Design And Implementation Of FFT Algorithm In OFDM System Based On FPGA

As the focus of the current communication technology research,wireless communication technology has received more and more attention.The OFDM is a high-speed transmission technology,has the advantages of anti multipath fading,high spectrum efficiency and so on,make it have widely application prospect in Wireless communication.Furthermore,FFT/IFFT is the kernel operation of the data processing in OFDM systems and the key to the quadrature modulation and demodulation.The results of FFT/IFFT influence the performance of OFDM directly,thus the study of it is very important to the realization and optimization of OFDM systems.This thesis introduces the fundamental principle,model and relative merits of the OFDM system,and analyzes the design requirements of FFT/IFFT module.This thesis designs an improved radix-4 MDC FFT/IFFT processing architecture with variable length.Aiming at the disadvantages of traditional MDC architecture,such as too many storage units,low utilization rate of butterflies and multipliers,the thesis improves the storage scheduling scheme of MDC FFT architecture,including input storage and rotation factor storage.There are 12 memory banks at the input stage for converting the parallel input streams into serial blocks,one butterfly at each stage can compute the four data streams without idle period.Therefore,the memory size is reduced and the utilization rate of butterflies and multipliers is 100%.Moreover,the thesis optimizes the rotation factor storage,storing part of rotation factor values in ROM,the mapping relation is established by the rule of the rotation factor,so that other rotation factors can be obtained,which can reduce the rotation factor storage and improve the overall performance of the architecture.In addition,the FFT/IFFT architectureis designed in detail,including butterfly processing unit,twiddle factor unit,complex multiplier unit,data reordering unit,etc.Finally,the FFT/IFFT module is realized with RTL level,simulation the FFT/IFFT module and verification of the system functions are carried on.Experimental results show that the MDC-FFT architecture that based on FPGA can realize the FFT of 128/512/1024/2048 points.The proposed architecture has effective throughput which is four times as large as clock frequency,and reduces the hardware resources at least 5%compared with the architecture without optimization.The FFT/IFFT has fine performance,it supports QPSK/16QAM/64QAM modulation while applying to OFDM system.The result of EVM test is less than 3%.The research results have certain practical engineering value for the application of OFDM technology in communication system.