Research On Key Technologies Of OFDM/OQAM Underwater Acoustic Communication System

The underwater acoustic channel has complex and changeable characteristics,which makes underwater acoustic communication have problems such as small available bandwidth,large delay,strong environmental noise interference,and serious multipath effects.Orthogonal Frequency Division Multiplexing(OFDM)is an effective method to combat multipath fading.However.OFDM underwater acoustic communication technology still has some shortcomings,such as low frequency efficiency,large out-of-band leakage and sensitivity to frequency deviation.Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation(OFDM/OQAM)has higher spectral efficiency and lower out-of-band radiation,but the imaginary non-orthogonality of its filter causes serious inherent interference,which makes the application of OFDM/OQAM in underwater acoustic communication needs further study.This thesis conducts research on underwater acoustic channel estimation and Peak to Average Power Ratio(PAPR)reduction in OFDM/OQAM system,the main contents can be summarized as follows:(1)Aiming at shallow sea acoustic channels,this thesis analyzes the underwater acoustic multi-carrier communication system and its application in underwater acoustics.Then builds an OFDM/OQAM underwater acoustic communication system,and analyzes its filter design,channel coding,channel estimation,and PAPR reduction modules.The roll-off raised cosine function is introduced,and an adaptive tunable filter is designed.In this system,the comparison proves that the designed filter has good adaptability to underwater acoustic channels.(2)In view of the serious multipath effect of underwater acoustic channel,an underwater acoustic channel estimation algorithm for OFDM/OQAM system is proposed.This algorithm designs the block pilot structure,and uses compressed sensing to estimate sparse channel,and reorganizes the compressed spatiotemporal multipath signal by time reversal to reduce multipath interference.In OFDM/OQAM system,experimental simulation verifies the effectiveness of the algorithm.(3)Due to the high PAPR in multi-carrier communication,which leads to signal distortion,an optimization algorithm of PAPR reduction based on index modulation is proposed.The algorithm uses index modulation,activates specific subcarriers based on the index bits,eliminates redundant sideband information,performs discrete Fourier transform expansion on the new subcarrier sequence,and selects the waveform with the smallest peak-to-average ratio to transmit.The results show that the algorithm can suppress the high PAPR and improve the system's ability to resist interference.(4)The designed filter,channel estimation and PAPR reduction algorithms are applied to OFDM/OQAM underwater acoustic communication system,and the effectiveness and robustness of the improved modules in shallow underwater acoustic channel are verified through semi-physical simulation and actual shallow sea experiment.