# 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
Another consideration for WBAN is to optimize the data rate to reduce resource consumption. This problem was addressed by polling based MAC protocol in [29]. [PERSON] et al. pointed out that temporal disconnection caused by mobility makes link quality worse and leads to changing optimal bit rate frequently. To implement this protocol, seven types of messages and special nodes called hubs need to be defined. Polling is determined by both transmission duration and optimal bit rate after measuring the channel quality. Finally, unbalanced energy consumption issues caused by mobility were addressed in a way of enhancing the On Increasing Network Lifetime (OINL) routing algorithm. Since original OINL tends to include a large number of intermediate nodes on the path, it suffers from huge energy consumption for data reception as well as aggregation. Thus, [PERSON] et al. proposed Balanced Energy Consumption (BEC) [30] to select proper relay nodes with remaining energy. To increase a network lifetime, reactive routing becomes active to transmit critical data when a node's energy level is below the threshold. In addition, [PERSON] et al. addressed the same issue and presented a new routing protocol in [31]. In the proposed scheme, a sink node selects a new forwarder with remaining energy in every round. After a sink node designates forwarder nodes, all sensor nodes transmit data packets to these forwarders, which perform aggregation. Aggregated data is transmitted to the sink node or the next forwarder node. Since a forwarder node is selected in every round according to current energy level, balanced energy consumption is naturally achieved. The proposed scheme operates in a similar way as SIMPLE protocol. Other energy aware protocols, Link-Aware and Energy Efficient protocol for wireless Body Area networks (LAEEBA) and COoperative (CO)-LAEEBA, were introduced in [32]. In LAEEBA, a sensor node broadcasts the packet containing locations of sink nodes, all paths to sink node, own ID, own location, and remaining energy. Upon receiving this packet, a neighboring node updates its routing table accordingly. Like SIMPLE, energy consumption is balanced by rotating forwarder nodes in specific time intervals. The selection of forwarder node is dependent on Cost Function (CF) that is computed by node's ID, distance, and remaining energy. Based on distributed CF value, each sensor node designates its forwarder as one having the minimum CF value. Fundamentally, CO-LAEEBA operates in the same way as LAEEBA, but a new cooperative node was newly introduced. CO-LAEEBA assumes heterogeneous architecture; therefore, cooperative and sink nodes have higher capacity of data transmission and computing power than normal nodes. While a forwarder is iteratively selected in predetermined intervals for balanced energy consumption in LAEEBA, a cooperative node is continuously updated in CO-LAEEBA. As a person moves, each sensor node on the body has a tendency to have multiple paths to sink nodes as compared to single paths in static situations. In order to utilize multiple paths in an efficient way, normal data is forwarded to a cooperative node, but emergent data is directly passed to the destination node. However, if the energy level of a cooperative node is lower than the threshold, normal data is transmitted to the destination node directly without relaying. The last approach to reducing energy consumption through the relay node was presented in [33]. In this study, direct communication was performed whenever the coordinator moved to the coverage area of the sensor or relay node due. Otherwise, a sensor node needs the help of sensor nodes or relay nodes to transmit data packets to the coordinator. Under this basic principle, there are three cases for the next hop selection. At first, the neighboring node having the shortest distance to the coordinate node is chosen primarily. The next considerable factor is relative velocity. That is, a node having the similar moving velocity to the coordinator is the next candidate.