This paper presents an analysis of the depolarization effect in off-body channels, based on a previously developed geometry-based channel model for polarized communications with dynamic users. The model considers Line-of-Sight propagation and components reflected from scatterers distributed on cylinders centered around the user. A mobility model for wearable antennas based on Fourier series is employed to take the effects of user’s motion into account. The focus is on scattered signal components, where the impact of a scatter’s position, its material properties, and the influence of user dynamics on signal depolarization are investigated. It is observed that the wearable antenna motion has a strong impact on the channel’s polarization characteristics, particularly for dynamic on-body placements, such as arms and legs. If the antenna motion is neglected, the error in cross-polarization ratio is greater than 23dB compared to a static approach. The antenna rotation during motion is found to be the dominant factor, while the corresponding displacement can be neglected, with the error not exceeding 1dB. This result justifies the channel model simplification proposed in this paper.
This paper presents an empirical validation of a polarized channel model for off-body communications with dynamic users, based on wideband indoor measurements at 5.8 GHz with a 500 MHz bandwidth. The model is based on geometrical optics, and takes the signal depolarization and influence of user dynamics into account. By considering a scenario with the user walking towards an access point with co-located vertical and horizontal dipole antennas, the simulated receiver (Rx) power is compared against measurements for wearable antenna placements on the chest, wrist and lower leg. The obtained root mean square error is found to be within 2.8 dB for the vertical off-body antenna polarization, and within 3.2 dB for the horizontal one. Fairly matching Rx power values are obtained even when only free space propagation is considered in the simulator, with the error being below 3.4 dB in most cases.
This paper analyses the impact of the human body on antenna radiation characteristics, with a focus on the polarization aspect. The effect of the body tissues on a wrist-worn ultra-wideband double loop antenna radiation characteristics is investigated at 3, 4 and 5 GHz, based on numerical full-wave simulations complemented with a voxel model of a hand. Results show a strong influence of the body on the gain and polarization characteristics; the radiation in the direction towards the body is suppressed by 20 dB or more, and the antenna polarization changes from a linear to an elliptical one. By simulating an off-body communications scenario with the user walking at a fixed distance from the off-body antenna, up to 6.5 dB lower received power is obtained by using the wearable antenna radiation pattern simulated with the hand phantom, compared to the case when the antenna in free space.
This paper presents an off-body channel model for polarized communications with dynamic users. The model is based on Geometrical Optics and Uniform Theory of Diffraction and accounts for free space propagation, reflections, and diffractions. It allows for arbitrary antennas’ polarizations and gain patterns and supports a number of on-body antenna placements. In order to take the influence of users’ motion into account, a mobility model for wearable antennas on dynamic users is used. Signal depolarization mechanisms are identified, and simulations are performed to analyze the influence of user dynamics on the channel. The results show that significant polarization mismatch losses occur due to wearable antenna rotations, resulting in received power variations up to 37.5 dB for the line-of-sight component and 41.4 dB for the scattered one. The importance of taking signal polarization into account is demonstrated by comparing the simulation results between polarized and nonpolarized channel models in a free space propagation scenario, where a difference up to 53 dB in between the two is observed.
This paper presents a mobility model for the variations in position and orientation of wearable antennas on dynamic users, considering walking and running motions. Motion is represented as a composition of a linear forward movement plus a periodic component, modeled by a Fourier series with up to two harmonics. The model is simple, yet realistic, as Motion Capture (MoCap) data are used to calculate its parameters. It is suitable for use with a variety of propagation channel models, including deterministic ray-tracing and stochastic geometry-based ones, but can also allow for analytical inference in simplified scenarios. Considering an off-body communication scenario, simulations show that the proposed mobility model provides similar received power as the skeleton-based model with MoCap data, the maximum difference in the considered scenario being below 1 dB. A significant influence of user’s motion on the channel is observed for both free-space and multipath propagation, yielding received power variations up to 28 dB in the considered scenarios.
This paper addresses the depolarisation effect in off-body body area networks channels, based on measurements performed at 2.45 GHz in an indoor environment. Seven different scenarios, involving both static and dynamic users, were considered, taking a statistical perspective. The analysis of the cross-polarisation discrimination is performed, as well as the analysis of path loss in co- and cross-polarised channels. Results show a strong dependence of the cross-polarisation discrimination and of channel characteristics on the polarisation and propagation condition, i.e. line-of-sight (LoS), non-LoS or quasi-LoS. Distance, varied between 1 and 6 m in the considered scenarios, is observed to have very little impact on the cross-polarisation discrimination. In the considered dynamic scenario, the channel is characterised by lognormal-distributed shadowing and Nakagami-distributed multipath fading. Parameters of the Nakagami distribution have essentially different values in the co- and cross-polarised channels, showing a trend towards Rice in the former and Rayleigh in the latter. Based on results, a model is proposed for a dynamic off-body channel.
This paper addresses the depolarisation effect in off-body body area networks channels, based on measurements performed at 2.45 GHz in an indoor environment. Seven different scenarios, involving both static and dynamic users, were considered, taking a statistical perspective. The analysis of the cross-polarisation discrimination is performed, as well as the analysis of path loss in co- and cross-polarised channels. Results show a strong dependence of the cross-polarisation discrimination and of channel characteristics on the polarisation and propagation condition, i.e. line-of-sight (LoS), non-LoS or quasi-LoS. Distance, varied between 1 and 6 m in the considered scenarios, is observed to have very little impact on the cross-polarisation discrimination. In the considered dynamic scenario, the channel is characterised by lognormal-distributed shadowing and Nakagami-distributed multipath fading. Parameters of the Nakagami distribution have essentially different values in the co- and cross-polarised channels, showing a trend towards Rice in the former and Rayleigh in the latter. Based on results, a model is proposed for a dynamic off-body channel.
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