U.S. patent application number 14/767574 was filed with the patent office on 2015-12-31 for method for shifting communications of a terminal located on a moving platform from a first to a second satellite antenna beam.
This patent application is currently assigned to OverHorizon (Cyprus) Plc. The applicant listed for this patent is OVERHORIZON (CYPRUS) PLC. Invention is credited to Pal Ekberg, James Gerow, Kennet Lejnell.
Application Number | 20150381263 14/767574 |
Document ID | / |
Family ID | 50390037 |
Filed Date | 2015-12-31 |
United States Patent
Application |
20150381263 |
Kind Code |
A1 |
Lejnell; Kennet ; et
al. |
December 31, 2015 |
Method for Shifting Communications of a Terminal Located on a
Moving Platform from a First to a Second Satellite Antenna Beam
Abstract
A method for shifting communications of a terminal located on a
moving platform from a first satellite beam to a second satellite
beam comprises determining a time for initiation of a beam shift
from the first satellite beam to the second satellite beam;
executing a first beam shift from the first satellite beam to the
second satellite beam; and executing a second beam shift from the
first satellite beam to the second satellite beam, wherein the
first and second beam shifts are performed using a switch
matrix.
Inventors: |
Lejnell; Kennet; (Ekero,
SE) ; Gerow; James; (Johnstown, PA) ; Ekberg;
Pal; (Lund, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OVERHORIZON (CYPRUS) PLC |
Nicosia |
|
CY |
|
|
Assignee: |
OverHorizon (Cyprus) Plc
Nicosia
CY
|
Family ID: |
50390037 |
Appl. No.: |
14/767574 |
Filed: |
February 13, 2014 |
PCT Filed: |
February 13, 2014 |
PCT NO: |
PCT/EP2014/000391 |
371 Date: |
August 12, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61764040 |
Feb 13, 2013 |
|
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Current U.S.
Class: |
370/316 |
Current CPC
Class: |
H04B 7/18541 20130101;
H04B 7/18513 20130101; H04B 7/18508 20130101; H04W 36/30 20130101;
H04B 7/18515 20130101 |
International
Class: |
H04B 7/185 20060101
H04B007/185; H04W 36/30 20060101 H04W036/30 |
Claims
1. A method for shifting communications of a terminal located on a
moving platform from a first satellite beam to a second satellite
beam, the method comprising: a. determining a time for initiation
of a beam shift from the first satellite beam to the second
satellite beam; b. executing a first beam shift from the first
satellite beam to the second satellite beam; and c. executing a
second beam shift from the first satellite beam to the second
satellite beam, wherein the first and second beam shifts are
performed using a switch matrix.
2. The method according to claim 1, wherein the first beam shift is
an uplink beam shift and the second beam shift is a downlink beam
shift.
3. The method according to claim 1, wherein the first beam shift is
a downlink beam shift and the second beam shift is an uplink beam
shift.
4. The method according to claim 1, further comprising examining
the quality of the connection to the second satellite beam, and
reverting back to the first satellite beam if the quality of the
connection is below a predetermined threshold.
5. The method according to claim 1, wherein the first and second
beams are broadcast by the same satellite or by two separate
satellites.
6. A system for automated shifting of a communications signal of a
terminal located on a moving platform from a first satellite beam
to a second satellite beam, the system comprising: a. an uplink
switch in the satellite for receipt of the communications signal
transmitted from the terminal, the uplink switch comprising: (i) a
regenerative payload comprising at least one demodulator for
extracting information received in the satellites, and an on-board
processor for processing data; and (ii) a switch matrix and/or a
channelizer for switching an uplink data channel from the first
satellite beam to the second satellite beam upon receipt of a
switch command; b. a downlink switch for transmission of
communications comprising: (i) a regenerative payload comprising at
least one modulator for encoding a data signal to be sent from the
satellites, and an on-board processor for processing data; (ii) a
switch matrix and/or a channelizer for switching a downlink data
channel from the first channel to the second channel; and (iii) at
least two demodulators with a corresponding switch functionality in
the terminal; and c. a computer configured with computer
instructions for determining optimal time for beam shift
execution.
7. The system according to claim 6, wherein the switch matrix
and/or channelizer of the uplink switch is configured to switch the
uplink data channel from the first beam to the second beam into a
common regenerative payload demodulator circuit in a synchronized
manner concurrently with a corresponding frequency switch in the
terminal uplink.
8. The system according to claim 6, wherein the downlink switch
comprises two demodulators, wherein the first demodulator is locked
on a downlink signal from the first beam and the second demodulator
is locked on a downlink signal from the second beam.
9. The system according to claim 8, wherein a user application on
the terminal is connected to either the first or second demodulator
through a command controllable switch.
10. The system according to claim 6, wherein: each satellite is
equipped with a software engine and control function connected to
respective on-board processors and switch matrixes and/or
channelizers; the terminal is equipped with a terminal software
engine and control function; and the software engines and control
functions of the system are synchronized with each other and are
configured to generate and transmit the switch command to execute
the shifting of the communications signal.
11. The system according to claim 6, wherein the system generates
the switch command on-board the satellite and the switch command is
sent to the terminal for execution.
12. The system according to claim 6, wherein the system generates
the switch command in the terminal and transmits the switch command
to one or more satellites for execution.
13. The system according to claim 6, wherein the switch command is
configured to contain specific information for synchronizing a beam
shift.
14. The system according to claim 6, wherein the terminal is
configured to request a beam shift based on its location and local
conditions.
15. The system according to claim 6, wherein the system is
configured to respond to input from sensors on the ground and from
information received from a network operations center for
improvement of satellite coverage.
16. The system according to claim 15, wherein: the system is
configured to increase signal capacity by switching in additional
power, moving additional beams into a desired service area, and/or
adding frequency slots in certain regions; and the system executes
automated satellite beam shifting as necessary in response to
newly-added signal capacity.
17. The system according to claim 6, wherein the system is
configured to gather information about issues affecting signal
conditions from traffic flowing through a network comprising the
system, from the OBP and network operations center, and/or from
ground sensors and atmospheric sensors, and the system informs
users in real time of such issues.
18. The system according to claim 6, wherein the system comprises
computer instructions and flight control configured to maintain
optimized communications signal capacity and quality during travel
of the moving platform.
19. The system according to claim 6, wherein the first and second
satellite beams are transmitted by the same satellite or by
different satellites.
Description
[0001] This application claims the priority benefit of U.S.
provisional application Ser. No. 61/764,040, filed on 13 Feb. 2013,
the contents of which are incorporated by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] Many airlines offer passengers the ability to engage in
wireless communications in flight, such as using a personal laptop
or tablet computer to access websites or E-mail services. These
wireless communications can take place over wife and over a
satellite link to a terrestrial gateway antenna.
[0003] When communicating using a terminal located on a moving
platform (such as an aircraft) covering large distances, the use of
conventional satellites having wide beam coverage can provide for
continuous connection for an extended period of time. When
switching from one satellite to another, or for multi-beam
satellites, from one satellite beam to another, the connection can
be lost, and this down time is typically of the order of minutes.
Although continuous continental and intercontinental communications
with wide-beam satellites can take place with a limited number of
satellite changes, a drawback of wide beams is that they provide
low power density and low sensitivity since the energy is
spread/received from a wide area, making it impossible to support
high data rates on the moving platform using small antennas.
[0004] A multi-spot beam satellite generally has a high power
density and high sensitivity with a wide coverage region, but the
wide coverage is defined by a large number of different beams.
Neighboring beams must use different network conditions such as
frequencies and/or polarization in order to reduce inter-beam
interference, and the individual beams will have a small spot beam
size. The small spot beam size will cause a frequent need to move
from one beam to another, and it is no longer acceptable to lose
communication during such shifts.
[0005] Although some of the beam shifts can be pre-planned before
the trip, such pre-planning can be very difficult since flight
delays, changes of itinerary, and weather can affect the planned
trip route. If the moving terminal travels into beams that were not
pre-planned, rapid coordination with the satellite operator is
needed to ensure continuous communications. Since the satellite
operator does not know at all times which frequencies may be
available in each beam, pre-planning is therefore complex and very
inefficient. The satellite operator does not want to reserve
frequencies in particular beams unless these frequencies are paid
for, thereby removing them from general usage and causing
inefficient use of spectrum, as well as significantly increasing
service costs. If route planning takes place long before the actual
trip, pre-planning which satellite frequencies to use becomes even
more difficult, and communications become even more expensive since
longer lead times may result in even further changes, both
environmentally and on the satellite.
[0006] The technical characteristics of a satellite connection when
moving from one beam to another will now be described with
reference to FIG. 1. FIG. 1 illustrates a mobile user located in an
aircraft communicating over a satellite to a terrestrial gateway
(GW) antenna, and the mobile user will be leaving one coverage area
(Beam 1, covering North America) and entering another coverage area
(Beam 2, covering Europe).
[0007] When switching from Beam 1 to Beam 2, the user will first
typically lose a connection to Beam 1, and then have to
re-establish a connection to Beam 2. This reconnection can be a
rather complicated process, and the communication line will be down
until the connection to the second beam can be established. In a
multi-beam environment where the beam diameter on the ground is
small, this reconnection problem grows since the mobile platform
will need to shift beams quite often, especially when moving
quickly such as in flight. When the mobile platform enters the beam
overlap region where a beam switch will have to be managed, the
actual time it takes to move from a good connection to a lost
connection is small.
[0008] One important parameter for multi-beam systems is inter-beam
isolation, and in order to get high isolation, it is necessary to
define the edge of coverage further down on the lobe as compared to
the theoretical optimum edge of coverage gain. This phenomenon is
illustrated in FIG. 2, which shows an exemplary antenna pattern for
a parabolic reflector antenna. The multi-spot beam edge is defined
at 7 dB below the beam peak (upper horizontal line). The 1 dB
higher gain contour, relative to the edge of coverage gain, is
indicated by the lower horizontal line and the angular distance on
the edge is 0.05.degree., which at nadir is approximately 19 miles
(31 km). The time it takes for an aircraft traveling at a speed of
530 mph (850 km/h) to traverse this distance is slightly more than
2 minutes, and hence, timely beam switching is needed.
[0009] For a multi-spot coverage beam where the edge of coverage is
defined at 0.5.degree. (approximately the size of the spots in the
Eutelsat Ka-Sat system), the region where the gain drops by 1 dB is
only 7 miles (11 km) and the corresponding time for an airplane to
travel this distance is approximately 46 seconds.
[0010] Accordingly, there is an unmet need for rapid automated
switching of satellite beams by terminals located in moving
platforms while maintaining continuous communications.
BRIEF DESCRIPTION OF THE INVENTION
[0011] The present invention is intended to address the above
problems associated with satellite communications. One aspect of
the present invention is directed to a method for shifting
communications of a terminal located on a moving platform from a
first satellite beam to a second satellite beam. The method
comprises determining a time for initiation of a beam shift from
the first satellite beam to the second satellite beam; executing a
first beam shift from the first satellite beam to the second
satellite beam; and executing a second beam shift from the first
satellite beam to the second satellite beam, wherein the first and
second beam shifts are performed using a switch matrix.
[0012] The invention is equally capable of handling beam shifts in
any order. For example, the first beam shift may be an uplink beam
shift and the second beam shift may be a downlink beam shift.
Alternatively, the first beam shift may be a downlink beam shift
and the second beam shift may be an uplink beam shift.
[0013] The invention can determine the connection quality of a
prospective beam switch prior to completing the beam switch. That
is, the invention examines the quality of the connection to the
second satellite beam prior to a beam switch. If the connection
quality is high, (for example, if there is little chance of a
dropped connection upon switching to the second beam), the
invention will undergo the beam switch. If the quality of the
connection to the second beam is below a predetermined threshold,
for example, due to noise, the invention will not undergo the beam
switch and will revert back to the first satellite beam. In this
manner, the invention seeks to maintain a high quality connection
to minimize outages or gaps in coverage.
[0014] The first and second beams may be broadcast by the same
satellite or by two separate satellites.
[0015] Another aspect of the present invention is directed to a
system for automated shifting of a communications signal of a
terminal located on a moving platform from a first satellite beam
to a second satellite beam. The system may comprise components such
as an uplink switch for receipt of the communications signal; a
downlink switch for transmission of communications; and computer
instructions for determining optimal time for beam shift
execution.
[0016] The uplink switch may comprise elements such as a
regenerative payload comprising at least one demodulator for
extracting information received in the satellites, and an on-board
processor for processing data; and a switch matrix and/or a
channelizer for switching an uplink data channel from the first
satellite beam to the second satellite beam.
[0017] The downlink switch may comprise elements such as a
regenerative payload comprising at least one demodulator for
encoding a data signal to be sent to the satellites, and an
on-board processor (OBP) for processing data; a switch matrix
and/or a channelizer for switching a downlink data channel from the
first channel to the second channel; and at least two demodulators
with a corresponding switch functionality in the terminal.
[0018] The switch matrix and/or channelizer of the uplink switch
may be configured to switch the uplink data channel from the first
beam to the second beam into a common regenerative payload
demodulator circuit in a synchronized manner concurrently with a
corresponding frequency switch in the terminal uplink.
[0019] The downlink switch can be configured to comprise two
demodulators, wherein the first demodulator is locked on a downlink
signal from the first beam and the second demodulator is locked on
a downlink signal from the second beam.
[0020] A user application on the terminal can be connected to
either the first or second demodulator, whichever is active with
respect to connecting the application traffic flow, through a
command controllable switch, a non-manual switch connected to the
controller software which controls the hardware of the switch. Such
an embodiment allows for ready control of the beam switching
process.
[0021] Each satellite can be equipped with a software engine and
control function connected to respective on-board processors and
switch matrixes and/or channelizers. Similarly, the terminal can be
equipped with a terminal software engine and control function, and
the respective software engines and control functions of the system
can be synchronized with each other and configured to generate and
transmit the switch command to execute the shifting of the
communications signal. Such embodiments allow for efficient
synchronization of a beam shift.
[0022] In one embodiment, the system can generate the switch
command on-board the satellite and send the switch command to the
terminal for execution. The system can also generate the switch
command in the terminal and transmit the switch command to one or
more satellites for execution. The switch command can be configured
to contain specific information for synchronizing or timing a beam
shift, and this timing is provided to the components of the system
for preparation for the beam shift.
[0023] The terminal can be configured to request a beam shift based
on its location and local conditions. That is, if the terminal
expects that the current beam signal will weaken for whatever
reason, such as poor weather or other atmospheric conditions, the
terminal can request a beam shift to a stronger signal.
[0024] The system can also be configured to respond to input from
sensors on the ground and from information received from the OBP
and/or a network operations center for improvement of satellite
coverage. For example, the system can be configured to increase
signal capacity by switching in additional power, moving additional
beams into a desired service area, or adding frequency slots in
certain regions. The system recognizes this newly-added signal
capacity and executes automated satellite beam shifting as
necessary in response to such newly-added signal capacity.
[0025] The system can also be configured to gather information from
various sources, such as from communications traffic flowing
through a network comprising the system, from an onboard processor
and a network operations center, and/or from sensors such as ground
sensors or atmospheric sensors about issues affecting signal
conditions, and to inform users in real time thereof. That is, the
system in the satellite may gather information from various sensors
located at any place on the ground or in the atmosphere to acquire
data about problems affecting link conditions, such as weather and
other local effects, and can inform mobile users in the system,
with effectively no delay, about such local problems. Users can
then take whatever action may be advisable, such as changing their
route, and thereby avoiding loss of communication caused by any
potential problems.
[0026] The system can also be configured so as to provide flight
control executed from the satellite which optimizes communications
capacity at all times. That is, the system can comprise computer
instructions and flight control configured to maintain optimized
communications signal capacity and quality during travel of the
moving platform. In this regard, the system is operationally linked
to the flight control system so that the moving platform remains in
a flight path which provides optimal signal quality.
[0027] Other aspects and advantages of the invention will be
apparent from the description below.
BRIEF DESCRIPTION OF THE FIGURES
[0028] FIG. 1 illustrates an aircraft flying over the Atlantic
region. The satellite is in communications with a first satellite
network (Beam 1), and the aircraft satellite communication system
must switch to another satellite network (Beam 2), to maintain
continuous communications. The beam switch must take place in the
beam intersection region.
[0029] FIG. 2 shows a typical antenna pattern for a parabolic
reflector system. FIG. 2 shows that the window going from good
signal to drop-off is short, and that there is the need for a
system that can automatically takes care of the beam shift
maneuver.
[0030] FIG. 3 is a schematic flow diagram illustrating continuous
monitoring of the need for a beam shift according to an aspect of
the invention. When this need to switch beams arrives, the system
according to the present invention will initiate a beam shift
procedure.
[0031] FIG. 4 is a schematic flow diagram illustrating an exemplary
process according to the present invention for determining whether
to shift the uplink or downlink first, and the sequence of events
that needs to take place.
[0032] FIG. 5 is a schematic flow diagram illustrating beam shift
execution on the uplink, and shows the timing of the beam shift and
the potential for changes in the need for a beam shift.
[0033] FIG. 6 is a schematic flow diagram illustrating beam shift
execution on the downlink.
[0034] FIG. 7a is a schematic diagram illustrating an exemplary
hardware implementation according to an embodiment of the
invention.
[0035] FIG. 7b is a schematic diagram showing the embodiment of
FIG. 7a after the beam switch has taken place.
[0036] FIG. 8 illustrates terminal receive blocks according to an
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Although the following discussion refers to a mobile
terminal located on an aircraft to exemplify the invention, the
principles of the invention are equally applicable for any moving
platform. The invention is applicable to any mobile platform moving
at a speed which makes it likely to cross between different beams
over a period of days, hours, or shorter increments of time.
[0038] The present invention addresses problems currently
associated with switching from a first satellite beam to a second
satellite beam. The current state of the art requires a complicated
manual procedure involving both the user and personnel at the
gateway/NOC during a beam switch. If the switch is unsuccessful,
the signal is dropped entirely, thereby leaving the mobile platform
without communication capabilities for a certain period of time. As
discussed above, the region going from a fair signal environment
down to drop-out conditions can be small and hence the
corresponding time window for a beam switch is short, and will
depend on the spot beam size, which is typically on the order of a
few minutes or less for an aircraft. A shift beam may be needed
quite frequently when the platforms move through a multi-spot grid.
Accordingly, multi-spot beams do not provide particular advantages
during high speed travel.
[0039] To address these and other problems associated with the
prior art, the present invention provides a system that
automatically detects and switches to new beam parameters when
going from one beam to another, both on the uplink and downlink
side, in a coordinated fashion and without dropping the
communication link. The system monitors the need for a beam shift,
and when the system determines that a beam shift will be necessary,
it will initiate the beam shift process. The present invention will
typically be installed at the factory during manufacture of the
satellite.
[0040] To solve the problem of maintaining continuous communication
to and from a moving platform when moving from beam to beam, the
present invention provides for a satellite switching system having
an input section comprising a switch matrix and/or a channelizer,
and a regenerative payload including an on-board processor (OBP)
and associated software engine. In the regenerative payload and
OBP, the signals are received and demodulated such that the
transmitted bit stream are uncovered for extraction of useful
information and commands for timely action on-board the satellite.
The on-board equipment also provides information about the link
quality, such as signal to noise measures, e.g. C/No or Eb/No. A
flow chart showing the beam shift process on uplink and downlink is
illustrated in FIG. 4.
[0041] A switch is a simple implementation of a channelizer in that
a switch takes the complete input of a transponder and switches
that data stream into a particular output transponder. In contrast,
a channelizer operates on a level between the input and output
transponders, and can take a portion of the input section of the
transponder and direct it to any of the output transponders,
thereby providing greater flexibility as compared to a switch. A
switch can be used instead of a channelizer when the manufacturer
designs complex satellites with small bandwidth transponders,
whereas wide bandwidth transponders will typically be coupled to a
channelizer.
[0042] When the beam shift process has been initiated, the
procedure for shifting on the uplink and the downlink is
coordinated by the system. The system first determines which link
(uplink or downlink) to shift. For example, if the link margin on
the uplink is smaller than the link margin on the downlink, it is
likely that the uplink will be lost first when the moving platform
moves out of the beam, and hence it would be preferable to switch
the uplink first. In other situations, the quality of service
parameters of the different beams or changes to the flight route,
might differ on the uplink and downlink sides, and these factors
can be considered when determining the beam shift sequence. In
certain instances, the decision to switch beams can be made by a
user upon review of the beam or connection quality.
[0043] If the beam shift is not successful, the system can shift
back to the previous parameters to reestablish the link to the
first beam to maintain continuous communications. The system will
then attempt to shift beams again, optionally after a short pause
(seconds or milliseconds) to clear out any buffers. Since both
uplinks and downlinks are not shifted at the same time, the
invention ensures that one of the uplink or the downlink will
always be connected even when a beam shift is not successful. This
feature of the invention enables the system to reestablish a lost
uplink or downlink connection.
[0044] A change of frequency in the terminal located on the moving
platform needs to be synchronized with the switch in the
channelizer on the satellite. Looking first at the uplink, when the
terminal executes a shift in transmission frequency from frequency
f.sub.0 to frequency f.sub.1, the signal travels from the terminal
up to the satellite which is approximately 36,000 km from Nadir in
approximately t=(distan{grave over (c)}e to satellite)/(speed of
light)=36000/300000=about 120 ms (milliseconds). When the switch
signal is received in the satellite, the channelizer in the
satellite will then make the corresponding switch. This sequence
for the uplink is illustrated in FIG. 5. If the heading or the
flight plan has changed in such a way that the projected need for a
beam shift is no longer valid, the beam shift process is
interrupted and the system maintains its current conditions. In
this embodiment, the communication parameters are shifted first in
the terminal or moving platform at t=t.sub.0 and after this shift
has propagated up to the satellite, the shift is then executed in
the satellite. The system at the terminal can be configured to
continuously sense the presence of other beams for potential
shifts, or the system can be configured to turn itself on when the
system expects that the moving platform will be near an overlap
region for an upcoming beam switch.
[0045] The corresponding but reversed execution sequence is
illustrated for the downlink in FIG. 6. This process is very
similar to the shift performed on the uplink (FIG. 5) but differs
in the sequence of shift commands. In FIG. 6, the shift is first
executed in the satellite, and after this shift has propagated down
to the terminal located in the moving platform, the shift is then
executed in the terminal. The implementation of the switching will
depend on the particular implementation of the invention and upon
the intended applications.
[0046] To enable the switch on the uplink side, the satellite input
section has a switch matrix and/or a channelizer to switch the
uplink signal from the terminal into a specific OBP channel on the
satellite, even when the uplink frequency changes as a result of
the user moving from one beam to another. FIG. 7a illustrates a
switch section and/or channelizer, on-board processor (OBP), and
the associated control software and interfaces. In FIG. 7a, the
switch section is set such that the frequency f.sub.0 which is
received in the satellite is connected to input channel 1, and this
data goes through the switch and/or channelizer section and is
output on output channel 1 which is connected to channel 1 of the
on-board processor.
[0047] In FIG. 7b, the communication link has shifted from
frequency f.sub.0 of Beam 1 to frequency f.sub.1 of Beam 2. The
dotted line illustrates that, the signal passing through the switch
section is adjusted such that communications from input channel 2
now passes to output channel 1 which remains constantly connected
to OBP channel 1. Hence, from the OBP perspective, the
communication link looks exactly the same as before the beam switch
since the signal received by the OBP channel 1.
[0048] As illustrated in FIGS. 7a and 7b, when shifting from Beam 1
at frequency f.sub.0 to Beam 2 at frequency f.sub.1 (optionally
involving polarization), the signal maintains a constant connection
to the same OBP channel (channel 1 in this example). A
corresponding switch functionality is implemented in the terminal
on the downlink side.
[0049] In one embodiment, two demodulators and a channelizer/beam
switch after the demodulators can be used to keep the active signal
switched into the application. This switching is illustrated in
FIG. 8, which illustrates an embodiment showing principal
components of the terminal and the downlink related blocks. The
terminal receive blocks comprise of a double set of demodulators, a
controllable switch, control blocks, and a control loop. The
control intelligence modules are connected to the demodulators to
enable setting the correct communications parameters when the
moving platform enters into new beams and for monitoring received
signal quality. Corresponding terminal functionality would be
implemented on the uplink side.
[0050] Similar switching means can be employed for both uplink and
downlink communications, although in certain embodiments, the
uplink and downlink systems may have different structural
configurations and components. Similarly, consistent with the
invention, the switching hardware located in the terminal and in
the satellite may be similar or may have a different structure.
[0051] The components of the present invention, such as the switch
section, channelizer, and on-board processor can be conventional,
although the system will generally be custom-configured for each
particular implementation. Examples of commercial vendors selling
components for use in the present invention include Advantech
Wireless (Suwanee, Ga.) for modulators on-ground; STM Group
(Irvine, Calif.) for SatLink hubs and VSAT modems; VT iDirect, Inc.
(Herndon, Va.) for satellite routers; Thales USA (Arlington, Va.),
Orbital Sciences (Dulles, Va.), Loral Space & Communications
(New York, N.Y.), Boeing (Berkeley, Mo.), and Astrium North America
(Houston, Tex.) for switch sections; Thales Alenia Space North
America (Cupertino, Calif.), Thales Alenia Space Spain (Tres
Cantos, Madrid, Spain), MDA Information Systems (Richmond, British
Columbia, Canada), and Astrium for on-board processors; and Boeing
and Astrium for digital channelizers.
[0052] Examples of terminals which are suitable for use in the
present invention include conventional antennas which communicate
to a satellite, as well as those which are designed for use
on-the-move.
[0053] In addition to the hardware components discussed, the
invention will also comprise the requisite computer instructions to
allow the system to perform the present invention. These computer
instructions can be implemented as in the form of software code
stored in volatile or non-volatile computer memory. Alternatively,
the computer instructions can be written to hardware, in the form
of a custom-designed and installed integrated-circuit (IC) chip,
such as an ASIC circuit, which comprises embedded hardware
instructions for performing the invention, or the instructions can
be written to a reprogrammable IC device which allows for updating
of the embedded computer code instructions with new
instructions.
[0054] The hardware components of the invention such as the switch
section and demodulators will generally be located on the moving
platform, whereas the space-based switch section, channelizer,
on-board processor, and the associated interfaces will generally be
located in the satellite. However, in certain embodiments of the
invention, the components may be located on either the moving
platform or on the satellite. Both the moving platform and the
satellite have a software engine on-board to perform the
invention.
[0055] The timing of beam switches can be achieved by different
methods as detailed below. For example, the invention may
communicate with other satellite systems to form a relay network
encircling the globe, or communications signals can be passed off
to other terrestrial gateways in order to reduce the distance that
a signal may have to travel.
[0056] Uplink System for Continuous Connection
[0057] Using inputs such as signal quality, altitude, speed and
direction data received from the moving platform, the present
invention can calculate when a beam switch will be necessary and
can generate a switch command. In one embodiment of the invention,
this switch command can be generated on-board the satellite and
sent down to the terminal located on the moving platform. The
terminal then executes the switch when the command is received or
after a pre-defined delay. The corresponding beam switch in the
satellite is executed, taking into account factors such as the time
it takes for the signal to go from the satellite to the terminal,
the time it takes for the command to be executed in the terminal
(including any pre-defined delay), and the time it takes for the
signal to go from the terminal up to the satellite.
[0058] An uplink beam switch can be achieved by an on-board
software program which connects with the channelizer/switch and the
on-board processor. Accordingly, a processor hosting the software
and an interface between the channelizer/switch and on-board
processor are required. For the downlink, a modified version of the
software used for the uplink can be employed. As the downlink beam
is typically in communications with a terrestrial terminal, and not
an orbiting satellite, the downlink hardware and software will
normally be customized for terrestrial communications in order to
maximize the performance of the communications link.
[0059] In another embodiment of the invention, the switch command
can be generated in the terminal and sent up to the satellite
provided that an open frequency in the second beam is available for
the switch. The switch command can include information for the
correct timing of the switch. For example, the switch command may
contain an instruction that the shift from f.sub.0 to f.sub.1 is to
be executed immediately upon receipt. This provision requires that
the time slot between signal frames be long enough to allow for
extraction and execution of the switch command before the next
frame arrives. Otherwise, additional delays may be necessary to
ensure that the switch command can take place at the intended
time.
[0060] In another embodiment of this invention, when the beam
borders are well-defined, the system can use knowledge in the
satellite about the speed, direction and altitude of the moving
platform to enable the software engine on-board the satellite to
compute the time when the platform will cross the border to the
next beam, and hence time the switching accordingly.
[0061] It is also possible to allow the terminal to request a beam
shift, based on the local conditions where the terminal is located,
and on the system's prior knowledge of the flight plan. Factors to
include when evaluating the timing for the beam switch may include
information related to the quality of service in the current beam,
prior knowledge about a quick maneuver shift that is not predicted
by linear extrapolation, or a pre-defined route only known locally.
If there is communication space free in the requested beam, then
the terminal will be free to shift to the second beam. The beam
shift is acknowledged by the on-board system, optionally in
connection with a ground-based Network Operations Center (NOC). The
shift can be initiated by a shift command sent from the terminal in
one frame containing instructions that a shift will take place X
frames after the current frame. The system would send X frames with
current communication parameters, and after counting X received
frames, at frame X+1, the beam will shift to the new beam and
resume continuous communications without a break.
[0062] Downlink System for Continuous Connection
[0063] To allow for the terminal to stay connected during flight,
it is necessary for the system to make both uplink and downlink
beam switches. An embodiment of a terminal receive (downlink)
system will now be discussed.
[0064] As mentioned above, an embodiment of a downlink system,
illustrated in FIG. 8, comprises two separate demodulator circuits.
With two demodulation circuits, it is possible to have one circuit
in active satellite communications and other circuit available for
switchover. When entering the overlap space between the beams, both
demodulator circuits will be able to lock on to the signals from
the different beams: the first demodulator stays locked on to the
original beam, and the second demodulator locks on the signal from
the new beam to which the switch shall be executed. When the signal
quality in the second beam is acceptable, the beam switch is
executed along the same principles as for the uplink switch.
[0065] Another embodiment of a downlink system comprises a single
demodulator. In this case, the system will rely on intelligence in
the software to predict when the switch should take place, and the
execution will be similar to the execution on the uplink. If there
is only a single demodulator, the uplink switch will be executed
either before or after and not at the same time as the downlink
switch. The separate switch timings will ensure that the system
maintains a connection to at least one satellite at all times.
[0066] In another embodiment of the invention, the downlink system
may comprise three or more demodulators. The third (and any
subsequent) demodulator can operate, for example, over a separate
communication and control channel having more robust signaling
properties. Such embodiments advantageously allow larger link
margins, thereby permitting the satellite to maintain link
connections, for example, over a non-spot beam if such is present
on the satellite. In such an embodiment, the link connection to the
third demodulator may be of a TDM (time division multiplexing) type
such that it uses a minimum of bandwidth and can be shared by many
users. The first and second demodulators can be used for more
demanding links with minimum link margins in the high density spot
beams.
[0067] Due to the frequency re-use scheme in the spot beam
allocation, it is often necessary to have different frequencies in
neighboring beams. In such instances, it is generally not feasible
to use a channelizer in the satellite to compensate for the
parameter switch when going from one beam to another on the
downlink. Accordingly, the dual demodulator function shown in FIG.
8 can be included in the terminal on ground, and the switch
function performed in this on-ground terminal, similarly to the
switch that is being done on the uplink side in the satellite with
the switch/channelizer. The dual demodulator can be two separate
demodulators, or it can be a single hardware element which contains
or emulates a plurality of demodulators, such as a multiple core
processor.
[0068] The transmit function in the satellite utilizes the
modulator which encodes the signal going down and the switch from
one downlink frequency to the next when the beam shift is executed.
This switch in the downlink frequency can be adjusted for in the
ground terminal by switching from one demodulator to the other in a
similar fashion as the switch is performed on the uplink side in
the satellite.
[0069] In another embodiment of the invention, the downlink can be
configured with larger link margins relative to the uplink, thereby
enabling the downlink to stay connected further into the overlap
region. In such an instance, the uplink switch can be executed
first, followed by the downlink switch.
[0070] General System Intelligence and Applications of the
Invention
[0071] Implementation of the invention as described advantageously
eliminates the time-consuming process of re-acquiring a lost
connection. When a respective uplink or downlink signal has entered
the OBP, the signal will be switched or routed to the uplink or
downlink, as required, and the user will not experience any
downtime. The system may be expanded to include additional system
intelligence to improve the overall quality of service, and may
also include special service offerings based on executable codes
uploaded to the software engine on-board the satellite. The quality
of service may be improved based on information about the users of
the system (such as but not limited to type of connection/device,
mobility data, and technical specifications), local weather, and
other local conditions which may be determined in the satellite
based on sensors located on the ground and information received
from the NOC.
[0072] The invention also allows for the use of information that is
gathered in the satellite from sensors and other gauges such as
traffic patterns, news, and political information to execute other
commands and processes. For example, if a news event on the ground
causes increased numbers of users in the aircraft wishing to
establish voice or data communications to learn about this new
event and consequently increasing the possibility of signal
congestion, satellite coverage can cope with this increased demand
by responding with switching in more power or additional frequency
slots in a certain region.
[0073] The invention also allows for data analysis on-board the
satellite to generate commands for different applications. For
example, the data analysis can be a trading platform uploaded
on-board the satellite which is receiving input from a plurality of
different locations, each trading in real time. By processing this
data, the system can generate commands such as buy/sell orders that
are sent down to the ground.
[0074] If the mobile platform is travelling according to a
pre-defined route, a beam shift plan can be pre-loaded into the
inventive system and the beam shift timings pre-programmed in
accordance with the methods previously described.
[0075] The invention also allows for sharing of information from
the on-board system on the satellite to the terminal on the moving
platform in regards to the quality of service of the different
beams in the system. For example, if certain well-characterized
regions are prone to have high signal congestion, these beams can
be avoided if the planned travel or flight route of the moving
platform is slightly changed. Alternatively, if the beam pattern
can be adjusted, additional beams can be moved to the region, more
power can be focused into the congested beams, or additional
frequencies can be switched into these beams.
[0076] When more than one mobile unit is travelling at the same
time, it is possible for the system to calculate optimal quality of
service and communication slot sharing properties for the different
mobile units before they enter new beams. This calculation can be
based on each terminal's type of service. For example, a premium
service terminal can be allowed communication space before a lower
priority terminal.
[0077] If several terminals are moving towards the same beam, the
present invention can determine preferred communication parameters
and beam switch times. Factors that may be considered include time
of arrival at the beam switch location and quality of service
parameters for each terminal. If there is a risk of congestion, a
warning can be sent to the lowest priority or quality of service
terminals before additional terminals enter the congested beam.
Such congestion data can be used to pre-plan a beam switch and make
changes to the anticipated flight route if necessary.
[0078] Knowledge of problems such as bad weather in certain areas
makes it possible to change a flight plan to avoid a potential loss
of communications by a new choice of route. In such instances, the
system may allocate additional capacity to those areas which can
accommodate additional units.
[0079] With the on-board intelligence and simultaneous connection
to many different geographical areas, for example, simultaneous
connections to London, Paris, New York and the mid-Atlantic Ocean,
the present invention can take information originating from
multiple areas and received on-board the satellite almost
simultaneously, and can process this information instantaneously
on-board the satellite. Using the intelligence data received and
the on-board software engine processing, the system can then send
commands down to different receivers or terminals connected to
different beams. This feature of the invention can be highly
advantageous in situations when new instructions need to be
transmitted to terminals in seconds or fractions of a second in
response to data shared and received from many different remote
locations at the same time. Because the inventive system is
satellite-based, the invention allows users to remain in continuous
communications from remote locations that are missing ground-based
infrastructure, such as the mid-Atlantic, and the users can engage
in time-sensitive financial transactions, such as securities or
commodity trading.
[0080] Other objects, advantages and embodiments of the various
aspects of the present invention will be apparent to those who are
skilled in the field of the invention and are within the scope of
the description and the accompanying figures. For example, but
without limitation, structural or functional elements might be
rearranged, or method steps reordered, consistent with the present
invention. Similarly, a terminal may comprise a single instance or
a plurality of devices, such plurality possibly encompassing
multiple terminal types. The types of equipment described in
various embodiments are not meant to limit the possible types of
hardware elements that may be used in embodiments of aspects of the
present invention, and other instrumentation that may accomplish
similar tasks may be implemented as well. Similarly, principles
according to the present invention, and methods and systems that
embody them, could be applied to other examples, which, even if not
specifically described here in detail, would nevertheless be within
the scope of the present invention.
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