Underwater wireless sensor network (UWSN) features many unique characteristics, including slow propagation speed, high endto-end delay, low available bandwidth, variable link quality, and energy constraint. All these problems pose a big challenge to devise a transmission efficient, energy-saving, and low delay routing protocol for UWSNs. In this paper we devise a relative distance based forwarding (RDBF) routing protocol, which aims to provide transmission efficient, energy-saving, and low delay routing. We utilize a fitness factor to measure and judge the degree of appropriateness for a node to forward the packets. Under the limitations of the fitness factor, RDBF can confine the scope of the candidate forwarders and find the beneficial relays to forward packets. In this way, only a small fraction of nodes are involved in forwarding process, which can distinctly reduce the energy consumption. Moreover, using only the selected beneficial nodes as forwarders can both enhance the transmission efficiency and reduce the end-to-end delay. This is because the distances of these nodes to the sink are the shortest and the hop counts of routing paths consisted by these nodes are minimum. We use the ns-2 based simulator to conduct our experiment; the results show that RDBF performs better in terms of packet delivery ratio, end-to-end delay, and energy efficiency. make it a challenge [1, 2] when we try to design a transmission efficient, energy-saving, and low delay underwater routing protocol. For all this, many routing protocols [3] for UWSNs have been proposed in recent years. These protocols can be sorted according to different emphases. When considering the communication path, these protocols can be divided into communication path based and non-communication-path based protocols. The former protocols [4-6] relay on the communication paths established ahead of time. When a source sensor has 2 International Journal of Distributed Sensor Networks packets to send, it just transmits the packets to its next hop nodes along the communication paths associated with this source node. And the next hop nodes will forward these packets to their next hop nodes. In this way, the packets can finally reach the destination node. The chie task of this sort of protocols is establishing the communication paths, which is a time-consuming and complicated process. In addition, the mobility of the sensor nodes can disorganize the topology of the established paths dramatically. Rebuilding the communication paths will cost extra energy and time, which will degrade the performance of the routing protocols. The latter sort of protocols is non-communication-path based. When the sender nodes have packets to send, there is no established path for them. They need to find the appropriate next hop nodes immediately according to the routing schemes. In this kind of protocols, it need not cost any energy and time to establish and maintain the communication paths. While the key point of these protocols is how to find the most appropriate next hop nodes; a packet can be sent to a single next hop node or multiple next hop nodes. Many routing protocols [7-10] utilize the broadcast technology and introduce some parameters to control the number of the next hop nodes. But the bounds used in these protocols are neither flexible nor accurate enough to select the most appropriate next hop nodes. In this paper, we propose a relative distance based forwarding protocol (RDBF) to overcome these challenges. The distance to the sink [11] node is an absolute parameter to decide the appropriateness of the node to be the next hop node. We use a fitness factor which reflects the appropriateness and priorities of a sender's neighbor nodes to relay the packets for it. RDBF utilizes the fitness factor to limit the scope of the candidate forwarders and find the beneficial relays to forward packets. Within the limitations of the fitness factor, only a small fraction of nodes are involved in forwarding process, which can distinctly reduce the total energy consumption. Moreover, using only the selected beneficial nodes as forwarders can both enhance the transmission efficiency and reduce the end-to-end delay. This is because the distances of these nodes to the sink are the shortest and the hop counts of routing paths consisted by these beneficial nodes are minimum. The rest of this paper is organized as follows. In Section 2, we introduce several proposed routing protocols for UWSNs and indicate their problems. In Section 3, we describe our new routing protocol (RDBF) in detail. In Section 4, RDBF is evaluated through an ns-2 based simulator and we analyze the results in some different ways.
A communication path based routing scheme called Relative Distance Based Forwarding (RDBF) is presented in REF .
Relative Distance Based Forwarding Protocol for Underwater Wireless Networks
International Journal of Distributed Sensor Networks
Computer Science