The present invention concerns a radio-based positioning system comprising one mobile station and at least one stationary station, and particularly for determination of the spatial position of the mobile station, and a method to increase the measurement precision of the radio-based positioning system.
Radio-based positioning systems are known in many embodiments; for example, “Wireless Local Positioning” by the authors M. Vossiek, L. Wiebking, P. Gulden, J. Wieghardt, C. Hoffmann and P. Heide, which appeared in Microwave Magazine of the IEEE (volume 4, issue: 4, December 2003, page 77-86) (“Wireless Local Positioning”), provides an overview.
Radio-based positioning systems function such that radio signals are exchanged between a mobile station and mostly a plurality of stationary stations. Either the relative distances between the mobile and one or more stationary stations or the relative angles between the mobile and every two stationary stations are determined based on the received radio signals. The spatial position of the mobile station can then be determined by way of trilateralization or triangulation on the basis of these measurement values.
Given a radio-based positioning system, a significant problem exists in that the radio signals here must largely propagate undirected in space. This is required since the relative position between the mobile unit and the stationary unit is not known in advance (for example, in contrast to radio links). However, the undirected emission of radio waves leads to the situation that the signals between the mobile unit and the stationary unit can be transferred not only via the shortest direct path but rather, for example, can be reflected on walls or objects and therefore also can be transferred via detoured routes.
Under the circumstances, a large corruption of the positioning result results from these detours. This problem, known as the multi-lane or, respectively, multi-path problem, is particularly critical given an interior application and is the leading factor that limits the achievable precision of radio-based positioning systems. As is also stated, for example, in the aforementioned article by M. Vossiek, et al., however, many applications that require a high measurement precision exist in the interior situation, and particularly in the field of virtual reality and automation engineering. Such applications are only to be executed in a very limited manner or not at all with the radio positioning systems known or available today.
It is also known that assisting sensors (for example, acceleration sensors, gyroscopes, odometers, compass sensors, inclination sensors, yaw sensors, linear or angle encoders, etc.) can be used very advantageously to improve the precision of radio positioning systems. These assisting sensors are for the most part relative sensors, thus those that determine not absolute position but rather the variations relative to an initial position in a reference space. These multi-sensor or, respectively, hybrid systems for the most part operate such that the measurement information of the different sensors can be combined with the measurement data of the radio positioning system (for example, in a Kalman filter) based on movement models.
From an information technology view, what is disadvantageous in such systems is that the individual end results are linked with one another instead of the raw data of the sensors, such that information can possibly be lost via the processing in the sensors. If, for example, the radio sensor were to determine a wrong distance value due to a critical multi-path situation, this strongly error-ridden value would enter into the evaluation/combination. The error could possibly be recognized and reduced via the hybrid approach, however the starting basis of the evaluation would be enduringly impaired via the incorrect measurement value.