Carrier Frequency Offset Estimation For OFDM And OCDM Underwater Acoustic Communication Systems

In recent years,underwater acoustic communication technology has been developed rapidly.Due to the low transmission rate of acoustic signals,the relative motion of communication machines and other problems,there is an obvious carrier frequency offset(CFO)in underwater acoustic communication.CFO will shift the frequency and phase of signals,affect the recovery of underwater acoustic signals,and reduce the communication quality.Therefore,it is very important to accurately estimate and compensate the CFO in underwater acoustic communications for the correct recovery of signals and the realization of high-quality communication.Due to the limited frequency band that can be used for underwater signal transmission,frequency band multiplexing technology is needed to improve the frequency band utilization.Orthogonal frequency division multiplexing(OFDM)is the most commonly used multiplexing technology,which utilizes multiple mutually orthogonal sub-carrier modulation signals,and the frequency of each subcarrier is constant.Orthogonal linear frequency modulation multiplexing(OCDM)is the latest multiplexing technology in recent years.It uses multiple orthogonal chirps for modulation,and the frequency of each chirp varies linearly with time.OCDM's anti-interference characteristics and good frequency diversity gain characteristics in the case of insufficient protection interval(GI)length give it unique advantages in the case of insufficient GI length and channel with frequency domain zero.The basis of modulation demodulation of OFDM and OCDM is the orthogonality between modulation waveforms,while CFO will destroy the orthogonality and have a great impact on its transmission.In order to overcome the influence of CFO on signal transmission,this paper mainly studies CFO estimation of OFDM and OCDM underwater acoustic communication systems,and designs a new CFO estimation algorithm.In this paper,channel modeling is carried out according to the characteristics of underwater acoustic channel,and then the CFO estimation system of OFDM and OCDM is modeled based on this channel.In this paper,the characteristics of pilot BER and pilot MSE are used to improve the traditional one-dimensional search algorithm,and the pilot BER pilot MSE is used to realize CFO rough estimation and fine estimation respectively.Finally,the simulation results show that the proposed method improves the estimation accuracy,reduces the root-mean-square error and bit error rate,and proves the performance improvement and feasibility of the algorithm.In order to meet the needs of underwater acoustic communication experiment,this paper designs and manufactures an underwater acoustic communication experiment platform.We carried out experiments on signal transmission in the swimming pool and artificial lake respectively,realized the actual transmission of OFDM and OCDM signals,and verified the CFO estimation algorithm.The main contribution of this paper is the design of a new CFO estimation algorithm and the realization of both OCDM channel estimation and CFO estimation for the first time.