From the view of routing protocols in underwater sensor networks (UWSNs), the presence of communication void, where the packet cannot be forwarded further using the greedy mode, is perhaps the most challenging issue. In this paper, we review the state of the art of void-handling techniques proposed by underwater geographic greedy routing protocols. To this, we first review the void problem and its negative impact on the category of the geographic greedy routing protocols, which does not entail any void recovery technique. It is followed by a discussion about the constraints, challenges, and features associated with the design of void-handling techniques in UWSNs. Afterward, currently available void-handling techniques in UWSNs are classified and investigated. They can be classified into two main categories: 1) location-based and 2) depth-based techniques. The advantages and disadvantages of each technique along with the recent advances are then presented. Finally, we present a qualitative comparison of these techniques and also discuss some possible future directions.
- routing protocol
- underwater sensor networks