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Description  |
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CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to commonly assigned United States Patent
Applications:
"Multibeam Position Ambiguity Resolution", by Keith Olds, U.S. Pat. No.
5,412,389; "Position Ambiguity Resolution", by Stanley Attwood, U.S. Pat.
No. 5,418,388; "Radio Telecommunications System and Method with Adaptive
Convergence Location Determination", by Keith Olds and Kristine Maine,
Ser. No. 08/105,219; and "Location System and Method with Acquistion of
Accurate Location Parameters", by Kristine Maine, Keith Olds and Stanley
Attwood, Ser. No. 08/105,227.
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to radio telecommunication systems
that provide communication services for the systems' users. More
specifically, the present invention relates to radio telecommunication
systems in which communications are relayed through satellites and in
which locations of users' subscriber units are determined.
BACKGROUND OF THE INVENTION
A need exists for a substantially global radio telecommunication system
that can provide communication services to substantially any point on or
near the surface of the earth. For such a system to achieve widespread
acceptance, it should be capable of operating with portable subscriber
units. In order for subscriber units to have acceptable portability, they
should be capable of low power battery operation, and they should be
capable of transmitting and receiving electromagnetic signals through a
relatively small antenna. In addition, such a system should use only
portions of the electromagnetic spectrum which are allocated to it by
governments within whose geopolitical jurisdictions the system is used.
In such a global radio telecommunication system, subscriber units may be
placed in the control of system users, and the users may move their
subscriber units to any place on or near the surface of the earth. In
short, the system and those who operate the system may have no control
over where the subscriber units are located. On the other hand, the system
may be responsible for granting or denying particular communication
services depending upon whether or not the system has received permission
to operate at a point where a particular subscriber unit may be located.
Moreover, the system may be responsible for billing in connection with the
use of communication services, and the rates charged for such services may
vary from location to location due to tariffs and the like.
A radio telecommunication system may carry out the job of granting and
denying particular communication services and assigning particular billing
rates to calls if it knows the locations of the subscriber units.
Accordingly, it would be desirable to configure the system so that the
locations of subscriber units may be determined and so that information
describing locations may be transmitted to controllers which are
responsible for making decisions regarding the granting or denying of
communication services, billing rates, and the like.
Many prior art location determination systems are known, such as Global
Positioning System (GPS), GLONASS, Loran, and the like. While subscriber
units could be configured to incorporate components which take advantage
of such location determination systems, these components would
substantially increase costs of the subscriber units. Moreover, relying on
such known location determination systems could reduce reliability of the
radio telecommunication system by introducing reliance upon an external
system.
The techniques used by such prior art systems to determine location could
potentially be incorporated into the radio telecommunication system, but
the introduction of such techniques could seriously degrade communication
services. For example, many prior art location systems require the use of
two or more transmitters or receivers ("locators") that are located at
distant positions and that are capable of transmitting or receiving
signals to or from a location to be determined.
The requirement for two or more locators to be within view over the entire
globe, when combined with a global telecommunication capability, makes
this approach unduly cumbersome. While this requirement might be met by
placing satellites in high or geosynchronous orbits around the earth,
higher orbits place satellites further away from subscriber equipment on
the earth. This larger distance causes the subscriber equipment to consume
excessive power or incorporate larger antennas just to participate in
communication services. Moreover, higher orbits require increased spectrum
allocation to carry a given amount of communications because the allocated
spectrum may be reused less frequently in a given area.
SUMMARY OF THE INVENTION
Accordingly, it is an advantage of the present invention that an improved
radio telecommunication system and method are provided.
Another advantage of the present invention is that locations for subscriber
units are automatically determined.
Another advantage is that the present invention may determine locations for
subscriber units using no more that a single satellite which orbits the
earth in a low earth orbit.
Another advantage is that the present invention utilizes location
information to qualify communication services.
The above and other advantages of the present invention are carried out in
one form by a method of operating a radio telecommunication system having
at least one satellite moving in an orbit around the earth and having at
least one subscriber unit located proximate the earth's surface. The
method calls for determining a Doppler component of an electromagnetic
signal traveling between the satellite and the subscriber unit. A location
of the subscriber unit relative to the earth is determined in response to
this Doppler component. Communication services provided for the subscriber
unit are qualified in response to this location.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention may be derived by
referring to the detailed description and claims when considered in
connection with the Figures, wherein like reference numbers refer to
similar items throughout the Figures, and:
FIG. 1 shows a layout diagram of an environment within which a radio
telecommunication system may operate;
FIG. 2 shows a cellular pattern formed on the surface of the earth by a
satellite portion of the radio telecommunication system;
FIG. 3 shows a block diagram of a node of the radio telecommunication
system;
FIG. 4 shows a flow chart of tasks performed by a measurement processor
portion of the radio telecommunication system;
FIG. 5 shows a flow chart of tasks performed by a location processor
portion of the radio telecommunication system;
FIG. 6 graphically depicts constant Doppler and constant propagation
duration curves which illustrate location determination in the radio
telecommunication system;
FIG. 7 shows a flow chart of tasks performed by a service processor portion
of the radio telecommunication system; and
FIG. 8 shows a flow chart of tasks performed by a call processor portion of
the radio telecommunication system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a layout diagram of an environment within which a radio
telecommunication system 10 operates. System 10 includes a constellation
12 of several satellites 14 placed in relatively low orbits around the
earth.
System 10 additionally includes one or more switching offices (SOs) 16. SOs
16 reside on the surface of the earth and are in data communication with
nearby ones of satellites 14 through RF communication channels 18.
Satellites 14 are also in data communication with one another through data
communication channels 20. Hence, through constellation 12 of satellites
14, an SO 16 may control communications delivered to any size region of
the earth. However, the region controlled by each SO 16 is preferably
associated with one or more specific geo-political jurisdiction, such as
one or more countries. SOs 16 couple to public switched telecommunication
networks (PSTNs) 22, from which calls directed toward subscribers of
system 10 may be received and to which calls placed by subscribers of
system 10 may be sent.
System 10 also includes any number, potentially in the millions, of
subscriber units (SUs) 24. SUs 24 may be configured as conventional
portable radio communication equipment. In other words, SUs 24 may be
battery powered, may consume relatively low power, and may include
relatively small antennas. System 10 accommodates the movement of SUs 24
anywhere on or near the surface of the earth. However, nothing requires
SUs 24 to move, and system 10 operates satisfactorily if a portion of the
entire population of SUs 24 remains stationary. SUs 24 are configured to
engage in communications with satellites 14 over portions of the
electromagnetic spectrum that are allocated by governmental agencies
associated with various geopolitical jurisdictions. SUs 24 communicate
with nearby satellites 14 through communication channels 26.
Any number of subscriber information managers (SIMs) 28 are also included
within system 10. Each SIM 28 maintains a subscriber database that is
relevant to only a discrete portion of the population of SUs 24. The
database may include information describing features associated with SUs
24, billing rates to be associated with SUs 24, current locations for SUs
24, and other information which is discussed below. Each SU 24 is assigned
to one of SIMS 28, and that one SIM 28 is considered the "home" SIM 28 for
an SU 24. In the preferred embodiment, an SIM 28 may be associated with
each SO 16. In fact, an SIM 28 and an SO 16 may utilize the same
computerized hardware. In such an embodiment, an SIM 28 and an SO 16 are
separated logically rather than physically. Each SO 16 may communicate
with any SIM 28 through constellation 12, PSTN 22, or internal computer
structures when an SO 16 communicates with its logical partner SIM 28.
In general terms, system 10 may be viewed as a network of nodes. Each SU
24, satellite 14, SO 16, and SIM 28 represents a node of system 10. All
nodes of system 10 are or may be in data communication with other nodes of
system 10 through communication channels 18, 20, and/or 26. In addition,
all nodes of system 10 are or may be in data communication with other
telephonic devices dispersed throughout the world through PSTNs 22. Due to
the configuration of constellation 12 of satellites 14, at least one of
satellites 14 is within view of each point on the surface of the earth at
all times. Communication services, including calls, may be set up between
two SUs 24 or between any SU 24 and a PSTN phone number. Except for
qualifying processes which are discussed below, calls may be set up
between any two locations on the earth. Generally speaking, each SU 24
engages in control communications with a nearby SO 16 through
constellation 12 during call setup. These control communications take
place prior to forming a communication path between an SU 24 and another
unit, which may be another SU 24 or a PSTN phone number. In particular, an
SU 24 communicates with the SO 16 via one or more satellites 14. This SO
16 may be considered the serving SO for that particular SU 24.
Due to the low earth orbits, satellites 14 constantly move relative to the
earth. In the preferred embodiments, satellites 14 move in orbits at an
altitude in the range of 500-1000 km above the earth. If, for example,
satellites 14 are placed in orbits which are around 765 km above the
earth, then an overhead satellite 14 travels at a speed of around 25,000
km/hr with respect to a point on the surface of the earth. Electromagnetic
signals traveling at or near the speed of light between an SU 24
positioned near the surface of the earth and a satellite 14 in such an
orbit will require a propagation duration of 2-3 msec or more, depending
on the satellite's angle of view. Moreover, electromagnetic signals
traveling between an SU 24 positioned near the surface of the earth and a
satellite 14 in such an orbit may experience a considerable Doppler
component of frequency shift, the precise value of which is dependent on a
source frequency and the satellite's angle of view.
Due to the relatively low orbits of satellites 14, line-of-sight
electromagnetic transmissions from any one satellite cover a relatively
small area of the earth at any point in time. For example, when satellites
14 occupy orbits at around 765 km above the earth, such transmissions may
cover areas around 4000 km in diameter.
FIG. 2 shows a cellular footprint pattern 30 formed on the surface of the
earth by a single satellite 14. Each satellite 14 includes an array 32 of
directional antennas. Each array 32 projects numerous discrete antenna
patterns on the earth's surface at numerous diverse angles away from its
satellite 14. FIG. 2 shows a diagram of a resulting pattern of cells 34
that a satellite 14 forms on the surface of the earth. Other satellites 14
(not shown) form other footprints (not shown) adjacent to the footprint 30
shown in FIG. 2 so that substantially the entire surface of the earth is
covered by cells 34.
Each cell 34 within footprint 30 occupies a unique position within
footprint 30. These positions are distinguished from one another through
the use of a cell ID, listed as 1 through 48 in FIG. 2. Some degree of
location information may be obtained by identifying a cell 34 that covers
a position of interest. Such location information defines a position
relative to a satellite 14. Satellites 14 preferably orbit the earth in
predictable orbits. In other words, a satellite's position at a particular
point in time may be determined by combining the point in time with well
known orbital geometry. By combining a cell's position within a footprint
30 with the satellite's position, a location on the earth may be obtained.
For convenience, FIG. 2 illustrates cells 34 and footprint 30 as being
discrete, generally hexagonal shapes without overlap or gaps. However,
those skilled in the art will understand that in actual practice equal
strength lines projected from the antennas of satellites 14 may be more
circular or elliptic than hexagonal, that antenna side lobes may distort
the pattern, that some cells 34 may cover larger areas than other cells
34, and that some overlap between adjacent cells may be expected.
System 10 (see FIG. 1) communicates through satellites 14 with all of SUs
24 (see FIG. 1) using a limited amount of the electromagnetic spectrum.
The precise parameters of this spectrum are unimportant to the present
invention and may vary from system to system. The present invention
divides this spectrum into discrete portions or channel sets. The precise
manner of dividing this spectrum is also unimportant to the present
invention. For example, the spectrum may be divided into discrete
frequency bands, discrete time slots, discrete coding techniques, or a
combination of these. Desirably, each of these discrete channel sets is
orthogonal to all other channel sets. In other words, simultaneous
communications may take place at a common location over every channel set
without significant interference. As is conventional in cellular
communication systems, the channel sets are assigned to cells 34 through a
reuse scheme which prevents adjacent cells 34 from using the same channel
sets. However, common channel sets are reused in spaced apart cells 34 to
efficiently utilize the allocated spectrum.
Each satellite 14 is associated with a nadir direction. The nadir direction
is defined by an imaginary line (not shown) extending from the satellite
14 toward the center of the earth. For a given satellite 14, a ground
point resides where the nadir direction intersects the surface of the
earth. As the satellite 14 moves around the earth in its orbit, this
ground point forms a satellite ground track 36. As shown in FIG. 2, a
first portion of cells 34 in footprint 30 resides to the left of ground
track 36 and a second portion of cells 34 in footprint 30 resides to the
right of ground track 36.
FIG. 2 shows a point 38, which illustrates an example position for an SU 24
on the surface of the earth at a particular point in time. Of course,
those skilled in the art will appreciate that this is merely an example
and that any SU 24 may reside at any point on or near the surface of the
earth. As satellite 14 moves relative to the earth, footprint 30 and cells
34 likewise move relative to the earth. As a result of this movement, a
subscriber unit cell track 40 is formed through cells 34. Those skilled in
the art will appreciate that point 38 need not actually move relative to
the earth as depicted in FIG. 2. Rather, point 38 moves primarily with
respect to cells 34 to form cell track 40.
On the surface of the earth, a boundary 42 separates a first jurisdiction
44 from a second jurisdiction 46. Any number of boundaries 42 may divide
the entire earth's surface into any number of different jurisdictions.
Boundaries 42 need not represent physical phenomena of the earth. Rather,
boundaries 42 represent lines imposed over the geography of the earth to
achieve some of the goals of radio telecommunication system 10 (see FIG.
1), and nothing prevents the existence of more than one set of boundaries
42 corresponding to the same sections of the earth. For example, one set
of boundaries 42 may divide the earth into geopolitical jurisdictions so
that system 10 can define where communication services are to be allowed
and where communication services are to be denied. The same or an entirely
separate set of boundaries 42 may divide the earth into rate jurisdictions
so that system 10 can define where various rate schedules are to be
applied. The same or yet another set of boundaries 42 may divide the earth
into feature jurisdictions so that system 10 can define where various
communication service features are to be applied. The geopolitical
jurisdictions, rate jurisdictions, and feature jurisdictions may, but need
not, observe the same boundaries.
FIG. 3 shows a block diagram of any node 48 of radio telecommunication
system 10 (see FIG. 1). As discussed above, any SU 24, satellite 14, SO
16, or SIM 28 represents a node of system 10. Node 48 includes one or more
receivers 50. Receivers 50 receive signals from communication channels 18,
20, and/or 26 (see FIG. 1). While an SU 24, SO 16, or SIM 28 may include
only a single receiver 50, a satellite 14 includes many receivers for
simultaneously communicating over numerous different ones of channels 18,
20, and 26 (see FIG. 1). Receivers 50 couple to receive buffers 52, which
temporarily store data received at receivers 50 until these data can be
processed.
A controller 54 couples to receive buffers 52 and to receivers 50.
Controller 54 couples to receivers 50 to control receive parameters, such
as frequency, timing, and the like. Controller 54 additionally couples to
a timer 56, a memory 58, transmit buffers 60, and transmitters 62.
Controller 54 uses timer 56 to help monitor real time through maintaining
the current date and time. Memory 58 includes data which serve as
instructions to controller 54 and which, when executed by controller 54,
cause node 48 to carry out processes which are discussed below. In
addition, memory 58 includes variables, tables, and databases that are
manipulated due to the operation of node 48. Transmit buffers 60 are used
to temporarily store data placed therein by controller 54. Controller 54
couples to transmitters 62 to control transmit parameters, such as
frequency, timing, and the like. While SUs 24, SOs 16, and SIMs 28 may
include only one transmitter 62, satellites 14 desirably include numerous
transmitters 62 for simultaneously communicating over numerous different
ones of channels 18, 20, and 26 (see FIG. 1). Transmit buffers 60 also
couple to transmitters 62. Transmitters 62 transmit signals modulated to
carry the data stored in transmit buffers 60. These signals are
transmitted over channels 18, 20, and 26.
In earth-based nodes 48, controller 54 also couples to an I/O section 64.
In an SU 24, I/O section 64 may include microphones, speakers, digitizers,
vocoders, decoders, and the like, to convert between audio and digitized
packets that are compatible with system 10 (see FIG. 1). Likewise, I/O
section 64 may include a keypad for controlling the operation of SU 24 by
a user. In an SO 16 or SIM 28, I/O section 64 may include keyboards,
displays, magnetic memory devices, printers, and other devices
conventionally coupled to computerized equipment. In an SO 16, I/O section
64 may additionally include components for coupling to a PSTN 22 (see FIG.
1).
In short, each node 48 represents a programmable machine which takes on the
character assigned to it by software programming located in memory 58 and
executed by controller 54. As is discussed below, the present invention
configures nodes 48 as measurement processors 66 (see FIG. 4), location
processors 68 (see FIG. 5), service processors 70 (see FIG. 7), call
processors 72 (see FIG. 8), and the like. Since each node 48 is or may be
in data communication with other nodes 48, the precise location and
distribution of many of these processors and the tasks they perform are
less important considerations. By way of example, the functions of SIMs 28
may be performed on the same hardware which performs the functions of SOs
16, or the functions may be performed on different hardware. While the
differences between processors 66, 68, 70, and 72 may be physical due to
their location in different ones of SUs 24, satellites 14, SOs 16, and
SIMs 28. Absent the controlling software, any physical differences may be
of only minor importance. Rather, the differences between processors 66,
68, 70, and 72 are logical. These logical differences results in different
physical operation of processors 66, 68, 70 and 72.
FIGS. 4-5 and 7-8 depict processors 66, 68, 70, and 72, which are
implemented by nodes 48 within radio telecommunication system 10. Those
skilled in the art will appreciate that the processors discussed below in
connection with FIGS. 4-5 and 7-8 are controlled by programming
instructions placed in a memory 58 of the node 48 where that processor may
be located. Moreover, in the preferred embodiment of the present
invention, all SUs 24, satellites 14, SOs 16, and SIMs 28 perform
substantially the same processes as other SUs 24, satellites 14, SOs 16,
and SIMs 28, respectively. Thus, while the description presented below is
directed toward a single SU 24, a single satellite 14, a single SO 16, a
single SIM 28, and a single call, the following description may be viewed
as applying to all SUs 24, satellites 14, SOs 16, SIMs 28, and calls.
FIG. 4 shows a flow chart of tasks performed by measurement processor 66.
The preferred embodiment of the present invention implements measurement
processor 66 in satellite 14. However, those skilled in the art could
adapt measurement processor 66 to SU 24 for other systems. Radio
telecommunication system 10 activates measurement processor 66 with
respect to a single specific SU 24 to obtain data which may be manipulated
to determine the location of the SU 24. Any one of several different
events may lead to the activation of processor 66. For example, processor
66 may be automatically activated when an SU 24 initially powers up, when
an SU 24 is requesting to setup a call to a called party, or when location
processor 68, discussed below (see FIG. 5), requests its activation.
Measurement processor 66 operates in-conjunction with communications taking
place between SU 24 and satellite 14. As is conventional in cellular
communications, these communications take place within a particular one of
cells 34 (see FIG. 2). Once activated by SU 24 accessing system 10, by SU
24 attempting to setup a call to a called party, by an instruction from
location processor 68 (see FIG. 5), or otherwise, processor 66 performs a
task 74 to initialize a measurement record. This initialization may, for
example, include the writing of an SU's ID to the measurement record along
with other parameters, such as frequency or channel ID, that describe the
communications taking place between satellite 14 and SU 24.
After task 74, processor 66 performs a task 76 to determine the Doppler
component of the frequencies used in communication channel 26 (see FIG. 1)
for any electromagnetic signal traveling between SU 24 and satellite 14.
This determination may, for example, be made by first synchronizing a time
base used in SU 24 to the time base of satellite 14, then measuring a
received signal to determine frequency offset from a predetermined
frequency. However, any alternate Doppler measurement technique known to
those skilled in the art may be used as well. Task 76 then adds data
describing the Doppler component to the measurement record.
In conjunction with task 76, or after task 76 as shown in FIG. 4, a task 78
determines signal propagation duration (i.e. the propogation delay) for
any electromagnetic signal traveling between SU 24 and satellite 14. As
discussed above, this duration may be in the range of 2-3 msec or more.
This determination may be made by first synchronizing a time base used in
SU 24 to the time base of satellite 14, then measuring a received signal
to determine any temporal offset from a predetermined point in time.
However, any alternate propagation delay measurement technique known to
those skilled in the art may be used as well. Task 78 then adds data
describing the propagation duration to the measurement record.
After task 78, a task 80 completes the measurement record by adding a time
stamp, the satellite's ID, and the ID of the cell 34 (see FIG. 2) within
which the measured communications were conducted. The time stamp defines
the point in real time at which the communications were taking place
between SU 24 and satellite 14. After task 80, a task 82 sends the
measurement record to location processor 68 (see FIG. 5) so that location
processor 68 may determine the location of SU 24.
In the preferred embodiment, a location processor 68 resides in each SIM 28
(see FIG. 1). The particular SIM 28 which receives the measurement record
is the home 28 for the SU 24 whose location is being determined. This
particular home SIM 28 may be distinguished from other SIMs 28 through the
SU's ID. After task 82, program control exits measurement processor 64,
and processor 64 becom | | |
