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標題: Adaptive Turbo Receivers for OFDM-CDMA Communication Systems-Design and Implementation
作者: 翁芳標
關鍵字: 非同調
noncoherent detection
渦輪碼(turbo code)
turbo code
摘要: Orthogonal frequency division multiplexing-code division multiple access (OFDM-CDMA) isthe basis for many of today's most advanced communication systems such as fourth-generationmobile communication systems. OFDM-CDMA systems combine the advantage of the OFDM withthe resistance to multipath fading and the CDMA with the suitability for multiuser systems. Theturbo encoding can furthermore improve the system performance. Besides, the generation of thecoherent reference at extremely low signal-to-noise ratio is difficult. Therefore, we desire to developa noncoherent 4G mobile communication receiver that is joint with the turbo decoding which canenhance the signal quality. The noncoherent receiver in this project is with BER performanceapproach to that of the coherent one. Our proposed receiver is the symbol-rate adaptive receiver anddesigned in such a way that the despreader output statistic would converge to the desired property.The computational complexity for our receivers is lower than that of the conventional chip-decisionmethods. This receiver does not require training sequence which means that it is a blind scheme.The decision-directed method is one of the simple blind adaptive schemes, but this method isobviously not related to the algorithm of turbo decoding. We intend to propose adaptive turboOFDM-CDMA receivers (coherent and noncoherent) for next generation communication systems.In the first year, the project will be devoted to establish the theoretical fundamentals of theadaptive turbo coherent/noncoherent schemes in multiuser environment for OFDM-CDMA systems.Topics for exploration include: (1) combination of adaptive OFDM-CDMA structure and turbodecoding receiver, (2) adaptive noncoherent receiver structure design, (3) combination of adaptiveturbo OFDM-CDMA receiver and noncoherent structure, (4) BER performance comparison indifferent iteration for turbo decoding, (5) BER performance comparison for different spreadingcodes, (6) BER performance comparison for the different number of interfering sources. In thesecond year, we will develop the receiver structure that is suitable for FPGA implementation. Then,its implementation will be conducted with the XILINX SPARTAN XC2S300E digital processor asthe FPGA platform. We will modify and finely tune our transceiver architecture and algorithmsaccording to other techniques for integration. For example, the multi-channel spreading, coding,synchronization and channel estimation technologies.
正交分頻多工分碼多重進接系統(OFDM-CDMA)是很多先進通訊系統所可能採用的架構。正交分頻多工分碼多重進接系統結合了OFDM 的抗多重路徑衰減以及CDMA 的適合多使用者系統的優點。而渦輪碼能更進一步的降低系統的錯誤率使其信號品質提昇。除此之外,在低訊雜比時,要產生同調(coherent)參考相位是一件困難的事。因此,我們希望能發展出一種結合渦輪碼且適用於第四代行動通訊之非同調接收機。此非同調接收機的系統錯誤率與其同調接收機接近。我們所提出的接收機架構將是以訊符率為基礎的適應性接收機,並且是根據解展頻輸出往期望訊號收斂的特性來設計的。其濾波器的權值是每個訊符期間更新一次。因此,此接收機的複雜度會比傳統的片元決定(chip-decisoin)方法來的低。此接收機將是不需要training sequence 也就是一種blind 的架構。基本的decision-directed 模式即為一種簡單的blind 適應性接收,但是此模式很明顯的並不會與解渦輪碼的演算法有相關。因此,我們將提出同調與非同調適應性渦輪碼OFDM-CDMA 接收機使其適用於下一代的行動通訊系統。本計畫第一年將致力於建構在多使用者環境中同調與非同調適應性渦輪碼OFDM-CDMA 接收機的演算法理論基礎。相關的研究主題包括:(1) 結合turbo decoding與適應性OFDM-CDMA 接收機之設計,(2)適應性非同調接收的架構設計,(3) 結合適應性turbo OFDM-CDMA 與非同調系統之最佳化接收機設計,(4) 接收機在各種iteration下之turbo decoding 的效能分析,(5) 接收機在不同種類之虛擬隨機序列碼的BER 效能分析及(6)接收機在不同用戶數下BER 效能分析。在第二年的計畫中,我們將研究重點移至XILINX SPARTAN XC2S300E 處理器為硬體實現之FPGA平台,同時發展適合FPGA實現之接收器架構。最後,我們預計將加入其他技術如多通道展頻技術、無線接取編碼技術、同步與通道估計技術等,有效調整並修正所發展之訊號處理架構,達成系統整合之目的。
其他識別: NSC97-2221-E005-006-MY2
Appears in Collections:電機工程學系所



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