Taketoshi Iyota

Indoor positioning for moving objects using a hardware device with spread spectrum ultrasonic waves

Moving objects, especially autonomous mobile robots, require information of indoor self-location with high accuracy to reach their destination safely and correctly. In this study, we aimed to measure the indoor position of a moving object using SS (spread spectrum) ultrasonic waves, and we discussed the accuracy of the moving distance measured using a newly developed hardware device. In the case of static object, we showed that because of the noise tolerance of SS waves, a distance up to 20 [m] could be measured between a transmitter and a receiver on cm-order. To detect the SS ultrasonic signals, correlation calculations were carried out between a range of received waves and same range of replica signals; the replica signals were the same as the transmitted SS signals. Popular positioning systems using SS electrical waves employ signal acquisition to calculate coordinates of objects from correlation values and signal tracking to measure the relative shift of distances of moving objects. It is difficult for the system using SS ultrasonic waves to continue tracking because of the decrease in the self-correlation value due to the Doppler effect that acted on a moving object. To solve this problem, we proposed a tracking method for keeping correlation values by limited range of correlation calculations. In this study, for obtaining real-time updates of positional information from the relative shift, an experiment of distance measurement was also conducted using a newly developed hardware device that was used to carry out signal acquisition and the proposed tracking method. The results show that real-time signal tracking with our method could be realized, same as existing software between +/- 0.5 [m/s]. This paper reports that we can expect self-localization of robots using this system.

Hardware design of vector code correlation method for high-speed template matching

Template matching has been applied to the image processing of the fields such as security and robot vision to recognize a target from images. The method used in those fields requires the high-speed processing and robustness to illumination change or occlusion. To accommodate this, we employ a method, named the vector code correlation (VCC) that codes the gradient of intensity change, but the method on software is not enough in aspect of image processing time. Therefore, the purpose of this study is to achieve the template matching in real-time by designing hardware to implement the VCC method at high speed. The hardware design consists of five modules doing pipeline processing and is able to realize in relatively small scale. In the present paper, experimental results of 60 fps obtained with the designed hardware and its configuration are shown.

Measurement accuracy on indoor positioning system using spread spectrum ultrasonic waves

This paper describes significant factors on spatial error distribution measured in a given indoor space with a local positioning system which utilizes spread spectrum ultrasonic waves generated by narrow directional ultrasonic transmitters. The positioning error has interestingly been discussed from the viewpoints of the dilution of precision (DOP) and the ranging error due to the transmitter directional characteristic, mainly. The indoor 3-D position is calculated by means of an algorithm using distances from the transmitters located at the four corners of the ceiling to a mobile receiver. From the result of these experiments, it has been usefully found that the positioning error can be more largely influenced on the DOP of vertical direction than it of horizontal direction and that its average is of 3.43[cm] rms for all 3-D measurable points. These findings obtained from the work imply that the 3-D indoor positioning can be realized with an acceptable centimeter-order of precision. Moreover, they suggest that it has to be considered from the viewpoints of not only the ranging error, which could be yielded by the distance measurement, but also the DOP, which is inevitably obtained by a geometrical arrangement relative to the transmitters and receiver.

FPGA-Based Image Processor for Sensor Nodes in a Sensor Network

A field-programmable-gate-array- (FPGA-) based image processor which can be used for sensor nodes in a sensor network has been proposed and developed. Image processors for the nodes must satisfy requirements such as low power consumption, small circuitry scale, and modifiability of the hardware architecture. By developing an image proces- sor designed using an FPGA, SRAM modules, and the vector code correlation method which is suitable for the construc- tion of the target hardware architecture, it was possible to ensure that the processor satisfies these requirements. In this paper, we present the details of this image processor, which employs the template matching method for target tracking as well as the background subtraction method for object extraction. In addition, in order to verify its applicability in sensor nodes, we demonstrate the usefulness of the image processor from the results of an experiment in which the template matching and background subtraction methods were implemented simultaneously.

Real-Time Distance Measurement for Indoor Positioning System Using Spread Spectrum Ultrasonic Waves

The fields of application for position information have been expanded along with developments in the information-driven society. Outdoor position information systems such as car navigation systems that use the global positioning system (GPS) have spread widely. On the other hand, indoor position information is also important for humans and robots for self-location and guided navigation along routes. However, as the signals from satellites seldom reach indoors, it is hard to convert a directly outdoor positioning system to an indoor one. Therefore, systems that use sensors such as pseudolites (Petrovsky et al., 2004), infrared rays (Lee et al., 2004), or ultrasonic waves (Shih et al., 2001) have been investigated for use in indoor positioning.

An information addition technique for indoor self-localization systems using SS ultrasonic waves

In this paper, we propose an information addition technique for a 3-D indoor positioning system using spread spectrum (SS) ultrasonic waves, and evaluate its effectiveness. The system can position a target with high resolution, noise tolerance, and an ability of implementing CDMA by SS code using a limited number of transmitting channels. An M-sequence is employed as the SS ultrasonic code. Our aim is a positioning system for self-localization of people and robots; the location of a receiver installed on a target can be measured with SS signals from transmitters mounted in the positioning area. To evaluate the effectiveness of the proposed technique, an experiment to measure the distance from transmitter to receiver was conducted with the original hardware used with this technique. In this experiment, 4-bit information in a period of the M-sequence, generated by an 8-bit shift register, was applied. The result showed that the distance from transmitter to receiver and the added information can be detected at the same time. This experiment demonstrated the effectiveness of the information addition technique for SS ultrasonic waves.

Code division positioning by continuous signals using spread spectrum ultrasonic waves

Indoor real-time positioning is required in order to realize self-localization for autonomous mobile robots. In particular, accurate control in plural mobile robots requires 3-D coordinate information. This paper presents the positioning accuracy and response time for a 3-D real-time indoor positioning system which uses continuous spread spectrum ultrasonic signals that are generated and detected using inexpensive all-purpose transducers, and a Code Division Multiple Access (CDMA) communication system. For application with moving targets, we propose signal acquisition and tracking using continuous signals in analogy to the already effective Global Navigation Satellite System (GNSS). The proposed calculation algorithm for coordinate acquisition is based on the Newton-Raphson method for continuous signals. The calculation time and accuracy of this method is verified by conducting a positioning experiment. The results show that the positioning error is less than 50 mm in a 4000 mm by 4000 mm experimental space with 4 transmitters. Moreover, the maximum response time to update a result is 80 ms, displaying the efficacy of this system for robot navigation.

Verification of CDMA and accuracy on echo ranging system using spread spectrum ultrasonic signals

This paper proposes the echo ranging system with spread spectrum ultrasonic signals for automobile robots. The spread spectrum signals have noise-proof property and an ability of code division multiple access (CDMA). To verify them on reflected waves, an experimental system for indoor echo ranging dealing with spread spectrum modulations was installed on original PCI hardware connected PC, and experiments for verification of CDMA and measurement accuracies were conducted. Results of the experiments indicated usefulness of the echo ranging system with spread spectrum ultrasonic signals.

Accuracy of distance measurements using signal tracking of spread-spectrum ultrasonic waves with CDMA

Autonomous robots moving indoors require information about their position with high accuracy in order to reach their destination safely and correctly. To realize self-localization for such autonomous robots, we aim to measure the indoor position of a moving object by using signal tracking with spread-spectrum (SS) ultrasonic signals. In this paper we investigate the accuracy of distance measurements using signal tracking of SS ultrasonic signals using Code Division Multiple Access (CDMA). To detect the SS ultrasonic signals, we perform correlation calculations between a range of received waves and a similar range of replica signals identical to the transmitted SS signals. Conventional positioning systems using SS signals employ signal acquisition to calculate the coordinates of objects from correlation values and signal tracking to measure the relative shift of distances of moving objects. After investigating the signal acquisition method, we found that 3-D positioning with an error of 50 mm was possible, even when transmitting simulcast ultrasonic signals with CDMA. Other studies using our proposed signal tracking method for moving targets without CDMA have maintained correlation values using a limited correlation range for correlation calculations, though they have yielded reduced correlation values for unmoving targets. In this paper, we develop a signal tracking method using the simulcasting of multiple signals with CDMA and discuss its effectiveness. We conduct an experiment on distance measurements to determine the methods measurable range and measurement error. We perform ten measurements of distances from 1000 to 6000 mm between a transmitter and a receiver, in 1000 mm intervals, using 50% of the correlation range. The results indicate an average measurement error of 11 mm, which is less than that of conventional signal acquisition methods.

Practical applications of the brightness approximation plane method with a simple parameter

When processing an image that contains complex intensity changes, it is generally difficult to select an appropriate processing technique and to determine suitable weighted coefficients for a specific purpose since such choices require an advanced level of understanding and experience of image processing technology. To overcome these problems that occur in actual applications, we have attempted to simplify the parameter setting for detecting complex intensity changes by using the brightness approximation plane method that is capable of detecting a wide range of intensity changes by adjusting the sizes of its parameters. This paper describes the advantages of applying this simplification to applications in real environments. In addition, we verified the effect of changing the section size on the ability of the method to detect intensity changes and how this detection ability was affected by using a one-parameter filter compared with using a conventional differential filter ; this was done by estimating the acceptable range for intensity gradients and the robustness to capture noise. The experimental results for detection ability and robustness demonstrated that the proposed method has considerable potential to be used on-site in practical applications.