We consider a system where users aboard communication-enabled vehicles are interested in downloading different contents from Internet-based servers. This scenario captures many of the infotainment services that vehicular communication is envisioned to enable, including news reporting, navigation maps and software updating, or multimedia file downloading. In this paper, we outline the performance limits of such a vehicular content downloading system by modeling the downloading process as an optimization problem, and maximizing the overall system throughput. Our approach allows us to investigate the impact of different factors, such as the roadside infrastructure deployment, the vehicle-to-vehicle relaying, and the penetration rate of the communication technology, even in presence of large instances of the problem. Results highlight the existence of two operational regimes at different penetration rates and the importance of an efficient, yet 2-hop constrained, vehicle-to-vehicle relaying.Optimal Content Downloading in Vehicular Networks
Traffic relaying through one or more vehicles that create a multi-hop path between an AP and a downloader, where all the links of the connected path exist at the time of the transfer. This is the traditional approach to traffic delivery in ad hoc networks. Although longer periods of time under coverage can undoubtedly favor the download of contents by vehicular users, important differences with our work exist.
Vehicular networks, as well as on the connectivity challenges posed by such an environment. the authors show that a random distribution of APs over the street layout can help routing data within urban vehicular ad hoc networks. The impact of several AP deployments on delay tolerant routing among vehicles is studied. More precisely, each AP is employed as a static cache for content items that have to be transferred between vehicles visiting the AP at different times. Other than in the scope, the works in differ from ours also because they do not provide theoretical justification of the AP placements they propose. AP deployment is formulated as an optimization problem in [13], where, however, the objective is not content downloading but the dissemination of information to vehicles in the shortest possible time. The study in [14], instead, estimates the minimum number of infrastructure nodes to be deployed along a straight road segment so as to provide delay guarantees to the data traffic that vehicles have to deliver to the infrastructure, possibly with the help of relays. A similar problem is addressed with the aim to support information dissemination. The different objectives of the above studies lead to completely different formulations, thus to results not comparable with the ones we present. Infrastructure placement strategies are proposed that maximize the amount of time a vehicle is within radio range of an AP. Although longer periods of time under coverage can undoubtedly favor the download of contents by vehicular users, important differences with our work exist. First, our analysis is not limited to direct transfers from APs to vehicles, but includes traffic relaying. Second, while the problem formulation in [3] guarantees a minimum coverage requirement and the one in [4] maximizes the minimum-contact opportunity, we optimize the actual throughput, accounting for the airtime conflicts deriving from the contemporary presence of an arbitrary number of vehicles.