Cooperative Content Distribution for Vehicular Ad Hoc Networks

The proliferation of low-cost wireless connectivity, combined with the growth of distributed peer-to-peer cooperative systems, is changing the way in which next-generation vehicular networks will evolve. In this paper, we address the problem of low-latency content distribution (multicast streaming) to a dense vehicular highway network from roadside infostations, using efficient multihop vehicle-to-vehicle collaboration. Due to the highly dynamic nature of the underlying vehicular network topology, we depart from architectures requiring centralized coordination, reliable MAC scheduling, or global network state knowledge, and instead adopt a distributed and minimally coordinated paradigm. We establish the viability of our approach with both analysis and extensive simulations. Our study is motivated by questions such as "what is the network capacity?" and "how many infostations are needed to realize a target throughput and latency?" The key ingredient in our approach is the use of multihop randomized network coding to efficiently distribute the content in the vehicular network. Specifically, we show that in the limit of a highly dense network, our decentralized approach can attain a multicast throughput that is up to a factor of 1/e of the throughput which could be achieved by perfectly scheduling all packets in the network. Further, the gains of using randomized network coding over classical store-and-forward multihop routing strategies can be significant, as measured by the throughput received at a vehicle as a function of the distance between that vehicle and the nearest infostation. This in turn translates into a significant decrease in the number of roadside infostations required to meet desired throughput and latency constraints for specific streaming applications.