## 4 Designed Schemes
### Data Forwarding and Cooperation  
The SRN advances the information packets toward the DSN and the RLN for further forwarding. The DSN checks the received packet BER, if the associated BER value is lower than the measured threshold value, the DSN accepts the information. The DSN checks the final DSN vicinity, if the sink lies inside the communication range then it sends the information directly towards the sink. However, if the received packet BER at DSN exceeds the threshold value, then the DSN sends a REQ towards the RLN to send the same information packet. The RLN waits for the specific interval of time and then amplifies the received packet and sends it back to the DSN with acknowledgment as shown in Figure 6.  
The DSN again checks the BER, if the BER again exceeds the threshold value then drops the data packet. Moreover, if the relaying packet BER is less than the threshold, the DSN combines these two received packets through MRC technique [33], and forwards optimal information towards the sink, if the sink is in range. However, in case of the sink does not exists in the communication range of the DSN, then it selects second DSN and second RLN by considering the above criteria. This process is continued until the packet reach to the upper sink nodes by using multi-hopping as shown in Figure 7. The sink node receives the packets and extracts the information and further forwards them to the offshore data center. Figure 6: ACK, NACK, and REQ scenario. After specifying the DSN and RLN, the SRN broadcasts the information packets and neighbors get them. However, only the DSN and RLN contribute to the forwarding of the information. The packet received at the DSN and transmitted by the SRN is modeled as [34],  
\[Y_{sd}=bG_{sd}+N_{sd} \tag{4}\]  
where \(Y_{sd}\) is the packet received at the DSN and \(b\) shows the original packet transmitted by the SRN. The variables \(G_{sd}\) and \(N_{sd}\) show the link gain and link noise form the source to DSN in the respective order. The information packet received by the RLN from the SRN is shown as [35],  
\[Y_{sr}=bG_{sr}+N_{sr} \tag{5}\]  
where \(Y_{sr}\) is the packet received at the RLN. \(G_{sr}\) is the path gain from the SRN to RLN and \(N_{sr}\) is the path noise between the SRN and RLN. The RLN amplifies the received packet by an amplifying factor \(\beta\) and forwards it towards the DSN. The received packet at the DSN transmitted by the RLN can be written as [36],  
\[Y_{rd}=\beta Y_{sr}G_{rd}+N_{rd} \tag{6}\]  
where \(Y_{rd}\) denotes the packet received at the DSN over the RLN, \(Y_{sr}\) is the packet at RLN from SRN. The parameter \(G_{rd}\) shows the link gain from RLN to DSN and \(N_{rd}\) is the noise of the path from RLN to DSN. The amplifying factor \(\beta\) is written as [37],  
\[\beta=\sqrt{\frac{1}{P_{s}|G_{sr}|^{2}+\sigma^{2}}} \tag{7}\]  
The above equation shows that the amplifying factor depends on source transmitted power \(P_{s}\), the SRN-RLN link gain \(G_{sr}\) and the noise power \(\sigma^{2}\). The DSN combines the two received packets through the MRC as a combining technique [38] as shown in Figure 8 and forwards the information further  
Figure 7: Cooperation model. The Algorithm 1 further shows the operation of EERD and CoEERD. The flow chart of CoEERD scheme is shown in Figure 9.  
```
Start Network initialization BER: Bit Error Rate SN: Source node T\({}_{x}\): Transmission range DN: Destination node RN: Relay node R.E :Residual energy BER :Bit error rate SKN :Sink node d: Distance Control packet broadcast Find optimal relay Calculate function Function(f)= R.E/ BER \(\times\)d if Node have maximum function value=then DN selected=do if BER > 0.5 Find RN=do RN found=true if BER < 0.5 Packet accepted=true check SKN vicinity if Sink exists the T\({}_{x}\) of the SN=then Packet reached to the SKN=true while Use multi-hoping Packet reached to the SKN=do Packet accepted=true endif endif endif endif endwhile break
```  
**Algorithm 1**Information sharing, path set up and data forwarding in EERD and CoEERD.