## 1 Introduction
### Impact of WuR in the Design of MAC Protocols  
In the last decade, the concept of ultra-low-power WuR [13] was introduced. Schematic architecture of the sensor node with WuR is shown in Figure 1. WuR operates together with the main radio with much lower power consumption than the main radio. The WuR reduces the energy consumption of wireless communication by switching the main radio to deep-sleep mode when no data is transmitted or received. It is operated with different duty-cycles and yields a good power budget for the sensor nodes. The WuR can either operate in the same band of the main radio or in a different band. Different innovative WuR designs already exist, which operate in the power range of nanowatts [14]. It has been shown that WuR reduces the overall power consumption of wireless communication in sensor nodes, provided that the duty-cycle of main radio is carefully selected and synchronized with the duty-cycle of the WuR [15].  
The main features of WuR to make it as a suitable technology for MAC protocols of IBSN are its low power consumption, reliable performance in short-range networks, ability to operate out-of-band with main radio, and not requiring complex hardware [16]. By turning the main radio on when it is really needed, WuR limits the power consumed by the main radio for idle listening along with the over-hearing problems preventing data collision from occurring. The data communication is then  
\begin{table}
\begin{tabular}{p{56.9 pt} p{341.4 pt}} \hline \hline \multicolumn{2}{c}{**Characteristics of Closed-Loop Medical Systems**} \\ \hline Self management & A closed-loop system needs to have detailed knowledge about its components, current status, ultimate capacity, and all connections to other systems to govern itself through effective resource management, utilization and sharing \\ \hline Self configuration & A closed-loop system should automatically and dynamically configure and reconfigure itself under varying conditions and changing environments \\ \hline Self optimization & A closed-loop system should constantly optimize its performance and resource utilization by monitoring its constituent components and fine tune work-flow to achieve predetermined performance and resource utilization goals \\ \hline Self healing & A closed-loop system should gracefully recover from routine and extraordinary events that cause component malfunction. It is able to discover problems and establish means of using alternative resources or configurations to maintain system functionality \\ \hline Self protection & A closed-loop system must be able to exert self-protection by automatically detecting and identifying different types of attacks to maintain overall system security and integrity \\ \hline Self adaptation & A closed-loop system must be context aware and adapt itself for improved interaction and performance under changing working environments and user requirements \\ \hline Self integration & A closed-loop system should fully function under heterogeneous infrastructure and be seamlessly and securely integrated with other systems \\ \hline Self scaling & A closed-loop system should anticipate the optimized resources required and scale its functionality while keeping its complexity hidden from the user \\ \hline \hline \end{tabular}
\end{table}
Table 2: Features of closed-loop medical systems. Inspired from [7].  
initiated and completed using the main radio, reducing the total amount of time that the main radio is turned on. The WuR of the transmitter broadcasts a node-id encoded wake-up signal, which is acknowledged by the WuR of the destined node, indicating that the main radio of the receiver node is actively listening. The main radio of the transmitter is turned on only when the acknowledgment is received for the wake-up signal, hence reducing energy consumption and increasing reliability.