A Mechanism Of Enhancing Multi-hop Device-to-Device Communications By Network Coding

With the evolution of mobile Internet,the future mobile communication system will focus on improving reliability,reducing latency and should provide fast access and continuous network services.To meet these challenging requirements,relay-assisted multi-hop Device-to-Device communications can be applied.It forms a major part of future mobile communication system,which can increase network capacity and brings multi-hop gain.In the multi-hop D2 D communications,the traditional storage and forwarding method will make the network forward the same data packet over and over again,and this makes the transmission bandwidth cannot be effectively used.In contrast,network coding technology using the intermediate nodes to encode and forward the received data packets can eliminate the correlation between the data packets to improve the forwarding efficiency.To further improve the performance of D2 D communications,the effect of network coding on multi-hop D2 D performance is studied in this thesis.The main contributions of this thesis are as follows.Firstly,this thesis summarizes existing work and shows the advantages and disadvantages of common network coding techniques such as physical layer network coding,analog network coding,instantly decodable network coding,random linear network coding(RLNC)and space-time analog network coding.The scenarios that each of network coding techniques can be applied is discussed.The impact of network coding on multi-hop D2 D communications performance is studied for specific scenarios such as cooperative communication,hotspot area,delay sensitive network,mobile cloud,content cache network and public security communication.Secondly,this thesis formulates the multi-hop D2 D communications system model based on RLNC and analyzes the establishment stage of a multi-hop D2 D session and studies the data packet coding and decoding method and packet forwarding process based on RLNC.The multi-relay assisted bidirectional D2 D communications process based on RLNC is simulated by using MATLAB.After that,the thesis establishes the relation from link outage probability to packet loss probability,and then analyzes the end-to-end packet loss probability and compares it against that without network coding.Finally,the model is verified by simulation experiments.The simulation results show that the network coding can improve the system capacity,reduce the frequency of data transmissions in multi-hop D2 D communications compared with the traditional storage and forwarding method and the end-to-end packet loss probability with network coding is slightly lower than that without network coding.Thirdly,the performance of retransmission mechanism based on network coding is studied.In multi-hop D2 D communications,the traditional data retransmission method cannot make the best use of transmission bandwidth.To solve this problem,this thesis researches the retransmission mechanism based on XOR operation and RLNC,and gives general expression of the average number of data transmissions for data retransmission mechanisms with and without network coding.The simulation results show that the retransmission mechanism based on network coding can greatly reduce the frequency of data retransmissions,and the performance of the retransmission mechanism based on RLNC is better than that of XOR operation.This thesis analyzes the application of network coding in multi-hop D2 D communication.It is shown that the network coding can increase the capacity of multi-hop D2 D communications system,reduce the end-to-end packet loss probability and improve the performance of data retransmission in multi-hop D2 D communications.