## 5 Open Research Issues, Challenges and Opportunities
### WBANs Performance Evaluation, Simulation and Experimentation Challenges  
Due to the high complexity of theoretical models and the unavailability of commercial IEEE 802.15.6 standard-compliant devices, simulation is currently considered as the most convenient methodology to evaluate the performance of Wearable WBANs and their protocol stacks.  
However, none of the existing simulation environments takes accurately into account the specific characteristics of WBANs, such as the physical layer (e.g., time-variant channel, temporal and spatial correlations of radio losses, body shadowing effects, _etc._) and the mobility behavior of humans (e.g., biomechanical body, group/social mobility behavior). Most research studies related to on-body and body-to-body communication networks are still based on unrealistic simulation parameters and physical models.  
Based on experimental channel measurements, abstracted radio link models as well as realistic Intra-WBAN and Inter-WBAN mobility models, existing simulation environments should be  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Body Position** & **Sensors** & **Sensors Location** & **Mobility** \\ \hline \multirow{8}{*}{Sitting} & Heart Beat & Wrist \({}^{\mathrm{R}}\) & Low Mobility OR Static \\  & Temperature & Wrist \({}^{\mathrm{L}}\) & Low Mobility OR Static \\  & ECG & Chest & Static \\  & EEG & Head & Low Mobility OR Static \\  & Oxygen Saturation & Shoulder & Static \\  & Accelerometer & Leg \({}^{\mathrm{R}}\) and arm \({}^{\mathrm{L}}\) & Low Mobility \\  & Gyroscope & Leg \({}^{\mathrm{R}}\) and arm \({}^{\mathrm{L}}\) & Low Mobility \\ \hline \multirow{8}{*}{Standing} & Heart Beat & Wrist \({}^{\mathrm{R}}\) & Low Mobility OR Static \\  & Temperature & Wrist \({}^{\mathrm{L}}\) & Low Mobility OR Static \\  & ECG & Chest & Static \\  & EEG & Head & Static \\  & Oxygen Saturation & Shoulder & Static \\  & Accelerometer & Leg \({}^{\mathrm{R}}\) and arm \({}^{\mathrm{L}}\) & Low Mobility \\  & Gyroscope & Leg \({}^{\mathrm{R}}\) and arm \({}^{\mathrm{L}}\) & Low Mobility \\ \hline \multirow{8}{*}{Walking} & Heart Beat & Wrist \({}^{\mathrm{R}}\) & Low-to-High Mobility \\  & Temperature & Wrist \({}^{\mathrm{L}}\) & Low-to-High Mobility \\  & ECG & Chest & Low Mobility \\  & EEG & Head & Low Mobility \\  & Oxygen Saturation & Shoulder & Low Mobility \\  & Accelerometer & Leg \({}^{\mathrm{R}}\) and arm \({}^{\mathrm{L}}\) & Low-to-High Mobility \\  & Gyroscope & Leg \({}^{\mathrm{R}}\) and arm \({}^{\mathrm{L}}\) & Low-to-High Mobility \\ \hline \multirow{8}{*}{Running} & Heart Beat & Wrist \({}^{\mathrm{R}}\) & High Mobility \\  & Temperature & Wrist \({}^{\mathrm{L}}\) & High Mobility \\  & ECG & Chest & Low-to-High Mobility \\ \cline{1-1}  & EEG & Head & Low-to-High Mobility \\ \cline{1-1}  & Oxygen Saturation & Shoulder & Low-to-High Mobility \\ \cline{1-1}  & Accelerometer & Leg \({}^{\mathrm{R}}\) and arm \({}^{\mathrm{L}}\) & High Mobility \\ \cline{1-1}  & Gyroscope & Leg \({}^{\mathrm{R}}\) and arm \({}^{\mathrm{L}}\) & High Mobility \\ \hline \hline \end{tabular}
\end{table}
Table 16: Sensors, their locations and corresponding mobility for various body postures. R and L in the superscript (of sensor location) represent right and left.  
enhanced. The ideal WBAN simulator should include a realistic abstraction of the Inter-body channel variations under mobility for the lower layers and realistic higher layers, hence easing the design and evaluation of new MAC and networking functionalities. In this context, one shall carefully mind the challenges resulting from the integration of different models into one single tool (e.g., in terms of interfaces, overall consistency, heterogeneous levels of abstraction, computational cost, _etc._). In particular, the best compromises between physical realism and computational tractability, as required by cooperative Inter-WBAN scenarios, should be determined in the future.