# A Survey on Mobility Support in Wireless Body Area Networks
## 4 Open Issues  
Even though lots of researchers addressed the importance of mobility support and proposed new networking technology for WBAN, it is still worthwhile to mention points for further study.  
1. Mobility Model for Network Simulator: most of the research works for WBAN include performance evaluation results to prove their suitability through simulation. The mobility model is very important and plays a significant role in evaluating the performance. This indicates that the mobility model should be operated with a network simulator in a cooperative way. Currently, OMNeT++ and NS-2/3 are general frameworks to conduct simulation for WBAN. Therefore, it is demanded to get a free, available WBAN mobility model as an add-on for these frameworks. To meet this requirement, mobility generating tools and analysis tools such as BonnMotion (University of Osnabruck, Osnabruck, Germany) [54] are essential for the mobility model. Furthermore, its analysis should be done to prove the accuracy of the mobility model.
2. Various Mobility Models: Generally, the mobility model is designed to explain the movement pattern of mobile nodes and how their locations change over time according to velocity and direction. Thus, it is desirable for mobility models to emulate the movement pattern of targeted real-life applications in a feasible way. Even though a few applications are now available and deployable nowadays, current mobility models are not enough to describe movement of nodes accurately. Therefore, further research for human behavior is required to enhance mobility models. In addition, current mobility models do not take external environments, such as roads in the city for walking and running postures into account; therefore, a combination of several mobility models that describe the moving boundary contributes to improvement of accuracy. One of the candidates is the Manhattan model. In addition, since human behavior is affected by the different situations such as age and living place, they should be taken into account for mobility design.
3. Integration with External System: one of the best sources to develop mobility patterns is to collect traces. If we have any device to track all movements in an efficient way, this will be the best option to get traces. Recently, smartphones have become pervasive so research work for smartphone-based human mobility prediction has been initiated. As [PERSON] et al. [55] proposed, it will be a good way to make use of smartphones to predict the movement and develop the mobility models. This is a reason to integrate mobility models with external systems. In addition, WSN, infrastructure for vehicular ad hoc networks and mobile networks can be good sources to  
Figure 8: Architecture of Cognitive Radio enabled Wireless Body Area Networks.  
collect human mobility, especially for group mobility. Therefore, interfaces to get the demanded information with external systems can accelerate the mobility model research.
* 4. Network Architecture: Current research work is assumed under homogenous as well as flat network architecture. However, recent routing protocol gradually takes clustering or hierarchical architecture into account as observed in [56]. To catch up with this trend, mobility support should be designed to operate under heterogeneous networks architecture. In this architecture, different mobility patterns need to be applied according to types of nodes. In addition, mobility relationships between two types of nodes is required to integrate them into a system.
* 5. Security: Contrary to benefitting from external systems, security is one of the important research challenges in WBAN. Furthermore, mobility results in more critical tasks for security because new authentication may be required to new topology, especially in the case of handovers. More seriously, when it comes to additional overhead to handle mobility, it leads to uncertainty of security support on a resource constrained node.