| On single-end to multi-ends communication,multicasting has smaller delay and larger system throughput than unicasting.Using traditional feedback and retransmission mechanism to achieve reliable multicast result in redundant feedback.Meanwhile,fountain code,as an erasure code,alleviates too much feedback effectively in the scenario of reliable multicast.Therefore,it is imperative to study the rateless fountain codes with low complexity and its applications on communication protocols.Firstly,this thesis analyzes and compares various erasure codes.Second,design the experiments of multicast transmission,compares and analyzes the throughput and other aspects of reliable multicast transmission based on fountain code compared with RS code,which provides a guideline for designing multicast protocol based on fountain code.Third,analyzed and tested the feedback mechanism and fountain code application of wireless multicast protocol.In order to increase the system throughput,this thesis analyzes and tests the feedback mechanism of wireless multicast protocol and the fountain code application,and designs a special fountain code suitable for multicasting and a feedback mechanism matching the fountain code.Finally,this thesis verifies and improves the wireless multicast system and multicast protocol in practical applications through physical testing.The main achievements of this thesis are summarized as follows.(1)Fountain code design for wireless multicasting.First,by analyzing and testing the complexity of encoding and decoding and the success rate of decoding of erasure codes,this thesis determines to design the fountain code based on Raptor10 coding structure.Then,a greedy algorithm based on hamming weight of row is proposed to select the degree distribution of fountain code and the construction method of coding matrix is given.Finally,a merging matrix method is designed,which can simplify the encoding and decoding process of fountain code to reduce its time overhead.(2)Wireless multicast protocol design.First,analyzed and tested the feedback mechanism and parameter setting method of NORM protocol,and pointed out that NORM protocol cannot take advantage of fountain code.Then,based on the NACK,a feedback mechanism with a smaller collision probability is designed by delaying the time for receivers to send feedback information.Finally,using NACK information,a greedy algorithm based on packet loss rate is proposed to adaptively adjust coding parameter,and finally a wireless multicast protocol matching the fountain code is got.(3)Implementation of wireless multicast protocol.The software framework of wireless multicast protocol was designed and the compilation and debugging of the program of encoding and decoding was completed.In addition,a wireless multicast transmission platform was constructed based on Raspberry Pi,and program testing was completed on it.The test results show that the wireless multicast protocol designed in this thesis can support single-end to multi-ends transmission,and when the number of receivers is 50,the throughput is 449.76% higher than TCP protocol and 175.88%higher than NORM protocol.The results of this thesis are embodied as a set of wireless multicast transmission programs with independent intellectual property rights,the programs can achieve better performance in actual air interface tests,which lays the technical foundation for the standardization of the wireless multicast protocol. |
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