converting the received optical signal into an electrical signal. Based on the internal quantum efficiency of the light emitting diode, the electro-optical frequency response of the light emitting diode is determined. Based on the electro-optical frequency response of the light emitting diode, the signal-to-noise ratio of the optical signal received by the photodiode is determined. Based on the electro-optical frequency response of the light emitting diode and the signal-to-noise ratio of the optical signal received by the photodiode, the corresponding circuit parameters of the driving circuit are adjusted. The driving circuit is connected to the light emitting diode, and the corresponding circuit parameters of the driving circuit include a driving current parameter and an AC signal amplitude parameter. The present invention can improve the communication performance of the visible light communication system.

Description

Technical Field

[0001] The present invention relates to the technical field of visible light communication, and in particular, to an optimization method and an optimization system for a visible light communication system. Background Art

[0002] Visible Light Communications (VLC) is a wireless optical communication technology that uses visible light to transmit information, and has advantages such as rich spectrum resources, immunity to electromagnetic interference, and high confidentiality. To achieve low-power, small-size, and low-cost VLC, a light-emitting diode (LED) is usually used as the light source of the VLC system.

[0003] The electro-optical frequency response (FR) of the LED is crucial for the VLC system. Optimizing the electro-optical frequency response of the LED can improve the performance of the VLC system (for example, bandwidth and DC gain, etc.), thereby achieving a higher signal-to-interference plus noise ratio (SNR) and a faster data transmission rate.

[0004] The FR of the LED is related to its internal quantum efficiency (IQE), and the IQE determines the efficiency of converting the injected current into optical power. When calculating the FR of the LED, the IQE of the LED is usually treated as a constant. However, the IQE changes with the change of the driving current. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an optimization method and an optimization system for a visible light communication system, which can improve the communication performance of the VCL system.

[0006] The technical solution of the present invention to solve the above technical problem is as follows:

[0007] On the one hand, the present invention provides an optimization method for a visible light communication system, including: in response to the light-emitting diode emitting a light signal to the photodiode, determining the electro-optical frequency response of the light-emitting diode based on the internal quantum efficiency of the light-emitting diode. Determining the signal-to-noise ratio of the light signal received by the photodiode based on the electro-optical frequency response of the light-emitting diode. Adjusting the circuit parameters corresponding to the driving circuit based on the electro-optical frequency response and the signal-to-noise ratio, and the driving circuit is connected to the light-emitting diode. The circuit parameters corresponding to the driving circuit include a driving current parameter and an AC signal amplitude parameter. The driving current parameter is used to adjust the modulation bandwidth, DC gain, and average luminous power of the light-emitting diode, and the AC signal amplitude parameter is used to adjust the extinction ratio of the light signal emitted by the light-emitting diode.

[0008] Based on the above technical solutions, the present invention can be further improved as follows.

[0009] Furthermore, the first relationship and the second relationship can be determined. Among them, the first relationship includes the relationship between the light-emitting power of the light-emitting diode and the drive current of the light-emitting diode. The second relationship is determined based on the equivalent circuit model of the light-emitting diode, and the second relationship includes the transfer function of the equivalent circuit model of the light-emitting diode. The equivalent circuit model of the light-emitting diode is connected to the signal source and the output impedance of the signal source. Among them, the equivalent circuit model of the light-emitting diode includes a first resistor, an inductor, a capacitor, and a second resistor. One end of the signal source is connected to one end of the output impedance of the signal source, the other end of the output impedance of the signal source is connected to one end of the first resistor, the other end of the first resistor is connected to one end of the inductor, the other end of the inductor is connected to one end of the second resistor, and one end of the second resistor is connected to the other end of the signal source. The capacitor is connected in parallel with the second resistor. Based on the first relationship and the second relationship, the power of the voltage of the signal source converted into the corresponding optical signal can be determined. Based on the power of the voltage of the signal source converted into the corresponding optical signal and the voltage of the signal source, the electro-optical frequency response of the light-emitting diode can be determined.

[0010] Furthermore, the first relationship includes:

[0011]

[0012] Among them, P is the light-emitting power of the light-emitting diode, I is the magnitude of the drive current of the light-emitting diode, η le is the light extraction efficiency of the light-emitting diode, η i (I) is the internal quantum efficiency of the light-emitting diode, h is Planck's constant, c is the speed of light, q is the charge amount of the elementary charge, and λ is the wavelength of the photon emitted by the light-emitting diode.

[0013] Furthermore, the second relationship includes:

[0014]

[0015] Among them, H LED (ω) represents the transfer function of the equivalent circuit model of the light-emitting diode, V O (ω) represents the voltage across the second resistor, V S (ω) represents the voltage across the signal source, R 1 represents the resistance value of the first resistor, R 2 represents the resistance value of the second resistor, R g represents the value of the output impedance of the signal source, L 1 represents the inductance value of the inductor, C 1C represents the capacitance of the capacitor, j represents the imaginary unit, and ω represents the angular frequency corresponding to the driving current of the light-emitting diode.

[0016] Furthermore, based on the first relationship, the second relationship, and the third relationship, the voltage of the signal source can be converted into the power of the corresponding optical signal. Among them, the third relationship is used to characterize the corresponding relationship between the first relationship, the second relationship, and the conversion of the voltage of the signal source into the power of the corresponding optical signal. The third relationship includes:

[0017]

[0018] Among them, P o (ω) is the power of the voltage of the signal source converted into the corresponding optical signal.

[0019] Furthermore, the electro-optical frequency response of the light-emitting diode can be determined based on the ratio of the power of the optical signal converted from the voltage of the signal source to the voltage of the signal source. The electro-optical frequency response of the light-emitting diode includes:

[0020]

[0021] Among them, H EO represents the electro-optical frequency response of the light-emitting diode,

[0022] Furthermore, the power of the optical signal emitted by the light-emitting diode can be determined based on the electro-optical frequency response of the light-emitting diode and the gain parameter corresponding to the light-emitting diode. The power of the optical signal emitted by the light-emitting diode includes:

[0023]

[0024] Among them, P o (t) is the power of the optical signal emitted by the light-emitting diode, β is the gain parameter corresponding to the light-emitting diode, A is the amplitude of the optical signal emitted by the light-emitting diode, x(t) is the expression of the optical signal emitted by the light-emitting diode, P DC is the DC component in the optical signal emitted by the light-emitting diode, is the input power corresponding to the 1 dB compression point of the light-emitting diode.

[0025] It is also possible to obtain the electrical signal output by the photodiode. Among them, the electrical signal output by the photodiode is determined based on the optical signal received by the photodiode. The electrical signal output by the photodiode includes:

[0026]

[0027] Among them, y o (t) is the electrical signal output by the photodiode, h c is the channel coefficient of the photodiode, is the maximum responsivity of the photodiode, and R f is the transimpedance gain of the transimpedance amplifier included in the photodiode, and n(t) is the fluctuation function corresponding to the fluctuation caused by Gaussian white noise in the time domain.

[0028] The variance of the fluctuation function can be determined as the power of the output noise of the photodiode, and the power of the output noise of the photodiode includes:

[0029]

[0030] Among them, is the power of the output noise of the photodiode, and P B is the power of the ambient optical signal received by the photodiode, and i d is the dark current in the photodiode, Δf is the bandwidth of the photodiode, k is the Boltzmann constant, and T is the absolute temperature.

[0031] Based on the power of the optical signal emitted by the light-emitting diode, the electrical signal output by the photodiode, and the power of the output noise of the photodiode, the signal-to-noise ratio of the photodiode receiving the optical signal can be determined.

[0032] Furthermore, the signal-to-noise ratio of the photodiode receiving the optical signal includes:

[0033]

[0034] Among them, SNR is the signal-to-noise ratio of the photodiode receiving the optical signal.

[0035] Furthermore, the transmitting-end device includes a preset number of light-emitting diodes for emitting optical signals. The preset number of light-emitting diodes for emitting optical signals are connected in series with each other.

[0036] On the other hand, the present invention provides an optimization system, which is connected to a visible light communication system. The visible light communication system includes a transmitting-end device and a receiving-end device. The transmitting-end device includes a light-emitting diode for emitting an optical signal, and the receiving-end device includes a photodiode for converting the received optical signal into an electrical signal. The optimization system includes: a memory, and one or more processors. The memory is coupled to the processor. Among them, computer program code is stored in the memory, and the computer program code includes computer instructions. When the computer instructions are executed by the processor, the optimization system provided by the present invention executes an optimization method for a visible light communication system provided by the present invention.

[0037] The beneficial effects of the present invention are:

[0038] 1) The present invention establishes an electro-optical frequency response model of LED based on IQE, characterizes the functional relationship between IQE and SNR, thereby providing a theoretical basis for the design of VLC systems and the determination of the optimal operating point of LEDs.

[0039] 2) Based on the electro-optical frequency response model, the present invention designs a driving circuit with an adaptive equalization function for the transmitting-end LED, which improves the communication system bandwidth while ensuring that the LED operates at the optimal operating point.

[0040] 3) The present invention uses cascaded LEDs to jointly optimize the VLC system. On the premise of maximizing the SNR of the VLC system, multi-chip LED series connection is adopted to achieve longer-distance communication in the VLC system. Description of the Drawings

[0041] Figure 1 It is a schematic structural diagram of the visible light communication system provided by the present invention;

[0042] Figure 2 It is a schematic flow diagram of an optimization method for a visible light communication system provided by the present invention;

[0043] Figure 3 It is an equivalent circuit diagram of the light-emitting diode provided by the present invention;

[0044] Figure 4 It is a schematic structural diagram of an optimized system provided by the present invention;

[0045] Figure 5 It is a schematic workflow diagram of an optimized system provided by the present invention;

[0046] Figure 6 It is a driving circuit diagram of a light-emitting diode provided by the present invention. Detailed Embodiments

[0047] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings in the embodiments of the present application. Among them, in the description of the present application, unless otherwise specified, " / " means that the objects associated before and after are in an "or" relationship. For example, A / B may represent A or B; "and / or" in the present application is only an association relationship describing associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. These three situations, where A and B may be singular or plural. And, in the description of the present application, unless otherwise specified, "a plurality of" means two or more than two. "At least one (item)" or its similar expression below refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, at least one (item) of a, b, or c may represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, c may be single or multiple. In addition, in order to facilitate a clear description of the technical solutions in the embodiments of the present application, in the embodiments of the present application, words such as "first" and "second" are used to distinguish the same items or similar items with basically the same functions and roles. Those skilled in the art can understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit to be different. At the same time, in the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions.

[0048] In recent years, the development of VLC systems has benefited from the continuous progress of LED technology. However, LEDs are mainly for lighting needs and do not consider the impact on VLC system communication during the design process. Therefore, it is necessary to study and optimize the transmission characteristics of LEDs in order to achieve goals such as increasing the transmission rate of VLC systems, increasing the communication distance of VLC systems, and improving the reliability and stability of VLC systems.

[0049] The present invention provides an optimization method and an optimization system for a visible light communication system, taking the IQE characteristic function of an LED as a key parameter for VLC system optimization to increase the transmission rate of the VLC system. Based on the IQE - FR model, the present invention establishes a functional relationship between the LED drive current and the received signal - to - noise ratio and bandwidth of the VLC system. While optimizing the signal - to - noise ratio using the IQE of the LED, it effectively expands the modulation bandwidth of the VLC system and improves the SNR of the VLC system, thereby making full use of the abundant bandwidth resources in the optical band and achieving high - energy - efficiency and long - distance VLC high - speed communication.

[0050] See Figure 1, the VLC system may include a transmitting device and a receiving device. Among them, the transmitting device includes a light-emitting diode, which is used to convert the received electrical signal into an optical signal and transmit the optical signal to the receiving device. The receiving device includes a photodiode, which is used to receive the optical signal transmitted by the transmitting device and convert the optical signal into an electrical signal to achieve communication between the transmitting device and the receiving device.

[0051] See Figure 2 , an optimization method for a visible light communication system provided by the present invention. The optimization method provided by the present invention can be applied to Figure 1 the VLC system shown in

[0052] S201: In response to the light-emitting diode transmitting an optical signal to the photodiode, based on the internal quantum efficiency of the light-emitting diode, determine the electro-optical frequency response of the light-emitting diode.

[0053] In some embodiments, a first relationship and a second relationship can be determined. Based on the first relationship and the second relationship, the power of the optical signal corresponding to the voltage of the signal source can be determined. Based on the power of the optical signal corresponding to the voltage of the signal source and the voltage of the signal source, the electro-optical frequency response of the light-emitting diode can be determined.

[0054] Among them, the first relationship includes the relationship between the luminous power of the light-emitting diode and the magnitude of the driving current of the light-emitting diode. The second relationship is determined based on the equivalent circuit model of the light-emitting diode, and the second relationship includes the transfer function of the equivalent circuit model of the light-emitting diode.

[0055] In some embodiments, see Figure 3 , the equivalent circuit model of the light-emitting diode (the part in the dashed box) is connected to the signal source V S (ω) and the signal source output impedance R g . Among them, the equivalent circuit model of the light-emitting diode includes a first resistor R 1 , an inductor L 1 , a capacitor C 1 and a second resistor R 2 . One end of the signal source V S (ω) is connected to one end of the signal source output impedance R g , the other end of the signal source output impedance R g is connected to one end of the first resistor R 1 , the other end of the first resistor R 1 is connected to one end of the inductor L 1 , the other end of the inductor L 1 is connected to one end of the second resistor R 2 , and one end of the second resistor R 2 is connected to the signal source VS (ω) at the other end. Capacitor C 1 is in parallel with the second resistor R 2 .

[0056] In some embodiments, the bandwidth of the LED is mainly affected by two factors: the RC time constant τ RC and the carrier recombination time τ rec . Generally, the RC time constant caused by the parasitic parameters of the LED is usually small, while the carrier recombination time is large, which determines the bandwidth. Therefore, the formula for calculating the bandwidth is:

[0057]

[0058] where q is the unit charge amount, and I is the LED drive current. N w0 represents the number of carriers in the quantum well of the LED internal resistance under DC steady state. Based on formula (1.1), it can be determined that the bandwidth of the LED is positively correlated with the drive current. Therefore, the relationship between the luminous power of the light-emitting diode and the injection current can be further determined, that is, the first relationship is determined as:

[0059]

[0060] where P is the luminous power of the light-emitting diode, I is the magnitude of the drive current of the light-emitting diode, η le is the light extraction efficiency of the light-emitting diode, η i (I) is the internal quantum efficiency of the light-emitting diode, h is Planck's constant, c is the speed of light, q is the charge amount of the elementary charge, and λ is the wavelength of the photons emitted by the light-emitting diode.

[0061] In some embodiments, the internal quantum efficiency η i (I) of the light-emitting diode is directly related to the carrier density and can be described based on the ABC model:

[0062]

[0063] where n represents the carrier concentration in the quantum well inside the LED, and A, B, and C respectively represent the Shockley–Read–Hall (SRH) non-radiative recombination coefficient, the bimolecular radiative recombination coefficient, and the Auger recombination coefficient. Taking the first derivative of formula (1.3) gives the drive current n i corresponding to the highest η p as:

[0064]

[0065] And the relationship between the carrier concentration n and the injection current I is:

[0066] I = qSWQD (An + Bn 2 + Cn 3 )(1.4)

[0067] where W QD is the thickness of the quantum well active region, and S is the cross-sectional area of the LED. According to Equations (1.2) and (1.3), the drive current I corresponding to the highest internal quantum efficiency of the LED can be obtained p . And according to Equations (1.3) and (1.4), the relationship between η i and I, η i (I).

[0068] Since η i (I) is not linear, the relationship between the luminous power of the LED and the input current is also not linear. The IQE of the LED gradually reaches a peak and then starts to decline as the injection current increases, which means that when the injection current exceeds I p , the luminous efficiency of the LED starts to decrease. However, for lighting, the drive current can still be increased to improve the luminous power.

[0069] In some embodiments, based on the equivalent circuit model of the LED, an accurate electro-optical frequency response model of the VLC system can be established based on its internal quantum efficiency IQE model, called the IQE-FR model. The amplitude-frequency characteristic of the LED can be calculated by the circuit model as shown in Figure 3 . The input impedance Z in (ω) of the QE-FR model can be expressed as:

[0070]

[0071] where j represents the imaginary unit and ω represents the angular frequency corresponding to the drive current of the light-emitting diode. The transfer function of this equivalent circuit can be calculated according to the ratio of the signals V O (ω) and V S (ω), that is, the second relationship can be obtained as:

[0072]

[0073] where H LED (ω) represents the transfer function of the equivalent circuit model of the light-emitting diode, V O (ω) represents the voltage across the second resistor, V S (ω) represents the voltage across the signal source; ω d is the corner angular frequency of the equivalent circuit of the LED; R 1 represents the resistance value of the first resistor, R 2 represents the resistance value of the second resistor, R gThe resistance value representing the output impedance of the signal source, L 1 The inductance value representing the inductor, C 1 The capacitance value representing the capacitor;

[0074]

[0075] In some embodiments, based on the first relationship, the second relationship, and the third relationship, the power of the optical signal corresponding to the voltage of the signal source can be determined.

[0076] Among them, the third relationship is used to characterize the corresponding relationship between the first relationship, the second relationship, and the power of the optical signal corresponding to the voltage of the signal source. The third relationship includes:

[0077]

[0078] Among them, P o (ω) is the power of the optical signal corresponding to the voltage of the signal source.

[0079] In some embodiments, the electro-optical frequency response of the light-emitting diode can be determined based on the ratio of the power of the optical signal corresponding to the voltage of the signal source to the voltage of the signal source. The electro-optical frequency response of the light-emitting diode includes:

[0080]

[0081] Among them, H EO represents the electro-optical frequency response of the light-emitting diode, and K EO is the DC gain (which can also be called the modulation gain). When η i (I) changes, K EO will also change accordingly.

[0082]

[0083] In some embodiments, based on Equation (1.8) and Equation (1.9), the electro-optical frequency response of the LED can be determined. The electro-optical frequency response of the light-emitting diode can be obtained based on obtained, is the amplitude-normalized electro-optical frequency response of the LED, which can reflect the change trend of the frequency response curve.

[0084] Based on the above calculations, it can be seen that the decrease in IQE will affect the modulation gain, that is, it will increase the drive current and improve the optical power, but still will not increase the modulation gain. By introducing IQE into the equivalent current model of the LED, it can theoretically provide more accurate guidance for the selection of the optimal operating point in VLC system design.

[0085] S202: Based on the electro-optical frequency response of the light-emitting diode, determine the signal-to-noise ratio of the optical signal received by the photodiode.

[0086] In some embodiments, the time-domain impulse response h 0 (t) of a known LED is given. If an input signal Ax(t) with an amplitude of A and a drive current I are provided, then the power P o (t) of the light signal emitted by the LED is:

[0087] P o (t) = (Ax(t) + I DC ) * h 0 (t) = Ax(t) * h 0 (t) + P DC (2.1)

[0088] where A is the amplitude of the light signal emitted by the light-emitting diode, x(t) is the expression of the light signal emitted by the light-emitting diode, and P DC is the DC component in the light signal emitted by the light-emitting diode.

[0089] In some embodiments, within the 3dB bandwidth, it can be considered that the electro-optical frequency response of the LED is flat, that is, the electro-optical frequency response is a constant. Therefore, this equation can be simplified to:

[0090] P o (t) = K EO Ax(t) + P DC (2.2)

[0091] Since K EO is determined by the characteristics of the LED and is only affected by the drive current. Once the magnitude of the drive current is determined, then K EO will no longer change. In addition, the average optical power P DC is also determined by the drive current and is not affected by the AC input signal. Considering that the electrical signal power input to the LED is relatively small, in order to improve the modulation effect, a power amplifier is usually added before the LED. Three important parameters of the power amplifier need to be concerned here: the gain parameter β, the output power corresponding to the LED at the 1dB compression point and the input power

[0092] In some embodiments, based on the electro-optical frequency response of the light-emitting diode and the gain parameter β corresponding to the light-emitting diode, the power of the light signal emitted by the light-emitting diode can be determined. The power P o (t) of the light signal emitted by the light-emitting diode includes:

[0093]

[0094] where, if The maximum output power of the power amplifier can be achieved while obtaining the maximum gain. That is

[0095] When the optical signal propagates through the free space channel and reaches the receiving end, it will be converted into an electrical signal by the photodiode. Since the average optical power P DC only causes a DC signal output, which is useless for communication, the DC component after conversion can be filtered out by using an AC-coupled output method. Assuming that the bandwidth of the photodiode is greater than the bandwidth of the LED, the electrical signal output by the photodiode can also be obtained. Among them, the electrical signal output by the photodiode is determined based on the optical signal received by the photodiode, and the electrical signal y o (t) includes:

[0096]

[0097] Among them, h c is the channel coefficient of the photodiode, is the maximum responsivity of the photodiode, R f is the transimpedance gain of the transimpedance amplifier included in the photodiode, and n(t) is the fluctuation function corresponding to the fluctuation caused by Gaussian white noise in the time domain.

[0098] The variance of the fluctuation function can be determined as the power of the output noise of the photodiode, and the power of the output noise of the photodiode includes:

[0099]

[0100] Among them, is the power of the output noise of the photodiode, P B is the power of the ambient optical signal received by the photodiode, i d is the dark current in the photodiode, Δf is the bandwidth of the photodiode, k is the Boltzmann constant, and T is the absolute temperature.

[0101] In some embodiments, based on the power of the optical signal emitted by the light-emitting diode, the electrical signal output by the photodiode, and the power of the output noise of the photodiode, the signal-to-noise ratio of the optical signal received by the photodiode can be determined. Among them, the signal-to-noise ratio SNR of the optical signal received by the photodiode includes:

[0102]

[0103] S203: Adjust the circuit parameters corresponding to the drive circuit based on the electro-optical frequency response and the signal-to-noise ratio.

[0104] Among them, the drive circuit is connected to the light-emitting diode.

[0105] In some embodiments, the circuit parameters corresponding to the driving circuit include driving current parameters and AC signal amplitude parameters. The driving current parameters are used to adjust the bandwidth, DC gain, and average luminous power of the optical signal emitted by the light-emitting diode, and the AC signal amplitude parameters are used to adjust the extinction ratio of the optical signal emitted by the light-emitting diode.

[0106] In some embodiments, the transmitting-end device includes a preset number of light-emitting diodes for emitting optical signals. The preset number of light-emitting diodes for emitting optical signals are connected in series with each other.

[0107] See Figure 4 , the present invention also provides an optimization system, which can collect the performance parameters of the VLC system, adaptively adjust the driving current of the LED according to the functional relationship between the performance parameters of the VLC system and the LED, so as to change the communication parameters of the LED, making the overall performance of the communication system optimal. The optimization system includes a VLC system performance monitoring module, an IQE-based optimizer, and an LED driving circuit module.

[0108] Next, in combination with Figure 5 , the VLC system performance monitoring module, the IQE-based optimizer, and the LED driving circuit module will be introduced in detail.

[0109] In some embodiments, the VLC system performance monitoring module can be used to measure the parameters in the VLC system that can reflect the performance of the entire VLC system. In the present invention, the signal-to-noise ratio SNR of the VLC system is selected as this index.

[0110] In some embodiments, the IQE-based optimizer can be used to take the SNR obtained from the VLC system performance monitoring module as an input, and obtain the driving parameters of the LED based on the IQE processing of the LED. The driving parameters at least include driving current parameters and AC signal amplitude parameters. Among them, the descriptions of the driving current parameters and AC signal amplitude parameters can refer to the descriptions in the foregoing embodiments and will not be elaborated here.

[0111] After considering the IQE-FR characteristics of the LED, the channel capacity under an AWGN channel with limited signal power and limited bandwidth can be written as:

[0112]

[0113] This part realizes the adaptive optimization control function of the LED. A software algorithm is deployed using a CPU or FPGA to calculate the DC bias value required to optimize the LED to adjust the modulation bandwidth, DC gain, and average luminous power of the LED, and at the same time calculate the amplification multiple value of the modulation signal amplitude to adjust the extinction ratio of the output optical signal of the LED.

[0114] In some embodiments, the LED drive circuit module is used to adjust the drive circuit of the LED. The drive circuit of the LED is as Figure 6 shown, and includes two parts: adjusting the DC bias current of the LED (which can also be referred to as programmable DC bias in the embodiments of the present application) and adjusting the modulation signal coupling (which can also be referred to as programmable amplifier in the embodiments of the present application).

[0115] Among them, the part for adjusting the DC bias current of the LED receives the DC voltage value calculated by the above-mentioned LED adaptive optimizer, realizes high-resolution and high-precision bias current adjustment, and at the same time, the non-linear change of the circuit load caused by changes such as bandwidth needs to be considered. The key technology of this part lies in the high-precision control of the bias current.

[0116] The part for adjusting the modulation signal coupling is intended to make the following improvements based on the coupling circuit of the existing VLC system: a programmable amplifier is newly added inside the module to adjust the amplitude of the modulation signal, so as to compensate for the change in signal-to-noise ratio and the intensity of the output optical signal caused by bandwidth adjustment. For the output impedance of the modulation signal and the input impedance change caused by frequency modulation of the LED driver, an impedance change circuit is designed to optimize the signal coupling efficiency.

[0117] In some embodiments, a strategy of cascading multiple LEDs can also be adopted. By cascading multiple LEDs together, the overall optical output power of the VLC system can be effectively increased, the power loss of a single LED can be compensated, and thus communication coverage over a longer distance can be achieved. This solution can not only maintain the high efficiency of the communication system, but also adapt to the communication requirements at different distances, improving the flexibility and applicability of the system.

[0118] In some embodiments, multiple LEDs can be connected in series and parallel ways, and these two ways can be combined to obtain more complex forms.

[0119] In some embodiments, in the series connection mode, all LEDs are driven by the same current and can only be modulated by the same AC signal. In the parallel connection mode, the LEDs in each branch can be driven by different currents and modulated by different AC signals.

[0120] In some embodiments, since the internal resistance of the LED is very small, and the slight difference in the internal resistance between parallel-connected LEDs may cause a large current in a certain branch, and in severe cases, the LED may be burned out. Therefore, an additional resistor can be connected in each parallel branch for current limiting.

[0121] In some embodiments, based on the equivalent circuit of a single LED, the equivalent circuit of multiple LEDs connected in series can be analyzed. Among them, in the equivalent circuit of multiple LEDs connected in series, the impedance Z of multiple LEDs connected in series n is:

[0122]

[0123] where n is the number of LEDs in series, it can be found that has not changed, that is to say, if the bandwidth of each LED is the same, then the bandwidth after these LEDs are connected in series is also unchanged. If the bandwidths of these LEDs are different, the bandwidth after series connection conforms to the bucket effect, that is, it is determined by the smallest bandwidth among these LEDs. Compared with τ rec , τ RC has changed, so the corresponding ω RC becomes:

[0124]

[0125] That is to say, as n increases, ω RC becomes smaller and smaller, and the frequency response curve of the series-connected LEDs will also change. If then the series connection of LEDs will not affect the bandwidth, otherwise, when n reaches a certain number, the bandwidth of the LEDs will be affected. The DC gain K EO,n of the series-connected LEDs is:

[0126]

[0127] Increasing the number of LEDs will not always increase the modulation gain. When n→∞,

[0128]

[0129] For the convenience of comparison, the ratio of the DC gain of the series-connected LEDs to the DC gain of a single LED is defined as G DC,n , then the following formula can be obtained:

[0130]

[0131] It can be seen that when n→∞, when nR 1 << R g at that time, the gain G DC,n of multiple LEDs connected in series is approximately equal to the number of LEDs, but as n increases, G DC,n increases more and more slowly.

[0132] In some solutions, multiple embodiments of this application can be combined and the combined solution can be implemented. Optionally, some operations in the processes of the method embodiments are optionally combined, and / or the order of some operations is optionally changed. Moreover, the execution order between the steps of each process is only exemplary and does not constitute a limitation on the execution order between the steps. The steps can also be in other execution orders. It is not intended to indicate that the described execution order is the only order in which these operations can be executed. Those of ordinary skill in the art will think of various ways to reorder the operations described herein. Additionally, it should be noted that the process details involved in a certain embodiment herein are also applicable to other embodiments in a similar manner, or different embodiments can be combined and used.

[0133] In addition, some steps in the method embodiments can be equivalently replaced with other possible steps. Or, some steps in the method embodiments can be optional and can be deleted in some usage scenarios. Or, other possible steps can be added to the method embodiments. Moreover, the method embodiments can be implemented separately or in combination.

[0134] From the description of the above embodiments, those skilled in the art can clearly understand that, for the convenience and conciseness of description, only the above division of each functional module is used as an example. In actual applications, the above functions can be allocated to different functional modules according to needs, that is, the internal structure of the system is divided into different functional modules to complete all or part of the functions described above.

[0135] In several embodiments provided in this application, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the system embodiments described above are only illustrative. For example, the division of the modules or units is only a logical functional division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling or direct coupling or communication connection between each other can be through some interfaces. The indirect coupling or communication connection of the system or unit can be in electrical, mechanical or other forms.

[0136] In addition, each functional unit in the various embodiments of this application can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

[0137] When the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a readable storage medium. Based on this understanding, the technical solution of the embodiments of the present application, in essence, or the part that makes a contribution, or all or part of the technical solution, can be embodied in the form of a software product. The software product is stored in a storage medium and includes several instructions for causing a device (which can be a single-chip microcomputer, a chip, etc.) or a processor to execute all or part of the steps of the methods described in the embodiments of the present application. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0138] The above content is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for optimizing a visible light communication system, characterized in that: Applied to a visible light communication system, the visible light communication system includes a transmitting end device and a receiving end device, the transmitting end device includes a light emitting diode for transmitting a light signal, the receiving end device includes a photodiode for converting a received light signal into an electrical signal, and the method includes: In response to the light emitting diode transmitting an optical signal to the photodiode, determining an electro-optical frequency response of the light emitting diode based on an internal quantum efficiency of the light emitting diode; Determining a signal-to-noise ratio of the optical signal received by the photodiode based on the electro-optical frequency response of the light emitting diode; Based on the electro-optical frequency response and the signal-to-noise ratio, adjusting the circuit parameters corresponding to the driving circuit; the driving circuit is connected to the light-emitting diode; the circuit parameters corresponding to the driving circuit include driving current parameters and AC signal amplitude parameters; the driving current parameters are used to adjust the modulation bandwidth, DC gain and average luminous power of the light-emitting diode; the AC signal amplitude parameters are used to adjust the extinction ratio of the light signal emitted by the light-emitting diode; Wherein, determining the electro-optical frequency response of the light emitting diode based on the internal quantum efficiency of the light emitting diode comprises: Determine a first relationship; the first relationship includes a relationship between the light emitting power of the light emitting diode and the driving current of the light emitting diode; Determine a second relationship; the second relationship is determined based on an equivalent circuit model of the light-emitting diode; the second relationship includes a transfer function of the equivalent circuit model of the light-emitting diode; the equivalent circuit model of the light-emitting diode is connected to a signal source and a signal source output impedance; wherein the equivalent circuit model of the light-emitting diode includes a first resistor, an inductor, a capacitor, and a second resistor; one end of the signal source is connected to one end of the signal source output impedance, the other end of the signal source output impedance is connected to one end of the first resistor, the other end of the first resistor is connected to one end of the inductor, the other end of the inductor is connected to one end of the second resistor, and one end of the second resistor is connected to the other end of the signal source; the capacitor is connected in parallel with the second resistor; Based on the first relationship and the second relationship, determining the power of the corresponding optical signal converted from the voltage of the signal source; Based on the power of the corresponding optical signal converted from the voltage of the signal source and the voltage of the signal source, the electro-optical frequency response of the light emitting diode is determined.

2. The method according to claim 1, characterized in that The first relationship includes: Wherein, P is the luminous power of the light emitting diode; I is the magnitude of the driving current of the light emitting diode; η le is the light extraction efficiency of the light emitting diode; η i (I) is the internal quantum efficiency of the light-emitting diode; h is Planck's constant; c is the speed of light; q is the charge of the elementary charge, and λ is the wavelength of the photon emitted by the light-emitting diode.

3. The method according to claim 2, characterized in that The second relationship includes: Among them, H LED (ω) represents the transfer function of the equivalent circuit model of the light emitting diode; V O (ω) represents the voltage across the second resistor; V S (ω) represents the voltage across the signal source; R1 represents the resistance value of the first resistor; R2 represents the resistance value of the second resistor; R g represents the value of the output impedance of the signal source; L1 represents the inductance of the inductor; C1 represents the capacitance of the capacitor; j represents an imaginary unit; ω represents the angular frequency corresponding to the driving current of the light emitting diode.

4. The method according to claim 3, characterized in that The step of determining, based on the first relationship and the second relationship, the power of the corresponding optical signal converted from the voltage of the signal source comprises: Based on the first relationship, the second relationship and the third relationship, it is determined that the voltage of the signal source is converted into the power of the corresponding optical signal; the third relationship is used to characterize the corresponding relationship between the first relationship, the second relationship and the power of the corresponding optical signal converted by the voltage of the signal source; the third relationship includes: Among them, P o (ω) is the power of the corresponding optical signal converted from the voltage of the signal source.

5. The method according to claim 4, characterized in that The step of converting the voltage of the signal source into the power of the corresponding optical signal and the voltage of the signal source to determine the electro-optical frequency response of the light emitting diode comprises: Based on the ratio of the power of the corresponding optical signal converted from the voltage of the signal source to the voltage of the signal source, the electro-optical frequency response of the light emitting diode is determined; the electro-optical frequency response of the light emitting diode includes: Among them, H EO represents the electro-optical frequency response of the light-emitting diode, 6. The method according to claim 5, characterized in that The step of determining a signal-to-noise ratio of the optical signal received by the photodiode based on the electro-optical frequency response of the light emitting diode comprises: The power of the light signal emitted by the light emitting diode is determined based on the electro-optical frequency response of the light emitting diode and the gain parameter corresponding to the light emitting diode; the power of the light signal emitted by the light emitting diode includes: Among them, P o (t) is the power of the light signal emitted by the light emitting diode; β is the gain parameter corresponding to the light emitting diode, A is the amplitude of the light signal emitted by the light emitting diode; x(t) is the expression of the light signal emitted by the light emitting diode; P DC is the DC component in the optical signal emitted by the light emitting diode; is the input power of the light emitting diode corresponding to the 1 dB compression point; Acquire an electrical signal output by the photodiode; the electrical signal output by the photodiode is determined based on the light signal received by the photodiode; the electrical signal output by the photodiode includes: Among them, y o (t) is the electrical signal output by the photodiode; h c is the channel coefficient of the photodiode; is the maximum responsivity of the photodiode; R f is the transimpedance gain of the transimpedance amplifier included in the photodiode; n(t) is the fluctuation function corresponding to the fluctuation caused by Gaussian white noise in the time domain; The variance of the fluctuation function is determined as the power of the photodiode output noise; the power of the photodiode output noise includes: in, is the power of the photodiode output noise; P B The power of the ambient light signal received by the photodiode; d is the dark current in the photodiode; Δf is the bandwidth of the photodiode; k is the Boltzmann constant; T is the absolute temperature; The signal-to-noise ratio of the optical signal received by the photodiode is determined based on the power of the optical signal emitted by the light emitting diode, the electrical signal output by the photodiode, and the power of the noise output by the photodiode.

7. The method according to claim 6, characterized in that The signal-to-noise ratio of the photodiode receiving the optical signal includes: The SNR is a signal-to-noise ratio of the optical signal received by the photodiode.

8. The method according to claim 7, characterized in that The transmitting end device comprises a preset number of light emitting diodes for emitting light signals; the preset number of light emitting diodes for emitting light signals are connected in series.

9. An optimization system, characterized in that: Connecting to a visible light communication system, the visible light communication system comprising a transmitting end device and a receiving end device, the transmitting end device comprising a light emitting diode for transmitting a light signal, and the receiving end device comprising a photodiode for converting a received light signal into an electrical signal; The optimization system comprises: a memory and one or more processors; the memory is coupled to the processor; wherein computer program code is stored in the memory, and the computer program code comprises computer instructions, and when the computer instructions are executed by the processor, the optimization system executes the optimization method for the visible light communication system as described in any one of claims 1 to 8.

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