Frequency Domain and Time Domain Approaches for Frequency Synchronization and Interference Reduction in MC-CDMA Systems

[[abstract]]在本報告中，我們先證明 ICI-自我消除法對 QAM- OFDM 系統無效，因為載波頻偏移誤差會導致訊號位置的旋轉。接著我們提出基於 ICI-自我消除法的決策回授估測機制執簡單而且耗費頻寬的頻偏移估測與追蹤。這個方法用供 ICI-自我消除的傳送訊符進頻偏移估測初值計算，接著本機制換至追蹤模式以執頻偏移變動的估測。最後將微調好的估測值用於 ICI-自我消除法中同時進訊號位置的旋轉校正與 ICI 消除。模擬的結果顯示我們所提出的機制允許頻偏移的變動達 9%。同 OFDM 接收機位元錯誤值模擬的結果亦證實我們的機制有效。[[abstract]]The Intercarrier interference (ICI) self-cancellation schemes cannot apply to QAM-OFDM systems due to a constellation rotation caused by carrier frequency errors. We propose a decision feedback estimation (DFE) scheme based on the self-cancellation scheme to perform a simple and bandwidth-efficient estimation and tracking of the frequency offsets. The transmitted data symbols employed for ICI cancellation allows an initial estimation of frequency offsets. Then the scheme switches to the tracking mode to carry out an estimation of deviations in the frequency offset. Finally this fine-tuned estimate is applied to the ICI self-cancellation scheme for concurrently correcting the constellation rotation and reducing the ICI. Simulation results showed that our scheme allowed a random variation in the frequency offset up to 9%. Numerical examples in bit error rate performance evaluations of various OFDM receivers proved the effectiveness of the proposed scheme.[[note]]NSC92-2213-E327-00