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Ka-band Broadband Mobile Earth Station
for WINDS Satellite
Akira AKAISHI1, Takashi TAKAHASHI2, Kazuyoshi KAWASAKI3,
Norihiko KATAYAMA4, Byeongpyo JEONG5 and Toshio ASAI6
†National Institute of Information and Communications Technology,
893-1 Hirai, Kashima, Ibaraki, 314-8501 Japan
The National Institute of Information and Communications Technology (NICT) has developed a Ka-band
mobile earth station which achieves 24 Mbps in land mobile regions using the wideband internet engineering
test and demonstration satellite. The mobile earth station is installed with a dual reflector antenna of 650 mm
diameter, a block up converter with an output of 20 W, and a mono-pulse tracking system with 3-axis gimbals
mechanisms for satellite tracking and communications.
Using this terminal, the transmission data rate of 18 Mbps were confirmed. High definition television
(HDTV) transmission was also conducted using an onboard HDTV camera in suburban and expressway
areas. In this test, successful HDTV transmission was confirmed under the moving conditions.
Nomenclature
NICT = National Institute of Information and Communications Technology
WINDS = Wideband Internet Engineering Test and Demonstration Satellite
HDTV = High Definition Television
MBA = Multiple Beam Antenna
USAT = Ultra Small Aperture Terminal
ABS = ATM-based Baseband Switch
BUC = Block Up Converter
iperf = A network testing tool to measure the throughput
UDP = User Datagram Protocol
SSPA = Solid State Power Amplifier
LNA = Low Noise Amplifier
ODU = Outdoor Unit
AIU = Antenna Interface Unit
IDU = Indoor Unit
TDMA = Time Division Multiple Access
I. Introduction
uring natural disasters, such as the Tohoku Region Pacific Coast Earthquake in 2011, all telecommunications
system were interrupted by damage to the terrestrial communication infrastructures. Telecommunication
satellites are considered the most effective means of maintaining communications in the worst-struck disaster zones.
Mobile earth stations that quickly and easily establish a telecommunications link are expected to become particularly
useful for this purpose.
Moreover, terrestrial communications systems have become increasingly linked with broadband internet systems
through optical-fiber networks. This has led to the need for modern satellite communications to have broadband
capability.
1Technical Staff, NICT, 893-1, Hirai, Kashima, Ibaraki, 314-8501, Japan/[email protected] 2 Research Manager, NICT, 893-1, Hirai, Kashima, Ibaraki, 314-8501, Japan/[email protected] 3 Senior Researcher, NICT, 893-1, Hirai, Kashima, Ibaraki, 314-8501, Japan/[email protected] 4 Researcher, NICT, 4-2-1, Nukuikitamachi, Koganei, Tokyo, 184-8795, Japan/[email protected] 5 Senior Researcher, NICT, 2-1-3, Katahira, Aobaku, Sendai, Miyagi, 980-0812, Japan/[email protected] 6 Technical Staff, NICT, 893-1, Hirai, Kashima, Ibaraki, 314-8501, Japan/[email protected]
D
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However, the populated C-band and Ku-band satellite systems are insufficient for broadband communications
because of their narrow frequency bandwidth and shortage of usable orbital locations. In contrast, Ka-band satellites
are less frequently used because their availability, which is limited by heavy rain attenuation. However, the Ka-band
offers a promising alternative to broadband communications because of its wide frequency bandwidth.
A wideband internet engineering test and demonstration satellite (WINDS) was successfully launched on
February 23, 2008. The aim was to establish an advanced broadband satellite communications network using the
Ka-band. Following the Tohoku Region Pacific Coast Earthquake, the National Institute of Information and
Communications Technology (NICT) has developed a broadband mobile earth station for disaster
telecommunications. This study presents the mobile ultra-small aperture terminal (USAT) developed by NICT. The
USAT has a 0.65 m diameter antenna with a 20 W block up converter (BUC) mounted on the roof of a van. The
USAT was subjected to satellite aquisition and tracking tests were and data transmission was eveluated by an iperf
user datagram protocol (UDP) test. A high-definition televisin (HDTV) transmission test was also successfully
conducted using an onboard camera in suburban and expressway areas under moving conditions.
II. WINDS Mobile Communications Test System
A. Satellite Links
This section gives an overview of the WINDS repeater1. WINDS supports both the regenerative and bent-pipe
repeater modes, which are based on a TDMA system. WINDS communications payload consists of two multiple
beam antennas (MBAs) with 2.4 m diameter dishes, two active-phased array antennas comprising 128 elements for
transmission and reception, an ATM-based baseband switch (ABS) for the regenerative repeater and IF switch
matrices for the bent-pipe repeater. The MBA dishes are used to establish communications over Japan and Southeast
Asia with 19 fixed-spot beams. Table 1 summarizes the satellite payload parameters of MBA.
The multi-rate demodulator supports four up-link transmission rates; namely, 1.5, 6, 24 and 51 Mbps. Through
this system, user can select the transmission rate suits the desired communications services. The modulator for the
down-link signal uses a fixed data rate of 155 Mbps. Table 2. lists the earth station parameters of the mobile station
road and all-weather conditions. For this purpose, the USAT antenna is equipped with a high-speed automatic
satellite tracking system and a radome to ensure protection from rain and dust.
B. Mobile Communications Test Network
The mobile communications test network was developed as an experimental system for applications such as
maintaining terrestrial communications during disasters. The configuration of the mobile satellite test networks
shown in Fig.1. The mobile earth station is an USAT with parameters listed in Table 2. The opposite earth station is
equipped with a 1.2 m diameter antenna with a 40 W SSPA. This test was conducted in regenerative repeater mode.
The test network was connected to the test PC, a teleconference system and an encoder/decoder. The test PC checks
the connection and data transmission test. The teleconference system establishes contact with both stations, and the
encoder/decoder is used in HDTV transmission. This system operates an internet protocol, which connects any
equipment via the LAN port and operates under the maximum transmission data rate.
Items MBA Remarks
Antenna Two 2.4 m Offset-feedCassegrain Antennas
Frequency RX : 27.5 GHz - 28.06 GHzTX : 17.7 GHz - 18.25 GHz Regenerative Mode
EIRP < 67.9 dBW 66.1 dBW for NICT Kashima
G/T >16.9 dB/K 20.0 dB/k for NICT Kashima
Service Area Japan beam : 9Asian beam : 10
Items Earth Station Remarks
Antenna 0.65 mRingfocus Antenna
Frequency TX : 27.5 GHz - 28.06 GHzRX : 17.7 GHz - 18.25 GHz Regenerative Mode
BUC Output Power 20 W
EIRP 55.5 dBW Nominal
G/T 16.0 dB/K Nominal
Off-axis e.i.r.p.density ITU-R S.524-9
Table 1. Satellite Payload Parameters Table 2. Mobile USAT Parameters
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C. Link Budget
Tables 3. shows the link budget between the USAT and the WINDS in regenerative mode under clear sky
conditions. The parameters are set to their measured or nominal values for a realistic estimation. According to the
link budget, the up-link and down-link realizes 24 Mbps transmission and 155 Mbps reception, respectively, with
link margins of 5.2 and 7.6 dB respectively.
Items Up-Link Remarks Down-Link Remarks
USAT⇒WINDS WINDS⇒USAT
Frequency 27.537 GHz 17.7925 GHz
Data Rate 24 Mbps 155 Mbps
EIRP 55.5 dBW Nominal 66.1 dBW WINDS MBA forNICT Kashima
Free Space Loss 212.7 dB NICT Kashima 208.9 dB NICT Kashima
Polarization Loss 0.2 dB 0.2 dB
Atmospheric Loss 0.3 dB 0.2 dB
G/T 20.0 dB/K WINDS MBA forNICT Kashima 16.0 dB/K Nominal
C/N0 90.94 dB-Hz 101.5 dB-Hz
Required C/N0 85.7 dB-Hz 93.9 dB-Hz
Margin 5.2 dB 7.6 dB
Figure 1. Mobile Communications Test Network
Table 3. Link Budget
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D. Mobile Earth Station
The mobile earth station was designed to track WINDS while mounted on a moving van. Figure 2. is a block
diagram of the communications system, which comprises an outdoor unit (ODU), an antenna interface unit (AIU)
and an indoor unit (IDU).
The ODU composed of an antenna with a mono-pulse feeder, low-noise amplifiers (LNAs), down-converters and
BUC installed 20 W SSPA. The designed antenna subsystem satisfies two main requirements. First, the RF and
antenna performance must support the required maximum up-link data rate (up to 24 Mbps), and the down-link data
rate (155 Mbps) under clear sky conditions. Second, the antenna must track the satellite within a certain permissible
pointing error. Because no pointing error had been decided for the Ka-band mobile systems, the Ku-band onboard
vessel antenna requirement of (±0.2° peak) was adopted for this system. The system is also installed with an
interlock functions that indicates when the pointing error exceeds the requirement and detect satellite beacon fade.
To satisfy the electromagnetic performance, tracking requirements, and acceptable dimensional constraints, a ring-
focus antenna of 0.65 m diameter was selected. The AIU provides DC power and the standard frequency of 10MHz
to the ODU, GPS data to modem and antenna control GUI data to the external computer. The antenna subsystem (comprising the ODU and the AIU) has three operating modes, namely searching, tracking and
gyro-holding, which are automatically selected by the internal computer. The searching mode, which is basically an open
loop tracking mode, is used for initial acquisition, and for re-acquisition when the satellite has not been tracked. The
tracking mode is a closed-loop tracking. The beacon is used to estimate the pointing error, which is then used to
continuously steer the antenna back to the satellite. A TE21 mode mono-pulse tracking was selected for this closed-
loop tracking because it provides quick and precise error determination properties. The gyro-holding mode points the
antenna toward a consistent 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. The requirements of the antenna subsystem are
listed in Table 4.
The IDU operates as a TDMA regenerative modem. The Up-link data rates are 1.5, 6, 24 and 51 Mbps and the
down-link rate is 155 Mbps. This modem has capabilities to track the TDMA timing using GPS positioning data
from AIU and to operate moving speed up to 100 km/h.
Figure 3. and 4. illustrate the outward appearance of the antenna subsystem without the radome and the mobile
earth station installed on the van respectively.
Figure 2. Block Diagram of the Mobile Earth Station
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III. Satellite Tracking Test
A. Satellite Acquisition
The satellite acquisition is performed automatically to turn on the power switch only. As experimental results,
the average acquisition time was approximately 4 minutes for the specified value of 12 minutes. After the
acquisition, the antenna will lock and track to the satellite automatically. When the satellite tracking is lost and the
lost time is less than 60 seconds, reacquisition will occurs immediately. This reacquisition is held by the gyro-
holding functions. When the tracking lost time exceeds 60 seconds, the antenna begins to search the satellite. The
acquisition of this case will need for several minutes.
B. Tracking Test
To verify the correct tracking operation of the antenna system, the moving tests were performed for various
situations. Figure 5. shows the moving test track at the expressway entrance. This traveling speed was approximately
30 km/h and the satellite was continuously tracked even on curved section of road and when obscured by obstacle:
namely, the over pass and the expressway gate. Figure 6. Shows the moving track along the expressway, where the
traveling speed was approximately 100 km/h. Again, the satellite was continuously tracked in the presence of
several obstacles such as the over pass and trees. Along these tracks, the red and black dots show the high and low
beacon C/N0 of about 50 dB-Hz and 30 dB-Hz respectively. Therefore, this antenna tracking functions were
operated correctly in the suburban and the expressway routes.
Table 4. Antenna Subsystem Requirements
F
Figure 3. Antenna Subsystem
F
Figure 4. Mobile Earth Station
Items Requirements Remarks
Antenna 650 mm φ Ring-focus Antenna
Frequency TX: 27.5 GHz - 28.05 GHzRX: 17.7 GHz - 18.25 GHz Regenerative Mode
BUC Output Power 20 W (Linear) 40 W (Saturated)
EIRP >55.0 dBW 55.5 dBW Nominal
G/T >13.5 dB/K 16.0 dB/K Nominal
Off-axis e.i.r.p. Density ITU-R S.524-9
Polarization Linear TX, RX parallel
Azimuth Tracking 360° Continuous
Elevation 20° - 90°
Cross Elevation ±15°
Tracking Accuracy <±0.2°
Satellite Acquisition <12 minute Cold Start<1s, for 60 s, lost
Tracking Performance 100 km/h for Seal Road20 km/h for Off-Road
Inter-Lock Beacon Fade or Lost Tracking
IF Interface TX: 1.9 GHz - 2.5 GHzRX: 1.38 GHz - 1.98 GHz Regenerative Mode
Operating Temperature -20 ℃ to +40 ℃
Installed Generator AC 100 V, 2.8 kVA
Power Consumption <1.5 kVA Include Cooling Unit
Mass <120 kg Include Cooling Unit
Dimensions 985 mm φ x 801 mm H x
1386 mm L Include Cooling Unit
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C. Beacon Level
The beacon signal levels were also measured simultaneously as beacon C/N0. Figure 7. shows the measured
C/N0 of the moving track presented in Fig. 5. The two C/N0 falls coincide with obstruction by the overpass and the
expressway entrance gate. Figure 8. shows the measured C/N0 of the moving track in Fig. 6. These C/N0 falls
coincide with obstruction by 7 overpasses, an antenna tower of the mobile phone and forest trees
D. Tracking Error
The tracking error was also simultaneously measured during the tracking operation. Figure 9. And 10. show the
measured tracking errors while moving along the tracks of Figs. 5 and 6, respectively. Along the expressway
entrance and expressway, the tracking errors remains bellow 0.09° and 0.11° respectively. According to these results,
the antenna tracking errors satisfy the requirements of < ±0.2°, and the whole error increase with proportion to the
vehicle speed.
F
Figure 5. Moved Track along Expressway
F
Figure 8. Beacon C/N0 along Expressway
F
Figure 7. Beacon C/N0 along Expressway Entrance
F
Figure 6. Moved Track along Expressway
F
Figure 9. Tracking Error along Expressway Entrance
F
Figure 10. Tracking Error along Expressway
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IV. Data Transmission Test
A. Link Performances
NICT developed two identical mobile earth stations installed on the van. Two mobile earth stations were
distinguished to USAT#1 and USAT#2. The up-link margins were measured using iperf UDP test varying the output
power for 24 Mbps and 51 Mbps modes. The down-link margin was measured from the C/N0 of the IDU modem.
The actual tested data rates of the up-link were reduced to 18 Mbps and 36 Mbps because of the TDMA slot
assignment constraints and the overhead of the transmission protocol. The results of the link margin measured at
NICT Kashima in Table 5. confirm good agreement between the expected and measured results.
B. Data Transmission Test
The HDTV transmission test was conducted on a city road2, and in suburban and expressway areas. For this
purpose, an onboard camera was installed on the vehicle exterior. Figure 11. And 12. are photographs captured by
the HDTV camera on the moving van in suburban and expressway areas respectively. In this test, the transmission
data rate was 8 Mbps.
Evaluating of the acquired images, we confirmed that the HDTV data were successfully transmitted in most
cases, but were interrupted by obstacles buildings, pedestrian overpasses and utility poles. Once the vehicle had
passed the obstacles, data transmission was frozen at one time but the data transmission was successfully resumed.
This mobile earth station is designed not only for land mobile use, but also ocean use. It has recently been
installed in a reseach ship and used in a tele-operation experiment3.
Table 5. Link Margins
F
Figure 11. Expressway Entrance Gate
F
Figure 12. Expressway Traveing about 100 km/h
Earth Station
Expected Measured Expected Measured Expected Measured
USAT#1 5.2 dB 6.0 dB 2.2 dB -0.1 dB 7.6 dB 6.6 dB
USAT#2 5.2 dB 5.4 dB 2.2 dB 0.3 dB 7.6 dB 7.4 dB
Up-link
24 Mbps Mode
Up-link
51 Mbps Mode
Down-link
155 Mbps Mode
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V. Conclusion
NICT has developed a Ka-band mobile earth station with a 650 mm aperture antenna and a 20 W BUC. The
developed mobile earth station can transmit the peak data rate of 24 Mbps using WINDS domestic beams. The
satellite acquisition and tracking performances satisfied the requirements. The earth station tested on a van in
suburban and expressway areas. We confirmed that the antenna operates at the moving speed of 100 km/h. We
further confirmed a transmission data rate of 18 Mbps using the regenerative repeater mode of WINDS. HDTV data
were successfully transmitted as the vehicle traveled along the expressway.
Acknowledgments
The authors thank JEPICO Corporation for the integration of the van, and also thank EM Solutions for the
development of the mobile antenna subsystem as a key subsystem.
References 1“Special Issue on Wideband Internet Engineering Test and Demonstration Satellite (WINDS)”, Journal of the
National Institute of Information and Communications Technology, vol. 54, no. 4, December 2007. 2Akira, A., Takashi, T., Kazuyoshi, K., Norihiko, K., Byeongpyo, J., and Toshio, A., “Ka-band Mobile Earth
Station for WINDS”, 29th International Symposium on Space Technology and Science. 3Takahashi, T., Naoko, Y., Akira, A., Norihiko, K., Morio, T., Naoto, K., Shojiro, I., Tatsuya, F., and Hiroshi, Y.,
“The Tele-operation Experiment of the Hybrid Remotely Operated Vehicle Using Satellite Link” Proceeding of the
34th International Conference on Ocean, Offshore and Arctic Engineering OMAE2015 May 31-June 5, 2015, St,
John’s, NL, Canada.
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