  The autonomous quadrotor's flying speed has kept increasing in the past 5
years, especially in the field of autonomous drone racing. However, the
majority of the research mainly focuses on the aggressive flight of a single
quadrotor. In this letter, we propose a novel method called Pairwise Model
Predictive Control (PMPC) that can guide two quadrotors online to fly through
the waypoints with minimum time without collisions. The flight task is first
modeled as a nonlinear optimization problem and then an efficient two-step mass
point velocity search method is used to provide initial values and references
to improve the solving efficiency so that the method can run online with a
frequency of 50 Hz and can handle dynamic waypoints. The simulation and
real-world experiments validate the feasibility of the proposed method and in
the real-world experiments, the two quadrotors can achieve a top speed of
8.1m/s in a 6-waypoint racing track in a compact flying arena of 6m*4m*2m.
