作者：江炳宏(Bing-Hung Chiang)
論文名稱：正交分頻多工系統之傳送分集塊狀編碼(Transmit Diversity Block Coding for OFDM System)
摘要
無線多媒體應用是目前之趨勢，因此對於能夠提供高速率傳輸之無線通訊系統的需求與日俱增。換言之，無線寬頻通訊系統必須能夠解決因多重路徑傳播而產生之頻率選擇性衰落及對於高速移動所產生之時間選擇性衰落具有良好之抵抗能力。           本論文將著重於兩項先進傳輸技術: 傳送分集塊狀編碼及正交分頻多工。這兩項技術已被列為國科會B3G規劃書中之重點研究項目。           時空碼為一傳送分集，其結合了天線分集與編碼之概念。在發射機使用時空編碼技術並在接收時運用訊號處理的技巧，使得多根傳送天線系統擁有分集以及編碼所帶來之好處，進而提高系統之效能與容量。尤其對下傳連結之接收機(手機)而言，這是非常必要之作法，因為手機體積越小，成本越少，功率耗損越低越好。在所有時空碼中，塊狀時空碼具有很低之複雜度以及非常優越之性能。於是，我們對同調塊狀時空碼及差分塊狀時空碼在窄頻時變衰落通道之效能作了相當詳細之探討。           正交分頻多工是一項相當卓越的技術，藉由把可用之頻譜分成許多子通道，可使得頻率選擇性衰落減輕為平坦衰落，它甚至被認為是未來第四代無線通訊之候選技術。因此，正交分頻多工系統在多重路徑時變衰落通道之效能評估與研究亦為本論文之一主要部份。           本論文主旨為建置一無線寬頻通訊系統，其利用正交分頻多工抵抗寬頻頻率選擇性衰落並運用傳送分集塊狀編碼技術來改善窄頻平坦衰落。藉由逐步探討傳送分集塊狀編碼正交分頻多工技術，我們首先完成一時變衰落通道模擬器，接著對傳送分集塊狀編碼技術及正交分頻多工技術作了完整且詳細之探討，最後建立了兩寬頻傳送分集塊狀編碼正交分頻多工系統之模擬平台，即時空塊狀編碼正交分頻多工系統與頻空塊狀編碼正交分頻多工系統。再者，利用最小平方解碼技術，我們進一步簡化了寬頻傳送分集塊狀編碼正交分頻多工系統之結構。
關鍵字：傳送分集塊狀編碼;正交分頻多工;頻率選擇性衰落;時間選擇性衰落;同調塊狀時空碼;差分塊狀時空碼;通道模擬器;無線寬頻通訊系統
ABSTRACT
Wireless multimedia application is the current trend and hence the wireless system that offers high data rate is of great demand recently. A wideband wireless communication system should be able to deal with the multipath propagation problem resulting in frequency-selective fading and compatible to time-selective fading.           In this thesis, we introduce two advance transmission schemes, transmit diversity block coding and orthogonal frequency division multiplexing (OFDM), which have been put in the B3G plan of nation science council.           Space-time coding (STC), a transmit diversity technique, is the combination of antenna diversity and coding. Equipped with the space-time coding at the transmitter and intelligent signal processing at the receiver, multiple transmit antenna system can achieve both diversity and coding advantage over single transmit antenna system. This is necessary since there is huge demand on decreasing the cost, size, power of the mobile unit. Among all space-time coding schemes, STBC is of little complexity and well performance. Thereupon, we make a great deal of work on studying and analyzing both coherent and differential STBC in mobile fading channel.           OFDM is a tremendous technique that capable to reduce the frequency-selective fading to flat fading by separating the available spectra into multiple subcarriers. Even it has been treated as the candidate of the fourth generation wireless communication. Hence, an investigation on DFT-based CP-OFDM system in multipath mobile fading channel is also an major part of this thesis.           The aim of this thesis is to implement the wideband wireless communication system, which employs OFDM to combat wideband frequency-selective fading and uses transmit diversity block coding to improve narrowband flat fading. We first completed the mobile channel simulator, and then investigated both transmit diversity block coding and OFDM in detail. Finally we completed two wideband transmit diversity block coded systems, i.e. STBC-OFDM and SFBC-OFDM. Furthermore, the structures of the wideband transmit diversity block coded systems are simplified by least square decoding.

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