Research On Performance And Transmission Security Of Improved OFDM System

With the development of communication technology,digital modulation technology is widely used.Orthogonal Frequency Division Multiplexing(OFDM)modulation and demodulation technology is one of the implementation methods of multi-carrier transmission scheme.OFDM with advantages of the fast data transmission,strong anti-narrowband interference,and effective multi-path fading is widely used in the field of wireless communications.It is a key technology of LTE and will play an important role in the future 5G wireless communication field.The N-continuous OFDM technology developed on this basis of original OFDM improves the symbol continuity,reduces the spectrum leakage of the system,suppresses side lobes,reduces interference,improves the utilization efficiency of spectrum resources,and finally improves the performance of the wireless transmission system.This paper focuses on N-continuous OFDM technology,introduces of the conversion of time-frequency domain,the improvement mechanism of smoothing signal changing prefix/suffix,and the Introduction of chaos.Then analyzes Power Spectral Density(PSD),Bit Error Rate(BER),complexity characteristics of implementation,and the transmission security of communication system.The specific work of this paper is mainly in the following four aspects:Firstly,the implementation principle,application status and research significance of the original OFDM technology are emphasized.Then the basic principles and characteristics of the traditional N-continuous OFDM technology are also analyzed.The differences between the two technologies are compared.The merits of the improved method for achieving sidelobe suppression are recognized.And the current research needs and research directions of rapidly developing OFDM technology in communication technology are analyzed.Secondly,based on several improved methods for traditional N-continuous OFDM technology,an improved time-domain N-continuous symbol padding OFDM technique is proposed,which is more suitable for OFDM transmission systems.A smoothing correction signal is proposed,which is obtained based on the relationship between two adjacent symbols of OFDM.Then the smoothing modified symbol is used for OFDM symbols of N-continuous OFDM technology to make adjacent symbols have continuity and smoother.The scheme of adding the smoothing correction signal to the guard interval,prefix,suffix and prefix/suffix are also studied.So the research on the time domain smoothing correction symbol is extended.Thirdly,the principle and implementation advantages of chaotic map encryption are introduced in detail.Then the chaotic maping is applied to the original OFDM system.The theory and implementation principle of chaotic encryption can be used for traditional N-continuous OFDM and improved time-domain N-continuous symbol padding OFDM method.It is confirmed that the safe transmission of the improved transmission system is reasonable and feasible.Finally,the system is studied as a whole.And the improved time-domain N-continuous symbol padding OFDM transmission system is simulated completely.Various parameters are set properly.Then the system transmission characteristics are studied under different parameters.Such as the effect of sidelobe suppression,achieve performance optimization and implementation complexity impacts that reduce complexity,and introduce chaotic encryption into a complete system that is both secure and easy to implement and performs well.