On The Study Of Color Shift Keying Modulations For RGB-LEDs

With the rapid development of modern society,more and more data are generated by all kinds of devices.Migrating from mobile Internet to the era of Internet of things,the high-speed data transmission is a fundamental requirement,moreover always-on network connection is needed.Visible Light Communications(VLCs),which benefits from the popularization of LED technology,is an attractive indoor high-speed data transmission solution compared with traditional radio frequency technologies because of its abundant spectrum resources and high confidentiality for the indoor environment.Compared with the Fluorescence white LEDs,RGB LEDs have faster state-switching speed,which enables faster data transmission rates.So that the Color Shift Keying(CSK)modulations based on RGB LED are also gradually become a potential viable solution.Therefore,aiming to improve the reliability of CSK systems,this thesis conducted theoretical research,simulated BER performance and proposed improvements over the CSK modulation systems.Firstly,CSK modulations are based on color domain to transmit data,while ensuring the the primary function of illumination.Therefore,this thesis began by introducing the human eye color perception concepts and the knowledge related to color space,then,thorough studies of the basic principle of CSK modulations were carried out from the simulation and theoretical perspective.Secondly,in order to improve the reliability of the CSK systems,Pulse-Position Modulation(PPM)with excellent anti AWGN performance is introduced to build CSK-PPM modulation systems.On the basis of which,this thesis studied the PPM variant modulation,namely,Complementary Pulse-Position Modulations(CPPMs).Because it distributes the signal energy in L-1 slots,CSK-CPPM modulations are able to achieve better BER performance than CSK-PPM modulations.Then,for the receive-end of CSK systems,the decoding process is converted from the two-dimensional color space to three-dimensional signal space,which increases the minimum Euclidean distance,thus further improved the achievable BER performance.Also,the joint decoding at the receiver was proposed in this thesis,so that the information contained in the spatial and color space can be optimized comprehensively when decoding,thus further reducing the bit error rate.Finally,error control technology is introduced into conventional CSK systems,and the convolutional code was used as the choice of channel coding,so that the ability of the system to resist random noise is further enhanced.