The FFT Research In OFDM Modulation Based On FPGA

Along with the digit electronic technology's development, the digital signal processing technology has widely applied in the communication, pronunciation processing, the computer and multimedia and so on domains. Simultaneously already applied in the numerous domains the Orthogonal Frequency Division Multiplexing (OFDM) the technology has become hot spot in the research and also has become the new generation mobile communication key technologies. OFDM is the more than one kind of carrier digital modulation technology, which is recognized for one kind that realizes a good method that can get the high speed in bidirectional wireless data communication. In the OFDM system, in each sub-carrier the data modulation and the demodulation are using FFT (the fast Fournier transformation) the algorithm to realize, therefore in the OFDM system, the realization of FFT is a key aspect in the plan, of which operation precision and the speed must be able to achieve the system's target ,to 512 sub-carriers regarding one, in the sub-carrier band width 10 kHz OFDM systems, it is to take200μs to complete 512 spots in the FFT operations.According to the OFDM system's actual need, this design proposed one kind that realized the FFT operation plan with FPGA, and taked 512 FFT as the example, based on the multianalysis of the- 2FFT algorithm's foundation, according to the algorithm characteristic, has conducted the research which was the FFT principle work and the structural design. Because in the FFT computational process the data frequent read-write is so big to the FFT processing speed influence, therefore to design the memory is the key , the design constructed two port RAM to enlarge the data volume of goods, used the pingpong to operate, the input and output both used a clock in common: In clock's drop along to write into the data, rise along to read out the data. This might calculate continuously to the input data stream, has realized the data stream line operation, satisfied the data processing with high speed, and the timely request so on . The design used the based - 2 the frequency extraction algorithm, took the Altera Corporation's Quartus II as the software platform, has designed the plural number block floating point structure FFT system that has 512 bot 8 bits in the VHDL description's way, which selected the Altera Corporation Cyclone series's FPGA chip EP1C6Q240C8, and was adopted the synthesis and the simulation finally on the Quartus II software. The result of simulation indicated that computed result achieved to the need of OFDM system, the operating speed has satisfied in the real-time signal processing the request.