# An Enhanced Energy Balanced Data Transmission Protocol for Underwater Acoustic Sensor Networks
## 4 EBET and EEBET: Proposed Techniques
### Route Establishment
#### 4.1.2 Eebet  
The EEBET more intelligently selects the relay node during route setup phase than the BTM and the EBET techniques. One of the major limitations of BTM technique is its relay node selection process which is purely based on the distance between sender, receiver and the sink node. In EEBET, it is assumed that all the sensor nodes know their location information along with their depth. Depthinformation helps to select node towards sink and eliminate multiple hops. It also helps in eliminating loop formation. Depth threshold is incorporated to restrain number of nodes to become forwarder and select a node near optimum transmission range. Initially, all the nodes share their depth along with location information with each other. A node selects all nodes within its transmission range which are placed at lower depth than itself. Then the depth based selected nodes are further passed through the process of distance based calculation. The \(N_{j}\) values for depth based neighbors are calculated using Equation (8). However, we need to choose only one relay node. Therefore, we also implement the process of distance based calculation to select only node at optimum transmission distance. A node selects only one node as a relay node, however, it maintains information of all of its neighbors along with their depth, \(N_{j}\) values and energy information in its routing table. This is required to reselect the relay node incase of decrease in the \(RL\) of a node. This process continues for all the nodes to select their potential relay node. The list of nodes is sorted on the basis of \(N_{j}\) values with minimum \(N_{j}\) node placed at the top of the list. In order to eliminate number of hops involved in data transmission. Another contribution is selection of relay node in alternate ring sector rather than the neighbouring ring sector. A node in \(R_{1}\) selects its relay node in \(R_{3}\) while an \(R_{2}\) node selects its relay in \(R_{4}\). In this way, the data load of nodes is shared among different nodes and overall network energy is balanced. Route establishment in both schemes, EBET and EEBET is shown in Algorithm 2. The route establishment in EEBET differs EBET, as it considers depth of sensor nodes and calculates their depth difference, which is further compared against depth threshold. The EBET only follows steps 10-15 defined in Algorithm 2 after receiving \(Q_{p}\). ```
1:\(Q_{p}\leftarrow\) Query packet
2:\(d_{th}\leftarrow\) Depth threshold
3:\(D_{sen}\leftarrow\) Depth of sender node
4:\(D_{rec}\leftarrow\) Depth of receiver node
5:\(D_{diff}\leftarrow\) Depth difference b/w sender and receiver node
6:\(RNT\leftarrow\) Relay Node Table
7:Upon receiving \(Q_{p}\)
8:if\(D_{rec}<D_{sen}\)then
9:if\(D_{diff}>d_{th}\)then
10:Compute \(N_{j}\) according to Equation eq:e8
11:if\(N_{j}=min(N_{j})\)then
12: Add node ID in \(RNT\)
13:else
14:drop \(Q_{p}\)
15:endif
16:endif
17:endif
```  
**Algorithm 2** : Route establishment in EEBET  
In BTM and EBET, nodes find their relays according to Equation (8). However, if there is a single node in the transmission range of a sender, it selects it as a relay node even if it is at higher depth than the sender. Also, the only receiver node may again select the same sender node as a forwarder which causes transmission loops. In this process, energy is consumed but the data packet cannot arrive at sink. If the high depth receiver node has its neighbor nodes and selects a node for data transmission other than the node from which it has received data packet, the hops are increased in number and energy dissipation occurs. We have proposed a solution for this problem which is discussed as follows. Loop Detection and Elimination  
During data transmission phase, nodes send data to their intended relay nodes. The initial energy of each sensor node is divided into Energy Levels. An Energy Level is calculated using Equation (9) while total optimum number of Energy Levels is calculated using Equation (29).