U.S. patent application number 09/267694 was filed with the patent office on 2002-01-10 for system for providing location-specific data to a user.
Invention is credited to CAMPANELLA, S. JOSEPH, JOHNSTONE, ROBERT L..
Application Number | 20020003495 09/267694 |
Document ID | / |
Family ID | 24999162 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003495 |
Kind Code |
A1 |
JOHNSTONE, ROBERT L. ; et
al. |
January 10, 2002 |
SYSTEM FOR PROVIDING LOCATION-SPECIFIC DATA TO A USER
Abstract
An FDMA/TDM satellite-based digital broadcast system is used to
provide digital maps and other types of data to users at remote
locations. User selection of the desired data is achieved by
monitoring the TDM downlink channels of the broadcast system in
accordance with a predetermined schedule or until a specific
identification code is detected. The user terminals are equipped
with Global Positioning System (GPS) receivers which allow the
positions of the users to be determined. Based on the user
positions, the user terminals are able to convert general data to
location-specific data tailored to the needs of the user. The
general data may comprise a digital map covering a wide geographic
area, and the location-specific data may comprise a map covering a
portion of the geographic region where the user is located.
Inventors: |
JOHNSTONE, ROBERT L.; (WEST
BOOTHBAY HARBOR, ME) ; CAMPANELLA, S. JOSEPH;
(GAITHERSBURG, MD) |
Correspondence
Address: |
ROYLANCE, ABRAMS, BERDO & GOODMAN, LLP
1300 19TH STREET, NW
SUITE 600
WASHINGTON
DC
20036-2680
US
|
Family ID: |
24999162 |
Appl. No.: |
09/267694 |
Filed: |
March 15, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09267694 |
Mar 15, 1999 |
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08746018 |
Nov 5, 1996 |
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5898680 |
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Current U.S.
Class: |
342/357.31 ;
701/453; 701/468 |
Current CPC
Class: |
H04B 10/118 20130101;
H04B 7/18523 20130101 |
Class at
Publication: |
342/357.13 ;
701/208 |
International
Class: |
G01C 021/30; G01C
021/32 |
Claims
What is claimed is:
1. A system for providing location-specific data to a user,
comprising: a broadcast station for transmitting general data
potentially usable by a plurality of users located at different
geographic positions; a relay satellite for relaying said general
data from said broadcast station to said plurality of users; and a
receiver terminal provided for each of said users, said receiver
terminal comprising a broadcast receiver for receiving said general
data from said relay satellite, a position determination unit for
determining the geographic position of the user, and a processor
for converting said general data to location-specific data based on
the geographic position of said user as determined by said position
determination unit.
2. A system as claimed in claim 1, wherein said position
determination unit comprises a geolocation radio receiver.
3. A system as claimed in claim 1, wherein said receiver terminal
further comprises an output device for visually presenting said
location-specific data to said user.
4. A system as claimed in claim 1, wherein said general data
transmitted by said broadcast station is encrypted, and wherein
said receiver terminal is adapted to decrypt said data using a
decryption key.
5. A system as claimed in claim 4, wherein said receiver terminal
further comprises an input device for receiving said decryption key
from an external source.
6. A system as claimed in claim 8, wherein said external source
comprises a magnetically encoded card and said input device
comprises a magnetic card reader.
7. A system as claimed in claim 1, wherein said general data
comprises map data for a geographic region, and wherein said
location-specific data comprises map data for a portion of said
geographic region where said user is located.
8. A receiver terminal for providing location-specific data to a
user, comprising: a broadcast receiver for receiving general data
transmitted by a broadcast station; a position determination unit
for determining the geographic position of the receiver terminal;
and a processor for converting said general image data to
location-specific image data based on the geographic position of
the receiver terminal.
9. A receiver terminal as claimed in claim 8, wherein said position
determination unit comprises a geolocation radio receiver.
10. A receiver terminal as claimed in claim 8, wherein said
receiver terminal further comprises an output device for visually
presenting said location-specific data to said user.
11. A receiver terminal as claimed in claim 8, wherein said general
data transmitted by said broadcast station is encrypted, and
wherein of said receiver terminal is adapted to decrypt said image
data using a decryption key.
12. A receiver terminal as claimed in claim 11, wherein said
receiver terminal further comprises an input device for receiving
said decryption key from an external source.
13. A receiver terminal as claimed in claim 12, wherein said
external source comprises a magnetically encoded card and said
input device comprises a magnetic card reader.
14. A receiver terminal as claimed in claim 8, wherein said general
data comprises map data for a geographic region, and wherein said
location-specific data comprises map data for a portion of said
geographic region where said user is located.
15. A method for providing location-specific data to a user,
comprising: transmitting general data potentially usable by a
plurality of users located at different geographic positions;
receiving said general data at one of said user locations;
determining the geographic position of said user; and converting
said general data to location-specific data based on the geographic
position of said user.
16. A method as claimed in claim 15, further comprising the step of
relaying said transmitted general data through a satellite.
17. A method as claimed in claim 15, wherein the step of
determining the geographic position of said user comprises
receiving geolocation radio signals.
18. A method as claimed in claim 15, further comprising the step of
displaying said location-specific data to said user.
19. A method as claimed in claim 15, wherein said transmitted
general data is encrypted, and wherein said method further
comprises the step of decrypting said image data at said user
location.
20. A method as claimed in claim 15, wherein said general data
comprises map data for a geographic region, and wherein said
location-specific data comprises map data for a portion of said
geographic region where said user is located.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Related subject matter is disclosed and claimed in a
co-pending U.S. patent application Ser. No. 08/569,346, filed by S.
Joseph Campanella on Dec. 8, 1995; in a co-pending U.S. Patent
Application of S. Joseph Campanella, filed on Nov. 5, 1996 and
entitled "Direct Radio Broadcast Receiver Providing Frame
Synchronization and Correlation for Time Division Multiplexed
Transmissions" (Attorney's File 33877A); in a co-pending U.S.
Patent Application of S. Joseph Campanella, filed on Nov. 5, 1996
and entitled "Direct Radio Broadcast Receiver for Time Division
Multiplexed Transmission" (Attorney's File 33877B); in a co-pending
U.S. Patent Application of S. Joseph Campanella, filed on Nov. 5,
1996 and entitled "System for Formatting Broadcast Data for
Satellite Transmission and Radio Reception" (Attorney's File
33877C); in a co-pending U.S. Patent Application of S. Joseph
Campanella et al, filed on Nov. 5, 1996 and entitled "System for
Managing Space Segment Usage Among Broadcast Service Providers"
(Attorney's File 33877D); in a co-pending U.S. Patent Application
of S. Joseph Campanella, filed Nov. 5, 1996 and entitled "Satellite
Payload Processing System for Switching Uplink Signals to Time
Division Multiplexed Downlink Signals" (Attorney's File 33877E); in
a co-pending U.S. Patent Application of S. Joseph Campanella, filed
on Nov. 5, 1996 and entitled "Satellite Payload Processing System
Using Polyphase Demultiplexing and Quadrature Phase Shift Keying
Demodulation" (Attorney's File 33877F); and in a co-pending U.S.
Patent Application of S. Joseph Campanella, filed on Nov. 5, 1996
and entitled "Satellite Payload Processing System Providing
On-Board Rate Alignment" (Attorney's File 33877G); all of said
applications being expressly incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to the transmission
and reception of data, and is particularly concerned with a system
for providing location-specific data to a remotely located user by
combining a broadcast receiver with a geographic position
determination unit.
BACKGROUND OF THE INVENTION
[0003] There are many situations in which a user at a remote
location wishes to receive updated information that is specifically
tailored to the user's needs. For example, an aircraft pilot may
require a current weather map or aeronautical chart for a specific
flight path before beginning a flight, or the crew of an
ocean-going vessel may require an updated nautical chart showing
local harbor anchorages, entrances, channels or the like.
Similarly, hikers, skiers and other individuals engaged in outdoor
sporting activities may wish to obtain current topographical maps
of the local region in which the activity will take place.
[0004] Typically, nautical charts and topographical maps are made
available in hard copy form and are updated on a relatively
infrequent basis. Weather maps (for which frequent updating is
essential) have in some cases been made available to pilots and
others by facsimile or modem, but the requirement for access to a
facsimile machine or computer may prevent the user from obtaining
updated weather maps as frequently as might be desired. Moreover,
in all of these cases, the maps are generally designed to cover a
wide geographic area and are not tailored to the needs of any
specific user.
[0005] There currently exists a satellite-based position
determination system known as the Global Positioning System (GPS),
in which a number of satellites in stationary orbits above the
earth broadcast precise timing signals that can be received by
mobile receivers in aircraft, ships and land vehicles to provide
position information using triangulation techniques. In addition to
providing latitude and longitude information, GPS receivers often
use various types of on-board data storage devices (such as disks
and cartridges) to provide map displays that are combined with the
satellite-derived GPS position data. This allows the position of
the user to be shown graphically on a moving map, for example.
While these receivers are very useful for navigation, the map data
must be updated frequently (typically by obtaining new disks or
cartridges through a subscription service) in order to remain
useful. Even with frequent updating, some types of map data (such
as weather map data) cannot be effectively provided in this
way.
SUMMARY OF THE INVENTION
[0006] In view of the foregoing disadvantages and limitations, it
is an object of the present invention to provide a system and
method for distributing data (particularly, but not exclusively,
map data and other types of image data) to users by means of a
radio frequency link, so that updated data can be obtained as
frequently as needed.
[0007] A further object of the present invention is to make it
possible for a user to obtain data, particularly map data, that is
specific to the user's location.
[0008] A further object of the present invention is to use a
satellite direct radio broadcast system to provide map data and
other types of data, on demand, to users located throughout a large
geographical area.
[0009] It is a still further object of the present invention to
utilize a position determination unit, such as a GPS receiver, to
allow general map data or other data to be made location-specific
for a particular user.
[0010] It is a still further object of the present invention to
provide a system and method for allowing remote users to obtain
data selectively, without requiring two-way communication between
the users and the source of the data.
[0011] It is yet another object of the present invention to make it
possible for maps and other types of data to be made available to
users who pay for the data, and to prevent unauthorized users from
obtaining access to the data.
[0012] These and other objects of the present invention are
achieved, in part, by providing remote users with receiver
terminals which incorporate both broadcast receivers and position
determination units. The broadcast receivers receive general data
(that is, data potentially usable by users located at different
geographic locations) from a broadcast station, and the position
determination units allow the general data to be converted to
location-specific data that is tailored to the needs of the user. A
relay satellite, such as a direct radio broadcast satellite, may be
used to relay the general data from the broadcast station to the
receiver terminals.
[0013] In one aspect, therefore, the present invention is directed
to a system for providing location-specific data to a user. The
system comprises a broadcast station for transmitting general data
potentially usable by a plurality of users located at different
geographic positions, and a relay satellite for relaying the data
from the broadcast station to the plurality of users. The system
also includes a receiver terminal that is provided for each of the
users. The receiver terminal includes a broadcast receiver for
receiving the general data from the relay satellite, a position
determination unit for determining the geographic position of the
user, and a processor for converting the general data to
location-specific data based on the geographic position of the user
as determined by the position determination unit.
[0014] In another aspect, the present invention is directed to a
receiver terminal for providing location-specific data to a user.
The receiver terminal comprises a broadcast receiver for receiving
general data transmitted by a broadcast station, and a position
determination unit for determining the geographic position of the
receiver terminal. The receiver terminal also comprises a processor
for converting the general data to location-specific data based on
the geographic position of the receiver terminal.
[0015] In a still further aspect, the present invention is directed
to a method for providing location-specific data to a user. The
method comprises the steps of transmitting general data potentially
usable by a plurality of users located at different geographic
positions, receiving the general data at one of the user locations,
determining the geographic position of the user, and converting the
general data to location-specific data based on the geographic
position of the user.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The various objects, advantages and novel features of the
present invention will be more readily apprehended from the
following detailed description when read in conjunction with the
appended drawings, in which:
[0017] FIG. 1 is a diagrammatic illustration of the manner in which
location-specific data can be provided to users through a satellite
direct radio broadcast system in accordance with a preferred
embodiment of the present invention;
[0018] FIG. 2 illustrates the reallocation of information from
uplink frequency division multiple access channels into a downlink
time division multiplexed channel in a satellite direct radio
broadcast system of the type shown in FIG. 1;
[0019] FIG. 3 illustrates the manner in which on-board satellite
signal processing may be carried out in a satellite direct radio
broadcast system of the type shown in FIG. 1;
[0020] FIG. 4 is a block diagram illustrating the manner in which
image data may be combined with audio data at a broadcast station
and uplinked to the digital broadcast satellite of FIGS. 1-3;
[0021] FIG. 5 is a block diagram illustrating the construction of a
user terminal which incorporates both a digital broadcast receiver
and a geolocation receiver in accordance with a preferred
embodiment of the present invention;
[0022] FIGS. 6-8 illustrate three different ways in which image
data can be downlinked from the digital broadcast satellite of
FIGS. 1-3;
[0023] FIGS. 9 and 10 illustrate two possible versions of a debit
card which can be used to allow access to image data to users who
have paid for the data, and to prevent unauthorized users from
obtaining access to the data;
[0024] FIG. 11 is a flow chart which summarizes the series of
operations carried out by the user terminal of FIG. 5 when audio
and image data are received; and
[0025] FIG. 12 is a front view of one of the user terminals,
illustrating the manner in which a map or other location specific
image data may be displayed to the user.
[0026] Throughout the drawing figures, like reference numerals will
be understood to refer to like parts and components.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] A system for providing location-specific data to a user in
accordance with the present invention is preferably implemented in
connection with a satellite direct radio broadcast system of the
type described in the aforementioned copending U.S. patent
application Ser. No. 08/569,346, filed Dec. 8, 1995. The direct
radio broadcast system preferably consists of three geostationary
satellites (one of which is indicated at 20 in FIG. 1), low cost
radio receivers or user terminals 22, and associated ground
networks. For position determination purposes, the existing
constellation of Global Position System (GPS) satellites 24 is also
used in the preferred embodiment of the present invention. The
manner in which the GPS satellites 24 and their associated
receivers operate is well known and need not be described
herein.
[0028] The preferred satellites 20 of the direct radio broadcast
system cover the African-Arabian region, the Asian region and the
Caribbean and Latin American regions from the following
geostationary orbits:
[0029] .diamond-solid. 21.degree. E orbital location, providing
service to Africa and the Middle East.
[0030] .diamond-solid. 95.degree. W orbital location, providing
service to Central and South America.
[0031] .diamond-solid. 105.degree. W orbital location, providing
service to Southeast Asia and the Pacific rim.
[0032] Coverage for other areas, such as North America and Europe,
can be provided with additional satellites.
[0033] The direct radio broadcast system preferably uses the
frequency band of 1467 to 1492 MHz, which has been allocated for
Broadcasting Satellite Service (BSS) Direct Audio Broadcast (DAB)
at WARC 92, that is, in accordance with resolutions 33 and 528 of
the ITU. The broadcasters 26 use feeder uplinks in X band, from
7050 to 7075 MHz.
[0034] The direct radio broadcast system uses digital audio coding
techniques. Each satellite delivers digital radio audio signals
having qualities equivalent to AM monaural, FM monaural, FM stereo
and CD stereo throughout its respective coverage area, together
with ancillary data such as paging, video and text transmissions
directly to the radios. The system may also deliver multimedia
services such as large database downloads to PCs for business
applications, map and printed text information for travelers (as
described in more detail hereinafter), and even color to augment
audio programs for advertising and entertainment.
[0035] System broadcasters organize their services in terms of
program channels, each consisting of one or more 16 kilobit per
second (kbps) prime rate channels. The number of prime rate
channels per program channel can range from 1 to 8, thus yielding a
program channel bit rate of 16 to 128 kbps in 16 kbps increments.
Each broadcaster selects the number of 16 kbps prime rate channels
in accordance with the broadcaster's specific application. For each
16 kbps increment, there is also a service control header that
carries 519 bits per second, bringing the total bit rate per prime
channel to 16.519 kbps.
[0036] To protect the broadcaster's program channel, a forward
error correction (FEC) method is used. It comprises a Reed Solomon
(255,223) coder concatenated with an interleaver, and a rate 1/2
Viterbi constant length 7 coder. This error correction coding
(together with the addition of a sync header) elevates the prime
rate channel to 19 kbps.
[0037] Each satellite 20 is preferably equipped with three downlink
spot beams, having beamwidths of about 6.degree.. Each beam covers
approximately 14 million square kilometers within power
distribution contours that are 4 dB down from beam center and 28
million square kilometers within contours that are 8 dB down. The
beam center margin may be 14 dB based on a receiver
gain-to-temperature ratio of -13 dB/K.
[0038] Each satellite 20 carries two types of payloads. One is a
"processing" payload that regenerates the uplink signals and
assembles 3 TDM downlink carriers, and the other is a "transparent"
payload that repeats the uplink signals on 3 TDM downlink carriers.
The TDM signals from the two payloads are each transmitted in 3
beams, with the processed and transparent signals in each beam
having opposite circular polarization (LHCP and RHCP). Each TDM
downlink signal carries 96 prime rate channels in assigned time
slots. To a radio receiver, all of the TDM downlink signals appear
the same, except for carrier frequency. The total capacity per
satellite is 2.times.3.times.96=576 prime rate channels.
[0039] FIG. 1 illustrates the overall operation of a
location-specific data delivery system in accordance with a
preferred embodiment of the present invention. In the case of the
satellite processing payload, uplink signals 28 issue from
broadcasters via individual frequency division multiple access
(FDMA) channels from broadcast stations 26 located anywhere within
the terrestrial visibility of the satellite 20 with elevation
angles higher than 100. Each broadcaster has the ability to uplink
directly from its own facilities to one of the satellites 20
placing one or more 16 kbps prime rate channels on the FDMA
carriers. Alternately, broadcasters which have no capacity for
direct access to the satellite 20 may have access through a hub
station. Use of FDMA for the uplink offers the highest possible
flexibility between multiple independent broadcast stations.
[0040] Conversion between uplink FDMA and downlink
multiple-channel-per-ca- rrier, time division multiplex (MCPC/TDM)
in the direct radio broadcast system of FIG. 1 is achieved on board
the satellite 20 by an on-board processor. At the satellite 20,
each prime rate channel transmitted by a broadcast station 26 is
demultiplexed and demodulated into individual 16 kbps baseband
signals. Individual channels are routed via a switch to one or more
of the downlink beams 30, each of which is a single TDM signal.
This baseband processing provides a high level of channel control
in terms of uplink frequency allocation and channel routing between
uplink and downlink. Uplink signals are received in the satellite
in X band and converted to L band by the on-board processor. The
downlinks 30 to the user terminals 22 use MCPC/TDM carriers. One
such carrier is used in each of the three beams on each satellite
20.
[0041] For the transparent payload, the TDM signals are assembled
at a broadcast station and appear in precisely the same structure
as do those assembled on board the satellite 20 by the processing
payload The TDM signal is sent to the satellite in the X band and
is repeated in the L band in one of the three downlink beams. The
power level is the same for downlink TDM signals generated by the
processing payload.
[0042] As will be described hereinafter, signals from the GPS
satellites 24 are also received by the user terminals 22 and are
used by the terminals 22 to determine their geographic positions.
This allows each user terminal 22 to convert general data received
from the broadcasters 22 to location-specific data tailored to the
needs of the user.
[0043] FIG. 2 illustrates the on-board re-allocation of prime rate
channels from uplink frequency division multiple access channels
into a downlink MCPC/TDM channel in the processing payload of the
satellite 20 of FIG. 1. The overall uplink capacity is preferably
between two hundred eighty-eight (288) and three hundred
eighty-four (384) prime rate uplink channels 32 of 16.519 kbps
each. Ninety-six (96) prime rate channels 34 are selected and
multiplexed for transmission in each downlink beam 36, time
division multiplexed onto a carrier of approximately 2.5 MHz
bandwidth. Each uplink channel may be routed to all, some or none
of the downlink beams. The order and placement of prime rate
channels in a downlink beam is fully selectable via a command link
from a telemetry, range and control (fRC) facility 38, shown in
FIG. 1.
[0044] The carrier frequencies in each downlink beam 36 are
different to enhance beam-to-beam isolation. Each TDM downlink
channel is operated in the satellite payload at saturation, giving
the highest possible power efficiency in terms of link performance.
Use of single carrier per transponder operation achieves maximum
efficiency in the operation of the satellite communication payload
in terms of conversion of solar power into radio frequency power.
This is far more efficient than techniques requiring simultaneous
amplification of a multiplicity of FDM carriers. The system
produces high receive margins suitable for stationary and mobile
reception indoors and outdoors.
[0045] The system carries out audio source coding using MPEG 2.5,
Layer 3 which achieves the cited qualities at bit rates of 16, 32,
64 and 128 kbps, respectively, and also includes the capability to
perform 8 kbps coding. Image coding is carried out using the JPEG
standard. Error rates over the system are less than 10.sup.-10 and
thus are suitable for high quality digital image and data
transmission for multimedia services. The MPEG 2.5, Layer 3 coding
offers a better bit rate efficiency than the previous MPEG 1, Layer
2 (Musicam) or MPEG 2 standards for the same audio quality. For
audio broadcasts, the digitally coded source bit rates are:
[0046] .diamond-solid. 8 kbps for utility monophonic voice;
[0047] .diamond-solid. 16 kbps for non-utility monophonic
voice;
[0048] .diamond-solid. 32 kbps for monophonic music, with near FM
quality;
[0049] .diamond-solid. 64 kbps for stereophonic music, with near FM
quality; and
[0050] .diamond-solid. 128 kbps for stereophonic music, with near
CD quality.
[0051] In the preferred implementation of the satellite direct
radio broadcast system, each satellite has the capacity to transmit
a total of 3072 kbps per beam (including the 2 TDM carriers for the
processing and transparent payloads, respectively), which may be
any combination of the above audio services. This corresponds to a
capacity per beam of:
[0052] .diamond-solid. 192 monophonic voice channels; or
[0053] .diamond-solid. 96 monophonic music channels; or
[0054] .diamond-solid. 48 stereophonic music channels; or
[0055] .diamond-solid. 24 CD stereophonic music channels; or
[0056] .diamond-solid. any combination of the above signal
qualities.
[0057] The overall satellite direct radio broadcast system delivers
the digital signals with a bit error rate (BER) of 10.sup.-4 or
better, providing the various service qualities previously defined.
For each downlink beam in L band transmitted by the satellites, the
Edge Of Coverage EIRP of the TDM carrier is 49.5 dBW. This EIRP,
together with specific Forward Error Correction, insures a minimum
9 dB margin for a 10.sup.-4 BER, using the baseline radio receiver
antenna. This margin helps combat signal loss due to obstacles in
the path between the satellite and the receiver, providing full
quality reception in the intended coverage area.
[0058] Radio receivers in obstructed locations can be connected to
a high gain antenna, or to an antenna located in an unobstructed
position. For example, reception in large buildings may need a
common roof antenna with indoor retransmission for the entire
building, or individual reception antennas near a window. At the 4
dB down contour of the earth coverages, the channels have an
estimated margin of 10 dB relative to the power density needed to
deliver a bit error rate of 10.sup.-4. At beam center this margin
estimate is 14 dB.
[0059] The operating margin of the system does not change for the
higher bit rates. Within the 4 dB contour, most radios will view
the satellite at elevation angles of greater than 60.degree.,
making interference from structures virtually nil. In some beams,
within the 8 dB contour the elevation angle to the satellite will
be greater than 50.degree., which may experience occasional
interference due to reflections or blockage from structures. Line
of sight reception even at low elevation angles (10.degree. to
50.degree.) is always possible with small 8 dBi gain antennas in
some beams pointed toward the horizon.
[0060] The direct radio broadcast system includes a baseband
processing payload in the satellite 20. Baseband processing allows
improved system performance for uplink and downlink link budgets,
management of broadcast stations, and control of the downlink
signals.
[0061] FIG. 3 illustrates satellite signal processing in the
preferred satellite direct radio broadcast system. The coded prime
rate uplink carriers are received at an X-band receiver 40. A
polyphase demultiplexer and demodulator 42 receives the 288
individual FDMA signals in 6 groups of 48, generates six analog
signals on which the data of the 288 signals is divided into 6 time
multiplexed streams, and performs demodulation of the serial data
on each stream. A routing switch and modulator 44 selectively
routes individual channels of the serial data into all, some or
none of three downlink signals, each carrying 96 channels, and
further modulates them onto the three downlink L-band TDM signals.
Traveling wave tube amplifiers 46 boost the power of the three
downlink signals, which are radiated to earth by L-band transmit
antennas 48. The satellite also includes a transparent payload
comprising a demultiplexer/downconverter 50 and an amplifier group
52, which are configured in a conventional "bent pipe" signal path
to frequency convert uplink TDM/MCPC signals for retransmission at
L band.
[0062] High redundancy in the spacecraft receivers, digital
processors and output high power amplifiers guarantees a 12 year
life for each satellite 20. Also, there is enough position keeping
fuel to maintain each satellite 20 to a location within .+-.0.10 of
its assigned orbit position for 15 years.
[0063] The time division multiplex frames have a duration of 0.138
second, each marked by a 96 symbol synchronization word. The
downlink MCPC/TDM carrier has a rate of 1.84 million QPSK symbols
per second.
[0064] The satellites 20 are operated by a ground control segment
and managed according to traffic requirements by a mission control
segment during the orbit lifetime. The bit rates and consequently
the service qualities can be mixed in any beam to meet the demand
for service. The bit-rate/quality complexion of a service can be
easily changed from ground command and can vary at different times
of the day. In the preferred embodiment, channel allocation may be
changed on an hour-by-hour basis according to a program schedule
established twenty-four hours in advance. Radio receivers, relying
on ensemble information included in the TDM frame and in each prime
rate channel, will automatically select those prime rate channels
necessary to generate the user-selected digital audio program or
other digital service program.
[0065] A block diagram of a broadcast station 26 which may be used
in connection with the present invention is illustrated in FIG. 4.
Two sources are shown in FIG. 4, one source 54 providing audio
programming and the second source 56 providing image data which may
be desired by certain users. (It will be understood that this
arrangement is merely exemplary, and that the broadcast station 26
may transmit only audio programming or only image data or other
broadcast services, if desired. Moreover, the number of sources
could be greater than two, and both audio and image data could be
produced by the same source in some cases.) The image data may
consist of weather maps, topographical maps, political boundary
maps, road maps, nautical or aeronautical charts, satellite or
radar generated images, or the like. Different types of image data
may be sent at different times (e.g., aeronautical charts may
alternate with nautical charts), or the same type of image data may
be sent on a continuously updated basis. For the purposes of the
present invention, it is desirable (although not essential) that
successive blocks of image data be sent in accordance with a
predetermined schedule that is known to the users in advance, so
that the users can selectively access desired blocks of image data
without requiring a two-way communication link with the broadcast
station. Thus, for example, if weather maps relating to different
geographic areas are transmitted sequentially at known times, a
user in a particular geographic area need merely wait until the
assigned time (obtained from a published schedule or the like) to
obtain the weather map that corresponds to the user's specific
geographic area.
[0066] As will be apparent from FIG. 4, the processing of digital
data from the audio source 54 and from the image source 56 is
essentially the same. The audio and images sources 54 and 56 are
first subjected to MPEG or JPEG source coding in blocks 58 and 60.
The source coded image data is then encrypted in block 61, using an
encryption method which can be decrypted using a decryption key.
(Optionally, the source coded audio data can also be encrypted, but
this is not shown in FIG. 4.) The source coded (and, in the case of
the image data, encrypted) digital signals are then
forward-error-correction coded in blocks 62 and 64, using a
concatenated channel coding scheme comprising a Reed Solomon
(255,233) block coder, block interleaving and rate 1/2 Viterbi
convolutional coding.
[0067] Use of such a concatenated coding scheme contributes to the
low bit error rate achieved over the system. Channel coding
multiplies the bit rate needed for transmission by a factor of
2.times.255/223. Thus, the prime rate is increased to 37.78
kilobits per second after error coding.
[0068] Depending on the program channel rate, the symbols of the
coded program channels are split among a set of coded prime rate
transmit channels. For example, a 128 kbps channel is split into
eight prime rate channels as follows:
[0069] Symbol 1 into physical channel 1
[0070] Symbol 2 into physical channel 2
[0071] Symbol 3 into physical channel 3
[0072] Symbol 4 into physical channel 4
[0073] Symbol 5 into physical channel 5
[0074] Symbol 6 into physical channel 6
[0075] Symbol 7 into physical channel 7
[0076] Symbol 8 into physical channel 8
[0077] Symbol 9 into physical channel 1
[0078] .
[0079] .
[0080] etc.
[0081] A control word is inserted into each coded prime rate
channel to identify the program channel to which it belongs and to
carry instructions that allow the receiver to recombine the coded
prime rate channels to reconstruct the coded program channels. An
exemplary eighty (80) bit control word is:
1 # Bits Indication 2 Quantity Of Related Ensembles (00 = no
relation, four related ensembles maximum) 2 Ensemble Identification
Number (00 = Ensemble #1, 11 = Ensemble 4) 4 Ensemble Type (0000 =
Audio, 0001 = Video, 0010 = Data, other types or reserved) 3
Quantity Of 16 kbps Prime Rate Channels In Ensemble (000 = 1
channel, 001 = 2 channels, ..., 111 = 8 channels) 3 Prime Rate
Channel Identification Number (000 = channel 1, ..., 111 = channel
8) 3 Quantity Of Sub-Ensembles (000 = 1, ..., 111 = 8) 3 Quantity
Of 16 kbps Prime Rate Channels In Sub- Ensemble (000 = 1, ..., 111
= 8) 2 Sub-Ensemble Identification Number (000 = Ensemble #1, ...,
111 = Ensemble 8) 3 Ensemble/Sub-Ensemble Blocking (000 = no
blocking, 001 = type 1 blocking, ..., 111 = type 7 blocking) 11
Reserved 40 CRC.
[0082] The control word entry for the Quantity of Related Ensembles
allows a relationship to be created between various groups of
ensembles. For example, a broadcaster may wish to provide related
audio, video and data services, such as electronic newspaper with
audio text, and additional information. The Ensemble Identification
Number identifies the ensemble number of which the channel is a
part. The Quantity Of 16 kbps Prime Rate Channels In Ensemble
defines the number of prime rate channels in the ensemble. The
Quantity Of Sub-Ensembles and Quantity of 16 kbps Prime Rate
Channels In Sub-Ensemble defines a relationship within an ensemble,
such as, in a CD quality stereo ensemble, use of four prime rate
channels for a "Left Stereo" signal and four different prime rate
channels for a "Right Stereo" signal. Alternatively, music may be
associated with multiple voice signals for announcers, each voice
signal in a different language. The Quantity Of 16 kbps Prime Rate
Channels In Sub-Ensemble defines the number of prime rate channels
in the sub-ensemble. The Sub-Ensemble Identification Number
identifies the sub-ensemble of which the channel is a part.
[0083] The Ensemble/Sub-Ensemble Blocking bits allow cooperative
blocking of broadcast information. For instance, some countries may
prohibit advertising for alcohol. Radios produced for that country
can be preset with a code, or a code can otherwise be loaded, so
that the radio would respond to the blocking signal and block the
specific information. The blocking function can also be used to
restrict the dissemination of sensitive information (such as
military or governmental information), or to restrict
revenue-bearing broadcast services to certain users.
[0084] Each prime rate channel is organized into frames having at
least a channel preamble to provide a timing reference between the
broadcast station and the satellite. The preamble may include a
unique word to identify the start of the block coding for each
frame. The preamble may also include a block of timing bits
containing 48 two-bit symbols. When the broadcast station and the
satellite are synchronized, the block contains 47 symbols. If, due
to differences in oscillators in the satellite and broadcast
station, the broadcast station lags behind or moves ahead by one
symbol, the block of timing symbols is shortened or lengthened
accordingly. All channels may use the same preamble. When a source
has been split among multiple prime rate channels, the preambles
for all related channels should be coincident. There is no master
clock synchronization between separate broadcast stations. Addition
of the control word and preamble code raises the transmitted prime
channel rate to 38 kilobits per second.
[0085] Each coded program source is divided into individual prime
rate channels. As an example, the audio source 54 may comprise four
prime rate channels, which represents an FM quality stereo signal.
Alternatively, audio source 54 may comprise six prime rate
channels, which can be used as a "near CD" quality stereo signal,
or an FM quality stereo signal linked to a 32 bit data channel (e
g., for transmitting a signal for display on a radio receiver
liquid crystal display (LCD)). As a further alternative, the six
prime rate channels can be used as a 96 kbps broadcast data
channel. The image source may comprise only one 16 kbps channel or
several channels. Images may be transmitted in a format allowing 12
million pixels for a high resolution map. This image can be passed
to any receiver within about 20 minutes. The time required would be
halved every time the number of prime rate channels is doubled.
JPEG image coding can be used for such images.
[0086] With continued reference to FIG. 4, the prime rate channels
are distributed by channel distribution blocks 64 and 68 to QPSK
modulation blocks 70 and 72, respectively. Within each QPSK
modulation block 70 and 72, a separate QPSK modulator (not shown)
modulates each prime rate channel to an intermediate frequency. An
upconverter 74 moves the separate prime rate channels to the FDMA
uplink band, and the upconverted channels are transmitted through
amplifier 76 and antenna 78. Broadcast uplink stations use VSAT
signals for transmission of elementary (16 kbps) channels, using
small antennas (2 to 3 meters in diameter).
[0087] The prime rate uplink channels are transmitted to the
satellite 20 on individual Frequency Division Multiple Access
(FDMA) carriers. Up to 288 uplink prime rate carriers can be
transmitted to the satellite 20 in its global uplink beam. Small
broadcasters' earth terminals equipped with 2.4 meter diameter
parabolic X-band antennas and 25 watt power amplifiers can easily
transmit a 128 kilobit per second program channel (comprising 8 of
the prime rate channels) to the satellite 20 from a site in the
country originating the program. Alternatively, program channels
can be connected to shared uplink earth terminals via leased PSTN
terrestrial links. The system has adequate uplink capacity for
every country in its world coverage to have its own satellite radio
broadcasting channel.
[0088] A block diagram of one of the user terminals 22 of FIG. 1 is
provided in FIG. 5. The user terminal 22 receives the L band signal
from the satellite 20, demodulates and extracts from the TDM stream
the useful audio or image signal, and reproduces the desired audio
or image information. The user terminal may be equipped with a
small compact patch antenna 80 having about 4 to 6 dBi gain, which
will require virtually no pointing. The user terminal 22 will tune
automatically to selected channels. An alternative higher end user
terminal may be equipped with an antenna that achieves 10 to 12 dBi
of gain. Since such an antenna would be quite directional, it is
pointed to achieve best reception. One version of this antenna may
be an array of patches. The array may be embedded conformally into
the surface of the user terminal case, attached as a lid, or be
completely detachable and connected to the user terminal by a thin
coax cable a few meters long. Another version of the antenna could
be a helix operating in either a broadside or end-fire mode.
Pointing is done by rotating the antenna in elevation and azimuth.
A detachable antenna can be mounted on a small tripod on the ground
or mounted to a window frame and pointed to achieve best reception.
A 10 dBi antenna has a beam width of approximately 650 and
consequently will be easy to point at the satellite 20 for
achieving optimum reception. The directivity of this antenna will
further enhance reception in locations where reflections might
otherwise cause interference. A phased array, rod shaped antenna
with wide beamwidth in one dimension but narrow in the other (i.e.,
a fan beam) is another alternative. Yet an alternate antenna is a
helical antenna for outdoor reception and most indoor reception. In
certain environments (mask, concrete or metal buildings), indoor
reception may require connection to an external antenna. For
reception by mobile user terminals, antennas with as little as 4
dBi of gain may be mounted on the vehicle. A single antenna of this
type operates very well in an open location at high elevation
angles, devoid of severe multipath reflectors. However, in an area
having multipath reflections, such as downtown cities, where
elevations are less than 60.degree., measures may occasionally have
to be taken to mitigate the multipath interference. One such
measure is to use two or three of the 4 dBi gain antennas in a
spatial diversity array mounted at various locations on the
vehicle. These can be dynamically added to achieve directivity or
combined so as to pick the maximum signal arrival at a given
instant. Another alternative is to install a steerable directional
antenna with 10 dBi of gain and cause it track the satellite 20.
This latter idea is expensive but may be preferable to obtain
maximum benefit from the high performance quality offered by the
system. As satellite mobile systems come into worldwide use in the
next decade, electronically steerable array antennas are expected
to drop in price and become generally affordable.
[0089] A time division multiplexed, multiple channel per carrier
technique is used for downlink transmission to the user terminal
22. Each of the prime rate (16.519 kilobits per second) channels
occupies its own time slot in the time division stream. These prime
rate channels are combined to carry program channels ranging from
16 to 128 kilobits per second. Use of digital techniques allows for
ancillary services to the radio including low rate video, paging,
mailing, fax, use of flat display screens, or serial data
interfaces. This data and information may be multiplexed within the
audio digital signal channels.
[0090] Each user terminal 22 can tune to one of the TDM carriers
transmitted in one of the beam coverages. As shown in FIG. 5, the
user terminal 22 includes a digital broadcast receiver 82 and
antenna 80, a GPS receiver 84, and antenna 85, a system controller
86, and a user interface 88. Within the digital broadcast receiver
82, a low noise amplifier 90 boosts the satellite signal, and the
boosted signal is received by an RF front end and QPSK demodulator
92. The output of the RF front end and QPSK demodulator 92 is
connected to a first time division demultiplexer 94 which recovers
the audio prime rate channels, and to a second time division
demultiplexer 96 which recovers the prime rate channels carrying
image data. Forward error correction (FEC) decoding is also carried
out in the blocks 94 and 96. The output of the block 94 is a
baseband digital signal carrying audio information, and the output
of the block 96 is a baseband digital signal carrying image
data.
[0091] The instructions needed for the receiver 22 to control
recombination of the coded prime channels into the coded program
channels are contained in the control words embedded in each coded
prime rate channel and in the TDM frames. The recombined coded
program channels thus recovered are decoded and deinterleaved to
recover the original baseband prime rate bit stream that entered
the system at the broadcaster's earth terminal. In the case of
audio data, the recovered bit streams are converted back to an
analog audio signal by an audio decoder 98 and a digital-to-analog
converter 100. The analog signal is boosted by an amplifier 102 and
is reproduced by a loudspeaker that forms a part of the user
interface 88. The receiver can reproduce various audio qualities
ranging from AM monaural to CD stereo depending on the program
channel bit rate.
[0092] In the case of image data, the recovered bit streams are
converted to a displayable format by an image decoder 106. If the
image data was encrypted at the broadcast station 26, as will
typically be the case where the user is required to pay for the
image data, decryption of the image is carried out in block 108.
The decrypted data is then provided to the system controller 86.
Decryption is performed by adding a random bit pattern to the
received broadcast channel frame. The pattern is generated by a
pattern generator that is seeded by a key code. The key code can be
sent over the system or can be provided by a smart card or debit
card. The key code is different for each user.
[0093] The system controller 86 has a number of functions. These
include monitoring and controlling the operation of the digital
broadcast receiver 82, receiving position information from the GPS
receiver 84 (for a purpose to be described shortly), controlling
the display, printing and storage of received image data,
administering decryption keys, and processing user inputs and
outputs through the intermediary of the user interface 88. The
principal components of the system controller 86 include a
microprocessor 110 having suitable amounts of random access memory
(RAM) 112 and read-only memory (ROM) 114, a real-time clock 116 and
a display controller 118. The display controller 118 controls the
formatting of image data (e.g., map data) to an LCD display 120
which forms part of the user interface 88. The user interface 88
also includes a keypad 122, a printer/plotter 124, a card reader
126 and disk drive 128. The keypad 122 is used for selecting
broadcast programs, controlling sound levels, making menu
selections, and similar functions. The printer/plotter 124 allows
the user to receive a hard copy output of any received image data
(such as an updated weather map or nautical chart), in addition to
viewing the image on the LCD display 120. The card reader 126 is
used in connection with a magnetically encoded debit card or smart
card to allow the user to obtain access to encrypted image data, as
will be described in more detail below. Finally, the disk drive 128
allows data or programs to be loaded into the system controller 86,
and also allows received image data to be stored for later viewing
or printing. One possible function of the disk drive 122 may be,
for example, to allow the system controller 86 to merge image data
that is being received in real time by the digital broadcast
receiver 82 with preexisting data stored on a magnetic diskette.
This is useful in allowing existing maps to be updated by
transmitting only the new or modified information, without
requiring the entire map to be transmitted.
[0094] It will be understood that some or all of the components of
FIG. 5 may be incorporated into a single case that is designed for
either fixed-site or mobile use. In the latter situation, power may
be provided by batteries, solar cells or a generator driven by a
spring motor or hand crank. If the user terminal 22 is carried by
vehicle such as a boat, aircraft or automobile, power may be
provided by the vehicle's power supply. As an alternative to
housing all of the components of the user terminal 22 in a single
case, the user terminal 22 may be made up of a system or network of
separate components interconnected by suitable cables.
[0095] FIGS. 6 through 8 illustrate three different ways in which
map data or other types of image data can be transmitted on the
downlink TDM channels 30 of FIG. 1. In FIG. 6, the image data is
transmitted in the "dead time" between audio programs, and preamble
or identification codes are used to distinguish audio data from
image data. As an example, audio programs may be transmitted during
daylight hours on a given TDM downlink channel (or set of TDM
downlink channels), but the same channel (or channels) may carry
image data during late evening or early morning hours when there is
less demand for audio programs. In FIG. 7, the audio programs and
image data occupy different TDM downlink channels and can therefore
be transmitted continuously. This option would be desired in cases
where the image data consists of weather maps, for example, since
such maps must be available on an around-the-clock basis and must
be updated very frequently. FIG. 8 is similar to FIG. 7 in that
separate TDM channels are used for the audio programs and data, but
in this example different types of images are transmitted at
different times on the image channel and are separated from each
other by preamble or identification codes. Thus, for example, a
broadcaster may transmit nautical charts during a first period of
time, and aeronautical charts during a second period of time. By
tuning to the image channel at the appropriate time (which may be
listed in a published schedule), or by programming the user
terminal 22 to automatically detect a specific code, the user may
select the desired image data for display, printing and/or
storage.
[0096] FIGS. 9 and 10 illustrate two possible versions of a
magnetically-encoded debit card or smart card which may be used in
connection with the user terminal 22 of FIG. 5. In FIG. 9, the
debit card 130 contains a magnetic strip 132 which is encoded with
a prepaid monetary amount that can be used to purchase maps or
other types of images. The magnetic strip 132 also contains a
decryption key that is used by the system controller 86 of FIG. 5
to control the decryption of image data that is transmitted by a
broadcast station in encrypted form. When the prepaid amount on the
debit card 130 is used up, the decryption key is no longer provided
to the system controller 86 and the user must obtain a new debit
card from the supplier of the image data.
[0097] FIG. 10 illustrates a modified debit card 130' which
contains a magnetic strip 132' similar to that shown in FIG. 9. In
the case of FIG. 10, however, the magnetic strip 132' is encoded
not only with a prepaid amount and a decryption key, but also with
information (such as image codes, program channels and/or broadcast
schedules) that allows the radio receiver 22 to automatically
select images that have been requested in advance by the user. For
example, if the user has a subscription agreement with a map vendor
under which the user obtains updated maps only for selected
geographic areas, the image codes and broadcast schedules will
cause the radio receiver 22 to automatically receive only those
maps without any action by the user. By contrast, the debit card
130 of FIG. 9 requires the user to enter the desired image codes,
program channels and/or broadcast schedules into the radio receiver
22 (via the keypad 122), or to manually tune to the desired program
channel at the time when a desired image is being transmitted.
[0098] FIG. 11 is a flow chart which summarizes the basic series of
operations carried out by the user terminal of FIG. 5 when audio
and image data are received. It will be understood that, due to the
TDM format of the downlink channels, the receiver 22 is capable of
receiving and reproducing audio and image data simultaneously.
Thus, except in cases where the selected audio program and the
desired image data alternate on the same TDM downlink channel (as
illustrated in FIG. 6), the user is not required to stop listening
to an audio program in order to receive a map or other type of
image. As a result, a user who wishes to obtain a weather map, for
example, can do so while continuing to listen to weather forecasts
over an audio program channel.
[0099] With specific reference now to the logic sequence shown in
FIG. 11, the first step in the program is a power-up and
initialization step that is carried out in block 134. After this
step, the program proceeds to block 136, where the receiver 22
decodes and plays an audio program which has been selected by the
user. In block 138, the program checks to determine whether image
data has been requested by the user. Typically, the user will make
such a request by using the keypad 122 of FIG. 5 to choose a menu
selection displayed by the LCD display 120. If no image data has
been requested, the program returns to block 136 and continues to
play the selected audio program. However, if image data has been
requested, the program proceeds to decision block 140 and checks to
determine whether the user is authorized to receive the requested
image data. This determination will typically include a check of
the prepaid balance on the user's debit card 130 or 130' (which has
been inserted by the user into the card reader 126) and a check of
the user's decryption key to be sure that it is valid. If either of
these checks fails, a user message is displayed on the LCD display
120 in block 142 to inform the user that proper authorization does
not exist.
[0100] Assuming that the receiver is found to be properly
authorized in decision block 140, the program proceeds to block 144
and begins to monitor the TDM carrier and channel on which the
desired image data will appear. Such monitoring may be carried out
automatically by the system controller 86 of FIG. 5, using the
image codes and broadcast schedules input from the debit card 130'.
Alternatively, the user may monitor the image channel manually by
observing the channel output on the LCD display 120, and then
initiating a data storage or printing operation when the desired
image appears. In decision block 146, a check is made (either
automatically or manually) to determine whether the desired image
has appeared. If not, monitoring continues in block 144 until the
image is received. After the image is detected, the program
proceeds to block 148 and performs any necessary decryption of the
image data using the decryption key on the user's debit card 130 or
130'. Once the image is decrypted, the program proceeds to block
150 and performs any necessary conversion of the general image data
received by the user terminal 22 to produce location-specific image
data tailored to the needs of the user. This is done by the system
controller 86 of FIG. 5 using the geographic position of the user
as determined by the GPS receiver 84. The conversion step may be
carried out in a variety of ways and may involve partitioning or
sectioning of the image, selection of one of several possible
images, merging of the image with other image or non-image data, or
any other processing, modification or reformatting of the image.
Thus, for example, if the image data consists of a weather or
topographical map covering a wide geographic area, the conversion
step performed in block 150 may involve restricting the image to a
smaller geographic area within a predetermined radius of the user's
GPS-determined position. Alternatively, or in addition to the
formation of a restricted image, the user's position coordinates
(e.g., latitude and longitude), direction and speed (for mobile
users), and other information may be overlaid onto the image by the
system controller 86 based on the received GPS information. The
manner in which these types of image conversion may be carried out
will be readily apparent to those of ordinary skill in the art,
since the principles involved are similar to those used in
providing GPS receivers with moving map displays. As an example of
another type of image conversion, two or more different maps (such
as a land map and a nautical chart) may be merged to form a
composite map, using the GPS position data for alignment purposes
and/or to produce an overlayof the user's position coordinates or
the like on the composite map.
[0101] Once the desired image conversion is carried out in block
150, the program proceeds to block 152 and either displays the
image on the LCD display 120, prints out the image in hard copy
form using the printer/plotter 124, or both, in accordance with
input commands provided by the user. The image may also be stored
for later viewing on a magnetic diskette using the disk drive 128,
and a moving map display may be generated if the user terminal 22
is a mobile terminal. In block 154, payment for the received image
is deducted from the user's debit card 130 or 130'. If a sufficient
balance remains on the user's debit card, the process of FIG. 11
may be repeated in order to obtain a different image. If the user's
debit card balance has reached zero, or an amount which is
insufficient to allow another image to be downloaded, the user can
purchase another debit card or restore an adequate balance to the
existing card at a bank or other institution.
[0102] FIG. 12 is an enlarged front view of one of the user
terminals 22, illustrating one type of image that may be provided
to a user on the LCD display 120. A map 156 covering a wide
geographic area is downloaded in digital form to the user terminal
22 via the satellite 20, and software within the user terminal
restricts the image 156 to a smaller portion 158 in which the user
is known to be located (based on position data from the GPS
receiver 84). The user's position is marked by a cross 160, and the
user's course (determined from successive GPS position
measurements) is marked by a dashed line. If desired, the user's
latitude, longitude, speed and direction may also be shown on the
LCD display 120.
[0103] It will be understood that the GPS receiver 84 shown in FIG.
5 is only one type of geolocation receiver that can be use in
connection with the present invention. Other types of geolocation
receivers, such as LORAN receivers, can also be used. To improve
the accuracy of the geolocation receiver, an altimeter may be
provided in the user terminal to correct for the user's elevation.
In some applications, it may also be possible to track the position
of the user with a device other than a geolocation receiver, such
as an inertial navigation unit.
[0104] Although the present invention has been described with
reference to a preferred embodiment thereof, it will be understood
that the invention is not limited to the details thereof. Various
substitutions and modifications have been suggested in the
foregoing description, and others will occur to those of ordinary
skill in the art. All such substitutions and modifications are
intended to be embraced within the scope of the invention as
defined in the appended claims.
* * * * *