Research Of Key Techniques And FPGA Implementation Of NC-OFDM System Based On Cognitive Radio

With the development of society and the updating and iteration of communication technology,spectrum resources are becoming increasingly tight.Under this background,cognitive radio technology with adaptive characteristics emerged at the historic moment.Cognitive radio can improve spectrum utilization by fully utilizing the spectrum holes left over a certain period of time,and alleviate the problem of tight spectrum resources.This paper is oriented to the cognitive radio-based NC-OFDM communication link.For some communication channels with unavailable or disturbed bandwidth,the NC-OFDM system signal synchronization technology and peak-to-average ratio suppression technology are studied and analyzed.Two algorithm schemes are completed.Design and implementation of hardware interface with RF module.The specific content of the paper is as follows:First,the basic principles and relationships of OFDM and NC-OFDM are briefly introduced,and the advantages and disadvantages of NC-OFDM system and key technical principles are analyzed.The link model of NC-OFDM system is introduced and the function of each sub-module is described.Secondly,the influence of time synchronization error and frequency synchronization error on system performance is analyzed.The typical maximum likelihood algorithm based on cyclic prefix in non-data-aided synchronization algorithm is applied to NC-OFDM system and Matlab simulation analysis is performed.Then according to the anti-interference synchronization requirements in the NC-OFDM system,an anti-interference synchronization scheme based on ZC training sequence is proposed.Time-frequency synchronization is carried out through the joint decision of multiple correlation values and it is applied to unavailable subcarriers.In the case of a strong interference NC-OFDM system,Matlab simulation analysis and Modelsim simulation are carried out and implemented on FPGA to verify the correctness of the synchronization scheme.Then the concept of peak-to-average ratio is introduced,and the peak-to-aver age power ratio of OFDM systems with different numbers of subcarriers is analy zed by Matlab simulation,and then the PAPR characteristics of the signals of di fferent subcarrier availability in NC-OFDM system are analyzed and given.The detailed formula derivation is given,and the PAPR and CCDF of OFDM system and NC-OFDM system are analyzed by Matlab simulation.Introduce and classif y common PAPR algorithms,and analyze the advantages and disadvantages of va rious PAPR algorithms.Aiming at the special PAPR nature of the NC-OFDM sy stem with non-continuous sub-carriers,the NS_CFR algorithm is applied to the NC-OFDM signal for peak-to-average ratio suppression,and PAPR,EVM,hardwa re are comprehensively considered within the scope of 3GPP standard specificatio ns and project requirements to achieve factors such as resource consumption,des ign a peak-to-average ratio suppression scheme that meets the requirements.Finally,FPGA modular design is carried out on the synchronization scheme,peak-to-average ratio suppression scheme,and hardware platform-related interfaces,giving different levels of implementation block diagrams,describing the implementation process in detail,giving Modelsim simulation results and actual FPGA circuit test results,and comparing Matlab simulations.The results are analyzed and compared.The hardware interface modules such as ADC/DAC,SPI,AGC,etc.involved in the system are written and data transmission is realized,and the interface performance is verified through the interface test.