LOCAL POSITIONING SYSTEMS VERSUS STRUCTURAL MONITORING: A REVIEW

SUMMARY Structural monitoring and structural health monitoring could take advantage from different devices to record the static or dynamic response of a structure. A positioning system provides displacement information on the location of moving objects, which is assumed to be the basic support to calibrate any structural mechanics model. The global positioning system could provide satisfactory accuracy in absolute displacement measurements. But the requirements of an open area position for the antennas and a roofed room for its data storage and power supply limit its flexibility and its applications. Several efforts are done to extend its field of application. The alternative is local positioning system. Non-contact sensors can be easily installed on existing infrastructure in different locations without changing their properties: several technological approaches have been exploited: laser-based, radar-based, vision-based, etc. In this paper, a number of existing options, together with their performances, are reviewed. Copyright © 2014 John Wiley & Sons, Ltd

Impact of Used Communication Technology on the Navigation System for Hybrid Environment

This paper deals with navigation of mobile device in outdoor and indoor environment by only navigation system or application. In the paper, the navigation system is proposed in the light of seamless navigation service. Main parts of the system from positioning point of view are based on GPS and WifiLOC system. WifiLOC is an indoor positioning system based on Wi-Fi technology. The proposal of the system will be described in detail. The system is implemented at the University of Zilina as a pilot, noncommercial project; therefore it is called University Mobile Navigation System (UMNS). The navigation system can be characterized as realtime system, that is, the system operations cannot be significantly delayed. Since delay of the system depends significantly on communication platform used for map information downloading or communication with the localization server. We decided to investigate an impact of the used communication platform on the time needs for some of the functions implemented in navigation system. Measurements were performed in the real-world application. Next experiment is focused on testing of the accuracy of used indoor positioning system. Outdoor positioning accuracy is not tested because GPS is utilized in outdoor, and this system was already exhaustively investigated

Indoor Positioning with GNSS-Like Local Signal Transmitters

Not all the techniques proposed have, of course, been based on radio techniques, but they are the most important ones for two main reasons: their level of development and maturity on the one hand and their ability to "cross" or to "get around" obstacles such as walls, furniture or people on the other hand. Optical based techniques, like laser based distance measurements or vision based (camera) scene analysis systems present some real advantages in terms of measurement accuracy (a few millimetres for the former) or orientation determination (very useful for any guidance system, available for the latter). Unfortunately, the foreseen use of positioning devices being mainly dedicated to pedestrians in urban environments, optical obstacles are numerous. These latter techniques are then considered as potential hybridisation candidates. Many types of sensors have also been studied for positioning, such as infrared or ultrasound. Once again, although accuracy can reach centimetre values, the environmental constraints are not compatible with the ubiquitous systems being sought. Another category is, of course, inertial systems which could be a valuable alternative to radio systems: time and distance associated position drifts are not yet sufficiently mastered and the given positioning is relative , which means the need for "something else" in order to provide the user with an absolute location. The object of this section is to focus on radio based approaches

Interference mitigation in a repeater and pseudolite indoor positioning system

International audienceThe present paper deals with indoor positioning based on a technique combining the characteristics of two systems: pseudolites and repeaters. This solution tries to combine the best of each method: for pseudolites, the ability to cope with carrier phase measurements to improve the accuracy and reduce the effect of multipath, and for repeater the simplicity of the infrastructure and the automatic synchronisation with the satellite constellation. A pseudolite is a long established and relatively well-known concept: it consists of ground based stations broadcasting GNSS-like signals. A receiver based on the ground can process this signal exactly as if it was a satellite signal and use it as satellite data in the computation of a navigation solution. Thus it is possible to deploy a ground based constellation of pseudo-satellites in order to compute a position inside buildings or any places where GNSS signals are too weak to be processed by classical or highly sensitive GNSS receivers. Since the signal has the same structure as the outdoor signal, precise measurements can be carried out like carrier phase measurements allowing the multipath error to be mitigated. However, there are limitations to this method. First is the synchronisation of the ground based constellation. As in any GNSS system, synchronisation is vital and it can be very expensive to have a stable clock on each pseudolite. Second is the potentiality of high interference between the pseudolites. As the distances of propagation are relatively small and the indoor environment has a propensity to raise obstacles in the signal trajectory, the difference of power between two signals can be high enough to lead to the disruption of the weakest by the strongest. (There is also potential interference with the GNSS signals but it does not concern the present discussion.) This phenomenon is called the Near-far problem. Thus, pseudolites are interesting but limited by the synchronisation and the Near-far problem. The repeater based technique has several declinations as shown in the section II.B of the paper, but the main principle remains. It consists of collecting GPS signals from an outdoor antenna and then forwarding them indoors in a sequential switching mode without any further treatment other than amplification. Each repeater, which consists of an antenna and a cable linked to the sequential switcher, transmits signals over a specific period while the others are switched off. Signal switching induces an offset of phase on the signal received by an indoor receiver. This offset corresponds to the difference of time of arrival between two successive repeaters. Four such Time of Difference Of Arrival measurements are then necessary to compute a position. With such a method, there is no interference between repeaters, thus no longer a Near-far problem. In addition, there is no need for expensive synchronisation of the constellation, but the switching induces signal discontinuities that limit the possibility of carrier phase measurements. Consequently, it increases the influence of multipaths on the computed solution. The proposed method, called the Repealite method, consists of transmitting a repeated signal as for the repeaters. But, instead of switching, the transmission on each antenna is delayed in such a way that the codes (Which are the same, though delayed, for all satellite signals received.) transmitted on each repealite do not interfere once they arrive at the receiver antenna. The principles of this method were presented in [1] and [2]. It is clear that the continuity of the signal allows carrier phase measurements and it is also clear that no synchronisation is required. However, the Near-far problem remains and can even be worse than in the case of pseudolites. The point we want to focus on this paper is the high level of interference than can occur because of simultaneous broadcasting of different satellite signals. This can induce severe interference that can disrupt the signal. This paper mainly focuses on methods developed in order to improve correlation mitigating the effect of the interference between repealites, interference that we call systemic interference. After the state of art of the GNSS based indoor positioning techniques in section II, the principles of the Repealite method are presented in section III which ends with a theoretical description of the received signal. Section IV provides simulations from a typical indoor positioning situation in standard conditions in order to illustrate the interference influences and to study solutions that could be carried out to mitigate them. Section V summarises the paper and describes future works