Research On Pulse Modulations Aided Visible Light Communication Systems

Nowadays,with the explosion of smartphone multimedia applications as well as the coming of the Internet of things era,the next generation communication systems need to ensure multiple smart devices always online and provide both high-speed and reliable data transmission services.Naturally,the abundant visible light spectrum resources become extremely attractive,when allowing more devices to access simultaneously and achieving a higher data transmission rate.Therefore,this thesis focuses on the designing of high-speed,low energy consumption visible light communications(VLCs)system with multiple access capacity.Firstly,owing to employing Intensity-Modulation/Direct-Detection(IM-DD)in VLC systems,the modulated signal,which is LED's intensity must be both real and positive.As a result,a variety of pulse modulation techniques are thoroughly investigated in Chapter 2.Theoretical analysis and performance simulations on BER are provided in order to demonstrate their performances.In addition,the spectrum efficiency and power efficiency of these modulations are also compared.Secondly,in order to improve Pulse Position Modulation's(PPM's)transmission rate,Carrier-less Position/Phase(CPP)modulation is proposed in Chapter 3.Furthermore,Multiband-Carrier-less Position/Phase(Multiband-CPP)modulation are proposed as an effort to further increase the transmission rate.Then,a novel variable bias algorithm aiming at reducing the energy consumption,when applying CPP and Multiband-CPP modulations to VLC systems is presented.After further considering transmission time slot's correlation,the variable bias algorithm can further improve the power efficiency of the proposed systems.Finally,for multi-user VLC systems,orthogonal Hadamard codes are employed as the spread spectrum sequence in Chapter 4,and then through power optimization for DC offset optical signals,the energy consumption of the multi-user PPM and Multiband-CPP system is effectively reduced.Moreover,numerous simulation results illustrate that the high-speed Multiband-CPP system only need to pay less than 2.5dB penalty of SNR in order to double user capacity,while guarantee the same BER performance.