Research On Frequency Offset Compression In OFDM Index Modulation System

As an improvement for the traditional orthogonal frequency division multiplexing(OFDM)system,the index modulation for OFDM system(OFDM-IM)transmits the information by the active subcarriers and their index combinations.Because the OFDM is sensitive to carrier frequency offset(CFO)which directly leads to its limitation in high-speed scene applications,while the OFDM-IM system has the potential to resist the intercarrier interference(ICI).Naturally,the ICI suppression for OFDM-IM is addressed in this thesis.The main work is arranged as follows:1.By comparing the technical principle with the system model analysis,it is clear that the OFDM-IM system have better frequency offset suppression than OFDM system,What's more,the adjacent active subcarriers in the OFDM-IM system need to maintain the orthogonality,so it is still sensitive to frequency offset.Therefore,this thesis proposes the ICI suppression method which utilizes the characteristics of selective activation of subcarriers in OFDM-IM system.2.For the OFDM-IM system,all subcarriers are divided into subblocks.Then a part of subcarriers are selected for activation,and the remaining subcarriers are silent.According to this particularity of divided subblocks,we analyze the ICI problem from the inter-subblock ICI and intra-subblock ICI.Aiming at the problem of leakage outside the subblock,this thesis proposes a method that the universal filtering is used to reduce energy leakage outside the subblock,which reduces the inter-subblock ICI.Simulation results show that the proposed universal filtered OFDM-IM system has better resistance to ICI.3.In order to improve the ICI suppression of the OFDM-IM system,a scheme that uses fractional Fourier transform instead of Fourier transform to improve the performance of the OFDM-IM system is proposed.The method improves the ICI suppression in OFDM-IM system by adjusting the order of fractional Fourier transform.The simulation results show that the proposed scheme can improve the ICI suppression of the OFDM-IM system.