## 6 Concept and First System Sketch  
In this section, we present a first system concept based on our previous experience and early outputs from firefighters in a new research effort. Figure 3 shows a sketch of this early system concept. During the course of this paper, it was clearly stated that infrastructure cannot be relied upon in firefighting mission. Thus, we re-use the Landmarke self-deployed ad-hoc infrastructure, which integrates well into firefighting practices [7] to become the reliable basis for novel services that can circumvent the communication problems previously described.  
Due to the multi-hop nature of the system, the throughput is limited. In Landmarke trials, hop depths of up to ten were encountered. Thus speech or video will hardly be transferred. Hence, the system is designed as a complementary communication channel that may be used in the case of breakdowns or uncertainties. While the previously developed and investigated system [7] featured a device using which the firefighters could interact with the nodes and other firefighters, the IC was not in the focus of the work. However, in firefighter frontline communication, firemen and the IC are equally important. Our system concept is based on three types of devices: the IC device, the firefighter device and the communication nodes. Using this system, three basic services shall be realized:  
**Basic telemetry:** Using this service, the IC receives continuous information from the deployed nodes (e.g., deployment event, temperature, status) and firefighters (temperature, air pressure), giving him an overview of the team's progress (nodes deployed) and the state of the scene.  
**Bi-directional text communication:** an on-site radio messaging system. Firefighters can answer and request to IC predefined text messages. This gives the ability to communicate without the trunked radio overhead, a more robust communication link and predefined messages that leave no space for ambiguities.  
**Implicit interaction:** Aimed to address the problem of uncertainties and radio-induced distraction by exploring implicit interaction methods for firefighters. Especially tactical relevant firefighter activities and anomalies should be recognized to inform the IC continuously of the mission progress and the state of his teams.  
In order to spawn a discussion with the experts, especially for the activity recognition, we introduced the concept of implicit activity monitoring/recognition using [26] and described the limits of the system. Firefighters showed a strong interest in the technologies and emphasized that the possibility to continuously monitor the attacking teams' activities would be extremely advantageous. Further interviews based on a thorough mission activity analyses showed that already a relatively restricted set of activities and the detection of accidents could help ICs monitor their teams' status without radio communication.  
Based on the nature of services, the device requirements become clear: team members need a system that holds the network nodes to be deployed, provides a UI to use the text communication and runs the sampling and recognition algorithms; ICs will need a device that can query the firemen using simple text messages and visualize the incoming data, possibly with their recognition accuracy in case of the activity information.  
Figure 3: _Right_: Firefighters with a water hose (gray) deploy WSN nodes (large boxes) during reconnaissance. Sensor units (small boxes) are attached to the SCBAs to recognize their activities and provide a simple message interface. _Left_: Activities, probability values, node and firefighter sensor information and messages are relayed to the IC tablet using the ad-hoc network.