Takuji Ebinuma

Dynamic characteristics of very-high-rate GPS observations for seismology

GPS observations with higher than once-per-second sampling are becoming increasingly important for seismology. A number of reports have shown that very-high-rate GPS receivers are capable of capturing dynamic ground displacements from significant earthquakes. The higher output rate, however, does not necessarily mean higher frequency content of the corresponding observations. In order to examine dynamic effects on very-high-rate GPS observations, the frequency response characteristics of several geodetic GPS receivers were evaluated using a GPS signal simulator in controlled laboratory conditions. The tested receivers include Trimble Net-R8, NovAtel OEMV, and TOPCON Net-G3A. The experiment results suggest that the dynamic characteristics of the signal tracking loops put a limit on the frequency of the received signals, and all the tested receivers except for Trimble show good signal tracking performance at up to 5 Hz under dynamic stress of 2 G acceleration. The power spectral densities of the kinematic solutions obtained from the simulated seismic motion of the 2008 Iwate-Miyagi Inland earthquake (Mw 6.8) are also evaluated. The power spectral densities of both the NovAtel and TOPCON receivers agree with the simulated ground displacement at up to 5 Hz. By contrast, the Trimble receiver provides a pronounced increase in spectral energy above 2 Hz.

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.

High-accuracy IMES localization using a movable receiver antenna and a three-axis attitude sensor

A method to improve positioning accuracy of an indoor messaging system (IMES) was developed. This method uses Doppler shifts (produced by moving a receiver antenna) and three-dimensional attitude to determine the position of the receiver. A rotation-type Doppler-measurement system applying this method was developed. To evaluate the system, two experiments were conducted: in one, rotation radius of a movable receiver antenna was varied; in the other, position where positioning is conducted was varied. The experimental results show that the method can achieve centimeter- to decimeter-level positioning accuracy.

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.

Design of triple-band CMOS GPS receiver RF front-end

This letter describes the design of a triple-band Global Positioning System (GPS) receiver that simultaneously covers the L1, L2 and L5 frequency bands. The proposed receiver uses an imagerejection technique that can separate signals from the three frequency bands to three corresponding ports. It uses a single RF path containing a low-noise amplifier (LNA), and active and passive mixers with a pair of local oscillator signals. The triple-band GPS RF front-end chip is fabricated using 130 nm CMOS technology, and has a noise figure of less than 7.1 dB and an S11 coefficient of less than −10 dB in the frequency range 1.15-1.6 GHz. The experimental results demonstrate a 35-40 dB image rejection ratio at each output port with a power consumption of 7.2 mW (LNA and mixers) using a 1.2 V supply voltage.

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.

RF front-end architecture for a triple-band CMOS GPS receiver

This paper describes a triple-band global positioning system (GPS) receiver that simultaneously covers the L1, L2, and L5 frequency bands. The proposed receiver uses an image-rejection technique that can separate signals from the three frequency bands to three corresponding ports. It uses a single RF path containing a low-noise amplifier (LNA), and active and passive mixers with a pair of local oscillator signals. A triple-band GPS RF front-end chip was fabricated using 130nm CMOS technology. The noise figure of this chip is less than 7dB and its S11 coefficient is less than - 10 dB in the 1.15-1.6GHz frequency range. The power consumption of the LNA and mixers is 7.2mW when using a 1.2V supply voltage. The image-rejection ratio (IMRR) between L1 and the other (L2 and L5) band signals is 40dB, while that between the L2 and L5 signals is 37-38dB. To improve the IMRR between the L2 and L5 signals, we investigated the utilization of a digital compensation technique. This technique was confirmed to have improved the IMRR by about 12dB.

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.

The study of the remote-sensing application using the GNSS reflected signal with the aperture synthesis

This paper presents the algorithm to synthesize apertures using reflected GPS signal. In this concept, while GPS satellite is utilized as non-cooperative transmitter, receiving platform flies much closer to the Earths surface and therefore there is an asymmetry in the geometry. Hence we refer to this geometry as quasi mono-static and by considering this asymmetry as well as the characteristics of GPS signal, we established the algorithm to reconstruct the PSF from the reflected GPS signal. We also conducted a hardware simulation by using GPS signal generator and confirmed the validity of our proposed theory.