# An Enhanced Energy Balanced Data Transmission Protocol for Underwater Acoustic Sensor Networks
## 4 EBET and EEBET: Proposed Techniques
### Route Establishment  
During the route establishment phase of EBET, sensor nodes look for suitable forwarder nodes. The sensor nodes form links with each other based on the value of optimum distance threshold \((O_{t})\). We assume that the sensor nodes and the sink are location aware, _i.e._, each node knows its own location. Every node exchanges its location information along with the coordinate position of sink to all the nodes in their transmission range. Each receiving node finds its neighbors using neighbour cost parameter \(N_{j}\)[9] as follows:  
\[N_{j}=\alpha|d(i,j)-O_{t}|+(1-\alpha)d(j,s) \tag{8}\]  
where \(\alpha\) is a system parameter set as 0.5, \(d(i,j)\) is the distance between two nodes namely \(i\) (sending node) and \(j\) (receiving node), and \(d(j,s)\) is the distance between node \(j\) and sink \(s\). The optimum threshold values (given in Table 2) set for node's transmission distance are calculated using [10]. Node with minimum \(N_{j}\) value is selected as a relay node. It is worth mentioning that \(N_{j}\) information is maintained in routing table of predecessor node as shown in Figure 4 such that its calculation helps a sensor node to select a relay node at optimum distance nearer to sink. Node with minimum \(N_{j}\) value informs its successor about its nomination as a relay node along with the number of nodes in its routing table containing \(N_{j}\) values. This information is sent to help a relay node to check the limit imposed on the number of packets it can forward. A node can forward maximum three data packets at a time. This is due to the limitation on the number of neighbors of a node. Each node maintains maximum two neighbors at a time. We imposed this limit to reduce burden of nodes. If we allow each node to have maximum neighbors, their energy levels start decreasing sharply and nearer nodes die within no time, thus, network lifetime shortens. Also, this limitation helps in balancing energy consumption in the  
Figure 3: Network field division into ring sectors. +++ ==ERROR: No output for this page==
A set of routes are obtained during route establishment phase. Therefore, data communication occurs over the same links between nodes during data transmission phase. The transmit energy is 100 times more expensive mainly for underwater communication. For balanced energy consumption, we have adopted the concept of RLs. Let the initial energy of each node be \(E_{o}\). The \(E_{o}\) of each sensor node is divided into Energy Levels \(RLs\). Equation (9) calculates the value of Unit Energy Level \((URL)\), \(0<URL<1\),  
\[URL=\frac{E_{o}}{L} \tag{9}\]  
where \(L\) is the optimum number of \(RLs\) which are to be calculated in this section. The total energy consumption of a node includes sensing energy \(R_{sen}\), receiving energy \(R_{rx}\) and the transmit energy \(R_{Tx}\). To calculate the total energy consumption \(R_{t}\) of source \(i\) and receiver node \(j\) at time \(t\), we have following equation. \[R_{t}^{i}(t)=R_{sen}(x)+R_{rx}(x)+R_{Tx}(x,d)\ \ where\ \ i\in Sr_{i} \tag{10}\]  
When the data transmission process starts all the network nodes in different Ring Sectors have same Residual RLs, \(R_{RL}\) as shown in Equations (11) and (12). Every node transmits data to its next hop neighbor (successor) using multi-hop method; \(R_{RL}^{j}\) and \(R_{RL}^{k}\) denote \(R_{RL}\) for \(j\in Sr_{i}\) and \(R_{RL}\) for \(k\in Sr_{i-1}\). \[R_{RL}^{j}=\frac{E_{o}}{\beta}\ \ \ \ \ \ where\ j\in Sr_{i} \tag{11}\]  
\[R_{RL}^{k}=\frac{E_{o}}{\beta}\ \ \ \ \ \ \ \text{where}\ k\in Sr_{i-1} \tag{12}\]  
Figure 6 shows the selection of relay node with variations in energy levels. As the nodes send data only to their next-hop node within their optimum transmission range. Here we use \(URL=\beta\). We assume \(R_{Tx}(x,d)\leq\beta\). Now we calculate the \(R_{RL}\) of sensor node (\(j\in Sr_{i}\)) at time \(t^{\prime}\), _i.e._, \(R_{RL^{\prime}}^{j}\) (the time when \(R_{RL}^{k}<R_{RL}^{j}\)).