正交分頻多工系統之協調多點傳輸環境技術之下，當使用者位於蜂巢系統裡的單位細胞邊界的時候，利用多個基地台或是中繼站使用相同的頻帶，並且同時間傳送相同的訊號給使用者，可以有效改善接收端的訊號性能。但是實體應用上，因為正交分頻多工系統容易受到載波偏移量的影響而造成載波之間互相干擾（ICI），導致正交性被破壞掉，使系統效能嚴重的變差，所以載波偏移量的估測與補償是必須的！然而傳統的載波偏移估測技術並不適用於多點傳輸環境，那是因為不同的傳送端都使用相同的頻帶，所以基地台彼此之間也會有互干擾的問題。因此我們設計出一種訓練序列，根據設計的方法給予數個傳送端不同的訓練序列，能夠讓彼此的互干擾達到最小，再有效的利用最大概似估計（ＭＬＥ），進而求的每個載波偏移量。最後為了讓系統效能更好，我們提出利用反覆性的消除干擾的演算法，根據模擬的結果，的確可以達到沒有互干擾的效果。

Orthogonal frequency division multiplexing (OFDM) combining with the coordinated multi-point (CoMP) transmission technique has been proposed to improve the performance of the receivers located at the cell border. However, the inevitable carrier frequency offset (CFO) will destroy the orthogonality between subcarriers and induce strong inter-carrier interference (ICI) in OFDM systems. To relieve the performance degradation, CFO estimation and compensation is essential. However, with the CoMP technology, the conventional CFO estimation schemes are not practical because of mutual interference between the signals from different transmitters. In this paper, we propose a maximum likelihood (ML)-based estimator for the estimation of multiple CFOs, and design the training sequences that are robust to different values of CFOs. To further improve the performance, we also propose an estimation algorithm that incorporates iterative interference cancellation. According to the simulations, our scheme can achieve the mutual interference-free performance.

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