Fixed-wing unmanned aerial vehicle (UAV) is widely considered as a vital candidate of aerial base station in beyond 5th-Generation (B5G) system due to its longer flight endurance and higher cruise altitude. Investigating and modeling the air-to-ground (A2G) wireless channel for fixed-wing UAV can better promote its development in various applications. In this paper, we present a wideband A2G channel measurement campaign for fixed-wing UAV with maximum altitude of 700 m. A comprehensive investigation of channel fading characteristics and channel modeling include path loss, shadow fading, spatial correlation, small-scale fading are provided. Particularly, unlike terrestrial channel a strong dependence of shadow fading and small-scale fading on UAV altitude is found. We propose to adopt Gamma distribution for modeling the shadow fading effect that has similar fitting performance with traditional Log-normal distribution but is more robust for theoretical analysis. Spatial correlation characteristics and modeling are presented. Results reveal that the decorrelation distance of shadow fading increases with the UAV altitude. We propose to use a model combining the exponential and sinusoidal functions that fit well to the autocorrelation function for shadow fading. Further, by using Kolmogorov-Smirnov (KS) test, Cramer-von Mises (CVM) test and Akaike information criterion (AIC) methods the Rician distribution is found to be the best candidate for modeling small-scale fading for UAV with altitudes above 300 m. The Rician K-factor is found to be strongly depending not only on the direct-distance but also on the UAV altitude. We finally propose a full dimension empirical K-factor prediction model.

Due to low cost and high operability, unmanned aerial vehicle(UAV) becomes a key component in future intelligent transportation system(ITS) for various use cases. Air-to-ground(A2G) communication is a fundamental technology for integration of UAV in the ITS, where accurate analysis and modeling of UAV A2G wireless channel are of great importance for communication algorithm development. In this paper, we present a comprehensive analysis and modeling of low altitude UAV A2G channel at 2.4 and 5.9 GHz based on multi-link channel measurement campaign. Based on the measured data, the value of path loss as a function of the elevation angle and distance is proposed. Further, the shadow fading(SF) is analyzed for different frequency bands and the spatial correlation is evaluated. Particularly, it is found that the influence of UAV altitude on shadowing is significant and should be considered when developing A2G communication system.

Recently, millimeter wave (mmWave) maritime communication with large bandwidth has attracted attentions as a part of future beyond 5th-Generation (B5G) space-air-ground communication networks. However, the researches on evaporation duct effect for beyond horizon maritime channel are below K-band so far. In this paper, we present a fixed-to-fixed point beyond horizon maritime channel measurement campaign at 25 GHz with bandwidth of 25 MHz. First, the received signal strength analyzed where the path loss at mmWave band via evaporation ducting is found to be on the order of free space loss in the best case. Further, the short-term variation in power is mainly caused by the environment change, where the standard deviation of the power is around 5dB. The decorrelation time of the channel is on the order of the period of the sea waves. The short term fading is found to be Rice fading. Further, we present empirical models for level crossing rate (LCR) and average fading duration (AFD) that outperform isotropic scatter based theoretical model.

As a key potential technology of future intelligent transportation system (ITS), the UAV-to-vehicle (U2V) communication has attracted widespread attention in recent years. The study of U2V propagation channel characteristics is of great importance for system design and testing. However, there is still a lack of extensive research on the U2V channel with high dynamic unmanned aerial vehicle (UAV) and vehicle in rural area for ITS applications. In this letter, we present a wideband U2V channel measurement campaign at 2.7GHz with UAV altitudes from 400m to 800m. A comprehensive investigation on large- and small-scale fading characteristics is presented. In particular, we find that the close-in (CI) model outperforms the floating intercept (FI) model in terms of prediction performance and robustness for theoretical analysis. In addition, we propose a simple altitude dependent decorrelation distance model for shadow fading. The observed K-factor under line-of-sight (LOS) condition is statistically higher than non line-of-sight (NLOS) condition with nonlinear dependency on UAV altitude. These findings help to design and optimize the U2V communication system for the future ITS.

In recent years, unmanned aerial vehicles (UAVs) have attracted attention in civil and military scenarios with advantages such as low cost and easy deployment. However, in the actual communication process, the aerial drone platform does not have fixed infrastructure support, and is significantly affected by the airflow, mechanical vibration of the body and other factors that affect the stability of UAV. This will also affect the air-to-ground (A2G) wireless channels. At present, most of the researches on UAV communication channel do not consider the impact of the jittering characteristics of the UAV platform. In this paper, we present a study of the influence of UAV jitter when hovering at different altitudes at 2.4 GHz band on the received signal, and on A2G wireless channels under different propagation scenarios. The results show that in the line of sight (LoS) scenario, the stability of the drone hovering has a greater effect on the signal than its influence in the non-line of sight (NLoS) scenario.

Fixed-wing unmanned aerial vehicles (UAVs) are widely considered as a vital candidate of aerial base station in beyond Fifth Generation (B5G) systems. Accurate knowledge of air-to-ground (A2G) wireless propagation is important for A2G communication system development and testing where, however, there is still a lack of A2G wideband channel models for such a purpose. In this paper, we present a wideband fixed-wing UAV-based A2G channel measurement campaign at 2.7 GHz, and consider typical flight phases, based on which a wide-sense stationary uncorrelated scattering (WSSUS)-based tapped delay line (TDL) wideband channel model is proposed. Parameters of individual channel taps are analyzed in terms of gain, amplitude distribution, Rice factor and delay-Doppler spectrum. It is shown that UAV flight phases significantly influence the channel tap parameters. Particularly, the “Bell”-type spectrum is found to be the most suitable model for the delay-Doppler spectrum under various flight scenarios for A2G propagation. The proposed channel model can provide valuable assistance and guidance for UAV communication system evaluation and network planning.