## 5 Open Research Issues, Challenges and Opportunities  
Research on Wearable WBAN systems started significantly, worldwide, a decade ago, and encompasses a wide range of multidisciplinary and cross-sectorial research topics, including on-body propagation and antennas, medium access control (MAC), networking, security, and so on.  
In the past, many ambitious research projects (as shown in Table 13) have been devoted to the design of efficient WBANs solutions, such as CodeBlue [106], ASNET [107], HealthService24 [108], AID-N [109], MIMOSA [110], SMART [111], CareNet [112], WiMoCA [113], BANET [114], ProFiTex [115], and MobiHealth [116]. More recently, new research projects have started. Some notable examples are WearABAN [117], WiserBAN [118], WearIT(r)Work [119], ALARP [120] and more recently CORMORAN [121], CAALYX-MV [122], Help4 Mood [123] and suWBAN [124].  
The proposed WBAN solutions target a wide range of applications, including ambient intelligence, healthcare monitoring, disaster aid network, sport, gesture detection, _etc._ However, as shown in Table 13, most of the proposed short-term Wearable WBAN solutions are generally based on existing communications standards such as PANs (e.g., Bluetooth), WSNs (e.g., Zigbee), MANETs (e.g., WiFi, Multi-hop IEEE 802.11), cellular, _etc._, and thus, do not meet the specific requirements and constraints of WBANs as already discussed in Section 2.  
Moreover, most of these projects are targeting closed or independent WBAN systems, which can only communicate with the outside world via pre-existing cellular, WiFi or static WSN network infrastructures, and with a specific focus on medical related applications.  
There have been so far only a few research studies related to the issue of self-organizing, cooperative and multi-hop communications between multiple WBANs (_i.e._, hybrid On-Body and Body-to-Body Communications) in infrastructure-less environments. All these major research issues have yet to be resolved in order to enable the emergence of future ubiquitous communication and monitoring systems enabling life-critical and rescue operations, public safety and preparedness.  
In the following sections, the major design challenges, open research issues, and opportunities are discussed in details using a top-down approach, from applications down to the lower layers.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Projects** & **On-Body Communications** & **Body-to-Body Communications** & **Off-Body Communications** & **Target Applications** \\ \hline CodeBlue (2005)[106] & Wired & Zigbee (Mesh) & N/A & Medical Care \\ \hline ASNET (2006)[107] & Wired or WiFi & Wired or WiFi & Internet/GSM & Remote Health Monitoring \\ \hline HealthService24 (2006)[108] & Wired & UMTS/GPRS & UMTS/GPRS Internet & Mobile Healthcare \\ \hline AID-N (2007)[109] & Wired & Zigbee (Mesh) & Wifi/Cellular/ Internet & Mass Casualty Incident \\ \hline MIMOSA (2008)[110] & \begin{tabular}{l} RFID/Bluetooth/Wibree \\ \end{tabular} & UMTS/GPRS & Internet & Ambient Intelligence \\ \hline SMART (2008)[111] & Wired & WiFi & N/A & Health Monitoring in Waiting Room \\ \hline CareNet (2008)[112] & N/A & Zigbee & \begin{tabular}{l} Internet/Multihop WiFi \\ \end{tabular} & Remote Health Monitoring \\ \hline WiMoCa (2008)[113] & \begin{tabular}{l} Wireless \\ Topology \\ MAC) \\ \end{tabular} & \begin{tabular}{l} (Star \\ Bluetooth \\ \end{tabular} & WiFi/Internet/ Cellular & Sport/Gesture Detection \\ \hline BANET (2008)[114] & \
\begin{tabular}{l} Star/Mesh \\ (Bluetooth LE) \\ \end{tabular} & Coexistence only & N/A & Medical, Health and Sport \\ \hline \multirow{4}{*}{
\begin{tabular}{} \end{tabular} } & \multirow{4}{*}{Wired} & \multirow{4}{*}{N/A} & \multirow{4}{*}{Wired} & Safety and efficiency of fire \\  & & & & \multicolumn{1}{p{113.8 pt}}{} \\ \cline{1-1} \cline{3-5}  & & & & \multicolumn{1}{p{113.