在本論文中將把目標放在適合IEEE Std 802.16-2004中，固定式的實體層OFDM之時間和頻率的同步上。利用IEEE Std 802.16-2004所規範的preamble來校正時間和頻率的偏移，且考慮大範圍的頻率偏移對時間同步和頻率同步的影響，並提出適當的解決方法。由於preamble包含兩個訓練序列，其具有週期性，所以我們利用其特性做時間和頻率的同步。在載撥頻率為3.41325GHz，通道頻寬為1.75MHz的情況下，接收端將會遭受正規化後的大範圍頻率偏移其包括整數部分和小數部分的頻率偏移，本論文將分別對這兩個部分做頻率估測，模擬顯示其能得到不錯的效果。
由於大範圍的頻率偏移會影響到時間的同步，而使得誤報率上升，所以我們設定兩個門檻值，使誤報率下降，相對的我們必須等待較多碼框來換取同步的成功率。我們希望用戶端在一開機時能用較少的時間來同步，模擬結果顯示在SNR為12dB時平均需要約4個碼框，也就是80ms的時間便能夠得到精確的同步結果。另外我們將討論在頻率偏移小於0.5時，分別利用CP和pilots來做頻率估測的優缺點。

In this paper, time and frequency synchronization for OFDM systems using the preamble specified by the IEEE 802.16-2004 standard is studied. The concerned synchronization methods are suitable for fixed broadband wireless systems. The influence of large frequency offsets on time and frequency synchronization is considered, and a suitable solution is proposed in this paper. There are two periodic training sequences in the preamble which are employed for time and frequency synchronization. In the case of a carrier frequency of 3.41325 GHz and a channel bandwidth of 1.75 MHz, large normalized frequency offsets are induced in the receiver, including fractional part and integer part frequency offsets; both components are estimated separately, and simulation results show good performance.
Since large frequency offsets affect time synchronization, two threshold levels are set in order to decrease the false alarm rate, but more frames are needed to obtain a good tradeoff for the synchronization success rate. A short synchronization time is desired when the subscriber requests a connection. Simulations show that a synchronization time of an average of 4 frames, that is 80ms, is necessary to obtain acceptable performance with SNR = 12dB. Finally, for frequency offsets smaller than 0.5, estimation using the CP and pilots are simulated, and their advantages and drawbacks are discussed.

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