Many mobility models currently used for evaluating wireless communication systems have weak resemblance to reality and there is a lack of understanding on which characteristics of human mobility affect system performance. In particular, most current mobility models assume a free flow of nodes and do not consider how mobility is affected by interactions with other persons and with the physical environment. They also assume a closed system, not considering the effect of node arrival and departure. The structure of space in which the mobility occurs is either not considered at all, or only in a limited way. In this work, we address human pedestrian mobility for evaluation of wireless communication to determine which of the aforementioned aspects need to be captured and to what level of detail. We focus on opportunistic communication in the form of ad-hoc and delay-tolerant networks. For the evaluation, we use mobility models from the field of transportation and urban planning that are used for designing and dimensioning public spaces for comfort and safety of pedestrians in rush hour and emergency evacuation. The models capture micro-mobility of pedestrians better than most mobility models used in mobile networking since the application domain requires realistic representation of node interactions with the physical environment and with other nodes. Our results show that the free flow assumption used in most models does not have a significant performance impact. We also conclude that performance is not very sensitive to accurate estimation of the probability distributions of mobility parameters such as speed and arrival process. Our results, however, suggest that it is important to capture the scenario and space in which mobility occurs since these may affect performance significantly.

Epidemic content dissemination has been proposed as an approach to mitigate frequent link disruptions and support content-centric information dissemination in opportunistic networks. Stochastic modeling is a common method to evaluate performance of epidemic dissemination schemes. The models introduce assumptions which, on one hand make them analytically tractable, while on the other, ignore attested characteristics of human mobility. In this paper, we investigate the fitness and limitations of an analytical stochastic model for content dissemination by comparison with experimental results obtained from real mobility traces. Our finding is that a homogeneous analytic model is unable to capture the performance of content dissemination with respect to content delivery delays.

A major challenge for wireless networks is to minimize the energy consumption in the mobile devices. This work evaluates potential performance gains of a dual-radio architecture in which a low power radio is used to wake up the primary high power radio. Our targeted domain is opportunistic communication directly between devices. We show that it can significantly reduce the energy consumption at a price of slightly decreased goodput. We also examine the effect of the MAC protocol on the performance of the dual-radio system and we point out that in dense scenarios MAC layer protocols, such as of 802.15.4, do not perform well. We observe that information on device density of an environment can be used to address this shortcoming.

In this paper we examine content distribution in opportunistic networks. We design and evaluate strategies by which a node fetches and shares contents on behalf of other nodes, even when the contents are not of its own interest. We propose four relaying/caching options for improving the use of network resources: relay request on demand, hop-limit, greedy relay request, and weighted relay request with allocated caching positions. We also compare our strategies with a strategy from the literature. The proposed strategies are implemented in the OMNeT++ simulator, and evaluated on mobility traces with different churn levels. The results show that the performance of opportunistic caching is strongly dependent on the level of churn in the network. However, we find a strategy that outperforms the rest in all of the explored network settings.

We present a demonstration scenario to validate a middleware architecture that we designed and implemented for distributing content between mobile users in an opportunistic manner. The peer-to-peer networking architecture allows content dissemination between mobile devices without relying on any infrastructure support. We developed a mobile application utilizing the services provided by the implemented middleware. The application facilitates opportunistic content distribution in both one-to-one and one-to-many dissemination modes.

Ad-hoc wireless peer-to-peer methods are an important and viable alternative to the more traditional infrastructure based ones for distributing contents among a population of users. The PodNet project is a ongoing effort to create a broadcasting system for delay-tolerant content, in which peer nodes exchange contents opportunistically when within range, and their mobility acts as a complementary mechanism for the dissemination. This paper introduces the design of a Pod-Net node. In particular, the special case of a gateway, which bridges the infrastructure world of the Internet and the ad-hoc domain, is considered.