| 摘要: | 隨著4G無線網路的到來，為了提升頻寬效益以及時間位元傳輸率對於無線通訊系統來說，經常利用正交分頻多工(Orthogonal Frequency Division Multiplexing, OFDM)的技術來做資料傳輸，因為OFDM系統子載波之間相互正交可以有效的節省頻寬，而且可以抵抗多重路徑通道的衰減，此技術已經應用在許多的通訊標準上；不過在OFDM系統上，使用者的個數增加使得頻寬效益以及時間位元傳輸率顯得非常重要。由於頻譜的重疊，假如沒有時間與頻率的同步，將會使OFDM系統效能失真，因此本論文將會探討雙通道中繼站時間同步的問題，並且利用扎德奧夫-朱序列(Zadoff-Chu Sequence)當作訓練符元來做時間延遲的估測。
傳統的單通道中繼站在傳輸資料時會分為四個時間點，傳送端會先將資料傳送到中繼站，中繼站再將資料送到接收端，接收端也會重複上述的動作完成雙方通訊。然而雙通道中繼站傳輸時只需要兩個時間點，也就是傳送端與接收端同時傳送訊號給中繼站，中繼站也會同時將兩個資料疊加後傳送回傳送端和接收端完成通訊，這說明了雙通道中繼站比單通中繼站在減少傳輸時間並且頻譜效益的提升都有很大的幫助。雙通道中繼站成為近幾年熱門研究的主題，由於雙通道中繼站會同時傳送兩方的資料，因此可以節省一半的傳輸時間來增加頻寬效益以及時間位元傳輸率。另外一個原因是在蜂窩網絡架構中，雙通道中繼站有許多未開發的潛力。
;Along with 4G wireless network, to promote effective bandwidth and transfer rate of bits , for wireless, we use the technique of Orthogonal frequency division multiplexing to transmit information frequently, because between subcarry of OFDM system orthogonal each other can not only save bandwidth effectively, but also defeat the fading of multipath channel. This system has already applied in many communication specifications. However, the users are increasing, so it’s very important about OFDM signal effective bandwidth and transfer rate of bits. Due to overlapped frequency spectrum, if the time and the frequency don’t synchronize, OFDM system will distort. Therefore, we will discuss the problem about time synchronization in two way relay network and use Zadoff-Chu Sequence as a training data to estimate time delayed in this paper.
Traditional one way relay will divide into four phases when it transmits data. Transmitter sends information to relay, and it will send information to receiver, and then receiver will do actions again to complete communications. However, when it transmits, two way relay only needs two phases. It means the transmitter and the receiver send information to relay at the same time, and relay will gather them, and send back again. We can know that it’s more useful about decreasing time transmission and increasing the bandwidth effectively than one way relay, two way relay becomes a popular research topic in few years. Because it transmits data to both sides, it can save half of transmitting time to increase the bandwidth effectively and transfer rate of bits. Moreover, it has many undeveloped potential in cellular network. |
