Exploration of power optimal implementation technique of 128-PT FFT/IFFT for WPAN using pseudo- parallel datapath structure

An optimal implementation of 128-Pt FFT/IFFT for low power IEEE 802.15.3a WPAN using pseudo-parallel datapath structure is presented, where the 128-Pt FFT is devolved into 8-Pt and 16-Pt FFTs and then once again by devolving the 16-Pt FFT into 4×4 and 2×8. We analyze 128-Pt FFT/IFFT architecture for various pseudo-parallel 8-Pt and 16-Pt FFTs and an optimum datapath architecture is explored. It is suggested that there exist an optimum degree of parallelism for the given algorithm. The analysis demonstrated that with modest increase in area one can achieve significant reduction in power. The proposed architectures complete one parallel-to-parallel (i.e., when all input data are available in parallel and all output data are generated in parallel) 128-point FFT computation in less than 312ns and thereby meeting the standard specification. The relative merits and demerits of these architectures have been analyzed from the algorithm as well as implementation point of view. Detailed power analysis of each of the architectures with different number of data paths at block level is described. We found that from power perspective the architecture with eight datapaths is optimum. The core power consumption with optimum case is 60.6mw which is only less than half of the latest reported 128-point FFT design in 0.18u technology. Apart from the low power consumption, the advantages of the proposed architectures include reduced hardware complexity, regular data flow and simple counter based control.