## 5 Open Research Issues, Challenges and Opportunities
### WBAN Design Challenges for Life and Safety Critical Applications  
The specific context of life and safety critical applications introduce several new design constraints and research challenges in comparison to general-purpose or medical WBAN solutions, as shown in Table 14. Indeed, classical WBAN solutions are essentially designed as closed systems, which are eventually open to the outside world via pre-existing network infrastructures. More specifically, life and safety critical related application scenarios are characterized by the following main differences in comparison to general-purpose or medical WBAN solutions. First, mobile workforces (e.g., rescue teams, workers, _etc._) are generally _deployed in harsh or disaster environments_ and require effective communication, coordination and monitoring capabilities: (i) to ensure their safety in presence of unhealthy environments or hazards ; (ii) to optimize their tasks on operational theaters; and (iii) to effectively communicate and transmit real-time information to their command center for proper decisions making and workforces management. Second, during practical cases of deployment in harsh or disaster environments: (i) _broadband or local network infrastructures_ (e.g., 4G, 3G, LTE, WiFi, _etc._) _might be absent_ (e.g., desert, offshore oil and gas fields), _damaged_ (e.g., in case of major fire) _or overloaded_ (e.g., in high density area such as stadiums or shopping malls); (ii) mobile workforces might face various _uncertainties and hazards_ (e.g., low visibility, high temperature, emanation of toxic gases, major fire, no a-priori knowledge of the building indoor layout, _etc._); and (iii) Sensitive and/or real-time information should still be transmitted from the deployed mobile workforces teams to external command centers to ensure timely and effective decisions making. To that end, each team's member will be fitted with a set of--physiological, environmental, communication and kinematics--Wearable Wireless Sensor Devices. On the first hand, short-range and multi-hop _on-body communications_ will be required to effectively collect and transmit all collected sensors readings at the WBANs coordinator (e.g., PDA). On the other hand, medium-range, cooperative and multi-hop _body-to-body communications_ will be required to: (i) ensure the end-to-end network connectivity with external command centers; (ii) route sensitive and real-time information to these centers; and (iii) improve the communication reliability in case of harsh propagation conditions and severe links obstructions. In this context, the resulting Wearable WBAN systems for safety and life critical applications should be autonomous, self-organizing, large scale, robust to external interferences, energy efficient, secure, support various data types and rates (e.g., voice, data, real-time traffic, periodic traffic, urgent alarms and events, _etc._). Moreover, they should enable cooperative (or collaborative), reliable and real-time communications while providing various quality of services (QoS) and security levels. In order to better understand the requirements of life and safety critical applications, a specific use case related to worker safety in a harsh environment is considered. Specific details about workers safety in a harsh environment as an application scenario is already provided in Section 2.2.2. In such an application context, WBAN systems should support various monitored data types and sensors. As shown in Table 15, the monitoring requirements for the workers safety scenario can be classified into three main categories. The first category deals with normal and daily worker health monitoring and protection in oil and gas fields and refineries, petrochemical and mining industries as well as roadside and building workers. The second category adds specific requirements concerning movement and activity monitoring, whereas the third category is about protection and safety from hazards and poison gasses, fall detection as well as detection of necessary safety equipment.