Underwater sensing via networked platforms (i.e., underwater wireless sensor networks – UWSNs) is extremely useful in a plethora of applications such as monitoring underwater assets and surveillance against submerged threats. Maintaining reliable connectivity is of utmost importance in UWSNs, which can be achieved through k-connectivity (i.e., each sensor node maintains at least k node-disjoint paths towards the base station – BS). However, the energy cost of k-connectivity is prohibitively high, especially with large k values. As a tradeoff, it is possible to mitigate the extra energy cost of k-connectivity by employing a non-uniform k assignment strategy in a UWSN (e.g., only the most critical sensors have high k values whereas the rest of the nodes have lower k values). Non-uniform k-connectivity is a novel concept which has never been systematically investigated in the literature, to the best of our knowledge. In this study, we investigate the tradeoff between network lifetime (NetL) and reliability via non-uniform k-connectivity through the use of a novel optimization framework. Our analysis reveal that it is possible to provide strong connection reliability to critical nodes by adopting a non-uniform k-connectivity strategy without deteriorating network lifetime significantly.

Underwater wireless sensor networks (UWSNs) are utilized for a wide range of monitoring and surveillance applications. Lifetime maximization and maintenance of network reliability are among the most important considerations in the deployment of UWSNs.$k$-connectivity is a robust approach for reinforcing reliability. However, maintaining$k$disjoint paths from each sensor node to the BS, inevitably, results in extra energy dissipation, which reduces the network lifetime (NLT). Yet, there is no systematic exploration to determine the extent of lifetime reduction due to the increase in the$k$value, in the literature, to the best of our knowledge. In this study, we create an optimization framework to be able to explore the tradeoff between NLT and$k$-connectivity-based reliability in UWSNs. Through the optimal solutions of the proposed optimization model for a large set of salient parameters, we characterize the interplay between lifetime and$k$-connectivity. Our analysis reveals that the$k$value to be maintained in a UWSN can affect the NLT significantly.

The severe nature of underwater channel poses a great challenge for prolonging underwater acoustic sensor networks (UASNs) lifetime and achieving a reliable communication performance. Traditional approaches to improve the reliability such as automatic repeat request (ARQ) negatively affect the network lifetime (NL) due to energy dissipation caused by ARQ retransmission. A forward error correction (FEC) technique called fountain codes (FCs) can solve the energy efficiency problem of ARQ by transmitting both the original packet and some redundant packets to ensure a targeted reliability with few or no retransmissions. In this paper, we investigate performances of both traditional ARQ- and FC-based FEC methods in terms of NL, end-to-end delay, energy consumption, and frame error rate (FER) for UASNs. In this context, we abstract energy dissipation characteristics of conventional ARQ- and FC-based FEC method at the link-layer. We propose an integer linear programming (ILP) framework that maximizes the NL, which is operated on top of developed link-layer energy consumption models. Our results reveal that FC-based FEC methods can prolong the NL at a minimum of 16% while end-to-end delay, energy consumption, and FER can be reduced at least by 11%, 14%, and 9% as compared to classical ARQ, respectively.

Recently, underwater acoustic sensor networks (UASNs) have been proposed to explore underwater environments for scientific, commercial, and military purposes. However, long propagation delays, high transmission losses, packet drops, and limited bandwidth in underwater propagation environments make realization of reliable and energy-efficient communication a challenging task for UASNs. To prolong the lifetime of battery-limited UASNs, two critical factors (i.e., packet size and transmission power) play vital roles. At one hand, larger packets are vulnerable to packet errors, while smaller packets are more resilient to such errors. In general, using smaller packets to avoid bit errors might be a good option. However, when small packets are used, more frames should be transmitted due to the packet fragmentation, and hence, network overhead and energy consumption increases. On the other hand, increasing transmission power reduces frame errors, but this would result in unnecessary energy consumption in the network. To this end, the packet size and transmission power should be jointly considered to improve the network lifetime. In this study, an optimization framework via an integer linear programming (ILP) has been proposed to maximize the network lifetime by joint optimization of the transmission power and packet size. In addition, a realistic link-layer energy consumption model is designed by employing the physical layer characteristics of UASNs. Extensive numerical analysis through the optimization model has been also performed to investigate the tradeoffs caused by the transmission power and packet size quantitatively.