# Multi-Objective Optimization of a Wireless Body Area Network for Varying Body Positions
## 3 Simplified Body Model for the Sitting Position  
Various human body models and full-wave electromagnetic codes can be used to evaluate the performance of on-body and off-body wireless channels. Simplified cylindrical models of the human body are particularly useful for modeling different poses [22; 23] because the positions of the body parts can be easily modeled by translation and rotation of the cylinders. Cylindrical models are also convenient when the antenna position is variable but its distance to the body surface is fixed. This is because the position of the antenna can be controlled easily with two coordinates in a cylindrical coordinate system. In the case of anthropomorphic models, where the body shape is complex (non-cylindrical), maintaining a fixed distance between the antenna and body (e.g., the average across the antenna surface, the minimum, or another distance metric) is difficult. The results of path loss simulations for the on-body channel obtained with the simplified cylindrical model are satisfactorily similar to those obtained with a heterogeneous model [23]. The geometry of the simplified model was adjusted to approximate the shape of the heterogeneous model, as shown in Figure 5.  
The simplified model was verified with computer simulations carried out using both the simplified and the heterogeneous models. The heterogeneous model was modified in the Remcom VariPose [17] program to obtain a sitting position. The results of measurements obtained for the cylindrical model are similar to those obtained with a human subject [22; 23]. Figure 6 shows a comparison of the path loss between the chest antenna (G\({}_{2}\)) and the leg antenna (G\({}_{3}\)) computed using XFdtd with the heterogeneous model and the simplified model. The maximum difference is around 3 dB. Figure 7 shows a very good agreement between the on-chest antenna (G\({}_{2}\)) radiation patterns calculated using the two models. A significantly worse agreement (up to 12 dB difference) can be observed in Figure 8 for the on-leg antenna gain. This discrepancy will be investigated in our future research since for the purposes of the present study the approximation of the antenna directivity pattern is good enough to test our optimization strategy. The simplified cylindrical model was therefore chosen for further optimization of WBAN antenna placement. Its geometry can be synthesized and integrated with the antenna's geometry within the XFdtd scripting language with very low computational effort in the optimization loop. The geometry allows for the convenient movement of the antennas around the parts of the body in the cylindrical coordinate system axis of the trunk or leg, maintaining a constant distance between the antennas and the body.  
Figure 5: The human body models: (**a**) simplified-cylindrical; (**b**) anthropomorphic (multitissue).  
Figure 8: The on-leg antenna (antenna 3) radiation pattern in the horizontal plane obtained using the heterogeneous model and the simplified model.  
Figure 6: The system loss between the chest antenna (2) and leg antenna (3) (see Figure 4) obtained using the heterogeneous model and the simplified model.  
Figure 7: The on-chest antenna (antenna 2) radiation pattern in the horizontal plane obtained using the heterogeneous model and the simplified model.