# Cooperative Opportunistic Pressure Based Routing for Underwater Wireless Sensor Networks
## 3 Our Proposed Work
### Role of Fixed Deployed Nodes  
The mechanism of backward transmissions is avoiding the void region however, it establishes lengthy recovery paths resulting in high energy consumption due to the involvement of more number of hops as shown in Figure 2a. To counter this problem, the strategic deployment of fixed nodes is adopted in Improved Hydrocast and Co-Improved Hydrocast for minimizing number of transmissions. The details are discussed below:  
Let \(n\) nodes be deployed at different strategic locations at sparse conditions. The objectives of strategic location is maximum coverage of the network and avoidance of void regions when the  
Figure 6: Higher pressure level neighbor is selected as forwarder incase all lower pressure level neighbors are in void region.  
network becomes sparse. These strategically deployed nodes find sparse regions with the objective to the reduce number of transmissions for delivering a data packet as shown in Figure 2b. The strategic locations are chosen according to Equation (6) as follows:  
\[TS_{Region}=\sum_{S_{reg}=1}^{S_{n}}\sum_{N=1}^{N}S_{region}(S_{n},N) \tag{6}\]  
where \(TS_{Region}\) shows the total number of sparse regions, \(S_{reg}\) is a region in which \(N\) are less and also they can not transmit data packets towards the destination. \(S_{reg}\) shows the index of the sparse region with the index of number of nodes \(N\). The number of strategic nodes depends on the number of \(S_{reg}\). More the \(S_{reg}\), greater number of strategic nodes are required to avoid lengthy recovery paths. The nodes that are deployed at strategic locations move in sparse networks with the speed of 0.3 m/s in one scenario discussed in simulation Section 4 and 7.71 m/s in other scenario in order to reduce the distance between the source and destination in sparse networks. The mobility of sensor nodes at strategic locations guaranteed the maximum coverage of the network. Strategic locations are computed according to Equation (7).  
\[SL_{node}=\sum_{SL_{node}=1}^{SL_{n}}\sum_{N=1}^{N}S_{region}(SL_{n},N) \tag{7}\]  
\(SL_{node}\) denotes the strategic node number and \(N\) shows the number of nodes from sparse region have \(SL_{node}\) in their transmission range. When all members of a sparse region are in the transmission that location is picked to forward the data from the sensor nodes of a sparse. \(SL_{node}\) re-establishes its data path after every 30 s with candidate nodes and transmit their sensed data after every 60 s. It moves randomly in a \(S_{reg}\), however always at lower pressure level than the void region nodes because the objective is to minimize the number of transmission for transmitting data between the sender and the receiver.  
The total energy consumption is computed according to Equation (8).  
\[ET_{i}=(E_{tx}(i)\times Dist_{std}+E_{rx}(i\times Neighbors(i))+EPM_{i} \tag{8}\]  
where \(ET_{i}\) denotes total energy consumed in data packet transmission from the source to the destination, \(E_{tx}(i)\) shows the transmission energy, \(E_{rx}(i)\) denotes energy reception, \(Dist_{std}\) is used to chose minimum distance from the source to the relay and the relay to the destination, \(Neighbors_{i}\) shows the number of neighbor nodes received the data packet and \(EPM_{i}\) is the energy consumed in path management after every 30 s.