Basic Research of Key Technologies for Next Generation Global Navigation Satellite System

Michito Imae(imae(AT)

Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184-8795, Japan

1. Introduction

GPS (Global Positioning System) is one of the most popular navigation systems and it is used in very diverse application areas, such as precise geodesy, time comparison, meteorological purposes.

On the other hand discussions for the next generation global navigation system (GNSS), and how Japanese government can contribute to this system has been made on several occasions.

Depending on such discussion, the committee of space development of Japan made a scenario for next generation GNSS.

Its basic policy is:
Japan should establish basic research and development items to contribute to the next generation GNSS, such as on board atomic clock, precise time and frequency transfer between ground clock and satellite on board clock and precise and real time orbit determination technique.

CRL has started research and development on the above items during this fiscal year.

2. R & D Items for Next Generation GNSS

CRL has initiated the following main research and development items this year:

(1)Development of on board Hydrogen Maser type frequency standard; Atomic standard section is in charge of this item. They started development of Hydrogen Maser type frequency standard in cooperation with a Japanese private company. They are going to construct a prototype within four years. It will be have almost same frequency stability as a laboratory type and its weight will be 50 - 70 kg.
(2)Highly accurate time and frequency transfer technology between ground station and satellites: Frequency and time standards section started development of an accurate time and frequency transfer technique between space and ground station. They are planning to use two way transmission mode to cancel the effects of propagation medium, such as ionosphere and troposphere, and use carrier phase of the signal to obtain precise measurement.
(3)Highly precise and real time orbit determination technique. Concerning this item, CRL has just started discussions concerning the method which should be most suitable for the next generation GNSS system.

3. Relation to the ETS-VIII Satellite

ETS-VIII satellite is "Experimental Technology Satellite VIII" which will be launched in 2002. NASDA (National Space Development Agency) has plans to equip this satellite with atomic clocks. The on-board atomic clocks will be commercial type Cesium clocks. By using these atomic clocks NASDA plans to carry out basic experiments in navigation.

A working group for the satellite navigation system was organized by the members of CRL and NASDA to discuss the function of the ETS-VIII on-board atomic clock equipment and experiments using it.

Updated on November 20, 1997. Return to CONTENTS