# SOUNET: Self-Organized Underwater Wireless Sensor Network
## 1 Introduction
They use the k-means technique for the selection of initial cluster-heads and then replace each one with the sensor node that has the highest remaining energy in the next round, thereby increasing the network's lifetime. However, KEER and EKEER cannot maintain high network performances because the sensor nodes may lose link connections during data delivery when the cluster-heads fail. The link holes cannot be recovered until new cluster-heads are selected at the beginning of the next round. Non-clustered tree topology-based networks have been studied as an alternate approach for data gathering [13; 14; 15; 16; 17], where long communication links between cluster-heads do not exist. In [13], the concept of SON was employed to initially construct tree topological UWSNs. The initial network was built in an autonomous way by flooding a control packet, which departed from a sink node, throughout the network. However, the network topology was maintained without adapting the changes in the situation afterwards. Thus, the network connectivity becomes worse when a sensor node is newly added or lost. The US Navy's Seaweb also employed a multi-hop tree topological network [14; 15; 16; 17]. Unlike the early stages where Seaweb relied exclusively on users for manually configuring all of the communication links, the recent version of Seaweb allows the sensor nodes to autonomously establish the network based on the breadth-first search algorithm without the central control. However, both Seaweb and the scheme in [13] (referred to as S\({}_{13}\) hereafter) rely on network reorganization that happens periodically or in an event-triggered way to deal with link holes caused by the addition and loss of nodes. To maintain high network connectivity, the reorganization should be done frequently, which causes the overall energy consumption to increase considerably. Recently, underwater routing protocols [19] consider self-organizing concept to cope with the poor underwater conditions. An efficient hop-by-hop dynamic addressing based protocol named H2-DAB [18] has both network topology discovery and maintenance parts. The H2-DAB also discovers an initial network based on the flooding of a control packet like S\({}_{13}\) and handles topological changes caused by link holes. For delivering data to a sink, a sensor node first obtains the hop-count of its neighbors, i.e., the number of hops required to reach the sink. Then, the sensor node selects the node with the smallest hop-count as a relay. This hop-by-hop forwarding continues until the data reaches the sink. By reconfiguring a link as required, a sensor node is able to handle the loss of neighbors adaptively during data forwarding. However, the H2-DAB also requires network reorganization to enable failed nodes in hearing control packets for network initialization or to aid newly added nodes in joining the network without causing extra delays. In addition, the H2-DAB has a large signaling overhead associated with the acquisition of neighbors' hop-count. Moreover, installing multiple sinks over a wide area is very expensive. In a pressure sensor based reliable routing protocol, named PSBR [20], sensor nodes exchange information of depth and residual energy with their neighbors. Then they calculate each neighbor's link quality and select the best one as their relay. Since the information exchange repeats periodically, newly added or lost nodes can join or leave the network naturally depending on the period. The period should be adequate for trade-off between throughput and energy consumption. In [21], a protocol for non-clustered and non-tree topological networks, called DIVE, was proposed for ID assignment and topology discovery. Nodes can obtain a globally unique ID and share topology information in a self-adaptive and distributed manner. However, DIVE does not consider the network maintenance. Thus, designing a network that can be controlled in simpler way without causing heavy signaling or long delays is highly desired.