Research On Packet Loss Recovery And Relay-assisted Retransmission Based On Network Coding In Wireless Network

Due to the wireless transmission medium particularity,wireless network reliability transmission has become the important factor to affect and limit the transmission performance improvement.Network coding(NC)can take multiple information into consideration to recover the lost packets comprehensively,and recover the multiple requested packets simultaneously.NC technology can bring its superiority into full play in wireless broadcast network,wireless cooperative communication can effectively resist the multipath fading and extend network coverage.Furthermore network coding as the lower layer coding technology has the innate corresponding nature with cooperative communication.NC has become the new and effective approach to improve transmission capacity and reliability.For the single hop wireless network,one-source and one-relay wireless network,and multi-sources and multi-relays wireless network,based on NC the corresponding packet recovery algorithms,the recovery schemes and the relay cooperative transmission scheduling mechanisms are proposed.The main research work and achievement are concluded as follows.(1)Due to the packet loss distribution with the spatial and the temporal correlation in IP datacast over DVB-H(DVB-IPDC)system,an effective complete decoding retransmission algorithm based on network coding(ECDR-NC)is proposed based on the dynamic information updating,which can find the current most effective complete decoding packet.ECDR-NC can not only avoid the redundant encoding packets due to the overlapping among packets encoded,but also reduce the computational complexity compared with the traditional encoding schemes.Furthermore,the retransmission upper bound of ECDR-NC is fully controlled.In time-sensitive applications,to maximize the aggregate number of recovery packets meanwhile minimize the total number of discarded packets due to the time limit according to the priority preference,an efficient priority packet recovery based on network coding(EPNC)is proposed to find the maximum-weighted encoding packets sequence according to the decoding gains.The simulation results show EPNC is more efficient and more rational,and the average discarded packets ratios of EPNC can be reduced about 18%~27% compared with the scheme.Furthermore,the idea can be extended to other types of recovery channels,such as Wi MAX,Wi-Fi.(2)The current retransmission packet selection mechanisms based on opportunistic network coding face the problems of low retransmission efficiency and high computation complexity.To these problems,an optimized encoding packet selection mechanism based on opportunistic network coding in wireless network retransmission(OONCR)is proposed.This mechanism is based on the concepts of mutual exclusion packets and decoding gain etc.,makes full use of opportunistic network coding advantages,and takes the encoding packet local and global optimization problems into consideration to achieve the optimized encoding packets set.Retransmission efficiency is evaluated according to the computation complexity,the throughput,the retransmission redundancy ratio and the number of average retransmission.Under the various conditions,the simulation results show that the number of average retransmission of OONCR is mainly lower than that of other typical retransmission packet selection schemes.The average retransmission redundancy ratios of OONCR are low about 5%~40% compared with other typical schemes.Simultaneously the computation complexity of OONCR is comparatively lower than that of other typical schemes.(3)To the problems of retransmission packet selection scheme and the relay-assisted transmission mechanism,an optimized selective retransmission protocol(OSRP)is proposed to maximize transmission gain so as to minimize completion time in one-relay one-source wireless network.OSRP includes the optimized retransmission encoding packet selection scheme(OREPS)and the optimized weighted scheduling scheme(OWS).In the initial transmission stage,based on the research of OONCR and considered with the link status,OREPS adopts the simple set operation and controls the upper bound of the number of packets encoded reasonably,to select the optimized global encoding packets and reduce the algorithm complexity simultaneously.In the selective retransmission stage,OWS selects the optimal encoding node to realize the dynamical scheduling,and focuses on the destination requests to improve retransmission efficiency.Performance analyses are conducted from the simple to the general relay-assisted multicast network model in sequence.Furthermore according to the simulation results,the whole average completion time of OSRP is apparently lower than that of selective retransmission-weighted packet scheduling(SR-WPS).(4)Current scheduling reseach in multi-relays wireless network limits at single source with the same link status,and the sequential-forward scheduling is used usually.To realize multi-relays cooperation transmission for multi-sources information,an optimized priority scheduling scheme based on network coding(OPSNC)is proposed,and the main ideas of opportunistic network coding and random linear network coding are combined.Particularly the packets accepting state or the linear relation among the encoding vectors is taken as the important reason to the corresponding feedback information generated in different transmission stage individually.With the different link status,the effective information of each relay node and the link transmission reliability are taken into consideration comprehensively to complete the priority scheduling.Especially when the link status differences are different,the optimal forwarding node can be chosen adaptively to improve the information transmission efficiency.According to the simulation results,this scheme can effectively improve network throughput and reduce the number of retransmission compared with the traditional scheduling schemes.