## 4 Evaluation
### Simulation Results
The gain in throughput of this figure is denoted as \(\Delta G_{\mathrm{thr},(q,1)}(\%)\) with \(q=2,3\), and is determined following (39). 11. Evaluation of the BLER for Case 1 (Detect-and-Forward NB-IoT), Case 2 (Decode-and-Forward with NB-IoT) and Case 3 (Decode-and-Forward with NB-IoT/DVB-S2(X)), whose performance curves can be found in Figures 17-19, respectively. From the simulations of the end-to-end BLER and throughput in terms of the SNR in the optical feeder link (uplink), assuming a very high SNR in the radio access link (see Figure 9), it is possible to observe the region in which the uplink communication limits the performance of the end-to-end transmission. In all these plots, the dotted lines represents the cases where the BLER is higher than the target BLER (i.e., BLER \(>0.01\)), whereas the continuous lines identify the situations in which the BLER is lower than the target BLER (i.e., BLER \(\leq 0.01\)). For a better indication, the grey area in the figure shows the region of SNRs in which the tested code rates for NB-IoT satisfies the target BLER. Thus, it is possible to observe that \(R_{c,\text{iot}}=0.3333\) provides the best throughput when the SNR of the feeder link is ranged between 13 and 19 dB, \(R_{c,\text{iot}}=0.6666\) is the best option when the feeder link SNR is between 19 and 22 dB, and finally \(R_{c,\text{iot}}=0.95556\) is the most convenient alternative when the SNR in the uplink direction of communication is larger than 22 dB. According to these results, we now consider that the SNR of the feeder link is 15, 20, and 25 dB, for determining the degradation that different wind speeds introduce on the end-to-end link. Figure 10 evaluates the degradation of the BLER (figures on the left) and throughput (figures on the right) when the wind speed is \(v=10\), 21 and 30 m/s, and the SNR in the uplink direction of communication is 15, 20 and 25 dB. According to these results, the higher is the SNR of the optical feeder link, the lower is the degradation that the wind introduces on the end-to-end BLER and throughput of the forward NB-IoT link. Consequently, a SNR of 15 dB is used as reference value in the optical feeder link from now on, to compare the performance of the three satellite relaying architectures under study. Figure 9: End-to-end BLER (left) and throughput (right) versus \(E_{\text{b}}/N_{0}\) in the feeder link for a NB-IoT frame (\(\text{SNR}_{\text{al}}=20\,\text{dB}\)). NB-IoT code rates: 0.3333 (square), 0.66667 (circle) and 0.95556 (diamond), when the wind speed is \(v=21\,\text{m}/\text{s}\). Solid (dashed-) lines with (un)filled markers: BLER \(\leq 10^{-2}\) requirement (not) fulfilled. Diameter of telescope aperture: \(W_{0}=21\,\text{cm}\). Figure 10: End-to-end BLER (left) and throughput (right) versus \(E_{\text{b}}/N_{0}\) in the access link for a NB-IoT frame (\(\text{SNR}_{\text{fi}}=15\), \(20\), and \(25\,\text{dB}\)). NB-IoT code rates: \(0.33333\) (square), \(0.66667\) (circle), and \(0.95556\) (diamond), when the wind speed is \(v=10\,\text{m}/\text{s}\) (red), \(v=21\,\text{m}/\text{s}\) (blue) and \(v=30\,\text{m}/\text{s}\) (magenta). Solid (dashed-) lines with (un)filled markers: \(\text{BLER}\leq 10^{-2}\) requirement (not) fulfilled. Diameter of telescope aperture: \(W_{0}=10\,\text{cm}\). Figure 11 presents the throughput for each overlapping factor and code rate for Case 1 (Detect-and-forward with NB-IoT). Simulation results show that the segment of the NB-IoT code rates that satisfies the target BLER is the lowest one (i.e., \(R_{\text{c,iot}}=0.2222\), \(0.259\), and \(0.3\)) for all the overlapping factors under study. The medium code rate of \(R_{\text{c,iot}}=0.4444\) could only achieve its maximum throughput with no overlapping (i.e., when \(\delta=0\%\)). Medium and larger code rates are mainly penalized by the SNR of the optical feeder link (uplink), and they are not able to achieve their maximum throughput (see Table 4).