Abstract-The paper addresses the control of Vertical Take Off and Landing (VTOL) Underactuated Autonomous Vehicles (UAVs) in hover flight, based on measurements provided by an on-board video camera and rate gyros. The objective is to stabilize the vehicle to the pose associated with a visual image of a planar target. By using the homography matrix computed from the camera measurements of the target, stabilizing feedback laws are derived. Explicit stability conditions on the control parameters are provided. It is shown that very good robustness and performance can be achieved without any apriori information on the visual target (like geometry, or orientation), by a proper tuning of the control parameters. Simulation results confirm the effectiveness of the approach.

A unirying framework for observer design by eigenstructure assignment is described. A new technique for structured residual generation, based on this framework, is proposed. One of the main features of this technique is that the equivalence between residual generation by means of observers or parity space devices are made conspicuous. More precisely, from a computational point of view, the equations to solve in both cases are shown to be similar, and for implementation, both devices are shown to be identical. A necessary and sufficient condition for the existence of structured residuals is given. Finally the sensitivity of structured residuals to nondecoupled failures is studied and a procedure for maximizing this sensitivity is described.

This paper studies a potential EM1 (ElectroMagnetic Interference) rejection technique for the GPS Standard Positioning Service in an avionics environment. Its generalisation to any Direct Sequence Spread Spectrum (DSSS) Systems is also considered. The paper gives a brief overview of Wavelet Theory, which is well established for noise reduction but which is applied here to Continuous Wave Interference (CWI) and narrowband interference. The originality of this work lies in a method for signal rejection, taking into account features in both time and frequency domains to account for the non-stationary characteristics of the interference. Because the software-based receiver is more flexible. less expensive and more accurate compared with typical hardware receivers, a Generic GPS Receiver has been implemented in software [ I ] to validate the antijamming technique developed in this paper. The aim of the Montecarlo simulations is to get a good idea of the Performances of the Wavelet Filter against a various types of Interferences and to compare the results with traditional processing. FONDAWENTAL BASIS OF THE N E W PROCESS References[3. 5, 7, 91 and [22, 241 provide a useful background to wavelet theory. Vol. 9. No. Z March -April 1998 191 [7] M. V. Wickerhauser: INRIA lecriires on wuvelcr packer cilgorithhms. March 27, 199 I .