## 2 State of the Art
### Architectures and Communications Technologies for WHMS
As a kind of conclusion and in order to illustrate current status on which are the most deployed communications technologies in each communications segment, Figure 2 shows the number of projects (from the subset of projects surveyed in Section 2.2) which use each communications technology in each communications segment. Figure 1: General Communications Architecture for WHMS. As for the BAN, it can be seen that nine projects use wired solutions and four projects use e-textiles (which is a kind of wired solution as well) to communicate the sensors deployed around the body and the gateway of the BAN, meaning that 36% of the surveyed projects use some kind of wired solution in the BAN. IEEE 802.15.4/Zigbee represents the most widely used wireless communications technology in the BAN. There are six projects that work directly on top of IEEE 802.15.4 and three projects that use Zigbee (which in turn relies on IEEE 802.15.4), what represents 25% of the surveyed projects. \begin{table}
\begin{tabular}{|c|c|c|c|c|c|} \cline{2-6} \multicolumn{1}{c|}{} & MICS & IEEE 802.15.6 & ANT & Zigbee & Bluetooth 4.0 (LE) \\ \hline \multirow{3}{*}{Radio \& MAC Stds} & FCC and ETSI & IEEE 802.15.6 & Propr. & IEEE 802.15.4 & IEEE 802.15.1 \\  & Stds & NB: 402–405/ & & & \\  & & 420–450/863–870/ & & & \\  & & 902–928/950–956/ & 2,4–2,524 GHz: & 868 MHz/ & \\ Frequency Band & 402–405 MHz & 2,360–2,400/ & 125 1 MHz & 915 MHz/ & 2.4 GHz \\  & & 2,400–2,483.5 MHz & channels & 2.4 GHz & \\  & & UWB: 3–10 GHz & & & \\  & & HBC: 16/27 MHz & & & \\ Data Rate & Up to 500 Kbps & NB: 57.5–485.7 Kbps & & 20–250 Kbps & 50–200 Kbps \\  & & UWB: 0.5–10 Mbps & & & \\ Range & 2 m & 1.2 m & Up to 10 m & 30 m & 30 m \\ Tx Power & 25 \(\mu\)W & 0.1 \(\mu\)W & 0.01–1 mW & 30 mW & \(\sim\)10 mW \\ Network Topology & & & Star, tree, mesh & Star, tree, mesh & Star \\ Stack size & & & 16 KB & 100 KB & 250 KB \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of Communications Technologies for WBAN. Figure 2: Communications Technologies and Communications Segments. projects. Proprietary RF solutions are also widely used in the BAN (seven projects, representing about 20% of the considered projects). Finally, MICS and ANT represent two communications technologies that, despite not having been so used for the time being, will play a key role in IBAN and in BAN for sport applications respectively. In the PAN/AN, wireless solutions are preferred instead of wired ones. Bluetooth is the most relevant communications technology for PAN. There are 10 projects which use Bluetooth in this segment. IEEE 802.15.4 is also widely used not only in PAN but also in AN, forming mesh networks which allow covering wide areas at low cost (there are five projects that use IEEE 802.15.4 as PAN/AN technology). Finally, Wi-Fi is the most widely deployed communications technology for AN, with seven projects using it in this segment. Regarding WAN, Figure 2 shows that cellular technologies are the most widely used technologies in this segment. There are 13 projects that deploy such technologies (three projects use GSM, five projects use GPRS, and five projects state using cellular technologies, including GSM, GPRS and UMTS); whereas only five projects use regular Internet connections (e.g., ADSL, cable). Nevertheless, this choice tightly depends on the specific requirements of the target application (e.g., mobility, pervasiveness, ubiquity). For example, in an application aiming at monitoring the health status of firefighters in the field, cellular technologies will be definitely used. However, in a telemedicine application aiming at monitoring health status of patients while they are at home, regular Internet communications technologies may be the best option. Next, the most relevant projects in this area that have paid special attention to the communications perspective are analyzed in detail.