U.S. patent application number 10/103070 was filed with the patent office on 2002-09-19 for interactive fixed and mobile satellite network.
This patent application is currently assigned to GLOBALSTAR, LP. Invention is credited to Wiedeman, Robert A..
Application Number | 20020132578 10/103070 |
Document ID | / |
Family ID | 25093826 |
Filed Date | 2002-09-19 |
United States Patent
Application |
20020132578 |
Kind Code |
A1 |
Wiedeman, Robert A. |
September 19, 2002 |
Interactive fixed and mobile satellite network
Abstract
A communications system includes at least one low earth orbit
first satellite (10), at least one second satellite (11) in other
than a low earth orbit, and a ground segment (12) that includes a
plurality of user transceivers (78, 80, 82, 84) and at least one
gateway (76) coupled to a publicly-accessible terrestrial
communications system, such as a PSTN and/or a fiber optic network.
The first satellite includes a first transceiver for communication
with the at least one gateway, a second transceiver for
communication with at least one user transceiver, and a third
transceiver for communication with the at least one second
satellite. The first, second and third transceivers are switchably
coupled together on-board the first satellite by on-board
processors and a switching matrix for relaying a user communication
between the at least one gateway and the at least one user
transceiver via the at least one second satellite. The plurality of
user transceivers can include a plurality of data processors which
are interconnected into a network through the at least one first
satellite. This network can be considered as a virtual network, and
can have a mesh, star, or other topology. In a presently preferred,
but not limiting embodiment of this invention, the user
transceivers are adapted to transmit and receive direct sequence,
code division/multiple access communications. Transmission of
signals to and from the user transceivers is accomplished by
spreading a digital data stream (e.g., voice, data, image, video)
with assigned spreading codes.
Inventors: |
Wiedeman, Robert A.; (Los
Altos, CA) |
Correspondence
Address: |
PAUL D. GREELEY, ESQ.
OHLANDT, GREELEY, RUGGIERO & PERLE, L.L.P.
10th FLOOR
ONE LANDMARK SQUARE
STAMFORD
CT
06901-2682
US
|
Assignee: |
GLOBALSTAR, LP
|
Family ID: |
25093826 |
Appl. No.: |
10/103070 |
Filed: |
March 21, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10103070 |
Mar 21, 2002 |
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09526919 |
Mar 16, 2000 |
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09526919 |
Mar 16, 2000 |
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09090521 |
Jun 4, 1998 |
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6160994 |
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09090521 |
Jun 4, 1998 |
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08772073 |
Dec 19, 1996 |
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5896558 |
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Current U.S.
Class: |
455/12.1 ;
455/13.1; 455/430 |
Current CPC
Class: |
H04B 7/18515 20130101;
H04B 7/195 20130101; H04B 7/216 20130101; H04B 7/18558
20130101 |
Class at
Publication: |
455/12.1 ;
455/13.1; 455/430 |
International
Class: |
H04B 007/185 |
Claims
What is claimed is:
1. A communications system, comprising: at least one low earth
orbit first satellite; at least one second satellite in other than
a low earth orbit; and a ground segment comprising a plurality of
user transceivers and at least one gateway coupled to a terrestrial
communications system; wherein said first satellite comprises a
first transceiver for communication with said at least one gateway,
a second transceiver for communication with at least one user
transceiver, and a third transceiver for communication with said at
least one second satellite, said first, second and third
transceivers being switchably coupled together on-board said first
satellite for relaying a user communication between said at least
one gateway and said at least one user transceiver via said at
least one second satellite.
2. A communications system as set forth in claim 1, wherein said at
least one first satellite further comprises a first on-board
processor that is bidirectionally coupled to said first
transceiver; a second on-board processor that is bidirectionally
coupled to said second transceiver; and a switching network that is
bidirectionally coupled to said first and second on-board
processors and to said third transceiver for selectively
establishing communication paths between said first and second
on-board processors and said third transceiver.
3. A communications system as set forth in claim 1, wherein said
publicly-accessible terrestrial communications system is comprised
of a fiber optic network that is bidirectionally coupled to said at
least one gateway.
4. A communications system as set forth in claim 1, wherein said
plurality of user transceivers are comprised of a plurality of data
processors, and wherein said plurality of data processors are
interconnected into a network through said at least one first
satellite.
5. A communications system as set forth in claim 1, wherein said
plurality of user transceivers are adapted to transmit and receive
direct sequence, code division/multiple access communications.
6. A communications system, comprising: at least one low earth
orbit first satellite; at least one second satellite in other than
a low earth orbit; and a ground segment comprising a plurality of
user transceivers and at least one gateway coupled to a terrestrial
communications system comprised of fiber optic infrastructure, said
at least one gateway comprising a gateway transceiver for
bidirectionally coupling said gateway to said at least one first
satellite; wherein a plurality of said user transceivers each
comprise a data processor that is bidirectionally coupled to said
fiber optic infrastructure through at least one of said first and
second satellites and said at least one gateway.
7. A communication system as set forth in claim 6, wherein said at
least one first satellite comprises a first transceiver for
communication with said at least one gateway, a second transceiver
for communication with at least one user transceiver, and a third
transceiver for communication with said at least one second
satellite, said first, second and third transceivers being
switchably coupled together on-board said first satellite for
relaying a user communication between said at least one gateway and
said at least one user transceiver via said at least one second
satellite.
8. A communications system as set forth in claim 6, wherein said at
least one gateway transmits digital information to and receives
digital information from said at least one satellite, the digital
information being comprised of at least one of voice, data, video
and image.
9. A communications system as set forth in claim 7, wherein said at
least one first satellite further comprises a first on-board
processor that is bidirectionally coupled to said first
transceiver; a second on-board processor that is bidirectionally
coupled to said second transceiver; and a switching network that is
bidirectionally coupled to said first and second on-board
processors and to said third transceiver for selectively
establishing communication paths between said first and second
on-board processors and said third transceiver.
10. A communications system as set forth in claim 6, wherein said
terrestrial communications system is comprised of a public switched
telephone network.
11. A communications system as set forth in claim 8, wherein said
at least one gateway transmits and receives the digital information
using a direct sequence, code division/multiple access
technique.
12. A communications system, comprising: a first constellation of
earth orbiting satellites; a second constellation of earth orbiting
satellites, said second constellation orbiting at a higher altitude
than said first constellation; a plurality of terrestrial mobile
user terminals each comprising a transceiver for bidirectionally
coupling said mobile user terminal to at least one satellite of
said first constellation using a first band of frequencies; a
plurality of terrestrial fixed user terminals each comprising a
transceiver for bidirectionally coupling said fixed user terminal
to at least one satellite of said first constellation using a
second band of frequencies; at least one first gateway that is
bidirectionally coupled to a first terrestrial communication
network, said at least one first gateway comprising a transceiver
for bidirectionally coupling said first gateway to at least one
satellite of said first constellation using a third band of
frequencies; and at least one second gateway that is
bidirectionally coupled to a second terrestrial communication
network that comprises a fiber optic infrastructure portion, said
at least one second gateway comprising a transceiver for
bidirectionally coupling said second gateway to at least one
satellite of said first constellation using a fourth band of
frequencies; wherein each of said satellites of said first
constellation is comprised of a plurality of transceivers operable
within said first, second, third, and fourth frequency bands, a
further transceiver operable for providing an inter-satellite link
with said at least one satellite of said second constellation, a
plurality of on-board processors that are bidirectionally coupled
to said plurality of transceivers, a switching matrix that is
bidirectionally coupled to each of said plurality of on-board
processors and to said further transceiver for selectably coupling
individual ones of said plurality of on-board processors and said
further transceiver together for routing communication signals
between said plurality of transceivers and said further
transceiver.
13. A communications system as set forth in claim 12, wherein said
first band of frequencies includes frequencies in at least one of
S-band and L-band, wherein said second band of frequencies includes
frequencies in at least one of Ka-band and Ku-band, wherein said
third band of frequencies includes frequencies in a C-band or Ka
band, and wherein said fourth band of frequencies includes
frequencies in at least one of Ka-band and Ku-band.
14. A communications system as set forth in claim 12, wherein said
first terrestrial communications system is comprised of a public
switched telephone network.
15. A communications system as set forth in claim 12, wherein said
transceivers of said at least one first and second gateways
transmit and receive RF signals using a direct sequence, code
division/multiple access technique.
16. A communications system as set forth in claim 12, wherein said
transceivers of said at least one first and second gateways
transmit and receive RF signals that are modulated to convey
digital information comprised of at least one of voice, data, video
and image.
17. A fiber optic communications network, comprising: a
terrestrially-based fiber optic network segment having at least one
gateway bidirectionally coupled thereto; and a space-based fiber
optic network segment comprised of a constellation of low earth
orbit satellites; at least one other satellite in other than a low
earth orbit; inter-satellite links between said constellation of
low earth orbit satellites and said at least one other satellite; a
first transceiver on-board each of said low earth orbit satellites
for bidirectional communication with said terrestrially-based fiber
optic network segment via said at least one gateway; and a second
transceiver on-board each of said low earth orbit satellites for
bidirectional communication with a terrestrial subscriber
transceiver, said first and second transceivers being coupled
together and to said inter-satellite links on-board each of said
low earth orbit satellites.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to communications systems
and, in particular, to communications systems that employ one or
more satellites to direct user communications through the
system.
BACKGROUND OF THE INVENTION
[0002] Satellite delivered individual services are emerging as a
new global enterprise. These systems utilize or are proposed to
utilize many individual circuits routed through one satellite or a
constellation of many satellites to effect communications. One
value of the satellite system is that it provides ubiquitous
coverage of large areas of the earth without the construction of
ground-based infrastructure. Since the recent availability of
portions of the frequency spectrum for these services, several
proposals have been advanced by a number of organizations. One
proposal would use Time Division Multiple Access (TDMA), while
several others would employ Code Division Multiple access (CDMA). A
feature of the CDMA systems is an ability to share the available
frequencies by co-frequency operation, while experiencing only a
percentage decrease in the capacity of each system.
[0003] Furthermore, Low Earth Orbiting Satellite (LEOS) systems,
also referred to as Non-GSO (geosynchronous orbit) satellite
systems, offer a new dimension in communications. For example, the
LEOS systems can provide diversity, as described in U.S. Pat. No.:
5,233,626, issued Aug. 3, 1993, entitled "Repeater Diversity Spread
Spectrum Communication System", to Stephen A. Ames. Another
capability provided by the LEOS systems is an ability to
interconnect users to a fixed point, typically referred to as a
Public Switched Telephone Network (PSTN).
[0004] High capacity, fiber optic-based communications is currently
being deployed world-wide, and in particular in the United States,
to directly connect to subscribers in their homes. In addition to
providing conventional voice communication capability, the fiber
optic-based networks can also provide video and high speed data
capabilities. The proliferation of networked personal computers
having multimedia capabilities can take advantage of the increased
speed and capacity provided by the fiber optic based networks.
However, the significant costs involved in providing fiber optic
lines is not economical in every locale, and it can be expected
that large non-urban areas will not be in a position to benefit
from the advantages provided by fiber optic networks within a
reasonable period of time.
OBJECTS OF THE INVENTION
[0005] It is a first object of this invention to provide a system
and a method for providing communications services to regions which
are not currently economical to serve with fiber optics.
[0006] It is a further object of this invention to provide a
satellite-based communications system that provides, in addition to
mobile and fixed voice and data service, a capability to provide
high speed video and data service.
SUMMARY OF THE INVENTION
[0007] The foregoing and other problems are overcome and the
objects of the invention are realized by a communications system
that is constructed and operated in accordance with this invention.
The communications system includes at least one low earth orbit
first satellite, and preferably a constellation of multiple low
earth orbit repeater satellites. The satellites of the
constellation are preferably in inclined circular orbits operating
at an altitude of less than 2000 kilometers. The communications
system also includes at least one, and preferably a plurality of
second satellites in other than a low earth orbit, such as a
geosynchronous orbit. The communications system also includes a
ground segment having a plurality of user transceivers and at least
one gateway coupled to a publicly-accessible terrestrial
communications system and/or to various private networks, such as a
PSTN and/or a fiber optic network. The first satellite(s) include a
first transceiver for communication with the at least one gateway,
a second transceiver for communication with at least one user
transceiver, and a third transceiver for communication with the at
least one second satellite. The first, second and third
transceivers are switchably coupled together on-board the first
satellite for relaying user communications, such as voice, data,
image, and video, between the at least one gateway and the at least
one user transceiver via the at least one second satellite.
[0008] The at least one first satellite further includes a first
on-board processor that is bidirectionally coupled to the first
transceiver; a second on-board processor that is bidirectionally
coupled to the second transceiver; and a switching network that is
bidirectionally coupled to the first and second on-board processors
and to the third transceiver for selectively establishing
communication paths between the first and second on-board
processors and the third transceiver.
[0009] The plurality of user transceivers can include a plurality
of data processors which are interconnected into a network through
the at least one first satellite. This network can be considered as
a virtual network, and can have a mesh, star, or other topology. In
a presently preferred, but not limiting embodiment of this
invention, the user transceivers are adapted to transmit and
receive direct sequence, code division/multiple access (DS-CDMA)
communications, wherein the transmission of signals to and from the
user transceivers is accomplished by spreading a digital data
stream (e.g., voice, data, image, video) with predetermined
spreading codes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The above-set forth and other features of the invention are
made more apparent in the ensuing Detailed Description of the
Invention when read in conjunction with the attached Drawings,
wherein:
[0011] FIG. 1 is a block diagram of a satellite-based
communications system in accordance with this invention;
[0012] FIG. 2 is a block diagram of one of the gateways illustrated
in FIG. 1;
[0013] FIG. 3 illustrates a constellation of LEO satellites having
inter-satellite links with a constellation of GSO, MEO, or other,
higher orbiting, satellites;
[0014] FIG. 4 illustrates various service types and their
connectivity through the LEO and GSO satellite constellations;
[0015] FIG. 5 schematically illustrates various geographical
regions having extensive, medium, and non-existent fiber optic
service; and
[0016] FIG. 6 schematically illustrates a plurality of data
processors that are connected directly and indirectly (through a
satellite and gateway) to a fiber optic network.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Reference is made to FIG. 1 for illustrating an exemplary
embodiment of this invention. At least one and preferably a
plurality of satellites 10 are provided in earth orbit. The
satellites 10 may form a constellation of low earth orbit
satellites (LEOS), such as a constellation of 48 satellites
orbiting at less than 2000 kilometers, such as about 1400
kilometers, in several inclined orbital planes. The orbits may be
circular, although the teaching of this invention is not limited
for use only with circular orbits. Coupled to the satellites 10 via
uplink and downlink RF signals and associated transceivers is a
terrestrial or ground segment 12. The satellites 10 operate so as
to interconnect various elements of the ground segment 12 through
different portions of the frequency spectrum via a plurality of RF
transmitters and receivers (transceivers), on-board processors, and
a switching matrix capable of interconnecting any one of the
on-board processors to another. A provision is also made for
coupling to other satellites of the same and/or a different
constellation though inter-satellite links (ISL), such as RF or
optical links.
[0018] In the presently preferred embodiment of this invention the
satellites 10 include circuitry 14 and antennas 16 and 18 for
providing inter-satellite links with other satellites 11, such as a
higher-orbiting geosynchronous orbit (GSO), medium earth orbit
(MEO), or Molniya constellation of satellites. In this manner a
given communication signal can be uplinked from a portion of the
ground segment 12 to one of the satellites 10, and can then be
routed through one or more other satellites 11 before being
downlinked back to the ground segment 12, either directly or
through another LEO satellite 10. This link may be bidirectional
(e.g., full duplex).
[0019] The antennas 16 and 18 may be either non-deployed phased
arrays or deployed reflectors with multiple beam feed assemblies
located in a reflector focal plane.
[0020] Describing FIG. 1 now in greater detail, the satellite 10
includes an S-band receive antenna 20, an S-band transmit antenna
22, an L-band receive antenna 24 and an S-band transmit antenna 26.
S-band antennas 20 and 22 may operate at frequencies of 2.2 and 1.9
GHz, respectively, with a bandwidth of 30 MHz. The L-band antenna
24 may operate at 1.6 GHz, while the downlink S-band antenna 26 may
operate at 2.5 GHz. The antennas 20 and 22 may be either
non-deployed phased arrays, deployed phased arrays, or deployed
reflectors with multiple beam feeds located at the focal plane of
the reflector. The bandwidth of the L-band and S-band transmissions
through antennas 24 and 26 may be 16.5 MHz. Coupled to antennas
20-26 are respective RF circuit blocks 28-34 respectively. The RF
circuit blocks 28-34 include suitable signal modulators and
demodulators, as appropriate. A presently preferred access
technique employs a direct sequence (DS), code division/multiple
access (CDMA) technique. This invention is not, however, limited to
only a DS-CDMA approach. By example, a suitable time
division/multiple access (TDMA) technique can also be used.
[0021] In the case of DS-CDMA, each RF circuit block includes
circuitry for phase demodulating and despreading received
communications using user-assigned pseudo-noise (PN) spreading
codes to separate a plurality of user signals that occupy a same
portion of the bandwidth of the uplinked RF signal. The result is a
plurality of digital data streams that are input to an on-board
processor (OBP) 36 for processing and routing. Transmission of
signals to the users is accomplished by spreading a digital data
stream (e.g., voice, data, image, video) that is received from the
OBP 36 with assigned spreading codes, and then phase modulating the
spread communications prior to transmission.
[0022] Bidirectionally coupled to the S-band antenna/RF block pair
20, 22, 28 and 30 is the first on-board processor (OBP) 36. Coupled
to the L-band, S-band antenna/RF block pair 24, 26, 32 and 34 is a
second on-board processor 38. As was indicated above, the on-board
processors 36 and 38 receive communications signals that have been
down-converted to baseband and demodulated (i.e., taken down to
bits) within the respective RF blocks 28 and 32. Routing and other
information within the communications, for example destination
addresses associated with data packets of speech, video, or data,
is examined by the OBP for destination and other information, and
is thence routed through an interconnector-router (ICR) block 70 to
another OBP for completing a required circuit. The ICR block 70 can
be comprised of a cross-bar or similar switching arrangement that
is programmed by the OBPs so as to establish and maintain
non-blocking communication paths between its various input and
output (I/O) ports 70a-70f. The ICR block 70 is thus able to
controllably route communication signals to and from the various
ones of the OBPs and also, if provided, other satellites 10 via the
inter-satellite links block 14 and its associated antennas 16 and
18, via the satellite(s) 11. This interconnection capability
enables a variety of ground segment terminal and equipment types to
be coupled together, and to be coupled to an underlying
communications infrastructure (e.g., PSTN and/or fiber optic
network) through one or more satellites 10 and/or 11.
[0023] The satellite 10 further includes a first Ka-band
(user-link) transmit antenna 40, a first Ka-band (user-link)
receive antenna 42, a second Ka-band (feederlink) transmit antenna
44, and a second Ka-band (feederlink) receive antenna 46. The
Ka-band antennas may operate at about 19 GHz (receive) and about 28
GHz (transmit), bandwidth 400 MHz, and provide the high speed, high
capacity user links that are a feature of this invention. These
antennas may be either non-deployed phased arrays, deployed phased
arrays, or deployed reflectors with multiple beam feeds located at
the focal plane of the reflector. Coupled to antennas 40-46 are
respective RF circuit blocks 48-54 respectively. The RF circuit
blocks 48-54 include suitable signal modulators and demodulators,
as appropriate. OBPs 56 and 58 are bidirectionally connected to the
RF circuit blocks 48, 50 and 52, 54, respectively, and also to the
ICR 70.
[0024] The satellite 10 also includes, by example, a Ka-band or a
C-band (feederlink) transmit antenna 60 and a Ka-band or a C-band
receive (feederlink) antenna 62. For a presently preferred C-band
embodiment the feederlinks operate in the range of 3 GHz to 7 GHz.
Coupled to antennas 60 and 62 are respective RF circuit blocks 64
and 66, respectively. The RF circuit blocks 64 and 66 include
suitable signal modulators and demodulators, as appropriate. The
OBP 68 is bidirectionally connected to the RF circuit blocks 64 and
66, and also to the ICR 70.
[0025] Turning now the ground segment 12, there are provided a
plurality of terrestrial data, or data and/or voice networks and
also fixed and mobile user terminals. The ground segment 12
includes first gateways 72 having transceivers for communicating
with the satellite C-band antennas 60 and 62. These transmissions
are feederlinks through which voice and data communications can be
directed to and from a terrestrial public switched telephone
network 74 (PSTN) and, by example, the user terminals 82 and 84.
The various terminals and other equipment designated as 78, 80, 82
and 84 may all be considered to be subscriber or user terminals or
transceivers.
[0026] FIG. 2 shows the gateway 72 in greater detail, it being
realized that typically a plurality of the gateways are provided
for serving different geographical areas. Each gateway 72 includes
up to four dual polarization RF C-band sub-systems each comprising
an antenna 90, antenna driver 92 and pedestal 94, low noise
receivers 96, and high power amplifiers 98. All of these components
may be located within a radome structure to provide environmental
protection.
[0027] The gateway 72 further includes down converters 100 and up
converters 102 for processing the received and transmitted RF
carrier signals, respectively. The down converters 100 and the up
converters 102 are connected to a CDMA sub-system 104 which, in
turn, is coupled to the Public Switched Telephone Network (PSTN)
though a PSTN interface 106. As an option, the PSTN could be
bypassed by using satellite-to-satellite links.
[0028] The CDMA sub-system 104 includes a signal summer/switch unit
104a, a Gateway Transceiver Subsystem (GTS) 104b, a GTS Controller
104c, a CDMA Interconnect Subsystem (CIS) 104d, and a Selector Bank
Subsystem (SBS) 104e. The CDMA sub-system 104 is controlled by a
Base Station Manager (BSM) 104f and functions in a manner similar
to a CDMA-compatible (for example, an IS-95 compatible) base
station. The CDMA sub-system 104 also includes the required
frequency synthesizer 104g and possibly a Global Positioning System
(GPS) receiver 104h.
[0029] The PSTN interface 106 includes a PSTN Service Switch Point
(SSP) 106a, a Call Control Processor (CCP) 106b, a Visitor Location
Register (VLR) 106c, and a protocol interface 106d to a Home
Location Register (HLR). The HLR may be located in a cellular
gateway or in the PSTN interface 106.
[0030] The gateway 72 is connected to telecommunication networks
through a standard interface made through the SSP 106a. The gateway
72 provides an interface and connects to the PSTN via a Primary
Rate Interface (PRI), or other suitable means. The gateway 72 is
further capable of providing a direct connection to a Mobile
Switching Center (MSC).
[0031] The gateway 72 may provide SS-7 ISDN fixed signalling to the
CCP 106b. On the gateway-side of this interface, the CCP 106b
interfaces with the CIS 106d and hence to the CDMA sub-system 104.
The CCP 106b provides protocol translation functions for the system
Air Interface (AI), which may be similar to the IS-95 Interim
Standard for CDMA communications.
[0032] Blocks 106c and 106d generally provide an interface between
the gateway 72 and an external cellular telephone network that is
compatible, for example, with the IS-41 (North American Standard,
AMPS) or the GSM (European Standard, MAP) cellular systems and, in
particular, to the specified methods for handling roamers, that is,
users who place calls outside of their home system.
[0033] Overall gateway control is provided by a gateway controller
108 which includes an interface 108a to a Ground Data Network (GDN)
110 which interconnects the various gateways one to another and to
Ground Operations Control Center (GOCC) 112. An interface 108b to a
Service Provider Control Center (SPCC) 114 can also be provided.
The gateway controller 108 is generally interconnected to the
gateway 72 through the BSM 104f and through RF controllers 116
associated with each of the antennas 90. The gateway controller 108
is further coupled to a database 118, such as a database of users,
satellite ephemeris data, etc., and to an I/O unit 120 that enables
service personnel to gain access to the gateway controller 108.
[0034] Referring now again to FIG. 1, the ground segment 12 further
includes a fixed terrestrial network having a second gateway 76
that is bidirectionally connected to the Ka-band antennas 44 and 46
of the satellite 10. Gateway 76 is also connected to the PSTN 74
and is also connected to a fiber optic network 75 through a
suitable fiber optic interface. The gateway 76 can communicate with
a number of different types of equipment such as data processors
(e.g., multimedia PCs 78 having a suitable RF interface 78a
connected to a suitable RF front end 78b and a Ka-band antenna
78c). Other devices, such as user entertainment equipment 80 (e.g.
television) can also be accommodated. The other devices can also be
interfaces to a wireless local loop (WLL) of a type that serves an
office building, residential area, etc. In these cases the other
equipment 80 is also provided with suitable RF circuitry and a
Ka-band antenna 80a. The units 78 and 80 can be considered to form
one or more virtual mesh, star or other network types having a
capability to be interconnected via the satellites 10, gateway 76,
the PSTN 74, and the fiber optic network 75. By example only, a 400
MHz bandwidth, 1 MB/sec data link capability is provided between
the units 78, 80 and the second gateway 76, thereby enabling the
delivery of, by example, video, image and Internet services.
[0035] In accordance with an aspect of this invention the system
disclosed in FIG. 1 can provide a global, wideband Internet access
capability with negligible connectivity time. The invention also
enables a direct video download to a TV/PC, enables the use of
interactive video, and also enables 2-way videophone capability.
Interoperability with mobile communication devices 82 and 84 (e.g.,
handheld or fixed user terminals) is also provided (via the first
gateway 72 or the second gateway 76), as is interoperability with
various terrestrial wireless local loop systems.
[0036] Reference is now made to FIG. 3 for illustrating a further
aspect of the instant invention. The sphere generally indicates the
surface of the earth over which traverse a plurality of the LEO
satellites 10. Each satellite 10 has a beam coverage area on the
surface of the earth indicated generally as 10a. The beam coverage
areas may overlap, thus providing for diversity reception by user
terminals and other equipment located within the overlap region.
Also shown are a plurality of the other satellites 11 which are in
a higher orbit, such a geosynchronous orbit (GSO) or a medium-earth
orbit (MEO). Other orbits, such as a Molniya orbit, can also be
used. Each satellite 11 has a corresponding larger coverage region
indicated by 11a.
[0037] In this aspect of the invention the LEO satellites 10 are
connected to, by example, the GSO satellites 11 via the
inter-satellite links (ISL). In this manner transmissions from the
region 10a can be relayed to the larger region 11a, and vice versa.
The regions can be closely spaced apart, or can be located on
opposite sides of the earth.
[0038] Reference in this regard can also be made to FIG. 4 for
illustrating various types of interconnectivity between and
functionality of the various terrestrial terminals and the LEO
constellation, either directly or via the synchronous or other
constellation type. By example, the block 122, designated First
Mobile Circuit Switched, communicates using the L-band and S-band
satellite antennas 24 and 26 of FIG. 1, and can include mobile
voice, cellular extension, GSM compatibility, and world roaming.
The block 124, designated Second Mobile Circuit Switched,
communicates using the S-band satellite antennas 20 and 22 of FIG.
1, and can include mobile voice, PCS extension, FPLMTS
compatibility, and world roaming. The block 126, designated Fixed
Circuit Switched, communicates using the Ka-band satellite antennas
40 and 42 of FIG. 1, and can include fixed voice and data, fiber
optics extension, medium speed data, private networks, and internet
services. The block 128 (also Ka-band), designated International
Circuit Switched, communicates via, by example, the GSO
constellation and can provide a transport facility, an extended
circuit switched network, international long lines, private
networks, and international Internet. The block 130, designated
International Wideband and Video, can include international video
and wideband data distribution, regional video, and wideband data.
The block 132, designated Domestic Wideband and Video, can provide
domestic video and wideband data distribution. All of these various
functions and features can be simultaneously active and
interconnected through the constellation of LEO satellites 10 and
the GSO (or other constellation type) satellites 11 via the ISL. It
should be noted in FIG. 4 that inter-satellite links are also
preferably provided between the GSO satellites 11.
[0039] FIG. 5 illustrates an exemplary case where fiber optic
cables are routed between major cities and metropolitan areas.
Within the major cities and metropolitan areas an extensive fiber
optic infrastructure may exist. Between these areas the fiber optic
service is only marginally provided, such as in the smaller city
and town regions that are tapped into the fiber optic trunks that
interconnect the larger cities and metropolitan areas. Other areas
have no local fiber optic service. However, and in accordance with
an aspect of this invention, the satellite service area 10a covers
this region of little or no fiber optic service and provides an
equivalent service via the fixed portion of the ground network 12
shown in FIG. 1 (i.e., the gateway 76, Ka links, satellites 10, and
terminals 78 and 80).
[0040] FIG. 6 illustrates the connectivity between various digital
TV/computers, the satellite 10, and local and long distance fiber
optic networks. As can be seen, the digital TV/computer designated
140 has a direct connection (DC) to a local fiber-optic line and
network which in turn is connected through a telephone or cable
company 142 to a regional fiber network. The regional fiber network
is connected via a long distance or cable company 144 to a long
distance fiber network. The long distance fiber network is
connected to a further telephone or cable company 146 (or other
entity) which in turn is connected to a distribution node 148. The
distribution node 148 includes the gateway 76 and is thereby
connected via one or more of the satellites 10 (or one of the GSO
or MEO satellites 11) to the antenna 78c, RF section 78b and
interface 78a of the PC 78 (refer also to FIG. 1). The connection
between the antenna 78c and the RF section 78b can be a wired or a
wireless connection. In this manner, the PC 78 is enabled to be
coupled to the fiber network in essentially the same manner as the
digital TV/computer 140 which has a direct connection to the
fiber-optic network, and is thus enabled to avail itself of network
and other services that are best served by the higher data rates
made available by fiber optic lines.
[0041] The PC 78 can thus be connected to others of similar type in
a mesh network, or in a star network, to the distribution node 148
and thence to the serving entity such as the telephone or cable
company. Further connections to the PSTN can also be made. The
further connections can be to other computers of similar type, to
servers and/or to larger computers providing network (e.g.,
Internet) services.
[0042] The antenna 78c may be directional, but is preferably
omni-directional with hemispherical or semi-hemispherical
coverage.
[0043] The use of the LEO constellation of satellites 10 provides
unique advantages when employed with the teaching of this
invention. Consider a mobile terminal which is moving under a tree
(or other RF obstacle, such as a building) and is blocked to one of
several satellites 10 serving the user (i.e., assume that the
mobile terminal is located in the overlap region of the coverage
areas shown in FIG. 3). The use of diversity combining from those
satellites that are not blocked provides improved service and
connectivity to the satellite constellation. It can be shown that
this performance increase is significant and provides mitigation of
shadowing and blocking due to movement of the user terminal. In
this regard the disclosure of U.S. Pat. No.: 5,233,626, issued Aug.
3, 1993, entitled "Repeater Diversity Spread Spectrum Communication
System", to Stephen A. Ames is incorporated by reference herein in
its entirety for illustrating suitable embodiments of a receiver
employing diversity combining.
[0044] When considering a LEO fixed system, the rain attenuation
can be severe in the frequency bands above 3 GHz, and especially
above 10 GHz. Rain fades of 20 db or more occur in the Ka band
frequencies. It is widely known that the availability of satellite
systems to deliver signals of the desired strength is affected by
these rain fades. It is also known by experimentation that the
duration and fade depth is affected by the rainfall zone that the
user is in (deserts have much improved availability as compared to
tropical forest areas). Furthermore, "rain cells", i.e., local rain
zones around the user, have characteristics which cause rapidly
changing conditions near user sites. In fact, for fixed locations
operating with GSO satellites a significant amount of analysis has
been done in predicting the availability of signals due to rain
attenuation. Since the rain cells cannot be avoided a certain
percentage of the time from coming between the fixed user and a GSO
satellite there is not much the fixed user can do to compensate for
the rain fade. In the past, it has been known to provide excessive
margin to partially overcome theses attenuations, and in some cases
to utilize another site located 35 to 50 or more miles away, to
provide a "diversity" site. Switching between these two sites can
increase the system signal availability. However, for a home or
office user it is not practical to provide such a diversity
site.
[0045] In accordance with an aspect of this invention, by providing
more signal paths to the user from two or more of the satellites 10
at different and changing azimuth and elevation angles, the effect
is to provide the "diversity site" at a single location. In effect
it is the opposite of the mobile user moving under the blocking
obstruction, as the rain cell moves with respect to the user
terminal site. One suitable diversity-type of receiver is described
in the above-mentioned U.S. Pat. No.: 5,233,626, issued Aug. 3,
1993, entitled "Repeater Diversity Spread Spectrum Communication
System, to Stephen A. Ames.
[0046] Although described above in the context of specific
frequency bands, bandwidths, data rates and the like, it should be
realized that these are exemplary, and not limiting, embodiments of
this invention. By example only, one or more of the Ka-band links
shown in FIG. 1 could be replaced by a Ku-band link. Furthermore,
the teaching of this invention can be practiced with but one LEO
satellite, or with one LEO satellite and one GSO or MEO satellite.
However, it is preferred to use larger numbers of satellites to
provide a wide area coverage, while also enabling the use of the
above-mentioned diversity reception techniques by the subscriber
terminals and equipment.
[0047] Thus, while the invention has been particularly shown and
described with respect to preferred embodiments thereof, it will be
understood by those skilled in the art that changes in form and
details may be made therein without departing from the scope and
spirit of the invention.
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