Design And Implementation Of Universal And High Speed FFT/IFFT Processor

Orthogonal Frequency Division Multiplex(OFDM) is a kind of digital modulation technology of multi-carriers. It is supply the demand of wireless communications in high speed, broad band and mobility and widely used in wireless communications, such as WIMAX(802.16e) and 3GPP LTE, for the charaeteristics of higher spectrum effieieney, stronger ability of anti-multi-path interference and so on.The key technology of OFDM is Fast Fourier Transform Algorithm(FFT). IFFT/FFT with high speed and variable-point is requested to complete the OFDM modulation and de-modulation for the amount of subcarriers in high speed and high capacity OFDM system is large and variable.A design of variable-point FFT/IFFT for non-power of 2 is proposed in consideration of the characteristics of the variable-length and non-power of 2 subcarriers in WIMAX and 3GPP LTE system. A high speed and configurable FFT/IFFT is designed by using the mixed radix with radix-2, radix-3, radix-4 based on pipelined ping-pong architecture. It will save about 100k storage space since all the twiddle factors are stored in the same space and RAM is shared by I/O data after optimizing address generation unit. Furthermore, radix-3 butterfly processor is optimized for reducing multiplying unit. The simulation results show that the design can satisfy the need of FFT/IFFT for different bandwidth in high-speed WIMAX and LTE system.