Katsuyoshi Arai

OICETS on-orbit laser communication experiments

We present the results of the on-orbit free-space laser communications between the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) and the Advanced Relay and Technology Mission (ARTEMIS) geostationary satellite. We first introduce the history of developing OICETS and add some descriptions on characteristics of OICETS, where the performance of the optical communication terminal named the Laser Utilizing Communications Equipment (LUCE) is also stated. We summarize the on-orbit investigation results of LUCEs function and finally make a report on the inter-orbit laser communication experiment carried out by ARTEMIS and OICETS.

Ground-to-satellite laser communication experiments

Ground-to-satellite laser communication experiments between the optical ground station located in Koganei, central Tokyo, and a low earth orbit (LEO) satellite were jointly performed by the Japan Aerospace Exploration Agency and the National Institute of Information and Communications Technology. In 18 trials during three non-consecutive months, the satellite was acquired and tracked 61 % of the time, when clear or partly-clear conditions were predominant. The optical link was maintained for about 6 minutes when the satellite was visible in spite of the high angular velocity of the satellite. In 3 of the 18 trials, the link was not interrupted due to clouds during the six-minute transit. The failures (39% of the time) occurred when cloudy or rainy conditions were predominant. Fluctuation in the uplink received signal power was minimized by using multiple laser beam transmissions. The measured uplink and downlink bit error ratios were 10-7-10-4. These results demonstrate the applicability of free-space laser communication for not only geostationary earth orbit-LEO optical links but also ground-to-LEO optical links.

Overview of the inter-orbit and the orbit-to-ground laser communication demonstration by OICETS

The experiment results on the inter-orbit laser communications between OICETS and a geostationary satellite and the results of two kinds of orbit-to-ground laser communications between OICETS and ground stations are summarized. The geostationary satellite for the inter-orbit demonstrations is the European Space Agencys geostationary satellite, ARTEMIS, and the ground stations for the orbit-to-ground demonstrations are of the National Institute of Information, and Communications Technology (NICT) in Japan and the German Aerospace Center (DLR), respectively. The descriptions of those experiments contain some statistically analyzed results as well as data samples measured during the demonstrations. The authors present the overview of these demonstration progresses and discuss on the results.

Ground-to-satellite optical link tests between Japanese laser communications terminal and European geostationary satellite ARTEMIS

Optical acquisition, tracking and communication tests were performed between a Japanese laser communications terminal placed within the ESAs optical ground station at Tenerife, Spain and a European optical payload onboard the ARTEMIS satellite in geostationary earth orbit at 21.5° East. The optical communications tests at Tenerife were to verify the end-to-end optical characteristics such as intensity, sensitivity, wavelength, and polarization, as well as the modulation scheme of optical signals and acquisition sequences of the terminals under fairly good atmospheric conditions. The downlinks bit error rate was on the order of 10-10 in spite of atmospheric turbulence. Atmospheric turbulence induced signal fading increased the uplink bit error rate, the best value of which was 2.5x10-5. The Japanese laser communication terminal itself autonomously established and maintained the ground-to-satellite optical link with the ESAs optical payload from the beginning to the end of a 20-minute session. The test results show that the laser communication terminal which is to be launched with the Japanese OICETS satellite is optically compatible with the optical communications payload onboard the European ARTEMIS satellite.

Data analysis results from the KODEN experiments

The first bi-directional laser communications demonstration between the optical ground station developed by the National Institute of Information and Communications Technology (NICT) located in Koganei, Tokyo and the Optical Inter-orbit Communication Engineering Test Satellite (OICETS) was successfully conducted in March, May, and September, 2006. The Kirari Optical communication Demonstration Experiments with the NICT optical ground station (KODEN) were jointly conducted by the Japan Aerospace Exploration Agency (JAXA) and NICT. Data from the uplink and downlink optical communication links were analyzed. For the downlink, the scintillation index agreed well with the theoretical results calculated based on the strong fluctuation theory. The aperture averaging effect was the dominant factor in reducing the variation of the downlink signals. The probability density functions as a function of elevation angles were measured and compared with the theoretical model, showing good agreement. For the uplink, the scintillation index disagreed with the calculated results based on the strong fluctuation theory. The multiple beam effect of the uplink transmission with large beams will have an additional reduction factor, which will help to establish ground-to-satellite laser communication links in the future. Four laser beams transmitted from the optical ground station to the OICETS satellite also helped to reduce the optical signals intensity fluctuation due to atmospheric turbulence.

Ground-to-OICETS laser communication experiments

Ground-to-satellite laser communication experiments between the optical ground station located in Koganei of downtown Tokyo and a low earth orbit (LEO) satellite, the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) called Kirari, were successfully performed in March and May, 2006. The optical communication demonstration experiment at the optical ground station was conducted in cooperation between the Japan Aerospace Exploration Agency (JAXA) and the National Institute of Information and Communications Technology (NICT). Ten trials over the course of two months were conducted during the test campaign. Acquisition and tracking of the satellite were successful on seven days out of the assigned test days. The tests were unsuccessful during three out of the four days when it was cloudy or rainy, but they were successful on all six of the days when partly clear skies were predominant. For the uplink, the fluctuation of the received signal power was well minimized by using multi-beam laser transmissions. The bit error ratio (BER) on the downlink was measured to be as low as 10-5. The applicability of the onboard optical terminal was demonstrated, aiming not only for geostationary earth orbit (GEO)-LEO links but also for ground-to-LEO optical links.

Tracking and pointing characteristics of OICETS optical terminal in communication demonstrations with ground stations

The tracking and pointing performance of the Laser Utilizing Communications Equipment (LUCE) equipped on the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) is presented. The operation characteristics of LUCE observed in the ground-satellite communication demonstrations are focused on. Since the angular movement of LUCEs optical antenna required in the ground-satellite trials exceeds the specification demanded in the inter-satellite communications, the marginal performance for proper tracking and pointing can be observed. During the ground-satellite communication trials, the ground stations found periodical discontinuances in the optical link. By looking at the LUCEs telemetries, the cause of the repeated breaks is revealed.

Laser beam propagation in ground-to-OICETS laser communication experiments

The first bi-directional laser communication demonstration between an optical ground station and the Optical Inter-orbit Communication Engineering Test Satellite (OICETS) was successfully conducted in March, May, and September, 2006, with an uplink of 2 Mbps and a downlink of 50 Mbps. The optical ground station, located in Koganei, Tokyo, Japan, is operated by the National Institute of Information and Communications Technology (NICT), Japan. Four laser beams were transmitted from the optical ground station to the OICETS satellite in order to reduce the optical signals intensity fluctuation due to atmospheric turbulence. The optical scintillation as a function of the number of beams and the frequency response were measured, and the uplink and downlink laser transmission results were obtained.

Observation of atmospheric influence on OICETS inter-orbit laser communication demonstrations

The experimental results of an inter-orbit laser communication performed under an atmospheric influence is presented. The demonstration was planned so that the optical link was supposed to graze the earths rim because of the satellite revolution around the earth. The trial was successfully carried out on 5th April, 2006. The measured experimental data are introduced to show the temporal behavior of the OICETSs optical terminal. The atmospheric influence on the optical link is calculated with a theoretical model to obtain a probability density of normalized intensity as a predictive value. The probability density is also estimated from the experimentally measured data. The comparison shows that the theoretical prediction well describes the experimental results.

An overview of the KODEN experiment between the OICETS satellite and the optical ground station in NICT

SummaryThe KODEN is a first in-orbit laser communication demonstration between a low earth orbit satellite called OICETS/Kirari and an optical ground station at the National Institute of Information and Communications Technology (NICT) in Koganei, Tokyo. Optical links could always be established even under atmospheric turbulence when partly clear skies were predominant in March, May, and September, 2006. The uplink and downlink bit error ratios were measured to be 10−7–10−3. This achievement is a milestone for future high-data-rate satellite communications.ZusammenfassungDas Akronym KODEN steht für die erste erfolgreiche Demonstration eines Laserkommunikationsexperiments zwischen dem Satelliten OICETS/Kirari in erdnaher Umlaufbahn (LEO) und der optischen Bodenstation des staatlichen Institutes für Information und Kommunikation (NICT) in Koganei, Tokio. Trotz atmosphärischer Turbulenzen konnte die optische Verbindung stets hergestellt werden, unter vorwiegend wolkenfreiem Himmel in den Monaten März, Mai und September 2006. Die Fehlerbitraten der beiden Kommunikationskanäle lag zwischen 10−7–10−3. Das Experiment stellt einen Meilenstein in der Entwicklung zukünftiger Satellitenkommunikationssyteme mit hohen Datenraten dar.