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

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

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