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Top1. Introduction
In recent years, the research of Underwater Acoustic Networks (UANs) is attracting attention due to their important underwater applications especially in disaster prevention or for military and commercial purposes. Underwater Acoustic Sensor Network (UWASN) is a kind of Wireless Sensor Network (WSN), consisting of underwater acoustic sensor nodes, which can be deployed for real-time warship monitoring, disaster prevention, oceanographic data collection, environmental monitoring, etc. (Akyildiz, Pompili, & Melodia, 2004). There are many challenges on designing a reliable data transfer protocol for UWASN due to the specific characteristics of acoustic channels: high error rates, limited bandwidth, high energy consumption, low transmission speed, and unstable packet delivery delay (Akyildiz, Pompili, & Melodia, 2004). Acoustic signal propagation speed in an underwater acoustic channel is about 1.5 × 103 m/s speed compared to RF, which is 3 × 108 m/s. The propagation delay in underwater is five orders of magnitude higher than in RF. The low speed of sound causes multi-path propagation to stretch over time delay.
Underwater Wireless Sensor Networks (UWSNs) are different from Terrestrial Wireless Sensor Networks (TWSNs) in many aspects, such as their high error probability of each node, high latency, and their high communication cost. UWSNs also have some disadvantages including, limited interaction between an onshore control center and the monitoring instruments, the unavailability of real-time monitoring, and lack of a mechanism to detect failures quickly (Akyildiz, Pompili, & Melodia, 2004). Due to these characteristics, TWSN is unsuitable as UWSNs. Reliability is a challenging factor for any communication, especially in underwater networks. Reliable data delivery between sensors and between senor to the surface sink is a challenging task as compared to forwarding the collected data to the control center. There are several techniques to enhance reliability such as: deployment of redundant sensors, so that even if some fail, we still obtain enough data for accurate detection, finding alternative path, designing network architecture to reliably transmit the sensor data to detection center, and designing communication protocols to reliably transmit the sensor data to the detect center. Our proposed algorithm, for underwater sensor network considers several factors related to the reliability enhancement such as the node residual energy, distance to sink, and link quality. RRP depends on both the DFR and VBVA protocol. It depends on DFR which is based on a directional flooding scheme which increases the reliability. But if none of the neighbors are closer to a sink than the forwarding node, we try to find an alternative path by using some functionality from VBVA protocol.
The main concern is to enhance the reliability of the routing protocols in the environment of underwater acoustic sensor network with respect to failure of the network due to failure of single or multiple sensors. The objectives are to develop routing protocol for UWSN that guarantees that data is reliably transmitted through survival sensors to the destination, to study the performance of the new scheme, and to compare the new proposed scheme with the UWSN current scheme.
The rest of this paper is organized as follows. In Section 2, we review some well-known routing protocols proposed for UWSNs with their drawbacks. Section 3 presents our proposed routing protocol, RRP, is described in detail. Section 4 presents the performance evaluation of RRP. Finally, some conclusions are drawn in Section 5.