| Summary: | Intelligent Transportation Systems (ITS) apply Information and Communication Technologies (ICT) to improve safety and efficiency as well as the passenger experience in modern transport systems. It is envisaged that dynamic vehicular networks, particularly, Vehicular Ad-hoc Networks (VANETs) based on dedicated short-range communications (DSRC) and cellular networks, will be important parts of the future ITS. Unlike traditional communication networks, VANETs are highly dynamic systems resulting in significant reliability issues for the communication protocols. In addition, cellular networks incur notable usage cost. Motivated by this, we investigate efficient and reliable geo-routing and transport protocols aimed at VANETs and VANET/cellular hybrid architectures. Specifically, first we develop an innovative, unicast, cross-layer, weighted, position-based routing protocol (CLWPR) that takes into account mobility and cross layer information about neighbour nodes. A heuristic algorithm based on analytic hierarchy process (AHP) is employed to combine multiple decision criteria into a unique weight parameter used to select the node to which the packet is forwarded. Comprehensive simulations are performed in realistic representative urban scenarios with synthetic and real traffic. Insights on the effect of different communication and environment parameters are obtained. The results demonstrate that the proposed protocol outperforms existing routing protocols for VANETs, including ETSI's proposed greedy routing protocol, GyTAR, and AGF in terms of combined packet delivery ratio, end-to-end delay, and overhead. To efficiently distribute location information, required for the proper functionality of geo-routing, we develop a centralised Location Service. Exploiting the availability of two interfaces (DSRC and LTE) in a hybrid system, we propose separation of signalling and data traffic. The former is transferred over a cellular network and the later over a short range ad-hoc network. For the evaluation of the proposed scheme, we develop an analytical model of the upper bound delay based on stochastic network calculus (SNC) theory. We compare the upper-bounds of three networks, namely a pure short-range ad-hoc network, a pure cellular based on 3GPP LTE and the proposed hybrid with signalling on cellular and data on ad-hoc network. The results of our investigation suggest that hybrid networks can significantly improve performance of vehicular networks in terms of end-to-end delay both for data and signalling traffic. In the light of these findings, we investigate transport protocols for hybrid networks benefiting from multi-homing support. As Stream Control Transmission Protocol (SCTP) is one IETF standard that supports multi-homing, we develop an analytical model for throughput calculation of a round-trip time (RTT)-aware SCTP variant. Finally, we propose a novel SCTP scheme that takes into account not only path quality but also the cost of using each network. We show that the combination of QoS and cost information increases economic benefits for provider and end-users, while providing increased packet throughput.
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