Characterizing the Impact of Doppler Effects on Body-Centric LoRa Links with SDR

Long-range, low-power wireless technologies such as LoRa have been shown to exhibit excellent performance when applied in body-centric wireless applications. However, the robustness of LoRa technology to Doppler spread has recently been called into question by a number of researchers. This paper evaluates the impact of static and dynamic Doppler shifts on a simulated LoRa symbol detector and two types of simulated LoRa receivers. The results are interpreted specifically for body-centric applications and confirm that, in most application environments, pure Doppler effects are unlikely to severely disrupt wireless communication, confirming previous research, which stated that the link deteriorations observed in a number of practical LoRa measurement campaigns would mainly be caused by multipath fading effects. Yet, dynamic Doppler shifts, which occur as a result of the relative acceleration between communicating nodes, are also shown to contribute to link degradation. This is especially so for higher LoRa spreading factors and larger packet sizes.

On the Doppler effect in radar

The possibilities of simultaneous use of the longitudinal and transverse Doppler effects have been analyzed, and expressions have been derived for the corresponding beat frequencies between the emitted and received signals. As a rule, only the longitudinal Doppler effect is used in modern radio engineering systems, which makes it possible to determine the radial component of the object's speed. In addition, there are situations for which it is generally impossible to determine the speed of an object without taking into account the transverse Doppler effect. The authors analyze the fundamental possibilities of improving the functioning of radar stations that simultaneously use both types of Doppler effects – longitudinal and transverse ones – making it possible to determine the total speed of the observed object in any situations. The authors have analyzed the longitudinal and transverse Doppler effects for the case of a moving emitting object, derived expressions for the Doppler shift and expressions for the beat frequency in the case of an active radar station for both types of Doppler effects, which make it possible to obtain the value of the object's speed in any situations. Variants of determining the total speed of a moving object have been proposed, accounting the determination of its radial and tangential components. Idealized situations in which only one of the Doppler effects appeared have been considered.

Surface-Wave Simulation for the Continuously Moving Seismic Sources

In exploration and earthquake seismology, most sources used in subsurface structure imaging and rock property estimation are fixed in certain positions. Continuously moving seismic sources, such as vehicles and the metro, are one kind of important passive sources in ambient noise research. Commonly, seismic data acquisition and processing for moving sources are based on the assumption of simple point passive sources, and the dispersion curve inversion is applied to constrain near-surface velocity. This workflow neglects the Doppler effects. Considering the continuously moving properties of the sources, we first derive the analytical solution for the Rayleigh waves excited by heavy vehicles and then analyze their Doppler effects and dispersion curves. We observe that the moving source data have the Doppler effect when compared with the changes in the frequency of the source intensity, but this effect does not affect the frequency dispersion of Rayleigh waves. The dispersion curves computed for moving source records are consistent with the analytical dispersion solutions, which provide a theoretical foundation for velocity estimation using moving source data.