**5. Conclusions**

In this study, an area-efficient FFT kernel was presented using the MRM2DF structure for multistandard MIMO-OFDM applications. The proposed design scheme allowed 64/128-point FFT in up to six streams through the efficient use of GI duration, thereby enhancing area efficiency per stream. Novel resource-sharing and operation-rescheduling schemes were developed using an area-reduced CMU to minimize multiplication hardware costs. Finally, a sophisticated sorting buffer was proposed using the minimum memory size to further reduce area overhead. A test chip was developed using UMC 90-nm technology, and was validated through post-layout simulation. The proposed design exhibited an area efficiency superior to that of previous 128-point-based FFT designs in terms of the throughput per area.

**Author Contributions:** S.-N.T. conceptualized and designed the proposed methodology. He also mainly wrote the manuscript. Y.-H.C. supported the technique consultation and co-wrote the article.

**Funding:** This work was supported in part by the Ministry of Science and Technology of Taiwan under project MOST 107-2221-E-033-009 and 107-2221-E-182-066, and the Chang Gung Memorial Hospital, Linkou under project CMRPD2H0301, CMRPD2H0051, CMRPD2G0312, and CIRPD2F0013.

**Acknowledgments:** The authors would like Hsiuan-Ting Wang and Chih-Chiao Tsai for materials preparation and technical supports in IC physical designs.

**Conflicts of Interest:** The authors declare no conflict of interest.
