Impact of asymmetric traffic densities on delay tolerant vehicular ad hoc networks

Vehicular networking can be achieved with short, medium, or long-range communication technologies. However, there are trade-offs in the adoption of these technologies including data capacity, continuity of connections, energy use and contention with other users. We focus on short range technologies that support both near-neighbor communication, for safety applications, and multihop communications for message propagation. Due to frequent network partitioning, opportunistic message exchange is required for message propagation. Earlier studies reveal that messages are suitably propagated in both directions of traffic as vehicle traffic density increases. In this paper we consider asymmetries in traffic density caused by directionality. For example, `rush hour' traffic fills one direction of a roadway while the other direction can be sparse. Performance analysis indicates that data dissemination under asymmetry produces a corresponding asymmetry in message propagation in the direction of higher-density traffic. This result is framed in the context of traffic density regimes and is useful in the design of vehicular networks that leverage short range communications. For a fixed traffic density in one direction, an increase in density from 0 to 20 vehicles/km in the other direction, yields a corresponding increase of 500 m/s to 1000 m/s in the messaging performance depending upon the regime.