No abstract

Ultrahigh frequency wireless signals are mainly influenced by the geomorphological environment during the transmission process, resulting in fading channels, especially in mountainous regions. The experiment was conducted in the Karst landform of Guizhou Province, China, in order to explore fading distribution characteristics for mainly analyzing electro magnetic compatibility (EMC) specialties between Five-hundred-meter Aperture Spherical Radio Telescope (FAST) and wireless radiation equipment around radio quiet zone of this telescope. Based on the channel variation data of six frequencies, which are mainly used by the electrical and electronic equipment of public facilities around FAST, the fading distribution was analyzed by using the Kolmogorov-Smirnov statistic method. And finally we determined the optimal distribution model with the fading range, fading depth, and fading rate. The results show that (1) the polarization type and signal frequency have a definite influence on the fading distribution types in the Karst landform; (2) Rice distribution is the optimal and stable distribution model in the Karst landform, and the log-normal distribution model is proposed to characterize the Rice K-factor distribution; and (3) the line-of-sight (LoS) components of the normalized envelopes are 0.6837, 0.8939, 0.5963, 0.6332, 0.5516, and 0.4806. And the multipath scattered components of those are 0.2134, 0.0630, 0.2436, 0.2224, 0.2678, and 0.2880. The research results provide a potential support for the deployment and optimization of wireless communication networks in Karst landform, especially around radio quiet zone of FAST.

As one of the key technologies of HF communication, the maximum usable frequency (MUF) prediction method has been widely discussed. To experimentally confirm the reliability of commonly used MUFs prediction models for high-frequency communication, we have compared maximum observed frequencies (MOFs) and predicted MUFs to assess the accuracy of two typical prediction models. The root-mean-square error (RMSE) and relative RMSE (RRMSE) between oblique sounding MOFs and the predicted MUFs were used to assess the model’s accuracy. The oblique sounding path was from Changchun to Jinyang, and the vertical-sounding ionosonde was located in Beijing, which was approximately the midpoint of the oblique sounding circuit. The statistical analysis results show that: (a) the trend of prediction results from the Lockwood and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) model are in good agreement with the observations: the mean RMSE and RRMSE of the INGV model are less than those of the Lockwood model; (b) in the four different periods (sunrise, daytime, sunset, and nighttime) of the whole day, the maximum difference of RMSE between the Lockwood and INGV model is 0.14 MHz (the INGV performs better than the LWM), with the corresponding differences of RRMSE being 0.31% at sunrise and 0.68% at daytime; (c) in the four seasons of spring, summer, autumn, and winter, the minimum RMSE values of the Lockwood and INGV models are 1.51 MHz and 1.37 MHz, respectively, which are obtained in winter, and the corresponding RRMSEs are 11.47% and 11.79%, respectively; (d) in the high and low solar activity epochs, the mean RMSEs of the Lockwood and INGV models are 1.63 MHz, and 1.54 MHz, with corresponding mean RRMSE values of 11.47% and 11.55%. In conclusion, the INGV model is more suitable for MUF prediction over Beijing and its adjacent mid-latitude regions from the RMSE comparison of the two models.

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To fully grasp the characteristics and provide a basis for establishing an evaporation duct communication system for the South China Sea (SCS), we constructed a regional statistical database based on remote sensing meteorological parameters and a numerical model. This database has the advantage of extensive spatiotemporal coverage and high resolution, which can provide accessibility and as a supplementary means for the maritime 6 th Generation communication network. Specifically, work has been completed in three areas. (1) The overall EDH in the central SCS varies periodically and remains intense throughout the day, decreasing only just before sunrise during 04:00-08:00. Moreover, a 20.0 m high channel appears at the "Golden edge" in the northern coastal area, which can expand as far as 300 km from the coast during May-July. (2) The characteristics of specific regions were analyzed, and the highest average EDH was determined as 18.4 m in the Taiwan Strait. The height in the central SCS fluctuates little with monthly and annual variation, and it is maintained between 10.0 and 12.0 m. (3) Based on the evaporation duct formation principle, we analyzed the spatiotemporal distributions of meteorological parameters. The Taiwan Strait maintains the highest EDH over the SCS, owing to the influence of the Kuroshio Current, and the average sea surface temperature (SST) reaches 28.41°C in June and 19.58°C in January. To the central SCS, high SST, low wind speed, and relative humidity of approximately 80% provide excellent conditions for maintaining an evaporation duct over the long term.