Research On The Transmission And Routing Performances Of Device-to-Device Opportunistic Communication

Due to the continuing development of personal communication technology, the Device-to-Device (D2D) communication pattern which directly builds up wireless links among mobile user nodes gradually shows its broad application prospects. D2D data transmission can improve the spectrum efficiency of cells, save the energy cost of mobile terminals and thus prolong their battery lifetime. As D2D devices become universal, the D2D opportunistic communication networks which are organized based on multi-hop links can realize stochastic data delivery and dissemination more widely, thus can relieve the increasing service load of cellular access networks. However, the real-time dynamic mobility patterns between D2D nodes directly determine the channel fading and packet loss performance of their wireless transmission, the social attributes of mobile users affects their mutual contact frequency and cooperative forwarding probability significantly, thus deciding the performance of D2D opportunistic delivery. Therefore, this dissertation chooses the aspects of wireless transmission via fading channel environment and opportunistic routing based on nodes’social relationship to launch our research focusing on the performance of D2D opportunistic communication.From the aspect of the wireless transmission between mobile nodes, we propose an optimal packet length selecting strategy based on the fading feature of Mobile-to-Mobile channel model. Through considering the impact of both packet loss due to channel fading as well as packet overhead on the payload data transmission performance, we give the expected time spent in transmitting unit payload which includes the cost of retransmission after packet loss. The throughput of payload transmission is maximized by selecting optimal packet length under certain condition. On such basis, we introduce Random Waypoint (RWP) mobility model which reflects the real-time varying feature of D2D nodes’moving velocity and deduce the fixed packet length which optimizes the transmission performance between D2D nodes that move with dynamic velocities under given RWP model. Corresponding simulation results verifies the rationality of theoretical deduction, which also shows that the payload data throughput between D2D nodes that transmit with optimal fixed packet length is close to the ideal performance bound that the packet length between communicating nodes can adapt to their changing velocities, thus can cope with most D2D mobile communication situations.From the aspect of D2D users’ social feature, we propose an advanced simulation modeling method for the routing D2D opportunistic communication. Such modeling method combines the social network distance and community division of any node pair that respectively reflects their micro and macro social attributes, decreasing their mutual contact frequency and cooperative forwarding probability as their social relationship is alienated. Simulation result shows that the distribution feature of node contact frequency resembles the same results gathered from real-world data trace. On such basis, we find that the introduction of social network structure greatly stratifies the mutual relationship and behavior feature of different node pairs and thus improves their opportunistic delivery performance. Both the intensity and distribution feature of node selfishness will significantly affect the average delivery ratio as well as delivery delay of opportunistic communication, the differentiation of node selfishness according to nodes’ relationships has positive effect on the delivery performance of the network in the presence of the node selfish behavior that is inevitable in real world. Hub nodes of the network, which undertake heavy relay mission, may play a more important role in forwarding activities under the model with social selfishness compared with unconditionally cooperative cases.