# An Efficient SC-FDM Modulation Technique for a UAV Communication Link
## 6 Results Analysis  
In this research, MATLAB was used to perform the PAPR simulations of SC-FDM and OFDM as well as the probability of bit error simulation for SC-FDM using different kinds of modulation schemes such as BPSK, QPSK, 8-PSK, 16-QAM, and 64-QAM. Of course, it is essential to select the optimal number of subcarriers, types of the pulse shaping filters and channel equalization when simulation parameters are inputted. The number of subcarriers and symbols depends on the cyclic prefix and the subcarrier spacing. When RC and RRC pulse-shaping filters are used to filter a symbol stream, they can minimize an ISI. Half of this filtering can be done on the transmitter and the second half can be done on the receiver. The impulse and frequency responses of the RC filter based on different roll-off factors have been plotted and shown in Figure 9. Furthermore, the equalizer can be used to get the recovery of the transmit symbols by reducing an ISI. By removing all ISI, the zero forcing equalizer can be the optimal choice in the noiseless channel. On the other hand, when a channel is noisy, this equalizer significantly amplifies the noise at frequencies. In this case, the minimum mean square error (MMSE) equalizer can be more efficient than zero forcing. The main function of an MMSE equalizer is minimizing the ISI components and the entire power of the noise in the output instead of eliminating ISI completely. Figures 10 and 11 plot the peak-to-average power ratio (PAPR) measurements of SC-FDM and OFDM against the complementary cumulative distribution function (CCDF). According to the simulation results, which are shown in Figures 10 and 11, the SC-FDM has an advantage over OFDM because of its lower PAPR that leads to an increase in battery performance for a UAV. As shown in Figure 10a,b, it can be seen that the PAPR value of SC-FDM for a BPSK modulation scheme (5.6 dB) is almost the same as that for QPSK (5.7 dB) when the CCDF is \(10^{-4}\). At the same point, the PAPR value of OFDM for BPSK is 8.8 dB and, for QPSK, it equals 8.6 dB. In addition, the simulation results show that 8-PSK has a slightly lower PAPR value than 16-QAM for both SC-FDM and OFDM. From Figure 11, it can be observed that increasing the order of QAM modulation scheme (16-QAM and 64-QAM) results in increasing the PAPR values of SC-FDM and OFDM from 8 dB and 10 dB to 10 dB and 12.2 dB, respectively. From Figures 10 and 11, we can conclude that the abrupt change in the CCDF value comes from the fact that PAPR values are expressed in logarithmic scale for both SC-FDM  
and OFDM modulation techniques. The PAPR values of SC-FDM and OFDM for different modulation schemes are presented in Table 2.  
Figure 10: The PAPR performances of SC-FDM and OFDM for M-ary PSK modulation schemes: **(a)** BPSK; **(b)** QPSK; **(c)** 8-PSK. Figure 9: The impulse and frequency responses of the remote control (RC) filter: **(a)** The impulse response; **(b)** the frequency response. The probability of bit error of different modulation schemes for SC-FDM is shown in Figure 12. From this figure, we can observe that the BPSK and QPSK modulation schemes achieve better performances than other modulation schemes. It is evident that BPSK and QPSK modulation schemes are very suitable for the SC-FDM modulation technique, according to their PAPR and the probability of bit error performances, see Table 2 and Figure 12.  
In our work, in order to evaluate the complexity of the proposed framework in terms of computation time, we used a computer with an Intel(R) Core(TM) i7-4790 CPU 3.60 GHz; RAM: 16.0 GB; Operating System: Windows 8.1 Pro 64-bit and MATLAB R2016a. As demonstrated in \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Modulation Scheme**} & \multicolumn{2}{c}{**PAPR (dB)**} \\ \cline{2-3}  & **SC-FDM** & **OFDM** \\ \hline BPSK & 5.6 & 8.8 \\ QPSK & 5.7 & 8.6 \\
8-PSK & 7.6 & 9.7 \\
16-QAM & 8 & 10 \\
64-QAM & 10 & 12.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: PAPR results for SC-FDM and OFDM.