Efficient Message Dissemination in Hybrid Vehicular Ad hoc NETworks (VANETs)

Abstract

The success of safety and non-safety-related applications in VANETs largely depends on effective dissemination of data among vehicles. Therefore, a suitable MAC protocol is required explicitly for VANETs which can deliver timely and reliably these sort of messages over a wireless collaborative environment. However, channel allocation remains as a challenging problem in VANETs, in fact, in any broadcast networks. The channel allocation among the vehicles in hybrid VANETs is normally done by a RSU. • In this research, an RSU controlled prioritized channel allocation strategy is proposed named as RCAPChA to minimize waiting time of the most deserving vehicle wanting to disseminate a message in the network. As the first contribution of the thesis, the proposed algorithm RCAPChA uses an MCDM tool named as AHP for prioritizing the vehicles. RCAPChA enables the RSU to compute the priority values for all the vehicles requesting for channels, and ranks them accordingly. The priority calculation is executed involving three criteria including severity of the message, vehicle speed, and channel occupancy time to compare our proposed scheme with the existing ones. The simulation results show that RCAPChA defeats the existing schemes regarding delay, PSR, PDR and Throughput at the expense of more energy in saturated data traffic condition. • VANETs can be a great help for WBAN users travelling in a vehicle for prompt and reliable transfer of alert messages to the caregivers. This research aims to minimize the delay of alert message dissemination and maximize the PDR and throughput of the network by applying priority scheduling of message transmission requests involving WBANs and hybrid VANETs. The proposed mechanism named as TRP which is the second contribution of the thesis, involves Prioritization of the sensors, Collection of physiological data from sensors, Detection of abnormality and alert message generation, Priority Scheduling by the RSU of the message transmission requests using MCDM tools named as FAHP and TOPSIS and finally delivers the alert message to its proper destination. The simulation analysis demonstrates that the outcomes of TRP are superior to those of the standard scheme. • MCDM approaches have been developed to support a wider range of application areas The AHP developed by Saaty, is capable of prior weight calculation of individual criteria using CPM and rank computation of alternatives as well. Another MCDM technique, termed TOPSIS, is a ranking technique that requires inputs of the weights of the criteria. As the third contribution of the thesis, this portion of research aims to analyze the impact on ranks of various alternatives for different CPMs using AHP-AHP method as well as AHP-TOPSIS method. For both the cases weights of criteria have been calculated using AHP prior to rank computation. In addition to that, this work deals with performance evaluation of VANETs for priority based channel allocation in terms of Request Service Rate and Average Waiting Time for various CPMs. It is observed that AHP-TOPSIS performs better in terms of Request Service Rate with the increasing number of alternatives. • The success of VANETs largely depends on effective data dissemination among vehicles. As the safety information intended for vehicles must be sent over the network in real time, the vehicles in the network must use a broadcast method for communication which can lead to broadcast storm problem which in turn leads to improper utilization of network resources. As a significant fourth contribution of the thesis, to mitigate the broadcast storm problem, an efficient relay vehicle selection mechanism named as ReUse is proposed for selecting the promising relay vehicle(s) in the network for broadcasting. The relay vehicle(s) is(are) chosen depending on a number of factors including mobility, link quality, buffer size, and number of neighbors using HSA and two MCDM tools named as FAHP and EDAS. ReUSe beats existing relay vehicle selection schemes in terms of reachability, redundancy rate, collision rate, delay, PDR, PSR, and throughput, according to simulation results. • In a dense vehicular network, high message generation rate demanding more transmissions could further increases the effects of the broadcast storm problem. In this context, message aggregation schemes could offer a great relief. As a strong fifth contribution of the thesis, a cluster based RSU enabled message aggregation protocol (CluRMA) is proposed which applies two levels of message aggregation — local aggregation at the cluster heads and global aggregation at the RSU. Before message aggregation process is performed, we make use of cosine distance for similarity checking between the messages for eliminating the duplicates. Then the syntactic aggregation is accomplished by employing message compression techniques — Adaptive Huffman Compression technique for safety messages, and Arithmetic Coding Technique for non-safety messages. The competence of CluRMA has been rigorously analysed and compared with the existing ones regarding several metrics including delay, PDR, collision rate, redundancy rate and overload.