在無線通訊系統中，所有無線傳輸通道是共享的，所有傳輸出去的訊號如同廣播，能讓不同接收端所接收。使用合作式通訊技術，來源端利用無線傳輸特性，傳輸訊號至中繼端與來源端，再藉由中繼端轉送資訊到目的端，讓來源端透過不同傳輸路徑傳輸資料至目的端，能使傳輸失敗的機率大幅降低。
合作式通訊系統中，中繼端不只單純轉送接收的資訊，在傳送前能對資訊位元加以處理。在我們所提的系統中，中繼端只能傳送高可靠度的資訊，而低可靠度的資訊不會被傳送，藉由此機制，能避免系統錯誤蔓延現象發生。由於目的端收到來源端與中繼端的訊號，透過機率式決策熔合方式將兩端訊號結合，使目的端能做出適當決策， 得到所要訊息。我們也試著分配傳輸功率於來源端與中繼端，促使系統位元錯誤率更小。但若透過模擬方式，找出系統最佳篩除範圍與功率分配方式相當耗時。已知通道響應前提下，藉由無通道編碼之合作式傳輸系統，我們推導出計算式得到平均位元錯誤率，其計算得到的錯誤率與模擬結果相當符合。在相同通道響應情況下，利用得到的最佳篩除範圍與功率分配係數，我們試著把這些參數套用在使用渦輪碼之系統架構。由模擬結果可知，其篩除範圍與功率分配方式皆與無使用通道編碼之系統相似，皆能得到最低位元錯誤率。因此本論文的主要貢獻是利用計算式能夠快速找到在最低平均位元錯誤率時之最佳篩除範圍與功率分配方式，再套用於渦輪碼之系統中，免除透過模擬找出最佳參數時耗費的時間。

In wireless communication, the channel is shared by many receivers because the message is broadcast over the entire coverage area. In a cooperative system, the source node broadcast data to the relay node and the destination node. Then the relay forwards the received signal to the destination. This transmission technology can reduce the probability of missing data.

In DF (decode and forward) cooperative systems, the relay node not only forwards the received signal to the destination but also has the ability to process this signal before retransmitting it. In the proposed scheme, first the relay checks the reliability of the received signal. Then it relays the data bit to the destination only if the reliability is high enough. Otherwise, the data bit is censored. In other words, it is not transmitted at all. By using this method, error propagation phenomenon is reduced. Because the destination gets the information from both the source and the relay, probabilistic decision fusion is used to fully exploit that information. We also try to allocate the power assigned for the source node and the relay node, so that the system bit error rate(BER) is minimized.

Finding the best censoring range and power allocation by using simulation is very time-consuming. We assume that channel state information is perfectly known. First we derive the formula to calculate the bit error rate of the cooperative system without turbo codes. We compare the numerical results with simulation results. Simulation result almost matches the bit error rate that is calculated by the derived formulas. Then we use turbo codes in cooperative system. The system performance has the similar trend as the one without turbo codes. By using the derived formulas, the best censoring range and power allocation can be found efficiently. This result is then used in the system with turbo codes. The extremely time-consuming simulation is avoided.

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