Moving From Topology-Dependent to Opportunistic Routing Protocols in Dynamic Wireless Ad Hoc Networks: Challenges and Future Directions

Introduction

Recent advances in wireless technology have led to the exponential growth and usage of wireless mobile devices worldwide. Today billions of wireless devices are connected with the help of infrastructure like access points and base stations. These infrastructure supported wireless networks provide an increasing number of wireless local area network (LAN) hot spots, allowing travelers and users with portable laptops and mobile phones to surf the Internet from hotels, airports, railway stations, coffee shops and other public locations. However, these infrastructure supported wireless network comes with a number of limitations. They consume plenty of time and money for installation and maintenance; have constraints in flexibility, suffer from low utilization of local wireless resources and are particularly vulnerable to natural disasters and unpredicted failures. To overcome these limitations, self-sustained, infrastructure-less and decentralized wireless networks have been proposed, known as mobile ad hoc networks (Giordano and Lu, 2001; Chlamtac et al., 2003; Menon & Prathap, 2016).

Mobile ad hoc networks (MANETs) are a collection of wireless devices like mobile phones, laptops, PC’s and iPads that can form instantaneous temporary networks without the support of any pre-existing network infrastructure or centralized control. It works as an autonomous system of mobile hosts connected by wireless communication links. The network is configured in a way that all the devices can dynamically join or quit the network at any time without disrupting communication between other devices. Every device in the network plays the dual role of a router and a host, cooperates and coordinates with each other to make routing decisions in the network. Data is transmitted in the network in a store and forward manner from the source node to the destination node via the intermediate nodes. Ease of deployment, speed of deployment and the ability to self-organize and self-adapt without the help of any underlying infrastructure has contributed to the growing popularity of MANETs in research as well as in industry. Today MANETs are used for communication and resource sharing in numerous challenging environments like earthquake and volcano affected areas (Mase, 2011; Menon et al., 2016), underground mines, battlefields etc. Figure 1 shows an example MANET used in disaster recovery operations

Figure 1.

MANETs in disaster recovery operations

One of the major challenges in these highly dynamic networks is to efficiently deliver data packets from the source to the destination device. Ensuring reliable and continuous communication between the devices is yet another major challenge in these networks. Over these years a number of routing protocols have been proposed for data delivery and communication in MANETs. Figure 2 gives the taxonomy of all the protocols proposed for MANETs. Recent advancements in wireless technology have enabled mobile devices in MANETs to move freely with higher speeds in random directions. The mobility and speed of these wireless devices have become highly unpredictable and is increasing day by day. Also the number of connected devices in the network is increasing rapidly leading to highly dense and scalable ad hoc networks. As the mobility and number of devices increases in the network the performance of most of the existing routing protocols comes down drastically leading to low transmission efficiency and reduced Quality of Service. Very few researches have been done to identify the reasons behind this performance degradation.

Figure 2.

Taxonomy of protocols proposed for MANETs