WINDS (Wideband InterNetworking engineering test and Demonstration Satellite) / Kizuna
WINDS (nickname: Kizuna meaning "ties" or "bonds" or "get together") is a collaborative Japanese broadband communication technology mission within the "i‐Space" project of JAXA/NICT (Japan Aerospace Exploration Agency/National Institute of Information and Communications Technology). The objective is to advance information and telecommunications and network technologies to a next-generation level by demonstrating in geostationary orbit technologies necessary to construct the spaceborne ultra high‐speed global fixed wireless communications networks (Ka‐band). 1) 2) 3) 4) 5) 6) 7) 8) 9)
The i‐Space initiative of JAXA and NICT is to explore various applications of satellite communications in a broader context, to maximize the space infrastructure of the next generation whose construction is in progress.
The WINDS project covers development of the following new technological elements to be put into the practical use around 2010:
• MPA (Multi Port Amplifier). MPS is a high output power amplifier having eight ports. The MPA is capable of flexibly distributing needed radiation power in response to local traffic demands and the attenuation effects of raindrops.
• An electronically steerable APAA (Active Phased Array Antenna). APAA makes it possible to control the antennas communication direction flexibly and rapidly, thus communication links can be established within the Asia/Pacific region.
• Onboard high-speed baseband switching router: The device can conduct packet cell based switching up to 155 Mbit/s x 3 channels between I/O ports (developed by NICT).
- Verification of key technologies for ultra high data rate satellite communications in Ka-band such as 155 Mbit/s data transmission using USAT (Ultra Small Aperture Terminal) with 45 cm diameter antennas, or a transmission of 622 Mbit/s using a VSAT (Very Small Aperture Terminal) with 2.4 m diameter antennas.
- WINDS aims for a communication speed of 155 Mbit/s for residential use and 1.2 Gbit/s for office use.
Once placed in the designated geostationary orbit, the WINDS satellite will conduct various experiments in cooperation with user organizations in Japan and the Asia/Pacific region. The experiments will include improving connectivity with Internet networks, constructing an information infrastructure for monitoring national territory and disasters and bridging the digital divide.
Figure 1: Artist's rendition of the WINDS spacecraft (image credit: JAXA)
The spacecraft is 3-axis stabilized (zero momentum control); it has a launch mass of about 4850 kg and an in-orbit mass of about 2750 kg, the S/C size is 2 m x 3 m x 8 m (21.5 m with solar panels deployed). The onboard multi-beam antenna system (MBA) consists of two 2.4 m diameter main reflectors, wave guides corresponding to 19 beams, and a truss shaped antenna tower to hold them up. The mission design life is 5 years. 10)
Figure 2: Illustration of the WINDS spacecraft (image credit: JAXA)
Table 1: Overview of the WINDS spacecraft parameters
The bent-pipe mode of WINDS amplifies the received radio wave after converting the frequency and sends it to the Earth station. A 1.2 Gbit/s link can be achieved in this mode. The regenerative mode recovers a signal received with the ABS (ATM-based Baseband Switch) subsystem installed onboard and switches data. Different data can then be sent directly to the target Earth station. 11)
Figure 3: Overview of the WINDS/Kizuna major components (image credit: JAXA)
Launch: The WINDS spacecraft was launched on Feb. 23, 2008 with the H-IIA F14 vehicle from the Tanegashima Space Center, Japan. JAXA confirmed that the solar panels deployed nominally and that the spacecraft was in good health. 12)
Orbit: Geostationary orbit (GEO) over the Pacific Ocean at 143º E longitude, altitude ~ 35,786 km.
• March 1, 2019: End of KIZUNA mission. For about two weeks since a communications anomaly was first detected in KIZUNA/WINDS , the JAXA project team was striving to re-establish the link from the ground stations with the satellite. However, repeated attempts failed, forcing JAXA to determine that ground communications with KIZUNA were lost for good and to send a command at 3:54p.m. on 27 February 2019 to power off the batteries and transmitter aboard the KIZUNA satellite. — KIZUNA was co-developed by NICT (National Institute of Information and Communications Technology) and JAXA and launched aboard the H-IIA Launch Vehicle No. 14 from the JAXA Tanegashima Space Center on 23 February 2008. Since then, the KIZUNA satellite was operational, far beyond its 5-year design life. KIZUNA operations have led to many achievements. Broad high speed satellite communications technology was demonstrated. At the Great East Japan Earthquake in March 2011, KIZUNA was used to offer temporary communication lines in the disaster-stricken area and to provide government and other official organizations with disaster data. JAXA would like to express its heartfelt appreciation to all for their cooperation shown to the KIZUNA operation. 13)
Summary of KIZUNA accomplishments:
1) Satellite high-speed internet communication technology
- Verification of high-speed transmission technology at 3.2 Gbit/s, the world's fastest at that time
- Selected as "Best of what's new 2008" of Popular Science, an American quarterly magazine
- Seaborne transmission of under-water super hi-vision imagery from a sea vessel to the ground station.
2) Verification of super high-speed communication model to reduce internet access disparities in the Asia Pacific region
- Simultaneous internet distribution at multiple overseas reception stations
- Remote e-learning and medical experiments
- Quasi realtime processing of the VERA (VLBI Exploration of Radio Astrometry) observation data of the NAOJ (National Astronomical Observatory of Japan).
3) Verification of emergency communications by satellite high-speed transmission
- Emergency communications testing at disaster drills
- Assisting disaster relief at the Great East Japan Earthquake.
• According to the JAXA website, the WINDS/Kizuna mission is in operation as of 2018 (10 years on orbit as of 23 Feb. 2018). 14)
• The WINDS/Kizuna mission is operational in 2016 completing its 8th year on orbit on Feb. 23, 2016. 15)
• October 2015: In March 2011, the Great East Japan Earthquake of magnitude 9.0 hit over the large areas from the Tohoku region to the Kanto region and the Pacific coast areas were engulfed by repeated surging tsunami which reached more than 10 m in height in some locations. A lot of communication facility collapsed or submerged and underground cables were severed by the earthquake and the tsunami. At the worst case, up to 1.9 million landline phones were out of service and up to 29,000 cellular base stations stopped transmitting and receiving. Even in areas with no damage to communication facilities, the batteries for emergency were exhausted by the long term disruption of commercial power supply, therefore, some communication services were temporarily suspended. 16)
- JAXA conducted communication support using geostationary satellites such as WINDS/Kizuna and ETS-VIII in the disaster areas. WINDS is Ka-band broadband satellite and ETS-VIII is an S-band mobile communication satellite. JAXA provided the emergency communication line via WINDS, and contributed to the reconstruction in Iwate Prefecture affected by the the Great East Japan Earthquake. Additionally, the operations team gained valuable experience in lessons learned from the process of the support.
• The WINDS/Kizuna mission is operational in 2014. NICT developed a digital Ka-band 3 x 3 channelizer with signal processing bandwidth of 200 MHz to conduct research on WINDS/Kizuma. The system was developed and tested in support for a potential satellite disaster communications support request. The developed prototype channelizer has the capabilities of de-multiplexing multiple signals of IF input ports, switching and multiplexing signals for re-allocation of these signals into multiple IF output ports. As shown in Figure 4, the prototype is 3 x 3 port channelizer, which consists of A/D converters, de-multiplexers, switches, multiplexers, D/A converters, and control unit. The main features of the channelizer are high speed A/D, D/A, FPGA, and I/O. 17)
Figure 4: Schematic of channelizer (image credit: NICT)
In the experiment, the channelizer was located on the ground and WINDS Ka-band links (intra-beam link and inter-beam link) were dedicated for the experiment. It is confirmed that the degradation of the link performance by the channelizer such as transmission rate, latency, and BER are small enough for a useful disaster support. In the resource re-allocation experiment, it is observed that the frequency bandwidth of the signal from the input port assuming disaster area is smoothly increased as expected. In the resource reallocation experiment for normal/disaster scenario, TV conference video transmission via the channelizer and the WINDS satellite link was succeeded for both normal scenario (two users, 4 Mbit/s/user) and disaster scenario (four users, 2 Mbit/s/user), respectively.- It is confirmed that the accommodated number of users is increased in a disaster scenario by changing the setting of the resource allocation of the channelizer. From these results of the communications experiments, it is confirmed that the developed channelizer is effective as an effective means in disaster satellite communications.
• On Feb. 23, 2013, the WINDS/Kizuna mission was 5 years on-orbit, providing nominal operations. 18)
• In January 2013, JAXA and JMA (Japan Medical Association) signed an agreement to jointly conduct application experiments of the WINDS /Kizuna satellite to support disaster medicine, after JAXA and JMA studied the utilization method of the Kizuna in support activities and measures at the time of a large-scale disaster. 19)
In July, 2012, JMA and JAXA held demonstrations with scenarios of a huge earthquake. As a result, the agreement this time was signed aiming at establishing a more useful information sharing method at the time of disaster via the Internet satellite under the common recognition of supporting as many disaster-stricken people as possible.
• In 2012, the WINDS/Kizuna spacecraft is operating nominally.
• WINDS/Kizuna is operating nominally in 2011. Since its launch in 2008, JAXA has evaluated the performance characteristics of the APAA and also has conducted various experiments using WINDS user terminals. 20)
The APAA onboard WINDS, and its beam center of the transmitting and receiving phased array antenna, is able to point to any targets of interest within its range of coverage. In fact, the service area of WINDS can be extended to the full coverage area from GEO (almost one third of Earth's surface), and flexible satellite communication links can be established between any places in the region. NICT has developed VSATs, referred to as HDR-VSAT and SA-VSAT, to be of service in the APAA coverage area (Ref. 20). 21)
Broadband communication verification between KIZUNA and the ocean surface: JAXA and Ferry Sunflower Limited verified the functions, performance and usefulness of an experimental ocean station that was set up on a passenger liner for the Wideband Internetworking Engineering Test and Demonstration Satellite "KIZUNA." During the verification, the project confirmed stable high-speed communications with a sailing ship in a changing environment including fluctuating wave heights and weather conditions as well as navigating directions, thus it was verified that high-definition and high-quality teleconference services and use of the Internet were possible between the onboard crew and ground staff. 22)
• In March 2011, JAXA and NICT established a broadband environment using the Wideband Internetworking Engineering Test and Demonstration Satellite "KIZUNA" (WINDS) as support for disaster measures for areas stricken by the Tohoku Region Pacific Ocean Coastal Earthquake. - With this support, high definition teleconference systems, IP telephones, radio LAN and other means became available to share and dispatch disaster information. 23)
• The Great east Japan Earthquake attacked eastern Japan on March 11, 2011. As a result, a power failure followed the massive earthquake and an ensuing tsunami; the terrestrial network, including cellular phones, was damaged. Fourteen thousand cellular phone base stations were rendered unusable and trouble affected 1.5 million telephone lines. Interference was widely generated by the rapidly increased communication traffic reaching 10 times of its capacity. 24)
- NICT set up the WINDS transportable station at Kesennuma and Higashimatsushima and established the temporal broadband satellite link between the disaster stricken area and the Tokyo region.
- NICT received a request from the Tokyo Fire Department for the establishment of a broadband link using WINDS between Tokyo and Kesennuma, the tsunami-hit and heavily damaged city, where a Fire Emergency Response Team was sent.
- On March 14, NICT prepared the transportable WINDS station and moved to Kesennuma with the Fire Emergency Response Team. The transportable station was set up atop the Kesennuma fire station, where the disaster control station established. The WINDS broadband link was established on March 15 between the Kesennuma fire station and Tokyo Fire Department headquarters.
Figure 5: Satellite connection between Kesennuma and Otemachi (image credit: NICT)
- NICT moved the WINDS earth station to Higashimatsushima. From March 20 to April 5, NICT established a temporally broadband satellite link between Higashimatsushima (Miyagi Prefecture) and Iruma (Saitama Prefecture). The NICT Kashima Space Technology Center was connected from Higashimatsushima, which gave the Internet access through NICT Kashima. Internet connectivity is extremely important due to the difficulty in obtaining information on the disaster in stricken areas. - An HDTV conference system, IP telephone, PCs, etc. were also connected to the WINDS station.
Figure 6: Satellite link between Higashimatsushima and Iruma (image credit: NICT)
The WINDS satellite communication turned out to be an important service in such a situation. NICT carried out support for the disaster-response activities using its WINDS broadband link. An HDTV conference system, IP phone, file transfer system, Internet connection and other facilities were then prepared. Disaster and crisis-management groups used the WINDS link to exchange information between the disaster stricken area and headquarters (Ref. 24).
• WINDS/Kizuna is operating nominally in 2010 - providing the world's fasted Internet connection (155 Mbit/s) to residential user terminals of 45 cm in diameter, and 1.2 Gbit/s for business terminal with a diameter of 5 m.
Figure 7: Comparison of antenna diameters for WINDS and conventional satellites (image credit: JAXA)
Figure 8: Large area coverage with MBA (Multi Beam Antenna) function (image credit: JAXA)
• Demonstrations with the APAA (Active Phased Array Antenna), the first hopping spot beam antenna developed in JAXA, is working well by performing some communication experiments. The EIRP, G/T values are higher than the specification, and smaller Earth stations can communicate using the APAA. 29)
Figure 9: Schematic view of the APAA hopping capability within the coverage area (image credit: JAXA)
• WINDS is operational as of summer 2008 (it was declared operational in July 2008).
• On May 2, 2008, JAXA and NICT successfully achieved ultra high data rate communication at a speed of 1.2 Gbit/s (622 Mbit/s x 2 waves), which represents the fastest communication speed in the world via RF communication satellites. The demonstration was conducted between Kizuna's multi-beam antenna and a super high data rate Earth station (a 2.4m diameter antenna) set on a car at the NICT Kashima Space Research Center. 30)
Figure 10: Schematic setup of the 1.2 Gbit/s communications test between Kizuna and an Earth station (image credit: JAXA)
• The GEO orbit was reached on March 14, 2008.
• After WINDS entered the initial functional verification phase on March 1 (2008), the functions and performance of its onboard mission equipment have been verified. The functions that have been verified so far include the automatic tracking control of the multi-beam antenna and the output of approximately 280 W from the multi-port amplifier.
It was also confirmed that the Internet protocol (IP) communications with a transmission speed of 155 Mbit/s were successfully performed, as a part of the initial functional verification jointly conducted by JAXA and NICT between March 28 and April 7, 2008. Data were also sent in reverse, from the 1.2 m antenna to WINDS at 155 Mbit/s and then from WINDS to the 45 cm antenna at 155 Mbit/s. Throughout these transmissions, WINDS was in the regenerative switching mode, in which data sent from a ground station to a satellite, is demodulated in the satellite and sent to the destination ground station. The transmission speed of 155 Mbit/s from a satellite to an ultra small-size user terminal (antenna diameter of 45 cm) is the fastest data rate in the world in this configuration as of 2008. 31)
• Since March 2, 2008, WINDS has been performing orbit control maneuvers to inject itself into a geostationary orbit from a drift orbit. Normal operations are planned to start in late June 2008.
The communication payloads of WINDS are comprised of two dishes of multi-beam antennas (MBA), APAA (Active Phased Array Antenna), TX/RX IF switch matrixes (IFS), an ABS (ATM Baseband Switching) and a Multi Port Amplifier (MPA). The MBA covers Japan and south-east Asia with 19 fixed spot beams; the APAA covers the globe with two scanning spot beams. 32)
WINDS has two communication modes, which are: 1) a regenerative mode using the ABS, and 2) a bent pipe mode relay using the wideband transponder of 1100 MHz of frequency bands. The regenerative mode has three paths through the ABS, and the bent pipe relay mode has six paths through BPFs (Band Pass Filters). The IFS can distribute the TDMA (Time Division Multiple Access) signals of each time slot to the beams.
Figure 11: Block diagram of the WINDS bent pipe relay mode (image credit: NICT)
In the regenerative mode, the data rates of the uplink are from 1.5 Mbit/s to 51 Mbit/s, and the data rate of the downlink is 155 Mbit/s. In the service area of the MBA, an ultra small Earth terminal (USAT) with a 45 cm diameter antenna or a very small Earth terminal (VSAT) with a 120 cm diameter antenna can be used. When a VSAT transmits three carriers of 51 Mbit/s, the data rate of the uplink also corresponds to the downlink.
MBA (Multi-Beam Antenna) system:
The objective is to provide fixed beam communications at 1.2 Gbit/s (max) to Earth station antennas. The coverage of the antenna system embrace Japan and Asia/Pacific regions - with 12 beams aiming toward Japan, and 7 toward Asia/Pacific, using a total of 19 beams.
MBA is equipped with two main reflectors, two sub reflectors, a polarization separation grid panel, and feeds. The two groups of feeds are arranged face to face with the grid panel between them. One group of feeds is horizontal in polarization and the other is vertical. The grid panel passes the horizontal polarization beams and reflects the verticals in such a way that 19 feeds are configured efficiently in the limited space of the antenna system.
Figure 12: Overview of the MBA system (image credit: JAXA)
The antenna system has heat generating sources. The feeds and the wave guides generate 37.8 W as these lose the electric power output from the 300 W amplifier mounted inside of WINDS. The polarization separation grid panel generates 10.5 W maximum as radio waves pass through the panel. The tracking receiver and the low noise amplifiers collectively heat 10.6 W. An extensive heat analysis by JAXA and NEC Toshiba Space Systems was conducted for the thermal design of the MBA and verified by a number of tests. 33)
Figure 13: Communication configuration of MBA system (image credit: JAXA)
APAA (Active Phased Array Antenna):
APAA was developed by JAXA and NICT. The APAA is comprised of a transmitting and a receiving antenna, each of which is providing two hopping spot beams. The direction of each beam can be controlled independently, flexibly and rapidly. The two multiple beams also realize the SS-TDMA (Satellite Switched Time Division Multiple Access) communication function. The overall objective of the hopping spot beam and the SS-TDMA communication system is to utilize these features for broadband communication experiments covering the Asia/Pacific region. 34) 35)
Next to the transmitting (Tx) and receiving antenna (Rx), the APAA includes the following components: a BSC (Beam Steering Controller), DC/DC converters, heaters, a HCU (Heater Control Unit), and PDUs (Power Distribution Units). All components are installed in the antenna structure unit, which consists of aluminum honeycomb panels having heat pipes and thermal radiation plates. The APAA dimensions are 1420 mm x 920 mm x 1500 mm, the mass is 183 kg. The APAA also has a self-controlled thermal dissipation function to maintain a specified temperature range.
Figure 14: Block diagram of the APAA (image credit: JAXA)
Each APAA antenna (Tx and Rx) is composed of 128 horn antennas, 128 high power amplifiers (HPAs), and a beam forming network (BFN) with 256 digital phase shifters (PSs) for the beam-forming functions (two independent beams). Each RF signal into the beam input port is amplified and distributed independently to 128 way ports. The distributed signals are shifted to the desired phase and combined with both beams. The combined signals are amplified by the HPAs, having an output power of 28 dBm, and are radiated by the horn antennas (Figures 15 and 16).
The BSC controls independently the phase of all PSs in the transmitting and receiving antennas at 2 ms intervals, so each antenna radiates two independent hopping beams in accordance with SS-TDMA operations. Eight spot beam directions for each beam can be selected in the SS-TDMA. The BSC controls also the attenuators in the BFNs to compensate for gain variations due to temperature inputs.
For an APAA configuration, the satellite operator sends the beam direction parameters to the BSC; the BSC then calculates the phase data of each PS from these parameters. The number of phase data is 4,096 (128 PSs × 4 beams × 8 beam directions), calculated and memorized at one configuration time. When the SS-TDMA operation starts, the satellite operator points the beam direction to the BSC (period of 2 ms), and the BSC creates the commands from memorized phase data and sends them to all PSs of the transmitting and receiving antenna.
Figure 15: Illustration of the APAA configuration (image credit: JAXA)
Table 2: Performance parameters of APAA
Figure 16: Block diagram of the APAA system (image credit: JAXA)
The BSC also controls all operation modes of the APAA. For example, the BSC controls the phase of each PS automatically and serially in case of an APAA health confirmation mode. The APAA also has a mode in which the beam direction is fixed.
The 50 V bus voltage is down-converted by the DC/DC devices to each secondary low voltage node. The conversion efficiency is expected to exceed 80%. The PDUs are bus power distributors using a capacitor bank. The HCU controls the heaters to maintain the operating temperature. The antenna structure consists of an aluminum honeycomb material. The heat pipes are embedded in the North and East panels for thermal radiation.
ABS (ATM Baseband Switching) is used for onboard processing. ABS is a regenerative mode subsystem developed by NICT.
Table 3: ABS parameters
Figure 17: Overview of ATM Baseband Switching concept (image credit: JAXA)
MPA (Multi Port Amplifier):
The objectives of the MPA are to: 1) amplify and to combine the input signals, 2) provide a one-to-one connection between an input and output port, and 3) provide one to N (N= 1, 2, 4, 8) output connections among an input and multiple output ports with a 90º phase shift function of D-Amp (Driving Amplifier). 36)
The technical challenging items in the development of the MPA are:
• Enhancement of output power
• Improvement of isolation among the output ports (high performance of output isolation represents a technological achievement)
• Development of a broadband and high power TWTA (Traveling Wave Tube Amplifier)
• Uniform signal performance (amplitude, phase, etc.) throughout the 1.1 GHz bandwidth. High MPA performance implies linearity of amplitude and phase for amplifiers and the power distribution equipment.
Figure 18: Block diagram of the MPA (image credit: JAXA)
MPA consists of the following components:
- TWTA (Traveling Wave Tube Amplifier)
- D-Amp (Driving Amplifier) for the compensation of individual TWTA characteristics
- INMTX (Input Matrix) and OUTMTX (Output Matrix). Both are consisting of 12 HYBs, respectively. Each HYB is connected through a bend (E- or H-bend) waveguide.
- Waveguide switches (INSW/OUTSW) for exchange of operating D-Amps and TWTA ports.
Table 4: Main characteristics of MPA (Multi Port Amplifier)
Figure 19: Overview of onboard mission configuration of communication payloads (image credit: JAXA)
• Regenerative mode: MBA/APAA + IF Switch MTx (time division) + ABS
• Bent pipe modes:
- TDMA (burst signal): MBA/APAA + IF Switch MTx (time division)
- Continuous wave signal: MBA/APAA + IF Switch MTX (fixed state)
The regenerative mode and the bent pipe relay modes are also being used for IP (Internet Protocol) connection of internetworking.
The Earth station used for the bent pipe relay mode requires a 2.4 m diameter antenna for a 622 Mbit/s high speed network SDR-VSAT (Super-high Data Rate VSAT) and a 5 m diameter antenna for a 1244 Mbit/s high speed network LET (Large Earth Terminal) applications.
Table 5: Earth terminal parameters
Figure 20: Schematic of TDMA bent-pipe mode (image credit: JAXA)
Figure 21: WINDS coverage of fixed and scanned beams
Mobile Satellite Network:
During natural disasters, such as the Tohoku Region Pacific Coast Earthquake, all means of telecommunications were interrupted due to damage to the terrestrial communications infrastructure. The use of a telecommunications satellite is considered to be most effective in maintaining communications in areas most affected by such a disaster. Mobile earth stations will be useful in these areas due to the ability to quickly and easily establish a telecommunications link. 37)
The mobile satellite network was developed as an experimental system for applications such as maintaining terrestrial communications during disasters and as a maritime broadband communications experiment. Figure 22. shows a configuration of the mobile satellite network. The mobile earth station is a USAT (Ultra Small Aperture Terminal) of 0.65 m diameter antenna and a 20 W SSPA (Solid State Power Amplifier). The opposite Earth station utilizes a VSAT (Very Small Aperture Terminal) of the 1.2 m diameter antenna and a 40 W SSPA. The satellite antennas are of two types, namely MBAs (Multi-Beam Antennas) and APAAs (Active Phased Array Antennas). The satellite communications subsystems are equipped with two repeater modes, namely a regenerative repeater mode and a bent-pipe repeater mode.
Figure 22: Illustration of the mobile satellite network (image credit: NICT)
The MBA subsystem, which uses the regenerative repeater mode, enables data rates of up to 24 Mbit/s for land-based mobile communications in areas within the Japan and Asian beams. The APAA subsystem, which operates in the bent-pipe repeater mode, enables data rates of up to 6.5 Mbit/s for maritime communications in the Pacific region.
Table 6 shows the Earth station parameters of USAT for the mobile station and VSAT for the fixed station. The USAT for the mobile Earth station was developed to establish telecommunications in disaster areas. It can be used while being moved in off-road and all-weather conditions.
For this purpose, the antenna is equipped with a high-speed automatic satellite tracking system and a radome to ensure protection from rain and dust. The Earth station was designed to support both the regenerative and bent-pipe repeater modes. The VSAT for the fixed Earth station is an existing station at the NICT's Kashima Space Technology Center. This station also supports both the regenerative and bent-pipe repeater modes.
Table 6: Specification of the Earth station
Mobile Earth Station:
The mobile Earth station was designed to track WINDS while mounted on a moving van-vehicle and a ship for the mobile communications experiments. Figure 23 shows the block diagram of the communications system, which is composed of an ODU (Out-Door Unit), an AIU (Antenna Interface Unit) and an IDU (In-Door Unit).
The ODU is composed of an antenna, an LNA (Low Noise Amplifier), an SSPA an up-converter and a down-converter. The AIU is a unit that provides DC power, the standard frequency, and signal interface ports. The IDU is composed of regenerative and bent-pipe modems.
Figure 23: Block diagram of the mobile Earth station communication system (image credit: NICT)
Antenna design aspects: The antenna design depended on two main requirements. First, the RF and antenna performance has to support the required uplink and downlink data rates of 24 and 155 Mbit/s for the regenerative repeater mode and 6.5 Mbit/s for the bent-pipe repeater mode in clear sky conditions, respectively. Secondly, the antenna has to track the satellite within a certain permissible pointing error. Because the pointing error requirement was not fixed for the Ka-band mobile systems, the Ku-band onboard vessel antenna requirement of ±0.2° peak has been selected for this system.
A center-feed Cassegrain antenna with a 0.65 m diameter has been selected (Figure 24) considering its electromagnetic performance, tracking requirements, and acceptable dimensional constraints.
Figure 24: Photo of the Cassegrain antenna with radome removed (image credit: NICT)
Closed-loop tracking, where the pointing error is determined from the satellite beacon, has been selected. Mono-pulse and gyro-tracking systems were selected for this closed-loop tracking because of the quick and precise error determination properties. Table 7 shows the specifications for the antenna subsystem.
Table 7: Mobile Earth station antenna specifications
Operating modes: The antenna subsystem has three operating modes, namely searching, tracking and gyro-holding. These modes are automatically selected by the internal computer.
4) Searching mode: The searching mode is basically an open loop tracking mode. It is used for initial acquisition, and re-acquisition when the satellite has not been tracked for an extended period of time. In this mode, the GPS and GPS compass are used to determine the vehicle position and attitude, and this information is used to point the antenna toward the satellite. Once the beacon has been detected, the control system switches over to the tracking mode.
5) Tracking mode: In this mode, the beacon is used to estimate the pointing error, which is then used to continuously steer the antenna back to the satellite. - If the estimated pointing error is too large, the control system sends a command to mute the Tx. - If the beacon strength suddenly drops (i.e. due to obstruction by trees), the control system sends a command to mute the Tx and switches to the gyro-holding mode.
6) Gyro-holding mode: This mode keeps the antenna pointed into the same location in the sky during periods when the beacon is suddenly lost. Once the beacon is reacquired, the antenna subsystem switches back to the tracking mode.
Tracking test: To verify the correct operation of the antenna subsystem, the satellite acquisition time, tracking accuracy and received beacon level were measured. These tests were performed on the manufacturer's premises. Figure 25 shows the antenna subsystem mounted on the van-vehicle. The tested ground resembled a dirt road covered by gravel and placed sand backs. The speed of the van-vehicle was approximately 10 km/h during the tracking test.
Figure 25: Photo of the van-vehicle and test ground (image credit: NICT)
1) Satellite acquisition time: Table 8 shows the measured satellite acquisition time. The experimental results indicated good performances for both stationary and moving conditions.
Table 8: Satellite acquisition time
2) Tracking accuracy: The tracking accuracy was measured in the test facilities. Figure 6. shows the acquired tracking graph for a period for 30 minutes. The maximum pointing error was 0.064°.
Figure 26: Measured tracking error (image credit: NICT)
3) Beacon level: The beacon signal level was also measured simultaneously. Figure 27 shows the measured relative beacon level. This average level was approximately -46.4 dBm, C/N0 can be calculated using this value and measured noise level. As a result, the measured C/N0 was approximately 47.4 dB.
Figure 27: Illustration of the measured beacon level (image credit: NICT)
Data transmission test: The project conducted the the iperf test and the HD-TV transmission test using a regenerative repeater mode. Two identical Earth stations were developed; the iperf UDP test was conducted between the the two stations. In this test, a data rate of 18 Mbit/s was confirmed with no packet error. According to the link budget, a data rate of 24 Mbit/s can be transmitted, but the actual data rate decreased due to the TDMA slot assignment constraints and transmission protocol overheads.
The HD-TV transmission test was conducted using an onboard camera in town and suburban areas. In this test, the HD-TV transmission data rate was 4 Mbit/s. On the basis of the evaluation of the acquired images, the HD-TV data transmission was successfully conducted for most cases, except for cases with obstacles such as buildings, pedestrian overpasses and utility poles. In these cases, the transmitted images were frozen, but once the vehicle passed the obstacles, the data transmission resumed.
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17) Amane Miura, Maki Akioka, Takashi Takahashi, Norio Komiyama, Yuichi Yamaguchi, Masayoshi Yoneda, "Development and Experiment of Digital Channelizer for Disaster Satellite Communications System," Proceedings of the 65th International Astronautical Congress (IAC 2014), Toronto, Canada, Sept. 29-Oct. 3, 2014, paper: IAC-14-B2.4.6
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32) J. Suryana U. Sastrokusumo, K. Tanaka K. Igarashi, M. Iida, "Study of Ka-band Satellite Link Performance at High Intense Rain Cities in Indonesia using WINDS," Proceedings of 25th ISTS (International Symposium on Space Technology and Science) and 19th ISSFD (International Symposium on Space Flight Dynamics), Kanazawa, Japan, June 4-11, 2006, paper: 2006-j-21
33) S. Ozawa, T. Maeda, Y. Nakamura, T. Kasuya , A. Kobayashi, "Thermal Model Identification of Multi-Beam Antenna System on WINDS Communications Satellite," Proceedings of 25th ISTS (International Symposium on Space Technology and Science) and 19th ISSFD (International Symposium on Space Flight Dynamics), Kanazawa, Japan, June 4-11, 2006, paper: 2006-c-08
34) M. Yajima, T. Kuroda, T. Maeda, M. Shimada, S. Kitao, K. Shiramatsu, "Active Phased Array Antenna for WINDS," Proceedings of 25th ISTS (International Symposium on Space Technology and Science) and 19th ISSFD (International Symposium on Space Flight Dynamics), Kanazawa, Japan, June 4-11, 2006, paper: 2006-j-17
35) Masanobu Yajima, Takafumi Horiuchi, Masahiro Nakao, "Health Check Experiment of Active Phased Array Antenna Elements on KIZUNA (WINDS) by Two Stations Simultaneous Measurement," Proceedings of the 29th ISTS (International Symposium on Space Technology and Science), Nagoya-Aichi, Japan, June 2-8, 2013, paper: 2013-j-11
36) T. Kuroda, M. Yajima, M. Shimada, M. Kitahara, M. Nakazawa, Y. Motohashi, I. Hosoda, "Ka-band High Power Multi-Port Amplifier (MPA) for WINDS Satellite," Proceedings of 25th ISTS (International Symposium on Space Technology and Science) and 19th ISSFD (International Symposium on Space Flight Dynamics), Kanazawa, Japan, June 4-11, 2006, paper: 2006-j-18
37) Akira Akaishi, Takashi Takahashi, Mitsugu Ohkawa, Toshio Asai, Byeongpyo Jeong, "Ka-band Mobile Earth Station for WINDS," Proceedings of the 29th ISTS (International Symposium on Space Technology and Science), Nagoya-Aichi, Japan, June 2-8, 2013, paper: 2013-j-14
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).