# A Two-Stage Routing Protocol for Partitioned Underwater Wireless Sensor Networks
## 2 Literature Review
In [19], the authors propose a Radius-based Multipath Courier Node (RMCN) routing scheme, a routing protocol for long-term sensing applications. The network is divided into two areas: the node area which takes \(\frac{3}{4}\) of the total area and the sink area which constitutes \(\frac{1}{4}\) of the total network area. The node area hosts equal numbers of static and mobile courier nodes whereas the sink area hosts sink nodes. Forwarders selection is based on the depth of the candidate node, its residual energy level its track ID and the outcome of a cost function. RMCN improves the PDR by well-organized coordination between static and mobile courier nodes, whereas energy consumption is controlled by avoiding flooding. However, as nodes are deployed according to a predefined criterion, RMCN may fail to perform in case of random deployment of nodes which is inherent in certain applications such as the cases where free mobility of nodes is considered. In [20], the authors propose a cross-layer routing scheme that includes information from physical, Medium Access and network layers to make forwarding decisions. It is a two-hop forwarding solution in which forwarding decisions are made keeping in view the status of nodes up to two hops away from the sender. The sender selects a one hop forwarder, a relay node and a two-hop forwarder. A relay node is used for reliability. The protocol works in three stages. In stage one, neighborhood information is disseminated in the network. Stage two is related to route selection, whereas stage three deals with the transmission of actual data. This scheme improves reliability and thus improves PDR by incorporating cooperative routing in the form of redundant relay nodes besides the actual forwarder. However, this redundant transmission every two hops increases communication overhead and contention, which consequently increases energy consumption. In [21], the authors propose a joint design of Power Control and opportunistic Routing (PCR). The proposed scheme aims at improving PDR. It carries out its operations in three stages: In Stage one, neighborhood information in the form of beacons is transmitted by every node using all available power levels. In stage two, candidate forwarders are selected based on the information received during phase one. This phase takes into account every possible power level and selects one forwarder corresponding to each of the available power levels. Energy consumption is considered in order to improve energy efficiency. Stage three deals with the transmission of data and coordination among forwarders in such a way that energy dissipation is balanced. As in PCR, beacons are transmitted using all available power levels, and hence multiple transmission of the same information creates a huge communication overhead which in turn increases the contention and energy consumption. This will lead to creation of connectivity holes and partitions in the network and, consequently, a low packet delivery ratio. Moreover, in the case of mobile network, stage one should be carried out periodically, thus increasing the energy consumption many-fold. Besides the above, many other routing schemes have been proposed. For instance, [22] is a cluster based Quality of Service aware routing protocol that deploys nodes in a hierarchical order to achieve balanced distribution of traffic and energy dissipation. Route establishment and forwarding are carried out in a greedy manner based on the link quality between clusterheads. Moreover, transmission range variation is used to deal with failed nodes and connectivity holes. In [23], the authors propose three routing schemes that work in collaboration to achieve high energy efficiency and fair load distribution. Transmission power is altered according to the energy level of the forwarder, traffic load and distance between the forwarder and the sender. It attains balanced distribution of traffic load by taking into account residual energy while selecting a forwarder. In [24], a reactive source routing scheme is proposed.