U.S. patent application number 12/861702 was filed with the patent office on 2011-01-13 for multi-beam satellite network to maximize bandwidth utilization.
This patent application is currently assigned to SPACE SYSTEMS/LORAL, INC.. Invention is credited to Douglas Burr.
Application Number | 20110007686 12/861702 |
Document ID | / |
Family ID | 42669679 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110007686 |
Kind Code |
A1 |
Burr; Douglas |
January 13, 2011 |
MULTI-BEAM SATELLITE NETWORK TO MAXIMIZE BANDWIDTH UTILIZATION
Abstract
A communications network (100) for maximizing bandwidth
utilization. An embodiment of the invention comprises a spacecraft
(11), at least one gateway (12) communicatively coupled to the
spacecraft (11) by a feeder link (13) operating within at least one
selected frequency band within a bandwidth, at least one user
terminal (16) communicatively coupled to the spacecraft (11) by a
user link (17), the user link (17) operable at any frequency band
within the bandwidth without regard to polarization; and, the
communications network (100) adapted to provide for simultaneous
operation of at least a portion of the feeder link (13) and a
portion of the user link (17) at a common polarization and
frequency band within the bandwidth.
Inventors: |
Burr; Douglas; (San Jose,
CA) |
Correspondence
Address: |
Weaver Austin Villeneuve & Sampson LLP
P.O. BOX 70250
OAKLAND
CA
94612-0250
US
|
Assignee: |
SPACE SYSTEMS/LORAL, INC.
Palo Alto
CA
|
Family ID: |
42669679 |
Appl. No.: |
12/861702 |
Filed: |
August 23, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11891086 |
Aug 8, 2007 |
7792070 |
|
|
12861702 |
|
|
|
|
60923263 |
Apr 13, 2007 |
|
|
|
Current U.S.
Class: |
370/316 |
Current CPC
Class: |
H04B 7/18582
20130101 |
Class at
Publication: |
370/316 |
International
Class: |
H04B 7/185 20060101
H04B007/185 |
Claims
1. A spacecraft, operable within a communications network, said
spacecraft comprising: an antenna subsystem providing a first
antenna beam pattern associated with a first user link, said first
user link operable at any frequency band within a first sub-band,
and a second antenna beam pattern associated with a second user
link, said first and second antenna beam patterns defining
respective first and second service regions; wherein the
communications network comprises: at least one gateway
communicatively coupled to the spacecraft by a feeder link
operating within at least one selected first sub-band of
frequencies within the bandwidth; a first user terminal
communicatively coupled to the spacecraft by the first user link; a
second user terminal communicatively coupled to the spacecraft by a
second user link, said second user link operable at any frequency
band within a second sub-band of frequencies within the bandwidth,
said second sub-band having no frequency in common with the first
sub-band; the communications network is adapted to provide for
simultaneous operation of at least a portion of the feeder link and
at least a portion of the first user link at a common polarization
and frequency within the bandwidth; and every gateway is located
within the second service region.
2. The spacecraft of claim 1, wherein at least a portion of the
first user link operates at a common polarization and frequency as
at least a portion of the feeder link.
3. The spacecraft of claim 1, wherein the first and second sub-band
together encompass substantially all of the bandwidth.
4. The spacecraft of claim 1, wherein at least one gateway is
located proximate to and communicatively coupled with an Internet
backbone.
5. The spacecraft of claim 1, wherein the spacecraft is a satellite
operable in geostationary orbit.
6. The spacecraft of claim 1, wherein the spacecraft is a satellite
operable in non-geostationary orbit.
7. The spacecraft of claim 1, wherein the user link and the feeder
link are operable at Ka band.
8. The spacecraft of claim 1, wherein at least one antenna beam
pattern is configured to provide a plurality of individual spot
beams.
9. The spacecraft of claim 1, wherein at least one antenna beam
pattern is configured to provide for frequency re-use in spatially
isolated spot beams.
10. The spacecraft of claim 9, wherein frequency re-use is
maximized according to a four color re-use plan wherein a color
represents a combination of a frequency sub-band and an antenna
polarization.
11. A gateway, said gateway communicatively coupled, within a
communications network, to a plurality of user terminals by a
feeder link between said gateway and a spacecraft, said feeder link
operating within at least one selected first sub-band of
frequencies within a bandwidth, and a plurality of user links
between said spacecraft and said user terminals; wherein a first
user terminal is communicatively coupled to the spacecraft by a
first user link, said first user link operable at any frequency
band within said first sub-band; a second user terminal is
communicatively coupled to the spacecraft by a second user link,
said second user link operable at any frequency band within a
second sub-band of frequencies within the bandwidth, said second
sub-band having no frequency in common with the first sub-band, the
communications network is adapted to provide for simultaneous
operation of at least a portion of the feeder link and at least a
portion of the first user link at a common polarization and
frequency within the bandwidth; an antenna subsystem disposed on
the spacecraft provides a first antenna beam pattern associated
with the first user link, and a second antenna beam pattern
associated with the second user link, said first and second antenna
beam patterns defining respective first and second service regions;
and the gateway is located within the second service region.
12. A communications network, comprising: a spacecraft; at least
one gateway communicatively coupled to the spacecraft by a feeder
link operating within at least one selected frequency band within a
bandwidth; at least one user terminal communicatively coupled to
the spacecraft by a user link, said user link operable at any
frequency band within the bandwidth, wherein the communications
network is adapted to provide for simultaneous operation of at
least a portion of the feeder link and at least a portion of the
user link at a common polarization and frequency within the
bandwidth; and an antenna subsystem disposed on the spacecraft,
said antenna subsystem providing at least one antenna beam pattern
associated with the user link, each said antenna beam pattern
defining a service region, wherein each gateway is located outside
of each service region, wherein the service region comprises one of
an eastern portion of the United States and a western portion of
the United States.
13. The communications network of claim 12, wherein at least a
portion of the user link operates at a common polarization and
frequency as at least a portion of the feeder link.
14. The communications network of claim 12, wherein the common
frequency band encompasses substantially all of the bandwidth.
15. The communications network of claim 12, wherein at least one
gateway is located proximate to and communicatively coupled with an
Internet backbone.
16. The communications network of claim 12, wherein the spacecraft
is a satellite operable in geostationary orbit.
17. The communications network of claim 12, wherein the spacecraft
is a satellite operable in non-geostationary orbit.
18. The communications network of claim 12 wherein the user link
and the feeder link are operable at Ka-band.
19. The communications network of claim 12, wherein the antenna
beam pattern is configured to provide a plurality of individual
spot beams.
20. The communications network of claim 12, wherein at least two of
the spot beams operate at a common frequency.
21. The communications network of claim 12, wherein the antenna
beam pattern is configured to provide for frequency re-use in
spatially isolated spot beams.
22. The communications network of claim 12, wherein frequency
re-use is maximized according to a four color re-use plan wherein a
color represents a combination of a frequency sub-band and an
antenna polarization.
23. A spacecraft, said spacecraft comprising: an antenna subsystem
in communication with (i) at least one gateway by a feeder link
operating within at least one selected frequency band within a
bandwidth and (ii) at least one user terminal by a user link
operable at any frequency band within said bandwidth, said antenna
subsystem being configured to provide for simultaneous operation of
said feeder link and said user link at a common polarization and
frequency band within said bandwidth, and to provide at least one
antenna beam pattern associated with the user link, each said
antenna beam pattern defining a service region, wherein: each
gateway is located outside of each service region; and the service
region comprises one of an eastern portion of the United States and
a western portion of the United States.
24. A gateway, said gateway communicatively coupled to at least one
user terminal by a feeder link between said gateway and a
spacecraft operating within at least one selected frequency band
within a bandwidth, and a user link between said spacecraft and
said user terminal(s), said user link being operable at any
frequency band within said bandwidth; wherein said feeder link and
said user link operate simultaneously at a common polarization and
frequency band within said bandwidth; an antenna subsystem disposed
on the spacecraft provides at least one antenna beam pattern
associated with the user link, each said antenna beam pattern
defining a service region; the gateway is located outside of each
service region; and the service region comprises one of an eastern
portion of the United States and a western portion of the United
States.
25. A user terminal, said user terminal communicatively coupled to
at least one gateway by a user link between said user terminal and
a spacecraft and a feeder link between said spacecraft and said
gateway(s), said feeder link operating within at least one selected
frequency band within a bandwidth, and said user link being
operable at any frequency band within said bandwidth; wherein said
feeder link and said user link operate simultaneously at a common
polarization and frequency band within said bandwidth an antenna
subsystem disposed on the spacecraft provides at least one antenna
beam pattern associated with the user link, each said antenna beam
pattern defining a service region; the gateway is located outside
of each service region; and the service region comprises one of an
eastern portion of the United States and a western portion of the
United States.
26. A communications network, comprising: a spacecraft; at least
one gateway communicatively coupled to the spacecraft by a feeder
link operating within at least one selected frequency band within a
bandwidth; at least one user terminal communicatively coupled to
the spacecraft by a user link, said user link operable at any
frequency band within the bandwidth, wherein the communications
network is adapted to provide for simultaneous operation of at
least a portion of the feeder link and at least a portion of the
user link at a common polarization and frequency within the
bandwidth.
27. The communications network of claim 26, further comprising: an
antenna subsystem disposed on the spacecraft, said antenna
subsystem providing at least one antenna beam pattern associated
with the user link, each said antenna beam pattern defining a
service region, wherein each gateway is located outside of each
service region.
28. A communications network, comprising: a spacecraft; at least
one gateway communicatively coupled to the spacecraft by a feeder
link operating within at least one selected first sub-band of
frequencies within a bandwidth; a first user terminal
communicatively coupled to the spacecraft by a first user link,
said first user link operable at any frequency band within said
first sub-band; a second user terminal communicatively coupled to
the spacecraft by a second user link, said second user link
operable at any frequency band within a second sub-band of
frequencies within the bandwidth, said second sub-band having no
frequency in common with the first sub-band, wherein the
communications network is adapted to provide for simultaneous
operation of at least a portion of the feeder link and at least a
portion of the first user link at a common polarization and
frequency within the bandwidth.
29. The communications network of claim 28, further comprising: an
antenna subsystem disposed on the spacecraft, said antenna
subsystem providing a first antenna beam pattern associated with
the first user link, and a second antenna beam pattern associated
with the second user link, said first and second antenna beam
patterns defining respective first and second service regions,
wherein every gateway is located within the second service
region.
30. A spacecraft, said spacecraft configured to: communicate with
at least one gateway by a feeder link operating within at least one
selected frequency band within a bandwidth; communicate with at
least one user terminal by a user link operable at any frequency
band within said bandwidth; and, simultaneously operate said feeder
link and said user link at a common polarization and frequency band
within said bandwidth.
31. A gateway, said gateway configured to: communicate with at
least one user terminal by a feeder link between said gateway and a
spacecraft operating within at least one selected frequency band
within a bandwidth, and a user link between said spacecraft and
said user terminal(s), said user link being operable at any
frequency band within said bandwidth, wherein said feeder link and
said user link simultaneously operate at a common polarization and
frequency band within said bandwidth.
32. A user terminal, said user terminal configured to: communicate
with at least gateway by a user link between said user terminal and
a spacecraft and a feeder link between said spacecraft and said
gateway(s), said feeder link operating within at least one selected
frequency band within a bandwidth, and said user link being
operable at any frequency band within said bandwidth, wherein said
feeder link and said user link simultaneously operate at a common
polarization and frequency band within said bandwidth.
Description
CROSS REFERENCES TO RELATED APPLICATION
[0001] This application is a continuation of and claims priority
under section 35 U.S.C. 120 to U.S. patent application Ser. No.
11/891,086, entitled MULTI-BEAM SATELLITE NETWORK TO MAXIMIZE
BANDWIDTH UTILIZATION filed on Aug. 8, 2007 (Attorney Docket No.
LORLP151) and claims the priority benefit of U.S. provisional
patent application 60/923,263 filed on Apr. 13, 2007, and entitled
"Multi-Beam Satellite Network to Maximize Bandwidth Utilization",
the entire disclosures of which are hereby incorporated by
reference in their entirety into the present patent application for
all purposes.
TECHNICAL FIELD
[0002] This invention pertains to the field of satellite
communications networks, and more particularly to the provision of
broadband communications services via a multi-beam satellite system
that efficiently utilizes allocated bandwidth.
BACKGROUND OF THE INVENTION
[0003] The assignee of the present invention manufactures and
deploys communications spacecraft. Such spacecraft operate within a
regulatory regime that licenses at least one operating frequency
bandwidth for a particular spacecraft communications service and
specifies, inter alia, the maximum signal power spectral density
(PSD) of communications signals radiated to the ground. A growing
market exists for provision of high data rate communication
services to individual consumers and small businesses which may be
underserved by or unable to afford conventional terrestrial
services. To advantageously provide high data rate communication
services to such users, the spacecraft must (1) provide a high PSD
so as to enable the use of low cost user terminals, and (2)
efficiently use the licensed bandwidth so as to maximize the
communications throughput for a particular licensed bandwidth.
[0004] A typical satellite communications network 100 is
illustrated in simplified form in FIG. 1. The system includes a
satellite 11, typically though not necessarily located at a
geostationary orbital location defined by a longitude. Satellite 11
is communicatively coupled to at least one gateway 12 and to a
plurality of user terminals 16. The user terminals 16 comprise
satellite terminals that may be handheld mobile telephones or car
phones, or may be embedded, for example, in laptop or desktop
personal computers, set top boxes or phone booths.
[0005] Each gateway 12 and the satellite 11 communicate over a
feeder link 13, which has both a forward uplink 14 and a return
downlink 15. Each user terminal 16 and the satellite 11 communicate
over a user link 17 that has both a forward downlink 18 and a
return uplink 19. A spacecraft antenna subsystem may provide an
antenna beam pattern wherein an entire service region is covered
using the available bandwidth a single time. Advantageously,
however, multiple satellite antenna beams (or cells) are provided,
each of which can serve a substantially distinct cell within an
overall service region.
[0006] Dividing the overall service region into a plurality of
smaller cells permits frequency reuse, thereby substantially
increasing the bandwidth utilization efficiency. Although frequency
reuse in this manner is known (see, for example, Ames, et al., U.S.
patent application Ser. No. 10/940,356), systems like the one
described in Ames require that a total bandwidth allocated to the
downlink be divided into separate non-overlapping blocks for the
forward downlink 18 and the return downlink 15. Similarly, prior
art solutions divide the total bandwidth allocated to the uplink
into separate non-overlapping blocks for the forward uplink 14 and
the return uplink 19.
DISCLOSURE OF INVENTION
[0007] A communications network (100) for maximizing bandwidth
utilization. An embodiment of the invention comprises a spacecraft
(11), at least one gateway (12) communicatively coupled to the
spacecraft (11) by a feeder link (13) operating within at least one
selected frequency band within a bandwidth, at least one user
terminal (16) communicatively coupled to the spacecraft (11) by a
user link (17), the user link (17) operable at any frequency band
within the bandwidth without regard to polarization; and, the
communications network (100) adapted to provide for simultaneous
operation of at least a portion of the feeder link (13) and a
portion of the user link (17) at a common polarization and
frequency band within the bandwidth.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Features of the invention are more fully disclosed in the
following detailed description of the preferred embodiments,
reference being had to the accompanying drawings, in which:
[0009] FIG. 1 is a system level diagram of an exemplary
communications network of the prior art.
[0010] FIG. 1A is a system level diagram of an embodiment of a
communications network of the present invention.
[0011] FIG. 2 is an exemplary map of gateway locations and user
beams as provided by one embodiment of the present invention.
[0012] FIG. 3 is an exemplary map of gateway locations and user
beams as provided by a further embodiment of the present
invention.
[0013] FIG. 3A is an exemplary map of gateway locations and user
beams in an embodiment of the invention, illustrating a frequency
re-use scheme.
[0014] FIG. 4 is an exemplary map of gateway locations and user
beams as provided by a further embodiment of the present
invention.
[0015] Throughout the drawings, the same reference numerals and
characters, unless otherwise stated, are used to denote like
features, elements, components, or portions of the illustrated
embodiments. Moreover, while the subject invention will now be
described in detail with reference to the drawings, it is done so
in connection with the illustrative embodiments. It is intended
that changes and modifications can be made to the described
embodiments without departing from the true scope and spirit of the
subject invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Specific exemplary embodiments of the invention will now be
described with reference to the accompanying drawings. This
invention may, however, be embodied in many different forms and
should not be construed as limited to the embodiments set forth
herein. Rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the invention to those skilled in the art. It will be
understood that when an element is referred to as being "connected"
or "coupled" to another element, it can be directly connected or
coupled to the other element, or intervening elements may be
present. Furthermore, "connected" or "coupled" as used herein may
include wirelessly connected or coupled.
[0017] The overall design and operation of spacecraft
communications networks are well known to those having skill in the
art, and need not be described further herein. As disclosed herein,
a user terminal 16 is adapted for communication with a satellite
11, and may be one of a plurality of different types of fixed and
mobile user terminals including, but not limited to, a cellular
telephone, wireless handset, a wireless modem, a data transceiver,
a paging or position determination receiver, or mobile
radio-telephones. Furthermore, a user terminal may be hand-held,
portable as in vehicle-mounted (including for example cars, trucks,
boats, trains, and planes), or fixed, as desired. A user terminal
may be referred to as a wireless communication device, a mobile
station, a mobile unit, a subscriber unit, a mobile radio or
radiotelephone, a wireless unit, or simply as a "user," a
"subscriber," or a "mobile" in some communication systems.
Furthermore, as used herein, the term "spacecraft" includes one or
more satellites at any orbit (geostationary, substantially
geostationary, inclined geosynchronous, Molniya, medium earth
orbit, low earth orbit, and other non-geostationary orbits) and/or
one or more other spacecraft that has/have a trajectory above the
earth or other celestial body at any altitude.
[0018] It will be understood that although the terms "first" and
"second" are used herein to describe various elements, these
elements should not be limited by these terms. These terms are used
only to distinguish one element from another element. Thus, for
example, a first user terminal could be termed a second user
terminal, and similarly, a second user terminal may be termed a
first user terminal without departing from the teachings of the
present invention. As used herein, the term "and/or" includes any
and all combinations of one or more of the associated listed items.
The symbol "/" is also used as a shorthand notation for
"and/or".
[0019] FIG. 1 shows an exemplary spacecraft communications network
100, comprising a spacecraft 11 communicatively coupled to at least
one gateway 12 and a plurality of user terminals 16. Feeder link 13
consists of forward uplink 14 and return downlink 15. User link 17
consists of forward downlink 18 and return uplink 19. There may be
several gateways 12 communicatively coupled to spacecraft 11, and a
large number of user terminals 16. Each gateway 12 is
advantageously located proximate to an Internet backbone (not
shown) and has a high data rate connection therewith.
[0020] A conventional multi-beam spacecraft 11 has an antenna
subsystem for providing a grid of antenna spot beams. The shape of
the grid in turn defines a service region. The grid of individual
spot beams (user beams) divides an overall service region, which
may, for example, coincide with the territory of the United States,
into a number of smaller cells. For example, U.S. patent
application Ser. No. 11/467,490, assigned to the assignee of the
present invention, describes a pattern of 135 spot beams covering
the continental United States (CONUS), Hawaii, Alaska, and Puerto
Rico.
[0021] Conventional systems locate gateway(s) 12 within the service
region. To avoid interference between user link signals 17 and
feeder link 13 signals, known systems such as the system described
by Ames, et al., U.S. patent application Ser. No. 10/940,356,
require that the total bandwidth allocated to the downlink be
divided into separate non-overlapping blocks for the forward
downlink 18 and the return downlink 15. Similarly, the total
bandwidth allocated to the uplink is divided into separate
non-overlapping blocks for the forward uplink 14 and the return
uplink 19. This approach substantially reduces the amount of
bandwidth available to the user link 17, since any bandwidth
allocated to the feeder link 13 is bandwidth that cannot be
allocated to the user link 17. As a result, the bandwidth
utilization efficiency for such systems is less than optimal.
[0022] In an embodiment of the present invention, a spacecraft
communications network 100, having been licensed to operate within
a certain amount of total frequency bandwidth, is enabled to
allocate the entire licensed bandwidth to the user link 17. Some or
all of the total licensed bandwidth is reused by the gateway(s) 12,
thereby providing for simultaneous operation of at least a portion
of the feeder link 13 and a portion of the user link 17 at common
frequencies. More specifically, the present invention enables
forward uplink 14 and return uplink 19 to reuse the same frequency.
Similarly, the present invention enables forward downlink 18 and
return downlink 15 to reuse the same frequency. Simultaneous
operation of the feeder link 13 and the user link 17 at common
frequencies means that the gateway(s) 12 may reuse any part of the
total bandwidth allocated to the user antenna beams. This may be
accomplished in various ways, as discussed hereinafter.
[0023] One embodiment of the present invention results in the
antenna coverage pattern shown in FIG. 2, and provides for spatial
separation between the gateway(s) 12 and a service region 21 to
enable non-interfering use of the same frequency by the gateway(s)
12 and user terminals 16. As shown in FIG. 2, the service region 21
is defined as the footprint made by a plurality of user beams 22,
and encompasses roughly the eastern half of the continental United
States. In this example, a user terminal 16, located within the
footprint of any of fifty three user beams 22, may be
communicatively coupled over user link 17 to spacecraft 11, and
spacecraft 11 may be communicatively coupled over feeder link 13 to
at least one of fifteen gateways 12. Each gateway 12 is located in
a gateway beam 23 and is coupled to the public switched telephone
network. Preferably each gateway 12 is proximate to, and
communicatively coupled with, a high speed Internet backbone access
point. Each gateway beam 23 is substantially spatially isolated
from the service region 21. Because of this spatial isolation, the
user link 17 advantageously is operable at the same frequency(ies)
as the feeder link 13. Moreover, in accordance with the present
invention, the frequency band common to both the feeder link 13 and
the user link 17 may encompass substantially all of the bandwidth
licensed to the network 100.
[0024] In a presently preferred embodiment, the antenna coverage
pattern of FIG. 2 is provided by means of a geostationary satellite
11 with a payload DC power capability of approximately 14 kW,
providing fixed satellite service at Ka-band. A satellite 11 having
this approximate payload power capacity can deliver the maximum
permitted power spectral density (PSD) to service region 21 or to
other, similarly sized service regions. Thus, the dual objectives
of simultaneously maximizing PSD and bandwidth utilization
efficiency may be achieved.
[0025] The antenna pattern coverage of FIG. 2 may be varied
substantially while remaining within the scope of the invention.
For example, user beams 22 may define a service region encompassing
a western portion of the United States, in which case the
gateway(s) 16 is (are) located in an eastern portion of the United
States, spatially isolated from the service region. Moreover, the
invention may be advantageously employed in connection with other
geographic service regions besides the United States.
[0026] Another embodiment of the invention results in the antenna
pattern coverage illustrated in FIG. 3, which shows that the user
beams 22 may be distributed across non-contiguous service regions.
For example, as illustrated in FIG. 3, a first service region 31,
defined by fifty three user beams, is disposed to coincide with
roughly the eastern half of the United States, and a second and a
third service region 32 and 33, defined, respectively, by three
user beams 22 and one user beam 22, are disposed along the western
seaboard of the United States. In this example, a user terminal 16,
located within the footprint of any of fifty seven user beams 22,
may be communicatively coupled over user link 17 to spacecraft 11,
and spacecraft 11 may be communicatively coupled over feeder link
13 to at least one of ten gateways 12. Each gateway 12 is located
within the footprint of a gateway beam 23. Each gateway beam 23 is
substantially spatially isolated from each service region 31, 32
and 33. Because of this spatial isolation, the user link 17
advantageously is operable at the same frequency(ies) as the feeder
link 13. Moreover, in accordance with the present invention, the
frequency band common to both the feeder link 13 and the user link
17 may encompass substantially all of the bandwidth licensed to the
network 100.
[0027] Spatial separation between gateway beams 23 is
advantageously provided to enable use of the entire bandwidth by
each gateway 12. Furthermore, the gateway(s) 12 is (are) preferably
disposed geographically to be proximate to the terrestrial Internet
backbone (not shown) and coupled to that backbone by broadband
communications links (not shown).
[0028] As previously discussed, a service region (for example,
service region 21) may be defined by a grid of individual user
beams 22. Frequency reuse by two or more user beams 22 may be
employed in various embodiments of the present invention. For
example, any two user beams may employ the same frequency without
regard to antenna polarization provided that the two user beams are
spatially isolated (i.e., not adjacent or overlapping).
Furthermore, even adjacent user beams may employ a common frequency
provided that each adjacent user beam operates at a different
antenna polarization. Frequency re-use within a plurality of user
beams 22 may be improved by using, for example, a "four color"
re-use plan. As illustrated in FIG. 3A, in a four color re-use
plan, each color represents a combination of a frequency sub-band
and an antenna polarization. Appropriate assignment of colors to
user beams 22 provides that no two adjacent user beams share both a
common frequency and a common polarization.
[0029] A further embodiment of the invention, illustrated in FIG.
1A, may provide the antenna pattern coverage illustrated in FIG. 4,
in which a subset of user beams, termed low density user beams 47,
are distributed so as to define a service region 46 wherein one or
more gateways 12 are also disposed. In this embodiment of the
invention, the available spectrum is allocated into, for example,
two non-overlapping unequally sized segments. The larger of the two
spectrum segments is assigned to a first user link 17a and the
smaller of the two spectrum segments is assigned to a second user
link 17b. The feeder link 13 preferably operates within the same
spectrum segment as user link 17a and outside the spectrum segment
assigned to user link 17b.
[0030] As illustrated in FIG. 4, a first service region 41 is
defined by a plurality of high density user beams 42 and
encompasses roughly the eastern half of the continental United
States. In this example, a user terminal 16, which may be located
in any of thirty-two user beams 42, is communicatively coupled over
user link 17a to spacecraft 11, and spacecraft 11 may be
communicatively coupled over feeder link 13 to at least one of
eight gateways 12. Each gateway 12 is substantially spatially
isolated from the first service region 41. Because of this spatial
isolation, the user link 17a advantageously is operable at the same
frequency(ies) as the feeder link 13. Moreover, in accordance with
the present invention, the frequency band common to both the feeder
link 13 and the user link 17a may encompass the entirety of the
bandwidth or an arbitrarily large fraction of the bandwidth
licensed to the network 100.
[0031] As further illustrated in FIG. 4, a second service region 46
is defined by a plurality of low density user beams 47 and
encompasses roughly the western half of the continental United
States. At least one gateway 12 is also disposed in second service
region 46. In this example, a user terminal 16, which may be
located in any of sixty-two low density user beams 47, is
communicatively coupled over user link 17b to spacecraft 11, and
spacecraft 11 is communicatively coupled over feeder link 13 to at
least one of eight gateways 12. Because the feeder link 13 operates
outside the spectrum segment assigned to user link 17b, spatial
separation between any gateway 12 and user beam 47 is not required
to avoid interference.
[0032] Of course, the methods of optimizing frequency reuse by two
or more user beams discussed above may also be employed in this
embodiment of the present invention. For example, any two user
beams may employ the same frequency without regard to antenna
polarization provided that the two user beams are spatially
isolated (i.e., not adjacent or overlapping). Furthermore, even
adjacent user beams may employ a common frequency provided that
each adjacent user beam operates at a different antenna
polarization. Frequency re-use within a plurality of user beams may
be improved by using, as discussed above, a "four color" re-use
plan.
[0033] The foregoing merely illustrates principles of the
invention. It will thus be appreciated that those skilled in the
art will be able to devise numerous systems and methods which,
although not explicitly shown or described herein, embody said
principles of the invention and are thus within the spirit and
scope of the invention as defined by the following claims.
* * * * *