  This paper presents a cooperative target defense strategy using nonlinear
model-predictive control (NMPC) framework for a two--targets two--attackers
(2T2A) game. The 2T2A game consists of two attackers and two targets. Each
attacker needs to capture a designated target individually. However, the two
targets cooperate to lure the attackers into a collision. We assume that the
cooperative target pair do not have perfect knowledge of the attacker states,
and hence they estimate the attacker states using an extended Kalman filter
(EKF). The NMPC scheme computes closed- loop optimal control commands for the
targets while respecting imposed state and control constraints. Theoretical
analysis is carried out to determine regions that will lead to the targets'
survival, given the initial positions of the attacker and target agents.
Numerical simulations are carried out to evaluate the performance of the
proposed NMPC- based strategy for different scenarios.
