## 3 Multichannel MAC Protocol with Directional Antenna for FANET
### Protocol for Avoiding Communication Interruption with Location Prediction  
In this section, we propose the avoiding communication interruption with location prediction (ACI-LP) protocol. In a FANET, the continuous movement of UAVs can be susceptible to directional transmission interruptions. To address this issue, each data packet adds the duration of transmission for clock synchronization information, location, speed, and motion direction. Upon receiving the data packet, the receiver sends an ACK that contains clock synchronization information, location, speed, and direction information to the transmitter. Using the information from the data packet or ACK, the receiver can calculate the transmitter location through (11) and distance between two UAVs through (12). Subsequently, the receiver can judge whether the distance is within the communication distance of TS2. In (12), \(\Delta\)t denotes the duration of the transmitted packet, while \((x_{\text{T}},y_{\text{T}})\) and \((x_{\text{R}},y_{\text{R}})\) represent the transmitter location and receiver location, respectively. \[\text{D}_{\text{T},\text{R}}=\sqrt{ \begin{array}{c}\left|x_{\text{T}}-x_{ \text{R}}+v_{\text{T}}\Delta\text{t}\cos\zeta_{\text{T}}-v_{\text{R}}\Delta \text{t}\cos\zeta_{\text{R}}\right|^{2}\\ +\left|y_{\text{T}}-y_{\text{R}}+v_{\text{T}}\Delta\text{t}\sin\zeta_{\text{T }}-v_{\text{R}}\Delta\text{t}\sin\zeta_{\text{R}}\right|^{2}\end{array} }\leq \text{D}_{\text{max}} \tag{12}\]  
To avoid interruptions in main lobe rendezvous caused by the high mobility of UAVs, it is necessary to predict the communication angle. For instance, in Figure 20, UAV \(A\) receives the data packet from UAV \(B\) and prepares to respond with an ACK to UAV \(B\). The angle between the straight line AB and the straight line A'B' is calculated through (13). \(\text{D}_{\text{max}}\) is the maximum communication distance. The straight line A'B' is the straight line AB after motion and is predicted by (14) and (15). \((x_{A},y_{A})\) and \((x_{B},y_{B})\) represent the locations of UAV \(A\) and UAV \(B\) at the time of the last main lobe rendezvous, respectively. \((x^{\prime}_{A},y^{\prime}_{A})\) and \((x^{\prime}_{B},y^{\prime}_{B})\) represent the predicted locations of UAV \(A\) and UAV \(B\) as the ACK is received successfully by UAV \(B\), respectively, which are calculated using (14) and (15). \(T_{CS}\) is the delay for sensing and judging channels availability. \(T_{TS2-RTS}\) and \(T_{TS2-CTS}\) are the delays of TS2-RTS and TS2-CTS, respectively. \(T_{\text{Inf}}\) represents the duration of the preparation-to-transmit information, which corresponds to the duration of the ACK in the given example. \(\Delta\)t is the sum of the duration of the data packet and \(T_{\text{Inf}}\). \(\zeta_{\text{B}-\text{ran}}\) represents the angle between the movement direction of UAV B and the positive x-axis direction at the time of transmitting the ACK. Through (13), if \(\alpha\leq\frac{\theta_{\text{P}}}{2}\), the next communication is not interrupted, and UAV \(A\) transmits ACK to UAV \(B\). If \(\alpha>\frac{\theta_{\text{P}}}{2}\), UAV \(A\) transmits TS2-RTS  
Figure 19: Main lobe rendezvous and channel rendezvous are achieved in a multihops distance of UAV \(a\) TS1 as well as UAV \(b\) TS1 according to ND-LP. Figure 18: The frame structure of TS1-RTS2 and TS1-CTS2. to UAV \(B\), and UAV \(B\) responds with TS2-CTS to UAV \(A\) in order to achieve main lobe rendezvous again. The frame structure of TS2-RTS and TS2-CTS is shown in Figure 21.  
\[\alpha=\cos^{-1}\frac{(x_{A}-x_{B},y_{A}-y_{B}).(x^{\prime}_{A}-x^{\prime}_{B},y^ {\prime}_{A}-y^{\prime}_{B})}{|(x_{A}-x_{B},y_{A}-y_{B})|*(x^{\prime}_{A}-x^{ \prime}_{B},y^{\prime}_{A}-y^{\prime}_{B})}\leq\frac{\pi}{N} \tag{13}\]  
\[ \begin{cases}x^{\prime}_{\text{A}}=x_{\text{A-tran}}+v_{\text{A-tran}}(T_{CS}+T _{TS2-RTS}+T_{TS2-CTS}+T_{\text{Inf}})\cos\zeta_{\text{A}}\\ y^{\prime}_{\text{A}}=y_{\text{A-tran}}+v_{\text{A-tran}}(T_{CS}+T_{TS2- RTS}+T_{TS2-CTS}+T_{\text{Inf}})\sin\zeta_{\text{A}}\end{cases}