Optimal Sensing Policies for Smartphones in Hybrid Networks: A POMDP Approach

The ubiquity of mobile devices is fostering a paradigm shift in the realm of Internet services. Consider, for instance, mobile users of social networks, that require frequent updates through small messages from their friends. If a user activates his mobile device and has a contact opportunity with an access point, an update can be received at the expense of monetary and energy costs. Thus, users face a tradeoff between such costs and the utilities of the messages received. The goal of this paper is to show how a user can cope with such a tradeoff, by deriving optimal sensing policies. A sensing policy consists of deciding, based on the age of the last message received and the belief about the future availability of a WiFi access point, whether to activate the mobile device or not. Alternatively, users may also decide to use 3G technology to receive updates, which provides broader coverage at the expense of higher monetary costs and lower bandwidth. To address the tradeo faced by the users, we propose an analytical model based on a Partially Observed Markov Decision Process (POMDP) with an average reward criterion. Using the proposed model, we show properties of the optimal sensing policy. The applicability of the model and of the derived policy is illustrated through numerical case studies.