在正交分頻多工系統上透過預先編碼的方法來降低峰均值功率比之研究

The Study Of PAPR Reduction By Precoding Method In OFDM System

廖玄鈞(Hsuan-Chun Liao)

指導教授 ： 許超雲

大同大學/電機資訊學院/通訊工程研究所/碩士(2009年)

摘要

正交分頻多工(簡稱OFDM)是多載波調變技術的一種，由於高速資料傳輸和有效對抗通道為選擇性頻率衰減的優點下，已成為現今為無線通訊廣泛所採用。但是OFDM系統中有一項主要的缺點就是會產生較高的峰均值功率比(簡稱PAPR)。較低的PAPR會使訊號涵蓋率上升且平均位元錯誤率(簡稱BER)下降，當涵蓋範圍變大，即所需基地台數目就可減少，建置基地台的成本就可下降。此外較低的PAPR可提升高功率放大器(簡稱HPA)的效能。高功率放大器恰好是射頻模組最貴的元件，而其價錢取決於設計上的複雜與否。較低的PAPR正可以減低其設計上的複雜度。綜合以上所述，對一個無線通訊系統而言，其成本正是能否商業化成功與否的關鍵之一，如同現今在台灣建置的WiMAX道理是一樣的。
根據先前論文所述降低PAPR可利用預先編碼(簡稱Precoding)的方法，其效果比我們實驗室所提出的利用離散富立葉轉換矩陣來的更加有效。以此方法應用在固定式WiMAX上所得模擬結果確實是有顯著的成效，但是當考慮導航(簡稱Pilot)子載波的加入後，其結果就沒有先前模擬結果來的顯著。同時根據先前Precoding矩陣的架構，本篇新定義出新的Precoding矩陣，在沒有考慮Pilot的情況下，其模擬結果比先前論文的結果還可以更精進。此外本篇也提出新的OFDM架構來降低PAPR，即以Precoding轉換基礎下結合選擇映射(簡稱SLM)的方法，此新架構其模擬結果證明了是可行且更有效降低PAPR。

關鍵字

微波存取全球互通 ； 峰均值功率比

並列摘要

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation technique. Because of its high-speed data transmission and effectiveness in combating the frequency selective fading channel, OFDM technique is widely used in wireless communication nowadays. But high peak-to-average power ratio (PAPR) is one of the major drawbacks for OFDM systems. Lower PAPR will enlarge the coverage of signal, and diminish the BER (Bit Error Rate) of signal. As the coverage of signal is increasing, the amount of BS (Base Station) is decreasing, that means the cost of BS's construction is down. Besides lower PAPR will upgrade the efficiency of high power amplifier (HPA). Unfortunately HPA is the most expensive device in RF module. The price of HPA is based on the design of complexity, and lower PAPR will reduce the complexity. As we know from the above, lower PAPR will greatly reduce the construction cost of systems. The cost is the key, whether the wireless communication systems will succeed or not, especially WiMAX is setting up in Taiwan presently.
Ascording to previous paper, the reduction of PAPR through precoding method (precoding matrix) is better than using the DFT matrix. This paper presents the simulation in Fixed-WiMAX, and gets the same results in previous paper. It also presents the influence while it considers the pilot insertion, and the simulations are not such good as the previous paper mentioned. According to the precoding matrix in previous paper, this paper introduces a new precoding matrix, and gets better results than previous paper. Furthermore, this paper also introduces new OFDM framework that a selective mapping scheme based on Precoding Transfer constellation-shaping. The simulation results show that the new framework have significant reduction of PAPR.

並列關鍵字

WiMAX ； PAPR

參考文獻

〔1〕Paulo S. R. Diniz, Eduardo A. B. da Silva, and Sergio L. Netto, Digital Signal Processing System Analysis and Design, Cambridge University Press, 2002.

〔2〕Richard Van Nee and Ramjee Prasad, OFDM wireless Multimedia Communication, Artech House, 2000.

〔4〕Bernard Sklar, Digital Communication, Prentice Hall, 2001.

〔8〕IEEE Std. 802.16e-2005, pp.357

〔10〕Slimane Ben Slimane, “Reducing the Peak-to-Average Power Ratio of OFDM Signals Through Precoding,“ IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, Vol. 56, No. 2, March 2007.