Optimized Void-Aware Routing Protocol For Underwater Acoustic Sensor Networks

Abstract

Underwater Acoustic Sensor Networks (UASNs) are the technologies used to ex- plore underwater resources. UASNs have been used in numerous applications such as environmental monitoring, underwater surveillance, underwater exploration, detection of resources and disasters, etc. However, UASNs face several fundamental issues like low bandwidth due to the environmental noise, high bit error rate as a result of fading and multipath propagation, energy constraints on nodes, security as they are vulnerable to active and passive attacks, complicated routing due to dynamic network topology and variation of the link quality between nodes. The UASNs architecture consists of sensor nodes deployed underwater for sensing the events and forwarding or routing the data, in one or multiple hops, to the sink nodes deployed at the water’s surface. Wireless routing has three significant categories, that are proactive, reactive, and geographic routing. However, proactive routing requires transmission of more number control packets, thus increasing energy consumption and overhead on the network. The reactive routing results in increased end-to-end delay due to high propagation delay. Geographic routing forwards the data, using the position information of the neighbors and the sink. It uses greedy forwarding, and every node determines only its next hop, rather than the end-to-end path. Geographic routing is the most suitable protocol to forward data from the source to the sink node in UASNs. However, communication void or void node is one of the major challenges in UASNs to deliver the data to the sink reliably. The non-availability of a neighbor, in the positive progress to a source or forwarding node, results in a communication void. Communication void impacts the performance of the UASNs in terms of packet loss, high end-to-end delay, waste of energy, etc. Primary reasons for communication void are, node movement due to water current, ship movement, or a drop in Signal-to-Noise Ratio (SNR) between nodes. Many methods are proposed in the literature to deal with the communication void, such as backward forwarding, topologyadjustment, transmission power adjustment, etc. The major drawbacks of these methods are, void nodes as a part of routing, loops, unreachable data to the sink, more duplicate packets, hidden-node issues, and more energy consumption. This thesis mainly addresses the issues of the communication void in underwater routing. In existing void-aware routing protocols, the source/forwarder node decides the next hop using multiple attributes, such as hop count, residual energy, distance with the neighbor, depth, Packet Delivery Probability (PDP), status (void or normal), etc., of the neighboring nodes. However, the priorities of the individual attributes are not considered in determining the next hop(s). Hence, this thesis presents the selection or identification of an appropriate combination of attributes of neighboring nodes. Ac- cordingly, this thesis proposes the Enhanced-Void-Aware Routing (E-VAR) protocol, which uses a combination of the neighbor’s status and Euclidean distance between the neighbor to the sink attributes to decide the next hop for delay-sensitive applications. Further, Link Quality-based Routing Protocol (LQRP) proposed in this thesis uses link quality between source to neighbors and neighbor to its best hop as attributes. Addi- tionally, applying appropriate weights, a suitable neighbor is selected as its next hop. The LQRP protocol achieves better reliability than the state-of-the-art protocol. The Location-Free Void Avoidance Routing (LFVAR) protocol proposed in this thesis uses status, hop count, and depth of neighbor as attributes. Further, by computing the cost of neighbors, one of them is selected as the next hop. The Link and Void-Aware Routing (LVAR) protocol proposed in this thesis uses status, PDP, and hop count of neighbor as attributes to select the next hop. The state-of-the-art routing protocols proposed in the literature do not consider Mul- tiple Attribute Decision Making (MADM) techniques to evaluate the neighboring nodes using identified attributes. Hence, this study proposes a Cluster-based Multi-Attribute Routing (CMAR) protocol. CMAR is a sender-based, opportunistic routing protocol. The source/forwarder node evaluates its neighbors using the Technique for Order Pref- erence by Similarity to Ideal Solution (TOPSIS) method. Additionally, it forms the cluster(s) of neighboring nodes, consisting of a threshold number of nodes in the vicin- ity of each other. The source/forwarder node forwards the data to the cluster using iiopportunistic routing. The protocols (E-VAR, LQRP, LFVAR, LVAR, and CMAR) designed, as a part of this research work, are simulated and evaluated in industry-standard simulators such as MATLAB and UnetStack. UnetStack is an agent-based simulator used to develop and evaluate underwater protocols. Further, E-VAR, LQRP, LFVAR, LVAR, and CMAR are evaluated in terms of various metrics such as the number of nodes reachable to the sink, number of nodes not reachable to the sink due to loops, packet delivery ratio, hop count, propagation distance from source to the sink, throughput, number of the clusters formed, number of times a void node is part of the routing, etc. In conclusion, the major contribution of this thesis, focuses on identifying the most suitable combination of attributes of neighbors to select the next hop(s) with E-VAR, LQRP, LFVAR, and LVAR, further evaluating neighboring nodes, using the MADM approach with CMAR protocol. Additionally, designed protocols are evaluated using MATLAB or UnetStack and are compared with state-of-the-art routing protocols.