適用於雙模式無線相容認證與全球微波存取介面之快速傅利葉轉換處理器設計與實現

Design and Implementation of the FFT Processor for Dual Standard Wi-Fi/WiMAX

林于婷(Yu-Ting Lin)

指導教授 ： 張慶元

國立清華大學/電機資訊學院/電機工程學系/碩士(2010年)

摘要

WiMAX(Worldwide Interoperability for Microwave Access全球互通微波存取)技術建立於IEEE 802.16標準上，而Wi-Fi無線相容認證技術建立於IEEE 802.11標準上的，其中IEEE 802.11n標準支援多重輸入多重輸出技術。WiMAX/IEEE 802.16標準及Wi-Fi/IEEE 802.11標準皆採用正交分頻多工(ODFM)技術，其擁有極佳的頻寬使用效率以及對抗非理想通道的能力，而在諸多調變方式中被視為熱門選擇。
快速傅立葉轉換處理器為所有正交分頻多工系統中的關鍵模組，為了適應不同應用，WiMAX中的規範主要有可調頻率及可變點數，而Wi-Fi需支援多重輸入多重輸出。然而這些技術的規範也為其關鍵模組的設計－一個支援雙重標準且可變點數與合理硬體成本的快速傅立葉轉換處理器，帶來極大挑戰。

在本論文中，我們提出一個擁有可變點數且高功率效率的快速傅立葉轉換處理器，主要是由4-path 128-point SDF(Single Delay Feedback) 模組與Multibutterfly模組所組合而成。Multibutterfly模組可以根據不同的快速傅立葉轉換的長度而操作radix-2、radix-2^2、radix-2^3、或radix-2^4的蝴蝶圖運算。4-path-SDF模組可以同時處理四個128點的快速傅立葉轉換，而且它有較快的操作速度與較高的輸出率以支援Wi-Fi標準。同時，一個有效率的記憶體存取方式被提出以及以常數乘法為基礎之乘法單元也被利用，可以有效地降低電路的複雜度、硬體面積及功率消耗。再者，一個新的多資料進位(Dynamic scaling)方法也在本論文中被使用，可以適時地截斷較長的字元長度而使資料的字元長度不會連續地增加。

整個可支援WiMAX與Wi-Fi雙重標準之快速傅立葉轉換處理器是使用UMC 90奈米製程所實現。面積是1,105,584 um^2。在20 MHz操作頻率下可運算12位元快速傅立葉轉換，而其功率消耗為6.84 mW，具有很高的功率效率。在2048點的快速傅立葉轉換下，SQNR為33.9247dB。而且只需要1.325N-word two-port的記憶體來完成連續流程的設計。因此，我們提出的快速傅立葉轉換處理器，針對未來同時支援全球互通微波存取系統及無線相容認證雙模式之實現，是一個極佳的解決方案。

關鍵字

快速傅利葉轉換處理器 ； 無線相容認證 ； 全球微波存取介面 ； 雙模式

並列摘要

WiMAX(Worldwide Interoperability for Microwave Access) and Wi-Fi are based on the IEEE 802.16 standard and the IEEE 802.11 standard, respectively with that the IEEE 802.11n standard supports Multiple-Input Multiple-Output (MIMO) technology. Both the WiMAX/IEEE 802.16 and the Wi-Fi/IEEE 802.11n standards have employed orthogonal frequency division multiplexing (OFDM) technology, that is regarded as a prospective modulation strategy, with great bandwidth efficiency and invulnerability to non-ideal channels.
FFT processor is the key module in the all OFDM communication systems. The specifications of WiMAX, scalable channel bandwidths by adjusting FFT size are employed for different applications, and Wi-Fi standard supports MIMO technology. However, it imposes a great challenge on the design of the key component, a dual mode Fast Fourier Transform (FFT) processor with acceptable hardware cost.

In this thesis, we propose a configurable and power-efficient FFT processor that is composed of the 4-path-SDF module and the multibutterfly module. The multibutterfly module can operate the radix-2, radix-2^2, radix-2^3, or radix-2^4 butterfly according to different FFT sizes. The 4-path-SDF module can deal with simultaneously the four 128-point FFTs with faster operation speed and higher throughput. Besides, an efficient memory-accessing scheme is proposed and a constant-based multiplier unit is adopted to achieve low complexity, small hardware area, and lower power consumptions. Also, the dynamic scaling method is adopted in the proposed architecture, which can truncate timely the longer word-length such that the word-lengths of data are not increased continuously.

The proposed FFT processor, supporting two kinds of wireless communication system standards Wi-Fi (IEEE 802.11n) and WiMAX (802.16e), is implemented by using Faraday 90nm cell library in a UMC 90nm 1P9M CMOS process. The word-length, area in gate level simulation, and power are, respectively, 12 bits, 1,105,584 um^2, and 6.84mW at 20MHz. The SQNR is 33.9247dB when performing the 2048-point FFT. And it only needs 1.325N-word two-port memory, where N is 2048, for continuous flow design. Therefore, the proposed FFT processor is a promising solution to the implementation of OFDM-based WiMAX and Wi-Fi systems in the future.

參考文獻

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