6. Concluding remarks
In this paper, we discussed a security framework for proximity services in order to provide additional coverage for users that are facing intermittent cellular connectivity. We exploited a game theoretical framework (i.e., in terms of the cluster formation), where social relationships among users and the effects of cellular transmissions are considered explicitly. In the reference scenario, we studied the case of the cellular BS providing partial coverage and helping disseminate certain content that has to be distributed among all the active users. In such a situation, the cluster formation game is utilized for the user clustering by employing either social or spatial proximity, whereas the information security procedures take advantage of the obtained group configuration to exchange the data in a protected way. The obtained results indicated that, even though the amount of signaling messages was slightly increased, the proposed security framework was able to deliver connectivity to those users that were outside the cellular network coverage, and consequently did not have a reliable connection to the cellular infrastructure. As a result, we can assert that the consideration of both network geometry and social metrics enables dissemination of information to larger numbers of users with higher throughput, but at the cost of some additional delay due to extra signaling messages exchanged locally within each cluster. In summary, we conclude that the proposed framework based on spatial and social notions of proximity significantly improves many performance metrics of interest in characteristic cellularassisted D2D scenarios, where users exchange traffic generated by their wearable devices while utilizing smartphones as data aggregators. Our modeling approach may thus become useful as a reference point for further research in this field.
