Milan Kvicera

Building Penetration Loss for Satellite Services at L-, S- and C-band: Measurement and Modeling

An extensive measurement campaign, covering a representative set of typical buildings in an urban area and aimed at building penetration loss for satellite services at L-, S- and C-band, was performed in Prague in the summer of 2009. Throughout the measurements, a remote-controlled airship was used as a pseudo-satellite carrying a transmitter which provided unmodulated continuous wave left-handed circularly polarized signals at 2.0 GHz, 3.5 GHz, 5.0 GHz, and 6.5 GHz. A description of the measurement campaign is provided here, together with a thorough analysis of the resulting experimental data. A significant dependence on elevation angle is reported for line-of-sight and non-line-of-sight propagation conditions separately. Subsequent steps to introduce elevation dependent empirical models at corresponding frequencies follow. Finally, a comparison to other studies dealing with building penetration loss for high elevation angles is presented.

Frequency Dependence of Attenuation Due to Vegetation for Satellite Services

This letter presents the results of vegetation loss measurements at 2.0, 3.5, 5.0, and 6.5 GHz for elevation angles ranging from 20° to 90°. The excess attenuation due to vegetation was measured at four different wooded locations using a remote-controlled airship as a pseudo-satellite. Measurements taken in an open field were used as a reference. The results are given as additional attenuation averaged over the whole range of azimuth and elevation angles for circular polarization. Average results from all four locations vary from 9 dB at 2.0 GHz to 14.5 dB at 6.5 GHz. Linear frequency dependence of vegetation attenuation was observed, and a corresponding empirical model providing the additional vegetation loss as a function of the frequency was derived in closed form. The results are then compared to the literature.

On a Definition of Building Penetration Loss for High Elevation Angles

Different methods of defining building penetration loss for high elevation angle paths exist. A key factor is the selection of the reference level. A comparison of four of the most common types of reference levels used to determine building penetration loss for high elevation angles is presented based on a measurement trial using unmodulated carriers at 2.0 GHz and 5.0 GHz performed at a three-storey office building. It was shown that the choice of reference level significantly affects the results obtained. Particular cases are discussed and general recommendations on the selection of the reference level for building penetration loss measurement are provided.

Seasonal Variations of Polarization Diversity Gain in a Vegetated Area considering High Elevation Angles and a Nomadic User

Seasonal variations of the polarization diversity gain are addressed for a nomadic user in a vegetated area taking high elevation angles and nongeostationary satellites into consideration. Corresponding experimental data were obtained at a frequency of 2.0 GHz at Stromovka Park in Prague, the Czech Republic, within the full in-leaf and out-of-leaf periods of 2013 and 2014, respectively. By detecting copolarized and cross-polarized components of the transmitted left- and right-handed circularly polarized signals, the corresponding diversity gain was obtained for multiple-input single-output (MISO), single-input multiple-output (SIMO), and combined MISO/SIMO cases. It was found that tree defoliation results in a significant decrease of the polarization diversity gain achieved for low time percentages in particular scenarios.

World Maps of Atmospheric Refractivity Statistics

Atmospheric refractivity and its vertical gradient affect electromagnetic wave propagation in the atmosphere. Consequently, their statistics are needed for propagation predictions. New world maps of refractivity and its vertical gradient statistics are derived from a global, long-term dataset of meteorological quantities as given by ERA-Interim reanalysis. The derived maps provide long-term statistics obtained from 33 years of meteorological data with a one-degree spatial resolution on a latitude/longitude mesh. A processing method is described and examples of the derived maps are shown. The consistency of the new maps is checked by comparing world maps provided by ITU-R. Accuracy is tested by comparing refractivity statistics obtained from high-quality local measurements using radiosonde and tower measurements. New global maps demonstrate enhanced statistical stability, spatial resolution, and accuracy.

Sensitivity Analysis of Multiple Scattering Theory Applied to Tree Canopies at Microwave Frequencies

A sensitivity analysis of the multiple scattering theory applied to propagation in tree canopies is presented. This analysis aims at addressing the influence of input parameters on the canopys equivalent scattering amplitude as well as the overall coherent and incoherent scattered fields. The main input parameters of interest were identified as frequency, number densities and dielectric parameters of branches and leaves, polarization, and a canopy shape. A number of graphical results are provided enabling to identify the key parameters of corresponding radio-wave propagation models based on the multiple scattering theory.

Short-Term Terrain Diffraction Measurements From L- to Q-Band: Results and Analysis

In response to the current need for a reliable interference and frequency coordination analysis, especially within the ground segment of satellite systems, atmospheric refraction and terrain diffraction phenomena play a key role from a radiowave propagation point of view. While it is convenient to use an ITU-R model for the case of the atmospheric refraction, several different types of models for terrain diffraction are identified in the literature. On the other hand, only a limited amount of experimental data is globally available to address their performance. This is why we carried out own short-term terrain diffraction measurements at the frequencies from L- to Q-band. During the trials, truck-mounted access platforms reaching up to 46 m above ground level were used and terrain profiles with path lengths from 7 km up to 50 km for various combinations of transmitter and receiver heights were addressed. Based on the obtained experimental dataset, the performance of the delta-Bullington and Deygout models, currently recommended by the ITU-R for the purposes of interference analysis, and the terrain diffraction models based on the UTD and parabolic equation approach has been addressed in terms of the testing variable defined in this paper.

A New Model for Scattering From Tree Canopies Based on Physical Optics and Multiple Scattering Theory

This paper presents a new model for scattering from tree canopies based on a modified physical optics approach. In this way, propagation through a canopy is accounted for by respecting the complex propagation constant, which can be obtained either by the multiple scattering theory (MST) or approximated based on the canopy specific attenuation. Unlike the case when MST is applied directly, the proposed approach offers significant benefits, including a straightforward software implementation, feasible computation times for high frequencies and electrically large canopies, and, most importantly, near-field calculations in regions close to a canopy. The new model is first tested against MST using two artificial single-tree scenarios at 2 and 10 GHz. Then, experimental data at 2 GHz obtained with the use of a remote controlled airship for an actual single-tree scenario are utilized as well. In this way, the model is thoroughly validated and its advantages over MST are presented in detail.

Channel modeling for GNSS. A physical-statistical approach

GNSS systems present an important challenge to the propagation modeler in that the requirements are different from those in communication systems: we are still interested in wideband modeling but the aim is knowing in much grater detail the arrangement of the near echoes, i.e., those within the excess delay of the ranging codes correlation peak. Also important is achieving a continuous modeling of the channel (preservation of the autocorrelation) as the terminal and the satellites move, as the previous history of the channel is relevant in the current computed position.

A New Propagation Channel Synthesizer for UAVs in the Presence of Tree Canopies

Following the increasing popularity of unmanned aerial vehicles (UAVs) for remote sensing applications, the reliable operation under a number of various radio wave propagation conditions is required. Assuming common outdoor scenarios, the presence of trees in the vicinity of a UAV or its ground terminal is highly probable. However, such a scenario is very difficult to address from a radio wave propagation point of view. Recently, an approach based on physical optics (PO) and the multiple scattering theory (MST) has been proposed by the authors, which enables fast and straightforward predictions of tree-scattered fields at microwave frequencies. In this paper, this approach is developed further into a generative model capable of providing both the narrowband and wideband synthetic time series of received/transmitted signals which are needed for both UAV communications and remote sensing applications in the presence of scattering from tree canopies. The proposed channel synthesizer is validated using both an artificially-generated scenario and actual experimental dataset.