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— Presentation at SII 2015 —
January 13, 2016
Fig. 1 Concept of IMES
The IEEE/SICE International Symposium on System Integration 2015 (SI International 2015; SII2015) was held in Nagoya, Japan on Dec 11 - 13, 2015 by the Institute of Electrical and Electronics Engineers, Inc. (IEEE) and by the Society of Instrument and Control Engineers (SICE).
In this conference, about 250 researchers from universities and enterprises in the world discussed various types of technologies such as Control technology, Robotics technology, Network system control, Plant engineering, System hardware, System software, and Integration platform. There were impressive presentations by many young researchers.
Research and Development Group, Hitachi, Ltd., made 2 presentations and this report shows one of them. This presentation is about the development of signal transmitters for IMES, which is an indoor positioning system proposed by JAXA to approach to seamless positioning with same GPS/GNSS receiver chip (Fig. 1). The title of the presentation is "Development of IMES Signal Transmitters".
Fig. 2 Prototype IMES signal transmitter
Smartphones with GPS/GNSS receiver chip have been platforms for location based services, which market is growing greatly. However, the radio signals from the GPS/GNSS satellites do not reach indoors such as inside buildings or underground areas. Therefore, another positioning system that can be used in indoor environments is necessary to locate the position of the users with smartphones.
Here, we focus on the IMES, which is expected to be an indoor positioning infrastructure because IMES receiver functions are implemented in some GPS/GNSS receiver chips.
However, conventional IMES signal transmitters have three major issues; oscillator's cost, low usability, and wired-configuration. In the present work, we developed an IMES signal transmitter from the three viewpoints corresponding to the conventional transmitters' issues mentioned above; respectively carrier wave generation with an HP-TCXO, the use of a 1/2 wave whip antenna instead of an RHCP antenna for the GPS, and wireless configuration using IEEE 802.15.4 transceiver module (Fig. 2).
Incidentally, multipath effect often occurs in indoor environments and decreases the C/N0 drastically. We found that IMES receivers are easily affected by a multipath caused by narrow dynamic range (Fig. 3). Hence, a transmission space diversity method (Fig. 4) is also proposed to improve the availability of IMES signal service area and the time to read positional messages of IMES signal.
A transmitter based on this method is developed (Fig. 5) and experimentally evaluated in underground shopping centers (Fig. 6).
IMES signal transmitter using this technology are introduced and used in public facilities.
IEEE: Institute of Electrical and Electronics Engineers
GPS: Global Positioning System
GNSS: Global Navigation Satellite System
JAXA: Japan Aerospace Exploration Agency
IMES: Indoor Messaging System
HP-TCXO: High-Precision Temperature Compensated Crystal Oscillator
RHCP: Right-Hand Circularly Polarized wave
(By KAWAGUCHI Takamasa)