Research On Orthogonal Time Frequency Space Modulation:PAPR Reduction And Clipping Noise Recovery

With the development of mobile communication,modern communications system must meet the high speed mobile scenarios of high quality communication,Orthogonal Time Frequency Space(OTFS)as a new two-dimensional modulation technology,converts the fading time-varying channel into a non-fading and time-independent channel with constant gain experienced by the OTFS modulation,improves the BER performance of the system in high-movement scenarios significantly.This paper mainly studies some effective methods to reduce the PAPR of OTFS and the method of clipping noise recovery in OTFS.Firstly,this paper introduces the signal model of OTFS system,analyzes the signal detection algorithm and channel estimation method of OTFS system in the time-delay Doppler domain,and compares the system performance of different detection algorithms in static and time-varying channels through simulation experiments.At the same time,the definition of peak to average power ratio(PAPR)of OTFS system and the probability distribution of PAPR are analyzed theoretically,which provides a basis for the subsequent design algorithm.Then,the method to reduce peak-to-average power ratio(PAPR)is studied in the pilot-embedded orthogonal time frequency space modulation where guard symbols with zero padding are introduced to avoid the interference between data and pilot symbols.By permitting the guard symbols to be padded with signals of small magnitudes,an efficient PAPR reduction method based on the iterative clipping and filtering(ICF)framework is proposed.In the proposed method,first,the clipping noise other than the clipped signal is filtered;second,the filtering coefficients for the clipping noises in the data-plus pilot region and guard region are set to be different values to achieve good trade-off between PAPR and bit error rate(BER)performance.Simulation results show that the proposed method can reduce the PAPR efficiently with mild BER performance loss.Finally,based on the compressed sensing algorithm,an efficient clipping noise recovery method using reliability-based compressed sensing(CS)is proposed for orthogonal time frequency space modulation with iterative clipping and filtering.Concretely,the message passing algorithm is first used to acquire the hard decision of transmit signal,along with the corresponding reliability.Then,an efficient method to determine the reliable observations of clipping noise is presented by utilizing the reliable hard decision signals and the sparsity of the equivalent delay-Doppler channel.And,from these reliable observations,the clipping noise can be recovered by CS techniques through utilizing its sparsity in the time-domain.Simulation results show that the proposed method can recover the clipping noise efficiently.