# An Energy-Efficient Routing Protocol for Reliable Data Transmission in Wireless Body Area Networks
## 2 Related Works  
More and more studies have proved that the two-hop or multi-hop method is more suitable for WBAN. It can balance network energy consumption and improve energy efficiency. Therefore, the selection of next-hop node is the hotspot of current research in multi-hop routing [13]. [PERSON] et al. [14] proposed a routing protocol, which considers the residual energy of the nodes for the selection of next-hop nodes, and selects the node with the largest residual energy as the best next hop. This method can balance the energy consumption of the network, but it will cause a large delay or packet loss rate. [PERSON] et al. [15] proposed a minimum hop routing protocol to select the best next hop node by the lowest hops from the sink. Although this method can satisfy the Qos demand of low delay, it is easy to cause some fixed nodes to quit the network due to frequent participation in data transmission and excessive energy consumption, thereby affecting the connectivity of the network. The adaptive thermal-aware routing protocol (ATAR) proposed by [PERSON] et al. [16] is a temperature-based routing protocol, which is designed to overcome the temperature rise issue of implanted bio-medical sensors nodes. This protocol is based on Multi-Ring routing approach to find an alternative route in the case of increasing temperature. Using the retreat strategy to avoid the node with high temperature will cause a large delay. Maintaining ring information, temperature and hops in the network also leads to increased overhead, which is not a good choice for a volume network with limited resources. A trust and thermal aware routing protocol ( TTRP) was proposed by [PERSON] et al. [17]. This protocol considers both the temperature and trust parameters of the node when selecting the best next hop to ensure the reliability communication between nodes and the safety of human body, but the energy consumption of nodes is not considered. [PERSON] et al. [18] designed a multi-hop routing protocol, the best next hop node selected has the characteristics of more residual energy and closer to the sink. This method considers the residual energy of the node, but fails to achieve the goal of energy efficiency. Its disadvantage is to accelerate the energy consumption of the node in the network center, which leads to the early death of the node and affects the connectivity of the network. [PERSON] et al. [19] proposed a modified new-attempt routing protocol, which constructs a cost function to select the next hop node. The cost function is calculated using the distance among the nodes, residual energy and the rate of the sending data. Therefore, this method meets the Qos of energy efficiency and low delay. [PERSON] et al. [20] proposed an enhanced mobility and temperature-aware routing protocol, and this protocol takes three routing metrics: hop count, temperature and link quality to select the best next hop. The disadvantage is that the energy consumption of nodes is not considered. [PERSON] et al. [21] proposed a thermal and energy-aware routing protocol, and consider the weighted average of three costs while selecting the routing path: energy consumption, heat dissipation, and link quality. The best next hop node has the characteristics of more residual energy, lower temperature and higher link quality, which can meet several Qos requirements. An energy-aware link-efficient routing protocol was proposed by [PERSON] et al. [22], and a multi-parameter cost function is constructed when selecting the best next hop node. The residual energy, link quality, hops and distance to the sink are considered comprehensively, and the weight factors of each parameter are set artificially. Although the protocol meets multiple Qos requirements, it does not consider the priority of data classification and transmission, so it cannot guarantee the timely and reliable transmission of emergency data. Similarly, [PERSON] et al.