# Cooperative Position Aware Mobility Pattern of AUVs for Avoiding Void Zones in Underwater WSNs
## 3 Proposed Schemes
### Position-Aware Mobility Pattern  
Let there be \(n\) gliders in the network volume where \(N\) nodes are deployed. With the help of a pump and magnetic compass, gliders can change their vertical and horizontal motion and direction. The concept of sojourn positions [2] is used to minimize the uncertainty in the estimation of the self-confidence (s-confidence) and neighbor-confidence (n-confidence) region. The gliders transmit and receive information during their stay at sojourn positions. The control information, like s-confidence region, direction and present position of a glider, is continuously shared with neighboring gliders during the stay time. On the basis of this information, a glider estimates its future position and the n-confidence region of a neighboring glider. With the help of a magnetic compass, the direction of gliders is maintained, and gliders in the excess zone move outwards in order to avoid the void zone. After the movement, gliders stop at sojourn positions for a predefined'stay time'. During this time, control information and data packets are shared between neighbors. On the basis of control information, a transmitting glider (sender) predicts the position of the receiving glider (receiver) and estimates the n-confidence region. On the basis of these estimations, transmission power is adjusted. Uncertainty in the estimation of the position and n-confidence region of any glider may lead to packet drop and the waste of energy in terms of the transmission power. The protocol operation of PAMP is shown in Figure 1.  
Position Extrapolation  
The control information shown in Figure 2, which is shared between neighbors, includes present position, future direction and the s-confidence region of gliders. Depending on the present state and properties, each glider estimates a few parameters, and the s-confidence region is one of these. Basically, volume around the glider'seen by a glider itself' is known as the s-confidence region. At the s-confidence region, the glider is confident that it will successfully receive any packet. The s-confidence region is calculated as follows:  
\[SC_{region}=((X^{2}+Y^{2}+Z^{2})\leq R^{2})+error(p) \tag{1}\]  
where \(X\), \(Y\) and \(Z\) are the coordinates of the neighbors in the s-confidence region of the glider. \(X\), \(Y\) and \(Z\) are used to check whether they lie in the depth range (\(R\)) of a glider; if yes, they are part of the s-confidence region that is the volume seen by the glider. \(error(p)\) is a constant for the uncertainty in the position of a glider, and it is same for all coordinates. The \(X\), \(Y\) and \(Z\) coordinates are computed as given in Equation (2). \[X =x_{0}+R\cos(L+\frac{\pi}{n})+error(p)\] \[Y =y_{0}+R\sin(L+\frac{\pi}{n}+error(p)) \tag{2}\] \[Z =z_{0}+R\sin(L+\frac{\pi}{n}+error(p))\]  
where \(x_{0}\), \(y_{0}\) and \(y_{0}\) are considered as the origin of the glider and \(L\) is the length of the slope to adjust the angle (\(\frac{\pi}{n}\)) for the future glider position to adjust the transmission power; which is calculated as given in Equation (3). \[TP_{total}=(\Delta R)P_{n+1}+error(p) \tag{3}\]  
\(TP_{total}\) represents the total transmission power; (\(\Delta R\)) is a range for which the transmission power (\(P_{n+1}\)) needs to be adjusted. Therefore, each glider shares its information regarding the s-confidence region with its neighbors to adjust their transmission power. Figure 1: Protocol operation of position-aware mobility pattern (PAMP). Figure 2: Control information packet format. Suppose that Glider 1 sends a control packet to Glider 2. After the successful reception of the control information, the neighboring glider does not rely only on the s-confidence region; rather, it estimates n-confidence region, which is the region around the glider'seen by its neighbors', and the neighboring glider (Glider 2) is confident that the receiving glider (Glider 1) will successfully receive any packet that reaches this region. It is (n-confidence region) calculated as given in Equation (1).