  In this paper we address the problem of adaptive state observation of
affine-inthe-states time-varying systems with delayed measurements and unknown
parameters. The development of the results proposed in the [Bobtsov et al.
2021a] and in the [Bobtsov et al. 2021c] is considered. The case with known
parameters has been studied by many researchers (see [Sanz et al. 2019, Bobtsov
et al. 2021b] and references therein) where, similarly to the approach adopted
here, the system is treated as a linear time-varying system. We show that the
parameter estimation-based observer (PEBO) design proposed in [Ortega et al.
2015, 2021] provides a very simple solution for the unknown parameter case.
Moreover, when PEBO is combined with the dynamic regressor extension and mixing
(DREM) estimation technique [Aranovskiy et al. 2016, Ortega et al. 2019], the
estimated state converges in fixed-time with extremely weak excitation
assumptions.
