Rom Reduction for OFDM System Using Time-Stealing Strategy

Modern communication systems frequently exploit the OFDM (Orthogonal Frequency Division Multiplex) technique to obtain a highly robust transmission of multimedia information, such as digital audio/video broadcast. OFDM and most of the other multimedia compression techniques usually require expensive computations, e.g., FFT (Fast Fourier Transform) and IMDCT (Inverse Modified Discrete Cosine Transform) processing. Traditionally, designing FFT and IMDCT separately involves a significant amount of redundancy in hardware. To reduce the required hardware, this investigation proposes a new ROM-sharing design for storing both FFT twiddle factors and IMDCT coefficients in a DAB (Digital Audio Broadcasting) receiver. We first analyze the correlation between FFT operations and IMDCT operations, and then the combinational logic circuit in the FFT processor is modified such that both IMDCT coefficients and FFT twiddle factors can be obtained simultaneously from a shared ROM. This design can also be applied for computing IFFT (Inverse Fast Fourier Transform) and MDCT for DAB transmitter. Compared with the traditional design using separate module scheme, our design does not need extra ROM for IMDCT/MDCT modules. Therefore, the new scheme offers superior solution for combining high-performance FFT (IFFT) operation and IMDCT (MDCT) operation.