## 4 Conclusions  
In the paper the influence of the indoor environment on the signal attenuation in body area networks was studied for several simple antenna and wall geometries in the 2.4 GHz ISM band (and beyond, _i.e._, 2.2-2.8 GHz). Both measured and simulated attenuation median values (needed e.g., to calculate the fade margin and RF power budget used in the design of BAN networks) and channel frequency responses are shown and compared. Simulations were carried out with XFdtd(r) software package and NMR Hershey numerical human body phantom. In contrast to many other similar studies, the FDTD simulation domain included both a numerical body phantom and the surrounding room walls, floor and ceiling which is more realistic than free-space approach to BAN channel modeling. Comparison of estimated path loss values for the considered scenarios gives a qualitative and quantitative insight into the properties of a typical indoor BAN channel (as opposed to a purely theoretical, idealized free-space BAN channel). As expected, the highest attenuation can be observed for the model with the ground plane only (90 dB) and antennas located on the chest and the back of the human torso. In a reflective multipath environment with walls, a typical value of path attenuation for the same on-body antenna locations is significantly lower (60 dB for ground plane and two walls). For the antenna pair located on the chest and on one arm the path loss is lower than for the antennas located on the opposite sides of the torso (chest and back). In this case a reflective environment also decreases attenuation of radio signal but, additionally, strong frequency selective fades can be observed. To summarize, the following main conclusions of practical (engineering) importance can be drawn from the results of measurements and numerical simulation of the indoor BAN propagation on-body scenarios in 2.4 GHz band:  
1. Free-space modeling of the coupling between BAN antennas located on the human body can be applied to real indoor scenarios only for the antennas located close one to another, e.g., in the arm-chest configuration, where direct coupling between the antennas prevails over the room multipath. However in such a case free space model can be used only to approximate the median value of attenuation over the bandwidth. Frequency selective fades will not be represented. 2. For some antenna pair locations e.g., chest-back, where free-space approach (mostly presented in the literature) shows strong attenuation through the body (even up to 90 dB) in typical indoor environment the attenuation is significantly decreased. In the studied case the difference was up to 30 dB. The propagation mechanism in such a case can be dominated by room multipath propagation. In these cases BAN channel models for engineering applications should include multipath effects-even only to obtain median attenuation values. 3. Multipath effects can be easily simulated with simple room model comprising only two conducting surfaces (floor and ceiling) and dielectric walls. Such a simplification can free indoor BAN designers from creating very complex indoor environment models of target buildings. These buildings have mechanical structures that might be unknown to the BAN designer. For instance hospital rooms that are located on the same floor can differ significantly in the location of wiring and pipelines. This simplified model can be created in any full wave modeling tool. The median values of signal attenuation obtained with simulation and measurements as well as the character of frequency dependent fades (depth and frequency separation) are in good agreement. For the case of antennas located on chest and back, the corresponding simulated and measured median values differ only by 1.1 dB. For the case of antennas located on the arm and the chest the difference was 4.7 dB.