Variable length FFT/IFFT Processor: Algorithm to Architecture Mapping and Implementation

In modern technologies, the DSP algorithms behind the VLSI architectures play a significant role. The latest standards in wireless communications rise the challenges in the implementations of future communications systems. The high-speed Wi-Fi (5G) technology is standardised a few years ago as IEEE 802.11ac standard that adopts an orthogonal frequency division multiplexing (OFDM) technique. The fast Fourier transform (FFT) is a traditional DSP algorithm, that plays a key role in wide range of applications in electrical engineering. In OFDM system, the FFT and inverse fast Fourier transform (IFFT) plays a crucial role. A multiple input multiple output (MIMO) OFDM system needs multiple FFT processors in the receiver and multiple IFFT processors on the transmitter side. The number of FFT/IFFT processors is linearly increased with the number of data streams. For example,an IEEE 802.11ac baseband processor handles up to eight spatial streams. The traditional approach employs eight IFFT processors for the transmitter and eight FFT processors for the receiver. Since the FFT/IFFT processors requirement linearly increases with the number of spatial data streams, implementation of a low power MIMO-OFDM system may not be feasible when the number of spatial streams is more. Hence, it is an interesting research problem to come up with a single FFT/IFFT processor that can handle multiple streams. To this end, there is a scope for developing new algorithms, architectures and design techniques for portable system applications. The objective of this work is to investigate the methodologies and architectures for a variable length multi-path pipelined FFT/IFFT, the input-output data scheduling, reordering and the twiddle coefficient multiplication. Here, the input data scheduling, reordering plays an important role in multiplexing various streams into a single pipeline processor. Output reordering unit aligns the FFT/IFFT output into the standard order. On the other hand, hardware com