Accuracy of approximated WBAN channel by fundamental modes of spherical wave functions

To design sufficiently reliable wireless body area network (WBAN) system for future health-care, channel modeling plays an important role. Especially from the viewpoint of antenna optimization, the channel modeling approach should be able to de-embed the antenna contribution to the channel response. Two modeling approaches using spherical wave functions (SWFs) and orthogonal dipoles (ODs) have been proposed so far for this purpose, and the simplified form of the SWF channel modeling involving only fundamental modes is equivalent to OD channel modeling. Although the modeling by SWF fundamental modes or the ODs is practical, the accuracy of their channel approximation should be clarified in advance, hence the purpose of this paper. For the analysis of the accuracy, deviated dipole is utilized to model the antennas in finite size which can emit the higher modes. Applying the finite-difference time-domain method to the deviated dipole and the animated human body, the approximated and the exact channel response are obtained. The error due to the approximation is then modeled by log-normal distribution, of which statistical parameters are empirically obtained as the function of either the antenna size or residual power.