Efficient Retransmission Approaches Based On Network Coding For Wireless Multicast

Wireless communication is one of the most important means of communication in the Internet of things and mobile Internet systems.With the development of social economy,science and technology,especially with the continuous improvement of the level of information technology,the application of wireless communication and wireless network in various fields is more and more widely.Multicast is one of the most commonly used methods of data transmission in wireless communication.In wireless multicast communication,the wireless channel is susceptible to interference,attenuation,fading and unreliable time-varying,which often leads to high bit error rate at physical layer,and poor wireless link quality.In such a case,the transmission of the data packet can be easily destroyed,thus affecting the transmission efficiency.In order to improve the reliability and efficiency of wireless data transmission,the retransmission technologies have been the subject of research in recent years.Among them,wireless retransmission based on network coding(NC-R)has now been one of the hot research topics because of its advantages of throughput performance.Although NC-R has brought so many advantages,it also brings lots of new problems and difficulities,such as the coding method,coding strategy and coding timing,etc.Hence,it is urgent to design efficient coding mechanisms to improve the retransmission efficiency,and to ensure the superior performance of coded retransmission in various wireless multicast scenarios.Under this background,based on the idea of joint optimization,relay cooperation and so on,this paper is concerned with the efficient NC-R approaches in wireless multicast.The main content of the research is to find the optimal network coding combination of the lost original packets and to maximize the gain of each retransmission,thus to reduce the number of retransmission,while maintaining the low complexity of the algorithm.The main work is summarized as follows:1.A variety of network coding techniques used in wireless multicast NC-R approaches are investigated and summarized,including the basic concepts and their evolutions.Then,the current research status and progress of wireless retransmission based on opportunistic network coding(ONC-R)are reviewed and outlined from the aspects of encoding and decoding optimization,delay constrained optimization,weighted link quality,etc.This will help the future researchers to understand the background of the topic systematically and quickly.2.The joint optimization method of coding and decoding for wireless multicast retransmission is investigated to improve the coding efficiency.According to the joint optimization of coding and decoding,the network coding problem of the lost packets is exposed,and an ONC-R approach based on hash neighborhood association search is proposed.This novel approach adopts the mechanism of hash neighborhood association search with joint decoding of a plurality of encoded packets.On one hand,the coding opportunities between the maximized decoding combinations of the lost original packets are further excavated.On the other hand,the receivers are allowed to recover their lost original packets from multiple encoded retransmission packets,in addition to recovering the lost original packets from the full rank encoded retransmission packet.In this sense,the coding efficiency and transmission performance are improved,and the number of retransmission is reduced,while keeping a lower algorithm complexity.On this basis,in order to improve the possibilities of successfully delivering the encoded retransmission packets,the online quality of wireless link is introduced into the selection calculation of the encoding combination,and a weighted optimization algorithm is proposed.The new method makes the decodable combinations of the lost original packets,which own the maximum encoding gain and can allow more receivers to recover the lost original packets,have a priority of retransmission.This results in the further improvement of the transmission efficiency.3.The efficient retransmission approach which is appropriate for the wireless multicast conditions,such as channel mutation,continuous packet loss and so on,is investigated.Since the source node is always used to implement packet retransmission in the conventional NC-R approaches,retransmission loss will be very serious because of the the damaged link qualities when the channels between the source node and some of the receivers are interfered,and continuous packet loss will lead to a sharp decline in performance.Based on the idea of cooperative retransmission,an efficient network coding based opportunistic relay retransmission approach is proposed.In this novel approach,firstly,the best suitable receiver whose channel qualities are better than the source node is dynamically selected as a relay,then it replaces the source node to implement packet retransmission to get better transmission efficiency.Online link quality estimation is obtained by network measurement,while opportunistic relay selection is based on the principle of clustering and nearest combination of the receivers.This approach can also be applied to the wireless multicast network where one or more of the receivers are in the position of "relay node".Compared with the existing NC-R approaches,the proposed approach has made a better use of the online network resources to improve the transmission efficiency.Theoretical analysis and simulation results verify the effectiveness of the proposed method.4.The continuous and dynamic NC-R mechanism is investigated to provide more optimal coding possibilities.Aim to solve the problems caused by packet transmission in generation and intra-block coding,such as the waste of coding opportunity,the difficulty to achieve the maximized efficiency of each retransmission packet,etc,a dynamic and continuous retransmission approach based on opportunistic network coding is proposed.By continuous transmission of the first buffer and subsequent packet-by-packet transmission of the original packets,the proposed approach ensures sufficient optimal coding opportunities.Retransmission is implemented instantly after the transmission of each original packet.Note that only the optimal or maximized combinations of the lost original packets are permitted to be retransmitted in each retransmission.Thus it can maximize the gain of each retransmission.The conditions for the retransmission of the maximized combination of the lost original packets are provided both for none-real-time and real-time applications.Compared with the classical retransmission approaches,the proposed approach has a better throughput performance and easiness to achieve delay control,while has no special requirements for the data buffer.However,the continuous coding process will increase the processing burden of the nodes,thus efficient hash Hamming search algorithm is provided to support this approach.When the number of receivers is small and the data transfer buffer is large enough,the novel approach has obvious advantages in the retransmission efficiency.Finally,mathematical analysis and simulation are given to demonstrate the effectiveness of the proposed method.