基于喷泉码的自适应解调技术研究

发布时间：2018-07-08 09:22

本文选题：自适应解调 + 无码率　；参考：《西安电子科技大学》2015年硕士论文

【摘要】：数字喷泉码是一种无码率码,对原始数据分组进行编码可以得到无限长的编码分组序列,在接收端只要接收到略大于源数据包数量的编码数据包就可以以很高的概率将源数据包恢复出来。利用喷泉码的这种特性,将其与调制解调技术结合起来,形成一种新的自适应速率方案——自适应解调技术(ADM)。自适应解调技术在发送端采用较高调制阶数和固定编码方式,而在接收端依据当前信道状况采用不同的解调速率。接收端只解调具有高可靠性的比特,而将可靠性低容易出错的位看作删除。自适应解调技术在保留了传统自适应方案优点的前提下又避免了它们需要反馈信道的缺点。本文主要研究了基于LT码和Raptor码的自适应解调方案,并给出一种低复杂度的新解调方式和自适应解调技术中删除不可靠比特的三种实现方法,第一种是以符号为单位,在每个符号内选择要删除比特的判决域方式;第二种是在整个包内进行删除的自由解调速率方式,该方式因为是在整个包删除的,所以丢弃不可靠比特的可能性更大,系统性能得到提高;第三种是通过设定门限来实现,该方式通过仿真得到不同信道条件下对应的删除似然比门限值,应用时只要将解调似然比值与该信道条件对应的门限值进行比较以决定删除与否即可,而不需要像前两种方式比较各个比特的似然比值相对大小,减少了比较运算次数。在本文中给出了自适应解调方案三种实现方式在加性高斯白噪声信道下的详细仿真,仿真表明在满足目标性能的前提下,系统性能均有提高。
[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.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN763

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