Constrained surface-level gateway placement for underwater acoustic wireless sensor networks

One approach to guarantee the performance of underwater acoustic sensor networks is to deploy multiple Surface-level Gateways (SGs) at the surface. This paper addresses the connected (or survivable) Constrained Surface-level Gateway Placement (C-SGP ) problem for 3-D underwater acoustic sensor networks. Given a set of underwater sensor nodes (USNs) which are floated at different depths to perform collaborative monitoring tasks over a given region, and a set of candidate locations where SGs may be placed, our objective is to place minimum number of SGs at a subset of candidate locations such that it is connected (or k-connected) from any USN to the base station. We first propose a general algorithm for the connected C-SGP problem and prove its approximation ratio. We also give a constant ratio approximation algorithm for the problem. Second, for the survivable C-SGP problem we also propose a general algorithm and prove its approximation ratio. Finally, we give a constant ratio approximation algorithm for the 2-connected C-SGP problem.