Reliability-Aware Cooperative Routing with Adaptive Amplification for Underwater Acoustic Wireless Sensor Networks  
[PERSON]  
1 Department of Electronics, University of Peshawawat, Peshawat 25120, Pakistan 11 Department of Electronics, University of Peshawat, Peshawat 25120, Pakistan 11 Department of Electronics, University of Peshawat, Peshawat 25120, Pakistan 11 Department of Electrical, University of Peshawat, Peshawat 25120, Pakistan 11 Department of Computing and Information Technology, Northern Border University, Rafha 76321, Saudi Arabia; [PERSON]ESS] (S.M.A. ); [EMAIL_ADDRESS] (A.U.R. )1 Department of Computer System and Technology, Faculty of Computer Science and Information  
water). Underwater routing protocols involving reliability ensure that packets are routed to the sink with minimum corruption by the adverse channel effects or the unavailability of the intermediate relay nodes [1]. This, in effect, enhances the probability that packets are received successfully at the sink. These protocols are particularly important to be applied in undersea tasks like military spying, prediction and prevention of a disaster such as Tsunami, earthquake and rescue operations [2; 3]. The existing protocols that address reliability in routing for UAWSNs have several demerits [4; 5; 6; 7]. Firstly, they do not consider the connectivity of the complete routing paths towards water surface. A source node at the bottom selects a neighbor as a forwarder and blindly forwards data packets to it irrespective of whether the selected relay node has further more neighbors or not for packets forwarding. Although the protocol proposed in [5] considers the number of neighbors of the relay nodes for path connectivity, it does not check the connectivity of the complete path towards water surface. This selects routing paths that are not connected to the water surface for reliable packets delivery. As a result, these protocols are subjected to packets loss during data routing. Secondly, even if some paths are connected to the water surface for data delivery, the reliability of such paths is not evaluated before packets transfer. This further threatens the reliable packets routing. Consequently, reliability in packets delivery is compromised in these protocols, which is of serious concern in the harsh and unpredictable underwater environment. Transferring packets reliably to the sink node in UAWSNs inherently carries several challenges [8]. The battery power of sensors nodes in these networks is limited and usually replacing batteries is costly. Therefore, low depth nodes are preferred for data routing as they are close to sink node at the water surface. As a result, such low depth nodes are subjected to early death due to early loss of battery power. With the death of low depth nodes, reliable paths are difficult to construct for data routing since dead nodes cannot forward data packets. In addition, the underwater scenario is associated with harshness and unpredictability. The condition of a link may change soon after its computation by a source node and prior to the initiation of data transfer [9]. This falsely estimates the channel and, therefore, interrupts reliable transfer of packets to the desired node. Moreover, construction of reliable paths for data routing involves the geographical locations of nodes to be known [10], which is cumbersome as the coordinates constantly change when nodes move with ocean currents. This paper proposes the RAR and RACAA routing protocols for UAWSNs. Unlike the existing protocols addressing packets reliability as described above, the RAR checks the connectivity and availability of all the possible routing paths towards the water surface prior to packets transmission. This reduces packets loss due to disconnected paths where connectivity of nodes with water surface cannot be established. A path with no connectivity is the one that lacks the presence of forwarder nodes for data routing or when forwarders nodes are dead.