## 2 WBANs for Life and Safety Critical Applications
### WBAN Requirements  
In order to address the increasing demand for Wearable Human Assistive solutions, the IEEE 802.15.6 (TG6) task group has recently approved and released a WBAN IEEE standard [9] for short-range wireless communications on, or inside, human bodies, and whose functional requirements are summarized in Table 1. Given the wide range of target WBAN applications the IEEE 802.15.6 norm was designed with several key requirements in mind, such as the achieved data rates, power consumption, network size and security. Indeed, the main requirements of the IEEE 802.15.6 are summarized as follows [7; 9; 24]:  
* The communication range of the WBANs nodes should be around a few meters (typically 3 m) under low data rates, and it should support the one-hop or two-hop star topology;  
Figure 4: WBANs for Mobile Workforce Safety and Health Management Application Use-Case 2.  
Figure 3: WBANs for Mobile Workforce Safety and Health Management Application Use-Case 1.  
* WBAN nodes should be able to be dynamically inserted and/or removed from the WBAN system in less than 3 s;  
* WBANs should support up to 64 nodes per WBAN, and up to four WBANs located on the same body (_i.e._, a total of 256 nodes per body);
* Due to the high heterogeneity of WBAN applications and on/in-body sensors, the typical data rates of the WBAN communication links should be between 10 Kb/s and 10 Mb/s depending on the considered application, as shown in Table 2;
* The achieved packet error rate (PER) should be less than 10%, assuming a data payload of 256 bytes, with a link success probability of 95% over all channel and movement conditions;
* The achieved communication latency should be less than 125 milliseconds for medical applications and less than 250 milliseconds for non-medical applications, whereas the jitter should be less than 50 milliseconds;
* The WBAN communication links should be reliable and support different quality of services (QoS) by providing, for example, fast alarm messages delivery (e.g., in less than 1 s) during emergency situations. Moreover, periodic and burst traffic patterns should be supported;
* The WBANs should support ultra-low power consumption, with devices able to operate from several hours up to several years depending on the target applications. For example, WBAN nodes should be able to operate for more than 1 year using a 500 mAh battery and 1% low duty cycle (LDC) protocols;
* Up to 10 WBANs should be able to coexist in a volume of 6 m\({}^{3}\), and should be robust against the presence of other heterogeneous communication standards and interferences, such as WiFi or Bluetooth;
* WBANs should support low-overhead and lightweight security features, such as the authentication of the WBAN devices, data integrity, and data encryption;
* Finally, WBANs devices should be ergonomic, in terms of sizing, functionalities, and lifetime, in order to enable the emergence of future body centric applications.  
\begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**WBAN Functional Requirements**} \\ \hline Topology & One-hop star, two-hop star, bidirectional link \\ Setup Time & Insertion/removal \textless{}3\) s \\ Devices Number & Typically 6, up to 256 \\ Data Rate & 10 Kb/s\textless{}10 Mb/s \\ Range & \(\approx\)3 m with low data rate under IEEE Channel Mode \\ PER & \textless{}10\% with a link success probability of 95\% over all channel conditions \\ Latency & \textless{}125 ms (medical); \textless{}250 ms (non-medical) \\ Jitter & \textless{}50 ms \\ Reliability & \textless{}1 s for alarm; \textless{}10 ms for applications with feedback \\ Power Consumption & \textgreater{}1 year (1% LDC + 500 mAh battery); \textgreater{}9 h (always ON + 50 mAh battery) \\ Intra-Coexistence & 10 WBANs in a volume of 6 \(\times\) 6 \(\times\) 6 m \\ Inter-Coexistence & Environment (WiFi, Bluetooth, _etc._) \\ \hline \hline \end{tabular}
\end{table}
Table 1: IEEE 802.15.6 WBAN Requirements [24].