Beacon | EPFL Graph Search

A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More modern examples include a variety of radio beacons that can be read on radio direction finders in all weather, and radar transponders that appear on radar displays. Beacons can also be combined with semaphoric or other indicators to provide important information, such as the status of an airport, by the colour and rotational pattern of its airport beacon, or of pending weather as indicated on a weather beacon mounted at the top of a tall building or similar site. When used in such fashion, beacons can be considered a form of optical telegraphy. For navigation Beacons help guide navigators to their destinations. Types of navigational beacons include radar reflectors, radio beacons, sonic and visual signals. Visual beacons range from

Dynamic bending compensation while focusing through a multimode fiber

Salma Farahi, Christophe Moser, Demetri Psaltis, David Ziegler

Multimode fiber endoscopes have recently been shown to provide sub-micrometer resolution, however, imaging through a multimode fiber is highly sensitive to bending. Here we describe the implementation of a coherent beacon source placed at the distal tip of the multimode fiber, which can be used to compensate for the effects of bending. In the first part of this paper, we show that a diffraction limited focused spot can be generated at the distal tip of the multimode fiber using the beacon. In the second part, we demonstrate focusing even when the fiber is bent by dynamically compensating for it. The speckle pattern at the proximal fiber end, generated by the beacon source placed at its distal end, is highly dependent on the fiber conformation. We experimentally show that by intensity correlation, it is possible to identify the fiber conformation and maintain a focus spot while the fiber is bent over a certain range. Once the fiber configuration is determined, previously calibrated phase patterns could be stored for each fiber conformation and used to scan the distal spot and perform imaging. (c) 2013 Optical Society of America

Optical Society of America2013

A Galileo E1b,c RF Front-End Optimized for Narrowband Interferers Mitigation

Cyril Botteron, Frédéric Chastellain, Pierre-André Farine, Davide Manetti, Giuseppe Zamuner

The current Search and Rescue (SAR) service, which is based on the Cospas-Sarsat system, suffers from major limitations such as poor position accuracy, long alert times and high false alarm rate. Two types of distress signals are used, the first 121.5MHz/(up to 100mW) and the second 406MHz/5W, the latter being able to carry digitally encoded identification and position data. The Galileo system will importantly contribute to the improvement of the SAR system. Indeed, the Galileo satellites will include a transponder in order to re-broadcast the 406MHz message, which will allow a better coverage (27 Galileo satellites plus the current seven Cospas-Sarsat satellites) and also a shorter alert time. They will also include a return link message (RLM) in the Galileo E1b open service signal, which will reduce the number of false alarms. The Galileo system is therefore a great opportunity for the development of a new generation of beacons which will include a Galileo receiver and therefore be able to take advantage of the better coverage provided by the Galileo constellation to provide shorter alert times and of the RLM to reduce the number of false alarms. One of the major issue when designing a Galileo receiver to be operated in a distess beacon is to design a front-end that is sensitive enough to pick the very weak Galileo signals and on the same time rejects the strong distress messages. Indeed, when the beacon is turned on, the Galileo receiver is in cold start conditions and a short amount of time is left to the receiver to get a first fix before any distress message is actually emitted. However, in some cases, the receiver is not able to determine its position sufficiently fast and the front-end therefore has to acquire the satellites in the presence of the distress signals. This paper presents a Galileo radio frequency front-end designed in order to operate in the presence of such signals.

2006

A flexible Galileo E1 Receiver Platform for the Validation of Low Power and Rapid Acquisition Schemes

Marcel Baracchi Frei, Cyril Botteron, Frédéric Chastellain, Pierre-André Farine, Davide Manetti, Giuseppe Zamuner

With the inclusion of 406 MHz transponders on the Galileo satellites and the new search and rescue (SAR) return link message (RLM) on the open service E1B signal, the availability of distress beacons equipped with a Galileo or combined GPS/Galileo receiver will be very important in the future to take advantage of the SAR RLM, thereby facilitating the rescue operations and helping to identify and reject false alerts. Consequently, this paper provides the status of the development of a flexible Galileo L1 receiver platform as well as an analysis and comparison of acquisition schemes suitable to be implemented in 406 MHz Cospas-Sarsat distress beacons. For each considered acquisition scheme, we compare the acquisition performance that can be obtained using GPS L1 C/A or Galileo E1B or E1C signals and consider and discuss the following main constraints: a very short time to first fix (TTFF) in cold start conditions (the beacon’s GNSS receiver may not be powered on for years before it is activated in an emergency); a low energy consumption per position fix (the beacon and GNSS receiver are battery powered); a possibly long coherent integration time to achieve synchronization and tracking in harsh environments (e.g., when some or all of the satellite signals are blocked or attenuated by an obstruction); the ability to demodulate the satellites signals in the presence of a 406MHz/5W and a 121.5MHz/(up to 100mW) beacon transmitters; and a low complexity (low price).

2006

A Galileo E1b,c RF Front-End Optimized for Narrowband Interferers Mitigation

Cyril Botteron, Frédéric Chastellain, Pierre-André Farine, Davide Manetti, Giuseppe Zamuner

2006