A Wavelet-FFT Based Efficient Sparse OFDMA Demodulator and Its Implementation on VLIW Architecture

In a practical OFDMA system, the terminal receiver often observes very low power in significant number of sub-carriers. The sparse energy distribution is because of the partial-load on sub-carriers, the beam-forming at basestation and the large amount of zero-sub-carriers obligated by communication standards. We present the algorithm and implementation of an energy-scalable OFDMA demodulator exploiting the afore-mentioned sparseness. The proposed scheme can dynamically reduce the computation-load and associated energy-consumption for OFDMA demodulator, which is one of the most energy-consuming parts of practical receivers. Our work applies Wavelet transform to perform decompositions based FFT, dropping low-energy bands and pruning useless dataflows. In addition, a new algorithm is proposed to significantly improve the accuracy of Wavelet-FFT with dropped bands. Our work has been implemented and tested on TI TMS320C6713, a typical VLIW baseband processor. In contrast to the well-studied partial FFT, our work is very friendly to the parallel execution on VLIW processor, enabling its application in contemporary programmable baseband implementations. In the case of 3GPP LTE receiver, 8.6% low-energy sub-carriers (in addition to the null sub-carriers) brings around 50% reduction of the cycle-count on TI TMS320C6713.