# Realistic Simulation for Body Area and Body-To-Body Networks
## 3 Proposed Simulator
### Semi-Deterministic (Stochastic) Radio Link and Mobility Modeling
#### 3.1.4 Body-to-Body Channel Model  
In B2B communications, the human body itself plays an important role, and when compared to other types of channels, body shadowing has a major influence on the channel characteristics. The result is that, for a given type of channel, the characteristics strongly depend on the reciprocal position of the bodies where the terminals are mounted. In [64], a comprehensive stochastic channel model that accurately predicts narrowband B2B channel behavior by exploiting the awareness of the mutual spatial position of the two terminals has been presented. In this model, the channel depends on the type of link, but it also is a function of the distance (\(d\)) and the mutual orientation (\(\alpha\)), defined as in Figure 7, between the two bodies in the following way:  
\[G\left(d,\alpha\right)=G_{0}\left(\alpha\right)-10n\left(\alpha\right)\log_{ 10}\left(\frac{d}{d_{0}}\right) \tag{7}\]  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Short-Term Fading** & \(\mu\) & \(\sigma\) \\ \hline
**Head-to-Belt** & 0.7661 & 0.4286 \\
**Head-to-Wrist** & 0.8407 & 0.3365 \\
**Belt-to-Wrist** & 0.8688 & 0.2677 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Rice parameters of short-term fading for each on-body link.  
Figure 6: Comparison between measured and implemented belt-to-wrist on-body channel.  
It is also important to note that for wrist-related links, the definition of \(\alpha\) is not sufficient to describe body shadowing condition. As depicted in Figure 8 for a given angle \(\alpha\), the link may be obstructed by the bodies or not. Therefore, an additional parameter has to be included to distinguish between those two possibilities.  
In Table 4, some examples of path loss parameterization are provided for head-to-head and belt-to-belt links to show the impact of body shadowing through body orientation. In the first case, there is no significant impact, as propagation was only minorly affected by the on-body antenna position, while in the second one, it is of major importance to include the body shadowing effects produced by the torso. A detailed model will be available in [64].  
Short-term fading has also been shown to have a non-negligible distance and mutual orientation dependence in some of the links, and this issue has to be taken into account to generate an accurate realization of this process [65]. Long-term fading is, instead, implemented with an AR model for  
\begin{table}
\begin{tabular}{l c c} \hline \hline  & **Path Loss Exponent (n)** & \(\mathbf{G_{0}}\) **(dB)** \\ \hline
**Head-to-Head (SR)** & \(1.28\) & \(-41.5\) \\
**Head-to-Head (2R)** & \(0.94\) & \(-46.9\) \\
**Belt-to-Belt (SR)** & \(-0.007\alpha+1.84,0\leq\alpha\leq 90\) & \(-0.19\alpha-29.5,0\leq\alpha\leq 100\) \\  & \(-0.027\alpha+3.64,90\leq\alpha\leq 130\) & \(-0.55\alpha+6.5,100\leq\alpha\leq 120\) \\  & \(0.011\alpha-1.3,130\leq\alpha\leq 180\) & \(0.06\alpha-66.7,120\leq\alpha\leq 180\) \\
**Belt-to-Belt (2R)** & \(1.7\) & \(-0.068\alpha-41\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Examples of parametrization of the path loss in a single-room (SR) or two-room (2R) scenario for head-to-head and belt-to-belt links.  
Figure 8: LOS position on the left and body-shadowed position on the right with the same reciprocal orientation angle.  
Figure 7: Reciprocal orientation angle.  
temporal correlation, in accordance with what has been done for the on-body links. In this case, no inter-link correlation is implemented. This is because most of the contribution to inter-link correlation is implemented by default by generating consistently the distance and mutual orientation-dependent channel gain. Figure 9 shows an example of the comparison between the measured and implemented belt-to-belt B2B channel, where it is also evident how the model is able to reproduce the short-term fading variations over time induced by the different reciprocal positions of the bodies.