Search in digital pockets: Retrieving remote content in mobile opportunistic networks

Due to the fierce competition for the wireless spectrum, operators have recently focused on short-range communications, which promises higher spectral efficiency, lower energy consumption, and less strain on the operators' core networks. Mobile opportunistic communications, that is, short-range communications without any network assistance, is of considerable practical value since it entails almost no monetary cost and does not rely on any infrastructure. Compared to the extensive work on opportunistic networks, the predominance of video and other content calls for new content-centric approaches. To this end, the motivation of this article is to explain how opportunistic search can discover the content stored in remote mobile devices and deliver it to the requesting node. We abstract the problem domain as three layers, network topology, content, and query; and describe the interactions among these components. After reviewing each layer, we introduce several schemes for content availability estimation that do not rely on any information exchange but simply use already available information. Additionally, we highlight some open research directions.