System Design for Opportunistic Networks

The proliferation of mobile devices has significantly changed the way users consume information. As a result, mobile data traffic has been increasing exponentially since 2009. According to current predictions, more than 24 exabytes of mobile traffic will be traversing operators’ networks by 2019, with 72% of this traffic being generated by multimedia. This shift in user behavior requires a thorough re-thinking of the current design of network infrastructure. Device-to-device (D2D) communication has been suggested as a complement to traditional cellular networks as a means of offloading cellular traffic. In this thesis we explore a solution for device-to-device communication based on opportunistic content distribution in a content-centric network. The term ’opportunistic’ implies lack of knowledge of the network topology and connectivity graphs. Communication opportunities arise as mobile nodes roam around in an area (according to some, often random, mobility pattern) and occasionally enter in direct communication range with one another. In the context of this thesis we consider a node to be a pedestrian equipped with a mobile device featuring at least one short-range radio interface, i.e. a smartphone; we thus explore the properties of opportunistic communication in the context of content dissemination in urban areas. The contributions of this thesis lie in three areas. We first study human mobility as one of the main enablers of opportunistic communication. We introduce traces collected from a realistic pedestrian mobility simulator and demonstrate that the performance of opportunistic networks is not very sensitive to the accurate estimation of the probability distributions of mobility parameters such as speed and arrival process. However, we show that capturing the space in which mobility occurs may be of high importance for proper evaluation of system performance metrics. Secondly, we design and implement a middleware for opportunistic content-centric networking, and we evaluate the middleware via a small-scale testbed, as well as through extensive simulations. We conclude that energy-saving mechanisms should be part of the middleware design, while caching should be considered only as an add-on feature. Thirdly, we present and evaluate three different energysaving mechanisms in the context of opportunistic networking: a dual-radio architecture, an asynchronous duty-cycling scheme, and an energy-aware algorithm which takes into account node selfishness. We evaluate our proposals analytically and via simulations. We further position the operation of opportunistic networks in the context of mobile data offloading, and demonstrate that when critical mass of participants is available, the performance of the opportunistic network is comparable to downloading contents directly via the cellular network in terms of energy consumption while offloading large traffic volumes from the operator. We demonstrate that opportunistic networking can be also applied to a class of near real-time multimedia services, such as music streaming. Finally, we position opportunistic networks in the context of current Third Generation Partnership Project (3GPP) standardization efforts in the area of D2D and argue that opportunistic communication should be considered the predecessor of modern device-to-device communication.