# Ionospheric Polarization Techniques for Robust NVIS Remote Sensing Platforms
## 5 Results
### BER CDF According to Polarization Techniques  
Once we have analyzed the main behavior characteristics of the signal received in different ways, we can analyze the behavior of different orders and modulations received by ionospheric waves or polarization techniques. First of all, we analyze the modulations of order 4. In Figure 8, we can see that the ordinary and extraordinary waves are affected in the same way as the 4 PSK and 4 QAM with a 80% probability to receive a BER lower than \(10^{-4}\). In contrast, the 4 FSK has a 57% probability to receive a BER lower than \(10^{-4}\). On the other hand, the selection combining looks to be the best option for the three modulations. To achieve a BER lower than \(10^{-4}\), the 4 PSK has a 96% probability, the 4 FSK has a 88% probability, and the 4 QAM has a 85% probability. In the case of using equal-gain combining to achieve a BER lower than \(10^{-4}\), the 4 PSK and 4 QAM has a 82% probability and the 4 FSK has a 59% probability. For the BER CDF figures, we set a threshold at \(10^{-4}\) because probabilistically we cannot ensure a BER lower than \(10^{-4}\) due to the number of bits transmitted in all the test performed.  
If we analyze the modulations of order 8, we can note a decrease of the probabilities to achieve lower BERs because of the decrease of the E\({}_{\text{b}}\)/N\({}_{0}\) received. In Figure 9, we can see that to achieve a BER lower than \(10^{-4}\) by the ionospheric waves, for the 8 PSK we have between a 42% and 55% probability, for the 8 FSK between a 8% and 26% probability, and the 8 QAM between a 1% and 24% probability. In this case, selection combining is still the best option for the 8 PSK and 8 FSK with a 70% and 40% probability, respectively, to achieve a BER lower than \(10^{-4}\). For the 8 QAM, selection combining and  
Figure 7: E\({}_{\text{b}}\)/N\({}_{0}\) vs Time for 4 QAM at 50 W.  
equal-gain combining have the same results in this test, with a 39% probability to achieve a BER lower than \(10^{-4}\), which is the same for the equal-gain combining of 8 FSK. The 8 PSK by equal-gain combining has a 50% probability to achieve a BER lower than \(10^{-4}\).  
Despite having some good results for the 8 PSK selection combining, when we increase the modulation order to 16, the power transmission is not enough to achieve an E\({}_{\text{b}}\)/N\({}_{0}\) that is enough to obtain a lower E\({}_{\text{b}}\)/N\({}_{0}\). As we can see in Figure 10, for 16 QAM and 16 FSK, to achieve a BER lower than \(10^{-2}\) by the ionospheric waves, the probability is 1%. The 16 PSK is the best option in this case in order to obtain about a 7% probability. The selection combining for the 16 PSK brings the best result of the graphic with a 25% probability to receive a BER lower than \(10^{-4}\) and for equal-gain combining a 21% probability to achieve the same result. Furthermore, 16 QAM and 16 FSK obtain a great improvement by the use of selection combining and equal-gain combining with the same results for both polarization techniques, nearly a 20% probability to obtain a BER lower than \(10^{-4}\).  
Figure 8: Bit error rate (BER) CDF order 4 modulations at 50 W.  
Figure 9: BER CDF order 8 modulations at 50 W.