Research On Carrier Frequency Offset Estimation Algorithms For OFDM Systems In Fast Fading Channels

In modern mobile communications,orthogonal frequency division multiplexing(OFDM)technology as the core technology of 4G and 5G,which has been widely used in the field of communication.It is well known that OFDM has the advantages of fast transmission rate,anti multipath interference,high frequency spectrum utilization and so on.But OFDM signal is vulnerable to the carrier frequency offset(CFO),CFO will introduce inter symbol interference(ISI)and inter carrier interference(ICI),and affect the normal communication of the system.Therefore,accurate CFO estimation is one of the key problems in OFDM communication system.In this paper,the carrier frequency offset estimation of OFDM system in fast fading channel is studied.At present,the carrier synchronization algorithm is generally divided into two kinds: the blind estimation algorithm and the pilot aided method.The so-called blind estimation algorithm adopts the inherent structure of OFDM system to achieve synchronous rectification;the pilot data aided algorithm adds some symbols before transmitting data to complete synchronization,which has the advantage of relatively high estimation accuracy but reduces data transmission rate in some degree.This paper first introduces the cyclic prefix(CP)algorithm based on blind estimation and the Moose algorithm and SC algorithm based on data pilot assisted,then this paper modified the Moose algorithm and compared the performance of two kinds of synchronization techniques.Secondly,by analyzing characteristics of fast time-varying channels,the base expansion model(BEM)is used to model fast time-varying channels in this paper.Then the maximum likelihood(ML)and the maximum a posteriori(MAP)algorithm for carrier frequency offset estimation of the joint channel based on the BEM are studied.The two algorithms in different BEM conditions were analyzed and compared,we see that both the two kinds of joint CFO and channel estimation algorithm can achieve good performance.However,considering the high complexity of the joint algorithm channel modeling,this paper proposes a MAP algorithm based on CPF-BEM,analysis and simulation results show that compared with the original algorithm in the performance simulation analysis,the proposed algorithm can maintain a good performance on with reduced complexity.Because that the classical algorithms cannot overcome the ICI caused by Doppler frequency shift in fast fading channel and have the disadvantages of high complexity or poor performance,the classical algorithms are subjected to certain limitations in the practical application.For this reason,this paper proposes a new Moose frequency offset estimation algorithm based on ICI self-cancellation precoding,which has a low complexity and is quite suitable for application in fast time-varying fading channels.In fast time-varying channels,the ICI introduced by channel time variation will cause a great impact to communication system so that the ICI self-canceling precoding pilot pattern is used to combine the processing at both ends and reduces the impact of ICI on CFO estimation.Specifically,we reduce the ICI of the receiver frequency domain signal by using the ICI self-canceling precoding pilot pattern in transmitting end,and derive the CFO based on the correlation analysis between the subcarriers in new received signal model.Finally,the proposed algorithm is analyzed in detail in computational complexity and performance simulation detailed.Compared with the classical Moose algorithm,the proposed algorithm can obtain significant performance improvement with only slight complexity increase,and is more robust for different CFO.Compared with the joint CFO and channel estimation algorithm,the proposed algorithm has much lower complexity,and also considerably performance improvement.