Acquisition and processing of sensor data has to cope with measurement uncertainties and complex failure modes. Additionally, multiple sensor types and modalities may be used to improve reliability of environment perception. Our work aims at providing an architecture for fault-tolerant sensors and offering a uniform interface to the application. In the paper, we present our fault-tolerant virtual sensor concept that is based on combining model-based estimation and redundant sensor data. To illustrate and evaluate our concept we simulate a mobile robot in an instrumented environment which integrates several smart position sensors. By using a mathematical model to evaluate sensor data we achieve a more reliable position estimation. The paper presents results of the fusion process and discusses methods for generalization.