Research On Visible Light Communication System Development And Device Characteristic Adaptation Technology Based On Silicon Substrate RGBY LED

Full-band communication is one of the major development directions of wireless communication.Among them,the LED-based visible light communication(VLC)technology is expected to realize the both indoor communication and lighting at lower cost and energy consumption,and has the advantages of high security,no EM interference,and broadband.Multi-color mixed white LEDs for lighting have high emission power,high modulation signal-to-noise ratio(SNR),and independent modulation channels with multiple wavelengths.They are suitable for high-speed VLC systems,but there are the following difficulties and challenges: based on simple parameters such as junction capacitance and time constant The AC small-signal model cannot fully reflect the modulation characteristics of the LED,which leads to the inaccuracy when describing the electro-optic modulation performance of the VLC system transmitter.Because the LED impedance and electro-optic modulation amplitude change rapidly with frequency,it cannot be directly adapted to the existing radio frequency driving circuits.In view of this,this thesis mainly uses the advanced silicon substrate Ga N fourcolor LED of the National LED Engineering Center to carry out the following key technology research and prototype system development work:(1)The DC and low-frequency AC characteristics of lighting LEDs are studied,including forward voltage drop,output optical power,efficiency,and changes in center wavelength with current.Based on the microstructure of the LED,a more accurate lumped parameter AC small-signal model of the LED is constructed,and a lowfrequency negative capacitance model based on the change of junction temperature is proposed.The problem of the LED AC parameter characterization is solved and the estimation of the instantaneous junction temperature change is achieved,so that the performance of the transmitting end of the LED-based VLC system can be accurately described.(2)A set of test methods for high-frequency modulation characteristics of LED devices based on impedance calibration is proposed.Using network analyzer and other equipment to carry out impedance calibration,the measurement of the electro-optical modulation bandwidth of the LED under any driving impedance is realized,and the parasitic parameters and modulation performance of the silicon substrate lighting LED device are analyzed in detail.The problem that the modulation characteristics of LED devices is difficult to be accurately measured is solved,and the correctness of the AC small signal model is verified.(3)Design a set of VLC analog front end based on silicon substrate mixed white LED for lighting.Among them,the transmitting module uses a transconductance amplifier scheme to drive silicon-based LED devices,and an active analog pre-equalizer is designed to compensate for the frequency response of the LED.The receiving circuit is composed of PIN detector and AGC amplifier.The modulation performance of the silicon substrate lighting LED in a practical environment is verified.The entire analog front end can provide an available bandwidth above 100 MHz under the divergent light path of the actual lighting scene.(4)Based on this analog front end,two complete systems have been implemented.The experimental system using QAM modulation is used to test the maximum bit rate.The communication rate of a single channel at a distance of 700 mm is obtained at600 Mbps,and the silicon substrate LED and analog transceiver circuit are verified.Performance in digital communication systems.The experimental system using OFDM modulation is used to verify the correctness of the actual business data transmission of the system in this thesis.Based on LabVIEW,smooth video transmission is realized,and the adaptability of the analog front end in actual business scenarios is verified.