Note: Descriptions are shown in the official language in which they were submitted.
CA 02221003 1997-11-13
SPACE-BASED COMMUNICATION SYSTEMS
Summary of the Invention
This invention relates generally to space-based telecommunication
systems and, in particular, to satellites in different orbits communicating
satellite control information to each other.
Background of the Invention
Some of the satellites in conventional satellite telecommunication
systems have the ability to communicate with adjacent satellites that share
the same orbiting altitude. This inter-satellite connection is referred to as
cross-links, whereby the cross-links carry voice and/or data from one
satellite to another satellite. If a base station located on earth transmits
command information destined for a satellite other than the first satellite
receiving the information, the command information may have pass
through many cross-links before the satellite that is selected to receive the
command information actually receives it. Such relaying of data or
information from one satellite to another satellite is commonly referred to
as hopping. Hcpping consumes valuable energy and bandwidth, especially
when command information is being relayed over many different
satellites. Accordingly, there is a significant need for a satellite
telecommunication system that reduces the number of hops it takes before
satellite control information or commands are received by the destined
satellite. Additionally, use of crosslinks for satellite control information
may consume crosslink bandwidth which could be used to carry revenue
generating traffic. Such traffic includes, but is not limited to voice, data, orfax information. Accordingly, there is a significant need for a satellite
telecommunication system that minimizes the satellite control traffic
carried on the crosslinks, therefore maximizing the available bandwidth
for revenue generating traffic.
Brief Description of the Drawings
~ CA 02221003 1997-11-13
FIG. 1 shows a high level diagram of a satellite telecommunication
system according to a preferred embodiment of the present invention; and
FIG. 2 shows an example of a highly simplified diagram of a
satellite.
Description of the Preferred Embodiments
The present invention has utility in that a network of satellites in
geosynchronous orbit can communicate with a network of low-earth orbit
10 satellites. By transferring satellite control information and commands
through the geosynchronous satellites, no low-earth orbit cross-links are
necessary for transferring this information. A base station (i.e., satellite
control facility) communicates directly to a geosynchronous satellite which
in turns passes it directly to the individual low-earth or medium-earth
15 orbit satellites. A geosynchronous satellite will have visibility and hence
direct communication with several low-earth orbit satellites at one time.
By linking three or four geosynchronous satellites, every satellite in the
low-earth orbit constellation would be visible.
FIG. 1 shows a highly simplified diagram of satellite
20 telecommunication system 10. As shown in FIG. 1, telecommunication
system 10 comprises at least two satellites 20 and 22, any number of
subscriber units 30 and at least one base station 40. Generally, satellites 20
and 22, subscriber units 30 and base station 40 of telecommunication
system 10 may be viewed as a network of nodes. All nodes of
25 telecommunication system I0 are or may be in data communication with
other nodes of telecommunication system 10 through telecommunication
links. In addition, all nodes of telecommunication system 10 are or may be
in data communication with other telephonic devices dispersed
throughout the world through public switched telephone networks
30 (PSTNs) and/or conventional terrestrial communication devices coupled
to a PSTN through conventional lel,es~lial base stations.
A "satellite" as used throughout this description means a man-
made object or vehicle intended to orbit the earth. A "constellation"
means a number of satellites arranged in orbits for providing specified
35 coverage (e.g., radio communication, remote sensing, etc.) of a portion,
portions or all of the earth. A constellation typically includes multiple
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rings (or planes) of satellites and may have an equal number of satellites in
each plane, although this is not essential.
The present invention is applicable to space-based
telecommunication systems 10 that assign particular regions on the earth
5 to specific cells on the earth, and ~referably to systems 10 that move cells
across the surface of the earth. Satellites 20 may be a single satellite or one
of many satellites 20 in a constellation of satellites orbiting earth. The
present invention is also applicable to space-based telecommunication
systems 10 having satellites 20 which orbit earth at any angle of inclination
10 including polar, equatorial, inclined or other orbital patterns. The present
invention is applicable to systems 10 where full coverage of the earth is
not achieved (i.e., where there are "holes" in the telecommunication
coverage provided by the constellation) and to systems 10 where plural
coverage of portions of the earth occur (i.e., more than one satellite is in
15 view of a particular point on the earth's surface).
In the preferred embodiment, satellites 20 have a low-earth orbit,
while satellite 22 is a geosynchronous satellite. In alternative
embodiment, satellites 20 may be in medium-earth orbit, while satellite 22
is a geosynchronous satellite. In another alternative embodiment,
20 satellites 20 may be in low-earth orbit, while satellite 22 may be in
medium-earth orbit. There may be more than one satellite 22 which
services satellites 20 and these satellites 22 may be able to communicate
with each other. Low-earth orbit satellite are typically at an altitude range
of 700Km to 1400Km (400 to 800 miles) altitude, while medium-earth orbit
25 satellite at an altitude of about 10,000Km (6200 miles), and geosynchronous
satellites are at an altitude of about 36000Km (23,000 miles).
Each satellite 20 communicates with other nearby satellites 20 via
cross-links. These cross-links form a backbone of space-based mobile
telecommunication system 6. Thus, a call or user communication,
30 including but not limited to voice, fax and data from subscriber unit 30
located at any point on or near the surface of the earth may be routed
through satellite 20 or a constellation of satellites to within range of
substantially any other point on the surface of the earth. A
communication may be routed down to subscriber unit 31 (which is
35 receiving the call) on or near the surface of the earth from another
satellite. How satellite 20 physically communicates (e.g., spread spectrum
CA 02221003 1997-11-13
technology) with subscriber units 30 and base station 40 is well known to
those of ordinary skill in the art.
Satellite 20 communicates with satellite 22 via a cross-link when
satellite 20 is in view of satellite 22. Satellite 20 is not always in view of
satellite 22, but is in view of satellite 22 for a period of time during its orbit
around the earth. In alternative embodiments, there are multiple
satellites 22, where each satellite 20 is able to communicate with one of the
satellites 22 no matter where they are in their orbit around earth.
Moreover, each satellite 22 may be able to communicate with adjacent
10 satellites 22.
Cross-links between satellites 20 and 22 carry satellite control
information, including but not limited to, satellite commands, telemetry,
traffic routing vectors, traffic connection establishment, release messaging,
cell channel frequency, satellite maneurvering commands, cell shutdown
15 schedules. Satellite control information may additionally include
telephony radio link management data such as time-tagged beam on/off
tables, time-tagged beam related radio channel data such as allocation and
deallocation of radio resources, and time-tagged beam related broadcast
channel data.
Satellite 22 receives satellite control information for one or more
satellite from base station 40 and communicates it to appropriate satellites
20. Since satellite 22 communicates satellite control information to
satellites 20, the cross-links between satellites 20 only carry user
information (e.g., voice, fax and data) to support a call from one subscriber
25 unit 30 to another subscriber unit 30.
Subscriber units 30 may be located anywhere on the surface of earth
or in the atmosphere above earth. Mobile telecommunication system 10
may accommodate any number of subscriber units 30. Subscriber units 30
are preferably communication devices capable of receiving voice and/or
30 data from satellites 20 and/or base stations 40. By way of example,
subscriber units 30 may be hand-held, mobile satellite cellular telephones
adapted to transmit to and receive transmissions from satellites 20 and/or
base stations 40. Moreover, subscriber units 30 may be computers capable
of sending email messages, video signals or facsimile signals just to name
35 a few.
~ CA 02221003 1997-11-13
How subscriber units 30 physically transmit voice and/or data to
and receive voice and/or data from satellites 20 is well known to those of
ordinary skill in the art. In the preferred embodiment of the present
invention, subscriber unit 30 communicates with satellite 20 using a
limited portion of the electromagnetic spectrum that is divided into
numerous channels. The channels are ~Leferably L-Band, K-Band, S-band
frequency channels or combination thereof, but may encompass Frequency
Division Multiple Access (FDMA) and/or Time Division Multiple Access
(TDMA) and/or Code Division Multiple Access (CDMA) communication
or any combination thereof. Other methods may be used as known to
those of ordinary skill in the art.
Base station 40 communicates with and controls satellites 20 via
satellite 22. There may be multiple base stations 40 located at different
regions on the earth. For example, there may be one base station located in
Honolulu, another base station located in Los Angeles and another base
station in Washington, D.C. Base stations 40 may provide satellite
signalling commands to satellite 22 so that satellites 22 and 20 maintain
their proper position in their orbit and perform other essential house-
keeping tasks. Base stations 40 may be additionally responsible for
receiving voice and/or data from satellites 20. How base station 40
physically communicates (e.g., spread spectrum) with satellites 22 and 20
and/or subscriber units 30 is well known to those of ordinary skill in the
art.
FIG. 2 shows an example of a highly simplified diag~am of satellite
20 or 22. Satellite 20 comprises at least two transceivers 30, processor 34
and memory 36. Some transceivers 30 of satellite 20 are capable of sending
and receiving satellite control information from satellite 22, while other
transceivers 30 are capable of sending and receiving user information (e.g.,
voice, fax and data) from other adjacent satellites 20, subscriber units 30
and base stations 40. Some transceivers 30 of satellite 22 are capable of
sending and receiving satellite control information from satellite 22 and
from base station 40. Processor 34 controls the whole operation of satellite
20, 22 and may be responsible for executing software application programs.
Memory 36 stores the software programs executed by processor 34.
Although one processor 34 and one memory unit 36 are shown in FIG. 2,
those skilled in the art understand that more than one processor and
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memory can be used in satellite 20 and 22. The number of processor and
memory size is unimportant to the present invention.
The advantages of the present invention is to eliminate the need to
use low-earth orbit satellite cross-links to provide control information to
5 other low-earth orbit satellites. Another advantage is that only one hop is
needed to communicate satellite control information from satellite 22 to
satellite 20. Thus, satellite control commands can reach the designated
low-earth orbit satellite much faster. Yet another advantage is that
bandwidth previously used for control information can be carried by
10 satellite 22, which allows more bandwidth for revenue-bearing traffic.
Accordingly, it is intended by the appended claims to cover all
modifications of the invention which fall within the true spirit and scope
of the invention. For example, the following combinations are possible:
geosynchronous satellite 22 communicating with medium-earth or low-
15 earth orbit satellites 20, or medium-earth orbit satellite 22 communicating
with low-earth orbit satellites 20.
