Research On Index Modulation Mapping And Constellation Map In Optical Wireless Communication

Optical Wireless Communication has large capacity,no need of spectrum permission and so on,but the optical signal is exposed to the atmosphere,so it is easy to be disturbed by atmospheric turbulence in the process of transmission,which seriously affects the system reliability.Therefore,it is imperative to provide an effective technology for the realization of high-capacity and high-reliability OWC system.In view of this,the authors put forward the O-OFDM-IM technology by combining the new transmission technology--Index Modulation with OFDM,it uses the state information of the sub-carrier to transmit additional information to greatly improve the system transmission rate.At the same time,the existence of silent sub-carriers can reduce Peak to Average Power Ratio,enhance the anti-jamming ability of the channel.Therefore,in order to accelerate the application of O-OFDM-IM,the research contents of this thesis are as follows:（1）O-OFDM-IM is affected by the atmospheric channel,which makes the bit error performance not optimal and can’t meet the demand of ultra-high quality communication.Therefore,based on the traditional O-OFDM-IM,an O-OFDM-IM system based on step-by-step optimal signal mapping is proposed,the set of sub-carriers is optimized according to the principle of channel norm maximization,and the constellation graph is optimized by traversing the rotated constellation symbol,which can improve the BER performance.The simulation results show that the Signal-to-Noise Ratio（SNR）of the proposed system is improved by 1.2d B compared with the traditional system under weak turbulence,8QAM andBER（28）10^-4.（2）The minimum Euclidean distance can not be maximized by using a two-dimensional constellation diagram,that is,the probability of the symbols being misjudged can not be minimized.Therefore,in order to improve the BER performance,a 3D-O-OFDM-IM system is proposed based on the principle that the greater the Euclidean distance between constellation symbols,the smaller the error probability.By extending the constellation symbol from two-dimensional to three-dimensional,and loading it on the active sub-carrier for information transmission,it can effectively resist atmospheric turbulence.The proposed scheme is compared with traditional O-OFDM-IM、optimized O-OFDM-IM in detail.The results show that,compared with the latter,the proposed system can improve the SNR by 2.7d B and improve the transmission rate by 1.8 times in the case of weak turbulence,16QAM andBER（28）10^-4.（3）In order to make full use of sub-carriers,using Discrete Wavelet Transform combined with 3D-O-OFDM-IM technology,a 3D Optical Discrete Wavelet Transform OFDM Secondary IM（3D-O-DWT-OFDM-SIM）system is proposed.It can increase the transmission rate by wavelet transform and secondary index.The orthogonality of wavelet transform and the Euclidean distance between constellation symbols are used to improve the BER performance.After introducing the mapping principle of the proposed scheme in detail,the theoretical bit error rate is derived and compared with the existing O-OFDM-IM scheme.The results show that the SNR of（8,2,2）3D-O-DWT-OFDM-SIM system is improved by about 3.5d B compared with（4,3）3D-O-OFDM-IM system under weak turbulence when the bit error rate is 10^-4.