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In the fog computing paradigm, fog nodes are placed on the network edge to meet end-user demands with low latency, providing the possibility of new applications. Although the role of the cloud remains unchanged, a new network infrastructure for fog nodes must be created. The design of such an infrastructure must consider user mobility, which causes variations in workload demand over time in different regions. Properly deciding on the location of fog nodes is important to reduce the costs associated with their deployment and maintenance. To meet these demands, this paper discusses the problem of locating fog nodes and proposes a solution which considers time-varying demands, with two classes of workload in terms of latency. The solution was modeled as a mixed-integer linear programming formulation with multiple criteria. An evaluation with real data showed that an improvement in end-user service can be obtained in conjunction with the minimization of the costs by deploying fewer servers in the infrastructure. Furthermore, results show that costs can be further reduced if a limited blocking of requests is tolerated.

In fog computing, processing, network, and storage resources are placed close to the end users to assure a low latency in comparison to the latency experienced when accessing services in the cloud. One limitation of this solution, however, is that fog nodes are usually fixed, whereas demands are variable over time at all locations, resulting in underutilization of the fog resources as well as unnecessary provisioning of fog resources. One way for dealing with this problem is the employment of mobile nodes to cope with the variability in resource demand.This paper studies how unmanned aerial vehicles (UAVs) equipped with processing capabilities can be used in this perspective, and proposes a solution to the fog node location problem considering both fixed and mobile nodes.It proposes the UAV Fog Node Location (UFL) algorithm to evaluate potential replacements of fixed servers by UAVs. The proposed algorithm can be used for long term planning under the assumption of changes in the prices of UAVs. An evaluation of the problem using data generated by real mobile users shows that UAVs can improve the design of future fog networks.

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