# Ionospheric Polarization Techniques for Robust NVIS Remote Sensing Platforms
## 6 Conclusions  
After analyzing the results obtained, we observed that the ordinary and extraordinary waves are not received with the same E\({}_{\text{b}}\)/N\({}_{0}\), which as we have seen can differ up to 3 dB. These E\({}_{\text{b}}\)/N\({}_{0}\) differences can provide us the possibility to apply polarization diversity techniques to take advantage of this fact. First of all, we can conclude that selection combining helps us receive the highest E\({}_{\text{b}}\)/N\({}_{0}\) between ordinary and extraordinary waves. Consequently, by this polarization technique, we can receive meanly lower BER results. On the other hand, equal-gain combining is also a polarization technique that can obtain an E\({}_{\text{b}}\)/N\({}_{0}\) 3 dB higher than the highest E\({}_{\text{b}}\)/N\({}_{0}\) received by the ordinary and extraordinary waves. However, this possibility depends on the received electromagnetic noise, and it is limited to a 1% probability, but it is 20% probable to receive a higher E\({}_{\text{b}}\)/N\({}_{0}\) than the highest received by the ordinary and extraordinary waves. Taking these results into account, if we make use of PSK, FSK, and QAM modulations orders between 2 and 32 with a power transmission of 50 W, we analyzed that even with using polarization techniques, the BER obtained for modulations of order up to 16 is not low enough to ensure communication. Moreover, analyzing the results, we see that by PSK modulations with selection combining, we obtain the best BER results. For 4 PSK and 8 PSK modulations with selection combining and power transmissions variations between 6 and 50 W, we can observe that the best BER results are similar for 4 PSK with power transmissions between 12 and 50 W. The second best BER results obtained are for 4 PSK with 6 W and 8 PSK with 50 W.  
In conclusion, we summarized in Table 2 three different options depending on the application and needs of the remote sensing system. Figure 12: Number of transmissions according to selection combining. If our remote sensing system requires a low power usage, we can opt to use of a 4 PSK with a power transmission of 6 W. In this case, we have a 71% probability to receive a BER lower than \(10^{-4}\) and a 99% probability if we make two retransmissions in the worst case. If our remote sensing system can make use of high power transmissions, the best option will be the usage of the 8 PSK with 50 W. This case will offer double the bitrate than 4 PSK as well as a probability of 70% to receive a BER lower than \(10^{-4}\) and a probability of 99% if we make two retransmissions in the worst case. Lastly, if our remote sensing system requires low power consumption and needs to receive all packets with a minimum of retransmissions, we can choose a 4 PSK with a power transmission of 12 W. In this case, we have a 92% probability to receive a BER lower than \(10^{-4}\) and a 99% probability if we make one retransmission. Moreover, the application of an error correction code (ECC) will highly increase the probabilities of receiving correctly the first packet transmitted. On the other hand, polarization techniques can compensate for the lower gains of compact antennas, making more feasible the use of them on HF communications. In addition, remote systems allow for using low power transmissions, which will decrease battery consumption and will make more feasible the use of renewable energies. Investigation, J.M.M., J.M. and J.P.; Methodology, J.L.P. and D.B. ; Software, J.M.M., J.M. and J.P.; Supervision, J.L.P. and D.B. ; Validation, J.L.P. and D.B. ; Writing--original draft, J.M.M., J.M. and J.P.; Writing--review & editing, J.M.M., J.P., J.L.P. and D.B. All authors have read and agreed to the published version of the manuscript.