## 2 Related Researches  
### Body Sensor Network  
WBAN is one of the wireless sensor network technologies introduced to monitor health conditions by attaching a tiny biosensor to the body so as not to interfere with normal human activity. A body sensor is a piece of technology that can detect body temperature, blood pressure, or one of various other external stimuli. The collected sensor information is wirelessly transmitted to the external device and messaged to the caregiver who is responsible for the patient, in real time. In the event of an emergency or hazardous situation, the system can send the collected sensor information in the form of messages and alarms to caregivers. As such, WBAN aims to improve human quality of life by providing real-time support for practical applications at low cost [9]. Figure 1 shows the basic framework of healthcare for the elderly in WBSN. The architecture consists of several sensor nodes and a coordinator node. The coordinator manages, collects, stores, and analyzes data received from the sensor nodes to connect to the WBSN for adjustment and monitoring. Wearable sensor nodes measure and process biophysical parameters, such as heart rate, body temperature, and blood pressure to send data to the fog server or base station (BS). On the sensor node side, the software architecture defines and extends a flexible modular architecture, making it important to provide common signal processing capabilities that are readily available [10]. To develop and deploy the WBSNs, below features should considered together, but it is hard to satisfy all these requirements. Therefore, a system that meets several requirements should be established depending on the specific application. 1. Data quality: The quality of data is of a high standard to ensure that the decisions made are based on the best information possible. 2. Data management: The need to manage bio-datasets is of utmost importance. 3. Sensor validation: It is of the utmost importance, especially within a healthcare domain, that all sensor readings are validated. This helps to reduce false alarm generation and to identify possible weaknesses within the hardware and software design. 4. Data consistency: Critical patient data may be fragmented across multiple networked PCs or laptops within the WBAN across multiple nodes. Security: WBAN transmissions require considerable effort to be secure and accurate. * Interoperability: WBAN systems must ensure seamless data transfer between standards such as Bluetooth and ZigBee to facilitate information exchange and plug-and-play device interaction. * System devices: The sensors used in the WBAN must be low in complexity, small in form factor, lightweight, energy efficient, user-friendly, and reconfigurable. * Energy vs. accuracy: The sensor start-up policy should be determined to optimize the trade-off between the BAN power consumption and the probability of misclassification of patient health. High power consumption often results in more accurate observations of the patient's health status and vice versa. * Privacy infringement: If WBAN technology exceeds \"security\" medical uses, people may think it is a potential threat to human freedom. Social acceptance of this technology will be the key to finding it in a wide range of applications. * Interference: The wireless link used for body sensors should reduce the interference and increase the coexistence of sensor node devices with other network devices available in the environment. Here is some related research regarding the MAC layer. One of main goals of MAC protocol is to reduce power consumption from sources such as idle times, bandwidth, overhearing, and collision. The composition of the BSN can be expressed as shown in Figure 2.  
[PERSON] et al. proposed an MAC protocol for a star-networked WBAN that supports TDMA to reduce the probability of collision and idle listening. Each slave node is assigned a slot by a central node. In any node, when an alarm is generated, additional slots for direct communication with the node can be allocated.