Optimizing Content Dissemination in Heterogeneous Vehicular Networks∗

Disseminating shared information to many vehicles could incur significant access fees if it relies only on unicast cellular communications. We consider the problem of efficient content dissemination over a heterogeneous vehicular network, in which vehicles are equipped with two kinds of radios: a high-cost low-bandwidth, long-range cellular radio, and a free high-bandwidth short-range radio. We formulate an optimization problem to maximize content dissemination from the infrastructure to vehicles within a predetermined deadline while minimizing the cost associated with communicating over the cellular connection. We mathematically analyze the dissemination process using differential equations and convex optimization and derive a closed-form optimal solution. We then examine numerically the tradeoffs between cost, delay and system utility in the optimum regime. We have found that, in the optimum regime, (a) system utility, which is essentially the extra benefits induced by the short-range radio, is more sensitive to the cost budget when the allowed delay for the dissemination is not large, (b) the system requires relatively smaller cost budget as more vehicles participate and more delay is allowed, (c) when the cost is very important, it is better not to spread the content if it needs small delay. Since our closed form analysis provides only a continuous solution, we also develop a polynomial-time algorithm to obtain the optimal discrete solution needed in practice. We verify our analysis using real GPS traces of 632 taxis in Beijing, China. The key finding of this work is that content can be spread to a large number of vehicles with minimal use of the cellular infrastructure at low cost, if some delay is allowed.