NEXT GENERATION BROADBAND SATELLITE COMMUNICATION SYSTEMS
Satchandi Verma, SMIEEE, Senior Staff, Eric Wiswell, MIEEE, Technical Fellow
TRW Inc.
One Space Park
Redondo Beach, CA 90278
310-812-1742
satchandi.verma@trw.com
•
Larger satellite capacity (higher link frequencies with
frequency reuse)
• Onboard Processing Payloads (Analog and Digital)
To meet the requirements of future systems TRW has
applied these design enhancements in developing the
Gen*Star [2, 3] payloads for next generation satellites. The
satellite payload was designed for operation at Ka band and
included the companion network and terminal infrastructure.
The first payload using this antenna design was completed
in December 2001 for the Astrolink satellite. Presently this
payload design is expanded to provide the efficient cost
effective system solution for the replacement and or
enhancement of Ku and C-Band satellite networks.
NEXT GENERATION SATELLITE ANTENNA
Most of the present satellites use relatively small size
solid antenna reflectors to provide the desired coverage. The
antenna size (2-3m) is limited by the launch vehicle fairings
and packaging constraints. Regional coverage is provided
by using the antenna shaped beam (wide) while the spot
area coverage is obtained by the high gain multiple narrow
spot beams. The radiated power coverage efficiency of these
shaped beam antenna is considerable reduced from the loss
of energy (power emission) in the undesired coverage
regions (desert, ocean) with no source of revenue. The small
gain reduction (slow antenna side-lobe roll offs) at the
coverage area edges also further degrades the system
performance.
Deployable Mesh Satellite Antenna
The next generation satellite antenna design will use the
lightweight large deployable reflector antenna to provide
high performance shaped and multi spot beam coverage’s.
For improving the system performance TRW Astro
Aerospace has developed the technology for manufacturing
lightweight, shaped beam, deployable mesh reflectors
antenna systems. These antenna (Figures 1) designs use
deployable mesh reflectors ranging from 6m to 30m in
diameters to provide 60-100% improvement in the shaped
directivity over the solid reflector antennas [4]. The antenna
is designed to provide regional or global service coverage at
both C and Ku Band frequencies. The antenna performance
is improved by flattening the coverage area radiation pattern
and creating the rapid gain reduction at the edge of
coverage. The sharper antenna side-lobe roll offs and higher
cross polarization which further enhances the system
capacity and reduction in satellite DC power consumption.
ABSTRACT
For next generation satellite systems to provide cost
effective network service it is essential to use efficient and
advanced technologies for adding new satellites or
upgrading legacy systems. This paper discusses the various
technologies that are being developed and utilized for
increasing the network capacity, improving service
performance and reducing the cost of satellite systems. An
overview of enabling technologies is presented describing
the key architecture, capability and performance of the
broadband satellite payload processor, digital transponder
and satellite antenna developed by TRW. The various
benefits of using these advanced features in satellites over
the conventional “Bent Pipe” satellite systems are
summarized.
INTRODUCTION
Over the last two decades the communication satellites
have extensively used “Bent Pipe” transponders at C and
Ku-Band frequencies to provide the audio, data, video and
VSAT services using narrow and wideband transmission
channels. These satellite systems are characterized by broad
regional coverage, rigid network configurations, relatively
low satellite antenna gain, EIRP and G/T with modest
channel data capacity rates. The network throughput
capacity is mostly limited by the availability of small
numbers of transponders in the satellite.
In recent years cost effective solutions for Multimedia
Broadband Global Communication systems are being
developed using next generation of communication satellite
designs. These systems require high quality of service,
affordable prices and good matching of customer demand
with the satellite system capacity for successful and
profitable business operation. The growth of satellite data
services in the next decade is estimated to be substantial
during this decade [1].
To meet the needs of these cost effective next
generation systems requirements the satellite may employ
following advanced techniques in antenna designs, onboard
payload processing and frequency reuse:
• Deployable large mesh reflector (Shaped and spot
beams) satellite antenna
•
High gain Solid Reflector Multiple Beam Antenna
(MBA) for Satellites
• Satellite Coverage Flexibility (Local, Regional, Global)
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Recently launched Thuraya (L-Band) satellite uses a 12.25m
mesh parabolic reflector while a 9m (L-Band) reflector is in
production for the INMARSAT4 satellite.
Global areas for transmission of specific contents.
Local Coverage
The local coverage contains transmissions in the
selected areas (City or country) to provide the local content
delivery services to meet the demand of customers located
in the city. The antenna spot beams in the satellite provide
high gain directivity in specific coverage areas. The beams
are optimized for the maximum system capacity and
performance for local service contents.
Regional Coverage
The regional coverage contains transmissions in
specific regions based on the language (eg: Spanish,
German) or country (eg: Spain, Germany). This coverage is
provided by a single shaped antenna beam or multiple
narrow spot beams covering the required regions. The
regional coverage is tailored to radiate the power for
customer in conformance with language needs and geopolitical concerns (Frequency coordination, content
restrictions). The regional beams provide higher directivity,
which could be used for increasing the satellite power
efficiency or reducing the user system costs on the ground.
Global Coverage
The satellite global coverage provides the transmissions
in the area covered by multiple regions (language, Geo
political) or countries. For example the Pan European
coverage beam provides the same service contents to all
customers located in different Europe countries
The wide shaped antenna beam covering the European
countries provides the Pan European coverage. A typical
example of Local, Regional and Global (Pan European)
coverage beams for satellites are shown in Figure 2. Using
multi spot beams for global coverages could also develop
cost effective systems
LARGER SATELLITE SYSTEM CAPACITY
The satellite system capacity is enhanced by using
larger useable bandwidth at higher frequency bands (Ka,V)
and by applying the frequency reuse including optimal
multicolor channel transmissions schemes. The number and
complexity of transponder implementation in satellite limits
the improvement in system channel capacity. The maximum
number of transponder in a satellite is controlled by the
capabilities (mass, power, ferrying size) of the spacecraft
bus used.
Figure 1 – Mesh Reflector Deployable Antenna
The mesh shaped antenna reflector consists of a pair of
doubly curved geodesic trusses, which are placed back-toback in tension across the rims of a deployable graphiteepoxy ring truss. This light and inherently stiff drum-like
structure provides high efficiency, thermal dimensional
stability, and stiffness-to-weight ratios. These L-Band
antenna designs and manufacturing processes are being
further optimized for the production of C and Ku Band
satellite systems.
High Gain Multiple Beam Antenna
TRW has developed Multi Beam Antenna (MBA) to
provide the high capacity flexible coverage beams for KaBand satellite systems. These MBA antenna designs provide
high-gain, multiple-hopping spot beams for national,
regional and global service coverage’s. The desired
coverage area is tiled with narrow beams using frequency
reuse and multi color operation schemes for enhancing the
system capacity. These antennas also provide low sidelobes, higher cross-polarization isolation and high degree of
network coverage flexibility to meet the dynamic market
demands from the customers [3]. Satellite systems using
Multi Beam Antenna have additional advantages of larger
channel capacity and on orbit coverage adaptability for the
changing usage patterns.
SATELLITE SYSTEM COVERAGE
The, types of network services, customer population
and required system performance, governs the design of
satellite system coverage. The satellite payloads are
developed to provide the services in Local, Regional and
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SATSAT- 1
SATSAT2
MHz) which is ten times of the transponders available in the
satellite using a single wide area beam:
ESB = (Number of Cells) x (Allocated Bandwidth)/
(Frequency Reuse Factor)
= (50x2)x (500 MHz)/4 =12.5 GHz
The Equivalent Number of 36 MHz Transponders
(ENT): ENT = 12.5 GHz/40 MHz = 310
SATSAT- 3
SATSAT- 3 Pan
European
Beam
SATSAT- 1
Regional
Beams
SATSAT- 2
Regional
Beams
9.00
Scandinavia
8.00
7.00
UK
London
-
-2
43.64
Paris
Spain
6.00 -1.70
Madrid
43.64
-3
5.00
43.30
43.30
-1.70
Stockholm
-1.70
-3
CTU
-3
20°
-3 -3
HAN
-3
-3
-3
Germany
-2
-2
-3
-3.00
-3
CAN
Berlin-2
Munich
France
43.30
0.00
TPE
-3
20°
-3
MNL
BKK-3
SGN
-3 -3
-3
KUL
-3
-3
-3 -3
POM
-2 -1.70
-2
-3
Rome
Italy
-2.00
-1.00
-3
HLP
-3
-3
-5.00
5.00
-4.00
HRB
-3
NAYSHE
SEL
-3
-3
ITM
SHA
-3
0.00
PER
-3
-3
-3
BNE
CBR
1.00
20°
Figure 2 – Satellite Coverage Area
Frequency Reuse
The system capacity is increased by reusing the
available frequency spectrum through optimum allocation of
frequencies and polarizations in the communication links.
Multi Beam coverage and Multi color frequency schemes
further expands the systems capacity. The frequency reuse
in the system for the Asia/Pacific regions is shown in Figure
3.
Figure 3 (b) – Multi Spot Beam Coverage
Multi Color Frequency Plans
The multi color schemes assign same frequency to
different sections of the coverage area having locations with
spatial diversity. The application of these techniques further
enhances the system capacity. For example the six regional
beams in Europe (Figure 2) could use three-color schemes
in association with twice the frequency reuse to obtain the
larger system capacity (Table 1).
Table 1 – European Regional beam Color and
Frequency reuse scheme
Region Beams Spatial Frequency
UK
Green
X
Italy
Green
X
Spain
Blue
X
Germany
Blue
X
France
Red
X
Scandinavia Red
X
By incorporating this scheme to a typical satellite (with
no frequency reuse and color scheme) the system capacity
could be increased over 58% (56 to 96) using the same
assigned frequency slots without changing any ground
equipment. The actual system capacity improvement
depends on the capability of the spacecraft bus to implement
the required hardware and operating power changes. The
system provides higher capacity in six regions speaking six
different languages.
Figure 3 (a) – Singe Wide Area Coverage
The region coverage is compared for both a single wide
area beam and the set of multi spot beams. For example for
a system using dual polarization links and 50 spot beams the
Effective System Bandwith is substantially increased. This
frequency reuse produces 310 equivalent transponders (36
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SATELLITE COMMUNICATION PAYLOADS
Most of the satellite communication payloads operate in
C and Ku frequency bands. Recently few Ka-Band
transponders are added in some satellites to support the
development of future Ka-Band systems. The payloads use
36 to 72 MHz bandwidth with both linear and circular
polarizations for providing “Bent Pipe” transponders.
Traveling Wave Tube Amplifiers (TWTA) are
extensively utilized in transponders for obtaining the
downlink EIRPs in the range of 30-40 dBW (C-Band) and
40-50 dBW (Ku-Band). The next generation satellites
employ communications payloads with advanced antenna,
on board switching and digital processing. The Onboard
Processors enables the use of Solid State Power Amplifiers
(SSPA’s) to enhance the system performance and capacity.
On board switching provides the needed network flexibility
both in analog and digital transponders.
Payload System Configuration
Generally the communication payloads system consists
of antenna, onboard processor and RF systems as described
in Figure 4. The antenna subsystem includes the antenna
(transmit, receive) and the associated feeds, control
electronics and the distribution networks (OMT, BFN).
Depending on the reflector size and operating frequencies
these TRW advanced shaped antenna could provide up to
15dB larger EIRP per beam than the current payloads of
equivalent power.
RF Subsystem
The RF subsystem includes the required RF
components for receiving and transmitting the signals in the
payloads. The receive RF subsystem uses low noise
amplifiers and down converts for changing the power levels
and frequencies of the signals received from antenna. The
signals are formatted to the required input interface of the
processor. The transmit RF subsystem up converts and
amplifiers the power of signals to produce the desired EIRP
at the payload antenna output. Using advanced technologies
Recieve RF Subsystems
Antenna
Subsystem
y
y
y
LNA Downconverter
Analog IF Conditioning
Frequency Source Unit
LNA
Dual
band
feed
BP
F
VG
A
Freuency
Source
Unit
in Gallium Arsenide (GaAs) high electron mobility
transistor (HEMT) devices TRW has produce compact low
noise amplifiers (LNA), downconverters and upconverters
for next generation satellites. The use of advances extremely
small MMIC (millimeter/microwave integrated circuit)
packaging provides small size LNA/Downconverter
modules, which are easily mounted directly on the antenna,
feed horns. This ability to collocate the first stage of
processing with the antenna feed eliminates the waveguides,
(prevents the loss of received signal power in the
waveguides) and reduces the payload mass and complexity.
For transmitting the downlink signals the upconverters are
mounted directly on the TWTAs reducing the signal losses
and payload complexity.
On Board Processor Subsystem
The next generation satellites extensively need to use
On Board Processors (OBP) to design cost effective system
solution for the customer needs. The OBP in satellites
eliminates the inherent disadvantages of the “Bent Pipe”
transponders. The payloads either employ partial or full on
board processing depending upon the system design
requirements and cost. Full on board processing enables an
ATM like switching process in payloads. The partial
processing on board is used in “Digital Transponders”.
Generally the processor in satellite provides the following
on board features and capabilities for system enhancements
[5]:
• Full network connectivity (Mesh, Star)
• On board switching of signals, beams & coverage areas
• Simplified payloads with efficient use of TWTA /SSPA
• Efficient bandwidth and power level control
(Automatic, Selectable)
• On orbit management of network traffic, capacity and
QOS
• Flexible system integration, operation and tests
Full On Board Processor
In full OBP satellite system the payloads transforms the
incoming signals into fixed length packets using range of
Transmit RF Subsystems
Processor Subsystem
y
y
y
Saw Filter Channelizer
Transponder Switch
Channel Amps & Summers
ca
mp
ca
mp
ca
y
y
I
Σ
mp
BPF
EPC
bpf
Σ
IF to RF Upconverter
EPC/LCAMP/TWTA
bpf
LCAMP
HPA
bpf
Figure 4 – Communication Payload System Configuration
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packet switch processor using a distributed system
architecture [6]. The processor design provides both the
point-to-point and multicast services up to 10 Gbps network
data rates with 128 ports.
The data information is routed through a self-routing,
non-blocking cross bar switch to provide the throughput
capacity up to 6.5 Gbps.
Digital Transponder
Figure 5 – Gen*Star On Board Processor Block
Digital transponders in communication satellite
Diagram [4]
payloads use circuit switching and data processing for
designing cost effective network services between different
1773
Resource
satellite coverage beams (Area, Spot). The various system
PCI Bus RH32
Controller 1553
advantages provided by digital transponder are [7]:
Computer NonBus
Controller
Module
• Transponder bandwidth flexibility and control.
Controller
Volatile
Module
Transponder provides circuit switching between
Module
Memory
different spot beams in fractions of transponder
bandwidth (0.5 MHz increments). Capacity
allocation at the transponder level provides the
Switch
flexibility of selling fractional bandwidth to
customers on demand.
Inbound
Outbound
•
Reconfigurable
Network Connectivity with Backward
Demodulator
Switch
Module
Module
Compatibility.
Fabric
Digital
The transponders can easily be reconfigured at the
IF
Outputs
Inputs
sub-transponder level to respond the system
connectivity requirements for changing markets and
traffic patterns. The backward compatibility to
Demodulator Router
Multicast Module
analog transponders in legacy systems is obtained
by the programmable bandwidth feature of (27, 36,
54, 72 MHz) in the design.
processing requires efficient channel routing, power control
• On Board Channel Aggregation.
and dynamic bandwidth reallocation. The ATM cell
This feature provides the on board capability of
switching provides flexibility and compatibility with
combining the Signals from multiple uplinks
existing protocols and interfaces. The scaleable feature of
located in different coverage regions into a single
switch meets the needs of both the users requiring very little
downlink channel. The system efficiency is
bandwidth as well as those with high bandwidth demands
improved by simpler frequency translation and
(large business users over a single network infrastructure).
time slot (TDM) switching.
For Gen*star payload TRW has built the broadband
PBI
protocols. The payload interprets and processes the data to
provide efficient downlink bandwidth, connectivity and
QOS. The block diagram of the on board processor using
ATM (asynchronous transfer mode) cells. is shown in
Figure 5. The router consists of an ATM switch and an onboard computer for performing the on board control and
processing functions. The packets (Cells) are dispatched
through the switch to the desired destinations. The signal
Antenna
Subsystem
Recieve RF Subsystems
Dual
band
feed
y
y
y
LNA Downconverter
Analog IF Conditioning
Frequency Source Unit
Transmit RF Subsystems
Processor Subsystem
y
y
y
y
y
y
Digital Channelizer
Circuit Channel Switch
Analog Reconstructor
I
Offst Fed
Mesh
Reflector
Spot Beam
Antenna
LNA
BP
F
VG
A
Freuency
Source
Unit
ADC
DFT
iDFT
DAC
IF to RF Upconverter
EPC/LCAMP/TWTA
Analog IF Conditioning
BPF
VGA
EPC
LCAMP
BPF
HPA
Dual
band
feed
Figure 6 – Digital Transponder Payload Configuration
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•
System Capacity and performance Enhancements.
The system capacity is increased by using more
efficient modulation (8-PSK, 16 -QAM) and
reducing the channel guard bands (filtering,
channel to channel amplitude power leveling). The
system performance is improved by using the
digital pre-distortion to HPA for increasing the
TWTA amplitude and phase linearity.
(ALC) normalizes the average power of the signal received
from each user to a constant level. Input power levels being
time-varying: rain attenuation, atmospheric scintillation,
etc., the control is needed to increase TWTA efficiency on
the downlink. The recombiner performs the inverse function
of the channelizer. It combines the 250 sub-channels into
125 MHz bandwidth channels. Reconstruction filter design
constraints ensure minimal signal distortion during this
process. The switch, commanded by a control processor,
routes sub-channel data from the channelizer to the
appropriate ports in the recombiner.
The block diagram of the Digital Transponder is
described in Figure 6. The antenna subsystem includes the
offset feed spot beam antenna (transmit, receive) including
the associated control electronics and distribution networks
(OMT, BFN). The RF subsystem includes the required RF
components for receiving and transmitting the signals in the
payloads for each beam. Using low noise amplifiers and
down converts the received signal power levels and
frequencies are changed. The transmit RF subsystem up
converts and amplifiers the power of signals to produce the
desired EIRP.
Digital Transponder Processor
The processor in Digital transponders performs five
major functions as shown in the concept diagram [7] of
Figure 6. The incoming analog signal is converted into 125
MHz digital signals at 640 MHz intermediate frequencies.
The digital channelizer divides the complex baseband input
signal into 250 overlapping 0.5 MHz sub channels. The user
signal power level is normalized to a constant level by the
Automatic Level control function in the digitizer. Using
subchannel mapping the digital switch routes subchannel to
the appropriate ports for broadcasting or multicasting. The
subchannels are reconstructed and recombined in the
recombiner to form one signal with a 125 MHz bandwidth.
Finally the digital samples are converted into analog signal
centered on 512 MHz
Digitizer
* Analog to digital conversion
* 125 MHz signal @ 512 Msps
Circuit
CircuitSwitch
Switch
** Remaping
of Subchannels
Remaps subchhanels
** Subchannel
routing
port
Routes subchannels totoports
Digital Channelizer
* Divides inputsignal into
sub-channels
* ALC function levels the power
Recombiner
* Subchannels reconstructed
* Recombines user channels
into a one signal
F r e q u e n c y R e sp o n se
0
-5
- 10
- 15
IL(dB)
-2 0
-3 0
-3 5
-4 0
-4 5
-5 0
-5 5
-6 0
0
20
40
60
80
10 0
12 0
14 0
F r e q u e n c y (M H z )
Figure 8 – 36 MHz & 72 MHz Channel Sharing
The switch is reconfigurable approximately every
microsecond and supports both point-to-point, multicast and
broadcast operations. Switch reconfiguration is performed
by the ground command. High-speed, indium phosphide,
integrated circuit devices convert the digital output of the
recombiner to 125 MHz analog beams
The channel bandwidth of 125 MHz can further be used
for carrying multiple transponder channels (36 MHz, 72
MHz). Figure 8 shows the frequency response of locating 36
and 72 MHz channels in 125 MHz using digital filters. The
use of digital filters provides improved performance of
insertion loss and frequency response over analog SAW
filters. The performance a 36 MHz bandpass SAW filter
(Best effort analog filter) is compared with an achievable
digital filter (using 4096) taps in Figure 9. The digital filter
provides substantial improvement in performance as
compared to analog SAW filters.
Anolog
Reconstruction
Converts digital
samples into
analog signals
Figure 7 Digital Processor Concept Diagram
The Uplinked signals are downconverted at the antenna
and input to the digitizer in 64 channels using a transmission
bandwidth of 125 MHz. The digitizer samples each channel
at the rate of 512 Msps (mega samples per second) and
sends signals to the Channelizer. The Channelizer divides
the baseband input signal, containing the user channels, into
250 sub-channels. An automatic level control function
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CONCLUSIONS
For next generation satellite systems to provide cost
effective and profitable network service it is necessary to
apply new technologies in satellite antenna and
communication payload designs. The satellite network
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02S00729.154
onboard processors developed for Ka-Band satellites in
along with multibeam antenna designs can easily provide
increased capacity and cost savings at these lower frequency
systems. The use of spot beams provides much higher
antenna gain with larger effective isotropic radiated power
(EIRP) and G/T than the conventional C and Ku-Band
systems supporting high performance communication links.
implementation requires upgrading the legacy systems and
adding new payloads with advanced features for system
enhancements. This paper discusses the different
technologies and designs employed in providing the
improved network flexibility, capacity and performance.
The key drivers for the designs and implementation of next
generation satellite systems employ: (a) Shaped and spot
beams large deployable mesh reflectors antenna (b) High
gain Solid Reflector Multiple Beam satellite antenna (c)
Satellite Coverage Flexibility for Local, Regional and
Global services (d) Satellite capacity enhancements through
frequency reuse (e) Onboard Analog and Digital Processing
Payloads.
Frequency Response, SAW Filter
5
0.730
0
0.670
-40
0.650
0.630
0.610
-50
IL(dB)
0.590
-55
GD(usec)
0.570
0.550
-60
505 509513 517521 525529 533537 541545 549
Frequency(MHz)
-5
16.030
-10
IL(dB)
-35
IL(dB)
0.690
Group Delay(usec)
0.710
-30
-45
[2] H. J. Morgan, Eric R. Wiswell, Joseph Freitag, “The
Gen*Star Program,” 18th AIAA International
Communication Satellite Systems Conference & Exhibit,
16.050
-15
16.010
-20
-25
15.990
-30
-35
15.970
-40
IL(dB)
-45
90
GD(usec)
100
110
Group Delay(usec)
-25
[1] Roger J. Rush “Success factors for Broadband Satellite
Systems”, Seventh Ka-Band Utilization Conference,
Taromina, Italy, October, 2001.
Frequency Response, Digital Filter
0.750
-20
REFERENCES
April 10-14, 2000.
[3] E. Wiswell, Z. Stroll, A. Baluch, J. Freitag, H.J. Morgan,
”Gen*Star Results Applicable to Ka-Band”, Proc. of the
Fifth Ka-Band Utilization Conference, Taromina, Italy,
October 18-20, 1999.
15.950
120
130
[4] Massih Hamidi, Eric Wiswell, Alan Cherrette, Oliver
Saunders, Hau Ho “TRW’s Broadband Communication
Payloads at C and Ku Frequency Bands”, 2002 IEEE
Aerospace Conference, Bigsky, Montana, USA March 9-16,
2002.
Frequency(MHz)
Figure 9 – Analog & Digital Filter Comparison
[5] Mark Bever, Scott Willoghby, Eric Wiswell, Kenton Ho,
and Stuart Linsky, “Broadband Payloads for The Emerging
Ka_Band Market,” Seventh Ka-Band Utilization
Conference, Santa Margherita, Italy, September 26-28,
2001
This paper reviews architecture and technologies
developed by TRW for the Broadband satellite systems. The
critical features, concepts, performance and benefits of
advanced satellite antenna, payload processor, and digital
transponder are summarized. It is shown that the design and
fabrication of multibeam systems designs using large,
deployable mesh antenna reflectors could provide higher
EIRP with increased system capacity and operation
flexibility.
The digital payload processors and switches on board
satellites also effectively increase the system network
capacity, billable bits and Quality of Service (QoS). The
network flexibility is further achieved through on board
programmable configurable processor for obtaining the
various point-to-point, star and full mesh connectivity in the
network. The multiplexing of multiple signals destined for a
downlink beam into a single high-rate data stream permits
use of high-efficiency (lower DC power consumption)
saturated TWTA operation.
Finally it is concluded that similar benefits of the large
spot beam antenna aperture coverage and onboard
processing can also be achieved in upgrading the legacy
satellite systems operating at C and Ku-Band. The same
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[6] S. Mishima, L. Moy-Yee, G. Yee-Madera, E. Yousefi ,
“Broadband Packet Switch Processor,” Seventh Ka-Band
Utilization Conference, Santa Margherita, Italy, September
26-28, 2001.
[7] Mark Bever, Eric Wiswell, Kenton Ho, and Stuart
Linsky, “TRW Broadband Payloads for Emerging Markets”
PTC Conference Hawaii, USA, February, 2002.
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