Off-body Propagation Research Articles

Measurement and Modeling of Wireless Off-Body Propagation Characteristics Under Hospital Environment at 6–8.5 GHz

A measurement-based novel statistical path-loss model with a height-dependent factor and a body obstruction (BO) attenuation factor for off-body channel under a hospital environment at 6–8.5 GHz is proposed. The height-dependent factor is introduced to emulate different access point (AP) arrangement scenarios, and the BO factor is employed to describe the effect caused by different body-worn positions. The height-dependent path-loss exponent is validated to fluctuate from 2 to 4 with AP height increasing by employing both computer simulation and classical two-ray model theory. As further validated, the proposed model can provide more flexibility and higher accuracy compared with its existing counterparts. The presented channel model is expected to provide wireless link budget estimation and to further develop the physical layer algorithms for body-centric communication systems under hospital environments.

Effect of the Receiver Attachment Position on Ultrawideband Off-Body Channels

An experimental characterization of the off-body propagation channel for the ultrawideband (UWB) band from 3.1 GHz to 8 GHz for body area networks (BAN) is presented in this letter. The channel is evaluated in terms of path loss (PL) and Root Mean Square (RMS) delay spread. Channel statistics from measurements carried out considering subjects of different gender in standing still position under line-of-sight (LOS) conditions are compared to the ones without the presence of the body to evaluate the variation on the statistics of the channel in presence of a human body. It is observed a high variation on the path loss and the RMS delay spread parameters for the same attachment position of the receiver antenna on the body of the subjects and a dependence of the statistics with the number of received multipath components (MPC) because of the shadowing effect of the body.

Theoretical and Experimental Investigation of a 60-GHz Off-Body Propagation Model

A fast computation and accurate analytical model for off-body propagation is derived in this paper. The paper discusses the off-body model propagation from an external source to a receiver located on the body. The model is developed for normal incident plane wave by describing the human body with a circular cylinder. We show that the total received electric field around the human body can be written as a creeping wave in the shadow region and as a geometrical optics result for the lit region. It is also shown that at 60 GHz, the shadow boundary width is negligible. The model shows perfect agreement with the experimental results conducted on a perfectly conducting cylinder. Measurements of the creeping wave path gain have been also conducted on a real body to assess the validity of the cylinder assumption. The results have shown a path gain of about 5 dB/cm for the TM case and 3 dB/cm for the TE case. The standard deviation between the measurements and the cylindrical model is about 3.5 dB for both TM and TE cases.

Propagation Models for Body-Area Networks: A Survey and New Outlook

This article is a review of wireless body-area network (BAN) channel models, with observations about the selection of the best channel model in terms of both first- and second-order statistics. Particular insight into the dominant factors that affect propagation for body-area networks is given. Important second-order statistical measures are discussed, where coherence times and fade durations are of particular interest. The IEEE 802.15.6 standard is used as a basis for the review, with observations and insights given about body-area networks. In this context, narrowband and ultra-wideband (UWB) models are summarized for different measurement environments and carrier frequencies. On-body, in-body, and off-body propagation models are discussed where appropriate. In general, lognormal fading or gamma fading models of the body-area network channel are most applicable. A goodness-of-fit criterion that directly trades off model error and complexity is presented, which gives a new outlook for channel modeling. By this new outlook it is demonstrated that through significant simplification of individual link propagation models for body-area networks, it is possible to combine link models with only a few parameters. Common misconceptions regarding the appropriateness of applying traditional path-loss measures to these short-range networks are then exposed. Finally, the use of relays, which is an option in IEEE 802.15.6, is shown to be important for maintaining reliability in various body-area-network propagation scenarios.

Experimental characterisation of ultra‐wideband off‐body radio channels considering antenna effects

Experimental investigation to characterise the ultra-wideband (UWB) off-body radio propagation channel for body-centric wireless communication is presented. The measurements were performed in an indoor environment using active UWB wireless tags. Two different kinds of receiver antennas have been used; namely a small form factor (SFF) antenna and miniaturised co-planar waveguide-fed tapered slot antenna to investigate their effects on the radio channel behaviour. Statistical analysis is performed on the radio channel data and the results demonstrated that the lognormal distribution provides the best fit for off-body propagation channel path-loss models. Comparison of results shows that a reduction of 29% path-loss exponent is noticed for the SFF antenna. In addition to this, second-order channel parameters such as fade probability, level-crossing rate and average fade duration are also investigated and compared for the two antennas.

Power delay profile modelling of the ultra wideband off-body propagation channel

This study presents a statistical power delay profile (PDP) model for the evaluation and design of ultra wideband (UWB) off-body communication systems. The analysis is based on extensive real-body measurements carried out in the frequency range between 3.5 and 6.5 GHz. Due to the dependence of the radio propagation channel on the body region (i.e. front, side and back), we gradually develop separate stochastic tapped-delay-line models for each body region. Based on the newly estimated parameters, channel simulation methods are provided for each of the proposed models. Finally, several comparisons between the empirical data and the simulations results are presented, by means of key properties of the recorded PDP profiles.