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Description  |
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TECHNICAL FIELD
This invention relates generally to paging communication systems, and more
specifically to wide geographic area paging systems, and is particularly
directed toward a satellite based acknowledge-back (Ack-Back) paging
communication system.
BACKGROUND
Historically, paging systems provided service to a limited geographic area
using a relatively high-power centralized transmitting site. This
arrangement worked well in small cities and municipalities, but often
proved unsuitable for large metropolitan areas. To adequately serve a
larger geographic area, paging systems began to simulcast (i.e., transmit
the same message at substantially the same time) from several transmitters
strategically positioned to provide wide-area coverage. In such a system,
an individual having a selective call receiver (pager) could receive
information anywhere in the metropolitan paging service area.
Today, the trend in paging communication is to provide even greater
geographic coverage. Nationwide paging systems are often contemplated in
an attempt to provide paging messages to customers without regard to where
they are in the United States (for example). One known multi-city paging
system employs satellites to transmit paging messages to ground repeaters
in approximately eighty cities so that their customers can be paged while
travelling in any of the covered cities. Regrettably, these contemporary
satellite paging systems suffer from designed-in energy and paging traffic
inefficiencies. That is, the system satellite link(s) often form a
bottle-neck as regards delivering the paging messages. Also, these
satellites are operated at full transmitter power, which is wasteful of
energy, and degrades overall system efficiency. Accordingly, a need exists
for a paging communication system that provides everyone with convenient,
reliable and efficient paging service.
SUMMARY Of THE INVENTION
Briefly, according to the invention, a paging communication system
comprises at least one satellite for communicating paging information with
at least one terrestrial receiver (e.g., pager). The terrestrial receivers
operate to acknowledge receipt of paging messages. By receiving (or not
receiving) this acknowledge signal, the location of the terrestrial
receiver can be determined, and the satellite's transmitter power can be
controlled.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of an orbiting satellite network in accordance
with the present invention.
FIG. 2 is a diagram illustrating system operation in accordance with the
present invention.
FIG. 3 is a block diagram of a satellite of FIGS. 1 or 2.
FIG. 4 is an illustration of a satellite transmission footprint.
FIG. 5 is a diagram illustrating satellite communication paths and links.
FIGS. 6a-6d are flow diagrams outlining the operation of the satellites of
FIGS. 1, 2 or 5.
FIG. 7 is a block diagram of the control station of FIGS. 2 or 5.
FIG. 8 is a flow diagram illustrating the operation of the control station
of FIG. 7.
FIG. 9 is a block diagram of an optional ground station in accordance with
the present invention.
FIGS. 10a and 10b are flow diagrams illustrating the operation of the
ground station of FIG. 9.
FIG. 11 is a block diagram of a selective call receiver (pager) in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Fundamentally, the present invention provides a world-wide communication
system designed to call (page) individuals having a selective call
receiver (pager). According to the invention, the selective call receiver
(pager) disclosed herein may be operated within the system to control the
satellite's transmitter power via the pager's acknowledge-back signal.
THE SYSTEM
Referring to FIG. 1, the inventive communication system of the present
invention can be seen to be based on a network of satellites 102 disposed
about a natural or artificial celestial body 104. Preferably,
seventy-seven (77) satellites are deployed in various orbits about the
celestial body (or planet) so as to be able to communicate a signal to a
receiver (e.g., pager) anywhere on the planet. Of course, more or fewer
satellites could be used depending on the transmission capabilities of the
satellites and the desired communication coverage of the planet. According
to the invention, the seventy-seven orbiting satellites are arranged in
seven (7) orbit planes to form a satellite network so as to provide
communication regardless of whether the receiver is operating on a land
mass, on a body of water, or traveling by aircraft (provided that the
aircraft is within the beam of the transmitting satellite).
Referring still to FIG. 1, three of the satellites are illustrated as
communicating with a respective area 106a-106c of a land mass 108. Each
area 106 is commonly referred to as the "footprint" of the transmitting
beam of each satellite. According to the present invention, each satellite
is capable of transmitting paging information either to paging receivers,
or to ground stations located within the footprint of a particular
satellite. Additionally, acknowledge-back signals from the pagers are
received and processed by the satellites to control the transmit power of
the satellites as will become hereinafter apparent. In the preferred
embodiment, the transmission footprint of each satellite comprises
thirty-seven (37) individual transmission lobes that allow the
transmission power and footprint of each satellite to be controlled and
fine tuned to deliver a paging message.
Within the satellite network, each satellite operates substantially
independently of the others; although the entire network is coordinated by
a centralized control facility. To provide a global paging system capable
of accommodating the various operational protocols developed for paging
receivers and systems, the present invention is capable of adapting a
portion of itself for each paging event to the receiver (or receivers)
designated to receive the paging information. That is, for example, paging
receivers operating in area 106a may receive paging information directly
from the satellite using Golay Sequential Coding (GSC). Simultaneously,
paging receivers operating in area 106b can receive information from its
satellite, or a terrestrial base station (or both), using the well known
POCSAG protocol. Further, selective call receivers (pagers) operating in
area 106c may comprise existing tone-only or tone-and-voice paging
receivers that receive information relayed from the satellite through an
existing contemporary paging system. Thus, the present invention adapts
that portion of the system required to communicate with the pagers to be
contacted.
Referring to FIG. 2, a more detailed illustration of a portion of the
global paging system is shown. As discussed in conjunction with FIG. 1,
the present invention employs an orbiting space-based backbone of
satellites 102a-102c (three shown) that orbit the planet in a plurality of
orbits. A coordinating intelligence for the system is provided by a
control station 110, which essentially comprises a large computing center
(or other suitable information storage and processing center) that
maintains a data library of every paging receiver registered to operate on
the global system, together with its preferred (or default) location to
receive paging messages, the current location of the paging receiver (if
known), the preferred paging protocol, and other parameters as may be
necessary or desired to provide an effective paging service. In the
preferred operation, the control station 110 receives messages from the
satellite presently positioned above the control station by an antenna
112, which routes all incoming paging requests from around the planet.
Outgoing paging information is provided by an antenna 114 to the satellite
network so that the paging information may be directed to the appropriate
paging receiver(s). Optionally, more than one control station could be
used, however, the maintenance of the data base library could be more
difficult. In any event, the paging information is processed by the
control station 110 to include information as to where and how the paging
message should be delivered. This processing would include frequency
selection, protocol selection, message routing information (depending upon
the paging receiver's current location), and other information such as
whether the satellite should deliver the page directly and/or via an
optional terrestrial station located in the approximate geographic area of
the paging receiver (if the system is so structured to allow terrestrial
station paging transmissions).
To initiate a page, individuals contact the control station (directly or
indirectly) via a public or private telephone-type network (not shown).
Optionally, the system may employ one or more terrestrial stations 116,
which may also be contacted using these telephone-type devices 118. In
this latter embodiment, the terrestrial station 116 relays the paging
message by any appropriate protocol to a satellite (illustrated as 102a)
via transmission 120. Upon receipt of this information, satellite 102a
determines that it is not currently over the control station, and
therefore relays this information via the satellite network to an
appropriate satellite for down-link transmission to the control station.
Thus, in this example, the message would proceed from satellite 102a to
102b, and then by another intersatellite link to satellite 102c. Since the
control station 110 resides within the transmission "footprint" of
satellite 102c, the paging request is broadcast to the control station 110
by a transmission 122.
Upon receipt of a paging request the control station analyzes the
identification (ID) code of the selective call receiver to be paged to
determine the current location of the paging receiver or the service area
requested by the paging receiver. That is, each individual having a paging
receiver operative in the present inventive system is permitted to define
the service area in which he or she wishes to receive paging information.
Thus, an individual may elect to receive paging information only within
one city or municipality. Others may wish to receive paging information in
multiple states. Still others may desire to receive information across
entire countries, continents, or globally so that they may receive a
paging message wherever they are in the world. The present invention
contemplates that the central station 110 will maintain this information
for each selective call receiver registered to operate within the global
system. In this way, the user may specify the default coverage area
desired. That is, the control station may cause the system to deliver the
paging message to each area specified by the paging user. Alternately,
however, if the current location of the paging receiver is known, the
paging message may be directed solely to that area to reduce paging
traffic over the satellite network. Accordingly, the control station
processes the incoming paging requests and instructs the satellite network
where the paging information should be delivered based upon the
instructions of the individual to be paged, and the current location of
the paging receiver (if known). Should this individual desire to travel or
otherwise change his or her default location(s) for receiving messages
(whether permanently or temporarily), that person must inform the paging
service provider so that the control station's data library may be
updated. Additionally, by examination of the geographic area of the
message delivery site(s), the required transmitter power of each satellite
may be determined. That is, if the paging message must be delivered to a
large city, the satellite over that city may be instructed to transmit the
message at full power so as to facilitate proper reception in the "noisy"
(e.g., high interference) metropolitan environment. Conversely, if the
message is to be delivered to a rural location, the satellite above this
location may be able to transmit the paging message at a reduced power
level since interfering signals should be greatly reduced as compared to a
large metropolitan area.
The control station 110 also determines how the paging message should be
delivered to the individual being paged by examining the data library to
extract information identifying the preferred paging protocol and
operational frequency(ies) of the selective call receiver to be paged.
This information is also preferably provided by the paging service
provider at the time of registration of a pager on the global system. Of
course, this information may be updated from time to time if the
individual purchases another selective call receiver or is temporarily
using a loaned pager during the repair of his or her registered receiver.
After determining where and how the paging information should be
delivered, the control station 110 returns the paging information to the
satellite network (satellite 102c in FIG. 2) via transmission 124. In this
example, satellite 102c receives the paging information that is to be
directed to the area below the transmitting "footprint" of satellite 102a.
Accordingly, the paging information is routed through satellite 102b to
102a, where the paging information is transmitted at a selected power
level to a paging receiver 126 operating in the geographic region covered
by the satellite 102a. Preferably, as will be hereinafter described in
further detail, each of the transmitting beams from the satellite
comprises thirty-seven (37) individual transmitting lobes; these lobes
collectively representing the largest "footprint" in which the satellite
may communicate information.
According to the invention, correct reception of the paging message by the
paging receiver 126 is acknowledged by the transmission of an acknowledge
signal 127. The acknowledge-back signal 127 is transmitted from the pager
126 to the satellite (102a in this example) at a power level that is
preferably specified (or selected) by the user of the pager. Alternately,
the acknowledge-back power level may be determined by analysis of the
incoming paging message using known techniques. In any event, when the
satellite receives the acknowledge-back signal, the control station 110 is
informed of the proper delivery of the paging message. Moreover, if the
paging message has been transmitted (by user instructions) to several
areas, the pager's location may be determined (in rough measure) by the
acknowledge-back signal. That is, since the pager will acknowledge only
the transmission it receives, the control station will be able to track
the paging receiver's current location by noting where the
acknowledge-back signal originated. In this way, future paging messages
need not be sent to several locations (even if specified by the user)
since the system knows approximately where the pager is. However, should
the pager fail to acknowledge the next paging message, the page will be
re-transmitted to each of the specified "default" areas per the user's
instructions. In this way, the pager can be located so the movement around
the planet may be tracked and satellite traffic can be controlled.
For delivery of other paging messages, the optional terrestrial stations
116 may be employed to receive information from the satellite network and
route the paging information through local transmitting sites 130. These
paging events may be executed using the same protocol as the down-link
transmission from the satellite, or by translating the down-link protocol
into another protocol (i.e., a protocol compatible with the selective call
receiver to be paged) so as to be adaptive to the paging receiver that is
intended to receive the paging message. Moreover, the terrestrial stations
of the present invention, can be coupled to a contemporary local paging
system 132, so as to provide paging messages to existing paging receivers
that are not capable of receiving paging messages directly from the
satellite network. Thus, a paging message received in transmission 134 by
the terrestrial station 116' can be processed and converted to paging
information recognizable by the existing local paging system 132. The
converted paging information would be processed and disseminated to the
transmitting sites 130 associated with the local system in the same manner
as any local paging request. As is known, the transmitting sites 130 may
represent centralized transmitting sites for different areas or cities, or
may be simulcast transmitting sites to provide contemporaneous
transmission coverage to a wider geographic area. In any event, the
present invention fundamentally contemplates communicating directly from
the satellite network to paging receivers, but also may include a full
planetary system network utilizing existing contemporary equipment, or
terrestrial based relay stations to repeat or simulcast paging information
on an appropriate paging protocol and frequency so as to support large
municipalities. In this embodiment, the terrestrial stations may be used
to off-load a portion of the paging traffic from the satellite network,
provide an alternate transmission point in circumstances where the paging
receiver cannot correctly receive the paging information directly from the
satellite network (i.e., shadowed), or convert the down-link protocol to a
protocol and frequency compatible with contemporary equipment.
According to the invention, ground station transmitted paging message are
acknowledged to the transmitting ground station, while satellite paging
transmissions are acknowledged to the satellite. This process allows the
optional ground station to also control its transmitter power, and
provides a route (directly or via the satellite network) to return the
pager's current location to the control station 110.
Additionally, those optional terrestrial stations and local systems
physically residing in the geographic area that the control station 110 is
physically located may communicate directly with the control station 110
via a direct communication link 136. This eliminates the need to go to the
satellite network to communicate paging requests. As will be appreciated
by those skilled in the art, the transmitting footprints of the satellites
102 cover a wide geographic area. Those terrestrial stations and local
systems within the same operating footprint as the control station may
therefore be coupled directly to the control station 110, since
communications between such sites would be repeated by the satellite above
both of them.
THE SATELLITE(S)
Referring to FIG. 3, a satellite 102 is shown in block diagram form.
Preferably, each satellite comprises a conventional low-orbiting satellite
such as those commercially available. Each satellite is placed in orbit by
a suitable launch vehicle such as via America's Space Shuttle Program.
According to the invention, the preferred orbit is one that is highly
inclined, so as to provide effective global communication coverage. Lower
inclination orbits may also be used, however, additional satellites would
be required to achieve effective communication coverage. Once in orbit, a
conventional solar cell array (see FIG. 2) is opened to provide power to
the satellite 102. Following this, the satellites are brought "on-line"
using known techniques, such as, for example, by using contemporary
telemetry, tracking, and control (TT&C) protocols to form a satellite
network. As is known, the solar cell array provides electrical power to
the satellite. This power is limited, however, by that portion of time
that the celestial body blocks solar rays from a star (sun) in the
particular solar system in which the celestial body resides. If each
satellite transmitted each paging message at full power, a satellite's
power supply may become critically limited or exhausted during the time
interval that the solar cell array is unable to replenish the satellites
energy storage means. Thus, the present invention operates to control the
satellite's transmitter power to conserve energy and promote efficient
system operation.
Up-link transmissions are received by an up-link antenna 300 and decoded by
an up-link receiver 302. The up-link receiver is coupled to a conventional
satellite controller 304 and a paging controller 306 so as to
appropriately route satellite control information and paging information
(including the acknowledge-back signals). The satellite controller 304
performs conventional satellite control functions such as orbit
maintenance, position tracking, and other appropriate functions as
directed by control personnel on the planet. The satellite controller 304
is also coupled to the satellite's down-link transmitter 308, so as to
provide any information requested by ground based control personnel.
As shown in FIG. 3, the payload of the satellite 102 is occupied by the
paging controller 306 and a paging signal generator 310. Upon receipt of
paging information, the paging controller must determine whether to
transmit the paging message toward the planet (i.e., page a selective call
receiver or optionally to send the page information to a ground station
for retransmission to the selective call receiver), or to another
satellite (for routing to the control station or another satellite for
transmission) in the satellite network. Accordingly, an inter-satellite
receiver 312 and transmitter 314 are coupled to the paging controller 306
so that the paging information can be appropriately routed. Additionally,
the satellite controller 304 is coupled to the inter-satellite receiver
and transmitter so as to communicate network control information as
required for the maintenance of the satellite network. Optionally, a
single inter-satellite transceiver may be used provided that its has a
steerable antenna system to be able to communicate with its neighboring
satellites in the satellite network. Also, multiple inter-satellite
transceivers could be used provided that the satellites size and weight
were not adversely impacted, and so long as it is not cost prohibitive.
The paging controller 306 determines what and how to transmit in large part
in response to the type of information received. For example, up-link
transmissions from a ground station (e.g., paging requests or acknowledge
signals) should ordinarily be routed to the control station, while up-link
transmissions from the control station usually contain information as to
where and how the paging message should be delivered. Inter-satellite
communications can, of course be either paging requests, acknowledge
signals, or paging information, and the paging controller determines
appropriate routing chiefly by examining its present position (which is
monitored by the satellite controller 304) and the destination of the
request or information. Should the satellite controller determine that the
received paging information should be transmitted toward the planet, the
paging signal generator 310 is used to provide the appropriate protocol
and frequency selection. That is, the paging signal generator may deliver
the paging information using any known paging protocol (or any convenient
protocol if transmitting to an optional ground station) when transmitting
to the selective call receiver hereinafter described. For each paging
transmission, this information is preferably provided by the control
station, or defaults to a predetermined protocol. Additionally, the
down-link frequency selection is also made in accordance with the delivery
instructions provided by the control station.
Prior to the actual transmission, the paging controller 306 examines the
paging information to determine the desired communication coverage
specified by the individual to be paged. According to the invention, this
information is provided to the paging controller by the control station
and is provided to an antenna control system 316 to adjust the "footprint"
of the satellite's transmission beam. This is preferably accomplished by
controlling which of a plurality of individual transmission lobes are
activated (via antenna control 316), and the power (via control line 307)
of each activated lobe. According to the invention, the down-link antenna
comprises one that has thirty-seven transmission lobes. In this way,
relatively fine control of the satellite's transmitting signal may be
achieved. That is, if the paging message is to be directed toward a large
metropolitan area, the transmitter power for each activated lobe may be
set at full power. Conversely, a lower transmitter power setting may be
used on one or more lobes to deliver a paging message to a rural area.
Also, regardless of the initial power setting, if the paging receiver does
not acknowledge receipt of the paging message, the transmitter power in
increased (up to full power) and the paging message is re-transmitted. In
this way, satellite power is conserved.
Referring to FIG. 4, a graphical depiction is provided to illustrate the
preferred satellite transmission "footprint". As previously mentioned, the
preferred satellite down-link transmitting system includes an antenna
having a plurality of individual lobes. In FIG. 4, the hexagonal cell
format commonly used in conjunction with cellular telephone service is
used for convenience to illustrate to user selectable coverage aspect of
the present invention. Those skilled in the art will appreciate that the
actual transmission patterns of the satellite's antenna lobes do not
comprise perfect hexagons.
According to the invention, each individual is permitted to specify the
areas in which he or she will receive paging messages. For example, if an
individual only wished to receive pages at home or in the office, areas 17
and 12 may be specified. In an alternate example, wider coverage may be
provided by specifying areas 12-14, 18-20, and 25-26. In fact, any
arrangement of coverage areas (contiguous or non-contiguous) may be
provided including receiving paging information under the entire
thirty-seven transmitting lobes of one satellite and some or all of the
lobes of any of the other satellites in the entire satellite network. In
this way, paging service may be provided using any paging format or
protocol on a global coverage basis for those desiring such coverage,
while local area coverage may also be provided to those desiring only
local coverage and the lower operational costs associated therewith.
The satellites' communication abilities may be further described in
conjunction with FIG. 5. Three satellites are shown engaged in both
inter-satellite communication and terrestrial up-link/down-link
communication. The illustrated satellites (N-1, N, and N+1) may be
satellites in the same orbiting plane, or may represent one satellite in
three contiguous orbit planes. In either event, inter-satellite
communications is the same. That is, each satellite is capable of
communicating with a previous and next satellite in the same orbiting
plane, and with a satellite in a previous and next orbit. This arrangement
provides a satellite network capable of effectively disseminating paging
information to any point on the orbited celestial body.
As shown in FIG. 5, satellite N communicates information with satellite N-1
via link N, and with sat | | |
