Memory reduction of IFFT using separated CIM (combined integer mapping) method

While the number of FFT stages increases logarithmically (log₂N) as the transform length (N) increases, the number of required registers (or, memories) increases linearly. In large transform length FFT designs, the registers occupy more than 70% of the chip area. Recently, combined integer mapping (CIM) method was proposed to reduce the memory size of IFFT for OFDM transmitters. The CIM method focuses on reducing the memory size in the first two stages of the IFFT architectures since the first two stages require 75% of the total memory. In this paper, we propose separated CIM (SCIM) method to further reduce the memory size of IFFT. By SCIM method, real data and imaginary data are mapped differently. By simulations, it is shown that the proposed SCIM design method achieves more than 20% memory reduction compared with CIM method.