# Biometric Authentication and Verification for Medical Cyber Physical Systems
## 2 Background of WBANs  
WBANs consist of several or more miniaturized low-power devices connected wirelessly in or near a human body. An example WBAN network is depicted in Figure 1. The patient has several sensors and actuators that record data, which is transmitted to the central unit. This information is passed on via the Internet to a medical center. The devices often perform sensing functions in a two-hop star topology and transmit information to the central receiver. These devices are extensively used in areas including medicine, sports, gaming, entertainment, and emergency response [2]. We focus on medical applications of WBAN devices. Devices that fall under this scope include pacemakers, glucose monitors, blood pressure monitors, etc. We will discuss the foundational components of WBAN systems. WBAN networks are broadly composed of the following hardware components: Sensors, actuators, and personal devices (PD) [5; 17]. The sensor node is responsible for responding to and recording information according to a physical stimuli. Data processing may occur if necessary prior to transmission. These sensors can either be external, as in added to clothing [21] on placed directly on the body (e.g., SpO\({}_{2}\), ECG, EEG), or internal, as in injected under the skin or into the blood stream (e.g., electrical impulses to mitigate the effects of [PERSON]'s disease) [10]. An actuator responds to data  
Figure 1: An example Wireless Body Area Network (WBAN) network. received from sensors or via direct instruction from the user. These can be responsible for administering medication or controlling a person's biometrics (e.g., blood pressure, body temperature). Physically, actuators and sensors share much of the same components (a power unit, a central processor (CPU), memory, and a receiver or transmitter). The personal device collects and processes all information from the sensors and actuators. Nowadays, these devices are typically smartphones, Personal Digital Assistants (PDAs), or dedicated unit. In some cases, the personal device can function as an actuator. The fundamental limitations of WBAN devices is caused by their inherently small form factor. This directly affects power consumption, efficiency, and long-term reliability. Since these devices are typically battery powered, the sensors must be capable of continuous operation for several years (e.g., pacemakers are required to operate for a minimum of five years [11]). During their service, the devices must perform their functions reliably and consistently. The Quality of Service (QoS) must be guaranteed by the wireless protocols WBAN devices adhere to. Furthermore, the various available WBAN applications demand a wide range of data transmission rates. The amount of data transmitted by the devices also depends on if the data is processed locally and only recorded parameters are transmitted [9]. Table 1 shows the data rate, bandwidth, and accuracy for several medical applications. Further research is necessary to improve cost, size, and lifespan of WBAN devices. WBANs are typically designed to operate in a star topology, where all sensors are associated with a master node [6]. In some scenarios where devices are internally mounted, the human body can become and obstacle for radio transmission. A more optimal topology for this situation would be a multi-hop network, where sensors communicate to neighboring nodes to exfiltrate data. Relay-based protocols can also alleviate this issue by implementing a mixed integer linear programming formulation of the topology problem, which minimizes the network usage while accounting for energy considerations [22]. Several protocols are available for wireless transmission in WBANs, as specified by IEEE 802.15.6, including Bluetooth, Bluetooth Low Energy (BLE), Zigbee, Thread, and 6 LoWPAN. Another requirement for WBAN devices is true coexistence. Most devices communicate at the 2.45 Ghz ISM band, which is shared with WiFi, Bluetooth, Zigbee, and other IEEE standards.