Spectrum-Aware Routing in Cognitive Ad Hoc Sensor Networks

Abstract

The earth, a watery place because of a higher percentage of water than the land, has several communication technologies that help to improve our living standards. Observing our planet in this regard, there exist different living organisms on the land surface, the sea surface and in the ocean which communicate daily with their species using different spectrum. Along with these living things, there are several non-living things with some similar characteristics of living things on the earth e.g., vehicles that need to be fed with petrol, sensors that have ability to adapt according to the environment and need energy to continue existing, machines or robots that can move, and many more, which utilize the same spectrum for communications. Nowadays, we are more than 60\% dependent on these non-living things to make rapid advancements in inter-networking. Inter-networking is a connecting phenomenon that requires a routing protocol to transfer the data packets between different networks by using gateways. Routing is a process that helps sensor nodes to establish a stable link to forward a message to its destination. Hence, to improve communications among different kinds of communicating devices on the land, the sea surface, and in the ocean, three types of sensor networks: terrestrial, maritime, and underwater are designed to deal with various applications, respectively.

As we are exposed to a plethora of mobile applications over the past few years, our living standards are becoming increasingly the part of smart networking. Among various kinds of other systems that are essential to improve our living standards all over the world, the intelligent transportation system is the one that overcomes serious issues due to road accidents. Millions of deaths are caused by road accidents. Therefore, in this thesis, we consider vehicular ad hoc networks as the terrestrial networks. Vehicular ad hoc network is a promising mean for safe driving by enabling cooperation among vehicles. And when it comes to safe and stable communications at the sea surface, maritime ad hoc networks are the ones that play an essential role in providing a variety of safety to users aboard. Similarly, communications in the ocean have also been attracting significant interests to deal with various applications for underwater networks. Hence, in this thesis, we consider three different types of communications systems: vehicular ad hoc networks, maritime ad hoc networks, and underwater acoustic networks to deal with the developing requirements of their applications by ensuring safe and stable communications; and intend to overcome the existing issues in each of them. Both vehicular and maritime ad hoc networks use electromagnetic radio waves as a medium of communications, whereas underwater acoustic networks use acoustic waves.

Ubiquitous wireless communications is an essential goal for numerous applications ranging from traffic safety to entertainment-related information for various users either on the land, the sea surface or in the ocean. The dedicated licensed spectrum for each of these communications systems has been found insufficient to fulfill the increasing needs of vehicular, maritime, and underwater applications. To alleviate the spectrum scarcity in these networks, cognitive technology is a viable solution as it can utilize spectrum in an environment-friendly manner (i.e., avoiding harmful interference with licensed users). To this end, stable links are essential for communications with different users in order to meet the growing demands of vehicular, maritime, and underwater applications. A link is formed only when two communicating nodes have consensus about a common idle channel. Therefore, novel cognitive routing protocols are required for each of these networks to ensure cooperation among the respective users; thereby retaining stable links for vehicular, maritime, and underwater communications.

Various routing techniques have been proposed for vehicular, maritime, and underwater networks, but the number of routing protocols that consider cognitive capability with a routing technique is very limited for vehicular networks. Nevertheless, safe and stable communications issues for cognitive vehicular networks are still under investigation in order to reach a robust and distinguished solution. Similarly, for maritime and underwater networks, combining cognitive principles with routing schemes have not yet been considered. Therefore, in this thesis, we first propose cognitive routing protocols that ensure stable routes between sources and destinations in order to overcome the problems of spectrum scarcity and high latency in vehicular, maritime, and underwater networks, respectively. Our goal is to maintain network stability by considering spectrum sensing and routing simultaneously for vehicular, maritime, and underwater communications. We prove better network performance in each of these cognitive routing protocols in terms of end-to-end delay, delivery ratio, and routing overhead. From these results, we observe that the performance of these networks can be further improved by considering a logically centralized controller that has a global view of the network states and is responsible for selecting the stable paths. This is only possible with the physical separation of network control plane and the forwarding plane.

Therefore, we then apply a new concept of software-defined networking (SDN) in these cognitive vehicular, maritime, and underwater networks to further overcome the shortcomings with the existing architectures in these domains. We find that the SDN-based cognitive routing protocols for each of these vehicular, maritime, and underwater networks improve network performance in comparison with non-SDN-based cognitive routing protocols. All nodes in non-SDN based networks perform all functions (routing, forwarding, and network management) individually resulting in an inefficient utilization of resources, high latency, and large amounts of overhead. Due to SDN approach, these nodes do not further need to configure individually. Any change in the network can be now done centrally by the logically centralized controller. We further comprehend from these results that the improvement is only for networks with specific applications. In order to support multiple applications simultaneously under the same infrastructure and enable users to satisfy each application service with improved network flexibility, we finally introduce two integrated architectures. The first one supports different vehicular applications with the integration of software-defined networking, network function virtualization, and fog computing. However, the second one is an integrated coastal city that instate cognitive vehicular-to-ship communications in hybrid environments. Consequently, we end up this thesis opening a new door for routing in integrated cognitive vehicular and maritime networks in order to run multiple applications simultaneously under the same infrastructure.