Search

Aviation is now heavily dependent on GNSS signals to get the PNT (Position, Navigation, Timing) elements with a high degree of accuracy, reliability and continuity. The International Civil Aviation Organization (ICAO) with the support of regional organizations like the FAA (Federal Aviation Authority) and Eurocontrol are now moving to concretize the recommendations of GANP (Global Air Navigation Plan) which make from GNSS the key technology of CNS/ATM concept (Communication, Navigation, Surveillance/Air Traffic Management). So, it is obvious that the security and the integrity of GNSS signals must be a concern of all actors in military and civil aviation. In this paper, we will present a survey of the anti-jamming techniques for airborne GNSS-based navigation systems and some approaches to detect, mitigate the jamming and provide a secure GNSS-based system.

In electron optics, the design of electron lens systems is still a challenge. To optimize such systems, the objective function which should be calculated, depends on the electric potential distribution in the space created by the lenses. To obtain the electric potential, the existing methods are generally based on some mathematical techniques which need to mesh the space of the lens system and derive the electric potential at all mesh points. Hence, calculation of the objective function for such systems are computationally expensive. Therefore, applying a fully automatic optimization routine has not yet been feasible, especially for lens systems with many free variables. Hence, the study of objective-function landscape of such problems has not yet been performed. One of the questions of interest for optical designers, that has not been studied in the literature, is whether this problem can be solved by a local optimizer or is it necessary to apply a global optimizer. Recently we succeeded in implementing a method (based on a so-called SOEM (Second Order Electrode Method) technique) which calculates the electric potential in a fast and reasonably accurate way. In this paper, that method, is implemented to perform the study of local versus global optimization for electron lens design. The global optimization method here is performed by GA (Genetic Algorithm). The objective function is taken to be the probe size of the electron beams at the image plane. The results of our study show that the objective function of this problem has many local minima and the optimization of such problems cannot be handled by a local optimizer. GA is shown to perform well by overcoming these multiple-local minima to arrive at a global minima.

Opportunistic routing (OR) is a new method of routing in wireless sensors networks schemes (WSN) which selects the nearest node to the target for data transmission.It uses the nature of the medium to spread information. Opportunistic routing has been proven as promising routing technique for wireless sensors networks it also increases their reliability and efficiency and effectively supports multiple simultaneous flows by using the right OR protocols. The main idea behind OR is overhearing and cooperation between the nodes. This paper reviews the basic concepts of OR and lists all it protocols.

Opportunistic routing (OR) protocols in wireless network schemes are a rich research field. These protocols select the best path in order to send information and take the broadcasting medium into consideration. OR tends to reach better reliability and performance than traditional routing (TR). However, they are both equally vulnerable to the same attacks because wireless networks might be deployed in hostile or unwatched environments. The approaches in terms of routing are mainly focusing on energy preservation, robustness, etc. However few work has been done to secure routing protocols especially in OR. In this paper, we are going to give an analysis of OR protocols their classifications as well as an overview on the security approaches available for opportunistic routing protocols.

It is an important technological challenge to ensure a LEO satellite ground terminal autonomy as well as to make it small, lightweight and power efficient along with the ability to predict the satellite visibility passes. Another important feature is to make it able to compensate for Doppler on the satellite link with an economical method. In this paper, an orbit and Doppler calculation methodology has been developed for a general orbital model. The algorithm that manages the ground terminal automatic operation ensures many advantages and is adapted to a microcontroller programming. Inputs to the algorithm are time, position and keplerian elements from NORAD. The NORAD elements are injected in the terminal memory via its serial port once before it is deployed on the operation field. Time is provided by a real time clock read and written by the terminal microcontroller. Terminal geographic position is provided by an internal integrated miniature GPS which makes the terminal free to move anywhere on the terrestrial globe and still be able to contact the satellite without any reprogramming. The orbit calculation methodology used expresses the satellite coordinates in the terminal relative topocentric (horizontal) coordinate system which easily yield the values of elevation and azimuth angles along with the slant range. This is achieved by means of satellite vector transformations through different coordinate systems. Doppler shift is obtained by deriving the slant range in time. A simple methodology for Doppler correction is also proposed in this paper and is adapted for low cost transceivers.