Hardware circuit design of high-speed visible light communication system in mobile scenarios
Visible light communication(VLC)has a broadband spectrum available without a license,which can effectively supplement the existing overcrowded spectrum to meet the demands of future high-speed wireless data transmission.However,achieving high-speed visible light communication still faces two key challenges:(1)The modulation bandwidth of VLC systems is limited,and common LED frequency responses have significant delays,which,to some extent,limit the LED modulation bandwidth.Moreover,the frequency domain response of LEDs severely attenuates at high frequencies,limiting their high-speed optical communication applications.(2)High-speed VLC systems require high alignment between the transmitter and receiver,and the movement of wireless terminals accelerates the attenuation of visible light signals,leading to communication interruption.Therefore,in response to the problems of fast signal attenuation and limited system bandwidth in high-speed VLC in mobile scenarios,hardware circuits that can achieve high-speed and stable VLC systems must be designed.As one of the important technologies for improving signal transmission quality and expanding system bandwidth,equalization can effectively solve the problem of frequency response attenuation in communication systems.Therefore,this study designed an analog pre-equalization and post-equalization circuit to improve the frequency response attenuation of VLC systems.Meanwhile,to further improve the reliability of VLC systems,soft equalization was introduced to reduce the bit error rate.In addition,due to the significant difference in signal amplitude received by the receiver at different positions illuminated by the light source,weak positions of the received signal may lead to a decrease in the system's data transmission rate and an increase in the bit error rate.To solve this problem,this study designed an improved adaptive amplification circuit composed of a variable attenuator,a detection circuit,and a gain voltage control circuit,which could automatically adjust the gain based on the signal strength.The gain voltage control circuit senses the change in signal amplitude through the detection circuit,thereby adjusting the attenuation of the variable attenuator to control the amplitude change of the signal.Finally,a VLC hardware testing platform was built based on the designed circuit.The experimental results showed the following:1)After using the equalization circuit,the system's-3-dB bandwidth increased from 4.1 MHz to～224 MHz.2)Based on the constructed VLC real-time internet access system for network speed testing,the VLC internet access system based on an adaptive equalization circuit can achieve an approximately 100-Mbps network transmission.3)The convolution neural networks-gated recurrent unit(CNN-GRU)soft equalization scheme based on adaptive amplification circuits in VLC hardware systems can significantly improve the reliability of VLC systems.This study mainly designed an adaptive equalization circuit for VLC systems in mobile scenarios,built a hardware testing platform,and applied it to ethernet communication.The transmitter and receiver of the VLC system were composed of a coaxial local converter,an equalization circuit,a light source driver,a photo detector,and an adaptive amplification circuit,mainly transmitting ethernet signals through the uplink and downlink.The transmitter module sends a signal,which is collected and processed by the receiver module through an equalization circuit.The adaptive amplification circuit adjusts the gain based on the signal amplitude and finally decodes and transmits the signal to the target device.The adaptive equalization circuit proposed in this study advantageously compensates for high-frequency characteristics,improves the frequency response,and ensures signal stability.According to experimental testing,the designed circuit can achieve network transmission of approximately 100 Mbps at a distance of 2.5 m.
visible light communicationequalization circuitadaptive amplification circuitethernet communication
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维普
