# Adaptive Thermal-Aware Routing Protocol for Wireless Body Area Network
## 2 Related Work
#### Taxonomy of Routing Protocols in WBAN
Previously visited lowest temperature node is saved in the list to avoid loop in the network. Loops are avoided by maintaining a list in the packet with the recently visited nodes. Adaptive Least Temperature Routing (ALTR) protocol [26] overcomes the problem faced in LTR. The approach of ALTR is similar to LTR with the variation changing _MAX_HOP_ by _MAX_HOP_ADAPTIVE_. In ALTR, instead of discarding the packet after it exceeds the threshold value of _MAX_HOP_ADAPTIVE_, it works as Shortest Hop Algorithm (SHA) to transfer the packet to the destination. Least Total Route Temperature (LTRT) [27] is the combination of LTR and shortest path routing [40]. In LTRT, the total route is selected from source to destination on the basis of temperature. LTRT selects a least temperature route to forward data instead of only considering the next hop. The temperature of sensors is transformed into graph weights and minimum temperature routes are obtained using [PERSON]'s algorithm. During the data transmission, the temperature of a sensor node rises by one unit upon receiving or transmitting data and decreases by one unit when it is inactive in transmission (defined time interval). In LTRT, hop count per packet and packet drop is decreased. It also aids in reducing overheating of sensors but the shortcoming in LTRT is that it requires to know the temperature of all sensors in the network. Moreover, energy consumption and overhead of acquiring the record of all temperatures is not measured. Hotspot Preventing Routing (HPR) [28] is another thermal-aware routing protocol that addresses delay during data transmission. It includes two phases i.e., setup phase and routing phase to avoid the delay and forming of hotspots in the network. In the first phase, all the sensor nodes exchange information about the shortest route and temperature of the nodes to build their routing tables. In routing phase, each node transfers data using the shortest available route in the routing table and maintains a hop-count. If the value exceeded than the threshold value of hop-count, the packet is discarded. If neighboring node is the destination node then the packet would be directly sent to it; otherwise, it chooses next hop from the shortest path based on temperature (equal or less than the threshold value). The threshold temperature of a sensor node is obtained by taking the average temperature of the neighboring nodes (including the temperature of sending node itself). In this approach, all nodes compute the threshold value of temperature on the basis of the temperature of its neighboring nodes and the temperature of the node itself, however, in other algorithms this value is predefined. [PERSON] et al. in [29] presented the goal of Routing Algorithm for Network of Homogeneous and ID-Less Bio-Medical Sensor Nodes (RAIN) is to decrease the average temperature rise and average power consumption of sensor nodes. It constitutes three phases i.e., setup phase, routing phase and status update phase. In the setup phase, temporary IDs are random, usable for its operational life and ID 'zero' is kept for the sink node. All nodes broadcast their IDs using hello packet. In the routing phase, a packet ID [\(N\), \(T\) and \(R\)] is forwarded towards the destination, where \(N\) is the ID of the sensor node, \(T\) indicates the time at which the data packet is generated at the sending node and \(R\) is any random number. Loops are avoided by maintaining a hop-count with every packet and if the hop-count of the packet exceeds the threshold value of \(HOP\_THRESH\), then it is discarded. The nodes also avoid retransmission by maintaining the list of the packets IDs and a data packet is dropped if its ID is previously resides in that list. Every node knows the temperature of neighboring nodes by observing their communication actions. The packet is forwarded directly if the destination is one of the neighboring nodes otherwise it is forwarded to the neighbor node using probability which is inversely proportional to its temperature.