Research On Key Technologies Of Digital Signal Processing For Index Modulated OFDM-VLC System

Visible light communication(VLC)has the technical advantages of considering lighting,no electromagnetic interference,wide bandwidth,and secure communication,and has attracted research interest in academia and industry.The application of VLC in indoor,high-speed wireless access,industrial Internet of Things,and other fields can solve the electromagnetic interference problem traditional wireless communication faces and provide safe and reliable indoor area communication.As a new modulation technology developed based on Orthogonal Frequency Division Multiplexing(OFDM),OFDM with index modulation carries additional information through sub-carrier index bits and uses sub-carrier activation or muting to reduce inter-carrier interference,which inherits the inherent characteristics of OFDM,such as the anti-multipath fading,further improving the bit error performance.However,index-modulated OFDMVLC systems still face sampling frequency offset(SFO),high peak-toaverage power ratio(PAPR),and high-frequency subcarrier fading effects.Therefore,this thesis adopts efficient digital signal processing technology to solve the problems mentioned above.The main work is as follows:1.Aiming at the problem of signal detection in index modulated OFDM-VLC system with SFO,a new detection method based on the rotated K-means clustering algorithm is proposed.Through two-stage centroid clustering and correction,the method achieves high-precision index bit and symbol bit detection.Furthermore,this detection method does not require additional SFO compensation and channel state information.The simulation and experimental results show that after 3.5 m free-space transmission,when the bit error rate is less than the 7% forward error correction threshold,the SFO tolerance of QPSK-OFDM singlemode index modulation and BPSK-OFDM dual-mode index modulation Tolerances are up to ±120 ppm and ±115 ppm,respectively.2.Aiming at the problems of high-frequency subcarrier fading,high PAPR,and low utilization of IFFT/FFT size in index modulated OFDMVLC system,a performance enhancement method combining nonHermitian symmetry and precoding is proposed.The scheme uses precoding to reduce PAPR,resists high-frequency subcarrier fading,and combines NHS to generate real signals to improve subcarrier utilization.The experimental results show that CAZACT,OCT,and ZCT can equalize the signal-to-noise ratio of high-frequency subcarriers to improve the bit error performance of the system,and CAZACT and ZCT can significantly reduce the PAPR of the signal.Compared with the traditional Hermitian symmetric index modulated OFDM-VLC system,the hardware overhead of the non-Hermitian symmetric index modulated OFDM-VLC system is reduced by half.