## 3 Multichannel MAC Protocol with Directional Antenna for FANET
### Neighbor Discovery with Location Prediction for FANET  
According to the BR-DA-FANET protocol, UAVs in a FANET can discover neighbors without coordination or prior information. Once the initial access is established, each UAV in the FANET obtains essential information about its neighbors, including their ID, location, speed, direction, and clock synchronization. According to this information, UAVs can reduce the neighbor discovery delay. In this section, we propose the neighbor discovery with location prediction (ND-LP) protocol for a FANET from this information to achieve quick main lobe rendezvous and channel rendezvous simultaneously. The sector of the switched beam antenna model is big,  
Figure 15: Frame structure of BARTS and BACTS. and the time between two neighbor discoveries is short. Hence, we can consider that UAVs move in a specific direction with a constant velocity. The location and speed of the \(i\)-th UAV in a FANET are marked as \((x_{i},y_{i})\) and \(v_{i}\), respectively. The angle between the movement direction of the \(i\)-th UAV and the positive direction of the \(x\)-axis is \(\zeta_{i}\). This information is transmitted at time \(t_{i}\). At time \(t_{j}\), UAV \(j\) transmits information to UAV \(i\), and the location of UAV \(i\), which is predicted by UAV \(j\), is shown as:  
\[ \begin{cases}x_{i}^{\prime}=x_{i}+v_{i}(t_{j}-t_{i})\cos\zeta_{i}\\ y_{i}^{\prime}=y_{i}+v_{i}(t_{j}-t_{i})\sin\zeta_{i}\end{cases}  \tag{11}\]  
According to (11), UAV \(a\), which prepares to transmit information to neighboring UAV \(b\), predicts the location of UAV \(b\) in the FANET. Then, the main lobe of UAV \(a\) points toward UAV \(b\), and UAV \(a\) transmits TS1-RTS, as illustrated in Figure 16, to UAV \(b\). When the main lobe UAV \(b\) points toward UAV \(a\), UAV \(b\) can receive TS1-RTS. Subsequently, UAV \(b\) responds with TS1-CTS, as shown in Figure 16, to UAV \(a\). According to the process, quick neighbor discovery can be achieved. \"Receiver ID\" and \"transmitter ID\" refer to the ID of the received UAV and transmitted UAV of this frame, respectively. \"Channel\" in TS1-RTS represents the available channels for transmitting data, while \"Duration\" indicates the transmission duration. \"Channel\" in TS1-CTS indicates the selected channel which is available for UAV \(a\) and UAV \(b\). In this paper, we focus on the one-hop of TS2. When UAV \(a\) intends to transmit data to UAV \(b\), it first judges whether UAV \(b\) is in the one-hop range of TS1 of UAV \(a\). If UAV \(b\) is in the one-hop range of TS1 of UAV \(a\), UAV \(a\) discovers UAV \(b\) according to the ND-LP protocol. UAV \(b\) chooses the available channel which is available for TS2 of UAV \(a\) and UAV \(b\) and transmits the available channel to TS1 of UAV \(a\) through TS1-CTS. UAV \(b\) predicts the location of UAV \(a\) through (11), and then, TS2 of UAV \(b\) points to UAV \(a\). TS2 of UAV \(b\) switches to the chosen channel and reception mode. From location prediction-based TS1-CTS, TS2 of UAV \(a\) points to UAV \(b\) and switches to the chosen channel. Main lobe rendezvous and channel rendezvous are achieved at the same time. The described process above is pictured in Figure 17.  
In order to discover all neighbors of TS2 according to TS1, the multihop method is used to extend the communication range for TS1. If UAV \(b\) is beyond the one-hop range for TS1 of UAV \(a\), TS1 of UAV \(a\) transmits TS1-RTS2 (as shown in Figure 18) to UAV \(b\) through multihop communication. Based on the location prediction obtained from TS1-RTS2, TS2 of UAV \(a\) points to UAV \(b\) and switches to the chosen channel. Subsequently, TS1 of UAV \(b\) responds with TS1-CTS2 (as shown in Figure 18) to UAV \(a\) according to the multihop method. Leveraging the location prediction, TS2 of UAV \(a\) points to UAV \(b\) and switches to the chosen channel. The process is shown in Figure 19.  
Figure 16: The frame structure of TS1-RTS and TS1-CTS.