以干擾消除技術改善上行正交分頻多重存取系統之載波頻率偏移

正交分頻多工（Orthogonal frequency division multiplexing, OFDM）是近年來最受矚目的無線通訊技術，其延伸之正交分頻多重存取（Orthogonal frequency division multiple access, OFDMA）則被視為下一世代（4G）無線網路的主要技術，但此兩系統對於載波頻率偏移（Carrier frequency offset, CFO）均極為敏感，因為載波頻率偏移會使子通道之間失去正交性，進而降低系統效能。不同於OFDM系統，OFDMA的上傳系統中，基地台（Base Station, BS）會同時接收多個使用者訊號，因而承受來自不同使用者的載波頻率偏移（CFOs），故會產生嚴重的子載波間干擾（ICI）與多用戶干擾（MAI）。在此情況下，BS無法對多個載波頻率偏移同時進行補償。為克服此困擾，本論文以區塊平行干擾消除法（Block Parallel Interference Cancellation）為基礎來消除MAI。由於區塊平行干擾消除法所得的MAI估計值仍存在相當的誤差，因此本論文提出MAI估計值加入權值的方法，以提高MAI估計值之精確度，進而達到有效補償CFOs的目的。實驗結果顯示，我們提出的方法可以有效改善CFOs。

關鍵字

正交分頻多工；正交分頻多重存取；載波頻率偏移；區塊平行干擾消除法

並列摘要

Orthogonal frequency division multiplexing (OFDM) has received much attention in recent years. Its version for multiple users, the orthogonal frequency division multiple access (OFDMA), has been considered a promising technique for next generation (4G) wireless communication system. However, a major problem encountered in OFDMA system is the loss of orthogonality due to carrier frequency offset (CFO), which may significantly degrade system performance. Moreover, in the uplink OFDMA system base station will receive CFOs from multiple users at the same time, which will result in serious inter-symbol interference (ICI) and multiple access interference (MAI), further degrading system performance. Therefore, base station is not able to compensate for CFOs simultaneously. To overcome this difficulty, this study mitigates MAI effect based on a block parallel interference cancellation technique. To increase the reliability of reconstructed signal, a weighting scheme is also proposed to effectively compensate for CFOs. Experimental results verify the effectiveness of the proposed method.

並列關鍵字

Orthogonal Frequency Division Multiplexing (OFDM) ； Orthogonal Frequency Division Multiple Access (OFDMA) ； Carrier Frequency Offset (CFO) ； Block Parallel Interference Cancellation (BPIC)

參考文獻

[1] J. A. C. Bingharm, “Multicarrier for Data Transmission: An Idea Whose Time Has Come,” IEEE Communications Magazine, pp. 5-14, 1990.

[2] H. Sari, G. Karam and I. Jeanclaude, “Transmission Techniques for Digital Terrestrial TV Broadcasting,” IEEE Communications Magazine, pp.100-109, 1995.

[3] B. Yang, K. B. Letaief, R. S. Cheng, and Z. Cao, “Timing Recovery for OFDM Transmission,” IEEE Journal on Selected Areas in Communications, pp. 2278–2291, 2000.

[4] I. Koffman and V. Roman, “Broadband Wireless Access Solutions Based on OFDM Access in IEEE 802.16,” IEEE Communications Magazine, pp. 96–103, 2002.

[5] L. Wei and C. Schlegel, “Synchronization Requirements for Multi-user OFDM on Satellite Mobile and Two-path Rayleigh Fading Channels,” IEEE Transactions on Communications, pp. 887–895, 1995.

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以干擾消除技術改善上行正交分頻多重存取系統之載波頻率偏移

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