The Research Of Key Technologies For Antiinterference OFDM System Receiver

Orthogonal Frequency Division Multiplexing(OFDM)has been widely used in numerous wireless communication standards and scenarios,such as LTE-A,DVB-T2 and IEEE802.11a/g/n/ac,because of its advantages of supplying high spectral efficiency,resisting frequency-selective fading,and realizing modulation and demodulation easily.Nevertheless,in the context of the ever-growing lack of spectrum resources and complex channel environments,OFDM systems face the risk of being disturbed,which may result in the information not being able to transmit successfully,whether it is natural interference in civilian scenes or man-made interference in military scenes.Therefore,assuring the reliability of OFDM signal during the process of transmission has become an important performance indicator of OFDM systems.Based on the established interference models,this article concentrates on the study of frame synchronization,interference detection and interference suppression techniques in OFDM systems.The key achievements are listed as follows:1)The reliable frame synchronization techniques in OFDM systems are researched.Firstly,the advantages and disadvantages of the commonly used frame synchronization algorithms in OFDM systems are analyzed by simulating.Secondly,by improving the traditional frame synchronization algorithm,a low-complexity and frequency-offset-robust synchronization algorithm based on CAZAC sequence is proposed,which can simplify the timing metric function constructed at the receiver because of using no additional weighted sequences,and eliminate the adverse influence of frequency offset on the performance of timing synchronization by using symmetric autocorrelation operation rather than delayed autocorrelation operation to generate the timing metric function during the timing synchronization.Specific simulation confirms that the improved algorithm ensures the excellent performance of timing synchronization as well as reduces the complexity of numerical operations in the timing synchronization stage,and solves the problem that traditional algorithms are sensitive to frequency offset.In the end,based on the improved algorithm,an anti-interference frame synchronization algorithm based on CAZAC sequence is proposed to ensure the reliability of frame synchronization when interference exists,and its anti-interference effectiveness under the interference channel environment is verified.2)The frequency domain interference detection techniques in OFDM systems are investigated.By analyzing several commonly used frequency domain threshold interference detection methods,a consecutive variance excision algorithm and a forward consecutive variance excision algorithm are proposed based on the consecutive mean excision algorithm and the forward consecutive mean excision algorithm,respectively.In order to distinguish the interference signal from the useful signal better,the two algorithms proposed are to adaptively adjust the threshold by using the variance value of the received signal instead of the mean value when interference exists.Simulation results show that the two algorithms proposed can effectively improve the probability of interference detection under the condition of high signal to interference ratio.3)The frequency domain interference suppression techniques in OFDM systems are studied.For single-tone interference or multi-tone interference,introducing the classic frequency domain zeroing algorithm and the interference suppression algorithm based on Compressed Sensing(CS),an interference suppression algorithm based on CS and interference detection is proposed to decrease the sensing noise which exists in the CS suppression algorithm and improve its effect of interference suppression.For partial-band interference,an interference suppression algorithm based on frequency diversity is proposed.The proposed algorithm implements frequency diversity for the subcarriers of OFDM systems to achieve the purpose of suppressing partial-band interference.Simulation results verify that the proposed algorithms effectively improve the performance of interference suppression in OFDM systems.