Early in the 21st century, the demand for personal communications using mobile, hand-held, and VSAT terminals will rapidly increase. In a future system, many different types of services should be provided with one-hop connection. The Communications Research Laboratory (CRL) has studied a future advanced mobile satellite communications system using millimeter wave and Ka band. In 1990, CRL started the Communications and Broadcasting Engineering Test Satellite (COMETS) project. The satellite has been developed in conjunction with NASDA and will be launched in 1997. This paper describes the COMETS payload configuration and the experimental system for the advanced mobile communications mission

Isobe, Shunkichi

Naito, Hideyuki

Ohmori, Shingo

Takeuchi, Makoto

English

NASA Technical Reports Server

wAdvancedMobileSatelliteCommunicationsN 9 4 - 2 2 8 2 9
Using COMETS Satellite in MM-wave and Ka-band""
Shingo Ohmori, Shunkichi Isobe,
Makoto Takeuchi, and Hideyuki Naito
Communications Research Laboratory
Ministry of Posts and Telecommunications
Koganei, Tokyo 184, Japan
Tel. +81423-27-7504
Fax. +81-423-27-6825
ABSTRACT
Early in the 21st century, the demand for
personal communications using mobile, hand-
held and VSAT terminals will rapidly increase.
In a future system, many different types of ser-
vices should be provided with one-hop connec-
tion. The Communications Research Labora-
tory (CRL) has studied a future advanced mo-
bile satellite communications system using mil-
limeter-wave and Ka-band. In 1990, CRL
started the Communications and Broadcasting
Engineering Test Satellite [COMETS) project.
The satellite has been developed in conjunction
with NASDA and will be launched in 1997.
This paper describes the COMETS payload
configuration and the experimental system for
the advanced mobile communications mission.
INTRODUCTION
Early in the 21st century, the need for per-
sonal communications will rapidly increase in
fixed and mobile satellite services. In this envi-
ronment, a mobile satellite communication sys-
tem will become place, not only for use in air-
planes, ships and automobiles but also in hand-
held terminals and portable VSATs. Personal
services offered will include many different
types of transmission, from low-bit-rate data
such as information of message or voice to the
high-bit-rate data of still picture or band-com-
pressed video. In to offer wide variety of ser-
vices, it will be important to provide a function
of one-hop connection among mobiles and
VSAT terminals. It will also be necessary to de-
velop essential techniques and devices such as
beam interconnecting and hand-held terminals
to realize low-cost and user-friendly systems.
The 1990's will be an era of commercial mo-
bile satellite communications, following upon
the research and development phase in the
1980's such projects as the ETS-V in Japan,
PROSAT in Europe and MSAT-X in USA. In
some countries, research on future mobile sat-
ellite communications systems using millime-
ter-wave and Ka-band has already started. For
example, the ACTS program in the U.S.A. is a
well-known satellite program in this category
[11.
In Japan, the Communications and Broad-
casting Engineering Test Satellite (COMETS]
project was authorized by the government in
1990. A COMETS satellite is scheduled to be
launched by an H-II rocket at the beginning of
1997. Its mission is to provide a test bed in the
development of advanced technologies for the
future satellite communications and broadcast-
ing systems. One of the main purposes of
COMETS is to study the feasibility of advanced
mobile communications systems in millimeter-
wave and Ka-band. This study will be carried
out on the basis of the vast amount of research
experiences of Communications Research
Laboratory [CRL), such as the ETS-V and ETS-
VI satellite programs [2][3].
This paper describes the COMETS payload
configuration and the experimental system for
the advanced mobile communications mission.
MISSON OF AN ADVANCED MOBILE
SATELLITE COMMUNICATIONS
COMETS Project
The COMETS is a joint project of CRL and
Japan's National Space Development Agency
(NASDA}. COMETS has three mission pay-
loads. The first is an advanced mobile satellite
549
https://ntrs.nasa.gov/search.jsp?R=19940018356 2020-06-16T15:56:07+00:00Z
communications system using millimeter-
wave and Ka-band, which is developed by
CRL. The purpose of this mission is to develop
basic technologies to realize advanced mobile
satellite communications systems. The second
is a 21 GHz band advanced broadcasting sys-
tem developed by CRL and NASDA. The third
is an inter-orbit communication system devel-
oped by NASDA using S-band and Ka-band.
Figure 1 shows a conceptual sketch of the
COMETS satellite and Table 1 shows its major
characteristics of COMETS. The COMETS is a
three-axis stabilized geostationary satellite and
has three deployable antennas and about 32 m
Table 1 Outline of COMETS
Launch data in Beginning of 1997
Launch
vehicle H-II rocket
Orbit
position 121" E longitude
Mission life 3 years
Shape/ Rectangular penzlfefepiped ( apOrox. 2 x 3 x 3 rn )
imenslons Approx. 32. m length along solar arrays
for Launch : 3.8 tons
Weight for Initial geostationary position : aloprox. 2 tons
Power Approx. 5.4 kiN or more at end of life
Attitude Three axes stabilization
stabilization
Method ( feed forward compensation when the antenna is driven )
from tip to tip along a solar arrays. Its mission
life is three years and the in-orbit weight is _ .... -_. _,_. __,
about two tons. fr4"_ "_ _ / ->_'" ;/
,, ;,,,,,.,,_,_c.o_m_._=_ /.,¢" "-.;A"_"r7 t I I, ' A at / / -- -
"x_ t..-_" I I l l/ _'/ia,a_, _. f /!< ....
For Ka-band Feeder Link and ,_/_,_f_ -,v _-_,,,,_ ...... j [;_;t_-,_
2m ,._4
Fig.2 Service Image of Advanced Mobile Satel
For Ka and S bands Inllar-salallite Corn. lite Communications System.
3.5m
Fig.1 Conceptual Sketch of COMETS satellite.
Objectives of Advanced Mobile Satellite
Communications Mission
Figure 2 shows a service image of an ad-
vanced mobile satellite communications sys-
tem. This system has an on-board multibeam
antenna, the beams of which must be connected
each other. With this system, it will be possible
to offer many different types of services as
voice or message communications using hand-
held terminals, TV phone or facsimile services
using mobile terminals, and TV conference ser-
vices using VSATs.
One of the objectives of the advanced mo-
bile satellite communications mission is to de-
velop key technologies and devices for applica-
tion in the future systems. These technologies
and devices are the following:
{a} One-hop connection between handy, mobile
and VSAT terminals
(b)Very small millimeter-wave and Ka-band
antennas for handy and mobile terminals {e.g.
active phased array), and antenna tracking
techniques
{c} A multi-beam interconnecting technique
(d)A link-control system for a regenerative
transponder
{e) New applications for mobile satellite com-
munications
The COMETS will develop the millimeter-
wave and Ka-band frequencies for advanced
mobile satellite communications. These fre-
quencies are suitable for future mobile satellite
communications because antennas of an earth
terminal can be made small enough for handy
terminals and they have sufficient bandwidth
to provide a large capacity for a great number
of terminals including personal users.
ADVANCED MOBILE SATELLITE
COMMUNICATIONS MISSON PAVLOAO
550
Outline
Table 2 shows an outline of the mission pay-
load of advanced mobile satellite communica-
tions mission of the COMETS. The antenna has
three beams; two adjacent Ka-band beams (To-
kyo and Nagoya beams) and a millimeter-wave
beam ( Tokyo beam). As shown in Figure 3, the
payload consists of the multibeam antenna,
millimeter-wave and Ka-band transmitters and
receivers, an IF filter bank and regenerative
MODEMs which have a function of 2x2 matrix
beam interconnecting.
The frequencies used in the COMETS sys-
tem are 47/44 GHz bands for millimeter-wave
communications and 31/21 GHz bands for Ka-
band communications.
Table 2 Outline of Misson Payload
_OoI bllm m _ed w_lh Id M_ I1_1K_
Anter_nll ( _od wilh k_l_ _ _lmv14 I_ k_ter<¢UI _c41on )
Oiw_mr : 2m. Ck(:xi_' p_Izi|on, Anlenna _ _lW_l
_am Orw MM_wve t:ow_ (T_ b_wn )
Kah-lmnd : 30.75-30._ GHz ( t_lak I
20,98-21 O7OHz ( downlnk )
Frlquel"Icy MM-wll_,o : 416.8746.90 GHz ( t_olnk )
43.7F_I,3,711GI_ ( dova111_ )
Km-blr_l : 2 (2OW and 10W SSPA)
Tl_pondor MM wl'_o : t (2OWTWTA)
IF r_ouilm :
2 x 2 rrullrix bu¢_ Inl_roonnedW_ by IF Iltmr I_alk
Wldl l:)ind IIII" ( 8 MHZ ) and _ bllld film" ( 500 kH z )
Operation
mode Regw_-M_ v_ma_ :
s 0h SCPC (uph_k) / "rDM ( do_nlnk )
Multibeam Antenna
The 2-m-diameter antenna is used for both
millimeter-wave and Ka-band communication.
Figure 4 shows footprints of the COMETS's re-
ceiving antenna. The antenna has one spot
beam in the millimeter-wave, of which the
maximum gain is 55 dB. It has other two spot
beams in the Ka-band, which cover Tokyo and
Nagoya areas, respectively. Maximum gains of
the receiving antenna are 48.3 dBi for the Tokyo
beam and 45.4 dBi for the Nagoya beam. The
Ka-band two beams are located close to each
other for purposes of an experiment on
interbeam interference. The 3 dB contour di-
ameter of each beam is about 300 km. The an-
tenna has an antenna pointing system which
tracks a beacon signal transmitted by an earth
station.
RF Section
The transponder consists of 20W and 10W
Solid State Power Amplifiers (SSPAs) for Ka-
band communications, a 20W TWTA for milli-
[- ................. I
4,o. _--. .......... -_]
Fig.3 Block Diagram of a Transponder
cONTOUR GAtN:-2,-3,_,-10dB
,-.F _
• °
AZIMUTH ANGLE (DEG)
IN MM-WAVE (47GHz)
CONTOUR GAIN:-2,-3,-6,-10dB
i
.:F"
AZIM*UTH ANGLE (DEG)
IN Ka BAND (31GHz)
Fig. 4 Footprints of COMETS Receive Antenna.
meter-wave communications, and LNAs. An
HEMT-LNA with a very low noise figure of 2.5
dB has been developed for millimeter-wave
communications. The transponders for the two
Ka-band beams can be switched if a malfunc-
tion occurs in either one. The frequency con-
verters have a common local oscillator which is
adopted to make it easy to compensate for fre-
quency drift in the satellite. A frequency of the
local oscillator is 14 MHz and its temperature
stability is 2 x 10-7.
IF Filter Bank
Signals from an uplink beam are divided by
the IF filter bank into three frequency sub-band,
and each sub-band interconnects between To-
kyo-Tokyo, Tokyo-Nagoya and Nagoya-
Nagoya. Each frequency band is preassigned
to each beam. With this simple and flexible
method, various types of signals can be trans-
mitted via a transparent transponder.
In using a transparent repeater, it is desir-
able to optimize a transponder gain and a fre-
quency bandwidth in order to increase satellite
transmitting power {EIRP) and reduce a noise
power. In order to carry out communications
experiments at various transmission speed,
551
transpondersareequippedwith two kinds of
filters with bandwidths of 6 MHz and 500 kHz.
The transponder gain can be changed within a
30 dB range.
Though the satellite has three beams, only
two of them, i.e., the Tokyo beam in Ka-band,
and either the Ka-band Nagoya beam or the
millimeter-wave beam can be used at the same
time. Then 2x2 matrix beam interconnection is
achieved in the IF filter bank. Figure 5 shows
the IF frequency allocation bound for the Ka-
band Tokyo beam. The IF filters of each beam
consist of two wide-band 6 MHz filters, and
two narrow-band 500 kHz filters, and an 800
kHz filter for a regenerative MODEM. There-
fore, the frequency bandwidth of each tran-
sponder is 36 MHz, including a guard band.
All filters are SAW filters.
Regenerative Transponder
Table 3 shows an outline of a regenerative
transponder. Eight-channel SCPC signals are
received at one regenerative MODEM and a
single TDM signal is transmitted. The SCPC
signal transmission rate is 24 kbps or 4.8 kbps
with a BPSK modulation. Eight-channel SCPC
signals are demultiplexed by a digital
polyphase-FFT filter and demodulated dis-
cretely. Convolutional coding with a rate 1/2
and a Viterbi decoding are used as a forward
error correction [FEC).
A link control system must have such func-
tions as channel set-up, and SCPC and TDM
channel assignment. This control is achieved in
the satellite by using one SCPC packet signal
channel and one TDM signal time slot. The sys-
tem has functions suitable for mobile satellite
Table 3 Outline of a Regenerative Transponder
Ul_ink :SCI_
Downlink :TDM
Numberofchannels: 8ch/ beam
6chforcontinuoussignals
2chforpacketsignals
( including1chforchannelassignment)
TransmissionRate : 24kb/sor4.8kb/s
Modulation :BPSK
Demodulation : Polyphaso-FFTfilterbankand
DiscreteBPSKdemodulation
FEC : Rate1/2convolutionale0de
Vitert_decode
Fig.5 IF Frequency Allocation for Ka-band Tokyo
Beam.
communications. In order to increase link oc-
cupancy, a set-up demand from an earth termi-
nal is stored once in a satellite buffer memory
with a capacity of 20-channels and signals are
assigned to a vacant channel in order. In the
case of land mobile communication, a link is
held for a given period of time when the link is
temporarily disconnected by shadowing, or
the link is disconnected automatically after a
limited time when, for example, an automobile
goes through a tunnel. Such a link control algo-
rithm is under study based on the experiences
of the mobile satellite communication experi-
ments using the ETS-V satellite in 1.6/1.5 GHz.
ADVANCED MOBILE SATELLITE
COMMUNICATIONS EXPERIMENTS
Example of Link Budget
The earth stations shown in Table 4 are con-
sidered to be used in the experiment. The base
station will be located in the Kashima Space
Research Center of the CRL.
Table 5 shows an example of a link budget.
The earth terminal is located at a point where
the satellite antenna gain is the maximum. In
the case of an IF filter bank, a 24 kbps or 4.8
kbps signal can be transmitted between land
mobile earth stations with 20-cm or 10-cm-di-
ameter antennas in Ka-band. In the case of a
regenerative transponder, the required trans-
mitting powerof an earth terminal shouldbe
enough to satisfy only the uplink C/No, be-
cause uplinks and downlinks are independent.
An earth terminal with a 10-crn-diameter an-
tenna can transmit a 24 kb/s signal at 1 W in
Ka-band.
The satellite antenna gain is not so high,
however, it is sufficient for experiments to
verify key technologies. At the crossover point
552
Table 4 Earth Stations for Experiments Table 5 Example of Link Budget
Antenna Transmitting Typical
Di=meter Power Data Rate
Base Station 3-'--5 m rnom man 20 W
VSAT about 30 cm about 4 W 300 kbps
Mobile Terminal 10--'-20 ¢m about 2 W 24 kbps
Handy Terminal 5_10 cm about 0,5 W 4.8 kbpa
of two Ka-band beams, the satellite receiving
antenna gain lowers by about 8 dB compared to
the maximum. A communication experiment
on crossing beams can be conducted when a
lower transmission rate is used or the experi-
ment is conducted on a fine day free from rain
attenuation. Communications experiments
with a few tens of terminals at the same time is
possible under restrictions such as no rain at-
tenuation and low bit-rate communications,
Experimental Items
Items of advanced mobile satellite commu-
nications experiments using COMETS are:
(a} Various communications experiments in-
cluding personal communications
{b} Experiments on a link control and an
interbeam connection
{c) Propagation experiments considering shad-
owing and rain attenuation
(d)Evaluation of the satellite antenna and the
transponders
(e) Evaluation of the land mobile earth stations
CONCLUSION
In this paper, the payload configurations of
the COMETS satellite for advanced mobile sat-
ellite communication experiments and the ex-
perimental system are described. As a mission
of advanced mobile satellite communications,
advanced technologies are onboard the satellite
such as multibeam antennas, 20 W and 10 W
SSPAs in an Ka-band, a 20 W TWTA, an LNA
with an excellent noise figure of 2.5 dB in a mil-
limeter-wave, an IF filter bank, and a SCPC/
TDM regenerative MODEM. The characteris-
tics of all these on-board equipment should be
proved in space for the first time in the world.
The COMETS program is now in progress
and the transponders are being developed.
Operation mode
Frequerv_/
Transm_eaion rile kb/I
Tx. lerth Italion
Tx. power W
Tx. inlenna (_arnaleJ om
Tx. antenna gain dB
Pass loss dB
Rain mlirgin dB
S/C (ricaiving)
Rx. Imtsnna gain dB
Rx. pov_r dBm
No dBm/H2
Uplink C/No dB. Hz
S/C (trinsmltling)
Transponder gain dB
Tx. power W
Tx. =ntenna gain dB
Pass loss dB
Rain margin dB
Rx, serlh Itatlon
Rx, sntenna gain dB
Rx. powur dB
No dBm/Hz
DownSnk C/No dB' Hz
Required C/No dB" Hz i
IF repseter Regan.Tmm.
Ki-bsd K=-bw'x:l MM-band IOi-bsnd
24 4.8 4.8 24/192
0.46 0.41 0.82 1.05
20.0 10.0 10.0 10.0
30.2 24.2 27.8 24,2
214.3 214.3 218.0 214.3
5.0 5.0 7.0 5,0
47,4 47,4 45.8 47.4
-115.1 -121.6 -122.2 -117.5
-160.7 -160.7 -16_.7 -160,7
54.6 48.1 47.5 52.2
140.0 145.0 145.0
0.31 0.22 0.19 4.20
45.0 45.0 47.8 45.0
21'L4 211.4 217.8 211.4
2.5 2.5 4.0 2.5
28.4 22.3 28.7 22.3
-115.6 -123.2 -122.4 -110.4
-171.5 -171.5 -171.5 -171.5
55.9 48.3 40.1 62.1
52.2 45.2 45.2
Location of earth Itation : Center of Tokyo beam
BPSK, RKluirid Eb/No-8.4 dB ( BER.10 4)
Further studies on the satelliteand earth termi-
nals are being carried out to establish basic
technologies in advanced mobile satellite com-
munications in millimeter-wave and Ka-band.
ACNOWLEDGEMEMNT
The authors would like to thank the member
of the COMETS project of CRL and NASDA for
their helpfull discussions and continuous sup-
port.
REFERENCES
[1] R.Richard et al., "Advanced Communica-
tions Technology Satellite (ACTS)", ICC'89,
52.1-12, 1989.
[2] N.Hamamoto et al., "Results on CRL's Mo-
bile Satellite Communication Experiments Us-
ing ETS-V", Space Communications, No.7,
pp.483-493, 1990.
[3] M.Shimada et all., "Experimental Millimeter-
Wave Satellite Communications System", 17th
Int. Symposium on Space Technology and
Sdence", 0-4-3, Tokyo, May 1990.
553

Session 12
Mobile Terminal Antennas
Session Chair--Lot Shafai, University of Manitoba, Canada
Session Organizer--Martin Agan, Jet Propulsion Laboratory, U.S.A.
Low Cost Antennas for MSAT Vehicular Applications
L. Shafai, University of Manitoba; and M. Barakat, InfoMagnetics
Technologies Corp., Canada ............................................................................ 557
K- and Ka-band Mobile-Vehicular Satellite-Tracking Reflector
Antenna System for the NASA ACTS Mobile Terminal
Art Densmore, Vahraz Jamnejad, T.K. Wu and Ken Woo, Jet Propulsion
Laboratory, U.S.A ............................................................................................ 563
An Active K/Ka-Band Antenna Array for the NASA ACTS
Mobile Terminal
A. Tulintseff, R. Crist, A. Densmore and L. Sukamto, Jet Propulsion
Laboratory, U.S.A ............................................................................................ 569
Microstrip Monopulse Antenna for Land Mobile Communications
Q. Garcfa and C. Martfn, TeDeCe, Spain; J.C. del Valle, DCG Ingenieros,
Spain; and A. Jongejans, P. Rinous and M.N. Travers, European Space
Agency/ESTEC, The Netherlands .................................................................... 575
Isolated and Coupled Superquadric Loop Antennas for Mobile
Communications Applications
Michael A. Jensen and Yahya Rahmat-Samii, University of California/
Los Angeles, U.S.A .......................................................................................... 581
L-Band Mobile Terminal Antennas for Helicopters
T.K. Wu, K. Farazian, N. Golshan, D. Divsalar and S. Hinedi, Jet
Propulsion Laboratory, U.S.A .......................................................................... 587
Aeronautical Satellite Antenna Steering Using Magnetic
Field Sensors
John Sydor and Martial Dufour, Department of Communications,
Canada .............................................................................................................. 593
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Advanced mobile satellite communications using COMETS satellite in MM-wave and Ka-band

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