## 4 Wireless Transmission in WBANs
### Frequency Bands for WBAN Channel Models  
The choice of frequency bands for WBANs is an elementary factor affecting wireless communication. Table 8 provides the operation frequency bands for medical WBANs [12]. These frequency bands can be further divided into two groups (in-body or on-body) depending on the location of the sensor. The medical device radio communications frequency band (401-406 MHz) is mainly used in implantable medical devices. It has quiet channel properties and worldwide availability; it cannot be substituted by wearable sensor node frequencies. Industrial, scientific and medical (ISM) bands in the 2360-2500 MHz zone are exposed to less interference compared to the 2400-2483 MHz band [11], which is an unlicensed band occupied by Wi-Fi, Bluetooth and ZigBee as of IEEE 802.15.6. Some frequency bands are only for specific countries, such as the general telemetry (868-870 MHz)  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sensor** & **Working Mechanism** & **Power Consumption** & **Data Rate** \\ \hline Accelerometer & Measures the acceleration & & High & High \\  & relative to freefall in three axes & & \\ \hline Carbon dioxide & \begin{tabular}{c} measures the gas absorption \\ using infrared light \\ \end{tabular} & Low & Low \\ \hline Gyroscope & \begin{tabular}{c} Measures the orientation based \\ on the principles of \\ angular momentum \\ \end{tabular} & High & High \\ \hline Pulse oximetry & \
\begin{tabular}{c} Measures the changes of \\ absorbance ratio by the red or \\ infrared light passing through \\ the fingertip or earlobe \\ \end{tabular} & Low & Low \\ \hline Humidity &
\begin{tabular}{c} Measures the \\ conductivity changes \\ \end{tabular} & Low & Very low \\ \hline \hline \end{tabular}
\end{table}
Table 6: _Cont._  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Specifications** & **Requirements** \\ \hline Topology & Star or star mesh hybrid, bidirectional link \\ Devices & Number Typically 6, Up to 16 \\ Data Rate & 10 Kb/s-10 Mb/s \\ Range & \textgreater{}3 m with low data rate under IEEE Channel Model \\ PER & \textless{}10\% with a link success probability of 95\% overall \\ channel conditions & \textless{}125 ms (medical), \textless{}250 ms (non-medical) \\ Reliability & \textless{}1 s for alarm, \textless{}10 ms for applications with feedback \\ Power Consumption & \textgreater{}1 year (1\% LDC and 500 mAh battery), \textgreater{}9 h (always \\ “on” and 50 mAh battery) \\ Coexistence & Less than 10 BANs in a volume of 6 m \(\times\) 6 m \(\times\) 6 m \\ \hline \hline \end{tabular}
\end{table}
Table 7: Main specifications for WBAN systems.  
and some ISM bands (902-928 MHz) with limited bandwidth. The IEEE 802.15.6 standard presented a new communication medium, human body communications (HBC), with a frequency range of 5-50 MHz. A capacitively coupled HBC channel was developed based on the induction of the transmitter to the near electric field around the human body, and the weak coupling changes in the electric field near the human body channel are detected by the receiver. According to the application scenarios of WBANs, selecting different channel frequency bands can effectively avoid interference and solve the coexistence problem.