QoS Control for Mission-critical Communication on Vehicles with IEEE802.11 Wireless LAN under Dynamic Interference

In this research, we propose a velocity-adaptive contention window (CW) control method that reduces the maximum delay under dynamic interference on automobiles with IEEE802.11 wireless LAN communication. The method is developed for mission-critical communications for tiny periodic data. In the proposed method, the average backoff time (random wait time) is reduced as the vehicle velocity decreases, and this is done to reduce the maximum delay in situations where the influence of interference is large. Additionally, increasing the average contention window at the time of retransmission is prohibited, and the window size is fixed. Developing the proposed method, we focused on the condition in which, the slower the velocity of the vehicle is, the smaller the distance to the surrounding vehicles (and therefore the greater the amount of interference). Furthermore, we did not focus on the fact that the CW size is not optimal; instead, we focused on interference as the main cause of retransmission. This can reduce the delay determined by the number of retransmissions (the number of transmission failures) and the backoff time. To research the effect of the proposed method, we evaluated the performance of a sensor network in a vehicle using a model that causes interference when other vehicles pass near the vehicle at various velocities. The effectiveness of the proposed method was clarified by comparing the conventional method with fixed control for interference and the proposed method with control according to vehicle velocity.