Research On Optimal Channel Access Method For Distributed Wireless Multicast Networks

As an important direction of wireless network technology,distributed network has the characteristics of flexible networking and strong anti-destruction ability,which has a wide range of applications in the construction of intelligent clusters.Compared with the centralized network,distributed network doesn’t require central nodes to manage user channel access,and the networking overhead is lower.However,there is competition among multiple users in distributed networks,which affects the channel access efficiency.The high time variability of the wireless link further exacerbates the inefficiency problem.Therefore,it is necessary to investigate the new distributed network channel access method to achieve efficient channel access by jointly designing the physical layer and the access control layer of the wireless networkMulticast communication technology is an effective way to improve channel access efficiency.When multiple users in a distributed network request the same data,multiple links are formed from the source to multiple destinations,that is,multicast communication.Multicast communication utilizes the broadcast characteristics of wireless channels to allow multiple users to transmit information on a shared channel,lead to a significant improvement in channel access efficiency.Compared with unicast communication,the design of multicast communication networks are more complicated.On the one hand,due to channel fading caused by multipath effect and building occlusion,users in the same multicast group experience different channel states,resulting in differences in channel access rates between users.On the other hand,it is difficult for multiple sinks to feedback channel state information to the source in time,which leads to the lack of reliability guarantees for transmission between sources and destinations.How to design a distributed channel access method based on multicast communication is of great significance and technical challenges.The main work of this thesis include three parts,which are described as follows:(1)To address the low spectrum utilization issue of the distributed network due to multiuser collision and channel time-varying nature,we investigate the channel-aware access problem for reliable multicast communication in a wireless network.Based on the optimal stopping theory,a statistical model of distributed channel access under wireless multicasts is established,and an optimal channel access method in terms of average system throughput under reliable communication is proposed.In it,the winner source determines whether to access the shared channel by comparing the availably reliable multicast rate with a pure threshold.Theoretic optimality of the method is proved rigorously.and the corresponding algorithm in low complexity is designed for system implementation.The effectiveness and efficiency are verified by numerical results.(2)To solve the problem that the service diversity in the wireless network restricts the overall performance improvement of the network,we investigate the distributed channel access problem for service-characteristics-aware reliable multicast communication network,based on Enhanced Distributed Channel Access(EDCA)mechanism and optimal stopping theory.The method we proposed achieve optimal average system throughput by utilizing the time diversity of wireless links between multicast groups and the diversity of network service characteristics.The numerical results verify the effectiveness of the proposed method.Compared with other access methods,the proposed method can significantly improve the network throughput performance.(3)To address the bottleneck problem of network throughput caused by reliable multicast communication,combined with the diversity of multicast network channels,we further investigate the channel access method under the constraint of transmission reliability probability.We also analyze the interaction between network throughput and reliable probability constraints.Numerical results demonstrate the effectiveness of the proposed theoretical method and the performance gain of the proposed method compared with other channel access methods is given.