The Research On Prediction Of Underwater-Acoustic Adaptive OFDM Imperfect Channel State Information Feedback

As a key technology in the underwater acoustic communication system,adaptive technology can make rational use of underwater acoustic channel state information(CSI),so that the transmitting device can adaptively adjust the transmission mode according to the underwater acoustic CSI.By referring to the widely used Orthogonal Frequency Division Multiplexing(OFDM)technology in terrestrial wireless communication systems,the advantages of OFDM system and the flexibility of adaptive technology are utilized to effectively improve the information transmission of the system while ensuring the original performance indicators.The rate has a very broad development prospect in underwater acoustic communication.For adaptive OFDM technology to be implemented better,accurate CSI must be obtained when transmitting signals.At present,relying on channel estimation technology alone is not sufficient to obtain accurate CSI,because the delay generated by CSI feedback to the transmitting end will change the underwater acoustic channel.If the inaccurate CSI is fed back to the transmitting end,it will affect the next transmission.Reliability leads to degraded system performance.In order to solve this problem,the channel prediction technology can be used to predict the CSI feedback,so as to obtain a more accurate CSI,and the transmission reliability of the system is effectively improved.In this thesis,the basic principle of underwater acoustic OFDM and the application of adaptive modulation in underwater acoustic communication are studied.A hydroacoustic adaptive OFDM system based on channel prediction is constructed.Two algorithms for channel prediction are analyzed:based on MMSE criterion.The channel prediction algorithm and the cubic exponential smoothing method propose a scheme of applying a channel prediction algorithm to a hydroacoustic channel with periodic variation.Combined with the actual environmental parameters of the underwater acoustic channel,a hydroacoustic adaptive OFDM system model was built.The system throughput was obtained by MATLAB software,and the corresponding adaptive modulation threshold was derived.Finally,the two algorithms are applied to the constructed system,and the system error rate performance curve is obtained.The verification results show that the cubic exponential smoothing method has better bit error rate performance index than the traditional MMSE-based prediction algorithm in the underwater acoustic channel with periodic variation.