# Study of NVIS Channel for USN Protocol Definition in Antarctica
## 5 Frame Protocol Defined and HF Frame Protocol Standards  
Once designed, the new frame protocol taking into account most of the measurements done for an NVIS channel, we can compare the designed frame protocol with related works and the HF Frame Protocol Standards STANAG and MIL-STD-188-110D. To evaluate the improvement, we run some simulations of our proposed frame protocol to compare it with real measured frame protocols based on the HF Frame Protocol Standards. The main focus of this comparison is the performance of the data block in front of the NVIS channel effects by the use of the preambles and modulation proposed. The NVIS channel simulation used for both multicarrier modulations is based on a Watterson channel model [36], which is obtained by adding two independent Rayleigh channels, each one with a frequency-shifted Gaussian Doppler spectrum to simulate the ordinary and extraordinary received waves as a bi-Gaussian Doppler spectrum. In Figure 19 we can see the results for both scenario cases of OFDM configurations in comparison with the real tested modulations used on the HF Frame Protocol Standards. Both OFDM simulations has been done with a total amount of 12 Mb. The channel simulation for the OFDM configuration of Table 1 has been  
Figure 18: OFDM frame protocol. set with two Rayleigh distributions, with a delay spread of 2.75 ms, an SNR of 6 dB and a Doppler shift of \(-17.5\) Hz. The result shows us 84% of probability to receive a packet with a BER less than \(3\times 10^{-4}\) in comparison of a BER less than \(2\times 10^{-3}\) for the 4 PSK and a BER less than \(6\times 10^{-2}\) for the 4 FSK. The channel simulation for the OFDM configuration of Table 2 has been set with two Rayleigh distributions, with a delay spread of 5.5 ms, an SNR of 6 dB and a Doppler shift of \(-17.5\) Hz. The result shows us an 81% of probability to receive a packet with a BER less than \(10^{-3}\) in comparison of a BER less than \(2\times 10^{-3}\) for the 4 PSK and a BER less than \(6\times 10^{-2}\) for the 4 FSK. As we can see, referring the simulation, we can realize that the new frame protocol configuration is more robust in front of the channel effects than the QPSK and 4 FSK of Figures 14 and 15 used on the HF standards. As we can see, the OFDM configuration of Table 2 is less robust than the OFDM of Table 1 because, for the same probability, it has a lower BER. If we compare the obtained results with related works, [PERSON] at [20] study polarization techniques based on MIMO to make increase robustness and the bitrate of ionospheric communications. Even so, the use of polarization techniques requires two antennas for the transmission and reception and still not avoid the ISI effects in contrast to the frame protocol designed. Despite this, according to [PERSON] [20], MIMO polarization techniques can increase the bitrate of the HF Standards to 8.52 Kbps in the best channel conditions without ISI effect in comparison of 2.139 Kbps and 1.81 Kbps of the frame protocol designed for skywave and groundwave respectively. Despite this, in the case of high ISI effects produced by the presence of groundwave or by the NVIS channel, polarization techniques will not have any effect, it being impossible to establish the communication. In the case of using the frame protocol designed in this article, the ISI effect will be avoided. To improve the communication, MIMO techniques can be used on the frame protocol designed, assuring the communication with a bitrate of 4.28 Kbps and 3.62 Kbps respectively for skywave and groundwave. By the other way, [PERSON] at [22] studied OFDM and direct sequence spread spectrum (DSSS) transmission techniques for an HF communication of 12,700 km and it compares with the HF Standards for a slow fading multipath long-haul HF channel.