U.S. patent application number 09/759659 was filed with the patent office on 2002-07-18 for method and apparatus for controlling spot beam configurations for a communications satellite.
Invention is credited to Brundrett, David L., Harmon, Garrick J., Linsky, Stuart T..
Application Number | 20020093451 09/759659 |
Document ID | / |
Family ID | 25056477 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020093451 |
Kind Code |
A1 |
Harmon, Garrick J. ; et
al. |
July 18, 2002 |
Method and apparatus for controlling spot beam configurations for a
communications satellite
Abstract
A communications satellite method and are provided for
controlling a configuration of spot beams produced by a
communications satellite. A plurality of spot beams are generated
by a communications satellite while maintained at a first orbital
position with respect to a first portion of the earth. The
plurality of spot beams are configured in a first cell pattern to
substantially encompass a first portion of the Earth. The satellite
is moved to a second orbital position with respect to a second
portion of the earth. Once moved, the satellite is reconfigured
such that a second plurality of spot beams form a second pattern 85
to substantially cover the new portion of the earth of interest. A
network of switches allows the satellite 10 to be reconfigured for
operation from multiple orbital positions. The switching network
directs individual feeds to different signal paths having different
bandwidth and power capabilities.
Inventors: |
Harmon, Garrick J.; (Newport
Beach, CA) ; Linsky, Stuart T.; (Rancho Palos Verdes,
CA) ; Brundrett, David L.; (Culver City, CA) |
Correspondence
Address: |
Patent Counsel
TRW Inc.
Law Department, E2/6051
One Space Park
Redondo Beach
CA
90278
US
|
Family ID: |
25056477 |
Appl. No.: |
09/759659 |
Filed: |
January 12, 2001 |
Current U.S.
Class: |
342/354 ;
455/13.3 |
Current CPC
Class: |
H04B 7/18519 20130101;
H04B 7/2041 20130101 |
Class at
Publication: |
342/354 ;
455/13.3 |
International
Class: |
H04B 007/185 |
Claims
What is claimed is:
1. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at a first discrete orbital position with
respect to a first portion of the earth; activating a first
plurality of active spot beams in a first beam pattern to
substantially encompass the first portion of the earth; moving the
satellite to a second discrete orbital position with respect to a
second portion of the earth; and activating a second plurality of
spot beams in a second beam pattern to substantially encompass the
second portion of the earth.
2. The method of claim 1, further comprising the step of:
activating at least one common spot beam in said first and second
pluralities of spot beams.
3. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at a first discrete orbital position with
respect to a first portion of the earth; activating a first
plurality of active spot beams in a first beam pattern to
substantially encompass the first portion of the earth; moving the
satellite to a second discrete orbital position with respect to a
second portion of the earth; and activating a second plurality of
spot beams in a second beam pattern to substantially encompass the
second portion of the earth, said second plurality of spot beams
being mutually exclusive from said first pluralities of spot
beams.
4. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at a first discrete orbital position with
respect to a first portion of the earth; activating a first
plurality of active spot beams in a first beam pattern to
substantially encompass the first portion of the earth; moving the
satellite to a second discrete orbital position with respect to a
second portion of the earth; and activating at least one new spot
beam when the satellite is moved to said second orbital position,
said activated new spot beam having been inactive when the
satellite was at said first orbital position.
5. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at a first discrete orbital position with
respect to a first portion of the earth; activating a first
plurality of active spot beams in a first beam pattern to
substantially encompass the first portion of the earth; moving the
satellite to a second discrete orbital position with respect to a
second portion of the earth; and deactivating at least one spot
beam when the satellite is moved to said second orbital position,
said deactivated spot beam having been active when the satellite
was at said first orbital position.
6. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at a first discrete orbital position with
respect to a first portion of the earth; activating a first
plurality of active spot beams in a first beam pattern to
substantially encompass the first portion of the earth; moving the
satellite to a second discrete orbital position with respect to a
second portion of the earth; activating a second plurality of spot
beams in a second beam pattern to substantially encompass the
second portion of the earth; and adjusting a signal attribute of at
least one spot beam that is active in both said first and second
pluralities of spot beams, said signal attribute including one of
spot beam bandwidth and power.
7. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at a first discrete orbital position with
respect to a first portion of the earth; configuring a first
plurality of active spot beams in a first beam pattern to
substantially encompass the first portion of the earth; moving the
satellite to a second discrete orbital position with respect to a
second portion of the earth; configuring a second plurality of spot
beams in a second beam pattern to substantially encompass the
second portion of the earth; and dividing said first and second
pluralities of active spot beams into first, second and common
subsets of spot beams, said first configuring step activating said
first and common subsets and deactivating said second subset, said
second configuring step deactivating said first subset and
activating said second and common subsets.
8. The method of claim 1, further comprising moving the satellite
between first and second geostationary orbital positions.
9. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at a first discrete orbital position with
respect to a first portion of the earth; activating a first
plurality of active spot beams in a first beam pattern to
substantially encompass the first portion of the earth; moving the
satellite to a second discrete orbital position with respect to a
second portion of the earth; and activating a second plurality of
spot beams in a second beam pattern to configure said first and
second beam patterns to encompass different portions of a desired
land means.
10. The method of claim 2, further comprising the step of: when
said satellite moves from said first orbital position to said
second orbital position, re-routing said common spot beam from a
first signal path to a second signal path, respectively to adjust
at least one signal attribute of said common spot beam.
11. A communications satellite, comprising: at least one antenna
for transmitting and receiving communications signals, said antenna
defining first and second spot beam patterns separately activated
when the satellite is located at first and second discrete orbital
positions, respectively; and a switch network activating a first
group of spot beams forming said first spot beam pattern when the
satellite is located at the first discrete orbital position, and
activating a second group of spot beams forming said second spot
beam pattern when the satellite is located at the second discrete
orbital position.
12. A communications satellite, comprising: at least one antenna
for transmitting and receiving communications signals, said antenna
defining first and second spot beam patterns separately activated
when the satellite is located at first and second discrete orbital
positions, respectively, said antenna comprising a plurality of
horn feeds, each horn feed generating a corresponding spot beam
when activated,; and a switch network activating a first group of
spot beams forming said first spot beam pattern when the satellite
is located at the first discrete orbital position, and activating a
second group of spot beams forming said second spot beam pattern
when the satellite is located at the second discrete orbital
position wherein a common horn feed generates a spot beam in each
of said first and second groups of spot beams.
13. A communications satellite, comprising: at least one antenna
for transmitting and receiving communications signals, said antenna
defining first and second spot beam patterns separately activated
when the satellite is located at first and second discrete orbital
positions, respectively, said antenna comprising multiple horn
feeds divided into first, second and common groups,; and a switch
network activating a first group of spot beams forming said first
spot beam pattern when the satellite is located at the first
discrete orbital position, and activating a second group of spot
beams forming said second spot beam pattern when the satellite is
located at the second discrete orbital position. said switch
network activating said first and common groups of horn feeds to
generate said first spot beam pattern when the satellite is at the
first orbital position, said switch network activating said common
and second groups of horn feeds to generate said second spot beam
pattern when the satellite is at the second orbital position.
14. The communications satellite of claim 11, further comprising:
first and second signal processors that support first and second
different signal attributes, said switch network connecting said
first and second groups of spot beams to said first and second
processors, respectively.
15. The communications satellite of claim 11, further comprising:
an array of horn feeds in said antenna, said switch network
connecting a horn feed to a signal path having a narrow bandwidth
when the satellite is in the first orbital position, and connecting
said horn feed to a signal path having a wide bandwidth when the
satellite is in the second orbital position.
16. A communications satellite, comprising: an antenna having an
array of feeds generating a configuration of spot beams to carry
communications signals; signal processors processing communications
signals carried over said spot beams to and from the satellite; and
a switch network defining signal paths between said signal
processors and feeds, said switch network activating at least one
feed when the satellite is located at a first discrete orbital
position and deactivating said at least one feed when the satellite
is located at a second discrete orbital position.
17. The communications satellite of claim 16, wherein said switch
network activates a subset of said feeds when the satellite is
located at said first orbital position.
18. The communications satellite of claim 16, wherein said switch
network deactivates a subset of said feeds when the satellite is
moved from said first orbital position to said second orbital
position.
19. A communications satellite, comprising: an antenna having an
array of feeds generating a configuration of spot beams to carry
communications signals; signal processors processing communications
signals carried over said spot beams to and from the satellite; and
a switch network defining signal paths between said signal
processors and feeds, said switch network activating at least one
feed when the satellite is located at a first discrete orbital
position and deactivating said at least one feed when the satellite
is located at a second discrete orbital position, said switch
network maintaining active a common subset of feeds used at both
said first and second orbital positions when the satellite is moved
from said first orbital position to said second orbital
position.
20. A communications satellite, comprising: an antenna having an
array of feeds generating a configuration of spot beams to carry
communications signals; signal processors processing communications
signals carried over said spot beams to and from the satellite; and
a switch network defining signal paths between said signal
processors and feeds, said switch network activating at least one
feed when the satellite is located at a first discrete orbital
position and deactivating said at least one feed when the satellite
is located at a second discrete orbital position; wherein the feeds
are divided into first and second feed sets, said switch network
routing said first and second feed sets to first and second signal
processors, respectively, when the satellite is moved from the
first to second orbital positions.
21. A communications satellite system comprising: terminals for
transmitting and receiving communications signals, said terminals
located around the earth in cells; and at least one satellite being
located at one of multiple predetermined orbital positions, said
satellite including an antenna having an array of feeds generating
spot beams associated with said cells on the earth, said satellite
activating different groups of feeds on the antenna to form
different spot beam patterns associated with different
predetermined discrete orbital positions.
22. The communications satellite system of claim 21, further
comprising: a gateway relaying communications signals between said
satellite and a land-based communications network.
23. The communications satellite system of claim 21, further
comprising: a control terminal directing the satellite to move from
one orbital position to another orbital position.
24. A communications satellite system comprising: terminals for
transmitting and receiving communications signals, said terminals
located around the earth in cells; at least one satellite being
located at one of multiple predetermined orbital positions, said
satellite including an antenna having an array of feeds generating
spot beams associated with said cells on the earth, said satellite
activating different groups of feeds on the antenna to form
different spot beam patterns associated with different
predetermined discrete orbital positions; and signal processors
controlling a power level associating with each spot beam, said
satellite switching at one feed from a low power signal processor
to a high power signal processor when the satellite moves from an
orbital position, at which low power is required of said feed, to
an orbital position, at which high power is required of said
feed.
25. The communications satellite system of claim 21, wherein the
satellite further comprises: a switching network connecting and
disconnecting combinations of feeds to change said spot beam
pattern formed by an active group of feeds.
26. A communications satellite system comprising: terminals for
transmitting and receiving communications signals, said terminals
located around the earth in cells; at least one satellite being
located at one of multiple predetermined orbital positions, said
satellite including an antenna having an array of feeds generating
spot beams associated with said cells on the earth, said satellite
activating different groups of feeds on the antenna to form
different spot beam patterns associated with different
predetermined discrete orbital positions; and signal processors
controlling at least one of power and bandwidth allocated to each
beam spot, said satellite switching at least one feed from a signal
processor having at least one of low power and narrow bandwidth, to
a signal processor having at least one of high power and wide
bandwidth, when the satellite moves from one orbital position to
another.
27. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at an orbital position with respect to a
first portion of the earth; activating a first plurality of active
spot beams in a first beam pattern to provide a first level of
service to first selected areas within said first portion of the
earth; and activating a second plurality of active spot beams in a
second beam pattern to provide a second level of service to second
selected areas within said first portion of the earth.
28. The method of claim 27, further comprising activating at least
one common spot beam in said first and second pluralities of spot
beams.
29. The method of claim 27, wherein activating said second
plurality of spot beams comprises activating said second plurality
of spot beams mutually exclusive from said first plurality of spot
beams.
30. The method of claim 27, further comprising activating at least
one new spot beam when the second plurality of spot beams is
activated, said activated new spot beam having been inactive when
the first plurality of spot beams was active.
31. The method of claim 27, further comprising deactivating at
least one spot beam when the second plurality of spot beams is
activated, said deactivated spot beam having been active when the
first plurality of spot beams was active.
32. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
providing a first plurality of spot beams on a satellite at an
orbital position with respect to a first portion of the earth;
activating a second plurality of spot beams in a first beam pattern
to provide a first level of service to said first portion of the
earth, said second plurality of spot beams being less than the
first plurality of spot beams; and activating a third plurality of
spot beams in a second beam pattern to provide a second level of
service to said first portion of the earth, the spot beams in said
second beam pattern being different from the spot beams in said
first beam pattern.
33. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
providing a first plurality of spot beams on said satellite at an
orbital position with respect to a first portion of the earth;
activating a second plurality of spot beams in a first beam pattern
to provide service to said first portion of the earth, said second
plurality of spot beams being less than the first plurality of spot
beams; activating a third plurality of spot beams in a second beam
pattern to provide service to said first portion of the earth; and
adjusting a signal attribute of at least one spot beam that is
active in both said second and third pluralities of spot beams,
said signal attribute including one of spot beam bandwidth and
power.
34. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
configuring a first plurality of active spot beams on said
satellite in a first beam pattern to provide service to said first
portion of the earth; configuring a second plurality of active spot
beams on said satellite in a second beam pattern to provide service
to said first portion of the earth; and dividing said first and
second pluralities of active spot beams into first, second and
common subsets of spot beams, said first configuring step
activating said first and common subsets of spot beams and
deactivating said second subset of spot beams, said second
configuring step deactivating said first subset of spot beams and
activating said second and common subsets of spot beams.
35. A method for controlling a configuration of spot beams produced
by a communications satellite, the method comprising the steps of:
positioning a satellite at a first orbital position with respect to
a first portion of the earth; activating a first plurality of
active spot beams in a first beam pattern to substantially
encompass the first portion of the earth; and activating a second
plurality of spot beams in a second beam pattern to configure said
first and second beam patterns to encompass different areas of the
first portion of the earth.
Description
BACKGROUND OF THE INVENTION
[0001] The preferred embodiments of the present invention generally
relate to a satellite communications system, and more specifically
to methods and apparatus for controlling and adjusting spot beam
configurations formed by communications satellites that are
relocatable between multiple orbital positions.
[0002] Communications satellite systems have, been proposed that
utilized satellites located in a geostationary (GEO) orbit at fixed
orbital positions about the earth. The geostationary satellites are
placed in orbit at fixed orbital positions to cover one or more
land masses. The geostationary satellites generally remain at a
predetermined orbital position throughout the life of the
satellite. Typically, geostationary satellites include antennas,
each comprising a reflector and one or more horn feeds that
generate a pattern of spot beams designed to cover an entire target
land mass. Each spot beam receives and transmits data signals to
and from the satellite. Examples of proposed satellite systems
include the Direct TV.TM. Network, Space Way.TM. proposed by
Hughes, and AstroLink.TM., proposed by the assignee of the present
invention.
[0003] In GEO satellite systems, the satellites maintain a fixed
position with respect to the earth's surface in order to cover
continuously a desired portion of the earth. Thus, as the earth
rotates, a geostationary satellite rotates at a speed necessary to
maintain a fixed line of sight at all times with a fixed portion of
the earth.
[0004] Conventional and previously proposed GEO satellite systems
have certain drawbacks. Satellites that use reflector antennas
include one or more horn feeds in a feed pattern on an antenna
platform. A spot beam pattern is determined when designing the
satellite communication system, and the spot beam pattern defines
the feed pattern, including the number and arrangement of feeds
relative to one another, and relative to a reference point on the
satellite. Conventionally, the feed pattern is designed for a
particular satellite. For example, geostationary satellites
intended for use over the United States are configured with a feed
pattern designed to produce spot beams that cover a long
rectangular land mass extending from California to Maine.
[0005] However, once the antenna is manufactured and fitted on the
satellite, the satellite is best suited for coverage only over the
United States. The same satellite is not configured with an antenna
designed for use over a different land mass shape, such as Europe,
Australia, Africa and the like. Europe, the United States and other
land masses are shaped differently and include major metropolitan
areas located in different relations with respect to one another.
For instance, the United States includes major metropolitan areas
in Los Angeles, Chicago and New York, that are configured relative
to one another in a different manner than the major metropolitan
areas of Europe, such as London and Paris. Thus, when designing a
satellite antenna, different feed patterns are used on a satellite
intended to cover the United States versus a satellite intended to
cover Europe. Also, different signal attributes (e.g., bandwidth,
power, etc.) are assigned to various horn feeds based upon the
corresponding spot beams and geographic market areas. Horn feeds
supporting Chicago are assigned more bandwidth and/or power than
horn feeds supporting Montana. Hence, conventional and previously
proposed antenna and satellite designs are limited to use with
specific land masses and market areas, and are not interchangeable
or moveable. A disadvantage of conventional and previously proposed
satellite systems is the lack of interchangeability.
[0006] Also, the demographics and/or communications demands of a
particular market may change or evolve in an unexpected or
unpredicted manner. For instance, demand within the Midwestern
United States may change or fail to increase at a projected rate.
Therefore, a satellite previously designed and launched to meet a
particular need in the Midwestern U.S. may not be utilized fully.
Further, demand may increase at an unexpectedly high rate in the
Southeastern U.S., thereby overloading the satellite resources
available to that area. Conventional designs would require a new
satellite to be manufactured and launched in order to operate
optimally for lower Midwestern demand and higher Southeastern
demand. It is undesirable to launch new satellites to meet these
needs.
[0007] A need remains for a communications satellite system having
satellites, each of which is capable of operation over multiple
separate land masses. A need also remains for a communications
satellite system capable of dynamically changing its capacity to
meet new and unexpected market needs and to facilitate the
phased-in introduction of new satellites. It is an object of the
preferred embodiments of the present invention to meet these and
other needs that will become apparent from the description set
forth below of the preferred embodiments.
BRIEF SUMMARY OF THE INVENTION
[0008] A method is provided for controlling a configuration of spot
beams produced by a communications satellite. The method includes
generating a first plurality of spot beams from the communications
satellite maintained at a first orbital position with respect to a
first portion of the earth. The first plurality of spot beams are
configured in a first beam pattern to encompass substantially a
first portion of the earth. The satellite is moveable to a second
orbital position with respect to a second portion of the earth. A
second plurality of spot beams are configured in a second beam
pattern to encompass substantially the second portion of the earth.
According to at least one preferred embodiment, at least one common
spot beam is utilized in the first and second pluralities of spot
beams. Alternatively, the spot beams in the first and second
pluralities of the spot beams may be mutually exclusive of one
another. When a satellite is moved to a second orbital position, at
least one new spot beam is typically activated and at least one old
spot beam is typically deactivated.
[0009] According to an alternative embodiment, a method is provided
that includes changing at least one signal attribute of at least
one spot beam included in the first and second pluralities of spot
beams. The signal attribute may be one of bandwidth, power and the
like. When the satellite is moved from the first orbital position
to the second orbital position, a spot beam utilized in both
configurations may be rerouted through a new signal path in the
satellite.
[0010] According to an alternative embodiment of the present
invention, a communications satellite is provided having at least
one antenna for transmitting and receiving communications signals.
The antenna defines first and second ground cell coverage patterns
associated with first and second portions of the earth when the
satellite is located at first and second orbital positions,
respectively. The satellite includes a switch network activating a
first group of spot beams forming the first ground cell coverage
pattern when the satellite is located in the first orbital
position. The switch network activates a second group of spot beams
forming the second ground cell coverage pattern when the cell is
located at the second orbital position.
[0011] The antenna may include a plurality of horn feeds, each of
which generates one spot beam when activated. One horn feed may be
used to generate a spot beam in each of the first and second groups
of spot beams directed to different portions of the earth. The
antenna may further include multiple horn feeds divided into first
and second groups. The switch network activates the first and
second groups of horn feeds to generate first and second groups of
spot beams, respectively, when the satellite is moved between the
first and second orbital positions, respectively. The first horn
feed group may include at least one horn feed not in a second horn
feed group.
[0012] The satellite may further include multiple signal
processors, each of which supports a different type or range of
signal attributes such as bandwidth and/or power capabilities. The
switching network may connect groups of spot beams to each signal
processor depending upon the needs of the spot beam. For instance,
beams having low demand require narrow bandwidth, and thus may be
assigned to a signal path associated with one or more signal
processors having a narrow bandwidth capacity. Similarly, beam
spots having high demand require wide bandwidth and thus may be
assigned to signal paths associated with signal processors capable
of supporting a wide bandwidth.
[0013] In yet another further alternative embodiment, the
communications satellite is provided with an antenna having
multiple horn feeds capable of generating multiple spot beams. The
horn feeds are divided into subsets that may or may not include
common feeds. The feed subsets are activated separately based upon
the orbital position of the satellite.
[0014] In yet a further alternative embodiment, a satellite
communications system is provided, including user terminals for
transmitting and receiving communications signals. The terminals
are located around the earth in various cells. The system includes
at least one satellite orbiting the earth at a predefined orbital
position. The satellite includes an antenna having an array of horn
feeds generating spot beams associated with the cells on the earth.
The satellite activates different groups of horn feeds on the
antenna to form different spot beam patterns associated with
different predetermined orbital positions. The user terminals may
include a gateway for relaying communications signals between a
satellite and a land based communications network, such as a phone
system, the internet, intranet, a wide area network, a local area
network, and the like.
[0015] The system may further include a control terminal directing
the satellite to move from one orbital position to another, such as
when demand justifies the change. A satellite may be moved when
another satellite fails in order to replace the failed satellite.
Alternatively, a satellite may be moved when market demands change
or do not reach expectations. For instance, a satellite having wide
bandwidth may be centered over a portion of the United States
expected to require large demand. However, after in use, it may be
determined that the satellite's capabilities are not fully being
utilized and may be better suited over a different land mass. As
yet a further alternative, the satellites may be moved during the
initial introduction of a constellation of satellites. All
satellites in a system are typically not launched at the same time.
Thus, for example, it may be desirable to locate a single satellite
over the Atlantic Ocean in order to cover simultaneously the
Eastern United States and Western Europe. Once a second satellite
is launched, it may be desirable to move the first satellite to a
location over the United States, while positioning the second
satellite over Europe.
[0016] As a further alternative embodiment, the satellite system
may switch individual beam spots between various signal paths when
a satellite is moved between positions. The satellite switches spot
beams in order to connect a particular spot beam spot to a
different signal processor affording different signal attributes,
such as more or less bandwidth, lower or higher power, and the
like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 illustrates a block diagram of a satellite
communications system according to a preferred embodiment of the
present invention.
[0018] FIG. 2 illustrates a pictorial view of a portion of an
antenna including a plurality of horn feeds arranged in accordance
with a preferred embodiment of the present invention.
[0019] FIG. 3 illustrates a signal path connection diagram in
accordance with a preferred embodiment of the present
invention.
[0020] FIG. 4 illustrates an exemplary cell pattern produced by a
satellite positioned over the United States at a first orbital
position in accordance with a preferred embodiment of the present
invention.
[0021] FIG. 5 illustrates an exemplary cell pattern produced by a
satellite positioned in a second orbital position over the United
States in accordance with a preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The locations of, and patterns for, the cells to be served
by a satellite for multiple discrete, different coverage areas and
orbital positions are defined at the time that the satellite
antenna is manufactured. For instance, an antenna may include a set
of horn feeds that produce spot beams by generating radiated energy
into, and receiving radiated energy collected by, a reflector. The
direction of each spot beam is determined by the fixed position and
orientation of the horn feed with respect to the reflector. The
location of a cell on the earth that is covered by a particular
spot beam has been determined by the position of the antenna horn
feed with respect to the reflector and by the position of the
satellite with respect to the earth.
[0023] According to at least one preferred embodiment of the
present invention, a single communications satellite is provided
that is capable of providing service to multiple different regions
on the surface of the earth depending upon which one of several
orbital positions are chosen for the satellite. In order to
accommodate these orbital positions, alternative horn feed
configurations are built into a single antenna, thereby enabling
the antenna to be manufactured before the final position for a
satellite is determined. The satellite system also enables the
satellite to be initially configured for operation in one orbital
position, and to be reconfigured at some time after launch for
operation in another orbital position. By reconfiguring the
satellite, it may be repositioned to better serve the user
community or may be maintained as an in-orbit spare to become a
replacement for other malfunctioning satellites within a
constellation of satellites, thereby minimizing the interruption of
service. Although hereinafter described with respect to the
movement of a satellite from one orbital position to a second
orbital position, the invention is not so limited, and is
applicable to the use of a satellite at a single orbital position.
This change of feeds may be desirable, for example, in those
circumstances where changing requirements of the user community
necessitate a modification of the bandwidth or power levels to
particular cells.
[0024] FIG. 1 illustrates an exemplary communications satellite
system 1 in accordance with a preferred embodiment of the present
invention. A communications satellite 10 provides service to a
region of the earth by producing a number of spot beams 15. Each
spot beam 15 covers a cell 20 on the surface of the earth. The
cells 20 collectively define a cell pattern 25 covering a region of
the earth. Cells 20 may be placed contiguous with one another or
spaced apart, individually, in order to provide coverage to
isolated population centers, such as the Hawaiian Islands and the
like.
[0025] The satellite 10 orbits the earth at one of multiple
predetermined orbital positions. By way of example, the satellite
10 may be a geostationary satellite located over a desired
continent or land mass. The satellite 10 includes an antenna 12
comprising a plurality of horn feeds 14 and a focusing reflector
(not shown). A subset of the horn feeds 14 are activated during
operation based upon the orbital position of the satellite 10. The
active horn feeds 14 generate spot beams 15 that define the cells
20 upon the surface of the earth. The cells 20 collectively form a
cell pattern 25 entirely encompassing a desired land mass, such as
the United States, Europe and the like. Each spot beam 15 supports
bi-directional communication between the satellite 10 and one or
more terminals 30. The bi-directional communications link includes
an uplink signal 32 and a downlink signal 34 for carrying
communication signals to and from the satellite 10 and the terminal
30. Optionally, a gateway 36 may be included in one or more cells
20. A gateway 36 supports a connection between the satellite 10 and
a land based communication network, such as the internet, a land
based phone system, a local area network, a wide area network and
the like. Terminals 30 may constitute individual user terminals
that are mobile or fixed, ground stations, and the like.
[0026] Spot beams 15 form a pattern on the Earth that is dependent
upon the location of the satellite 10 selected between multiple,
predetermined orbital positions. The horn feeds 14 are arranged to
configure the active plurality of spot beams 15 in a pattern
designed to substantially encompass a desired land mass. During the
life of the satellite 10, a control station 38 may direct the
satellite 10 to move to a different one of the multiple
predetermined orbital positions in order to cover a different land
mass or rearrange to spot beams located over different markets in a
portion of the earth. By way of example, a satellite may be moved
from an orbital position over the United States to an orbital
position over Europe. Alternatively, the satellite 10 may be moved
from an orbital position centered over New York to an orbital
position centered over Los Angeles. When the satellite 10 is moved
to the new orbital position, it activates a new subset of the total
available horn feeds 14, wherein the active feed subset is
configured to generate a plurality of spot beams in a new pattern
that substantially conforms to and encompasses the new land mass
over which the satellite 10 is located.
[0027] FIG. 2 illustrates the feed pattern of an exemplary antenna
configured in accordance with a preferred embodiment of the present
invention. The antenna 12 includes multiple horn feeds 14 mounted
securely on a platform 40. The horn feeds 14 are positioned at
predetermined locations with respect to one another and to their
parent reflector. In the example of FIG. 2, the horn feeds 14 are
divided into three sets designated by bracketed feed sets 42-44. In
the example of FIG. 2, the first feed set 42 includes three horn
feeds 14, while the second and third feed sets 43 and 44 include
sixteen and three feeds 14, respectively.
[0028] The location of each horn feed 14 on platform 40 is defined
by the pointing direction of its associated spot beam. The
positions of the horn feeds 14 are based upon the multiple land
masses over any one of which the satellite 10 may be positioned.
For example, the satellite 10 may be designed to cover three to
five different land mass shapes, such as land masses having
horizontal rectangular shapes (U.S.), square shapes (Europe),
triangular shapes (Mexico) and the like. A combination of horn
feeds 14 in each of feed sets 42-44 are arranged relative to one
another and relative to horn feeds 14 in the other feed sets 42-44,
in order to cover each expected land mass shape.
[0029] For instance, the horn feeds 14 within feed sets 42 and 43
may be positioned and oriented with respect to the platform 40 to
cover the United States, including Alaska and Hawaii, when the
satellite 10 is centered over Chicago. In addition, feeds 14 in
feed set 44 may be positioned and oriented with respect to the
platform 40 and with respect to feed set 43 to cover, in
combination, the Eastern United States and Western Europe when the
satellite 10 is centered over the Atlantic Ocean.
[0030] FIG. 3 illustrates a signal path connection diagram in
accordance with a preferred embodiment of the present invention.
FIG. 3 illustrates an exemplary group of feeds 50 that communicate
through a switching network 52 and a signal processor section 54.
The feed group 50 includes feeds #1, #14, #26, #3, #12, #4, #5 and
#2 for purposes of illustration only. The switching network 52
includes signal paths 55-64 and switches 65-70 to connect the feed
group 50 to the signal processing section 54. The signal processing
section 54 includes at least first and second signal processors 71
and 72 designated as processors A and B.
[0031] When the satellite is located at a first orbital position,
the switches 65-70 are set to establish signal connections between
a desired subset of feeds in feed group 50 and one or both of
signal processors 71 and 72. In the example of FIG. 3, when the
satellite is at a first orbital position, the switches 65-67 are
set to connect feeds #5 and #12 to signal processor 73, while
switches 68-70 are set to connect feeds #3 and #14 to processor 71.
Feeds #4 and #26 are hardwired via paths 57 and 62 to processors 71
and 73, respectively. Feeds #1 and #2 are inactive while the
satellite is located at the first orbital position.
[0032] When the satellite is moved to a second orbital position,
the switching network 52 is reconfigured to establish new signal
connections with the signal processing section 54. For instance,
switches 65-70 may be toggled to connect feeds #2 and #3 to
processor 73 and feeds #1 and #12 to processor 71, while feeds #14
and #5 are rendered inactive. Feeds #4 and #26 remain hardwired and
actively connected to processors 71 and 73.
[0033] FIGS. 4 and 5 illustrate typical cell patterns that may be
generated by projecting a number of spot beams onto the surface of
the Earth from a satellite in the first and second orbital
positions, respectively. The cell patterns are designed to provide
communication services to specific regions of the Earth. Each spot
beam is formed by precisely positioning an antenna feed relative to
a reflector on board the satellite. Each cell is assigned a number
which identifies the specific antenna feed used to create the
corresponding spot beam and a letter identifying the signal
bandwidth/power or some other signal attribute that is required for
a particular cell. In the example of FIGS. 4 and 5, 36 cells are
shown corresponding to 36 different antenna feeds.
[0034] The satellite is configured to produce beam spots only for
those cells that cover the desired regions from the defined orbital
positions. Cells that are needed to serve the desired regions of
coverage are designated as active and are depicted by heavy black
circles. Each of the feeds employed to create an active cell is
connected by a signal path to a signal processor that supports the
required bandwidth for the particular cell. Of the 36 cells
located, 24 are shown to be active in FIG. 4. Twelve of the active
cells are shown to be assigned signal attribute A, while the
remaining 12 are shown to be assigned signal attribute B. Any
number of possible signal attributes may be supported up to the
total number of active cells, and the number of cells assigned to a
particular attribute may vary.
[0035] FIG. 4 illustrates an exemplary cell pattern 75 produced by
a satellite located at a first orbital position over the United
States, such as centered over Los Angeles. The overall cell pattern
75 is defined by discrete spot beams numbered #1 to #36. The spot
beams #1-#36 are arranged such that a first beam group 74 is
arranged contiguous to form a rectangular configuration
encompassing the United States, with inactive spot beams located
off the West Coast of the United States. The cell pattern 75
further includes individual spot beams #31-#36 oriented to cover
islands, such as Hawaii, Puerto Rico and the like.
[0036] In the example of FIG. 4, each spot beam is assigned a
number 1-36 and a letter, A, B or N. The reference letters A, B and
N denote the signal processor to which the spot beam #1-#36 is
assigned. For instance, spot beams #35 and #34 include a reference
numeral A indicating that a connection via the switching network 52
to the signal processor 71. Spot beams #31, #33 and #36 include a
reference numeral N indicating that the feeds associated therewith
are not active.
[0037] After launching the satellite, it may be moved to a second
defined orbital position which would shift the beam pattern 74
relative to the United States, as shown in FIG. 5. Once the
satellite move is completed, a control station 38 transmits a
signal to the satellite for the purpose of instructing the
satellite to reconfigure itself for operation in the new orbital
position. The satellite reconfigures itself with a network of
on-board switches that are used to reconnect antenna feeds to new
signal paths appropriate to provide service to a second set of
desired regions on the surface of the Earth that may wholly or
partially overlap the regions served from the first orbital
position. The number of orbital positions and configurations
supported by a given satellite is not limited to two and may be
increased by including the necessary switching circuitry and signal
processors to account for the demands placed upon each feed while
the satellite is in any desired orbital position.
[0038] FIG. 5 illustrates a cell pattern that may be produced by
projecting the spot beams onto the surface of the Earth from the
satellite when in a second orbital position. The Nadir pointing
direction associated with the second defined orbital position is at
a more easterly longitude than the Nadir pointing direction
associated with the first orbital position. The regions served from
the first orbital position have therefore shifted to the West
relative to the position of the satellite. Once again, 24 cells may
be employed to provide coverage, however the cells that have been
designated as active differ from those in the previous example. The
active cells differ since the footprint for the spot beams has
shifted as the relative position of the satellite has shifted.
[0039] Although many of the feeds depicted as active in FIG. 5 were
also depicted as active in FIG. 4, the required signal path
connections for many of the feeds may change. The feed signal path
connections may change because each cell now covers a different
area on the surface of the Earth than while in the previous orbital
positions. Some cells that were previously inactive, such as cell
#1, are now connected to a processor that supports a bandwidth A.
Other cells that previously supported bandwidth A, such as cell #3,
are now connected to a processor that supports bandwidth B.
[0040] FIG. 5 illustrates an exemplary embodiment in which the
satellite 10 has moved to a second orbital position, at which the
beam group 74 still encompasses the United States, but extends
beyond the East Coast of the United States. The switching network
52 is changed at the instruction of the satellite 10 and/or the
control center 38, when the satellite 10 is moved to the second
orbital position. The switching network 52 is switched in order to
reroute predetermined feeds 14 to different signal processors 71,
73 where necessary and to deactivate predetermined feeds 14
associated with spot beams that no longer cover a desired area,
land mass, water area or otherwise. For instance, in FIG. 5, a
group of inactive spot beams 86 are located off the East Coast of
the United States and have been turned off as they no longer cover
a desirable market area. Spot beams #32, #34 and #35 are
deactivated, while spot beams #31, #33 and #36 are activated.
[0041] In the examples of FIGS. 4 and 5, it may be seen that the
signal paths for feeds #3 and #12 associated with spot beams #3 and
#12 are changed when the satellite is moved from the first orbital
position to the second orbital position. For instance, the feed #12
associated with spot beam #12 is assigned to signal processor 73 in
the configuration illustrated in FIG. 4, while the spot beam #12 is
assigned to signal processor 71 in the configuration illustrated in
FIG. 5.
[0042] It may be desirable to change the signal path associated
with a particular feed when a satellite is moved to an orbital
position that aligns a particular spot beam with a geographic area
having significantly different demand than previously required of
the spot beam. For instance, in the example of FIG. 4, spot beam
#12 initially was located over the Western states of Utah, Idaho
and Montana. Spot beam #12 may not require an overly large
bandwidth or power demand when located over Utah, Idaho and
Montana. Thus, a signal path with narrow bandwidth and/or low power
may be assigned to feed #12 through processor 73.
[0043] However, when the satellite 10 moves to the second orbital
position illustrated in FIG. 5, the spot beam #12 is realigned over
the Chicago Metropolitan Area and the surrounding states. Hence,
spot beam #12 may be required to support significantly more user
demand and thus greater bandwidth and/or power. Accordingly, the
feed #12 is reassigned by the switching network 52 to a signal path
connected to the signal processor 71 which may afford feed #12
greater bandwidth and/or power.
[0044] Similarly, spot beam #3 may be rerouted from processor 71 in
FIG. 4 to processor 73 in FIG. 5 as the spot beam #3 is moved from
the West Coast to an area substantially covering upper Montana and
North Dakota. Multiple switch configurations and signal paths may
be assigned to certain feeds based upon the number of potential
positions and markets, at which the spot beam associated with the
feed may be located.
[0045] In the example of FIGS. 4 and 5, a satellite supports two
different orbital positions and two different signal bandwidths.
Feed #1 is inactive in the configuration of FIG. 4 and active with
bandwidth A in the configuration of FIG. 5. Feed #14 is active with
bandwidth A in the configuration of FIG. 4 and inactive in the
configuration of FIG. 5. Feeds #1 and #14 may be paired to share a
signal path with bandwidth A by means of a two input, one output
switch that connects feed #14 to the processor in one configuration
and connects feed #1 to the processor in the other
configuration.
[0046] Similarly, feed #2 is inactive in the configuration of FIG.
4 and inactive with bandwidth B in the configuration of FIG. 5,
while feed #5 is active with bandwidth B in the configuration of
FIG. 4 and inactive in the configuration of FIG. 5. Feeds #2 and #5
may share a connection to a signal path with bandwidth B by using a
similar switch. Feed #26 is active with bandwidth A in both
configurations, while feed #4 is active with bandwidth B in both
configurations. Each of feeds #4 and #26 may be allocated a
dedicated signal path with no switching requirements. Feed #3 is
active with bandwidth A in the configuration of FIG. 4 and inactive
with bandwidth B in the configuration of FIG. 5, while feed #12 is
active with bandwidth B in the configuration of FIG. 4 and inactive
with bandwidth A in the configuration of FIG. 2. Feeds #3 and #12
are paired by using a set of four switches to provide each feed
with one of two possible signal path connections.
[0047] The switches are changed en masse so that at any given time
each feed is connected to one signal path, and each signal path is
connected to one feed. The same basic principles may be applied to
constructing a network of switches that supports any number of feed
configurations and signal processor attributes. The network of
switches used to reconfigure the satellite for operation in
different orbital positions may be employed equally as well toward
changing the signal path bandwidth assignments of the various
ground cells served by the satellite from one orbital position, in
response to the changing requirements of a particular user
community. For instance, a cell may be located over a suburban area
that requires low demand. However, over the years, the suburban
area may expand and require greater bandwidth from the cell. In
this example, the signal path for the cell may be rerouted to a
higher bandwidth processor, while the satellite is not moved from
its initial orbital position.
[0048] It is to be understood that the preferred embodiments of the
present invention are not limited to the particular configurations
and signal path connections illustrated in the drawings. For
instance, more signal processors may be used to afford larger
bandwidth and/or power, or to afford a wider range of selections
between particular bandwidth and power demands. In addition, the
signal processors 71 and 73 may vary other signal attributes,
besides and/or in addition to bandwidth and power. The signal
processors 71 and 73 may be simple or complex. For instance, a
simple configuration for the signal processors 71 and 73 may simply
represent circuits including gain control and filter components,
such as when the satellite operates in a bent-pipe type
configuration. In a bent-pipe configuration, the satellite does not
analyze the substance of incoming messages, but instead simply
relays incoming messages to a predetermined outbound carrier signal
and/or spot beam.
[0049] Alternatively, the signal processors 71 and 73 may be
semi-smart, whereby they partially decode uplink signals in order
to select between one of several downlink signals and/or spot
beams. For instance, the signal processors may route all incoming
communication signals from Chicago to a downlink directed to a
gateway or ground station located in Minnesota. As a further
alternative, the signal processors 71 and 73 may be very
sophisticated, such as by supporting demodulation, error detection
and error correction of incoming uplink signals and encoding and
modulation of downlink signals. The satellite may demodulate the
uplink signals and route each individual communications signal to a
particular spot beam and downlink signal associated with a
destination terminal.
[0050] The preferred embodiments of the present invention may be
implemented in a variety of signal protocols, such as frequency
division multiple access (FDMA), time division multiple access
(TDMA), and/or code division multiple access (CDMA). One or more of
the foregoing protocols or any other conventional signal protocol
(ATM, etc.) may be used to support the communications signals
carried over the spot beams.
[0051] The signal processors 71 and 73 may be configured with
digital or analog circuitry or a combination thereof. The antenna
may support carrier frequencies in any frequency range.
[0052] The preferred embodiments of the present invention allow a
satellite to provide coverage from one or more orbital positions.
The satellite includes antennas designed with more feeds than are
needed to cover the cells associated with a particular orbital
position. One group of feeds is positioned to produce spot beams
which cover a set of desired cells from one predetermined orbital
position, while additional feeds are positioned such that other
cells (which may include some or all of the same regions on the
Earth as the first set) are covered from alternative predetermined
orbital positions. A different group of feeds may be used to
produce the spot beams relevant to each separate orbital position
supported by the antenna design. It is expected that a large number
of feeds may be used in more than one orbital position, albeit to
cover different individual ground cells in each case.
[0053] The switching network allows the antenna to be configured
for operation from a particular orbital position. The switches are
used to activate specific feeds that are required to produce the
spot beams needed for providing coverage to cells from a present
orbital position. For a system in which each spot beam may be
assigned to one of a number of possible processing groups based on
some signal attribute such as bandwidth or power, the same switch
network may also serve to route the signal from each feed along a
signal path to an appropriate signal processor.
[0054] The foregoing embodiments in accordance with the present
invention provide a flexible communication system that is designed
in a manner that is not tied to a single orbital position. The
preferred embodiments improve the time to market for the system
since manufacturing of the antennas may precede the final selection
of an orbital position for the satellite. The preferred embodiments
allow on board reconfiguration of satellite spot beams to be
commanded from a control center on the Earth and allow
reconfiguration of the signal path for each beam. The same antenna
feeds may be used in different orbital positions for providing
coverage to different ground cells. The preferred embodiments allow
a satellite to be moved to a different orbital position in order to
better serve a particular user community and to allow a satellite
to be launched as a spare to become an immediate replacement for
any malfunctioning member of a satellite constellation.
[0055] It is understood that spot beams may be directed to areas
not necessarily associated with land masses. For instance, it may
be desirable to direct one or more spot beams to areas or bodies of
water, such as shipping lanes or seas, and such as busy air traffic
areas. While particular elements, embodiments and applications of
the present invention have been shown and described, it will be
understood that the invention is not limited thereto since
modifications may be made by those skilled in the art, particularly
in light of the foregoing teachings. It is, therefore, contemplated
by the appended claims to cover such modifications as incorporate
those features which come within the spirit and scope of the
invention.
* * * * *