## 4 Proposed Protocol Design
### T-Based Routing Topology  
In the proposed method, the metal detector is attached to the pole with GPS, and camera is mounted on the vehicle head. The metal detector pole is rotated from \(0^{\circ}\) to \(180^{\circ}\) in the moving direction. If the metal detector detects the land mine, then the moving pole is immediately locked the particular place. The locked location is identified with the help of GPS information and the camera is used to take a photo of the marked location. Finally, the USV sends the GPS information and photo the BS through the router node. Using this information, the trained person easily reaches the landmine buried location and removes safely. This article mainly focuses to cover the entire searching area with minimal numbers of sensor deployed USVs. For this, the sensing area is divided into strips based on the sensing range of metal detector and pole length. The number of strips in the sensing area is derived based on the Equation (2) and each strip is covered by a single USV which means that the number of USVs is equal to the number of strips. The CN moves vertically alongside its neighbouring deployed nodes and drops the router nodes based on the transmission range, so that it can easily establish the multi-hop T-based routing topology. Thus, it ensures the connectivity between the mobile nodes and BS, as shown in Figure 3.  
Figure 3: T-based routing topology. The proposed mechanism makes use of event-based data collection mode by transmitting the Path Reservation Message (PRM), in which the source node reserves the routing to the CN when it detects the events. Only the direct neighbours of each node are aware of information like neighbours ID and distance. Initially, the source node transmits PRM using its default transmission range, which includes the source node ID and hop count. The nodes located in the source node transmission range open the PRM message and determine whether it is from its immediate neighbour or not. The source node identifies that the next hop node has been successfully reserved when it receives the acknowledgment (ACK) from its direct-hop neighbour before the timeout. If the source node does not receive the acknowledgment from its immediate neighbour, then it retransmits the PRM with incremented hop count value (HC = 2). It means that the source node receives the ACK from its second-hop neighbours and other nodes in the \(tr\) of source nodes will discard this PRM. If the source node does not receive the ACK before the maximum attempt, then it will expand the transmission range by \(Xtr\), where (X = 1, 2, 3...). By this manner, the intermediate nodes reserve the routing to BS. Additionally, the sensor nodes can adjust the power of their data transmission based on the received signal strength of PRM and ACK. The process of PRM-ACK based routing is described in Algorithm 1. ```
1 begin Selection of next hop node
2 Notation\(node_{SN}\)--Source node; \(node_{NN}\)--Neighbor Node; \(node_{IN}\)--Intermediate Node
3 Initialization Source node broadcast the PRM message
4\(x=1\); \(9\)x is hop count%
5 whiletransmission range \(t_{r}\) (\(x\times t_{r}<=M\times t_{r}\))do\(node_{SN}\) or \(node_{IN}\) broadcast the PRM message
6 if(\(node_{NN}(x)\).receive == PRM message)then
7 if\(node_{NN}(x)\)==idlethen
8 send ACK message to \(node_{SN}\) or \(node_{IN}\)
9
10 else
11 send WAIT message to \(node_{SN}\) or \(node_{IN}\)
12
13 end if
14 if\(node_{SN}\) or \(node_{IN}\) receives ACK before time-outthen
15 Respective node will act as next hop \(node_{IN}\)
16
17 else
18\(node_{SN}\) or \(node_{IN}\) increments the value \(x+1\)
19
20 end if
21
22 end if
23
24 end if
```  
**Algorithm 1**PRM-ACK based route formation. As shown in Figure 4, node \(B\) is currently sending its data to the CN, at the same time node C wants to send its data and node \(C\) sends PRM to node \(B\). But, node \(B\) sends back the wait message instead of ACK which means that node \(B\) either currently sends its own data or processes the PRM message of other node.