| In recent years,as countries attach great importance to the development of marine resources,the study of high-speed underwater acoustic communication systems is imminent.Orthogonal Frequency Division Multiplexing(OFDM)technology has high frequency spectrum utilization because its subcarriers are orthogonal to each other,OFDM has strong antimultipath interference capability and can well adapt to the underwater acoustic channel environment with narrow available bandwidth and severe multipath.However,OFDM technology is sensitive to synchronization errors.The accuracy of synchronization algorithms will directly affect the performance of OFDM systems.This article focuses on the detection and synchronization algorithm of signal frames in underwater acoustic OFDM systems.The main tasks are as follows:1.The characteristics of underwater acoustic channels and the basic principle of OFDM are introduced.The influence of synchronization bias on OFDM performance is briefly analyzed.2.The false alarm probability and detection probability of sliding dual-window energy detection in OFDM system are deduced theoretically,The performance of the simulation is compared with that of the sliding single window.Finally,the performance of the two methods in the signal detection process is simulated.The results show that the threshold of dual-window energy detection is less affected by signal and noise,and it is more practical.3.The classic OFDM timing synchronization algorithm based on autocorrelation and cross-correlation operations is discussed and its performance is analyzed.Aiming at the fact that the cross-correlation timing synchronization algorithm is sensitive to frequency offset,a timing synchronization algorithm based on FM signal is proposed,and the influence of carrier frequency offset is eliminated by designing a specific preamble structure.The new algorithm can directly synchronize the baseband oversampled data.The simulation results show that the algorithm has better timing performance.4.Combining signal detection and timing synchronization,a frame synchronization and Doppler compensation scheme for practical underwater acoustic communication systems is proposed.By analyzingthe experimental data of Qiandao Lake,a good synchronization compensation effect is achieved and high-speed underwater acoustic communication is realized. |
