Improving the radio signal intensity loss model between the drone and the base station

The purpose of the study was to develop a radio signal propagation model that considers the drone’s flight altitude and the specifics of the ground-to-air channel to improve the accuracy of signal loss estimation. The study used comparative analysis of classical models, calculation of signal losses at different altitudes and distances, estimation of the effect of line-of-sight and birefringence propagation, and development and verification of an improved exponential model depending on the height of the drone. It was determined that these models do not account for the substantial influence of the drone’s flight altitude and the increased probability of a line of sight between the drone and the base station, which leads to an overestimation of the predicted signal loss by tens of decibels. Based on the analysis, an improved analytical model was proposed, in which signal losses are defined as the sum of losses in free space and the height-dependent additional term. This additional term is described by an exponential function that decreases with increasing drone altitude and reflects a gradual transition from indirect visibility conditions to line-of-sight conditions. In addition, the model introduced distance correction, taking into account the actual geometry of the ground-toair channel. Calculations performed for the frequencies of 868 MHz and 1,800 MHz showed that the improved model is in good agreement with experimental observations and provides results close to the free space model at significant altitudes. Comparison with the Hata models confirmed that the new model reduces the forecast error in urban conditions to tens of decibels. Considering the flight altitude and gradually moving from indirect to direct visibility greatly increases the accuracy of predicting signal loss for unmanned aerial vehicles. The practical importance of the study lies in the fact that the proposed model enables a more accurate prediction of radio signal losses in the ground-to-air channel, which is the basis for designing reliable communication systems with unmanned aerial vehicles