Estimation And Compensation Of Doppler Shift For OFDM-IM In Wireless And Underwater Acoustic Channels

At present,Orthogonal Frequency Division Multiplexing(OFDM)has been widely applied in commercial wireless communication systems.Based on OFDM,Orthogonal Frequency Division Multiplexing with Index Modulation(OFDM-IM)is regarded as a competitive modulation scheme for communications of next generation.In recent years,some scholars have generalized OFDM-IM to underwater acoustic communication.Most existing researches aimed to enhance spectral efficiency of OFDM-IM,while reliability should not be neglected.Compared to single carrier systems,OFDM-IM is more susceptible to Doppler shift.The relative motion between receiver and transmitter induce Doppler shift,which is non-negligible for wireless and underwater acoustic communications.Especially,Doppler shift cause more signal distortion,which is required to be corrected effectively.An algorithm to estimate and compensate frequency offset for OFDM-IM in wireless channel is proposed in this paper,which makes use of inactive subcarriers in OFDM-IM and then improves accuracy.Its theorectical performance is derived and validated by computer simulations.As for time-varying underwater acoustic channel,non-uniform path speed model is considered.An iterative algorithm for partial block-type pilots is proposed,which estimates channel by both pilots and detected symbols and reduces errors of channel and Doppler scale estimations.Simulations show its superiority over OMP algorithm.These two algorithms improve resistance of systems against Doppler shift then facilitate demodulation.This paper focus on robustness of OFDM-IM,aim to propose advanced algorithms to estimate and compensate Doppler shift for OFDM-IM,and provide valuable references for researches of wireless and underwater acoustic communications.