Title: Satellite communication system with gateway switch networks
Abstract: A communication system having gateway filter and switching networks in forward and return channels of a frequency reuse communication satellite. The system couples subscriber terminals to the Internet or other terrestrial network by way of one or more gateways. The system cross-straps gateway-to-user beam connectivity provided by the communication satellite to allow full coverage of all user beams with a subset of the gateways having reduced frequency reuse. An exemplary system comprises a communication satellite having a return channel and a forward channel. One or more gateways are coupled to the Internet or other terrestrial network and communicate with subscriber terminals by way of the return and forward channels provided by the satellite. The return and forward channels each comprise a filter and switching network that selectively couple signals between the one or more gateways and the subscriber terminals. The filter and switching networks selectively couples signals between selected gateways and selected subscriber terminals using predetermined beams.
Patent Number: 6,898,428 Issued on 05/24/2005 to Thorburn, et al.
| Inventors:
|
Thorburn; Michael (Glendale, CA);
Ziegler; Craig (Sunnyvale, CA);
Holme; Stephen C. (San Ramon, CA)
|
| Assignee:
|
Space Systems/Loral, Inc. (Palo Alto, CA)
|
| Appl. No.:
|
871075 |
| Filed:
|
May 31, 2001 |
| Current U.S. Class: |
455/427; 370/316; 370/325; 370/335; 370/336; 370/353; 370/401; 455/12.1; 455/422.1; 455/428; 455/430; 455/562.1 |
| Intern'l Class: |
H04Q 007/20 |
| Field of Search: |
370/441,335,336,353,316,325,535,401
455/427,428,430,121,422.1,562
|
References Cited [Referenced By]
U.S. Patent Documents
| 6317420 | Nov., 2001 | Schiff.
| |
| 2001/0021195 | Sep., 2001 | Miller et al.
| |
| 2002/0128045 | Sep., 2002 | Chang et al.
| |
Primary Examiner: Banks-Harold; Marsha D.
Assistant Examiner: Peaches; Randy
Attorney, Agent or Firm: Karambelas & Associates
Claims
1. A communication system comprising:
one or more gateways coupled to a terrestrial network;
one or more subscriber terminals that are to be coupled to the terrestrial network;
a communication satellite providing forward and return communication links between
the one or more gateways and the one or more subscriber terminals that each comprise
a switching network that selectively couples signals between selected gateways
and selected subscriber terminals using predetermined beams wherein the forward
communication link implemented in the communication satellite comprises: a plurality
of first switches that receives data transmitted from a respective plurality of
gateways; one or more forward channel gateway multiplexers selectively coupled
to one of the plurality of first switches; a plurality of second switches selectively
coupled to outputs of the plurality of first switches and selectively coupled to
outputs of the one or more forward channel gateway multiplexers; and one or more
regional multiplexers selectively coupled to the plurality of second switches that
output data to a plurality of regions servicing the one or more subscriber terminals.
2. The communication system as recited in claim 1 wherein selected ones of the
pluralities of first and second switches comprise power dividing hybrids.
3. The communication system as recited in claim 1 wherein the forward communication
link implemented in the communication satellite comprises:
a first switch for receiving data transmitted from a first gateway;
a third switch for receiving data transmitted from a second gateway;
a forward channel gateway multiplexer coupled to the first switch;
a second switch coupled to the first switch and to a first output of the forward
channel gateway multiplexer;
a fourth switch coupled to the third switch and to a second output of the forward
channel gateway multiplexer;
a first multiplexer coupled to the second switch that outputs data to a first
plurality of regions; and
a second multiplexer coupled to the fourth switch that outputs data to a second
plurality of regions.
4. The communication system recited in claim 1 wherein the return communication
link implemented in the communication satellite comprises:
one or more regional multiplexers that receive data transmitted from subscriber
terminals located in a plurality of regions;
a plurality of third switches respectively coupled to the one or more regional
multiplexers;
one or more return channel gateway multiplexers selectively coupled to the plurality
of third switches; and
a plurality of fourth switches selectively coupled to the one or more return
channel gateway multiplexers and plurality of third switches that output data to
the one or more gateways.
5. The communication system as defined in claim 4 wherein one of the pluralities
of third and fourth switches comprises power dividing hybrids.
6. The communication system as defined in claim 1 wherein the return communication
link implemented in the communication satellite comprises:
a first multiplexer for receiving data transmitted from a first plurality of
regions;
a second multiplexer for receiving data transmitted from a second plurality of
regions;
a first switch coupled to the first multiplexer;
a second switch coupled to the second multiplexer;
a return channel gateway multiplexer selectively coupled to the first and second
switches;
a third switch selectively coupled to the first switch and the return channel
gateway multiplexer that outputs data to a first gateway; and
a fourth switch coupled to the third switch that outputs data to a second gateway.
7. The communication system as defined in claim 1 wherein each communication
link implemented in the communication satellite comprises:
one or more first switches that communicate with corresponding gateways;
one or more gateway multiplexers coupled to the one or more first switches;
one or more second switches selectively coupled to the one or more gateway multiplexers
and selectively coupled to the one or more first switches; and
one or more regional multiplexers coupled to the one or more second switches
that communicate with plurality of regions.
8. The communication system as recited in claim 7 wherein selected ones of the
first and second switches comprise power dividing hybrids.
Description
BACKGROUND
The present invention relates generally to satellite communication systems, and
more particularly, to a satellite communication system employing gateway switch
networks that permit full coverage of all user beams with a subset of the gateways
having reduced frequency reuse.
Typical frequency reuse satellite communication systems support one or several
gateways and provide a connection between each gateway and the multiple beams it
supports. The frequency reuse of the communication system is achieved because the
satellite supports a number of gateways and beams in parallel.
It would be desirable to have a communication system that permits a gradual increase
in communication bandwidth commensurate with an increase in usage. It would be
desirable to have a communications system employing a frequency reuse satellite
that may be deployed to serve the full coverage area at reduced bandwidth with
a subset of the full complement of gateways for which the satellite system was
designed. It would be desirable to have a communications system employing satellites
to back up one gateway using another (backup) gateway by partitioning and sharing
the backup gateway's reused bandwidth.
It is therefore an objective of the present invention to provide for an improved
communication system employing gateway switch networks that permit full coverage
of all user beams with a subset of the gateways having reduced frequency reuse.
SUMMARY OF THE INVENTION
The present invention provides for a communication system that comprises gateway
switching networks in forward and return channels of a frequency reuse communication
satellite that are used to couple subscriber terminals to the Internet or other
terrestrial network by way of one or more gateways. The present invention cross-straps
gateway-to-user beam connectivity provided by the communication satellite to allow
full coverage of all user beams with a subset of the gateways having reduced frequency reuse.
An exemplary communication system comprises a communication satellite having a
return channel and a forward channel. One or more gateways are coupled to the Internet
or other terrestrial network and communicate with subscriber terminals by way of
the return and forward channels provided by the satellite. The return and forward
channels each comprise a switching network that selectively couple signals between
the one or more gateways and the subscriber terminals. The switching networks selectively
couples signals between selected gateways and selected subscriber terminals using
predetermined beams.
The advantages of the present invention over a conventional communication system
that does not employ gateway switch networks are that the infrastructure, including
the gateways and backbone fiber optic network for the communication system can
be deployed as the customer base increases. In addition, a temporary loss of a
gateway and the resulting loss of coverage can be overcome by switching to a reduced
frequency reuse mode wherein a backup gateway is used to provide connectivity to
the satellite in place of the inoperative gateway.
The present invention allows a communications system employing a frequency reuse
satellite that is deployed to serve a full coverage area to operate at a reduced
bandwidth using a subset of the full complement of gateways for which the satellite
was designed. The present invention also allows a communications system employing
a satellite to back up one gateway using another (backup) gateway by partitioning
and sharing the backup gateway's reused bandwidth.
BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of the present invention may be more readily
understood with reference to the following detailed description taken in conjunction
with the accompanying drawings, wherein like reference numerals designate like
structural elements, and in which:
FIG. 1 illustrates an exemplary satellite communication system in accordance
with the principles of the present invention;
FIG. 1
a illustrates details of the exemplary satellite communication
system shown in FIG. 1;
FIG. 2 illustrates a return channel of the satellite communication system;
FIG. 3 illustrates an exemplary forward channel of the satellite communication system;
FIGS. 4
a-m illustrate details of an exemplary switch network employed
in the satellite communication system; and
FIG. 5 illustrates a generic switch network in accordance with the principles
of the present invention.
DETAILED DESCRIPTION
Referring to the drawing figures, FIG. 1 illustrates an operating environment
of an exemplary communication system
10 in accordance with the principles
of the present invention. The exemplary communication system
10 is used
to interconnect a plurality of subscriber terminals
13 to the Internet
16
or other terrestrial network
16.
The exemplary communication system
10 comprises one or more gateways
12
that are coupled to the Internet
16 or other terrestrial network
16
by way of a fiber optic network
17, for example. A frequency reuse communication
satellite
11 communicates with the one or more gateways
12 and generates
a plurality of beams that transmit signals to and receive signals from a plurality
of regions. Reuse of the frequency bandwidth of the communication satellite
11
is achieved when multiple gateways
12 are employed.
In the exemplary system
10 shown in FIG. 1, a first gateway
12
communicates
with region
1 and region
2, while a second gateway
12 communicates
with region
3 and region
4. Further implementation details of the
system
10 are discussed below.
FIG. 1
a illustrates details of the exemplary satellite communication
system
10. The communication satellite
11 comprises a return channel
20 and a forward channel
30. The return channel
20 comprises
receive and transmit antennas
21,
22, and the forward channel
30
also comprises receive and transmit antennas
21,
22. The improvements
provided by the present invention are implemented in the return and forward channels
20,
30.
Each of the gateways
12 are coupled to the Internet or other terrestrial
network
16 by way of the network
17. The plurality of subscriber
terminals
13 are coupled to the Internet or other terrestrial network
16
by way of the satellite
11, the one or more gateways
12 and the fiber
optic network
17. The subscriber terminals
13 communicate with the
Internet or other terrestrial network
16 by way of the satellite
11
to make requests for data using a return path
14 comprising the return channel
20 of the satellite
11. Data derived from the Internet
16
or other terrestrial network
16 is forwarded to the subscriber terminals
13 by way of the fiber optic network
17, a selected gateway
12,
and a forward path
15 through the forward channel
30 of the satellite
11.
Thus, the satellite
11 provides for bi-directional communication between
the subscriber terminals
13 and the gateways
12. The satellite
11
provides a "last mile" connection from the Internet
16 or other terrestrial
network
16 to the subscriber terminals
13.
In a normal operational scenario, the communication system
10 is designed
to operate using its full bandwidth, which supports multiple gateways
12.
However, early on in the lifetime of the system
10, the number of subscriber
terminals
13 is far less than the number that may be supported by the system
10.
Heretofore, in order to properly operate the system
10, all required
gateways
12 would need to be operational at commencement of system operation.
For example, a system
10 implementing six-time frequency reuse, requires
six gateways
12 for full-up operation. This is expensive due to the cost
of the gateways
12, and in light of the fact that typically few subscriber
terminals use the system
10. The full system bandwidth capacity is typically
not required when the system
10 is initially made operational. However,
in accordance with the principles of the present invention, the system
10
may be made operational without using all required gateways
12, and may
be implemented using from one to all of the gateways
12 supported by the
satellite
11.
This is accomplished using switch networks
25,
37 in accordance
with the present invention in the return and forward channels
20,
30.
The switch networks
25,
37 are described with reference to FIGS.
2-5. Use of the switch networks
25,
37 allows use of a limited number
of gateways
12 using less than full-system bandwidth.
The switch networks
25,
37 allow complete beam coverage from the
satellite
11 using a minimal subset of gateways
12. As capacity requirements
of the system
10 increase, additional gateways
12 are provided, switches
and/or filters and/or switching multiplexers of the switch networks
25,
37 are reconfigured, and the capacity of the system
10 is increased
to support more gateways
12 and subscriber terminals
13. The total
bandwidth of the system
10 is used initially, and frequencies are reused
with added gateways
12.
Referring now to FIG. 2, it illustrates details of the return channel
20
of the satellite
11 used in the exemplary satellite communication system
10. The return channel
20 comprises the receive antenna
21
which is coupled by way of a plurality of hybrid couplers (H)
23 to one
or more combining multiplexers
24. The outputs of the one or more combining
multiplexers
24 are coupled to a return channel switch network
25
which receives inputs from each of the combining multiplexers
24.
The return channel switch network
25 has a plurality of outputs that are
coupled to a first switch ring
26. Respective outputs of the first switch
ring
26 are individually coupled by way of a plurality of downconverters
(D/C)
27 to a second switch ring
28. The output of the second switch
ring
28 is coupled by way of a high power amplifier
29 to the transmit
antenna
22.
FIG. 3 illustrates details of the forward channel
30 of the satellite
11 used in the exemplary satellite communication system
10. The forward
channel
30 comprises the receive antenna
31 which is coupled by way
of a plurality of feeds
33 to a plurality of preselect filters
34.
Outputs of the preselect filters
34 are coupled to low noise amplifiers
35. Outputs of selected low noise amplifiers
35 are coupled to a
corresponding diplexer
36, while others of the low noise amplifiers
35
are coupled to a forward channel switch network
37 or a diplexer
36.
Outputs of each of the low noise amplifiers
35 or diplexers
36
are coupled to the forward channel switch network
37. The forward channel
switch network
37 has a plurality of outputs that are coupled to a first
switch ring
38. Respective outputs of the first switch ring
38 are
individually coupled by way of a plurality of downconverters (D/C)
39 to
a second switch ring
40. The output of the second switch ring
40
is coupled by way of a high power amplifier
41 to the transmit antenna
32.
Details of the design and operation of exemplary return and forward channel
switch networks
25,
37 will now be discussed. FIGS. 4
a-m illustrate
details of an exemplary simple switch network
25,
37 that may be
employed in the return and forward channels
20,
30.
Referring to FIG. 4
a, it shows a standard approach used in the system
10, which is the scenario shown in FIG.
1. With full capacity, the
first gateway
12 services regions
1 and
2, while the second
gateway
12 services regions
3 and
4. Region
1 serviced
by the first gateway
12 is covered between frequencies f
1 and f
2.
Region
2 serviced by the first gateway
12 is covered between frequencies
f
2 and f
3. Region
3 serviced by the second gateway
12
is covered between frequencies f
1 and f
2. Region
4 serviced
by the second gateway
12 is covered between frequencies f
2 and f
3.
In contrast to this technique, using the present invention, initially regions
1-
4 are serviced by all gateways
12. All gateways
12
service regions
1 and
2 using frequencies between frequencies f
1
and f
2, and service regions
3 and
4 using frequencies between
frequencies f
2 and f
3.
FIG. 4
c shows the conventional forward link repeater (implemented by
the satellite
11) that transmits data from the gateways
12 to users
(subscriber terminals
13). The first gateway
12 (gateway
1)
transmits data by way of a first multiplexer
51a to regions
1
and
2. The second gateway
12 (gateway
2) transmits data by
way of a second multiplexer
51b to regions
3 and
4.
FIG. 4
d shows a simple configuration of a system
10 in accordance
with the present invention using two gateways
12 servicing four beams. FIG.
4
d shows a forward repeater in accordance with the present invention (implemented
by the satellite
11) that transmits data from the gateways
12 to
users (subscriber terminals
13) in various regions (regions
1-
4).
Data transmitted from a first gateway
12 (gateway
1) is coupled
to a first switch
52. A first output of the first switch
52 is coupled
to a switching (gateway) multiplexer
54. A first output of the switching
(gateway) multiplexer
54 and a second output of the first switch
52
are coupled to a second switch
53. An output of the second switch
53
is coupled to a first regional multiplexer
51a. Outputs of the first
regional multiplexer
51a service regions
1 and
2.
Data transmitted from a second gateway
12 (gateway
2) is coupled
to a third switch
55. An output of the third switch
55 is coupled
to a first input of a fourth switch
56. A second output of the switching
(gateway) multiplexer
54 is coupled to a second input of the fourth switch
56. An output of the fourth switch
56 is coupled to a second regional
multiplexer
51b. Outputs of the second regional multiplexer
51b
service regions
3 and
4.
With reference to FIG. 4
e, the first regional multiplexer
51a
takes the frequency band between frequency f
1 and frequency f
3
and divides it into two regions. As is shown in FIG. 4
f, the switching (gateway)
multiplexer
54 has two outputs. The first output (output
1) is the
upper trace of FIG. 4
f, while the second output (output
2) is the
lower trace of FIG. 4
f.
As is shown in FIG. 4
g, the first output (output
1 shown in FIG.
4
f) is combined in the first regional multiplexer
51a to produce
regions
1 and
3. As is shown in FIG. 4
h, the second output
(output
2 shown in FIG. 4
f) is combined in the first regional multiplexer
51a to produce regions
2 and
4.
As is shown in FIG. 4
i, the output of the switching (gateway) multiplexer
54 combined with the output of the regional multiplexers
51a,
51b produces the desired regional coverage which meets channelization
requirements of the system
10. The switches
52,
53, and
56
also route the bandwidth appropriately.
FIG. 4
j shows a conventional return link repeater (implemented on the
satellite
11, which transmits data from the users (subscriber terminals
13) and the gateways
12. This configuration is the complement of
the configuration shown in FIG. 4
c. Data from regions
1 and
2
are multiplexed in a first multiplexer
51a and transmitted to the
first gateway
12 (gateway
1). Similarly, data from regions
3
and
4 are multiplexed in a second multiplexer
51b and transmitted
to the second gateway
12 (gateway
2).
FIG. 4
k shows a configuration in accordance with the present invention
illustrating a return link repeater that uses two gateways
12 servicing
four beams. The return link repeater transmits data from the users (subscriber
terminals
13) to the gateways
12.
Data transmitted from regions
1 and
2 are input to a first regional
multiplexer
51a. The output of the first regional multiplexer
51a
is coupled to a first switch
52. A first output of the first switch
52 is coupled to a first input of a second switch
53. A second output
of the first switch
52 is coupled to a second switching (gateway) multiplexer
54a.
Data transmitted from regions
3 and
4 are input to a second regional
multiplexer
51b. The output of the second regional multiplexer
51b
is coupled to a third switch
55. A first output of the third switch
55 is coupled to a first input of a fourth switch
56. Second inputs
of the third and fourth switches
55,
56 are each coupled to a load.
A second output of the third switch
55 is coupled to the second switching
(gateway) multiplexer
54a. The output of the second switching (gateway)
multiplexer
54a is coupled to a second input of the second switch
53. The output of the second switch
53 is coupled to a first gateway
12 (gateway
1). The output of the fourth switch
56 is coupled
to a second gateway
12 (gateway
2).
As is shown in FIG. 41, the second switching (gateway) multiplexer
54a
(switching multiplexer
2) has two inputs, shown as the upper and lower
traces at the left side of FIG. 4
l. The filter response of the second switching
(gateway) multiplexer
54a is shown as the upper and lower traces
at the right side of FIG. 4
l. The outputs of the second switching (gateway)
multiplexer
54a are combined to produce the output which is shown
in FIG. 4
m.
Thus, in the present invention, a switch network
25,
37 is installed
in both the forward and return channels
30,
20, or links
30,
20, of the frequency-reuse satellite
11. The switch network
25,
37 is designed so that initially, the available bandwidth comes from a subset
of the full complement of gateways
12. For example, a system
10 having
a satellite
11 that provides six-times frequency reuse may require six gateways
12 to service North America. The present invention permits total coverage
of North America by a single gateway
12 without frequency reuse, or by two
gateways
12 providing two-times frequency reuse, by three gateways
12
providing three-times frequency reuse, and so forth.
The reconfiguration of the switch network
25,
37 with frequency
reassignment can be implemented switching that interconnects available filters
or switching multiplexers. The reconfiguration of the switch network
25,
37 may be set using ground commands uplinked to the satellite
11.
The switch network
25,
37 is preferably installed in low-power
sections of both the forward and return links
30,
20, thus limiting
impact to a gain/noise temperature (G/T) figure of merit and Equivalent Isotropic
Radiated Power (EIRP) budgets.
In practice, the communication system provider may roll out the system
10
with a minimal set of gateways
12 and the communication satellite
11.
As subscriber terminals
13 increase, more gateways
12 may be added
to provide additional bandwidth to each region in the coverage area. Eventually,
the full complement of gateways
12 for which the satellite
11 was
designed can be operational to provide maximum bandwidth through frequency reuse.
This reduces the initial cost of establishing the gateway infrastructure prior
to establishing the customer base and revenue stream.
FIG. 5 illustrates a generic and more complex switch network
25,
37
in accordance with the principles of the present invention. FIG. 5 illustrates
the flexibility and expandability of the present invention. FIG. 5 shows a complex
configuration of a system
10 using multiple (N) gateways
12 servicing
multiple beams.
Data transmitted from a plurality of gateways
12 (gateways
1-N)
are coupled to a plurality of first switches
52a-
52n.
The plurality of first switches
52a-
52n are selectively
coupled to a plurality of gateway (switching) multiplexers
54a-
54n,
are selectively coupled to each other, and are selectively coupled to a plurality
of second switches
43a-
43n. The plurality of second
switches
43a-
43n are respectively coupled to a plurality
of regional multiplexers
51a-
51q. The plurality of
regional multiplexers
51a-
51q respectively service
regions
1-R
1,
1-R
2 and
1-RQ.
As should be evident from looking at FIG. 5, signals transmitted from the respective
gateways
12 may be selectively routed via the plurality of first switches
52a-
52n through one or more of the gateway multiplexers
54a-
54n and plurality of second switches
43a-
43n
to one or more of the plurality of regional multiplexers
51a-
51q.
The signals transmitted from one, two, or all of the gateways
12 may be
appropriately routed to one, two, or all of the regional multiplexers
51a-
51q.
Each of the regional multiplexers
51a-
51q services
regions supported by the system
10 and allows one, two, or all of the gateways
12 to be operational and fully support the system
10.
Thus, it should be clear that the system
10 may be made operational
without using all gateways
12, and may be implemented using from one to
all of the gateways
12 supported by the satellite
11. The system
10 incorporating the present switch networks
25,
37 cross-straps
gateway-to-user beam connectivity provided by the communication satellite to allow
full coverage of all user beams with a subset of the gateways
12 with reduced
frequency reuse.
Thus, an improved communication system employing satellite-based gateway switch
networks has been disclosed. It is to be understood that the above-described embodiments
are merely illustrative of some of the many specific embodiments that represent
applications of the principles of the present invention. Clearly, numerous and
other arrangements can be readily devised by those skilled in the art without departing
from the scope of the invention.
*
