A New Adapted Back off Scheme for Broadcasting on IEEE 1609 4 Control Channel in VANET
This paper shows that the current works in the field of optimizing the contention window follow:
Propose a static minimum contention window for VANETs
Try to adjust the contention window in function of the vehicle density.
After all, the authors said that regardless of how the local density estimation is accurate, does not solve the problem because the local density cannot show the real data load.
Therefore, they propose two mechanisms:
1- They choose the starting time for each node in the CCH interval based on its geographical position
2- they propose a new back-off mechanism so that the node doesnt frozen its back-off timer by finding a new transmission and continue it until find it zero and then send the packet if find the channel free, otherwise, repeat the same routine.
These scheme shows better performance even if there are some GPS position errors.
Final point: this work distribute the nodes starting time based on their geographical position instead of choosing the optimized contention window. It can decrease the collision probability but it didnt find any answer for adapting the MAC based on the real data load.