This paper addresses a telecommunication payload project approved by the R.O.C. NSPO's ROCSAT-1 space program. This project will enable several innovative experiments via the low-earth-orbit satellite ROCSAT-1, including multipath fading channel characterization, ionospheric scintillation measurement, real-time voice communications, and CDMA data communications. A unified L/S-band transponder payload is proposed for conducting these experiments in an efficient way. The results of these experiments would provide the evolving mobile communication communities with fruitful information

Chang, J. F.

Chu, T. H.

Chung, C. D.

Kiang, Y. W.

Li, H. S.

Lin, H. D.

Shih, M. P.

Su, S. L.

Su, Y. T.

Taur, R. R.

English

NASA Technical Reports Server

N94-22770
ROCSAT-1 Telecommunication Experiments
J.F. Chang7 R.R. Taur_ T.H. Chu, H.S. Li,* Y.T. Su _
Y.W. Kiang, _ S.L. Su!l M.P. Shih, H.D. Lin,**C.D. Chung _t
March 8, 1993
Abstract
This paper addresses a telecommunication pay-
load project approved by the R.O.C. NSPO's
ROCSAT-1 space program. This project will en-
able several innovative experiments via the low-
earth-orbit satellite ROCSAT- 1, including multi-
path fading channel characterization, ionospheric
scintillation measurement, real-time voice com-
munications, and CDMA data communications.
A unified L/S-band transponder payload is pro-
posed for conducting these experiments in an effi-
cient way. The results of these experiments would
provide the evolving mobile communication com-
nmnities with fruitful information.
1 Introduction
Due to the increasing demands of universal
personal communications services, there has re-
cently emerged the idea of using multiple low-
earth-orbiting (LEO) satellites to provide ad-
ditional mobile voice and data communications
services, supplementing the evolving terrestrial
mobile communication services. To carry out
this idea, several projects, for examples, Iridium,
Odysseys, and Globalstar, have been proposed by
Motorola, TRW, and Loral ([1], [2]), respectively.
"J. F. Chang is with National Central University, Tai-
wail, R.O.C., Tel # : 011-886-35-4267113, Fax # : 011-
886-35-425-4028.
tR.T. Taur is with LMSC Co., Inc..
tT.tt. Chu and H.S. Li are with National Taiwan
University.
§Y.T. Su is with National Chiao-Tung University.
¶Y.W. Kiang is with National Taiwan University.
tlS.L. Su is with National Cheng-Kung University.
*°M.P. Shih and tI.D. Lin are with Telecommunication
Laboratories, Taiwan, R.O.C..
ttc.D. Chung is with National Central University.
The operating quality of these proposed com-
munication systems will be the primary subject
for communications through highly dynamic en-
vironments, precisely the multipath fading chan-
nel resulting from the surface scattering effect.
Since the relative speed between LEO satellites
and ground terminals is extremely high and fast
time-varying, a highly nonstationary fading chan-
nel that is fairly different from any existing mul-
tipath fading channel model, is expected. Due to
the unique environment in Taiwan, fade charac-
teristics can be quite different from that of other
major cities in the world (for example, Chicago).
Recently, a long range space program, pro-
posed by the National Space Program Office
(NSPO) of the Republic of China (R.O.C.), has
been approved by the Executive Ynan of the
R.O.C. government. Within the program, the
NSPO schedules to launch in 1997 her first (low-
earth-orbiting) satellite, ROCSAT-1, with a de-
signed life of about four years to perform several
science and telecommunications experiments. A
mixture of circular and elliptic orbits at 35 ° in-
clination have been suggested to accomplish the
mission. On board ROCSAT-1, a telecommu-
nication payload has been allocated to perform
several ROCSAT-1 Telecommunication Experi-
ments ([3], [4]). The major intent of this telecom-
munication payload is to evaluate the aforemen-
tioned cellular LEO satellite projects and to ac-
quire adequate channel characteristic informa-
tion for a better system design in Taiwan. To-
ward these ends, we have proposed four ex-
periments, namely Fading Channel Character-
ization, Ionospheric Scintillation Measurement,
Real-Time Voice Communications, and CDMA
Data Communications. The purposes of the pro-
posed experiments are:
1. To characterize the multipath fading chan-
199
https://ntrs.nasa.gov/search.jsp?R=19940018297 2020-06-16T18:29:33+00:00Z
nels of the L- and S- band LEO-satellite-
basedcellularvoiceanddatacommunication
systems. The fade characteristicsmay be
uniquefor variousspecificenvironmentsin
Taiwan.
. To measure the L- and S- band ionospheric
scintillation in Taiwan area simultaneously,
and to further define the density and size
distributions of the irregularities that are re-
sponsible for the scintillation.
. To evaluate the end-to-end LEO personal
CDMA space communication system perfor-
mance by measuring the bit error rate (BER)
and voice quality. Various vocoder tech-
niques and rates will be employed for the
experiments. Compatibility with terrestrial
cellular CDMA systems will also be evalu-
ated.
. To perform the LEO CDMA space telecom-
munication using on-board store and for-
ward processor. Global data collection, pag-
ing, and message broadcasting experiments
will be conducted.
This payload project is currently under feasi-
bility study. We shall give more details on the
proposed experiments and the conceptual design
of the proposed payload in what follow.
2 Experiment Description
2.1 Fading Channel Characterization
The measurement system is based on a spread
spectrum communication technique. The ap-
proach is to transmit pseudo-noise (PN) sequence
modulated S- and L- band carriers from a LEO
satellite and observe channels' complex impulse
response by despreading the received signals with
a local PN replica. Basically, this system follows
the approach proposed by [5] for cellular land mo-
bile channel measurement. The high dynamics
LEO environment, however, calls for extra efforts
to remove the Doppler frequency and differen-
tial Doppler that are embedded in the received
signal but undesirable to the channel character-
ization. For this reason a dual-channel archi-
tecture (synchronous and measurement channels)
for the ground measurement system is necessi-
tated. The synchronous channel receives down-
link beacon signal by use of a L-band tracking
antenna with 26 dBi gain. It is responsible for
tracking the variations of those variables induced
by the satellite orbit dynamic (i.e., Doppler, dif-
ferential Doppler, jerk, code Doppler) and acquir-
ing the transmitted test signal (i.e., carrier fre-
quency and PN code phase). This information is
needed so that the "clean" channel responses free
of orbit dynamic effects at desired delays can be
obtained at the measurement channel.
Experiments will be conducted for various
ground environment modes, including (1) sub-
urban and rural, (2) vegetation, (3) marine, (4)
hilly, and (5) metropolitan. These selected envi-
ronments contain both typical mobile communi-
cation environments and special geographic fca-
tures and terrains in Taiwan. The PN code rate
will be 10 Mcps which yields a multipath resolu-
tion of 100 ns. For a code length of 8191 chips, the
duration of the measured delay profiles is equal
to 0.8191 ms. Table 1 gives the S-band power
budget for the multipath resolution, in which the
fade margin is fixed at least 15 dB. The EIRP
at 10 degree elevation angle on the ground is
10 dBW for both S- and L- band measurement
signals. The expected outputs of the whole ex-
periment will include (i) an exhaustive collection
of power delay profiles as well as delay Doppler
power profiles for typical geographical features
and terrains, (ii) the corresponding statistical de-
scription of path delays, amplitudes, and phases
for all the significant paths, and (iii) relevant sta-
tistical quantities, such as rms delay and Doppler
spreads, -3 dB and -7 dB profile widths, etc.. The
outputs will provide communication system engi-
neers with a thorough statistical description of a
typical mobile LEO-satellite multipath channel.
2.2 Ionospheric Scintillation Measure-
ment
Taiwan is in the equatorial anomaly crest re-
gion where the ionosphere quite often exhibits
rather irregular behavior and GHz scintillation
has been observed. Since the LEO satellite can
scan a large area of about several thousands of
kilometers wide and provide more spatial infor-
mation than the geostationary satellite, our ex-
periment is meaningful and wiLl contribute signif-
icantly to the global morphology of ionospheric
20O
scintillations.
L- and S- band beacon signals with EIRP of 3
dBW at EOL will be transmitted downlink simul-
taneously. Both amplitudes and phases will be
sampled with a rate of 1000 samples/second, and
recorded at tile receiver. This is accomplished by
using the S-band beacon as a reference to cali-
brate the phase of the L-band beacon. In order
to maximize the link availability, circular polar-
ization with axial rate lower than 5 dB is uti-
lized. Dynamic range for amplitude is 16 dB with
a resolution of 0.5 dB. The resolution for phase
measurement is 5 ° . With the recorded data,
we shall obtain useful physical quantities, such
as correlation at the different frequencies, time
instants, and positions, scintillation index, fre-
quency power spectra for the log-amplitude and
the phase, etc.. By using the Rytov solution of
scintillation theory, several physical parameters
of the ionospheric irregularities, such as turbu-
lence strength, spectral index, etc., can then be
derived. These results will be of much importance
in understanding the structure and dynamics of
the F-region nighttime irregularities. Moreover,
they can also be correlatively compared with the
VHF radar data, the total electron content data,
in-situ measurements on board ROCSAT-1, and
the spread-F data, to give us a deeper under-
standing of the ionosphere in Taiwan area.
2.3 Real-Time Voice Communications
The experiment system consists of a L-band
transmitter, bentpipe transponder, and S-band
receiver (as shown in Fig. 1). The programmable
data pattern is used for BER measurement and
error statistics analysis, while the voice input is
also allowed for demonstration and evaluation
of voice quality. Both standard and improved
CELP (Code Exited Linear Predict Code) tech-
niques at data rates of 9600, 4800, and 2400 bps
are adopted in vocoder realization. A (2,1,7) con-
volutional code and corresponding soft-decision
Viterbi decoder are employed for a 5 dB of BER
improvement. The encoded symbol rate is fixed
by 19.2 Kbps; henceforth, repetition codes of
different code rates are employed prior to con-
volutional encoding. To reduce burst error ef-
fect, a block interleaver is used to span the en-
coded sequence over 30 ms. The interleaved se-
quence is then modulated by the DS/BPSK mod-
ulator. The PN period is programmable (rang-
ing from R6 to R13) at two chip rates 1.23
and 4.92 Mcps for evaluation of the underlined
multipath fading effect. In order to resolve se-
vere Doppler effects due to ROCSAT-1 motion,
a pre-compensation/post-correction approach is
adopted, which requires a tracking antenna of
gain 26 dB at the receiver. The power budget for
this experiment is given in Table 2. It is shown
that 13 dBW of transmission power is needed to
maintain a BER of 10 -4.
2.4 CDMA Data Communications
Three sub-experiments will be conducted,
namely global data collection, global paging, and
store-and-forward message transmission. CDMA
scheme will be adopted as the access scheme.
The data collection experiment consists of a
small number (8 to 12) of transmit only re-
mote terminals and a receive only tIub termi-
nal, for the collection of meteorological, oceano-
graphic, hydrological, flood control, and seismic
data. Though the basic packet data rate of 4.8
Kbps is assumed and the sampling rate will be no
more than 20 Hz, a wide range of channel, data
formatting and burst architecture, burst ranges,
and access techniques will be possible for testing.
The global paging is a receive only experi-
ment. It is intended to answer several impor-
tant unsolved issues for future satellite handheld
personal communications, such as phase noise
effects, polarization effects, polarization or an-
tenna diversity (inside buildings), interleaving,
and FEC coding for low bit-rate transmission and
reception. Since the paging signal is expected to
be low bit rate to provide additional link margin
for building penetration, this experiment will use
S band small antenna to verify the reception phe-
nomena at various floor levels and depths within
a building, inside a moving vehicle, with the re-
ceiver carried on the person or inside a briefcase.
Since a LEO satellite is in a view for only a few
minutes, store-and-forward message transmission
will exercise an important feature for LEO satel-
lite commuincations. A remote terminal may
send a non-real-time message to the satellite
stored and re-transmitted when the satellite pass-
ing through the receiving terminal. CDMA tech-
nology will be used for message transmission
and acquisition. The proposed store-and-forward
message experiment will be used to evaluate the
feasibility and integrity of such a communication
201
!
system. Statistics on the message integrity, in
terms of bit error rate, packet error rate and
miss and false acquisition probabilities, will be
obtained for various reception conditions.
3 Payload Description
A unified L/S-band transponder payload with
components that have been flown on other satel-
lite programs or are available in flight qualifi-
able form is proposed for this project. This
payload consists of L/S-band antennas, an L/S-
band bentpipe transponder, an L-band transmit-
ter, and a baseband store-and-forward CDMA
processor. Since ROCSAT-1 is a 1000 lbs class
satellite with only about 400 W of total elec-
trical power available for six different payloads,
this payload will utilize a compact L- to S- band
transponder with about 43 W of DC power con-
sumption within Taiwan area, and about 8 kg of
weight. The nominal DC voltage from satellite
bus is 28 V. In order to minimize payload weight
and power, mechanical tracking antenna is not
recommended. Shaped antenna pattern to com-
pensate for the free path loss difference within
the coverage area is used instead. The spacecraft
antenna will have beamwidth of about 120 °.
The proposed payload is a space-qualified
solid-state transmitter/receiver with L-band up-
link and L- and S- band downlink, whose concep-
tual design is illustrated in Fig. 2. This payload
is designed to provide the flexibility of dual mode
operation at L- and S- bands. In one mode, the
bypass switches may be exercised to make the
payload as a transponder for transmission of real-
time voice. In the other mode, it serves as either a
store-and-forward CDMA regenerative transpon-
der or a PN sequence transmitter. In both modes,
the L- and S- band coherent beacon signals are
always transmitted for scintillation measurement
experiment. The payload is operated by an on-
board computer unit interfaced to the satellite
command and data handling subsystem, which
also records the payload housekeeping data.
4 Conclusion
A L/S-band transponder payload has been pro-
posed for the R.O.C. NSPO's ROCSAT-i pro-
gram, and will enable the following innovative
experiments via the LEO satellite:
• Multipath fading channel characterization
• Ionospheric scintillation measurement
• Real-time voice communications
CDMA data communications (store-and-
forward message transmission, global data
collection, and global paging)
These proposed experiments would promote a
broad based participations by the scientific and
technical communities as well as local industries
in the R.O.C.. They would also stimulate and en-
hance the earth terminal technology readiness in
Taiwan for competition in the emerging market
place of digital wireless and personal communi-
cations. In particular, the measured LEO multi-
path fading channel characteristic and evaluation
of the LEO personal CDMA space systems would
provide the evolving mobile communication com-
munities with fruitful information.
References
[1] Global Personal Communications Satellite
Services, Motorola Inc. and Lockheed Mis-
siles and Space Company, Nov. 1991.
[2]P.A. Monte and M. Louie, "GLOBAL-
STAR: A new mobile communications sys-
tem" NASA publication No. 3132, pp. 1-9,
Nov. 12-14, 1991.
[3] "Communications and Scintillation Exper-
iments," NSPO ROCSAT-1 payload pro-
posed by National Taiwan University and
Lockheed Missiles and Space Company, July
1992.
[4] "L/S-Band Personal Communications Pay-
load," NSPO ROCSAT-1 payload proposed
by Telecommunication Laboratories and
COMSAT Laboratories.
D.C. Cox, "Delay-Doppler characteristics of
multipath propagation at 910 MHz in a
suburban mobile radio environment," IEEE
Trans. Antennas Propagat., vol. AP-20, pp.
625-635, Sept. 1972.
2O2
(s-ioar_, EOL I_dget) Nat4INAL TOL */"
===xIz=zw=l==lzu=l=.=.uz=w=
• I PAYLOAD SGL E]RP, DDW (SW, 3dB) IO.OO 0.UO
* 2 POINTING LOSS, DB 0.00
• 3 PATH LOSS, DB |_5._2
3a RANGE, KH 2000.00
3b FREQUENCY, GEZ 2.56
6 ATMOSPHERIC LOSS, DB 0.50
S POLARIZAT|O_ LOSS, DS 1,00
6 RA[_ ATTE_LJAT{(_, DE 0.00
J 7 SCIETILtATIOW LO$_, _B 0.00
8 SGL RECEIVED POUER, DB_I -157.92
• 9 RECEIVER G/T, DE/K (ODD, 200K, omni) -23.01 0.00
10 UNBUDGETED RECEIVE LOSS. DB 0.00
11 BOLT2_[A_N'S CONSTAET, D8_/HZ-K -228.60
12 SCL P/No, DR-HZ _7.67
_3 PAYLOAD RETUN_ EkMDU|DTH, NHZ TO.DO
I_ nEFE_ENCE BANDWIDTH, DR-NZ 70,00
"15 SIGNAL SUPPRESSI0_, _D 0.00
16 SGL P/N (TOTAL), OB "22.33 0.00
17 C/N AT GROUND. DB -Z2.33
18 C/No AT GROUk'D, DB-HZ _7.67
"19 TDL DgELL TINE, DB [(2"'13 -1)*Tc] -30.87
20 _ATCNEO FILTER OUTPU1 C/_, DB 16,E0 0.00
21 tEOUIRED C/U, DR 15.00
"22 |MPLENENTATIOg LOSS, 08 2.00
"?3 OTHER SYSTEK LOSSES, DB O.OO
24 ]OTAL REQUIRED C/X, DB 17.00
25 MARGIN AGAINST RECUtEEH£NT, OR -O.2O
Z6 MARGIN TOLE!_ANCEo %- -0.20
Table I. Power budget for channel characterization experiment.
UP-LI_K
Transmat _ower (20 W) 13 dBW
AJ_tenna Gain 0 dB
EI_P 13 dBW
Range 2000 1_
Frequency 1.6 GHZ
Free Space LOSS -162.S dB
Atmospherlc Attenuation -0.5 dB
Total Propagation Loss -163.o dB
Re_elver's Antenna Gain 3 dBi
Polarizatzon Loss -I dB
RF Loss -I dB
Received Carrier Power -149 dB
Receiver's Noise Te=p (400 K) 26 d_K
No_se Density (No] -202.6 dB
Received C/No $3.6 dB
Bandvzdth (5 tIHz} 67 dB
Recezved C/N -13.4 dE
DOWN-LINK
.====_.==== ..... ========================================= ..... = ....
Transmit Power (D.I W, Signal only) -10 dBW
*** AssU_e 5W full power output **"
Antenna Galn 3 dBi
£1RP -7 dBW
Range 2000 K_
Frequency 2.5 GHz
Free Sp_ce Loss -166._ dB
Atmospheric Attenuation -0.5 dS
Total propagation Loss -166.9 dB
Receiver's Antenna =ain (lm dish] 26 dBi
Polarization LOSS -I dB
RF LoSS -i dB
ReCeived Carrier Power -149.9 dB
Receiver's Noise Temp (100 _) 20 dBR
Noise Density (No) -208,6 dB
Received C/No (Downllnk) 58._ dB
O_a _at_ _ _D d_
Table 2. Power budget for real-time voice communications.
203
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ROCSAT-1 telecommunication experiments

ROCSAT-1 telecommunication experiments

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