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Software-defined cellular networks (SDCN) have been recently introduced to enable flexible cellular network design that facilitates fulfilling 5G design requirements. Placement of controllers within the SDCN plays a crucial role in optimizing its performance. In this paper, we study the controller placement problem in SDCN, considering the uncertainty in cellular user locations. Specifically, our contributions are as follows. First, we develop C ³ P ² , a static joint stochastic controller placement and evolved node B (eNB)-controller assignment problem. The objective of C ³ P ² is to minimize the number of controllers needed to control all eNBs, while ensuring that the response time to each eNB will exceed seconds with probability less than 1-β. Second, we develop CPPA, a joint stochastic controller placement and adaptive eNB-controller assignment problem. In contrast to C ³ P ² , in CPPA the eNB-controller …