## 2 Related Researches
### Body Sensor Network
This network connection system greatly reduces the possibility of collisions and idle listening, and can save significant amounts of power. In addition, time-slot allocation is dynamically controlled by the master, so a slave time slot could be changed every time by communicating with the master. This enables the system to better cope with fluctuating traffic [11]. An H-MAC protocol uses rhythm information of the heartbeat of a human being to perform time synchronization of a TDMA. Accordingly, the biosensor can achieve time synchronization without turning on the radio. The algorithm is verified with actual data but assumes a specific buffer. The simulation does not show any energy gain, and the protocol is designed only for the star-topology WBAN. When considering wireless transmission around and on the body, important issues are radiation absorption and heating effects on the human body. To reduce tissue heating, the radio's transmission power can be limited, or traffic control algorithms can be used [12]. Figure 1: Framework for healthcare for the elderly using wireless body area networks (WBANs). Rate control is used to reduce bioeffect in a single hop network. Another possibility is a protocol for balancing the communication of the sensor node. The bioeffects model is both near-field and far-field, in relation to specific absorption rate (SAR). A normalized bioeffect metric, equivalent coefficient of absorption and bioeffects (CAB), was derived to evaluate and design the communication protocols for wireless biosensor networks. This shows that the bioeffects can be reduced via power scheduling and traffic control algorithms [13]. The thermal aware routing algorithm (TARA) model routes data away from high temperature areas (hot spots). Some factors lead to temperature increase, and the process for calculating SAR and the temperature increases of implanted biosensors uses the finite-difference time-domain (FDTD) method. The CH is switched based on the leadership history and the sensor locations. Packets are withdrawn from heated zones and rerouted through alternate paths. TARA suffers from low network lifetime and a high ratio of dropped packets, and does not take reliability into account [14]. The improvements to TARA are LTR (lowest routing) and ALTR (adaptive least temperature routing), which reduce unnecessary hop loops by maintaining a list of packets on the node most recently accessed. An ALTR converts to shortest hop routing when it reaches a predetermined number of hops to reduce energy consumption and heat generation on a network. This algorithm routes the packet to the coolest adjacent node without inducing a routing loop. In comparison with the shortest hop routing algorithm, this algorithm is much better executed in terms of reducing heat, delay, and power consumption generated [15; 16]. \"AnyBody\" is a data gathering protocol that uses clustering to reduce the number of direct transmissions to the BS. Each node sends out a hello message in which it puts its unique identifier. No message is sent if the node has a higher density than all its neighbours. The join messages are relayed by the receiving nodes until it reaches a node with highest local density. Through this messaging process, the CH is elected to be the node with the highest density and nodes are grouped into clusters. After clustering, nodes need to be interconnected. All these connections beteen CHs will form a virtual backbone network. Finally, the routing paths are set up. A network in this protocol has a constant number of clusters, even though the number of sensor nodes is increased [17]. Another improvement of LEACH is hybrid indirect transmissions (HIT) which uses clustering to reduce the number of direct transmissions to the BS and allows parallel and multi-hop indirect transmissions, even in the case of multiple and adjacent clusters. The energy efficiency is improved but data reliability is not considered [18].