Research On Data Transmission Schemes Based On Rateless Codes In Unmanned Aerial Vehicle Networks

Unmanned aerial vehicle(UAV)network is one of key technologies in the present world,and UAV communication plays an important role in constructing stable UAV networks.In the future,it will be a common case that several classes of UAVs work for different tasks in the air and UAVs keep connection to lowearth-orbit(LEO)satellites.Thus,UAV communication systems are required to be reliable,flexible,and robust to large round-trip time(RTT)and fluctuating packet error ratio(PER).Rateless code,known as a flexible technology providing reliable transmission,is suitable for future UAV networks.Therefore,it is significant to investigate transmission schemes based on rateless codes in UAV networks to combat the difficulties.This dissertation aims to solve the communication problems in future UAV networks and the outline is formed as follows.Performance analysis is first conducted in UAV networks.Transmission schemes based on rateless codes are then designed for random access and data transmission,respectively.The detailed research contents are described as follows.In the first part,asymptotic performance and transmission efficiency are analyzed by considering the features of UAV network.In asymptotic analysis,the interference nodes in distributed UAV networks are considered,and the asymptotic performance is analyzed in rateless coded random access systems over erasure-slot channel and Gaussian-slot channel,respectively.Numerical results show that the rateless coded random access scheme has better asymptotic performance than the scheme based on fixed codeword set.In transmission efficiency analysis,rateless codes are analyzed with limited buffer size and general arrival process.A queue model of rateless coded systems is established as a two-dimension Markov chain model.Numerical results show that rateless code is able to achieve higher efficiency in UAV-satellite links.In the second part,the requirement of reliable random access in UAV networks is considered,and the rateless coded random access scheme is proposed.Based on the conclusion of the first part,the Raptor coded random access model is established.A modified successive interference cancellation algorithm,which reduces significantly the complexity with negligible performance loss,is proposed.Then,a three-step optimization process is proposed following the thread of estimation of number of slots,optimization of access probability and design of access approach.Numerical results validate the accuracy of estimated number of slots and show that the proposed random access scheme outperforms the existing schemes,which indicates that rateless codes can help to achieve reliable random access in UAV networks.In the third part,high-rate transmission in UAV networks is considered,and radio link control scheme based on rateless codes is investigated.Guided by the results of the first part,relative-entropy-based fountain(REF)code is proposed to utilize the feedback message on radio link control layer.REF code is proved to have excellent intermediate performance and low overhead.REF codes are also extended in multicast scenarios and modified over imperfect feedback channels to apply to UAV networks.Furthermore,REF coded RLC scheme is proposed in UAV communication links to preserve the advantage of both ARQ and rateless codes.Numerical results show that compared with the existing RLC scheme,REF coded RLC scheme brings a little improvement in terms of throughput in UAV-to-UAV links,and brings significant improvement in UAV-to-satellite links,which indicates that REF coded RLC scheme can provide efficient transmission in UAV networks.