In order to improve the average throughput performance of user effective data under highway scenario,a distributed channel access mechanism is proposed.The protocol sequence set is reused by road division.According to the characteristic of UI(User Irrepressibility) sequences,a few bits of feedback information are introduced for detecting the channel access order among nodes.Distributed TDMA(Time Division Multiple Access) is proposed for maximizing the throughput performance with a competition zone.The simulation results show that the throughput performance of UI-TDMA mechanism is more superior to classical method in a sparser distributed network or a higher PHY data rate or a larger communication range of node.

According to the characteristics of vehicular networks, this paper presents a identity-based signcryption scheme using the bilinear pairings and proves its security in the random oracle model.The proposed scheme is proved to be secure assuming that the Bilinear Diffie-Hellman problem is hard.Compared with the existing identity based signcryption schemes, the new scheme has lower computation cost and communication overhead.It is suitable for secure communication of vehicular networks.

The fast-moving characteristic of VANET(Vehiche Ad-hoc NETwork) leads to a high complexity of network structure that the conventional methodology of network cannot figure out.The solution proposed was based on the complex networks theory since its applicability is straightforward for this high complexity of VANET.And a mobility model was also proposed based on the process of network construction of VANET.The combination of the complex networks theory and the mobility model can be used to analyze the degree distribution,robustness,and the rate of connection change of VANET.Meanwhile,the method be simulated and validated.The results show that the proposed mobility model can represent the process of network construction of VANET,and the complex networks theory is very effective in its property analysis.

Considering that the delay tolerant character of VANETs(Vehicular Ad hoc NETworks),a packet dissemination strategy is introduced for duplicate controlling in VANETs of urban area.A packet transmission delay model of road is constructed based on Markov chain and vehicles distribution.The delay model is used to build the expected transmission delay of vehicles.And then the priority of vehicles is determined by the expected transmission delay and destination position.Current data carrier inserts decision segment of candidates into packets and select next hop vehicle by acknowledgement.Therefore,it is guaranteed that the vehicle with the highest priority can be selected as the next carrier.Furthermore,the paper deduces the ratio of quantities of received and transmitted packets.The ratio can be used to limit the unnecessary transmitting attempt,so as to inhibit duplicate packets.Simulation results demonstrate that the strategy achieves higher throughput and delay performance than the trajectory prediction based algorithms by limiting duplicate packets.

In order to solve low efficiency and frequent updates of vehicles' public keys and private keys, a certificateless aggregate signature authentication and key agreement scheme with anonymity in vehicular Ad-Hoc network (VANET) is proposed. In our scheme, by using temporary identity and pre-signature, vehicles' privacy protection and anonymity authentication can be realized. On the other hand, the suspected vehicles can be tracked by the trust authority with the index database of the temporary identity to satisfy conditional anonymity. Meantime, if the temporary identity is changed, it is not necessary to update vehicles' public keys and private keys in this scheme, so the cost of system can be reduced. Moreover, the pairing-free aggregate signature technology is used to improve the efficiency further, which makes the number of signatures and the verification cost of the server be decreased. It is shown that our protocol is provably secure in eCK model under the computational Diffie-Hellman (CDH) assumption.

In the three-dimensional vehicular ad-hoc networks (3D-VANET), high-speed moving vehicle nodes and changeable link states lead to unstable inter-vehicle communication links. Aiming at this problem, the time-space evolution graph model is constructed by introducing software define network technology to obtain network state in real-time and predict the process of time change and the link utility index is defined to quantify the wireless link performance. Then the weighted time-space evolution graph model based on link utility is established.Finally, the routing decision-making problem is transformed into a multi-attribute decision-making problem, and a link utility based reliable routing (LURR) algorithm is designed. Simulation results show that, compared with the existing four routing protocols, LURR algorithm has significantly improved packet transmission rate, end-to-end delay and routing load rate.