Shadowed Fading in Indoor Off-Body Communications Channels: A Statistical Characterization using the κ – μ / Gamma Composite Fading Model

This paper investigates the characteristics of the shadowed fading observed in off-body communications channels at 5.8 GHz. This is realized with the aid of the κ–μ/gamma composite fading model, which assumes that the transmitted signal undergoes κ–μ fading, which is subject to multiplicative shadowing. Based on this, the total power of the multipath components, including both the dominant and scattered components, is subject to non-negligible variations that follow the gamma distribution. For this model, we present an integral form of the probability density function (PDF) as well as important analytic expressions for the PDF, cumulative distribution function, moments, and moment generating function. In the case of indoor off-body communications, the corresponding measurements were carried out in the context of four explicit individual scenarios, namely: line of sight (LOS), non-LOS walking, rotational, and random movements. The measurements were repeated within three different indoor environments and considered three different hypothetical body worn node locations. With the aid of these results, the parameters for the κ–μ/gamma composite fading model were estimated and analyzed extensively. Interestingly, for the majority of the indoor environments and movement scenarios, the parameter estimates suggested that dominant signal components existed even when the direct signal path was obscured by the test subject’s body. In addition, it is shown that the κ–μ/gamma composite fading model provides an adequate fit to the fading effects involved in off-body communications channels. Using the Kullback–Leibler divergence, we have also compared our results Manuscript received March 23, 2015; revised November 8, 2015; accepted March 31, 2016. Date of publication April 21, 2016; date of current version August 10, 2016. This work was supported in part by the Leverhulme Trust, U.K., under Grant PLP-2011-061, in part by the Engineering and Physical Sciences Research Council under Grant EP/H044191/1 and Grant EP/L026074/1, and in part by the U.K. Royal Academy of Engineering under Grant EP/H044191/1. The associate editor coordinating the review of this paper and approving it for publication was R. J. Pirkl. S. K. Yoo and S. L. Cotton are with the Institute of Electronics, Communications and Information Technology, Queen’s University Belfast, Belfast BT3 9DT, U.K. (e-mail: syoo02@qub.ac.uk; simon.cotton@qub. ac.uk). P. C. Sofotasios was with the Department of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, U.K. He is now with the Department of Electronics and Communications Engineering, Tampere University of Technology, Tampere 33101, Finland, and also with the Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece (e-mail: p.sofotasios@ieee.org). S. Freear is with the Department of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, U.K. (e-mail: s.freear@leeds.ac.uk). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TWC.2016.2555795 with another recently proposed shadowed fading model, namely, the κ–μ/lognormal LOS shadowed fading model. It was found that the κ–μ/gamma composite fading model provided a better fit for the majority of the scenarios considered in this paper.