Research On Modified Unipolar Optical OFDM Technology

Visible light communication(VLC)is rich in spectrum resources,low energy loss,low cost,good security and other advantages.In recent years,OFDM technique for VLC system has gained great attention among research institutions and major manufactures because of its high-speed data rate.OFDM designed for intensity modulated/direct detection(IM/DD)is gaining constantly increasing research.This paper mainly further studies the unipolar optical-OFDM technology and proposes a number of modified schemes.The main contents of this paper are as follows:Firstly,introduces basic principle of traditional unipolar optical-OFDM systems.The principle and performace of schemes are analized and simulated respectively including DCO-OFDM,ACO-OFDM and Polar-OFDM.Secondly,peak-to-average-power ratio(PAPR)performance improvement in DCO-OFDM system.Pilot embedded technique proposed for PAPR reduction in DCO-OFDM is introduced based on studying statistic models of the time domain OFDM and optical-OFDM.The paper utilizes the selective level mapping theory to characterize the PAPR distribution of PE-DCO-OFDM system of one data symbol within a frame.Theoretical analysis and simulation results demonstrate that modified DCO-OFDM scheme can achieve considerable PAPR reduction without sacrificing bit error ratio(BER).Thirdly,spectral and power efficiency improvement in ACO-OFDM system.Based on the study of ADO-OFDM system principle,ACO-OFDM noise cancellation and frequency domain diversity improvement scheme,the following research is doing:On the one hand,Hartley transform is proposed for ADO-OFDM(HADO-OFDM)to reduce computation and design complexity.On the other hand,the improvement schemes of ACO-OFDM receiver are applied to HADO-OFDM system.The simulati-on results show that ADO-OFDM receiver improvement schemes can achieve better performance in terms of power efficiency.Fourthly,reliability improvement in Polar-OFDM system.Constellation collabor-ated Polar-OFDM is proposed based on the study of uniquely factorable constellation pair(UFCP)and QAM constellation optimal design.The simulation results show that Polar-OFDM can have a better tradeoff between the average symbol error ratio and PAPR for power allocation schemes and the modified schemes can further improve both of code gain and degrees of freedom for optimal design.