## 3 Physiological Signal Monitoring and WBSNs Overall System
### Wbsn System Architecture  
Figure 3 illustrates a WBSN architecture for a health monitoring system, the emergency area can be divided into different disaster sites depending on the number of injured persons. Devices (e.g., PDAs, GPS, smartphones with video cameras, and vital sign sensors) could be managed by a local server. a) Sensors send data to smartphones by Bluetooth (BT), or b) ZigBee (ZB) technologies. Video and vital signs of patients are sent to a Relay Point (RP), which could be located in the emergency site or in the hospital. c) RP encodes and compresses the signals from each vital sign and sends them wirelessly (Wi-Fi or 4G) to a database server for record keeping and real time medical attention. Once data reaches the server, qualified staff will be able to manage the situation. For the emergency scenario, we integrate the WBSN communications architecture in three layers: Intra-WBSN communication, and Inter-WBSN communication, and Beyond WBSN communications [11].  
* _Intra-WBSN Communication_: This layer considers communication between sensors and personal servers (usually less than 10 m away). Sensors have a direct wireless communication with PS through ZB or BT (star topology). The PS has capacity to take video of the patient's condition, and collect and/or compress the physiological signals. The PS can directly transmit the video and physiological data, e.g., via 4G LTE to the second layer, but if the PS do not have this technology, the PS transmits the information to an ambulance via Wi-Fi or BT, and later the ambulance rebroadcasts the information via 4G LTE or Wi-Fi (modem enabled). According to [32], this tier should fulfill some hardware and software requirements. In terms of hardware, sensors must be lightweight, easy to use and comfortable for the patient, with high degree of accuracy. For the software, proper communication protocols, energy efficiency and handling of collected data are important considerations to make. Among these requirements, there are quality standards that must be implemented in the development of the system like: availability of data; usability (wearable or implantable); security/privacy, according to HIPPA; and QoS, for service guarantee.
* _Inter-WBSN Communication_: This tier corresponds to the communication between the PS to the internet or between PS and one or more RPs and then to the internet. If the signal drops, data could be sent to an RP/PC server (inside the ambulance) and afterwards, the information will be sent wirelessly (Wi-Fi) to the data base server. At this level, a gateway, PDA, PC, or 4G antennas are the link between de Intra-BAN and Beyond-WBSN layers. This tier needs some hardware and software requirements due to the specifications of the device, in terms of developing friendly user interfaces, and collecting and processing efficiently the sensors' data in real-time [32].
* _Beyond-WBSN Communication_: This is the final layer which facilitates the real time medical attention. Medical staff could handle through internet video conference or mobile calls an emergency situation of an accident. With the help of a database server, all patient data collected will be stored to create the patient health profile, which could be consulted at any time needed. The inclusion of this tier depends on the application of the platform for a specific situation [32]. Some specifications are needed to implement the data server with respect to high capacity and processing, and should be located in the medical institution.  
Figure 3: Wireless Monitoring Platform for Emergency Situations. (**A**) Intra-WBSN communication; (**B**) Inter-WBSN communication; (**C**) Beyond-WBSN communication.