# Temperature State Awareness-Based Energy-Saving Routing Protocol for Wireless Body Area Network
## 1 Introduction  
The Wireless Body Area Network (WBAN) is an important branch of Wireless Sensor Networks (WSNs). The WBAN is mainly used in the medical and health field. It can realize early identification and prevent patients' potential diseases through remote medical monitoring [1]. A WBAN is composed of miniature sensor nodes implanted in the human body or worn on the surface of the human body through an ad hoc network. These sensor nodes sense various physiological data of the human body and forward the sensed data to a sink. The sink further sends the data to a medical service terminal wirelessly for corresponding processing. Figure 1 presents the communication structure of a WBAN. The WBAN can realize the long-term and real-time monitoring of patients' vital signs by medical terminals, and patients can grasp their health status more intuitively and obtain the emergency response capability for emergencies [2, 3, 4, 5, 6]. Although WBAN belongs to an important branch of WSN, WBAN has its unique network characteristics, which makes it difficult to establish communication paths between sensor nodes [7; 8; 9], such as human mobility and frequent data transmission between sensor nodes. The node temperature rises and the dead node caused by continuous energy consumption. Therefore, the routing protocol proposed for WSN is not suitable for WBAN [7]. Taking into account the small size of the sensor node in a WBAN, low battery capacity, and the difficulty of replacing the battery for implanted sensors, the power consumption of WBANs needs to be limited [10]. In order to ensure that WBANs can effectively transmit data under limited energy conditions, in addition to the circuit design of wireless sensor nodes to save energy, efficient energy-saving routing plays a vital role in reducing network energy consumption. The energy-saving routing of a WBAN often introduces the concept of multi-hop transmission into it [11; 12], using forwarding nodes to forward data between the source node and the target node to reduce the energy consumption of long-distance transmission between the source node and the target node. Furthermore, data transmission between sensor nodes not only consumes the energy of the node but also causes the temperature of the node to rise. The heat dissipation of nodes is another important challenge faced by the WBAN routing protocol. In WBANs, the reason for the increase in node temperature is that, on the one hand, the sensor nodes use radio frequency (RF) signal communication, and the radio frequency transmits the heat dissipated; on the other hand, it is the heat generated by the internal circuit of the sensor when processing the collected data [8]. When the temperature of a node increases to destroy human tissues or organs, it is called a hot node. The generation of hot nodes makes WBANs a security risk, and it is also not conducive to the normal transmission of data, which may cause data loss or delay. Therefore, the heat generated by sensor nodes is controlled to effectively transmit the data of WBANs in the routing process. This paper proposes a temperature state awareness-based energy-saving routing protocol to solve the problem of energy consumption and hot nodes in WBANs. The main contributions are as follows:  
1. Two thresholds are set for the temperature state of the node, namely a high-temperature threshold and heating threshold. The heating threshold is set before the node reaches the high-temperature threshold. Use these two thresholds to divide the node temperature state into a normal interval, a heating interval, and a high-temperature interval, calculate the data reception probability of the node in the three  
Figure 1: Communication structure of WBAN. temperature intervals, respectively, and delay the node temperature from reaching the high-temperature state. 2.