## 1 Body Area Network Propagation Channel  
Wireless Body Area Networks (BANs) use radio transmitters which can be located inside of the human body (implants), on the body, or in its proximity. This implies at least three corresponding possible communication scenarios: in-body, on-body, and off-body. The on-body scenario includes transceivers located either directly on the human body or embedded in clothes. The off-body scenario covers the systems in which the communication takes place between transceivers located on-body and in a near range around the person (depending on the case the distance can vary from meters to even hundreds of meters). In-body communication allows the transmission of data between the devices that are located inside the body and in its proximity. This case encompasses mainly wireless endoscopes and heart pacemakers. Readers interested in a general characteristics of these communication scenarios may for instance refer to [1]. This paper will only concentrate on the on-body scenario, where antennas of the communicating devices are located either directly on the human body or in its direct vicinity at distances in the range of millimeters. BAN systems also differ by the physical-layer channel type, which can be narrowband or ultra-wideband. Galvanic coupling may also be used instead of electromagnetic waves--where electrodes positioned on the skin replace antennas. In the paper, an Industrial Scientific Medical (ISM) 2.4 GHz band narrowband indoor channel is considered, which is used in many contemporary medical applications, such as wireless physiological sensor networks. BAN radio signal transmission is strongly affected by the presence of the human body which is a lossy medium with a complex structure, comprising tissues that have various values of dielectric permittivity and conductivity. When the radio wavelength is considerably greater than the cross-section of the body the resultant attenuation is low, however it becomes significant at gigahertz frequencies. In that case choosing radio propagation channel models for BAN is difficult because expected values of path loss through the body are high (up to about 90 dB) and may be critical for the proper operation of the network [2,3]. An in-depth simulation based analysis of the coupling between body mounted antennas using computational electrodynamics methods, such as the finite difference time domain (FDTD) method and numerical phantoms, can be found in literature, e.g., [4, 5, 6, 7]. However, some of these considerations focus on an unrealistic case of BAN operating in free space and the influence of reflecting objects in the environment around the human body is neglected [6,7]. An interesting but specific simulation scenario is described in [5], where body communication channel in a hospital environment is considered with focus on subject-specific body mass index influence. Experience shows that for some antenna configurations (for example chest to back) it can be expected that the relatively short direct propagation path through the body introduces greater attenuation to the signal than the indoor multipath formed by the reflecting environment (floor, walls, ceiling and other objects) surrounding the BAN. Some research results provide insight into selected factors that affect propagation for body-area networks, for instance, in [8] effects of earth ground is considered. In [9] a comprehensivestatistical characterization of body-to-body communication channel in a complex fire and rescue indoor training environment has been presented. In [10, 11] a FDTD body channel model and a Geometrically Based Statistical Channel indoor multipath environment model are separately considered first and then combined into an indoor BAN deterministic/statistical channel model. This approach assumes independence of the two models. Also intricate analytical models for free-space BAN, for instance applying dyadic Green's function have been elaborated [12]. Some channel models are based solely on a statistical processing of measurement results [13].