Lifetime enhancement in sparse underwater acoustic sensor networks using mobile elements

Underwater Wireless Sensor Networks (UWSNs) enable a wide range of aquatic applications. Due to node mobility, harsh environment, sparse deployment, and resource constraints, the network can be easily partitioned. UWSNs under such scenarios need to be treated as Intermittently Connected Networks (ICN) or Delay Tolerant Networks (DTN). Unlike the conventional routing schemes, the routing objective of DTN is to maximize the possibility of eventual data delivery. Since the conventional multipath DTN approaches are not suitable for time-critical and resource-constrained underwater scenarios, we consider an application-oriented and energy-efficient data collection scheme using a mobile sink (MS). The scheme uses a new approach for reducing and balancing the energy consumption of sensor nodes, but the associated latency may be large due to the limited travel speed of the MS. However, the reduced and balanced usage of energy, resulting in increased lifetime of the network, is more important than latency for some sensing applications which are not time-critical. We investigate through analytical models, energy saving, the network lifetime, and latency in mobility-assisted data collection in UWSNs and also conduct simulation study using NS-2 based Aqua-Sim simulator. The analytical and simulation results show superior performance of the MS-based data collection scheme, in terms of delivery ratio and network lifetime, at the cost of increased message delay.