Fernando Machado

This paper investigates the development of a clutter loss model specifically for slant paths involving directive antennas . Conventionally, clutter loss is characterized by using isotropic antennas to facilitate standard link budget calculations via single antenna gain values. Clutter loss may represent a significant excess loss relative to free‐space propagation . In scenarios such as coexistence interference between cellular and satellite systems, the former can employ highly directive, beam‐steering architectures . Since the transmitter–receiver (Tx‐Rx) link comprises multiple discrete propagation paths , each is subject to different antenna gains. This study proposes an extension to the five‐ray model (5RM) for clutter loss to account for these differential gains. The methodology effectively characterizes paths from terrestrial transmitters to elevated platforms , including satellites, airborne systems, and Unmanned Aerial Vehicles (UAVs).

In this paper, we present our work toward the development of a clutter loss model for slant paths. This loss must be added to that due to free space to work out the overall signal decay between a transmitter on the ground and an elevated receiver: satellite, airborne platform, UAV, etc. and vice versa. The calculation of this parameter is relevant in interference studies, especially at this point where there is a significant demand for spectrum and there is the need to share bands between different applications and services. We propose here a physical-statistical approach which is elevation-dependent while it encompasses all possible azimuths. It smoothly covers a wide range of frequencies from the low UHF to millimeter waves. The modeling is mainly oriented toward interference calculations. This paper presents material we have contributed to ITU-R efforts for developing an improved recommendation (ITU-R Rec. P.2108) on clutter loss modeling.

In this article, we present a method for extending the unidimensional Synthetic Storm Technique, SST, when used in simulation mode, that is, for synthesizing rain attenuation time series. (The alternative mode being the production of yearly rain attenuation statistics.) Such extension is to the two-dimensional, 2D, case with a validity limitation to distances not too far from where the input rain rate recording has been made. This is possible thanks to the fact that we are interested in slant links where the path length subjected to rain is only of a few km. Similarly, this technique would be valid for short terrestrial paths. We need to bring in the second dimension: we are interested in site and orbit diversity simulations involving spaced locations and/or converging links. We introduce the simultaneous modeling of rain at different, not too far off, locations by taking into consideration the Gaussian multivariate characteristics of the natural logarithm of rain rate fields. Spatial effects thus introduced are achieved with the addition of realistic (even non-isotropic) cross-correlation functions.

Satellite tropospheric propagation studies strongly rely on beacon receiver measurements. We were interested in performing a measurement campaign to characterize rain attenuation statistics. In this article, we outline some of the characteristics and drawbacks one faces when trying to perform a radio wave satellite beacon propagation experiment at the Ka-band with low-cost measurement equipment. We used an affordable beacon receiver consisting of a commercial low-noise block down-converter, an outdoor dual-reflector antenna, and a software-defined radio unit. To measure rain attenuation events, we needed to work out where the reference signal level was at all times. However, as we did not have a radiometer to remove the impact of gases and clouds, since it is a very expensive device, we used a procedure that involved the subtraction of a stable and reliable reference level (template) from the raw received beacon level. This template was extracted from observations during non-rainy periods. The procedure implemented for extracting the template was based on the same data processing methodology used by other authors in this field. Here, we describe through specific examples the main characteristics of the templates extracted on non-rainy days, as well as the impact of some meteorological parameters and unavoidable, but small antenna pointing errors.

In this article, we present implementation details of a generative satellite maritime propagation channel model at L-band. In an earlier paper, we presented the parameterization of the channel model for the narrowband case based on recordings of GPS L1 $C/N_{0}$ time-series in different sea state conditions. Additionally, we performed wider band measurements using GPS E5a (≈10 Mcps—chips per second— > 20 MHz bandwidth) and obtained estimations of power delay profiles. Due to lack of dynamic range and delay resolution, in these measurements, no conclusive information was gathered on the time spreading caused by the channel. What was clear is that the time spreading was not significant outside the first signal chip, i.e., $\approx 0.1~\mu \text{s}$ . Still wideband modeling is required within this spreading range. Now, we want to extend the model to the wideband case. To achieve this goal, we have used a rough surface scattering model applicable to sea surfaces and employed it to characterize the time dispersion to be expected. Additionally, we also used this scattering model to help verify the validity of the existing Doppler spread model. Furthermore, ship movements in the waves play a role. We try and analyze this issue. Finally, we present a detailed discussion on various implementation issues we came across when coding the simulator.

In this article, we present a statistical narrowband mobile satellite maritime propagation channel model at the L-band based on empirical observations using GPS C/N ₀ measurements from a receiver onboard a vessel in different sea conditions. The model is fully parameterized for all possible elevation angles. In the measurements, we have used a low-gain, 6.2 dBi, hemispherical antenna. The parameters provided, thus, are valid for this and similar antenna gains.

In this paper new assumptions are introduced into the well-known Synthetic Storm Technique, SST, proposed by Drufuca and further developed by Matricciani, to address the orbital diversity in satellite links. The new approach receives as input information on collocated rain rate recordings and instantaneous estimates of the storm direction and speed; and assumes that the rain event is transversely constant to the storm movement. The achieved improvements are evaluated by analyzing two example measured rain attenuation events “seen” by two Ka-band beacon receivers looking at two different satellites spaced around in azimuth. A study is made of the crosscorrelation coefficient between rain attenuation series for these two links. Moreover, a methodology is sketched as to how multiple non-GEO satellite constellation availability (for global Internet access at Ka-band) could be evaluated in the frame of the SST.

This paper presents the design of an instrument for satellite beacon monitoring based on field programmable gate array (FPGA). The aim of this paper is to receive a beacon transmitted by a satellite in the Ka-band (18-21 GHz), process this signal, and obtain results for propagation studies (attenuation, fading, scintillation, etc.). The analog front-end performs the frequency down-conversion from the Ka-band RF beacon frequency to an intermediate frequency (IF) of 10.7 MHz. This IF signal is processed with the developed FPGA-based beacon detector to obtain the amplitude fluctuations of the received signal. The amplitude data is stored and later processed in a computer to obtain the experimental results (scintillation and rain attenuation measurements). This paper describes in detail the satellite beacon monitoring instrument structure, analyzes the receiver characteristics, and presents some operational test results.