Research On High Efficient Hierarchical Transmission Fountain Coding

With the rapid development of wireless communication technology,the number of users increased dramatically,which led to a variety of problems.First,the dramatic increase in number of users makes the wireless spectrum resources shortage more severe.Second,as the network structures are more and more complex,it is more difficult to ensure the reliability and efficiency of data transmission.The increase in the number of users also increases service category,which leads to many kinds of reliability and timeliness requirements for various kinds of data.To ensure the efficient and reliable transmission of all kinds of data,the hierarchical transmission schemes are needed,where the hierarchical transmission indicates in which scheme the data are divided into various levels to be transmitted,each level corresponding to a different reliability or timeliness requirement.To ensure the efficient and reliable transmission of various kinds of data in wireless communication systems,this thesis attempts to design high efficiency hierarchical transmission fountain coding schemes based on LT codes.The research in this thesis starts from the following issues:Firstly,as the definition of moment when decoding process of LT codes are finished is not clear,which makes the decoding overheads hard to be determined.Hence,a method has been proposed in this section to determine the optimal decoding overhead of LT codes.This method is based on the idea of spectral efficiency for traditional forward error correction codes.By proposing the concept of recovery ratio per symbol and proving that there exists only one maximum value of recovery ratio per symbol,a LT code with the overhead corresponds to the maximum value can provide optimal transmission efficiency,which is defined as optimal decoding overhead of LT codes.The concept of optimal decoding overhead can be used to design fountain coding schemes by quantifying the transmission efficiency of LT codes with a numerical method,and provides theory basis to improve the transmission efficiency of fountain coding schemes.Secondly,as the existing analysis methods of LT codes evaluate the symbol error rates not enough accurately and hard to be used to quantify the BP decoding process of LT codes,a novel analysis method named stage evolution analysis is proposed.The stage evolution analysis can quantify the BP decoding process of LT codes by dividing the serial BP decoding process into a parallel version,which makes all the complex decoding parameters quantifiable.The stage evolution analysis can evaluate the symbol error rates of LT codes more accurately than the other existing ones,and can be used to design the fountain coding schemes with hierarchical transmission capabilities.Thirdly,to overcome the low transmission efficiency due to the various reliability requirements of data on single source conditions,the class of edge constraint UEP-LT codes is proposed,which can provide both unequal error protection and low overhead properties.By using the idea of stage evolution analysis,we analyze how the output symbols with various degrees can influence the decoding performance of LT codes,and summarize the origin of unequal error protection and low overhead properties.After that,a class of fountain codes named edge constraint UEP-LT codes is proposed.In an edge constraint UEP-LT encoding process,the selection probabilities of each block are divided by a special degree,and two different design rules are assigned for selection probabilities in the the two sides.Finally,the selection methods and the special degrees are given by numerical derivation,so that the edge constraint UEP-LT code can improve the overall transmission efficiency while guarantee that all kinds of data are transmitted according to their reliability requirements.Fourthly,aimed to solve the problem of low efficiency of timeliness hierarchical data transmission in single source conditions,the staged growth codes are proposed,which can provide low overhead property as well as guarantee the timeliness hierarchical transmission.Firstly,the unequal timeliness requirements are divided into two kinds,then the drawbacks of the existing fountain coding schemes which can provide these two kinds of unequal timeliness requirements are analyzed.By quantifying the origin that how output symbols influence the recovery time property using the idea of stage evolution analysis,the staged growth codes are proposed.Staged growth codes have a staged encoding process,and each stage has its own unique coding scheme.The staged growth codes can provide intermediate performance,unequal recovery time and low overhead properties,which make such codes capable to improving the transmission efficiency of timeliness hierarchical data transmission in the single source conditions.Finally,a class of UEP-LT codes with low overhead property is proposed to overcome the large overall decoding overhead of the existing distributed UEP-LT codes,hence improved the transmission efficiency of reliability hierarchical networks.The proposed codes are also easier to be designed than the existing ones.Firstly,the two classes of existing distributed UEP-LT codes are introduced and analyzed in this section.By summarizing and analyzing the disadvantages of such existing codes,and considering the concept of optimal decoding overheads,an important phenomenon that the EEP-LT codes can provide lower optimal decoding overheads than all the class of UEP-LT codes is found.For this reason,a new class of distributed UEP-LT codes with EEP-LT sub codes for all nodes is proposed.The proposed codes are termed as low overhead distributed UEP-LT codes because they can provide lower overall decoding overheads than the other existing classes of distributed UEP-LT codes.Therefore,the proposed codes can be used to improve the transmission efficiency for the networks with reliability hierarchical transmission requirements.