U.S. patent application number 10/769242 was filed with the patent office on 2004-09-23 for location estimation in narrow bandwidth wireless communication systems.
Invention is credited to Gilkes, Alan M., Panasik, Carl M..
Application Number | 20040185873 10/769242 |
Document ID | / |
Family ID | 25359923 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040185873 |
Kind Code |
A1 |
Gilkes, Alan M. ; et
al. |
September 23, 2004 |
Location estimation in narrow bandwidth wireless communication
systems
Abstract
The phase difference between a known stable reference signal
(11) and a known signal output by a wireless mobile communication
device (5, 5B) is determined at several known locations (1-4,
1B-4B). The location of the wireless mobile communication device is
then determined from the phase difference information. Also, the
approximate location of a wireless mobile communication device (5A)
can be estimated by transmitting a message from the device at a
predetermined power level (71), and determining where among a
plurality of predetermined locations (1A-4A) the transmitted
message has been received.
Inventors: |
Gilkes, Alan M.; (Plano,
TX) ; Panasik, Carl M.; (Garland, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
25359923 |
Appl. No.: |
10/769242 |
Filed: |
January 30, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10769242 |
Jan 30, 2004 |
|
|
|
09872598 |
Jun 1, 2001 |
|
|
|
6700535 |
|
|
|
|
Current U.S.
Class: |
455/456.2 ;
455/456.1 |
Current CPC
Class: |
G01S 5/06 20130101; H04W
64/00 20130101 |
Class at
Publication: |
455/456.2 ;
455/456.1 |
International
Class: |
H04Q 007/00 |
Claims
What is claimed is:
1. A method of determining the location of a wireless mobile
communication device operating in a wireless communication system,
comprising: the wireless mobile communication device transmitting a
first waveform over a wireless communication link; receiving the
first waveform at each of a plurality of known locations; receiving
at each of the plurality of known locations a reference waveform
produced by a stationary source; for each of the known locations,
producing information indicative of a phase difference between the
first waveform as received at the known location and the reference
waveform as received at the known location; and using said
information to determine the location of the wireless mobile
communication device.
2. The method of claim 1, wherein said transmitting step includes
the wireless mobile communication device transmitting the first
waveform in response to a message transmitted by a further wireless
mobile communication device.
3. The method of claim 1, wherein said first waveform and said
reference waveform are periodic waveforms, said producing step
including, for each of the known locations, determining a plurality
of phase differences between cycles of the first waveform and
corresponding cycles of the reference waveform.
4. The method of claim 3, wherein said producing step includes, for
each of the known locations, averaging the associated plurality of
phase differences to produce an average phase difference.
5. The method of claim 4, wherein said producing step includes, for
each of the known locations, adjusting the associated average phase
difference to produce an adjusted phase difference that accounts
for a known phase delay associated with providing the reference
waveform from the stationary source to the known location.
6. The method of claim 5, wherein said producing step includes, for
each of the known locations, converting the adjusted phase
difference into a quantity of time.
7. The method of claim 1, wherein said using step includes
determining respective distances between the wireless mobile
communication device and a plurality of the known locations.
8. The method of claim 1, wherein the wireless mobile communication
device is a Bluetooth device.
9. A method of determining the location of a wireless mobile
communication device operating in a wireless communication system,
comprising: the wireless mobile communication device transmitting a
first wireless signal at a predetermined transmission power level;
receiving the first wireless signal at a known location and
transmitting a second wireless signal from the known location in
response to the first wireless signal; and determining the location
of the wireless mobile communication device based on the second
wireless signal and the predetermined transmission power level.
10. The method of claim 9, wherein the second wireless signal
includes information indicative of the known location.
11. The method of claim 9, wherein said step of receiving the first
wireless signal includes receiving the first wireless signal at a
plurality of known locations, and wherein said step of transmitting
a second wireless signal includes transmitting a second wireless
signal from each of the plurality of known locations, said
determining step including determining that the wireless mobile
communication device is located within a predetermined distance of
each of the plurality of known locations from which the second
wireless signal has been transmitted.
12. The method of claim 9, wherein said determining step includes
determining that the wireless mobile communication device is
located within a predetermined distance of the known location.
13. The method of claim 9, wherein the wireless mobile
communication device is a Bluetooth device.
14. The method of claim 9, including identifying the known location
based on the second wireless signal.
15. The method of claim 14, wherein said identifying step includes
the wireless mobile communication device receiving the second
wireless signal and identifying the known location based on the
second wireless signal.
16. A wireless communication system, comprising: a wireless mobile
communication device for transmitting a first waveform over a
wireless communication link; a stationary reference source for
producing a reference waveform; a plurality of stationary location
markers respectively provided at a plurality of predetermined
locations for receiving the first waveform, each said location
marker coupled to said reference source for receiving the reference
waveform; each said location marker responsive to the first
waveform and the reference waveform for producing information
indicative of a phase difference between the first waveform and the
reference waveform as received at said location marker; and a
location determiner coupled to said location markers for receiving
said information from said location markers and determining from
said information the location of said wireless mobile communication
device.
17. The system of claim 16, wherein said location determiner is
coupled to said location markers via a wireless communication
link.
18. The system of claim 16, wherein said location determiner is
coupled to said location markers via a wired connection.
19. The system of claim 16, wherein said reference source includes
one of a GPS receiver, an oven-stabilized quartz oscillator, a
Cesium atomic oscillator and a Rubidium atomic oscillator.
20. The system of claim 16, including a further wireless mobile
communication device coupled to said first-mentioned wireless
mobile communication device via a wireless communication link for
requesting said first-mentioned wireless mobile communication
device to transmit said first waveform, and wherein said location
determiner is provided in said further wireless mobile
communication device.
21. The system of claim 20, wherein the wireless communication link
that couples said further wireless mobile communication device to
said first-mentioned wireless mobile communication device includes
one of said location markers.
22. The system of claim 16, wherein said wireless mobile
communication device and said location markers are provided as
Bluetooth communication devices.
23. An apparatus for use in determining the location of a wireless
mobile communication device operating in a wireless mobile
communication system, comprising: an input fixed at a known
location for receiving a first waveform from the wireless mobile
communication device via a wireless communication link; a second
input fixed at said known location for receiving a reference
waveform from a stationary source; a phase comparator coupled to
said inputs for determining a phase difference between said first
waveform and said reference waveform as received at said inputs;
and an output coupled to said phase comparator for outputting
information indicative of said phase difference to a location
determiner which can use said information to determine the location
of the wireless mobile communication device.
24. The apparatus of claim 23, wherein said first waveform and said
reference waveform are periodic waveforms, said phase comparator
operable for determining a plurality of phase differences between
cycles of the first waveform and corresponding cycles of the
reference waveform.
25. The apparatus of claim 24, including an averager coupled to
said phase comparator for receiving said plurality of phase
differences and averaging said phase differences to produce an
average phase difference.
26. The apparatus of claim 25, including a storage section for
storing information indicative of a phase delay associated with
providing said reference waveform from the stationary source to
said second input, and including a phase adjuster coupled to said
averager and said storage section, said phase adjuster responsive
to said phase delay information and said average phase difference
for adjusting said average phase difference to produce an adjusted
phase difference that accounts for said phase delay.
27. The apparatus of claim 23 provided as a Bluetooth device.
28. A wireless mobile communication device, comprising: an output
for transmitting a wireless signal at a predetermined transmission
power level; an input for receiving a wireless response to said
wireless signal, said wireless response including information
indicative of a location of a source of said response; and a
location determiner coupled to said input and responsive to said
information and said predetermined transmission power level for
determining a location of said wireless mobile communication
device.
29. The wireless mobile communication device of claim 28, provided
as a Bluetooth device.
30. The wireless mobile communication device of claim 28, wherein
said input is for receiving a plurality of wireless responses to
said wireless signal, each of said wireless responses including
information indicative of a location of a source of said wireless
response, said location determiner responsive to said predetermined
transmission power level and said information in said plurality of
wireless responses for determining the location of said wireless
mobile communication device.
31. The wireless mobile communication device of claim 30, wherein
said location determiner is operable for determining that said
wireless mobile communication device is located within a
predetermined distance of each of the plurality of sources.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to location determination in
wireless communications and, more particularly, in narrow bandwidth
wireless communication systems.
BACKGROUND OF THE INVENTION
[0002] Present telecommunication system technology includes a wide
variety of wireless networking systems associated with both voice
and data communications. An overview of several of these wireless
networking systems is presented by Amitava Dutta-Roy,
Communications Networks for Homes, IEEE Spectrum, pg. 26, December
1999. Therein, Dutta-Roy discusses several communication protocols
in the 2.4 GHz band, including IEEE 802.11 direct-sequence spread
spectrum (DSSS) and frequency-hopping (FHSS) protocols. A
disadvantage of these protocols is the high overhead associated
with their implementation. A less complex wireless protocol known
as Shared Wireless Access Protocol (SWAP) also operates in the 2.4
GHz band. This protocol has been developed by the HomeRF Working
Group and is supported by North American communications companies.
The SWAP protocol uses frequency-hopping spread spectrum technology
to produce a data rate of 1 Mb/sec. Another less complex protocol
is named Bluetooth after a 10.sup.th century Scandinavian king who
united several Danish kingdoms. This protocol also operates in the
license-free 2.4 GHz band and advantageously offers short-range
wireless communication between Bluetooth devices without the need
for a central network.
[0003] The Bluetooth system provides a 1 Mb/sec data rate with low
energy consumption for battery powered devices operating in the
2.4-GHz ISM (industrial, scientific, medical) band. The current
Bluetooth system provides a 10-meter range and a maximum asymmetric
data transfer rate of 723 kb/sec. The system supports a maximum of
three voice channels for synchronous, CVSD-encoded transmission at
64 kb/sec. The Bluetooth system treats all radios as peer units
except for a unique 48-bit address. At the start of any connection,
the initiating unit is a temporary master. This temporary
assignment, however, may change after initial communications are
established. Each master may have active connections of up to seven
slaves. Such a connection between a master and one or more slaves
forms a "piconet." Link management allows communication between
piconets, thereby forming "scatternets." Any Bluetooth device can
assume the role of master or slave. For example, typical Bluetooth
master devices include cordless phone base stations, local area
network (LAN) access points, laptop computers, or bridges to other
networks. Bluetooth slave devices may include cordless handsets,
cell phones, headsets, personal digital assistants, digital
cameras, or computer peripherals such as printers, scanners, fax
machines and other devices.
[0004] The Bluetooth protocol uses time-division duplex (TDD) to
support bidirectional communication. Frequency hopping permits
operation in noisy environments and permits multiple piconets to
exist in close proximity. The frequency hopping scheme permits up
to 1600 hops per second over 791-MHZ channels or the entire 2.4-GHz
ISM spectrum. Various error correcting schemes permit data packet
protection by 1/3 and 2/3 rate forward error correction. Further,
Bluetooth uses retransmission of packets for guaranteed
reliability. These schemes help correct data errors, but at the
expense of throughput.
[0005] The Bluetooth protocol is specified in detail in
Specification of the Bluetooth System, Version 1.0A, Jul. 26, 1999,
which is incorporated herein by reference.
[0006] Techniques have been developed for identifying the
geographic location of a wireless communication device, for
example, in emergency situations or to provide travel directions.
However, these techniques can be particularly difficult to
implement when the devices are operating indoors. Global
Positioning System (GPS) satellite reception may be impossible, and
wireless telephony may be difficult at best in many locations, such
as the inside of factories, high-rise buildings, parking garages,
shopping malls, subway/train stations and airport terminals.
[0007] It is therefore desirable to provide the capability of
identifying the geographic location of a wireless mobile
communication device that is operating indoors.
[0008] Many conventional approaches to precision location
identification make use of so-called "time of arrival" techniques.
One difficulty with time of arrival techniques is the uncertainty
of time, which can occur at several locations. For example, if it
is desired to locate a particular wireless mobile communication
device, and that device broadcasts a beacon in several time slots,
with each time slot dedicated to a respective base station, then
the uncertainty of the wireless mobile communication device's clock
can be a source of error in the location identification operation.
If the base stations are operated with respectively independent
clocks, then the uncertainty associated with the independent clocks
can also be a source of error in the location identification
operation.
[0009] It is therefore desirable to provide location identification
techniques that avoid disadvantageous time uncertainties.
[0010] Some conventional techniques utilize a wide frequency signal
for location identification. Such a wide bandwidth signal permits a
very narrow pulse width, the timing of which can be precisely
measured. However, this wide bandwidth signal is not available in
narrow bandwidth wireless communication systems such as Bluetooth
systems. For example, the communication bandwidth in Bluetooth
systems is only 1 MHz. Therefore, the smallest bit length is 1
microsecond. Disadvantageously, an error of 1 microsecond in timing
corresponds to a distance uncertainty of 300 meters
(3.times.10.sup.8 meters/second.times.10.sup.-6 seconds). Another
problem encountered in systems such as Bluetooth is that the
preamble defined by the Bluetooth protocol is only long enough to
insure that all data bits are sampled without error. There is no
determination of the start of a bit, or definition of the bit
edge.
[0011] It is therefore desirable to improve the precision of
location identification in narrow bandwidth wireless communication
systems.
[0012] It is also desirable in view of the foregoing to provide
location identification techniques that do not require the
capability of determining a start bit or defining a bit edge.
[0013] The present invention determines, at several known
locations, the phase difference between a known stable reference
signal and a known signal output by the wireless mobile
communication device that is being located. The location of the
wireless communication device can be determined from the phase
difference information obtained at the predetermined locations.
This advantageously permits precise location estimation indoors,
using a relatively narrow bandwidth signal, and also advantageously
avoids the aforementioned problems of time uncertainties and bit
definition. Further according to the invention, the approximate
location of a wireless mobile communication device can be estimated
by transmitting a message from the device at a predetermined power
level, and determining where among a plurality of predetermined
locations the transmitted message has been received.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 diagrammatically illustrates pertinent portions of an
exemplary embodiment of a wireless communication system including
location determination according to the invention.
[0015] FIG. 2 diagrammatically illustrates pertinent portions of
exemplary embodiments of a location marker according to the
invention.
[0016] FIG. 2A illustrates a portion of FIG. 2 in greater
detail.
[0017] FIG. 3 diagrammatically illustrates further capabilities of
the embodiment of FIG. 1.
[0018] FIG. 4 diagrammatically illustrates pertinent portions of an
embodiment similar to FIG. 1 but wherein the location solution
processor is provided in a mobile device which can initiate
location estimation with respect to another mobile device.
[0019] FIG. 5 illustrates exemplary operations which can be
performed by the embodiments of FIGS. 1-4.
[0020] FIG. 6 diagrammatically illustrates pertinent portions of an
exemplary embodiment of a wireless communications system according
to the invention that can roughly approximate the location of a
mobile communication device.
[0021] FIG. 7 illustrates exemplary operations which can be
performed by the embodiment of FIG. 6.
DETAILED DESCRIPTION
[0022] The present invention recognizes two possible approaches to
precision location estimation in narrow bandwidth systems. A first
approach is the use of spread spectrum waveforms. A spread spectrum
waveform can be sent, for example in a conventional Bluetooth data
packet. A Barker code could be used for such a spread spectrum
application, because all of its compressed-pulse time sidelobes are
of uniform size, and the peak value is the bit-length (or
processing gain). The use of a compressed pulse would permit
precision location (by a factor of the processing gain) using a
comparator to find the exact sample time. Although the longest
Barker code is 13 bits, Barker codes can be concatenated by
multiplying each successive Barker code by another. For example, a
length 3 Barker code can be multiplied (convolved) with a length 13
Barker code to generate a unique code of 36 bits.
[0023] To determine the exact bit transition in the spread spectrum
waveform, the waveform must be oversampled by several factors of
the bit rate. In fact, each bit transmitted by the mobile device
that is being located would need to be oversampled, and the time
position of the bits would need to be determined within
nanoseconds. It can therefore be seen that the use of spread
spectrum waveforms can be expected to require an undesirably large
amount of signal processing.
[0024] Another approach according to the present invention is to
match the phase of a narrowband signal (transmitted by the mobile
device to be located) with a network timing reference. For example,
a 1 MHz signal will have a 1 microsecond periodicity. As long as
the geographical distances within the location estimation
environment are less than 300 meters, the phase of the 1 MHz signal
can be detected (relative to a common reference signal) at each of
a plurality of known locations, and the distances to the respective
locations can then be calculated from the relative phases detected
at those locations. Each of the detected phases will be different
from the others, and this will provide the needed positioning
information.
[0025] FIG. 1 diagrammatically illustrates pertinent portions of an
exemplary embodiment of a wireless communication system which can
implement location estimation techniques according to the
invention. The embodiment of FIG. 1 includes a wireless mobile
communication device 5 whose location is to be determined by the
system of FIG. 1. In the example of FIG. 1, the mobile
communication device 5 is a Bluetooth device, for example a
personal digital assistant (PDA), a palmtop computer, an ultralight
laptop computer, or a wireless telephone, operating in a Bluetooth
system. The device 5 includes a Bluetooth transceiver for use in a
variety of short distance wireless information exchanges. One such
information exchange is a "Locate Me" message which is transmitted
via a Bluetooth wireless communication link at 15 to a plurality of
location markers 1-4 which can be conventionally configured to
receive Bluetooth wireless communications. As shown in FIG. 1, the
locations markers 14 are located at different geographic locations.
For example, location marker 1 is located at Cartesian coordinates
x.sub.1, y.sub.1, z.sub.1 and location marker 2 is located at
Cartesian coordinates x.sub.2, y.sub.2, z.sub.2, location marker 3
is located at Cartesian coordinates x.sub.3, y.sub.3, z.sub.3, and
location marker 4 is located at Cartesian coordinates x.sub.4,
y.sub.4, z.sub.4. The "Locate Me" message transmitted by the mobile
device 5 arrives at the various location markers 1-4 at respective
arrival times, namely t.sub.1 for location marker 1, t.sub.2 for
location marker 2, t.sub.3 for location marker 3 and t.sub.4 for
location marker 4.
[0026] According to the invention, the "Locate Me" Bluetooth
message includes, for example, a 1 MHz signal embedded therein, and
the location markers 1-4 measure the phase difference between this
embedded signal and a 1 MHz sine wave frequency reference signal 11
that is produced at a fixed location by a stationary reference
oscillator 6 and is distributed to the location markers 1-4. The
reference signal 11 can be distributed, for example, by coaxial
cable, modified Ethernet or latency-free wireless means. The
reference oscillator 6 can be a GPS reference receiver, or any
suitable stable reference source, for example, an oven-stabilized
quartz oscillator or a Cesium or Rubidium atomic standard
oscillator. One reference oscillator 6 may be used to distribute
the reference signal 11 over an entire building or campus. In some
embodiments, the reference signal 11 has a stability at least four
times that of the internal clock of the mobile device 5.
[0027] The 1 MHz signal embedded in the "Locate Me" message can be
set, for example, to 101010101010. For the set of location markers
1-4 that receive the same "Locate Me" message from the mobile
device 5, the phase difference determined at each location marker
is indicative of the time of arrival of the "Locate Me" message at
that location marker, relative to the time of arrival of the
"Locate Me" message at the other location markers.
[0028] Each of the location markers 1-4 provides to a location
solution processor 7 information indicative of the relative time of
arrival of the "Locate Me" message at that particular location
marker. This relative time of arrival information is designated in
FIG. 1 as t.sub.1RA for location marker 1, t.sub.2RA for location
marker 2, t.sub.3RA for location marker 3 and t.sub.4RA for
location marker 4. The location solution processor 7 uses this
relative time of arrival information, together with other
information indicated in FIG. 1 and discussed in more detail below,
to estimate the location of the mobile device 5. The estimated
location is designated as x.sub.M, y.sub.M, z.sub.M in FIG. 1. This
estimated location information can then be provided, for example,
to emergency service personnel, a location monitoring application,
etc.
[0029] Also as shown in FIG. 1, the "Locate Me" message transmitted
by the mobile device 5 includes a unique identifier which is
uniquely associated with the mobile device, designated as
"unique_ID" in FIG. 1, and also includes a sequence number that the
mobile device 5 assigns to each individual "Locate Me" message,
which sequence number is designated in FIG. 1 as
"sequence_number.sub.N". Thus, if the mobile device 5 transmits a
sequence of individual "Locate Me" messages, the eighth message in
the sequence would have a sequence number of, for example, 8. In
addition to the aforementioned relative time of arrival
information, the location markers 1-4 provide to the location
solution processor 7 the unique identifier and the sequence number
associated with the "Locate Me" message from which the relative
time of arrival information has been determined. The location
markers 1-4 also provide their respective Cartesian coordinates to
the location solution processor 7 along with the relative time of
arrival information. In other embodiments, the location markers can
simply identify themselves to the location solution processor, and
the corresponding Cartesian coordinates of the respective location
markers can be retrieved by the location solution processor from
its own internal storage.
[0030] The combination of the unique identifier, unique_ID, and the
sequence number, sequence_number.sub.N, provides a unique "tag"
associated with the relative time of arrival information and the
Cartesian coordinates provided by a given location marker. The
relative time of arrival information and Cartesian coordinates
supplied by the different location markers must all have the same
"tag" in order to be used by the location solution processor 7 to
calculate the location of the mobile device 5 (or any other mobile
device).
[0031] FIG. 2 diagrammatically illustrates pertinent portions of
exemplary embodiments of the location markers of FIG. 1. The
location marker illustrated in FIG. 2 includes a non-volatile
storage section designated generally at 25. The Cartesian
coordinates x.sub.K, y.sub.K, z.sub.K of the location marker can be
stored in the storage section 25 when the location marker is
initially positioned, for example affixed to a ceiling or wall of a
building or other structure. Site surveys and interior plans used
to construct the surrounding structure can be used to provide the
Cartesian coordinates precisely. The Cartesian coordinate system
may be defined relative to a local origin that is particularly
useful for identifying relative locations within the structure. As
another example, the coordinate system could be the Earth-Centered
Earth-Fixed (ECEF) coordinate system conventionally used in GPS
position calculations. This may be useful for identifying locations
within the structure relative to locations at some distance outside
of the structure.
[0032] Also at the time that the location marker is installed, a
system calibration procedure can be used to measure the propagation
delay from the source of the stable frequency reference 11 (see 6
in FIG. 1) to the location marker. The resulting phase delay
parameter .PHI..sub.K is then also stored in the storage section
25. For a set of location markers covering a given area, such as
illustrated in FIG. 1, the differences between the phase delay
parameter values must be accounted for in the location solution
processing (see 7 in FIG. 1), but the phase delay parameter values
themselves are not required. Thus, for example, in the exemplary
illustrated system using a 1 MHz frequency reference, the phase
delay parameters .PHI..sub.K of the respective markers can be
expressed in radians, and a phase delay value of 0.0 radians can be
assigned to the location marker having the shortest propagation
delay from the frequency reference source 6 of FIG. 1.
[0033] The exemplary location marker of FIG. 2 includes a Bluetooth
wireless transceiver having a radio and baseband section 21 and a
message processing section 22. The Bluetooth wireless transceiver
permits the location marker to exchange Bluetooth wireless
communications with other Bluetooth transceivers. For example, the
location marker can receive the "Locate Me" message of FIG. 1 via
the antenna 29 of the Bluetooth wireless transceiver. Also, the
location marker can use the Bluetooth wireless transceiver to
transmit to the location solution processor 7 of FIG. 1 the tag, as
shown at 202. In other embodiments, this information can be
transmitted to the location solution processor 7 via a wired
connection, as illustrated generally at 201 in FIG. 2.
[0034] The exemplary location marker of FIG. 2 also includes a 1
MHz phase comparator 23 which can measure the phase difference
between the stable 1 MHz reference signal 11, and the 1 MHz
waveform embedded in the "Locate Me" message. This latter waveform
is extracted from the "Locate Me" message by the radio and baseband
section 21, and is forwarded to the phase comparator 23. In the
example of FIG. 2, the phase comparator 23 has a 0.001 cycle
(6.2832 milliradian) phase difference resolution capability, which
corresponds to an 11.8 inch resolution in the distance between the
location marker and the mobile device 5 of FIG. 1. To compensate
for phase jitter in the "Locate Me" message, the phase comparator
23 measures the phase difference 206 for several successive 1 MHz
cycles (e.g., 1000 or more cycles of the embedded waveform), and
these successive measurements are averaged by a phase difference
averager 24 to produce a phase difference average 205 for the
entire "Locate Me" message.
[0035] The averager 24 outputs the average phase difference 205 to
a relative arrival time generator 26 which also receives the
location marker's phase delay parameter .PHI..sub.K from the
storage section 25, and generates therefrom the relative time of
arrival, t.sub.RA of the "Locate Me" message. The relative time of
arrival generator 26 adds the average phase difference 205 to the
phase delay parameter .PHI..sub.K, thereby adjusting the average
phase difference for the relative phase delay associated with
distribution of the reference signal 11 from the source 6 of FIG. 1
to the location marker. The result is divided by 2.pi. to provide
the relative message arrival time t.sub.RA in units of
microseconds. The above-described average phase difference
adjustment and division operations are respectively performed by
the phase difference adjuster and divider of FIG. 2A. The relative
message arrival time t.sub.RA is then provided to a location
solution data output 27 along with the Cartesian coordinates of the
location marker (from the storage section 25) and the
aforementioned "tag" information (sequence number of the "Locate
Me" message and unique identifier of the mobile device 5). The
location solution data output combines the relative message arrival
time information, the Cartesian coordinates, and the tag
information in a message that is transmitted to the location
solution processor 7 via either the wired connection 201 (e.g.,
ethernet) or the wireless connection 202 (e.g., a Bluetooth radio
link).
[0036] The above-described operations of the location marker of
FIG. 2 are initiated when the Bluetooth transceiver detects the
start of an arriving message. At this time, the radio and baseband
section 21 activates the phase comparator 23 and the phase
difference averager 24. When the Bluetooth transceiver has received
the complete message and has identified it as a "Locate Me"
message, the message processing section 22 applies a start signal
204 to both the relative arrival time generator 26 and the location
solution data output 27. Also after the complete message has been
received and identified as a "Locate Me" message, the message
processing section 22 provides the aforementioned tag information
to the location solution data output 27.
[0037] Referring again to the location solution processor 7 of FIG.
1, this processor can be, for example, dedicated to a particular
network of location markers for the purpose of calculating precise
locations using information received from those location markers.
In one exemplary embodiment, the location solution processor 7 uses
information from at least 4 non-coplanar location markers and
solves simultaneous equations derived from the Cartesian
coordinates of the location markers and the differences between the
relative times of arrival t.sub.RA reported by the location
markers.
[0038] Exemplary FIG. 3 is generally similar to FIG. 1, but
illustrates that, even when information is available from only
three location markers, namely location markers 1, 2 and 4, the
location solution processor 7 can still determine the relative
proximity of the mobile device 5 to those location markers. In the
example of FIG. 3, the location solution processor uses the
information reported by the location markers 1, 2 and 4 to
determine that the mobile device 5 is 31 meters closer to location
marker 2 than to location marker 4, and is 7 meters closer to
location marker 1 than to location marker 2. This relative
proximity information is output from the location solution
processor 7 at 35, and can be used, for example, by Bluetooth
network control for routing messages and balancing message traffic
in a Bluetooth network.
[0039] Exemplary FIG. 4 is also generally similar to FIG. 1, except
another wireless mobile communication device 51 (a Bluetooth device
in the example of FIG. 4) initiates the process of estimating the
location of a mobile communication device 5B. The process is
initiated when the mobile device 51 broadcasts at 52 a digitally
signed "Where Is" message that includes the unique identifier of
the mobile device 5B. The message at 52 can be relayed through the
Bluetooth network to device 5B, for example via the transceivers of
one or more of the location markers 1B-4B, as shown at 42 and 44.
This "Where Is" message relaying is also illustrated in FIG. 2,
where the "Where Is" message can be recognized by the message
processing section 22 and relayed accordingly.
[0040] When the mobile device 5B receives the relayed message and
recognizes that the message includes its unique identifier, the
mobile device 5B first examines the digital signature to determine
whether the originator of the "Where Is" message (mobile device 51)
is authorized to know the location of mobile device 5B. If the
mobile device 51 is authorized to know the location of the mobile
device 5B, then the mobile device 5B begins transmitting the
aforementioned "Locate Me" messages, and the location estimation
can thereafter proceed generally as described above with respect to
FIG. 1. Note that the location markers 1B-4B make their respective
reports to the mobile device 51 (which is identified by the digital
signature in the "Where Is" message) via the Bluetooth network as
illustrated generally at 53. The mobile device 51 can include the
functionality of the location solution processor 7 of FIG. 1 in
order to calculate the precise location of the mobile device 5B.
The above-described operation of the FIG. 4 embodiment can be
useful, for example, when a parent in possession of mobile device
51 wants to determine the location of a lost child who possesses
the mobile device 5B.
[0041] FIG. 5 illustrates exemplary operations which can be
performed by the embodiments of FIGS. 1-4. After transmission of
the "Locate Me" message at 55, a single timing reference (e.g., a
stable 1 MHz sine wave) is used at 56 to determine the times of
arrival of the "Locate Me" message at a plurality of known
locations. Thereafter at 57, the differences between the respective
times of arrival are used to estimate the location of the mobile
device that transmitted the "Locate Me" message.
[0042] FIG. 6 diagrammatically illustrates pertinent portions of a
further exemplary embodiment of a wireless communication system
according to the invention. In the embodiment of FIG. 6, a
Bluetooth-equipped wireless mobile communication device 5A
broadcasts an "Approximate Location?" message over a Bluetooth
wireless communication link at 62. Each of the location markers
1A-4A that receives the "Approximate Location?" interrogatory
responds by transmitting its Cartesian coordinates to the mobile
device 5A. As one example, if the mobile device 5A transmits the
"Approximate Location?" message at a predetermined, relatively low
power level, and receives one or more responses from the location
markers 1A-4A, then the location of the mobile device 5A lies
within a predetermined distance (e.g., approximately 10 meters) of
the Cartesian coordinates specified in the location marker
response(s). As another example, if the mobile device 5A transmits
the "Approximate Location?" message at a predetermined, relatively
high power and receives one or more responses, then the mobile
device 5A is known to be located within another predetermined
distance (e.g., approximately 100 meters) of the Cartesian
coordinates specified in the location marker response(s). The
device 5A includes a location estimator which receives the
response(s) and can estimate the device's location based on the
response(s) and the corresponding Cartesian coordinates.
[0043] For example, in FIG. 6, if only the location marker 1A
responds to the low-power message, then the mobile device 5A is
located within, in this example, approximately 10 meters of the
Cartesian coordinates x.sub.1, y.sub.1, z.sub.1. Also, if all four
location markers 1A-4A in FIG. 6 respond to the high-power message,
then the mobile device 5A is located, in this example, within
approximately 100 meters of the Cartesian coordinates of each of
the location markers 1A-4A. The location information obtained by
using the "Approximate Location?" message can then be used by the
mobile device 5A to determine, for example, where the nearest
automated teller machine is located, or travel directions from its
current location to a desired location. The above-described
interaction of the location markers 1A-4A with the mobile device 5A
is also illustrated in FIG. 2, where the "Approximate Location?"
message can be recognized (or not) by the message processing
section 22 and responded to appropriately.
[0044] FIG. 7 illustrates exemplary operations which can be
performed by the embodiment of FIG. 6. The "Approximate Location?"
message is transmitted at a predetermined power level at 71.
Thereafter, the mobile device receives the response(s) from the
known location(s) at 72. Thereafter at 73, the approximate location
of the mobile device 5A is estimated based on the power level that
was used to transmit the "Approximate Location?" message and the
location(s) that responded to the message.
[0045] It should be clear from the foregoing description that the
operational features of the exemplary location markers 1, 1A and 1B
can be combined together in a single location marker embodiment
according to the invention, and that the operational features of
the mobile devices 5, 5A and 5B can be combined together in a
single mobile device 5 embodiment according to the invention.
Moreover, it will be evident to workers in the art that the
above-described wireless mobile communication device embodiments
according to the invention can be readily implemented by, for
example, suitable modifications in software, hardware, or a
combination of software and hardware in conventional wireless
mobile communication devices, for example Bluetooth devices.
[0046] As demonstrated above, the present invention does not depend
on the ability to receive signals directly from GPS satellites
while inside large structures whose walls and ceilings attenuate or
block satellite signals. Also, location estimation according to the
invention does not depend on communication between wireless
telephones and their base stations. If the location markers of the
present invention are affixed to the ceilings and permanent walls
of a large structure, a user's location can be determined anywhere
within the structure, without any need for the user to exit the
structure or move to its periphery for better wireless reception.
Advantageously, the invention also does not depend on any clock in
the mobile device that is being located, does not use measurements
of range or transmission direction in the location estimation
process, and does not utilize received signal power measurements as
indirect measures of range. There is also no dependence on
multi-element steerable antennas to determine the direction from
which a transmitted signal is coming. Other exemplary advantages of
the invention include the fact that the location markers of the
invention can be used to transmit (e.g., relay) any desired
information to the mobile devices operating in the wireless
communication system, and the location markers do not require
accurate and expensive clocks.
[0047] Although exemplary embodiments of the invention are
described above in detail, this does not limit the scope of the
invention, which can be practiced in a variety of embodiments.
* * * * *