# A Survey on Mobility Support in Wireless Body Area Networks
## 3 Mobility Model and Communication Protocol
### Individual Mobility
#### 3.1.2 Protocols for General Mobility
While LLF in PRPLC represents a node's meeting probability to sink node, LCF totals all of the nodes' LLF along the path from source to sink node. Based on LCF value, a similar forwarding policy to PRPLC is applied. If a node is within the sink node coverage, a packet is delivered directly. If not, a node \(i\) selects \(k\) with the least LCF value among the neighboring nodes and then forwards packet to \(k\). When forwarding procedure is done, LCF value between \(i\) and sink is updated by adding two LCF values, that is, LCF between \(i\) and \(k\) and \(k\) and sink node. However, if there is no available node tosatisfy the two conditions above, the packet is kept in the buffer until encountering a node satisfying the forwarding policy. Opportunity Routing [20] was proposed to introduce relay nodes that are intended to overcome Line of Sight (LOS) limit in WBANs. They assume that relay function is embedded into all sensor nodes while the sink node is on the wrist. A sink node is not within LOS transmission path when a man takes his arms back. In this situation, a data packet is sent to relay node and then transmitted to sink node consequently. Detailed operating procedures for Opportunity Routing are as follows. As the first step, each node sends a Request to Send (RTS) message to the sink node. If a sink node is located in LOS, it sends an ACKnowledgement(ACK) message. Upon receiving an ACK message, a node sets up direct communication. However, if a node cannot receive an ACK message within the predetermined period, it becomes aware of the nonexistence of the node in LOS. In this case, a node sends a WAKE UP message to the relay node to turn its status to Receive Ready. Followed by the above procedures, a connection between a node and sink node via relay node is established. At the next step, a sink node sends a Receive ACK (RACK) message to the source node via a relay node. This procedure is repeated iteratively until a sink node does not get RACK message. Another approach to deploy a relay node is Relay based Thermal aware and Mobile Routing Protocol (RTM-RP) [21]. In this work, two types of mobility models are concerned: static and mobile set. The former refers to slow movement such as sitting, laying, and standing, whereas the latter includes fast movement such as walking and running. There are three time slots: Random Access Period (RAP) slotted Carrier-Sense Multiple Access (CSMA), Relay Buffer TDMA and Relay DATA TDMA. In RAP Slotted CSMA, each node tries to occupy the same channel as CSMA. A relay node exchanges buffered information with relay nodes in Relay Buffer TDMA. Based on obtained information during the Relay Buffer TDMA time slot, each relay node can predict the starting time and required number of slots. At last, a relay node transmits the data in buffer in the Relay DATA TDMA period. In addition to posture modeling, [PERSON] et al. [14] studied a relay node based scheme which consists of initialization, forwarder selection, scheduling, and data transmission phase. At the initialization phase, a sink node broadcasts the HELLO message carrying the location of sink, location of neighbors, and all possible route information to the sink. After each node gets this HELLO message, the routing table is updated with the obtained information. Furthermore, each sensor involved in one of the two groups, \(A\) and \(B\), according to distance to the sink node, selects a forwarder in the next phase. The forwarder decides the time slot for the child node in the TDMA scheme, which contributes to reducing energy consumption and collision. Finally, at the data transmission phase, each node transmits data to the forwarder during the allocated time slot. The forwarder aggregates the received data from many child nodes and forwards them to the sink node. Another approach to introducing a link quality matrix was proposed in Prediction to enable Secure and Reliable routing (PSR) [22]. PSR is prediction based routing protocol to prevent data injection attack.