## 3 WBAN Sensor Techniques  
Sensors, which convert physical parameters into electronic signals, are the crucial components in the WBAN. Sensors have been mainly categorized into three types according to their functions [53]. Physiological sensors measure ambulatory BP, glucose (continuously), body temperature, blood oxygen, ECG, EEG, EMG, etc. ; biokinetic sensors measure acceleration and the angular rate of human motion rotation; and ambient sensors measure humidity, light, sound pressure level and environmental temperature. Generally, WBAN sensors for obtaining physiological parameters of the human body are categorized into two groups: invasive (i.e., implanted sensors) and non-invasive (i.e., external sensors) [14], as shown in Table 5. Implanted sensors are inserted into the human body or under the \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Characteristic**} & \multicolumn{1}{c}{**Requirement**} & \multicolumn{1}{c}{**Desired Range**} \\ \hline Operating distance & In, on or around the body & Typically limited in 3 m \\ \hline Peak power consumption & Ultra-low & \(\mu\)W level in sleep mode, up to 30 mW \\  & & & fully active mode \\ \hline Data rate & Scalable & From 1 kb/s to 10 Mb/s \\ \hline Network size & Modest & \(\sim\)50 devices per BAN \\ \hline Frequency band & Global unlicensed and medical bands & MedRadio, ISM, WMTS, UWB \\ \hline MAC & Scalable, reliable, versatile, self-forming & Low power, synchronization, listening, \\  & & & wake up, turn-around \\ \hline QoS & Real-time data, periodic parametric data, & P2P latency: from 10 ms to 250 ms, BER: from 10-10 to 10-3, reservation and prioritization \\  & & & \\ Coexistence & Coexistence with legacy devices and & Simultaneous co-located operation of up \\  & self-coexistence & & to 10 independent WBANs \\ \hline Topology & Star, Mesh or Tree & Self-forming, distributed with \\  & & & multi-hop support \\ \hline Environment & Body shadowing, attenuation & Seamless operation of multiple nodes in \\  & & & and out of scope with each other \\ \hline Setup time & Not to be perceived & Up to 3 s \\ \hline Security & Various levels & Authentication, Encryption, \\  & & & Authorization, Privacy, Confidentiality, \\  & & & Message integrity \\ \hline Safety/Biocompatibility & Long-term continuous use without & & regulatory requirements \\  & harmful effects & & & and form factors \\ \hline Ergonomic consideration & Size, weight, shape and form factors & Non-invasive, appropriate size, weight \\  & limited by location and organ & & and form factors \\ \hline Reprogramming, Calibration, & Personalized, configurable, integrated & reprogram, recalibrate, tune and \\ Customization & and context-aware services & configure devices wirelessly \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of technical requirements and their desired ranges. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Application**} & \multicolumn{1}{c}{**Data Rate**} & \multicolumn{1}{c}{**Nodes Number**} & \multicolumn{1}{c}{**Topology**} & \multicolumn{1}{c}{**Setup Time**} & \multicolumn{1}{c}{**P2P**} & \multicolumn{1}{c}{**BER**} & \multicolumn{1}{c}{**Duty Cycle**} & \multicolumn{1}{c}{**Battery Lifetime**} \\ \hline ECG & 72 kb/s & \(<\)6 & Star & \(<\)3 s & \(<\)250 ms & \(<\)10–10 & \(<\)10\% & \(>\)1 week \\ EMG & 1.54 Mb/s & \(<\)6 & Star & \(<\)3.5 & \(<\)250 ms & \(<\)10–10 & \(<\)10\% & \(>\)1 week \\ EEG & 86.4 kb/s & \(<\)6 & Star &  
skin with the help of surgery, whereas external sensors are directly attached to the skin or around the body. Table 6 describes the mechanisms of several common sensors and their data rates in WBANs [54]. One important requirement is that the sensors can continuously monitor the patient's health conditions without disturbing their activities. Since the physiological parameter signals are very weak, the correct detection and precise processing of these signals by sensor nodes is very crucial: these collected data are the basis of clinical diagnostics.