載波頻率偏移估測法於正交分頻多工存取上鏈系統效能改進

Performance Improvement of Carrier Frequency Offset Estimation Methods in OFDMA Uplink Systems

耿浩勛(Hao-Hsun Keng)

指導教授 ： 呂振森

國立臺北科技大學/電資學院/電機工程系研究所/碩士(2010年)

摘要

正交分頻多重存取（OFDMA）技術能夠提供可靠多重存取、良好的頻譜效益，以及避免多路徑傳輸所造成的影響。然而載波頻率偏移（CFO）對於正交分頻多重存取系統影響很大，會因為不同使用者載波頻率偏移而產生載波間干擾（ICI）與多用戶存取干擾（MAI），使系統效能大幅降低。本論文針對接收端本地振盪器非理想狀況所造成的頻率偏移進行研究，使用已知資料領導碼搭配最大概似估測法（MLE）以及結合載波間干擾自我消除等演算法，探討載波頻率偏移在正交分頻多重存取系統的影響。為了避免多用戶存取干擾的影響，最後選用了區塊(Block)載波配置法，再將估測法結合載波頻率偏移補償來改善系統效能。由電腦模擬分析，此一方法能增加載波頻率偏移估測範圍，並提高其準確度，對於系統效能也有顯著的提升。

關鍵字

正交分頻多重存取 ； 載波頻率偏移 ； 最大概似估測法 ； 領導符碼 ； 多用戶存取干擾

並列摘要

The technique of orthogonal frequency division multiple access (OFDMA) has the excellent bandwidth efficiency and good resistance to multi-path effects while providing reliable multiple access capability. However, the performance of the OFDMA system is extremely influenced by carrier frequency offsets (CFO). The carrier frequency offset of each user will result in both inter-carrier interference (ICI) and multiple access interference (MAI) which cause severe degradation on the system performances. In this thesis, we focus on the carrier frequency offsets induced by the imperfection of local oscillator’s frequency at receiver in OFDMA systems. We investigate the effects of carrier frequency offsets in the OFDMA system by using the pilot-based carrier frequency offset estimation method which combines the maximum likelihood estimation (MLE) and inter-carrier interference self-cancellation algorithm. To avoid the effect of multiple access interference, we choose the block carrier assignment scheme and use the carrier frequency offset estimation method integrating with compensated carrier frequency offset to improve the system performance. According to the computer simulation, this method shows that it can extend the estimation range of CFO, give better estimation of CFO, and therefore increase the system performance.

並列關鍵字

OFDMA ； carrier frequency offset ； maximum likelihood estimation ； multiple access interference ； pilot symbol

參考文獻

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