  In this paper, we propose a suboptimal moving horizon estimator for nonlinear
systems. For the stability analysis we transfer the
"feasibility-implies-stability/robustness" paradigm from model predictive
control to the context of moving horizon estimation in the following sense:
Using a suitably defined, feasible candidate solution based on the trajectory
of an auxiliary observer, robust stability of the proposed suboptimal estimator
is inherited independently of the horizon length and even if no optimization is
performed.
