Computationally efficient fast algorithm and architecture for the IFFT/FFT in DMT/OFDM systems

Abstract

The discrete multitone (DMT) modulation/demodulation scheme is the standard transmission technique in the application of asymmetric digital subscriber lines (ADSL). Although the DMT can achieve rate-adaptive data transmission compared with other modulation/demodulation schemes, its computational complexity is too high for cost-efficient implementations. For example, it requires 512-point IFFT/FFT as the modulation/demodulation kernel. The large block size results in heavy computational load in running programmable digital signal processors (DSP). We derive a computationally efficient fast algorithm for the IFFT/FFT. The proposed algorithm requires only 22% of the multiplications needed with the conventional butterfly approach. Also, it can avoid complex-domain operations that are inevitable in conventional IFFT/FFT computation. The resulting software function requires less MIPS count and program storage in firmware development of the IFFT/FFT module. Hence, it is very suitable for DSP-based DMT implementation. The proposed algorithm can also be applied to the technology of orthogonal frequency division multiplexing (OFDM) which is the processing kernel of the digital audio/video broadcasting (DAB/DVB) systems.