CoSiM-RPO: Cooperative Routing with Sink Mobility for Reliable and Persistent Operation in Underwater Acoustic Wireless Sensor Networks  
[PERSON]  
1 Department of Electronics, Quaid-i-Azam University Islamabad, Islamabad 45320, Pakistan; malifeele.qua.edu.pk (M.A. ); [EMAIL_ADDRESS] (H.M.); [EMAIL_ADDRESS] (N.B.) [PERSON]  
2 Department of Electronics, University of Peshawar, Peshawar 25120, Pakistan 2  
bit error rate (BER). Moreover, energy-efficient algorithms are required because of the limited energy source of the nodes, and it is tough to replace or re-energize the battery [9]. Furthermore, GPS is required for location information acquisition, which is difficult underwater [10]. Many other techniques have been proposed that use optical waves for localization of the network [11; 12]. However, the optical waves are used for short distance communication. Likewise, the water currents change the position of the nodes and randomly move in the network [13]. Therefore, determining the exact position is a difficult task. Moreover, an energy-efficient and low-cost modem is required for the UA-WSNs' communications [14]. Furthermore, the ocean covers 70% of our planet, and most of the area has almost been unexplored even after much research [15]. Due to the aforesaid applications, reasons, and challenges, it has attracted the attention of researchers, academia, governments, and engineers. Data exchanging is accomplished in two ways in UA-WSNs. The first is that in which the data are transferred through a single path without the help of relays to the desired destination, known as the non-cooperative scheme. While in the second case, the relays assist in more accurate data reception, termed cooperative algorithms [16]. Due to data exchanging through a single path compromised of the data loss probability in a non-cooperative algorithm, using cooperative techniques provide reliable data exchanging by utilizing broadcast nature. In cooperative routing, the relays work together with the sender to deliver data more accurately to the destination. The relay assists in two ways: in the first, which is specified as fixed cooperation (FC), the data delivery to the destination is accomplished as it receives data from the sender without any conditions; in the second case, named incremental cooperation (IC), the relay waits for the signal reception from the destination [17]. After signal reception, the data are delivered by the relay. The data forwarding through a relay is done in two ways. The relay either boosts the received data, named amplify and forward (AF), or fully decodes them, titled decode and forward (DF) [18]. Due to the simplicity of the AF scheme, it is mostly used instead of DF. The cooperative algorithms enhance the chances of successful data delivery and compromise on the energy cost and delay. The energy cost, latency, and data loss probability of the multi-hop algorithms [19; 20; 21; 22] are high and have less stability due to the involvement of many nodes for a single-packet delivery. Moreover, performance decreases as holes (void regions) are created due to the death of the nodes. A node stuck in a void region is useless because of no link available to the surface. The multi-hop cooperative routing [23; 24; 25; 26] provides high data accuracy and less packet dropping due to the exchanging of a single packet through many paths. However, the remaining aforesaid issues in multi-hop algorithms increase to a high extent in cooperative algorithms. On the other hand, the routing algorithms with sink mobility provides persistent operation of the network. The mobile sinks (MSs) try to reach every node to collect data from it directly to gain better throughput with less resources, which overcomes the concerned challenges of the multi-hop algorithms. In the existing algorithms with sink mobility and cooperation in [27; 28], the MSs do not cover all the network and still require multi-hop routing. Furthermore, data forwarding in a cooperative manner leads to an increase in the energy cost of the network.