本文選題：自適應解調 + 無碼率��； 參考：《西安電子科技大學》2015年碩士論文

【摘要】：數字噴泉碼是一種無碼率碼,對原始數據分組進行編碼可以得到無限長的編碼分組序列,在接收端只要接收到略大于源數據包數量的編碼數據包就可以以很高的概率將源數據包恢復出來。利用噴泉碼的這種特性,將其與調制解調技術結合起來,形成一種新的自適應速率方案——自適應解調技術(ADM)。自適應解調技術在發(fā)送端采用較高調制階數和固定編碼方式,而在接收端依據當前信道狀況采用不同的解調速率。接收端只解調具有高可靠性的比特,而將可靠性低容易出錯的位看作刪除。自適應解調技術在保留了傳統(tǒng)自適應方案優(yōu)點的前提下又避免了它們需要反饋信道的缺點。本文主要研究了基于LT碼和Raptor碼的自適應解調方案,并給出一種低復雜度的新解調方式和自適應解調技術中刪除不可靠比特的三種實現方法,第一種是以符號為單位,在每個符號內選擇要刪除比特的判決域方式;第二種是在整個包內進行刪除的自由解調速率方式,該方式因為是在整個包刪除的,所以丟棄不可靠比特的可能性更大,系統(tǒng)性能得到提高;第三種是通過設定門限來實現,該方式通過仿真得到不同信道條件下對應的刪除似然比門限值,應用時只要將解調似然比值與該信道條件對應的門限值進行比較以決定刪除與否即可,而不需要像前兩種方式比較各個比特的似然比值相對大小,減少了比較運算次數。在本文中給出了自適應解調方案三種實現方式在加性高斯白噪聲信道下的詳細仿真,仿真表明在滿足目標性能的前提下,系統(tǒng)性能均有提高。
[Abstract]:Digital fountain code is a rate free code. At the receiving end, the source packet can be recovered with a high probability as long as it receives a bit more than the number of source packets. Based on this characteristic of fountain code, a new adaptive rate scheme, adaptive demodulation (ADM), is formed by combining it with modulation and demodulation techniques. The adaptive demodulation technique adopts high modulation order and fixed coding mode at the transmitter, and different demodulation rate at the receiver according to the current channel condition. The receiver demodulates only the bits with high reliability and treats the low reliability bits as error-prone. Adaptive demodulation technology not only preserves the advantages of traditional adaptive schemes, but also avoids their disadvantages of requiring feedback channels. In this paper, the adaptive demodulation scheme based on LT code and Raptor code is studied, and a new demodulation method with low complexity and three methods to remove unreliable bits from adaptive demodulation technology are given. Select the decision domain mode to delete bits within each symbol; the second is a free demodulation rate mode that deletes throughout the packet, which is more likely to discard unreliable bits because it is deleted throughout the packet. The performance of the system is improved, and the third method is realized by setting the threshold, which is simulated to get the corresponding threshold value of the deletion likelihood ratio under different channel conditions. In application, it is only necessary to compare the demodulation likelihood ratio with the threshold value corresponding to the channel condition to decide whether to delete or not, instead of comparing the relative size of the likelihood ratio of each bit like the former two methods, thus reducing the number of comparison operations. In this paper, the detailed simulation of adaptive demodulation scheme in additive Gao Si white noise channel is presented. The simulation results show that the performance of the system is improved on the premise of satisfying the target performance.
【學位授予單位】：西安電子科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TN763

【參考文獻】

相關期刊論文 前1條

1 何燕鋒,楊鴻文,郭文彬;高階調制的軟輸出算法比較[J];北京郵電大學學報;2003年01期

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本文編號：2106968