應用於感知無線電系統之多重輸入輸出正交分頻多工基頻收發機設計

隨著無線通訊的日漸普遍，頻寬需求量愈來愈大，然而目前頻譜使用方式效率並不高，因此，感知無線電系統的概念開始被提出並逐漸受到重視。所謂感知無線電系統是一種能隨著外界環境的改變，動態的調整其傳輸頻寬、功率、調變方式及其它各項參數以達到更有效率傳輸的無線電系統，而本論文的目標頻帶設定於5GHz的UNII頻帶，希望能與該頻帶的主要使用者—IEEE802.11a系統共存且不干擾到主要使用者的運作，以提高該頻帶的使用效能。本篇論文首先根據感知無線電系統的訴求設定其系統規格及適合的傳送封包格式，接著根據此規格建立一2x2 MIMO-OFDM基頻收發機。在接收機架構的資料接收方面主要可分為初始同步、迴路追蹤以及資料回復等三大部份，其中同步是利用封包最前端的前置碼來達成符元時序與載波頻率偏移的估計，之後便利用FFT運算器將訊號由時域轉至頻域，根據領航碼的相位旋轉作殘餘的載波頻率偏移與取樣時脈偏移的估測並利用追蹤迴路達到收斂，而資料回復的部份，先完成最小方差的通道估計之後，再根據MIMO-VBLAST的等化方式而後解碼；除此之外，接收機同時有一通道品質評估區塊對通道特性持續估測，以掌握外界環境變化調整本身的設定。就整體設計而言，感知無線電系統在基頻接收機設計的考量主要可分成兩個部份，首先便是參數化的設計，須隨著動態的頻譜配置改變其各項設定，收發機根據不同的系統頻寬大小、頻帶分布位置等調整內部各區塊的參數設定，而封包格式如前置碼的訊號、次載波分布等亦是隨之調整；另外則是通道環境之估測，感知無線電系統將偵測環境的變化，以期作適當的調整而提升傳輸的效率。

關鍵字

正交分頻多工；感知無線電系統；多重輸入輸出

並列摘要

As the wirelsss applications become more and more sophisticated and widely used, the demand for more bandwidth will increase substantially. However, wide ranges of potential spectral resources are only used rarely nowadays. In order to enhance the spectrum efficiency, the concept of cognitive radio has been proposed. Cognitive radio system is a radio system that can sense the spectrum environment and use the spectrum only if communication does not interfere with primary users, and also adjust the transmission parameters adaptively to increase spectral efficiency. In this thesis, the system specifications and packet formats are proposed according to the functional requirement of cognitive radio systems. Under the proposed system specifications, the 2x2 MIMO-OFDM baseband transceiver for cognitive radio systems has also been developed. The design of baseband transceiver has the two main considerations. One is parameterized design, that is, the parameters of all functional blocks need to be adjusted adaptively according to dynamic spectrum allocations, and the packet format including signal design of preamble and subcarrier allocation do as well. The other aspect is the sensing capability. The receiver will estimate the channel environment to access the channel quality and thus adapt its transmission parameters. The system design is developed with sample-based floating-point C++ programs, so the latency and complexity of hardware is also evaluated and thus can fasten the IC design procedure in the future.

並列關鍵字

OFDM ； Cognitive Radio ； MIMO

參考文獻

[29] H. Schober, F. Jondral, R. A. Stirling-Gallacher, Z. Wang, "Delay Spread Estimation for OFDM Based Mobile Communication Systems," Proceedings European Wireless 2002, pp625-628, Feburary 2002

[3] FCC. ET Docket No. 03-322. Notice of Proposed Rule Making and Order, December 2003

[8] Weiss, T.A.; Jondral, F.K. “Spectrum pooling: an innovative strategy for the enhancement of spectrum efficiency,” IEEE Communications Magazine, vol: 42, pp:8–14, Mar 2004

[9] Chi-Yeh Yu, “MIMO-OFDM Baseband Transceiver Design for High Throughput Wireless LAN,” MS Thesis, NTU, 2004

[10] John G. Proakis, “Digital Communications” 4th Edition, McGraw-Hill Publisher, 2001

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應用於感知無線電系統之多重輸入輸出正交分頻多工基頻收發機設計

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