## 1 Introduction  
With the development of industry, the aging of mankind, and increasing medical costs, research on the new healthcare system has expanded. As semiconductor manufacturing technology advances, tiny implanted (Bio) sensors are used to measure the biometric signs. These sensors can analyze and store measured data, which can also be transmitted to an external device such as a medical server to diagnose the patient's or the elderly's status. For that purpose, hardwired connections are difficult for patients to wear, and expensive for deployment and maintenance. This makes it easier and cheaper to apply sensors to patients using a wireless interface [1,2]. The increasing usage of wireless network and the miniaturization of sensors have bolstered the development of wireless body area networks (WBAN). In these networks, various sensors are attached to clothes or bodies or implanted under the skin. The wireless characteristics of the network and various sensors provide numerous new, practical, and innovative applications to improve healthcare and the quality of life. Body sensor networks can help people live comfortably by providing users with various activities and behavioral monitoring servicers through applications in healthcare, emergency treatment, fitness, etc. [3]. Users can screen their health status through various sensors in real time with personal desktops and smartphones. Medical institutions can obtain their sensor information and analyze it remotely or offline. By collecting and analyzing users' biometric information from sensors, body sensor-based medical services can provide users with accurate medical services. Due to the convenience of mobile devices such as smartphones and the development of WBAN, research on mobile healthcare is actively carrying on [4]. Mobile healthcare is expected to facilitate the prevention and management of diseases, since the sensor information can be obtained through mobile devices and the medical service area can be expanded to the observer rather than the medical institution center. Therefore, mobile healthcare systems can provide the users with ease of use, reduced risk of infection, reduced risk of failure, reduced user discomfort, and lower cost of care delivery [5,6]. The functionalities of a mobile healthcare system are:  
1. To alert its user of the approach or development of a potential medical emergency, so that precautionary action can be taken. 2. To alert the medical emergency system if vital signs drop below a certain threshold. 3. To measure a real-time bio-signal for local processing. WBANs imply a ubiquitous environment in which sensor devices have formed a network near the human body. Unlike sensor networks, sensor devices deployed in WBANs are very small in size, and there is another limitation that requires a long operational lifetime of the sensors: it is difficult to replace or recharge batteries in cases in which sensors are placed in a person's body or clothing. Therefore, a sensor device's energy technology is a very important in WBAN. One of innovations used in WBAN to extend the lifetimes of sensors is to use transmission power control algorithms. The transmission power control algorithm regulates the transmission power of a transmitter to reduce energy consumption for every transmitting channel [7]. Existing transmission power control algorithms perform transmission power regulation based on the closed-loop mechanism. A closed-loop-based algorithm means a method in which a node sensor, usually called cluster head or sink, informs other sensors of transmission power level through a control message channel when conducting communication between a sensor and a cluster head (CH). A sensor can transmit the collected data with the transmission power received from CH. This closed loop mechanism, however, has the disadvantage of high energy consumption due to excessive control messages [8]. Another innovation used in WBAN to extend the lifetimes of sensors is a cluster-based routing protocol.