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Analysis of the Ordinary and Extraordinary Ionospheric Modes for NVIS Digital Communications Channels

机译：NVIS数字通信通道普通和非凡电离层模式分析

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Sensor networks have become more popular in recent years, now featuring plenty of options and capabilities. Notwithstanding this, remote locations present many difficulties for their study and monitoring. High-frequency (HF) communications are presented as an alternative to satellite communications, being a low-cost and easy-to-deploy solution. Near vertical incidence skywave (NVIS) technology provides a coverage of approximately 250 km (depending on the frequency being used and the ionospheric conditions) without a line of sight using the ionosphere as a communication channel. This paper centers on the study of the ionosphere and its characteristic waves as two independent channels in order to improve any NVIS link, increasing its robustness or decreasing the size of the node antennas through the appliance of specific techniques. We studied the channel sounding of both the ordinary and extraordinary waves and their respective channels, analyzing parameters such as the delay spread and the channel’s availability for each wave. The frequency instability of the hardware used was also measured. Furthermore, the correlation coefficient of the impulse response between both signals was studied. Finally, we applied polarization diversity and two different combining techniques. These measurements were performed on a single frequency link, tuned to 5.4 MHz. An improvement on the mean bit energy-to-noise power spectral density (Eb/N0) was received and the bit error rate (BER) was achieved. The results obtained showed that the extraordinary mode had a higher availability throughout the day (15% more availability), but a delayed spread (approximately 0.3 ms mean value), similar to those of the ordinary wave. Furthermore, an improvement of up to 4 dB was achieved with the usage of polarization diversity, thus reducing transmission errors.
机译：近年来传感器网络变得更加流行，现在具有大量的选择和能力。尽管如此，远程位置对他们的学习和监测呈现许多困难。高频（HF）通信作为卫星通信的替代方案，是一种低成本且易于部署的解决方案。近垂直发射Skywave（NVIS）技术提供约250公里的覆盖范围（取决于所使用的频率和电离层条件），没有使用电离层作为通信通道的视线。本文研究了电离层的研究及其特征波作为两个独立通道，以改善任何NVIS链路，通过特定技术的设备增加其鲁棒性或降低节点天线的大小。我们研究了普通和非凡波的频道声音及其各自的信道，分析了诸如延迟扩展的参数和每个波的通道的可用性。还测量了所用硬件的频率不稳定性。此外，研究了两个信号之间的脉冲响应的相关系数。最后，我们应用了偏振分集和两种不同的组合技术。这些测量在单个频率链路上进行，调谐到5.4MHz。接收到平均能量 - 噪声功率谱密度（EB / N0）的改进，并且实现了误码率（BER）。所得到的结果表明，非凡模式全天有更高的可用性（更多可用性），但延迟扩散（约0.3ms平均值），类似于普通波的差异。此外，利用偏振分集实现了最多4dB的改善，从而减少了传输误差。

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