本論文將探討2G與3G系統共站時，可能發生的干擾情形；並使用合理的頻率規劃方式，降低干擾的影響；最後評估干擾對系統影響的程度。
　　由於使用的頻率規劃方式，避免2G的鄰頻干擾與第三階互調變干擾，因此在論文中只討論3G系統的干擾情形。3G系統分別有3個頻率(f1、f2及f3)，3G的頻率配置方式首先是先全面配置f1，接著在較多人使用的地點配置f2或/及f3；本論文中討論的3G頻率分配情形分為五種：(1)全部細胞只配置頻率f1，(2)選擇一個細胞同時配置頻率f1及f2，(3)選擇一個細胞同時配置頻率f1及f3，(4)全部細胞配置頻率f2，再選擇一個細胞配置f3，(5)選擇一個細胞同時配置三個頻率。造成干擾的情形有接收端的互調變失真、傳送端的互調變失真、鄰頻干擾及同頻干擾，在本論文中將分別討論。
　　論文模擬計算各種干擾造成的Eb/No值，藉此表示各種干擾造成的影響程度，主要結果如下：
1. 經由Okumura–Hata的路徑損失模式，計算出可接受的路徑損失，再算出細胞範圍為680公尺，論文中手機與基地台間的距離是以10 – 600公尺作亂數分配。
2. 第三階互調變干擾的部分，上鏈的部分是基地台的接收型互調變失真，計算出第三階互調變干擾訊號的功率，基地台收到訊號的Eb/IIMD相當大，因此推論影響很小；下鏈包含基地台傳送端及手機接收端的互調變失真，計算手機收到訊號的Eb/IIMD也相當大，因此推論影響很小。
3. 在上鏈中，未作功率控制的狀況時，手機皆以最大功率傳送訊號，造成所謂的Near – far效應，因此每支手機傳送的訊號皆無法達到基地台所需的Eb/No臨界值，經過粗略的功率控制後，便可滿足Eb/No的臨界值，可見功率控制在上鏈的重要性，可透過功率控制增加可使用服務的手機數目。
4. 在下鏈中，討論的最壞情形是在邊界的手機，同樣不作功率控制，基地台以最大功率傳送訊號，發現位於邊界的手機還可以使用，下鏈的功率控制用於控制細胞的大小，當細胞外圍都沒有手機時，基地台可以降低功率，對鄰近細胞的干擾便會減小，對可使用服務的手機數目影響不大。
5. 功率控制是相當重要的課題，本論文中主要討論最壞情況，只做粗略的功率控制作比較，但由上鏈的同頻/鄰頻干擾的結果可看出功率控制的重要性，實際情形3G手機每秒作1500次的功率控制，功率控制的議題可作為後續的研究。

　　In this thesis, we will discuss the possible interfering situation when 2G and 3G systems are co-sited, and then use the reasonable frequency planning to reduce the extent that the interference cause, and finally evaluate the effect of the interference in the system.
　　Because of our frequency planning method, we will consider only the interference in 3G system. We will discuss the worst case, and in 3G system we assume 5 situation such as A. assigning f1 to all cells, B. choosing one cell to assign f2, C. choosing one cell to assign f3, D. assigning f2 to all cells and then choosing one cell to assign f3, and E. choosing one cell to assign f1, f2 and f3. Interference includes the third-order intermodulation distortion, the adjacent channel interference and the co-channel interference. We simulate the Eb/No values that result from the interference. Our main results can be summarized by the following 5 points:
1. By the Okumura–Hata model, we calculate the acceptable loss path, and then calculate the cell range about 680 m. The distance between the mobile and the base station is the random distribution in the range of 10–600 m.
2. The signal powers of the 3rd intermodulation distortion in uplink and downlink are far lower than the wanted signal power, so we infer the effect is very small.
3. In uplink, without power control, all mobiles use the largest power to send signal, and it will cause near – far effect. In the situation, the Eb/No values of all signal power the base station receives can not exceed the threshold. When we do the rough power control, the signal will satisfy the Eb/No. It means the importance of the power control.
4. In downlink, the worst case is the mobile at the cell border, without power control, and the base station use the largest power to send signals. Then we find that the mobile still can use, meaning that the Eb/No value is more than the threshold of the mobile. The power control in downlink is used to control the cell range. When there is not any mobile at the border, base station can use less power to send signals, and reduce the interference to other adjacent cells.
5. From uplink situation, we can know the power control is an important topic. In fact, the 3G mobile has power control by 1500 times per second. Power control can be the following researching topic.

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