Note: Descriptions are shown in the official language in which they were submitted.
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Technical Field
This invention relates to methods and systems for
communicating high rate data to customers in satellite-based
communications networks.
Background of the Invention
A number of applications continue to drive the need for
high-speed data transport. Industry Specific examples include remote film
1 o editing, medical image transport, and financial service data consolidation
and backup. Business communications and training further accelerate
information transfer needs across all sectors. As business, government and
educational institutions disseminate more information, greater importance
is attached to data transfer. In this environment, reliable, high-speed video
and data transport becomes even more critical.
Furthermore, a tremendous growth in Internet traffic has
caused a strain on the capacity of telephony networks. Network
shortcomings include network outages. insufficient access bandwidth, and
insufficient internode bandwidth. Currently, providers need to make
significant investments, as well as experience installation delays, to
upgrade network infrastructure, yet they cannot pass the costs on to the end
users.
Corporate LANs/WANs also generate an insatiable demand
for higher bandwidth. The demand for bandwidth goes up as more and
more users are connected. The users. in turn, demand more services and
improved network speed. Personal computers are being used to process not
only text. but graphics and video as well. all on networks that are
increasingly global. Widespread implementation of corporate intranets and
extranets further drive the move to increased bandwidth applications.
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High-speed networking is also driven by the growth of video distribution.
client/server technology, decentralized systems. increased processing
power and developments in storage capacity.
To meet the high demand. networks of satellites are used to
provide varied coverage as well as provide capacity. These satellites may
be in geostationary, middle or low earth orbit. In many systems, not all the
satellites are used to capacity at any given time.
Another drawback to various networks is that the life cycle
of a network may exceed 10-15 years. During the life of the network, the
1 o needs of users will most likely change, but due to lack of flexibility of
the
electronics. the system may not be able to address all of the new user needs.
Therefore, more satellites may have to be launched or the system will
remain inadequate.
Known systems are typically deployed with little internal
flexibility to accommodate changing requirements over the life of the
system. Also, if a satellite within the system fails, service may be
interrupted. Other satellites in the network may be called upon to provide
back-up. However, some net loss in service is likely since the electronic
payload may not be configurable to match the service provided by the
failed satellite. If, however, the payload characteristics do not match, then,
a net loss of overall service capacity will result.
A system such as that disclosed in U.S. Patent No. 6,125,261,
issued September 26, 2000 and U.S. Patent No. 6,272,317, issued August 7,
2001 have fixed spot beams and scanned spot beams. The beams are
reconfigured to provide satellite coverage to various areas upon the earth. By
changing the phase and amplitude coefficients, various spot beam areas of
coverage may be configured. One drawback to such a system is that other
system parameters such as the communication frequencies are generally fixed
in the satellite. Thus, the satellite is not usable for other satellites
within the
3o system.
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It would therefore be desirable to provide a satellite-based
communications system capable of minimizing service coverage loss within a
satellite
system if a satellite fails. It would further be desirable to provide a
satellite with the
capability to be reconfigured over the life of the satellite to meet the
changing
requirements of system users.
Disclosure of The Invention
According to an aspect, there is provided a payload circuit for a
satellite comprising:
a receive array;
a receive beam forming network;
a transmit array;
a transmit beam forming network;
a communications control circuit for controlling communications of
said satellite, said communications control circuit being an up converter and
a down
converter; and
a reconfiguration circuit coupled to the communications control circuit
for reconfiguring the communications control circuit, said reconfiguration
circuit
comprising a programmable frequency synthesizer coupled to the up converter
and
down converter, an on-board computer and a routing table having tuning
information
stored therein, said on-board computer controlling a reconfiguration of said
communications control circuit from a first frequency range to a second
frequency
range through said programmable frequency synthesizer in response to said
tuning
information.
One advantage of the invention is that a reconfigurable satellite system
may be provided with little cost penalty to the overall system cost.
Other features and advantages of the present invention are readily
apparent from the following detailed description of the best mode.
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for carrying out the invention when taken in connection with the
accompanying drawings.
Brief Description Of The Drawings
Figure 1 is a schematic illustration of a portion of a
constellation of communications satellites, in which at least one satellite is
reconfigurable to form a reconfigurable network according to the present
invention.
FIGURE 2 is a schematic view of a payload system
employing an example of a suitable antenna.
FIGURE 3 is a schematic view of a reconfigurable satellite
payload system according to the present invention using a TDMA switch.
FIGURE 4 is alternative schematic view of a portion of the
reconfigurable satellite system according to the present invention wherein
the TDMA switch is replaced by a packet switch.
Description Of The Preferred Embodiments
In the following description, identical reference numerals
are used to identify identical compounds in the figures. The present
invention applies to various types of satellites suitable of fixed, broadcast
or mobile applications. The present invention is also suitable for satellites
in various orbits such as low, medium and geostationary orbits. Various
shaped orbits such as inclined, elliptical or eccentric may be employed.
Referring to Figure 1. the present system is suitable for use
in a reconfigurable satellite system 300 generally having satellites 302 and
having at least one reconfigurable satellite 304. Satellites 302 form a
satellite network 306. Reconfigurable satellite 304 acts as an orbital spare.
or. as described below. may be a part of network 306. Satellite 302 and
304 may be interconnected by a radio frequency (RF) or an optical link
CA 02464167 2004-05-07
generally represented by arrows 308. Satellites 302. 304 may be medium
earth orbit satellites (MEOs), low earth orbit satellites(LEOs) or
geosynchronous orbit satellites (GSOs) having various shaped orbits such
as elliptical, circular or inclined.
5 Satellites 302, 304 communicate with a ground station 310
located on earth 312. Satellites 302, 304 may communicate with fixed and
mobile user terminals on earth 312. Spot beams may be used to
communicate with earth 312. Ground station 310 generates command
signals as well as communication network signals to satellites 302, 304.
Each satellite 302, 304 has an uplink antenna 314 and a
downlink antenna 316. Uplink antennas 314 receive communication
signals and command signals from ground station 310. Communication
signals to ground station 310 from satellites 302, 304 are transmitted via
downlink antennas 316.
If one of satellites 302 becomes non-functional or is no
longer capable of providing the coverage desired, reconfigurable satellite
304 may be moved into the orbital slot of the satellite to be replaced.
Reconfigurable satellite 304 may also be used for replacing more than one
satellite as well.
Referring now to Figure 2. the reconfigurable satellite has a
payload 317 and a communication control circuit 318 that is coupled to a
receive array 320 and a transmit array 322. Receive array 320 may be part
of uplink antenna 314. Transmit array 322 may be part of downlink
antenna 316.
Communications control circuit 318 has a plurality of
receive beam-forming networks 324 that are each coupled to a transponder
326. Transmit array 322 is coupled to a plurality of transmit and beam
forming networks 328. Each beam formine network 328 is coupled to a
transponder 326.
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Each transponder 326 has a preamplifier 330 coupled to
beam forming network 324. Preamplifier 330 is coupled to a frequency
down converter 332. Preamplifier 330 and frequency down converter 332
amplify the received signal from receive array 320. Frequency down
converter 332 controls the frequency that is received by receive array 320.
Frequency down converter 332 is coupled to an intermediate frequency (IF)
amplifier/filter 334. IF amplifier/filter 334 is coupled to a frequency up
converter 336, which is coupled to a transmit power amplifier 338.
Transmit power amplifier 338 is coupled to transmit beam forming network
to 328. Transponder 326 receives information from receive array 320,
processes the information, and transmits the information through transmit
array 322.
To form reconfigurable satellite 304, a reconfiguration
circuit 339 has a programmable frequency synthesizer 340 coupled to
frequency down converter 332 and frequency up converter 336.
Programmable frequency synthesizer 340 is used to change the frequency
of frequency down converter 332 and frequency up converter 336. An
onboard computer 342 may receive information from uplink antenna 314
and may transmit information to downlink antenna 316. Other information
transmitted and received by onboard computer 342 may be amplitude and
phase weighting coefficients for controlling the direction of the transmit
and receive phased arrays. This information can be received by the satellite
on dedicated RF links or by means of an "order wire" circuit coupled into
the onboard computer. Alternatively, the weighting coefficients can be
computed onboard the satellite as well. The amplitude and phase weighting
coefficients are used to reconfigure the beam to obtain the desired beam
pattern. Beam patterns may vary from narrow spot beams and to broader
coverage beams such as regional area beams.
Programmable frequency synthesizer 340 uses a digitally
controlled phase lock loop for tunability over a narrow frequency range.
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Programmable frequency synthesizer 340 is used to align the frequencies of
the reconfigurable satellite with the satellite that is to be replaced. Due to
the flexibility of a programmable frequency synthesizer, the reconfigurable
satellite may be used to match the characteristics of the satellite it is
replacing.
Referring now to Figure 3, an alternative payload 317' is
illustrated from that of Figure 2. A receive array 320' and a transmitter 322'
are coupled to a communication control circuit 318'. Communication
control circuit 318' has receive beam forming networks 324' coupled to
receive array 320'. Each beam forming network 324' is coupled to a
preamplifier 330'. A down converter 344 is coupled to preamplifier 330'.
Each down converter 344 has a local oscillator input 346 that is used to set
the down converter frequency.
Each down converter 344 is coupled to a switch circuit 348.
Switch circuit 348 has channel filters 350 coupled to down converter 344.
A time division multiple access switch (TDMA) 352 is
coupled to channel filters 350. TDMA switch 352 has an onboard
computer input 354 that may be coupled to a routing table as will be further
described below. TDMA switch 352, as described above, provides
interlinking of all beams, services, and users, and dedicated point to point
and point to multi-point services. TDMA switch 352 switches signals to be
transmitted either to the same uplink beam as the source signal was
transmitted from or by another downlink beam based on the time interval
assigned to the source signal according to onboard computing input 354.
TDMA switch 352 is gated within the time domain to provide precise
windows of time to different desired outputs. Various TDMA switches 352
are known in the art.
Channel multiplexers 356 are also included within switch
circuit 348. Channel multiplexers 356 have various inputs from TDMA
switch. The output of channel multiplexers 356 are coupled to an up
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converter 358. Each up converter 358 has a local oscillator input 360.
Each up converter 358 is coupled to a power amplifier 362. Each power
amplifier 362 is coupled to a beam forming network 328' such as those
described above. Each beam forming network 328' is coupled to transmit
array 322'.
Communications control circuit 318' has a reconfiguration
circuit 339' that has a programmable frequency synthesizer 364.
Programmable frequency synthesizer 364 has programmable frequency
synthesizer outputs 366 that are coupled to local oscillator inputs 346 of
to down converter 344 and local oscillator inputs 360 of up converter 358.
Programmable frequency synthesizer 364 has an input 368 coupled to an
onboard computer 370. Onboard computer 370 provides tuning
information to programmable frequency synthesizer 364 through input 368.
Onboard computer 370 is coupled to a routing table 372.
Routing table 372 is coupled to onboard computer input 354 of TDMA
switch 352. Routing table 372 stores information as to the desired beam
width and times associated with each beam. Onboard computer 370 may
be coupled to an order wire and to and from uplink and downlink control.
Onboard computer 370 may also control amplitude phase and weighting
control as described above.
Referring now to Figure 4. an alternative switch circuit 348'
is shown that may be substituted for switch circuit 348 of Figure 3. Switch
circuit 348 has channel filters 350' and channel multiplexers 356' that are
respectively coupled to down converters 344 and up converters 358. In
Figure 4. the TDMA switch 352 of Figure 3 has been replaced by a signal
processor packet switch 374. Various types of packet switches 374 are
known to those skilled in the art.
In operation, when various portions of payload are desired to
be reconfigured such as antenna reconfiguration. frequency recon-
figuration. or beam to beam reconfiguration. a ground station by way of an
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order wire or control channel may be transmitted to the satellite to update
the on-board look-up table. The onboard computer may be used to
calculate amplitude and phase weighting coefficients necessary to
synthesize uplink and downlink beams. The programmable frequency
synthesizer coupled to onboard computer is used to control the
communication frequencies.
Alternatively, onboard computer may be used to update the
routing table periodically or occasionally from an order wire or RF control
channel from the ground station during operation of the satellite.
to If a reconfigurable satellite is to be moved to replace a
satellite within a network, east/west and north/south station keeping may be
used in a conventional manner so that the reconfigurable satellite may be
placed in the proper orbital position. When the satellite is moved into the
proper position and after the satellite has been properly configured to
replace the satellite from the network, the reconfigurable satellite may
continue to operate. The reconfigurable satellite may also be reconfigured
at any time during the operation of the satellite.
While the best modes for carrying out the invention have
been described in detail, those familiar with the art to which this invention
relates will recognize various alternative designs and embodiments for
practicing the invention as defined by the following claims.
