Due to the significant advances of wireless sensor networks (WSNs), researchers are eager to use this technology in the subsea applications. Because of rapid absorption of high radio frequency in the water, acoustic waves are used as communication medium, which pose new challenges, including high propagation delay, high path loss, low bandwidth, and high-energy consumption. Because of these challenges and high movement of nodes by water flow, end-to-end routing methods used in most of existing routing protocols in WSNs are not applicable to underwater environments. Therefore, new routing protocols have been developed for underwater acoustic sensor networks (UWASNs) in which most of the routing protocols take advantage of greedy routing. Due to inapplicability of global positioning system (GPS) in underwater environments, finding location information of nodes is too costly. Therefore, based on a need for location information, we divided the existing greedy routing protocols into two distinctive categories, namely, location-based and location-free protocols. In addition, location-free category is divided into two subcategories based on method of collecting essential information for greedy routing, including beacon-based and pressure-based protocols. Furthermore, a number of famous routing protocols belonging to each category are reviewed, and their advantages and disadvantages are discussed. Finally, these protocols are compared with each other based on their features.

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Congestion avoidance in emergency situations is among one of many overlooked localization issues. During emergency situations (such as fires), sometimes the rescuers find it hard to find the best exit route from the inside to the outside of a building. Any time delay in decision making will risk the loss of lives. Therefore, an efficient Emergency Rescue Localization (ERL) system is needed to help rescuers find the best route from the inside to the outside of a building. Thus, we propose a new ERL that is based on the integration of a Global Positioning System (GPS), Wireless LAN and camera. In this proposed ERL, the integrated Wireless LAN (WLAN) and Camera are used to retrieve location information inside a building. Then, localization methods will be adapted to GPS-based localization when subjects are in open areas outside the building. Finally, we present our experimental results to illustrate the performance of the localization system for indoor and outdoor environment set-up.