鐘嘉德特聘教授的個人資料 - Profile of Char-Dir Chung

鐘嘉德 Char-Dir Chung

國立台灣大學電機工程學系 特聘教授
Distinguished Professor, Department of Electrical Engineering, National Taiwan University

主要研究領域:

通訊系統及理論,無線通訊,展頻通訊

Major Research Areas:

Communication System and Theory, Wireless Communications, Spread Spectrum Communications

研究領域摘要:

    鐘嘉德教授近年戮力於數位調變理論學術研究,已成功地設計了頻域預編碼正交分頻多工系統,主要技巧為將正交分頻多工(OFDM)的資料符元於頻域透過線性的方式組合,以介入資料符元的關鏈性。於國際通訊理論學界首先提出頻域預編碼正交分頻多工(SP-OFDM)系統,詳細內容已以論文型式發表於IEEE Trans. Commun.IEEE Trans. Wireless Commun.期刊。此頻域預編碼OFDM系統除了可以套用現行的OFDM的標準系統規格,還可以提供非常快速的功率頻譜旁波衰落,亦即可提供更高的頻譜效益。此SP-OFDM亦可結合循環字首與補零等技術以對抗信號自干擾,可以提供以f^{-2L-2}衰減的功率頻譜旁波。尤其值得一提的,鐘教授發掘了透過預編碼的方式改善OFDM的功率頻譜旁波的衰落速度,同時也可提升信號的頻譜效益。此外,對於相鄰頻帶的信號所造成的干擾,也獲致大幅度的降低,因此可取代OFDM於無線通訊應用,極具實用潛力。為了確認在未來通訊系統中頻譜預編碼的價值,鐘教授持續的投注心力於與頻譜預編碼相關的系統設計課題,其中包括:帶有相關性資料的頻譜育編碼、多重輸入多重輸出傳輸、通道互干擾、封均值降低方法、可適性調變、位元與功率的配置、通道估測、區塊編碼、與多重接取OFDM通訊。鐘教授深信此SP-OFDM的問世,將擴大正交多工數位調變訊號的研究動能,特別是其快速衰落的功率頻譜旁波有助於上述通訊議題之研習,將可提供新穎的研究視野及統合的研究推論,並對於現行的以OFDM調變訊號而獲得的同領域研究造成有趣的衝擊,而且可激發新穎的研究內涵及啟示。

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.

 

Photo of Char-Dir Chung