## 5 Conclusions and Futures Extensions
### Concluding Remarks
For Decode-and-Forward with NB-IoT, the gain in throughput observed with time-packed signalling with respect to no-time packed going from 45-65% for low \(E_{\text{b}}/N_{0}\) of the access link to 10% for medium-to-large \(E_{\text{b}}/N_{0}\) values. Therefore, the decoding of the information permits to achieve higher gains at lower \(E_{\text{b}}/N_{0}\). However, at larger \(E_{\text{b}}/N_{0}\), the behavior of time-packed and no-time-packed signals is quite high and, as consequence, the improvement in throughput when comparing both schemes is reduced. Finally, for the Decode-and-Forward with NB-IoT/DVB-S2(X), the gain in throughput varies between 50-65% for medium \(E_{\text{b}}/N_{0}\) values in the access link to 45% for high \(E_{\text{b}}/N_{0}\) ones. In this scenario, the large error correction capability of LDPC codes enables one to remove the residual ISI that the equalizer is not able to eliminate. Consequently, it can deal successfully with the strong ISI that time-packing with large overlapping factors introduce. Next, when comparing the aggregate throughput that the three relaying strategies offer, it can be concluded that the ones based on the Decode-and-Forward architecture provide the largest values. Specifically, the Decode-and-Forward with NB-IoT offers a better throughput for low \(E_{\text{b}}/N_{0}\) in the access link, whereas the Decode-and-Forward with NB-IoT/DVB-S2(X) provides a larger throughput for medium-to-high \(E_{\text{b}}/N_{0}\) values. Note that Decode-and-Forward with NB-IoT regenerates the NB-IoT signal in the satellite, whereas the Decode-and-Forward with NB-IoT/DVB-S2(X) protects the NB-IoT symbols by introducing the code rate of DVB-S2(X) in the optical feeder link. In this situation, when the \(E_{\text{b}}/N_{0}\) of the access link was low, the LDPC decoder of DVB-S2(X) did not converge and, due to that, it introduced errors in the NB-IoT frames that were decoded on-board the satellite for re-transmission in the radio access link. In this situation, these NB-IoT frames were protected with a code rate larger than their equivalent for the other cases; therefore, it can be concluded that at a low \(E_{\text{b}}/N_{0}\) in the radio access link, the Case 3 relaying strategy is not the optimum one. However, when the \(E_{\text{b}}/N_{0}\) of the access increased, the LDPC decoder started to converge and, due to that, it managed to remove the erroneous bits that were introduced by the optical feeder link in the NB-IoT frames that were encapsulated in the DVB-S2(X) signal. Here, as the NB-IoT frames had a higher code rate than the code rates that were used for other configurations, it offered the largest throughput. Finally, it is remarked that the link layer should be prepared for adjusting dynamically the transmission architecture according to the \(E_{\text{b}}/N_{0}\) of the access link. Therefore, a control channel from the NB-IoT terminals to the gateway would be necessary, such that the estimated \(E_{\text{b}}/N_{0}\) of the access link can be known in advance when selecting the MCS of the NB-IoT frame, enabling to improve the end-to-end throughput. In all cases, the IoT terminal would receive the data in NB-IoT signalling format. Note that all required modifications of the Decode-and-Forward of NB-IoT with and without DVB-S2(x) encoding would be transparent to the IoT terminal, since the time-packing signalling, NB-IoT regeneration, and the DVB-S2(X) encapsulation would be performed at the satellite feeder link.