## 2 Background
### WBASN Standards  
The implementation of WBASNs is usually done using WPAN communication protocols, including ZigBee (IEEE 802.15.4), IEEE 802.15.6 and Bluetooth, etc. Various other wireless technologies can be potentially used for WBASNs. Standardised bodies such as the IEEE, the International Society of Automation (ISA) and the IETF have created new wireless standards, and most of these standards are available as commercial products. In the literature, there are various contributions towards lower-power network-based devices for WBASNs, such as ZigBee, 6 loWPAN [57], 6 lo [58], 6 tisch [59], ISA SP-100 [60], IEEE 802.15.4 [61] and IEEE 802.15.6 [62]. (1) IEEE 802.15.6 was developed by a task group in 2007 for the standardisation of WBANs and approved in 2012 [63; 64; 65]. This standard is used for implantable as well as wearable sensors and works at lower frequencies within a short range. This standard presents a MAC and physical layer design to support various applications, including medical and non-medical applications. Medical applications refer to a collection of vital information in real-time (monitoring) for the diagnoses and treatment of various diseases with the help of different sensors (accelerometer, temperature, BP and EMG, etc.). It defines a MAC layer that works with three PHY layers, i.e., human body communication (HBC), ultra-wideband (UWB) and narrowband (NB). IEEE 802.15.6 also provides a specification for the MAC layer to access the channel. The coordinator divides the channel into superframe time structures to allocate resources. Superframes are bounded by equal-length beacons through the coordinator. Table 4 describes the different frequency bands for IEEE 802.15.6. \begin{table}
\begin{tabular}{c c} \hline \hline  & Human-Body Communication \\ \hline Frequency & Bandwidth \\ \hline
16 MHz & 4 MHz \\ \hline
27 MHz & 4 MHz \\ \hline  & Narrowband Communication \\ \hline Frequency & Bandwidth \\ \hline
402–405 MHz & 300 KHz \\ \hline
420–450 MHz & 300 KHz \\ \hline
863–870 MHz & 400 KHz \\ \hline
902–928 MHz & 500 KHz \\ \hline
956–956 MHz & 400 KHz \\ \hline
2360–2400 MHz & 1 MHz \\ \hline
2400–2438.5 MHz & 1 MHz \\ \hline  & UWB Communication \\ \hline
13.2–4.7 GHz & 499 MHz \\ \hline
6.2–10.3 GHz & z \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Frequency bands of IEEE 802.15.6. (2) IEEE 802.15.4  
IEEE 802.15.4 is the standard that states the physical layer and MAC layer functionality for LR-WPANs. It was established by the IEEE 802.15 working group, which provided the basis for the WPAN standard. IEEE 802.15.4 discusses different device roles, including full-function devices and reduced-function devices. The physical layer of IEEE 802.15.4 uses three frequency bands, including 2.4 to 2.4835 GHz with 16 channels, 902 to 928 MHz with 10 channels and 868 to 868.6 MHz with a single channel. The data link layer is made of two sub-layers, MAC and logical link control. The MAC layer manages activities such as beacon management, GTS management, and channel access. The standard acts as a basis for ZigBee, WirelessHART and ISA 100.11a, etc., and uses 6 LoWPAN to provide connectivity with the internet. Various WBASN standard-based commercial products operate with the IEEE 802.15.4 standard. The standard claims to provide energy-efficient communication and provides appropriate throughput, limited latency and acceptable reliability. A survey in 2016 of 100 users found that IEEE 802.15.4 was used by 63% of them for a variety of IoT applications, which indicates its market acceptability and strong relation with IoT applications [66]. IEEE802.15.4 with ZigBee has become a popular industrial choice for IoT applications. Moreover, various task groups of IETF, e.g., \"routing over low power and lossy networks\", have recommended using IEEE 802.15.4. The task groups of IEEE 802.15.4 can be summarised as follows. IEEE 802.15.4a provides an amendment to IEEE 8021.5.4 by incorporating two PHYs, including UWB and Chirp.