The H∞ estimation problem is investigated for a class of discrete-time Lipschitz nonlinear time-varying delay
systems. By using state augmentation approach, the time-varying delay system is converted into a delay free system with
time-varying parameters. Combing H∞ performance with Lipschitz nonlinear conditions, an indefinite quadratic form is
constructed and a relation is built with Krein space H2 estimation. By applying innovation analysis approach and Krein
space projection formula, a sufficient condition for the existence of the H∞ estimator is proposed and the estimator is
derived in terms of Riccati difference equations. Finally, the effectiveness of the proposed algorithm is illustrated through a
numerical example.