Eihisa Morikawa

CURRENT STATUS OF NeLS PROJECT: R&D OF GLOBAL MULTIMEDIA MOBILE SATELLITE COMMUNICATIONS

The paper presents the recent situation of the research and development on global multimedia mobile satellite communications system using non-geo type satellite constellations. This system is called Next-generation LEO system (NeLS). NeLS research center has carried out the key technology development of the satellite constellation system, which would provide a global mobile satellite service with broadband handheld terminals. The paper presents the development results of key technologies including the digital beam forming (DBF) satellite antenna, optical inter-satellite link system, on-board switching system.

Optical terminal for NeLS in-orbit demonstration

This paper presents outline of the optical terminal for Next-generation LEO System (NeLS) in-orbit demonstration, which will be conducted as part of Phase 2 of NeLS project. Two small satellites are assumed to launch into GTO orbit changing distance between them from 500km to 3000km. Acquisition and tracking experiments with a star or planet and 2.4Gbps data transmission between two SmartSat is also planned. The design of optical terminal is briefly presented.

Components development for NeLS optical terminal

Next-Generation LEO System (NeLS) Research Center is now conducting continuous effort to demonstrate feasibility of key technologies for optical inter-satellite links in space. Evaluation of critical components for the NeLS optical terminal, such as Wide-range FPM, RX-collimator combined with a fine tracking sensor and devices for optical receiver, were carried out using trial models. In this paper, performance evaluation results are presented including mechanical environmental test and radiation test.

Development of Thermal Control for Phased Array Antenna

A direct radiating phased array antenna is expected as a next generation communication antenna on the low earth orbit (hereafter LEO). A thermal control plate, Looped Heat Pipe plate (hereafter LCHP) made of a pulsating heat pipe (hereafter PHP), is promising for thermal device (1) . It is applied to the antenna panel which is directly boarded a communication device of high heat flux density, that is a solid state power amplifier (hereafter SSPA), a digital beam forming (hereafter DBF), and so on. Two development models are manufactured; the one is a thermal verified model (1000mm x 1300mm x 2 pieces) and the other is a coupon panel (708mm x 708mm). In both the above LCHP are laid down the component side of the antenna panel opposite to RF radiation side. LCHP is double in layer; the PHP fine tube of upper layer and that of the lower one are crossed at right angle each other. We obtain by vacuum test of the thermal model in LEO thermal environment that a temperature difference all over the LCHP side is a several degree C and a thermal conductivity of LCHP is at least from 10 to 20 times higher than one of a typical aluminum alloy. We also confirmed by a thermal test of coupon panel in temperature controlled air flow (ambient camber) and thermal vacuum test that the effective thermal conductance depends on a position of heater, it little depends on the inclination of LCHP, and an effective thermal conductance of the dissipation heat case is higher than the other heat cases (top heat case and bottom heat case). This paper describes the thermal design of the array antenna panel, the development model (thermal verification model, and the coupon panel), a test (a thermal vacuum test, and a test in temperature controlled air flow).

Evaluation of a high-power optical amplifier for intersatellite links

NeLS project is a Japanese effort aiming to develop key technologies for global multimedia mobile satellite communications service. In the NeLS System, all satellites are connected to four neighboring satellites by using optical inter-satellite link (ISL) considering four-wave WDM technology. Optical ISL requires very high optical output power. And to meet such requirements, a high power optical amplifier such as EDFA will be used. In such case, nonlinear effects of an EDFA will casue degradation of communication performance of OISL. We develoepd an OISL-WDM Simulator to eavluate such degradation experimentally. A Yb co-doped EDFA is used as OHPA. In the experiment, BER characteristics were measured and found that degradation is 0.4dB up to 2W output and 0.9dB at 4.5W output. From these results we concluded this technology could be applicable to WDM optical intersatellite link applications.

STUDY OF OPTICAL AMPLIFIERS FOR INTER-SATELLITE LINKS

global multimedia mobile satellite communications service with a user data rate around 2 Mbps for handy terminals. The target year for commercial implementation is 2010. Nextgeneration LEO System Research Center (NeLS) was formed in the end of 1997 as a research group under the Telecommunications Advancement Organization of Japan (TAO), in cooperation with the telecommunications operators, manufacturers, universities and governmental research organization. In prosecuting this project, two-phase approach, phase 1 and phase 2, is considered. Phase 1, which is the system definition and development of key technologies, has been completed. From last year Phase 2 has started to develop flight hardware targeting in orbit demonstration around

A Study of CDMA User Link for NeLS Global Multimedia LEO Satellite System

This paper deals with the configuration of a user link and proposes a CDMA based multimedia transmission scheme for the up link of the next generation low earth orbit satellite (NeLS) system. To realize the proposed NeLS system, this paper deals with user link part, and proposes QS-CDMA as a candidate for up link multiple access method. In order to simplify the initial acquisition and synchronization scheme to establish connection, the position information of the user terminals assume to be known. The required accuracy of the position information is evaluated.

Development of A Distortion Feedback C-Band Amplifier for Phased Array Antenna

The next-generation LEO System Research Center of TAO has been developing a C-band solid-state amplifier (SSPA) for the active phased array antenna at the LEO satellites. We have proposed distortion feedback amplifier to meet the requirements for realizing the antenna array – compact-sized, lightweight and high-linearity. In our distortion feedback amplifier, input and output signals of the amplifier are compared, amplifier distortion is extracted and the distortion is fed back with the inverse phase of the input signal. By using this principle, less power consumption has been realized in comparison with a feed-forward amplifier because of its low output power loss and lack of sub-amplifiers having high power consumption. Phase and attenuation in the distortion feedback amplifier should be controlled so as to adapt to changes of environment such as temperature under operating. We have also developed a parameter control method in which no additional RF circuit is necessary and controller can be kept small and lightweight even for plural amplifiers in array antenna system. Through evaluation experiments for prototype amplifiers, it was clarified that the principle of distortion feedback achieves a high-linearity amplifier which can reduce the third order distortion by 15 ~ 20 dB and can get the distortion of less than -53 dBc. It was also shown that output power can increase by 8 dB (6.3 times) at a distortion of -54dBc.