Bit-Rate Selection in Multi-vehicular Networks

IEEE 802.11 PHY supports multiple transmission rates, varying from as low as 1 Mbps in 802.11b, up to 54 Mbps in 802.11g, and higher in 802.11n, with each Wi-Fi station selecting its transmission rate according to its own algorithm. The per-packet fairness scheme adopted by the 802.11 MAC reduces the effective throughput to that of the lowest sending rate. In multi-vehicle opportunistic downloading scenarios the communicating nodes will achieve the maximum transmission rate at some point, therefore in such scenarios the preferred bit-rate selection algorithm is: transmit at the highest bit rate or remain silent. We have implemented this policy and our experimental evaluation demonstrates that there is only a small loss in throughput in single-vehicle scenarios, while throughput is approximately 15% higher than the best alternative in multi-vehicle scenarios, with significantly less contention, and thus loss, on the medium.