鐘嘉德 Char-Dir Chung

Distinguished Professor, Department of Electrical Engineering, National Taiwan University

Major Research Areas:

Communication System and Theory, Wireless Communications, Spread Spectrum Communications

Research Summary:

        In recent years, Prof. Char-Dir Chung has been fully devoted to the academice reseacrh on digital  modulation theories. By introducing correlation among OFDM data symbols in frequency domain, Prof. Chung has  proposed several spectrally-precoded OFDM (SP-OFDM) schemes. These schemes are important in that they not only reshape the power spectrum of the rectangularly pulsed OFDM signal to exhibit very small sidelobes, but also permit implementation and analysis with ease. These schemes apply to rectangularly pulsed OFDM with cyclic prefix (CP-OFDM) or zero padding (ZP-OFDM). Particularly, these SP-OFDM schemes exhibit extremely small power spectral sidelobes decaying asymptotically as f^{-2L-2}, where L denotes the precoding order. Because of the desirable characteristic of high spectral compactness, SP-OFDM is very promising for use in future broadband communications, especially in wireless communications. In order to justify the use of spectral precoding as a valuable element in future systems, Prof. Chung is progressively working toward the following advanced subjects regarding the interaction of spectral precoding with other important system functions. These issues include spectral precoding on correlated data, multiple-input multiple-output (MIMO) transmission, interchannel interference (ICI), peak-to-average power ratio (PAPR) reduction, adaptive modulation, bit and power loading, channel estimation, block decoding, and multiple-access OFDM communication. The studies in these lines of research will advance the knowledge of SP-OFDM. The possible research results have a potential in practical OFDM applications in that much higher spectral efficiency can be achieved and the guard band can be largely sized down. It is believed that such research contents are in perfect synchronism with worldwide research streams on OFDM-based wireless communications. Possible outcomes will bring the domestic efforts in these streams into international attention. Because the spectral precoding can be easily incorporated into the state-of-art OFDM system architecture, the developed algorithms may also be applied to future wireless communication systems and give practical value.