# An Improved Forwarding of Diverse Events with Mobile Sinks in Underwater Wireless Sensor Networks  
[PERSON] 1  
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1 Department of Telecommunication Engineering, UET Taxila, Taxila 47080, Pakistan;  
[EMAIL_ADDRESS] (W.R.); [EMAIL_ADDRESS] (F.A.) Institute of Management Sciences (IMS), Peshawar 25000, Pakistan; [EMAIL_ADDRESS] 1  
Footnote 1: email: wwm.mdpi.com/journal/sensors  
Footnote 2: email: [EMAIL_ADDRESS] (W.R.); [EMAIL_ADDRESS] (F.A.) Footnote 3: email: [EMAIL_ADDRESS] (W.R.); [EMAIL_ADDRESS] (F.A.) Footnote 4: email: [EMAIL_ADDRESS] (W.R.); [EMAIL_ADDRESS] (F.A.) Footnote 5: email: [EMAIL_ADDRESS] (W.R.); [EMAIL_ADDRESS] (F.A.) Footnote 6: email: [EMAIL_ADDRESS] (W.R.); [EMAIL_ADDRESS] (F.A.) Footnote 7: email: waseemraza844  
candidate for the longstanding and reliable [1] monitoring and data gathering applications. However, UWSN faces lots of challenges due to; the dynamic underwater environment, changing network topology due to water current, and shipping and aquatic life activities. It incurs the substantial cost of deployment, maintenance, and device recovery to cope with unpredictable underwater circumstances. Water absorbs lots of RF (Radio Frequency) energy hence radio communication is not feasible in underwater environments. Hence the communication in underwater is accomplished using acoustic links. Acoustic communication is mainly in low frequency typically less than 30 KHz which limits the available bandwidth and hence lower data rates are observed in underwater communications. The instruments used in underwater devices are also vulnerable to tedious subaquatic challenges, for example, algae and salt accumulation on camera lens, decreasing the effectiveness of sensors and other important devices. Generally, large number of energy constrained nodes are deployed on different depths to sense the required parameter(s) in underwater environment. These nodes are not aware of their exact position; however, their depth can be found using depth (pressure) sensors. In underwater, nodes communicate with each other through acoustic links. As described earlier, there are some immanent characteristics of acoustic communication like, limited bandwidth (<100 KHz), larger delays, and time varying multi path fading [2] which may cause larger doppler shift. All the deployed nodes also have energy constraint so their efficient energy consumption is of prime importance. It is almost impossible to replace or recharge the batteries of deployed nodes. The packets generated by each node are transmitted to surface sink using broadcasting and multi-hop communication [3]. In this communication, sending node includes its depth and the routing information in data packet and broadcasts it to all the nodes within its transmission range. However only shallower nodes (i.e., a node with depth lesser than the transmitting node) are allowed to respond to this broadcast. Only those shallower nodes which are farther than the depth threshold become eligible for forwarding. All the eligible nodes holds the packet for their respective holding time which is inversely related to forwarding function. If these packet holding nodes receive the copy of the same packet with-in their holding time they discard the packet and assume that a more eligible node has forwarded the packet. However if holding time is elapsed and no copy is received, node considers itself as the best forwarder and broadcasts that packet. This process is repeated by all nodes till the packet is reached to surface sinks. In this way each time a node with maximum value of forwarding function, gets minimum value of holding time and becomes next forwarder. This communication process involves certain terms which are needed to be explained. * Depth Threshold: Depth threshold is a global depth parameter to control the number of nodes involved in forwarding process. Greater the values of depth threshold lesser the number of nodes involved in forwarding process.