# Cooperative Position Aware Mobility Pattern of AUVs for Avoiding Void Zones in Underwater WSNs
## 3 Proposed Schemes
### Cooperative Position-Aware Mobility Pattern  
The objective of Co PAMP is to achieve high network throughput. In Co PAMP, two best neighboring gliders of the source glider are selected as the relay, and they cooperate with the source glider to enhance the SNR of the received signal by re-transmitting the data packet at the destination and combine by using the MRC as the diversity technique.  
During the data transmission phase, the source glider transmits a data packet towards the destination glider, and neighboring gliders also receive that data packet. When the packet is received at the destination glider, the instantaneous SNR is calculated at the destination as follows [31]:  
\[\gamma_{AF}=\gamma_{sg,rg,dg}+\gamma_{sg,dg} \tag{17}\]  
where \(\gamma_{sg,dg}\) is the link SNR between the source glider and the destination glider and \(\gamma_{sg,rg,dg}\) is the equivalent SNR between the source glider and the destination glider through a relay glider. The equivalent SNR of the relayed signal by the glider is calculated as follows [31]:  
\[\gamma_{sg,rg,dg}=\frac{\gamma_{sg,rg}\gamma_{rg,dg}}{\gamma_{sg,rg}+\gamma_ {rg,dg}+1} \tag{18}\]  
If the SNR is greater than the packet acceptance threshold \((PA_{th}\geq 0.8)\), then the packet is marked as successfully received, and no glider is bothered to relay the same data packet for cooperation towards the destination. On the other hand, if the SNR of the received packet is less than the \(PA_{th}\), destination gliders send the negative acknowledgment (NACK) to the source glider. On receiving NACK, the first glider in priority according to the gliding depth relays the data to cooperate with the source glider by sending the same data packet towards the destination. Again, the SNR is checked at the destination; if the SNR is still less than the \(PA_{th}\), then the second best relay glider takes part in cooperative communication and transmits the data packet towards the destination. The relationship between the transmitted signal to the source node and relay nodes is computed according to Equations (19) and (20) [31].  
\[Y_{(sg,rg)}=X_{sg}g_{(sr,rg)}+n_{(sg,rg)} \tag{19}\]  
\[Y_{(sg,dg)}=X_{(sg)}g_{(sg,dg)}+n_{(sg,dg)} \tag{20}\]  
The relayed signal from the relay to the destination is represented as [31]:  
\[Y_{(rg,dg)}=Y_{(sg,rg)}g_{(rg,dg)}+n_{(rg,dg)} \tag{21}\]  
\(X_{sg}\) is the signal sensed and transmitted by the source glider \(sg\); \(Y_{(sg,dg)}\) and \(Y_{(sg,rg)}\) are the signals received by the destination glider \(dg\) and the relay glider \(rg\), respectively. \(Y_{(rg,dg)}\) is the relayed signal from the relay glider \(rg\) to the destination glider \(d\). \(g_{(sg,dg)}\) is the channel gain from the source glider to the destination glider; \(g_{(sg,rg)}\) denotes the channel gain from the source to the relay glider; \(g_{(rg,dg)}\) represents the channel gain from the relay to the destination glider. \(n_{(sg,dg)}\) shows the channel noise from the source to the destination glider; \(n_{(sg,rg)}\) is the channel noise from the source to the relay glider; and \(n_{(rg,dg)}\) is the channel noise between the relay and the destination glider.  
The two signals received at the destination are then combined by using MRC as the diversity combining technique to achieve a better good-put result. We target delay-sensitive applications and considered the amplify and forward mechanism instead of decode and forward, because we aim to achieve high reliability by choosing a route with high \(lq\).  
Consider Figure 6 for the protocol operation of Co PAMP. Except cooperative routing, the protocol operation of Co PAMP is the same as that of PAMP.