Wireless communications prompt our society to become more and more connected every day. Resource constraints and technical problems yet to be solved become harder to overcome in the wireless domain. Users often experience data rate limitations or services unavailability.

Figure 1. WSDN Architecture

Software Defined Networking (SDN) which sometimes is also called programmable networking is often defined as the decoupling of the control and the forwarding planes. This means that the set of rules that defines how interconnection elements forward information can be defined in any way with software, independently with the hardware devices and equipment providers. SDN bears very high potential in wireless domain, say Wireless Software Defined Networking (WSDN), which can bring lots of opportunities and benefits,

• Improving end-user connectivity and QoS;
• Helping multi-network planning;
• Increasing security;
• Making end users or device localization easier;
• Improving resource efficiency.

However, it faces several challenges at the same times,

• Slicing and channels isolation:  

WSDN requires at least being able to isolate communication channels to different slices so that it can represent non-interfering networks to different coordinators. Defining more slices than the number of channels defined by the technology (TDMA, FDMA, WiFi, etc.) is challengeable. For example, WSDN has to manage the three non-overlapping Wi-Fi channels in the 2.4 GHz band to satisfy a tremendous number of non-interfering networks.

• Monitoring and status report:

WSDN needs to have the vision of the whole system to make effective decisions. This requires that network elements are able to report their status. WSDN should achieve environment assessment, such as estimating wireless channels status (load, etc.), and the links characterization (delay, loss rate, stability, etc.), and topology discovery. The devices' CPU load or available memory, etc. are also should be considered. There are too much information to be obtained for the WSDN controller.

• Handoffs:

WSDN should make multiple handoffs for load balancing, topology control or environment adaptation. Network elements may migrate from one access point to another. e.g., mobile users can switch from WiFi to cellular or broadcasting networks. Handoff will occur both in homogeneous and heterogeneous networks and service interruption should be avoided in the complex WSDN system.

Figure 2. campus experimental platform for 4G and B4G networks

We have built up a campus experimental platform for 4G and B4G networks, which includes the heterogeneous network of broadcasting, WiFi, Satellite communication and Cellular systems. The WSDN challenges such as handoff among these different networks, monitoring and status report etc. can be achieved with our experimental platform to assess the performance and benefits of WSDN.