## 4 Gdgor-Ia
### Next-Hop Forwarder Set Selection Criterion  
In geographic routing single forwarder node is nominated to transmit data towards the destination. The primary disadvantage associated with the single forwarder selection is packet loss in case of bad link quality or void hole. Therefore, we have incorporated the geo-opportunistic routing paradigm to utilize the broadcast nature of wireless channel to nominate multiple forwarder node. This forwarding enables the selection of the potential forwarder set to ensure the reliable data delivery with minimal retransmissions in worst scenarios. However, it incurs more delay because all neighbor nodes wait till packet reaches the farthest node. To overcome this problem, we intend to select TC with less number of nodes but within a threshold set after considering link quality in Equation (2). This shows the error probability \(P_{BER}\) and collision rate probability \(P_{CR}\) where \(L\) is the size of packet [36]. The selection of TC with minimum number of neighbors helps in reduction of interference because minimum number of neighbors access the wireless channel. Moreover, the delay is reduced up to significant amount due to the participation of few nodes from the NC. Furthermore, within the TC, election of next-hop forwarder set is done through advancement towards the destination (ADV). The ADV is calculated for the set of nodes \(N_{k}=\{N_{1},N_{2},N_{3},...\}\) in the TC. The nodes are prioritized on the basis of highest advancement towards the destination. \[\alpha=\frac{1}{P_{CR}}\times(1-P_{BER})^{L} \tag{2}\]  
\[ADV(n_{i})=D(n_{k},s_{n}^{*})-D(n_{i},s_{i}^{*}) \tag{3}\]  
\(ADV(n_{i})\) shows the advancement of \(n_{i}\), and neighbor of the source node is represented with \(n_{k}\) towards its closest sonobuoy in Equation (3). For node \(n_{i}\) belonging to the potential neighbor set \(F_{set}(k)\) taken from Equation (1), normalized advancement towards the destination is calculated according to Equation (4) [5]. \[NADV(n_{i})=ADV(n_{i})\times P(d_{k}^{i},L) \tag{4}\]  
Algorithm 2 illustrates the selection of next hop forwarder in GDGOR-IA. Firstly, source node acquires the information about the neighbor nodes which is performed as discussed in Algorithm 1. Once, we have the neighbor information, source node proceeds to the next step for the nomination of potential forwarder node to execute the network operations. Let's assume that source node \(n_{a}\) deployed in downstream target cube which has neighbor cubes consists of numerous set of neighbor nodes \(PF_{set}(n_{a})\) named as potential forwarders of \(n_{a}\). This set is a subset of \(F_{set}(n_{a})\) in all nodes meet the selection conditions imposed through Equation (2). If \(PF_{set}(n_{a})\) is an empty set, we take help from the information of Algorithm 1 providing the set of available NCs which can be used as target cubes. Each node differentiates itself from the other based on the cube ID. In case of multiple available target cubes, we obtain multiple forwarder sets \(F_{set}(n_{a})\) for \(n_{a}\). In such conditions, we compare the accumulated NADV of all sets to select the cubes which has less node number for avoiding the interference and minimizing the delay. ```
1 begin
2 Procedure: select next-hop forwarder
3 for\(n_{b}\in F_{set}(n_{a})\)do
4 Select nodes residing in TC from \(F_{set}(n_{a})\)
5 Endfor
6 end for
7 Put selected nodes in \(PF_{set}(n_{a})\)
8 if\(PF_{set}(n_{a})\leq F_{set}(n_{a})\)then
9 if\(PF_{set}(n_{a})=\{\}\)then
10 Run phase I of the algorithm
11 Select cube placed at second priority in \(NCs(n_{a})\)
12 else
13 Calculate NADV for \(PF_{set}(n_{a})\) according to Equation (4)
14 Order all the nodes in \(PF_{set}(n_{a})\) according to their NADV
15 Select node with highest NADV as next hop forwarder
16 Calculate \(T_{hold}\) according to Equation (5) for \(PF_{set}(n_{a})\)
17 end if
18 Endif
19 end for
20 Endif
21 end for
22 End procedure
23 end for
```  
**Algorithm 2**Next-hop forwarder selection.