Heterogeneous SDN controller placement problem—The Wi-Fi and 4G LTE-U case

The widespread deployment of 5G wireless networks has brought about a radical change in the nature of mobile data consumption. It requires the deployment of Long Term Evolution to the unlicensed spectrum (LTE-U) to alleviate the shortage of available licensed spectrum while Wi-Fi is the most dominant radio access technology in the unlicensed spectrum. This has led to suggestions concerning the coexistence of multi radio access technologies such as Wi-Fi and LTE-U. Clearly, Software Defined Networks (SDN) can utilize the LTE-U radio bandwidth efficiently. The SDN paradigm decouples the network's control logic from the underlying routers and switches, which promotes centralization of network control. The controller placement problem is crucial to SouthBound interface optimization and involves the location of the controllers, their number and the assignment function of switches to controllers. In this paper, a novel strategy is presented to address the wireless controller placement problem, which improves the throughput, link failure probability and the transparency on the SouthBound interface in cases where hybrid providers choose either LTE-U or Wi-Fi as link layer technologies. The problem of determining the placement of LTE-U and Wi-Fi based controllers is modeled and two heuristic solutions are proposed. Simulations show that the proposed algorithms provide a fast and efficient solution.