Research On User Cooperation Technologies Based On Network Coding In Multicast System

Due to the unreliability of wireless link,users' packet losses are hard to avoid in wireless multicast system,which will lead to a decline of multicast service.By recovering users' lost packets through cooperative communication among users,user cooperative retransmission has been considered as an effective scheme to solve the problem of packet loss.This scheme not only alleviates the retransmission pressure of the source node,but also has the advantage of high transmission efficiency due to the high reliability of user links.By allowing users to encode multiple packets,network coding has high efficiency in packet transmission process.Using network coding in user cooperative retransmission can further improve the transmission efficiency.In this thesis,user cooperation technologies based on network coding in multicast system are studied.The main work is summarized as follows.1.By introducing network coding to sector ring clustering scheme,two novel sector ring clustering schemes based on XOR-based network coding(XOR-NC)and random linear network coding(RLNC)are proposed respectively.The transmission efficiency and energy consumption of the proposed schemes are also analyzed.Simulation results show that the proposed schemes have higher transmission efficiency and lower energy consumption compared with the original ring clustering scheme.2.Focusing on the problem that high transmission efficiency is always incompatible with low optimization complexity or low computation overhead in the existing user cooperation schemes based on network coding,the hybrid network coding based cooperative peer-topeer repair(HNC-CPR)scheme is proposed.HNC-CPR scheme split the lost packets into high rareness part and low rareness part.For these two parts,RLNC and XOR-NC are applied,respectively.Theoretical analysis and simulations show that the proposed HNCCPR scheme reduces the optimization complexity and computational cost in comparison with the existing schemes.3.Through the application of diversity technique in group cooperation scheme,a novel group cooperation scheme based on transmit diversity is proposed.In the proposed scheme,each user combines signals from multiple retransmission users,to reduce the signal attenuation caused by rayleigh fading.Simulation results show that the proposed group cooperation scheme has lower power consumption compared with the original group cooperation scheme.4.By using network coding in group cooperation scheme,two group cooperation schemes based on network coding are proposed.In the proposed schemes,in order to improve the transmission efficiency,the transmitters of each group encode the packets to be sent by using XOR-NC or RLNC.Simulations show that the proposed schemes have lower energy consumption than the original group cooperation scheme.