# Realistic Simulation for Body Area and Body-To-Body Networks
## 3 Proposed Simulator
### Deterministic (Bio-Mechanical) Radio Link and Mobility Modeling
#### 3.2.2 Intra-BAN and Inter-BAN Channel Models  
Once the space-time varying links and mobility traces are properly generated for a given mobility scenario, channel models can be applied in order to assess the performance of radio links. The IEEE 802.15.6 standard has proposed various channel models, including the _CM3_ (body surface-to-body surface) and CM4 ( body surface-to-external) models. CM3-Approposed a log-normal distributed channel model. During the experimentation, the transmitter antenna was placed at the waist, and a receiver antenna was placed on different parts of the body, including the head, ear, shoulder, wrist, waist, leg and ankle. The path loss model was derived using a regression line through least square fitting for both frequency bands at narrow-band (_i.e._, 900 MHz and 2450 MHz) and is expressed as:  
\[PL(d)[dB]=a\cdot log_{10}(d)+b+N \tag{8}\]  
where \(a\) and \(b\) are the coefficients of the linear fitting, \(d\) is the distance between (transmitter and receiver in mm), \(N\) is the normally-distributed random variable with standard deviation \(\sigma\), which has different values based on the frequency bands and the environment, _i.e._, hospital room or anechoic chamber, and the values are presented in Table 5[71]. However, it was shown that these models provide only basic distance-based path loss without any time-varying effects and correlation features [66]. The enhanced IEEE 802.15.6 path loss models as proposed in [66] utilize dynamic mobility and obtain space and time-variations. For the case of CM3-B, the transmitter was worn at approximately shoulder height at two different positions. The receiver was placed directly below the transmitter at seven positions separated by 10 cm covering the range from the shoulder to the knees. Six different locations were considered inside an office room, and at each of the locations, 49 points were arranged at the height of a \(7\times 7\) square grid. The separation distance between each array element is 6 cm for 2.45 GHz and 16 cm for 900 MHz. The resulting path loss model is a combination of the exponential function of the distance and average indoor attenuation, which is expressed as:  
\[PL(d)[dB]=-10\;log_{10}(P_{0}\;e^{-md}+P_{1})+N \tag{9}\]  
where \(P_{0}\) is the average loss close to the antenna and will depend on the type of antenna, \(m\) represents the average decay rate in dB/cm for the surface wave traveling around the perimeter of the body, \(d\) is the distance in centimeters, \(P_{1}\) is the average attenuation of components in an indoor environment radiated away from the body and reflected back towards the receiving antenna and \(N\) is the random Gaussian variable with zero mean and 3.6-dB variance (\(\sigma_{P}\)) [72], measured at different body and room locations. This parameter depends on variations in the body curvature and antenna radiation properties at different body locations, and their typical values are presented in Table 6.  
Both above-explained IEEE channel models (_i.e._, CM3-A and CM3-B) are static models. In order to practically utilize these models, dynamic space and time variations are injected through bio-mechanical model. To highlight the full potential of the deterministic approach, we exploit many mobility scenarios that contain space and time-varying link types, as shown below. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Path Loss Model** & & \\ (**Parameters**) & **Hospital Room** & **Anechoic Chamber** \\ \hline a & 6.6 & 29.3 \\ b & 36.1 & 16.8 \\ \(\sigma_{N}\), dB & 3.8 & 6.89 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Channel model for the narrow band (_i.e._, CM3-A). After obtaining the time-varying distances, these are used to accurately model the channel behavior. For example, static _versus_ time-varying path loss comparisons of CM3-B and Enhanced Channel Model (E -CM3-B) are shown in Figure 12. As an example, the results are shown for a 2450-MHz frequency under walking scenarios.