Design of an application-specific instruction set processor for high-throughput and scalable FFT

Various orthogonal frequency division multiplexing (OFDM)-based wireless communication standards have raised more stringent requirements on throughput and flexibility of fast Fourier transformation (FFT), a kernel data transformation task in communication systems. Application-specific instruction set processor (ASIP) has emerged as a promising solution to meet these requirements. In this paper, we propose a novel ASIP design tailored for FFT computation. We reconstruct the FFT computation flow into a scalable array structure based on an 8-point butterfly unit (BU). Any-point FFT computation can be carried out in the array structure which can easily expand along both the horizontal and vertical dimensions. We incorporate custom register files to reduce memory access. The data address for custom registers in each FFT stage is changed accordingly, and we derive a regular address changing (AC) rule. With the microarchitecture modifications, we extend the instruction set with three custom instructions correspondingly. Our FFT ASIP implementation achieves great performance improvement over the standard FFT software implementation, one TI DSP processor, and one commercial Xtensa ASIP, with the data throughput improvement as 866.5X, 5.9X, 2.3X, respectively. Meanwhile, the area and power consumption overhead of the custom hardware is negligible.