This contribution focuses on extracting the theoretical framework for the assessment and evaluation of the joint effect of rain, beam misalignment and hardware imperfections at long-range outdoor terahertz (THz) wireless systems. In this direction, we first report an appropriate system model for outdoor THz wireless systems that take into account the impact of different design parameters, including antenna gain and transceivers hardware imperfections, atmospheric conditions, such as rain, and parameters, like temperature, humidity and pressure, as well as stochastic beam misalignment that can be caused by thermal expansion, dynamic wind loads and/or weak earthquakes. For this model, we extract novel closed-form expressions for the probability density and cumulative distribution functions of the THz wireless channel that captures the impact of geometric loss, beam misalignment and rain attenuation. We capitalized the aforementioned expressions by presenting closed-form formulas for the outage probability and achievable throughput of the system. Finally, we document an analytical policy that returns the optimal transmission spectral efficiency that maximizes the achievable throughput.

The use of the Ka band (30/20 GHz) in satellite-communication systems is expected to grow in the next few years, with the launches and planned launches of more than 10 satellites in 2010 and 2011 that include some Ka-band capacity. New technical standards, such as DVB-S2 and OVB-RCS, can be used in this band. A better knowledge of the channel characteristics is required, as well as experimental time series of attenuation. A propagation experiment is being carried out in Madrid, Spain, with the objective of characterizing the propagation channel in the downlink subband. Propagation results are related to meteorological data obtained from co-located instruments. Results obtained after two years of the experiment are presented in this paper. Rain attenuation is the main propagation impairment in this band. That is why rain-propagation effects are analyzed in more detail, although other propagation effects are also considered, as well as their relative importance.

Tropospheric scintillation can become a significant impairment in satellite communication systems, especially in those with low fade-margin. Moreover, fast amplitude fluctuations due to scintillation are even larger when rain is present on the propagation path. Few studies of scintillation during rain have been reported and the statistical characterization is still not totally clear. This paper presents experimental results on the relationship between scintillation and rain attenuation obtained from slant-path attenuation measurements at 50 GHz. The study is focused on the probability density function (PDF) of various scintillation parameters. It is shown that scintillation intensity, measured as the standard deviation of the amplitude fluctuations, increases with rain attenuation; in the range 1-10 dB this relationship can be expressed by power-law or linear equations. The PDFs of scintillation intensity conditioned to a given rain attenuation level are lognormal, while the overall long-term PDF is well fitted by a generalized extreme value (GEV) distribution. The short-term PDFs of amplitude conditioned to a given intensity are normal, although skewness effects are observed for the strongest intensities. A procedure is given to derive numerically the overall PDF of scintillation amplitude using a combination of conditional PDFs and local statistics of rain attenuation.

Although the deployment of 5G networks has already started, there are still open questions regarding propagation at millimeter-wave frequency bands. Several propagation campaigns have been carried out at several bands previously identified by regulatory organizations, but due to the wide range of allocated segments of spectrum and the variety of possible propagation scenarios, more measurement campaigns are needed. In this regard, the Universidad Politécnica de Madrid (UPM) has taken millimeter-wave measurements at 26, 32, and 39 GHz bands in an indoor corridor scenario in line-of-sight (LOS) conditions with two antenna configurations (a horn antenna has been used in transmission whereas horn and omnidirectional antennas have been used in reception), and the main results are presented in this paper. The obtained path loss results have been compared with existing millimeter-wave propagation models.

The experimental characterization of tropospheric effects on electromagnetic waves relies on the reception of a beacon signal transmitted by a satellite. The total tropospheric attenuation can be derived from these measurements in combination with additional information, specifically the attenuation due to atmospheric gases, in turn derived from ancillary instruments or data sources. When available, this information is obtained from a co-sited radiometer. This paper presents three alternative procedures to estimate the gas attenuation that can be used in the absence of this instrument: the first one makes use of zenith total delay data obtained from GNSS (Global Navigation Satellite System) receivers and additional meteorological data, the second one relies on atmospheric profiles gathered from radiosonde observations and/or NWP (Numerical Weather Prediction) products and the third one only makes use of standard atmospheric profiles. The accuracy of the procedures when used in this application is compared with the reference total tropospheric attenuation derived with the support of radiometric data, exploiting the Alphasat beacon measurements collected in Milan, Italy, in 2017. The results indicate that a better accuracy (average RMS error below 0.1 dB when compared with the use of a radiometer) is achieved by using GNSS data because of their finer temporal resolution; nonetheless, the three procedures can be equally recommended, their use being conditioned to the availability of the appropriate data in the area around the experimental site.

This contribution presents a comprehensive methodology for the real-time estimation of the rain intensity from downlink satellite signals. The enhanced system leverages on extremely randomized tree classifiers to automatically perform rainfall detection along earth–satellite links and successively employs an improved procedure to determine the corresponding slant-path rain attenuation. The latter quantity is then exploited to yield real-time rainfall rate estimates with a 1-min time resolution. The accuracy of the proposed methodology is tested using the Ka - and $Q$ -band propagation data, collected in two different sites (Milan and Madrid) and in the framework of the propagation experiments. The results demonstrate the reliability of the automated rain event detector, as well as a satisfactory accuracy in estimating the slant-path rain attenuation and the point rainfall rate. The accuracy is assessed both on a statistical and on an instantaneous basis through the evaluation of different error figures and by inspection of individual time series.