| Visible light communication(VLC)technology is based on existing lighting infrastructure that uses light emitting diodes(LED)as its core,enabling high-speed communication through the modulation of the LED’s driving current.With outstanding advantages in "low carbon" and "safety," VLC has become one of the candidate solutions for indoor high-capacity hotspots in 6G.However,the natural bandwidth of LEDs used for lighting is approximately 10 MHz,which is significantly lower than the communication rate required for high-capacity hotspots.Equalization is the only way to expand the LED bandwidth,and existing equalization techniques achieve this by attenuating the high response frequency bands of the LED,which reduces power efficiency and is inconsistent with the goal of sustainable development.This paper focuses on the method of expanding LED bandwidth while maintaining LED energy utilization efficiency,which has significant academic and practical value,as follows:(1)Firstly,this paper studies the microstructure of four-color silicon substrate Ga N LED,and constructs a more accurate small-signal model of LED.Further,the electrical characteristics of LED are studied and analyzed as the basis for the design of analog transmission link,and the advantages and disadvantages of various driving methods are analyzed as the basis for the design of transmission link driving.(2)Secondly,in response to the drawbacks of traditional equalization methods,this paper proposes a multi-channel digital analog hybrid equalization method to achieve bandwidth expansion while retaining low-frequency signal power.The analog part uses the attenuation law of the red LED frequency response curve as the basis for frequency band selection,and adopts a multi-stage low-complexity RC equalization for segmented equalization compensation based on the attenuation characteristics within each channel,which has a higher fitting degree with the traditional ideal compensation curve.In the digital part,compensation is made for special frequency bands,and the problem of amplitude-phase inconsistency caused by different devices within channels is analyzed and tested.The method of mapping the signal source to multiple channels is proposed to increase the signal isolation between frequency bands and avoid repeated signal processing.(3)Finally,a wide light source transmission link based on multi-channel digital analog equalization is designed.In this design,the signal is segmented and compensated using a multi-stage parallel RLC resonant circuit and a low-complexity RC circuit.A fixed gain amplifier(FG)is combined with a variable gain amplifier(VGA)to compensate for different channel amplitudes,and the LED device is driven by a Bias-Tee constant current driving scheme.A pulse response test system,frequency response test system,and constellation diagram test are built using the transmission link.Under the condition of a communication distance of 30 cm,the bandwidth of the red LED system reaches 300 MHz,and the communication rate under 4QAM modulation is 600Mbit/s.The phase difference between the two channels has decreased to 2°.Through practical verification,this paper proposes a multi-channel digital-analog hybrid equalization method,and validates it with a 2-channel equalization compensation method,which extends the bandwidth of the LED to 300 MHz,ensuring that the error vector magnitude(EVM)is not greater than 17%rms,and the radiated power of the LED is 450 m W,while effectively avoiding an additional power loss of140 m W.This method has important academic and practical value. |
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