Kenjiro Fujii

Positioning of vehicle on undulating ground using GPS and dead reckoning

A method of positioning vehicles on undulating ground is proposed. This method uses GPS data and internal sensor data (fiber optic gyro, roll pitch sensor, and wheel encoders) and improves the positioning accuracy by compensating the error of each sensor data. A prototype of autonomous mower using this positioning method was developed and its positioning performance was evaluated. The experimental results show that the fusion system is more accurate than using only the GPS or internal sensor system. When the accuracy of the GPS is 1 m, the accuracy of the fusion system is 0.2 m; this accuracy is enough to control the vehicles. We expect that the positioning system for vehicle control can be realized using a differential GPS with accuracy of 1 m instead of an expensive kinematic GPS.

GPS-compatible indoor-positioning methods for indoor-outdoor seamless robot navigation

The difficulty of applying “pseudolites” (i.e., pseudo-satellites) and the “indoor messaging system” (MES) to indoor robot navigation is investigated. Moreover, as an alternative to these methods, “high-accuracy IMES using real-time kinematic Doppler positioning” is introduced and experimentally evaluated. The evaluation showed that this method can achieve centimeter- to decimeter-level positioning accuracy. This result implies the feasibility of indoor-outdoor seamless robot navigation with a GPS/IMES receiver.

Doppler positioning with a movable receiver antenna and a single pseudolite for indoor localization

Pseudolites are one of the most promising technologies for indoor localization because they can directly use off-the-shelf GPS/GNSS receivers with minor change of their firmware. However, pseudolites have some fundamental issues such as near-far, multipath, and synchronization problems. Many of these issues derive from using more than one transmitter and trilateration. In this paper, we propose a novel indoor positioning method using a movable receiver antenna and a single pseudolite. In this method, the position is determined by using the Doppler shift produced by a moving antenna. We conducted an experiment by testing different conditions of the moving antenna. The results show that our method has the potential to achieve the positioning with decimeter level accuracy.

Position estimation and path control of an autonomous land vehicle

A method for estimating the vehicle position by using a fiber optic gyroscope and wheel rotation encoders, as wall as a method for controlling the vehicle path using a path attracting force model, has been proposed. A method for improving the estimation accuracy by using the Global Positioning System (GPS), along with the above sensors, has also been proposed. An autonomous mobile robot is developed bases on a manually driven lawn-mower, and the performance of the proposed methods has been studied experimentally. The experimental results show the effectiveness of the proposed methods, and practicality as an autonomous lawn-mower has been confirmed.

Doppler pose estimation using multiple IMES transmitters for indoor localisation

We propose a Doppler pose estimation method for an indoor messaging system (IMES) (‘pose’ refers to both position and orientation). With this method, both the position and orientation of a receiver are estimated simultaneously by using Doppler shifts produced by moving a receiver antenna with two or more IMES transmitters. The proposed method is evaluated through the identical experiments conducted in two different locations. In these experiments, the position and orientation of the receiver is estimated using two transmitters, and the achievable accuracy is evaluated by changing the separation distance between the transmitter antennas. The experimental results demonstrate that a positioning accuracy higher than a few decimetres and orientation estimation accuracy of higher than a few degrees are achievable when the measurement condition is relatively good (i.e. when the proper separation distance is set between two transmitter antennas and cycle slips do not occur). We also conducted an analysis for the convergence of initial values (which are used for the iterative position and orientation calculation in the nonlinear least-squares method). The results show that the initial values basically converge to appropriate position and orientation values as long as an inverse matrix in the position and orientation estimation process can be calculated. Moreover, we analysed the effect of the number of transmitters on position and orientation estimation precision. The results show that, as the number of transmitters increases, the precision of the position and orientation estimation also increases, and the precision is particularly high in the area surrounded by the transmitters.

Doppler positioning with orientation estimation by using multiple transmitters for high-accuracy IMES localization

A Doppler positioning method with orientation estimation for an indoor messaging system (IMES) is proposed. With this method, both position and orientation of a receiver are estimated simultaneously by using Doppler shifts produced by moving a receiver antenna under the use of two or more IMES transmitters. The proposed method is evaluated through an experiment in which the interval of two transmitters is varied. The results of the experiment demonstrate that centimeter- to decimeter-level positioning accuracy and orientation-estimation accuracy of ±3 degrees are achieved; these results were largely consistent with the theoretical values calculated from dilution of precision. In addition, magnetic-compass error indoors was experimentally investigated; the results show that a magnetic-compass is a large error source if it is used indoors. Lastly, which initial values of a nonlinear least-square used for the proposed method converge to appropriate position and orientation solutions is analyzed; the results of the analysis suggest that if an initial position is set to the midmost of two transmitters, a proper solution is obtained except in the case that initial orientation is 180 degrees opposite from the correct orientation.

Real-time kinematic Doppler pose estimation for IMES

In order to achieve the indoor localization with centimeter- to decimeter-level positioning accuracy under the use of the transmitters of “indoor messaging system” (IMES), a method called “real-time kinematic (RTK) Doppler pose estimation” is proposed. In this method, Doppler shifts are produced in the carrier waves transmitted from the IMES transmitters by moving the receiver antennas. The pose (position and orientation) of the receiver is then determined in real-time by using the Doppler shifts, inclination of the receiver, and geometric relation between the receiver antennas and transmitters. To evaluate the proposed method, an experiment with a mobile robot is conducted. The results of the experiment show that the proposed method can achieve a positioning accuracy of about 10 cm.

A combined approach of Doppler and carrier-based hyperbolic positioning with a multi-channel GPS-pseudolite for indoor localization of robots

A combined method of Doppler positioning and carrier-based hyperbolic positioning with a multi-channel GPS-pseudolite is proposed for indoor localization. This method uses carrier-phase output from a GPS/pseudolite receiver. The carrier-phase observable is precise but does not provide range information between the pseudolite and receiver antennas necessary for position calculation. This is because of the existence of carrier ambiguity. This problem can be solved by using the proposed combined method. In the present work, the positioning theory is established and experimentally evaluated with actual devices including a robot. The experimental result shows that a positioning accuracy of more than 10 cm is achievable.

Improving IMES Localization Accuracy by Integrating Dead Reckoning Information

Indoor positioning remains an open problem, because it is difficult to achieve satisfactory accuracy within an indoor environment using current radio-based localization technology. In this study, we investigate the use of Indoor Messaging System (IMES) radio for high-accuracy indoor positioning. A hybrid positioning method combining IMES radio strength information and pedestrian dead reckoning information is proposed in order to improve IMES localization accuracy. For understanding the carrier noise ratio versus distance relation for IMES radio, the signal propagation of IMES radio is modeled and identified. Then, trilateration and extended Kalman filtering methods using the radio propagation model are developed for position estimation. These methods are evaluated through robot localization and pedestrian localization experiments. The experimental results show that the proposed hybrid positioning method achieved average estimation errors of 217 and 1846 mm in robot localization and pedestrian localization, respectively. In addition, in order to examine the reason for the positioning accuracy of pedestrian localization being much lower than that of robot localization, the influence of the human body on the radio propagation is experimentally evaluated. The result suggests that the influence of the human body can be modeled.

Accurate indoor positioning using IMES radio

Indoor positioning still remains as an open problem, for the reason that it is difficult to achieve a satisfactory level of accuracy within indoor environment, using current radio based localization technology. Thus we try to investigate the utilization of IMES radio for high accuracy indoor positioning, because of its higher resolution radio map. Signal propagation model of IMES radio has been well investigated, based on which algorithms of trilateration and extended kalman filter are developed for both static and dynamic localization of a mobile robot using IMES radio. Experiments results show that a higher localization accuracy could be achieved.