Research On Equalization And Improvement Of OCDM Systems Over Fading Channels

With the continuous development and innovation of communication technology,future communication technology will face more challenging application scenarios to meet the explosive demand for information growth.5G technology has significantly improved in enhanced mobile bandwidth,massive machine-type communication,and ultra-reliable and lowlatency communications.In this background,new physical layer waveform design is particularly important.Orthogonal Frequency Division Multiplexing(OFDM)is a multi-carrier modulation technology with a strong anti-multipath fading ability.However,the OFDM system is difficult to meet the development in future mobile communication technologies of B5G and 6G because of its high Peak to Average Power Ratio(PAPR),high Out of Band Emission(OOBE),sensitivity to carrier frequency offset and phase noise,and other shortcomings.Orthogonal Chirp Division Multiplexing(OCDM)technology utilizes Fresnel transform to orthogonal multiplexing Chirp waveforms with different Chirp rates within the same bandwidth and achieves high spectral efficiency and communication rate.Due to the broadband characteristics of Chirp carrier,OCDM is insensitive to Doppler frequency shift and can effectively utilize multipath diversity gain,which possesses a stronger anti-fading ability than OFDM.Firstly,based on the OCDM system,this paper analyzes the basic principles and performance of the OCDM system.Through theoretical and simulation results,the similarities and differences between OCDM and OFDM systems are analyzed.This lays a theoretical foundation for mining and analyzing other characteristics of the system in the later content.Secondly,the characteristics of wireless transmission channels are introduced,and the mathematical model of fading channels used in this paper is established.The theoretical derivation and simulation verification of the bit error rate(BER)performance of OCDM linear equalization in frequency-selective fading channels.The three low-complexity equalization algorithms are suitable for OCDM systems are emphatically studied.Through the algorithm structure diagram and formula derivation process,the implementation processes of different algorithms are introduced in detail.In doubly-selective fading channels,the performance of the frequency domain minimum mean square error(MMSE)equalization algorithm declines.A Damped-LSQR algorithm is proposed based on an approximate banded matrix,as a least square iterative algorithm for sparse matrix.To alleviate Inter-carrier Interference(ICI)in rapidly timevarying channels,an LSQR-BDFE algorithm is proposed based on an approximate banded matrix.Combined with decision feedback equalization,LSQR algorithm is used for iterative calculation.The complexity of the proposed algorithm and the simulation results are analyzed,and the performance advantages over the OFDM system are compared.Finally,an integrated waveform framework is proposed to meet the expansion needs of future diversified mobile communication for waveforms.This paper aims at the improved OCDM system,combines the Weighted-type Fractional Fourier transform(WFRFT)precoding and vector grouping techniques,proposes a WFRFT-V-OCDM system scheme,constructs a system framework,and gives the formula derivation process.This paper focuses on analyzing the signal characteristics of the system,giving an MMSE receiver scheme and a PAPR characteristic analysis process.Simulation results show the BER performance advantages of VOCDM systems over V-OFDM systems in doubly-selective fading channels.Meanwhile,WFRFT-V-OCDM systems possess BER flexible transformation characteristics.This paper proposes an improved OCDM system,which provides a new approach for integrated waveform expansion and can be considered a promising multi-carrier system framework.