Simon L. Cotton

An experimental investigation into the influence of user state and environment on fading characteristics in wireless body area networks at 2.45 GHz

Using seven strategically placed, time-synchronized body worn receivers covering the head, upper front and back torso, and the limbs, we have investigated the effect of user state: stationary or mobile and local environment: anechoic chamber, open office area and hallway upon first and second order statistics for on-body fading channels. Three candidate models were considered: Nakagami, Rice and lognormal. Using maximum likelihood estimation and the Akaike information criterion it was established that the Nakagami-m distribution best described small-scale fading for the majority of on-body channels over all the measurement scenarios. When the user was stationary, Nakagami-m parameters were found to be much greater than 1, irrespective of local surroundings. For mobile channels, Nakagami-m parameters significantly decreased, with channels in the open office area and hallway experiencing the worst fading conditions.

Characterization and Modeling of the Indoor Radio Channel at 868 MHz for a Mobile Bodyworn Wireless Personal Area Network

This letter reports the statistical characterization and modeling of the indoor radio channel for a mobile wireless personal area network operating at 868 MHz. Line of sight (LOS) and non-LOS conditions were considered for three environments: anechoic chamber, open office area, and hallway. Overall, the Nakagami-m cdf beast described fading for bodyworn operation in 60% of all measured channels in anechoic chamber and open office area environments. The Nakagami distribution was also found to provide a good description of Rician distributed channels which predominated in the hallway. Multipath played an important role in channel statistics with the mean recorded m value being reduced from 7.8 in the anechoic chamber to 1.3 in both the open office area and hallway

A Statistical Analysis of Indoor Multipath Fading for a Narrowband Wireless Body Area Network

A thorough statistical analysis of multipath effects for on-body propagation channels in wireless body area networks (WBANs) is presented. Experiments were conducted at 868 MHz for both stationary and mobile scenarios in an anechoic chamber and two typical indoor environments. When the WBAN is stationary, fading in bodyworn channels is determined by body-centric processes with Nakagami fading (m Gt 1) shown to provide the optimum fit. Equivalent Rician KdB-factors for these channels are also shown to be high, peaking at 36.1 dB for channels which cross the anterior chest region. However, mobile fading channels were predominantly Rice distributed in multipath environments. Movement in a multipath environment also caused a reduction in m and K values beyond that observed in anechoic conditions

Channel Characterization for Single- and Multiple-Antenna Wearable Systems Used for Indoor Body-to-Body Communications

In this paper, an analysis of radio channel characteristics for single- and multiple-antenna bodyworn systems for use in body-to-body communications is presented. The work was based on an extensive measurement campaign conducted at 2.45 GHz representative of an indoor sweep and search scenario for fire and rescue personnel. Using maximum-likelihood estimation in conjunction with the Akaike information criterion (AIC), five candidate probability distributions were investigated and from these the kappa- mu distribution was found to best describe small-scale fading observed in the body-to-body channels. Additional channel parameters such as autocorrelation and the cross-correlation coefficient between fading signal envelopes were also analyzed. Low cross correlation and small differences in mean signal levels between potential dual-branch diversity receivers suggested that the prospect of successfully implementing diversity in this type application is extremely good. Moreover, using selection combination, maximal ratio, and equal gain combining, up to 8.69-dB diversity gain can be made available when four spatially separated antennas are used at the receiver. Additional improvements in the combined envelopes through lower level crossing rates and fade durations at low signal levels were also observed.

A Time-Domain Approach to the Analysis and Modeling of On-Body Propagation Characteristics Using Synchronized Measurements at 2.45 GHz

Modeling of on-body propagation channels is of paramount importance to those wishing to evaluate radio channel performance for wearable devices in body area networks (BANs). Difficulties in modeling arise due to the highly variable channel conditions related to changes in the users state and local environment. This study characterizes these influences by using time-series analysis to examine and model signal characteristics for on-body radio channels in user stationary and mobile scenarios in four different locations: anechoic chamber, open office area, hallway, and outdoor environment. Autocorrelation and cross-correlation functions are reported and shown to be dependent on body state and surroundings. Autoregressive (AR) transfer functions are used to perform time-series analysis and develop models for fading in various on-body links. Due to the non-Gaussian nature of the logarithmically transformed observed signal envelope in the majority of mobile user states, a simple method for reproducing the fading based on lognormal and Nakagami statistics is proposed. The validity of the AR models is evaluated using hypothesis testing, which is based on the Ljung-Box statistic, and the estimated distributional parameters of the simulator output compared with those from experimental results.

Higher Order Statistics for Lognormal Small-Scale Fading in Mobile Radio Channels

Lognormal small-scale fading has recently been reported in a number of indoor propagation studies. However, until now, no method of generating higher order statistics for this distribution in short-term fading channels has appeared in the literature. In this letter, we present a lognormal fading model which is based on the Bessel-derived autocorrelation function frequently used in Rayleigh-, Rice-, and Nakagami-fading simulators. In addition, we present exact, closed-form expressions for the level crossing rate and average fade duration (AFD) observed in lognormal small-scale fading channels for arbitrary and . The accepted ability of the lognormal distribution to approximate Nakagami second-order statistics for high values of the Nakagami- parameter is used in combination with simulated data, generated using a rank-matching approach, to validate the new model. Theoretical second-order distributions are also compared with empirical measurements obtained for mobile indoor on-body propagation channels. In all cases, the theoretical equations and test data are in good agreement.

Human body shadowing in cellular device-to-device communications: channel modeling using the shadowed κ−μ fading model

Using device-to-device communications as an under- lay for cellular communications will provide an exciting opportu- nity to increase network capacity as well as improving spectral efficiency. The unique geometry of device-to-device links, where user equipment is often held or carried at low elevation and in close proximity to the human body, will mean that they are particularly susceptible to shadowing events caused not only by the local environment but also by the users body. In this paper, the shadowed κ − μ fading model is proposed, which is capable of characterizing shadowed fading in wireless communication channels. In this model, the statistics of the received signal are manifested by the clustering of multipath components. Within each of these clusters, a dominant signal component with arbitrary power may exist. The resultant dominant signal component, which is formed by the phasor addition of these leading contributions, is assumed to follow a Nakagami-m distribution. The probability density function, moments, and the moment-generating function are also derived. The new model is then applied to device-to-device links operating at 868 MHz in an outdoor urban environment. It was found that shadowing of the resultant dominant component can vary significantly depending upon the position of the user equipment relative to the body and the link geometry. Overall, the shadowed κ − μ fading model is shown to provide a good fit to the field data as well as providing a useful insight into the characteristics of the received signal.

A Statistical Model for Shadowed Body-Centric Communications Channels: Theory and Validation

This paper presents a new statistical signal reception model for shadowed body-centric communications channels. In this model, the potential clustering of multipath components is considered alongside the presence of elective dominant signal components. As typically occurs in body-centric communications channels, the dominant or line-of-sight (LOS) components are shadowed by body matter situated in the path trajectory. This situation may be further exacerbated due to physiological and biomechanical movements of the body. In the proposed model, the resultant dominant component which is formed by the phasor addition of these leading contributions is assumed to follow a lognormal distribution. A wide range of measured and simulated shadowed body-centric channels considering on-body, off-body and body-to-body communications are used to validate the model. During the course of the validation experiments, it was found that, even for environments devoid of multipath or specular reflections generated by the local surroundings, a noticeable resultant dominant component can still exist in body-centric channels where the users body shadows the direct LOS signal path between the transmitter and the receiver.

Millimeter-wave soldier-to-soldier communications for covert battlefield operations

Mobile ad hoc networking of dismounted combat personnel is expected to play an important role in the future of network-centric operations. High-speed, short-range, soldier-to-soldier wireless communications will be required to relay information on situational awareness, tactical instructions, and covert surveillance related data during special operations reconnaissance and other missions. This article presents some of the work commissioned by the U.K. Ministry of Defence to assess the feasibility of using 60 GHz millimeter-wave smart antenna technology to provide covert communications capable of meeting these stringent networking needs. Recent advances in RF front-end technology, alongside physical layer transmission schemes that could be employed in millimeter-wave soldier- mounted radio, are discussed. The introduction of covert communications between soldiers will require the development of a bespoke directive medium access layer. A number of adjustments to the IEEE 802.11 distribution coordination function that will enable directional communications are suggested. The successful implementation of future smart antenna technologies and direction of arrival-based protocols will be highly dependent on thorough knowledge of transmission channel characteristics prior to deployment. A novel approach to simulating dynamic soldier-to-soldier signal propagation using state-of-the-art animation-based technology developed for computer game design is described, and important channel metrics such as root mean square angle and delay spread for a team of four networked infantry soldiers over a range of indoor and outdoor environments is reported.

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In this letter, we perform a novel characterization of the fading experienced in body to body communications channels for fire and rescue personnel using the recently proposed kappa - mu distribution. A transmitter positioned on the lead fire person and four strategically placed, time-synchronized 2.45-GHz receivers situated on the protective helmet and shoulders of another team member allowed small-scale signal variation to be recorded while a rescue team of four persons performed a building sweep and search type operation. A general kappa - mu model with parameters kappa=2.31 and mu=1.19 was obtained using maximum likelihood estimation and shown to provide a good fit to measured data. Level crossing rates for these channels are also presented.