  In this paper, we propose a swarming approach and optimize the one-hop delay
for interplatoon communications through adjusting the minimum contention window
size of each backbone vehicle in two steps. In the first step, we first set a
small enough average one-hop delay as the initial optimization goal and then
propose a swarming approach to find a minimum average one-hop delay for
inter-platoon communications through adjusting the minimum contention window of
each backbone vehicle iteratively. In the second step, we first set the minimum
average one-hop delay found in the first step as the initial optimization goal
and then adopt the swarming approach again to get the one-hop delay of each
backbone vehicle balance to the minimum average one-hop delay. The optimal
minimum contention window sizes that get the one-hop delay of each backbone
vehicle balance to the minimum average one-hop delay are obtained after the
second step. The simulation results indicate that the one-hop delay is
optimized and the other performance metrics including end-to-end delay, one-hop
throughput and transmission probability are presented by using the optimal
minimum contention window sizes.
