## 5 Numerical Results  
### Simulation Results of Time Synchronization Offset and Channel Estimation in LOS and NLOS Channels  
In the first simulation, we evaluate the impact of the LOS and NLOS channels on the time synchronization offset, as well as the results of channel estimation in CP/CS-SC-FDE. Table 1 contains the parameters and respective settings of the simulations.  
The channel considered includes a LOS UAV channel and two NLOS UAV channels, corresponding to channels 1, 2, and 3, respectively. The LOS UAV channel is an outcome of the Rice fading channel. The two NLOS UAV channels are outcomes of the Rayleigh fading channel. The channel is assumed constant during a transmission block in all the results. The CIRs of three channels are shown in Figure 5. As seen from Figure 5, each of the three channels has 8 non-zero taps. Channel 1 is the LOS channel, whose PwMP is the first path. Channel 2 and channel 3 are NLOS channels whose PwMPs are the middle and  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Parameters** & **Settings** \\ \hline Modulation type & QPSK \\ \hline Preambles type & Zadoff-Chu Sequences \\ \hline The length of preambles (\(M\)) & 128 \\ \hline The length of data (\(N\)) & 1024 \\ \hline FFT Size & 128/1024 \\ \hline The length of CP (C) & 64 \\ \hline The length of CS (\(D\)) & 0 or 64 \\ \hline Channel Model & Rice/Rayleigh fading channel with 8 non-zero taps \\ \hline \(E_{b}/N_{0}\) & 20 dB \\ \hline \hline \end{tabular}
\end{table}
Table 1: Simulation parameters.  
last paths, respectively. The selection of three channels is very representative. Moreover, the key parameters of these three channels are shown in Table 2.  
The sliding correlation values for time synchronization under these three channels are presented in Figure 6. As shown in Figure 6, in channel 1, the correlation peak is \(u_{C}\), which corresponds to the synchronization point \(C=64\), and there is no TO. Under channels 2 and 3, the correlation peak is \(u_{C+E}\), which corresponds to the synchronization point \(C+E=92\) and 124, and there is a TO, which is equal to \(E\). The results of \(u_{\text{max}}\) are also shown in Table 2. Therefore, there is no TO under the LOS UAV channel, whereas there is a TO with the value \(E\) under the NLOS UAV channel.  
Figure 7 shows the channel estimation results in a CP-SC-FDE system. Due to the TO in the CP-SC-FDE system, the FFT region of channel estimation and equalization will introduce LISI. Comparing Figures 5 and 7, it can be seen that there is an error in the channel estimation in the CP-SC-FDE system. As a comparison, Figure 8 shows the channel estimation result in a CP/CS-SC-FDE system. We can observe that the channel estimation is the cyclic shift of the channel in Figure 5 as deduced in Section 3. In channel 1, \(E=0\), and the channel estimation result has no cyclic shift. In channel 2, \(E=28\), and the channel estimation result is \(u_{C+E}=10\). The results of the channel estimation result in a CP/CS-FDE system are shown in Table 2.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Parameters** & **Channel 1** & **Channel 2** & **Channel 3** \\ \hline \(E\) & 0 & 28 & 60 \\ \hline \(F\) & 51 & 32 & 0 \\ \hline \(u_{\text{max}}\) & \(u_{C}\) & \(u_{92}=u_{C+28}\) & \(u_{124}=u_{C+60}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Simulation parameters  
Figure 5: The CIR of three channels of the first simulation.  
Figure 6: The sliding correlation value for time synchronization.  
estimation result corresponds to a 28-point cyclic shift. In channel 3, \(E=60\), and the channel estimation result corresponds to a 60-point cyclic shift.