CAP Based Hybrid Modulation Technology For Indoor Visible Light Communication

Nowadays,with the explosion of smart terminal devices and the increasing demand of Internet users,visible light communication(VLC)has the potential to become an important supplement and alternative technology to traditional wireless communication technologies,thereby alleviating the growing tension in wireless communication spectrum resource.However,due to the limited modulation bandwidth of ordinary commercial LEDs,the transmission rate of the VLC system is limited.Therefore,this thesis focuses on high-speed and high-power efficiency VLC systems based on Carrierless Amplitude and Phase(CAP).Firstly,this thesis gives the theoretical analysis of multi-dimensional multi-level CAP technology with high throughput and Multi-Pulse Position Modulation(MPPM)technology with high power efficiency,respectively.A hybrid CAP-MPPM modulation scheme combining CAP and MPPM is proposed and the performance of the hybrid modulation system using hard-decision and soft-decision decoding algorithms is studied.Then the theoretical symbol error rate(SER)expression of the hybrid modulation scheme over Gaussian channels is derived.Through flexible selection of modulation parameters,this scheme can obtain bandwidth-utilization efficiency and reliability superior to ordinary CAP and MPPM,and can achieve multiple-access.Secondly,the channel characteristics of the static VLC link is studied.Then an indoor VLC transmission model is constructed.In view of the real value and positive value constraints of signals for VLC system,this thesis gives the system model and theoretical analysis of DCO-CAP scheme and CAP-OFDM scheme,also the system performance is analyzed by simulation.Thirdly,the CAP-MPPM signal is processed by adding DC bias and the DCO-CAP-MPPM scheme is proposed.The relationship of DC bias and SER performance is discussed.When the constellation size of CAP is the same,the SER performance of DCO-CAP-MPPM is better than that of DCO-CAP.For the indoor VLC environments with people movement,the channel characteristics of the dynamic VLC link is studied.Then the transmission performance of DCO-CAP and DCO-CAP-MPPM over fading channels is studied,and the theoretical SER expressions of both schemes are derived.The system performance within indoor VLC environment with different people density is analyzed using numerous simulation experiments.Finally,in order to solve the problem of low power efficiency of the DCO-CAP-MPPM,the Flip-CAP-MPPM scheme is proposed.The positive and negative polarity grouping method is used to unipolarize the modulated signal.In addition,the bandwidth-utilization efficiency and the reliability of different single-polarization CAP-MPPM schemes are compared.