Research On VLC-OFDM Technology Based On Index Modulation

With the rapid development of modern mobile communication technology,people have higher and higher requirements for its traffic.Visible light communication not only has rich spectrum resources,but also can transmit information while lighting.The combination with orthogonal frequency division multiplexing technology can significantly improve the communication characteristics of the system,but there are some problems such as noise frequency offset interference and high peak-to-average ratio,thus reducing the system performance.Therefore,this paper proposes to introduce index modulation technology into VLC-OFDM system.This technology adopts traditional constellation modulation to transmit information in signal domain and activated carrier bearer information in frequency domain,which can not only improve the reliability of system communication,but also effectively reduce the peak-to-average ratio of the system.The main research parts are as follows:1.Direct line-of-sight link and non-line-of-sight link in visible light communication are modeled,and the two channel link models are simulated.The simulation results confirm that indoor multi-path channel has a certain influence on optical communication.The time-domain and frequency-domain characteristics of DCO-OFDM and ACO-OFDM systems are compared,and the system performance is analyzed and compared in terms of spectral efficiency and peak-toaverage ratio.2.On the basis of DCO-OFDM system,carrier index modulation technology is introduced into DCO-OFDM system,DCO-OFDM index modulation method suitable for visible light transmission is given,and DCO-OFDM-IM system model is established.By keeping part of the molecular carrier silent,the sparsity between signals is improved.The simulation results show that at the same modulation order and index combination(L=4,k=2),the signal-to-noise ratio performance of DCO-OFDM-IM system is improved by 2 d B compared with that of DCO-OFDM system.3.At the receiving end,the VLC-OFDM-IM system needs to synchronously detect the modulation information of constellation and the position information carried on the active carrier.The system performance of three detection algorithms,maximum likelihood detection algorithm,greedy detection algorithm and logarithmic likelihood detection algorithm,are respectively compared.The simulation results show that under the same conditions,the detection algorithm improves the system performance by 2 d B compared with the detection algorithm,and 7 d B compared with GD detection algorithm.4.Since the silent subcarrier distribution of DCO-OFDM-IM system is irregular and the previous pilot insertion is not suitable,a pilot assisted channel estimation algorithm is designed to ensure the reliability and peak-to-average performance of the system using Zadoff-Chu sequence with low correlation and peak ratio.The simulation results show that when the index combination is(L=4,k=2),the peak-to-average ratio of DCO-OFDM-IM system is 2.4 d B lower than that of DCO-OFDM system.Considering the influence of errors in the channel estimation process of DCO-OFDM-IM system,the receiver does not get the ideal channel state information.The least mean square error channel estimation algorithm is used to improve the effectiveness of channel estimation and the system performance.