Distributed Underwater Clustering Scheme (DUCS)
Energy efficiency is a major concern for UWSNs because sensor nodes have batteries of limited power, which are hard to replace or recharge in such environments. It is a fundamental problem to design a scalable and energy-efficient routing protocol for these networks. Domingo and Prior (2007) presented a distributed energy aware and random node mobility supported routing protocol called Distributed Underwater Clustering Scheme (DUCS) for long-term but non-time critical applications.
DUCS is an adaptive self-organizing protocol where the whole network is divided into clusters using a distributed algorithm. Sensor nodes are organized into local clusters where one node is selected as a cluster head for each. All the remaining nodes (non- cluster heads) transmit the data packets to the respective cluster heads. This transmission must be single hop. After receiving the data packets from all the cluster members, cluster head performs signal processing function like aggregation on the received data, and transmits them towards the sink using multi-hop routing through other cluster heads. Cluster heads are responsible for coordinating their cluster members (intra-cluster coordination) and communication among clusters (inter-cluster communication). The selection of cluster head is completed through a randomized rotation among different nodes within a cluster in order to avoid fast draining of the battery from the specific sensor node. DUCS completes its operation in two rounds. The first round is called setup, where network is divided into clusters, and in the second round, which is called network operation, transfer of data packets is completed. During the second round, several frames are transmitted to each cluster head where every frame is composed of a series of data messages that the ordinary sensor nodes send to the cluster head with a schedule. Simulation results have shown that DUCS not only achieves high packet delivery ratio, but also considerably reduces the network overhead and continues to increase throughput consequently.
Although DUCS is simple and energy efficient, but it has a couple of performance issues. First, node movements due to water currents can affect the structure of clusters, which consequently decreases the cluster life. Frequent division of sectors can be a burden on the network as the setup phase is repeated many times. Second, during the network operation phase, a cluster head can transmit its collected data towards another cluster head only. Again, water currents can move two cluster head nodes away, where they cannot communicate directly even a few non-cluster head nodes are available between them.