Research On Mobility-aware Content Transmission Mechanism In Vehicular Networks

As Adam Smith said in The Wealth of Nations, "transportation accounts the greatest of all improvement". Along with the increasing importance of the automobile in people’s daily life, the realization of intelligent transportation system (ITS) has been referred to an unprecedented height. With the goal of an optimized resource utilization on the passen-ger, vehicle, and road, ITS is essential on the national economic development. For most vehicular applications, the reliability, validity, and stability of the communication system should be first guaranteed.This dissertation conducts a research on the mobility-aware content transmission mechanism for vehicular networks, including "model construction","mechanism de-sign","theoretical analysis",and "performance evaluation". The innovation of the dis-sertation mainly includes:1) The dissertation proposes a theoretical model that provides the mathematical expres-sions on the link duration to better represent the effect of the vehicular motion cor-relation and the channel fading correlation on the radio link characteristic. Based on a two-dimensional discrete Markov chain model, the time/space correlations are modeled as the transitions between different transceiver distance states, and then the probability mass function of the link duration is obtained. The theoretical analysis and simulation results verify the effectiveness of the proposed link duration model.2) The dissertation proposes a backoff timer based beaconless protocol, which helps enhance the efficiency and stability for content transmission in decentralized vehicu-lar networks. The proposed beaconless protocol synthetically takes the propagation distance and the link duration into account on the backoff timer design, and then a semi-Markov chain based model is proposed to mathematically describe the link construction delay. The theoretical analysis and simulation results show that the pro-posed beaconless scheme constructs a more stable multi-hop transmission path and reduces the transmission delay. Moreover, the proposed analytical model can effec-tively describe the delay in the path establishment with different traffic density and vehicular mobility characteristic.3) For the content delivery between a vehicle and the road side unit (RSU), a multi-hop transmission path selection mechanism is designed for the sparsely deployed RSU environment. With the help of relay vehicle, the coverage performance of an RSU is enhanced. In such circumstance, a transmission scheduling problem with the relay vehicle selection and modulation and coding scheme (MCS) allocation is formulated,and two heuristic approximation algorithms are proposed for the direct link case and the relay-assisted path case respectively. The theoretical analysis and simulation re-sults show that the proposed scheme reduces the integral content offloading time with a relatively low calculation complexity.4) Considering the various subscriber information requirements in multicast transmis-sion scheduling for vehicular networks, the target video content is first coded into one basic layer and multiple enhancement layers before delivery. Afterwards, the multicast scheduling problem is divided into two sub-problems, including the "Basic Layer Full Coverage" sub-problem and "Enhancement Layer Throughout Maximiza-tion" sub-problem. Aiming at solving these sub-problems, two heuristic approxima-tion algorithms are proposed, which realize a high throughput while guaranteeing the basic layer coverage for all content subscribers.5) The dissertation proposed a mobile crowdsensing architecture, where the sensing task is initiated by vehicle or passenger that need recruits other vehicles for observation.The influence of indeterministic future vehicular trajectory, variable observation e-poch recruitment, and limited cost budget are taken into consideration. A proba-bilistic trajectory estimation model is used, based on which the target space cover-age property is mathematically proposed. A space coverage maximaztion problem is formulated with limited cost budget, and then a two step heuristic approximation method is proposed with both the candidate vehicle selection process and the variable observation epoch allocation process. The theoretical analysis and simulation results show that the proposed scheme enhances the space coverage performance with low computation complexity and good scalability.