# An Energy-Efficient Routing Protocol for Reliable Data Transmission in Wireless Body Area Networks
## 1 Introduction  
The wireless body area network (WBAN) is a special branch of the wireless sensor network (WSN), and has great potential in the field of medical and health. WBAN can be used for clinical medical monitoring, chronic disease monitoring, and daily monitoring of elderly or special groups, which can rid patients of the shackles of wired monitoring and allow them to benefit from ubiquitous medical services at anytime and anywhere [1, 2]. Therefore, the development of WBAN is attracting more and more attention, becoming one of the hot spots of current and future research [3]. WBAN is a body-wide network whose basic architecture can be divided into three layers [4], as shown in Figure 1. Tier-1 is composed of sensors attached to the body surface or implanted into the body. Its function is to collect and transmit various physiological information about the human body. Tier-2 is composed of smart phones, personal computers, or other intelligent electronic devices. The information sent by sensors is forwarded to the terminal data center by a wireless mode. In tier-3 of WBAN, the terminal data center is mainly composed of remote servers providing various applications. Its function is to collate and analyze the received data, and thereby provide a dynamic response. Emergency transmissions and alarms are performed when sensor nodes collect abnormal data, which speeds up emergency handling and rescue. One of the difficulties in the design of a wireless body area network is energy limitation [5], because the nodes are powered by micro-batteries, which have limited energy and are difficult to replace. Moreover, since the body is a special transmission medium, human tissue will also absorb a part of the energy [6; 7], which is generally defined as the specific absorption rate (the electromagnetic radiation energy absorbed by human tissue per unit time). When the electromagnetic energy accumulated in the human body exceeds a certain value, it will also cause certain damage to human tissue. Therefore, the energy consumption problem this poses will be a research direction in the future. In addition, the deployment of nodes will also affect the energy consumption; frequent use of a node will cause these nodes to prematurely consume their own energy and quit the network [8]. To solve these problems, we can consider the two directions of open source and throttling. The open source method is a variety of wireless energy collection technologies [9; 10; 11], and the throttling method is a variety of energy-efficiency design. Designing the reasonable routing is one of the methods to improve energy efficiency. Routing is responsible for establishing the path in the network, the design principles of routing are stability and energy efficiency. How to improve the energy efficiency, prolong the network lifetime and avoid network splitting has become an important issue in research of routing protocols for wireless body area networks [12]. Based on the above analysis, this paper proposes an energy-efficient routing protocol for reliable data transmission in WBAN, the protocol not only ensures reliable and efficient routing transmission of data, but also balances the energy consumption of the network and prolongs the network lifetime. The specific contributions are as follows:  
1. A maximum benefit function is constructed to dynamically select the next hop node with the good state. The function takes multiple parameters into account, such as the remaining energy, transmission efficiency, available bandwidth and hops from the sink, which can achieve reliable multi-hop data transmission. 2. Based on the different priority data of WBAN, we dynamically adjust the weight of the maximum benefit function to achieve timely and reliable transmission of emergency data and also satisfy the Qos requirements of periodic data. 3. A simulation experiment platform was established to compare the proposed protocol with the PERA and NEW-ATTEMPT routing protocols.