# Software Defined Networks in Wireless Sensor Architectures
## 5 Wireless Cellular Networks
### Software Defined Networks in Wireless Cellular Networks  
Applying SDN in WCN removes the load of the Packet data network Gateway since decoupling data and control planes allows scalability and network manageability. At the same time, such facts reduce hardware components and also hardware cost. Consequently, having a centralized controller improves the performance and stability of the network achieving global resource allocation and interference management. The Software Defined Wireless Cellular Networks (SDWCN) design is comprised of the control plane (set of application modules that provide load balancing, QoS, mobility management, and connection establishment) and data plane (base stations and cellular towers), as is shown in Figure 6.  
WCN physical deployment is based on sets of cells in order to provide communication services to network users. Therefore, phones must be within the access point coverage to be connected in such networks. Thus, WCNs use sets of cells to increase the network performance in terms of users' traffic  
Figure 6: SDWCN layers. demands. Particularly, cells are divided into smaller ones that are administrated by access points. Due to this division, the interferences across cells eventually limit network capacity producing cells from overlapping. Hence, the paradigm of cell splitting (number of cells and their size) opens up difficult problems such as mobility management and load balancing in these networks [73]. Several works have been proposed using the SDN model in WCN to allocate resources in the best possible way [74; 75; 76]. We have divided these solutions into three different groups attending to the component of the WCN that is being improved. The first group belongs to works focused on RAN, the second group is targeted to CN, and, finally, solutions that use resource allocation through RAN and CN at the same time. * Regarding resource allocation in RAN, works like SoftRAN [73] propose a centralized radio access control plane in order to abstract a group of base stations in a single virtual base station. It builds a three-dimensional grid of resources based on abstraction of space, time and frequency dimensions. Nevertheless, this design takes into account the network delay even when the resource allocation is performed quickly. Hence, the logical centralized control is responsible for global network control aspects, while the data plane devices are handled by a tasks distribution process. Moreover, SoftRAN is able to improve the handover process and resource allocation based on interferences and also assigns power to resources that are placed at a base station in a dense WCN. [PERSON] et al. propose SoftMobile [77], an approach that provides an alternative tasks' distribution to solve three sub-problems: how can state information be distributed, how can the cells be coherently configured, and, finally, how can live inter-cell operations be handled. Each one of these problems are managed by three separated controllers. * There exists a need of resource allocation at the cellular CN where RAN connects devices to the Internet. Traditional cellular networks centralize this resource allocation at the base station. Packet data network Gateways are responsible for checking the resource availability to satisfy a resource demand with priority that belongs to a user or an application or taking the correspondent actions (denying request or releasing the resource). This model raises scalability problems requiring expensive Packet data network Gateways to satisfy this challenge. In this way, SoftCell [78] proposes a solution to remove the complexity from Packet data network Gateways in order to access switches placed at base stations. Nevertheless, this solution presents important bandwidth requirements that are translated as congestion and also a limitation of network scalability. To meet this matter, SoftCell presents an algorithm that aggregates multidimensional packets in order to decrease the forwarding table size in data plane devices.