# Adaptive Thermal-Aware Routing Protocol for Wireless Body Area Network
## 2 Related Work
#### Taxonomy of Routing Protocols in WBAN  
Over the years, a lot of WBAN routing protocols has been proposed in the literature. These protocols could be segregated into five categories, i.e., Thermal-aware routing protocols, Energy-Aware based routing protocols, QoS-aware based routing protocols, Postural-movement-based routing protocols, Cluster-based routing protocols and Cross-layered routing protocols [46]. The overview of all these protocols is presented in Figure 1.  
The sensor nodes of WBAN are embedded and both produce electrical and magnetic fields during the transmission [25]. This issue can result in absorption of radiation and increased heat in the human body that leads to harm of sensitive organs by the minute temperature rise. For instance, lens contraction gets effected due to lack of blood flow occurred because of temperature rise of a node [16]. In [45] a Specific Absorption Rate (SAR) is introduced as an indicator at which the energy is immersed from the body of human when it gets revealed to a radio frequency (RF) electromagnetic field. The formula to calculate SAR is presented in Equation (1). \[SAR=\sigma|E|2/\rho(W/Kg) \tag{1}\]  
where \(\sigma\) is electrical conductivity of body tissue, \(E\) is induced electric field by radiation, \(\rho\) is density of body tissues, \(W\) and \(Kg\) represent the units of watts per kilogram. Primarily, \(SAR\) defines the upper limit of the transmitting power. Therefore, WBAN routing protocols should be designed to reduce the radiation emission to transmit data. Considering safety, radiation absorption is required to be reduced either by controlling \(SAR\) or using an appropriate routing protocol. [PERSON] et al. in [27], a model is proposed to handle the upshot occurred during the communication by the bio-medical sensors on human body. In this study, a rate controlled recommendation model for WBAN transformation is presented based on the observation. Thermal-aware routing techniques are significant to discuss while designing the Intra-WBAN. To evade the temperature rise and radiation that cause harm to the human body, diversified routing protocols related to thermal-aware have been introduced in the literature. The contemporary thermal-aware routing protocols discussed in the literature include, TARA [25], LTR [26], ALTR [26], LTRT [27], HPR [28], RAIN [29], TSHR [30], M-ATTEMPT [31], TMQoS [32], RE-Attempt [33], \(M_{2}E_{2}\)[34], TLQoS [35], DRC [36], TTRP [37], TRPL [38]. Figure 1: Taxonomy of WBAN routing protocol. The first temperature sensitive routing algorithm i.e., Thermal-Aware Routing Algorithm (TARA) is presented in [25], [PERSON] et al. The proposed algorithm aims to reduce the possibility of temperature rise of the implanted bio-medical sensor in the human body. TARA defined the overheated nodes as hotspots and routes away the data from these nodes during communication. The author defined the Temperature Increase Potential (TIP) to calculate the temperature rise of a node on the basis of SAR. During data transmission, each node observes the communication of neighboring nodes by counting the packets, calculating communication radiation and power consumption to evaluate the present temperature of nodes. This algorithm does not involve a node in data transmission when its temperature rises above the defined threshold value. TARA enforces the equal temperature dissemination among all the nodes within the network by considering temperature as a metric. As the temperature is the only metric, TARA has to face the issues such as network lifetime, packet drop and reliable transmission. Least Temperature Rise (LTR) is an enhanced version of TARA to address the overheating of implanted sensors and delay. In LTR is proposed in [26], the selection of the next hop is based on the temperature of neighboring nodes and the node with least temperature is selected as a next hop. To avoid the bandwidth consumption, predefined _MAX_HOP_ limit is defined in algorithm and when a packet exceeds that limit it is discarded.