Research On Channel Estimation Based On Preamble Design In FBMC/OQAM System

The orthogonal frequency division Multiplexing(OFDM)technology used in the fourth generation mobile communication technology(4G)can not meet the needs of future mobile communication,because of its low spectrum resource utilization high peak-to average ratio and poor ability to resist carrier interference.As one of the candidate technologies for some technical scenarios of the fifth generation mobile communication technology in the future,the filter bank multi-carrier(FBMC)adopts the techniques of prototype filter with good time-frequency focusing characteristics and OQAM modulation,which has the advantages of low peak-to-average ratio and high spectrum utilization.Since the FBMC system is orthogonal to the real number field,there is an imaginary part inherent interference between the FBMC subcarrier symbols.Therefore,the traditional channel estimation method cannot be directly applied to the FBMC system when performing channel estimation.In addition,many channel estimation algorithms are based on estimation of the pilot structure,but most of the algorithms have problems of excessive pilot overhead and low pilot utilization.Aiming at the problem that the subcarrier symbols have inherent imaginary interference,excessive pilot overhead and low pilot utilization,several channel estimation schemes under FBMC systems are proposed.The specific work and contributions of the paper are listed as follows(1)We propose a weighted channel estimation algorithm based on intrinsic interference cancellation in FBMC systems.The research shows that the preamble based channel estimation algorithm uses a series of effective pilots for channel estimation,while other column pilots are not fully utilized.Obviously,there is a problem of low pilot utilization.Through the analysis,it is known that all pilot columns have available information with different weights for channel estimation.Therefore,a new two-column pilot structure is designed,in which the inherent interference of two columns of pilots can be eliminated from each other by the adjacent pilot symbols,but the inherent interference of the data is still present.Then,using two columns of pilots for coarse channel estimation respectively.Finally,through the weighting of the data to the pilot symbol interference,the coarse channel estimation is weighted for the refined channel estimation,thereby further improving the channel estimation performance.The simulation results show that compared with the traditional imaginary interference cancella-tion algorithm(IIE),the new pilot structure algorithm can achieve 1dB-2dB performance improvement when the bit error rate is 1%.(2)We propose a channel estimation algorithm based on complex conjugate symmetric preamble in FBMC system.Aiming at the problem of excessive pilot overhead and poor channel estimation performance,a single column complex pilot structure is designed.Through derivation and analysis,it is found that if the pilots of even and odd rows are complex conjugate symmetric structures,the sign of the inherent interference of the pilot symbols at the receiving end is exactly the opposite.The received symbols of even and odd rows can be linearly combined to eliminate the inherent interference of imaginary parts.The simulation results show that compared with the traditional POP algorithm and IAM algorithm,the new pilot structure algorithm can effectively improve the BER and MSE performance of the FBMC system under the condition of reducing the pilot overhead.At the same time,the algorithm can obtain better channel estimation performance when the set moving speed is 120Km/h.