U.S. patent application number 14/284044 was filed with the patent office on 2015-03-12 for gps-assisted source and receiver location estimation.
This patent application is currently assigned to MaxLinear, Inc.. The applicant listed for this patent is MaxLinear, Inc.. Invention is credited to Curtis LING, Stuart Strickland.
Application Number | 20150073706 14/284044 |
Document ID | / |
Family ID | 43449868 |
Filed Date | 2015-03-12 |
United States Patent
Application |
20150073706 |
Kind Code |
A1 |
LING; Curtis ; et
al. |
March 12, 2015 |
GPS-ASSISTED SOURCE AND RECEIVER LOCATION ESTIMATION
Abstract
A mobile communication device includes, in part, a first
wireless receiver adapted to determine, as it travels along a path,
a multitude of positions of the mobile communication device using
signals received from a primary positioning source, a second
wireless receiver adapted to receive signals from one or more
ambient wireless sources as the mobile communication device travels
along the path, and a positioning module. An internal or external
memory stores estimated positions and corresponding time references
of the signals of the one or more ambient sources. The positioning
module uses the data stored in the database to estimate the
position of the mobile communication device when no primary
positioning source signal is available. The positioning module
optionally uses the data stored in the database to improve
estimates of the position of the mobile communication device when
primary positioning signal is available.
Inventors: |
LING; Curtis; (Carlsbad,
CA) ; Strickland; Stuart; (Carlsbad, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MaxLinear, Inc. |
Carlsbad |
CA |
US |
|
|
Assignee: |
MaxLinear, Inc.
Carlsbad
CA
|
Family ID: |
43449868 |
Appl. No.: |
14/284044 |
Filed: |
May 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12839362 |
Jul 19, 2010 |
8766849 |
|
|
14284044 |
|
|
|
|
61226629 |
Jul 17, 2009 |
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Current U.S.
Class: |
701/491 ;
701/519 |
Current CPC
Class: |
G01S 5/0045 20130101;
G01S 19/48 20130101; G01S 5/10 20130101; G01S 5/0236 20130101; G01C
21/20 20130101 |
Class at
Publication: |
701/491 ;
701/519 |
International
Class: |
G01C 21/20 20060101
G01C021/20 |
Claims
1. A mobile communication device comprising: a first wireless
receiver adapted to determine, as it travels along a path, a
plurality of positions of the mobile communication device using
signals received from a primary positioning source; a second
wireless receiver adapted to receive signals from one or more
ambient wireless sources as the mobile communication device travels
along the path; and a positioning module adapted to use the
determined plurality of positions of the mobile communication
device and the received ambient wireless signals to estimate
positions of the ambient sources.
2. The mobile communication device of claim 1 further comprising a
database operative to store estimated positions and corresponding
time references of the signals of the one or more ambient
sources.
3. The mobile communication device of claim 1 further comprising a
transceiver operative to access and store estimated positions of
the one or more ambient sources and their corresponding time
references in an external database.
4. The mobile communication device of claim 1 wherein said primary
positioning source comprises satellite based communication sources
and wherein said ambient sources comprise digital television
sources, digital radio sources and cellular phone sources.
5. The mobile communication device of 4 wherein said primary
positioning source is selected from a group consisting of GNSS and
GPS systems.
6. The mobile communication device of 4 wherein said ambient source
is selected from a group consisting of DVB-T, DVB-H, ISDB-T, CMMB,
MediaFLO, ATSC, DAB, CDMA, W-CDMA, GSM, LTE, WiFi, and WiMax.
7. The mobile communication device of 1 wherein the module is
further adapted to estimate differential distances to the ambient
sources and apply trilateration technique to the estimated
differential distances to estimate distances to the ambient
sources.
8. The mobile communication device of 1 wherein said module
estimates positions of the ambient sources using markers carried by
signals transmitted by the ambient sources.
9. The mobile communication device of 1 wherein said module
estimates positions of the ambient sources using one or more fields
disposed in the frames transmitted by the ambient sources.
10. A system comprising: an external database accessible to a
plurality of communication devices and adapted to store estimated
positions of a plurality of ambient sources, said external database
further adapted to receive and store updates of the estimated
positions as the estimates are generated, said external database
being further adapted to supply estimates of the positions of the
ambient source to the plurality of communication devices in order
to enable the plurality of communication devices to estimate their
positions using data stored in the external database.
11. The system of claim 10 wherein each of the plurality of
communication devices comprises a receiver receiving signals
generated from one or more ambient sources and a transceiver for
accessing the external database, each of the mobile communication
devices operative to estimate its position using the signals
received from the one or more ambient sources and the estimated
position data stored in the external database.
12. A method comprising: determining a plurality of positions of a
mobile communication device using signals received from one or more
primary positioning sources as the mobile communication device
travels along a path; receiving signals from one or more ambient
wireless sources as the mobile communication device travels along
the path; and estimating positions of the ambient sources using the
determined plurality of positions and the received ambient wireless
signals.
13. The method of claim 12 further comprising: storing estimated
positions and corresponding time references of the one or more
ambient sources in an internal database.
14. The method of claim 12 further comprising: storing estimated
positions and corresponding time references of the one or more
ambient sources in an external database.
15. The method of claim 12 wherein said one or more primary
position sources comprise satellite based communication sources and
wherein said ambient sources comprise digital television, digital
radio and cellular phone transmission sources.
16. The method of claim 12 wherein said primary position sources
are selected from a group consisting of GNSS and GPS systems.
17. The method of claim 12 wherein said ambient source is selected
from a group consisting of DVB-T, DVB-H, ISDB-T, CMMB, MediaFLO,
ATSC, DAB, CDMA, W-CDMA, GSM, LTE, WiFi, and WiMax.
18. The method of claim 12 further comprising: estimating
differential distances to the one or more ambient sources; and
applying a trilateration algorithm to the estimated differential
distances to estimate positions of the ambient sources.
19. The method of claim 12 further comprising: estimating positions
of the ambient sources using markers carried by signals transmitted
by the one or more ambient sources.
20. The method of claim 19 wherein said marker represents a
boundary frame.
21. A mobile communication device comprising: a wireless receiver
adapted to receive signals from one or more ambient wireless
sources as the mobile communication device travels along a path; a
transceiver operative to access a database storing data
representative of estimated positions of the one or more ambient
sources; and a positioning engine operative to use the data stored
in the database to estimate a position of the mobile communication
device.
22. The mobile communication device of claim 21 wherein said
positioning engine to estimate the position of the mobile
communication device without using data from a satellite
communication system.
23. A method of estimating a position, the method comprising:
receiving by a mobile device signals from one or more ambient
wireless sources while traveling along a path; accessing data
representative of estimated positions of one or more ambient
sources; and using the estimated positions of the one or more
ambient sources to estimate a position of the mobile device without
using a satellite communication system.
24. The method of claim 23 further comprising: estimating the
position of the mobile device without using a satellite
communication system.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This Application is a continuation of U.S. application Ser.
No. 12/839,362, filed on Jul. 19, 2010 and entitled "GPS-ASSISTED
SOURCE AND RECEIVER LOCATION ESTIMATION", which Application claims
benefit under 35 USC 119(e) of U.S. provisional application No.
61/226,629, filed on Jul. 17, 2009 and entitled "GPS-ASSISTED
SOURCE AND RECEIVER LOCATION ESTIMATION," the contents of which are
incorporated herein by reference in their entirety.
[0002] The present application is related to U.S. application Ser.
No. 12/830,245, filed Jul. 2, 2010, the content of which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0003] Traditional means of location estimation using a wireless
receiver and known beacons, as is implemented in a traditional GPS
system, require knowledge of the position of four or more beacons
and the distance of the receiver from each beacon. Three beacons
may be used if assumption about location on the earth's spherical
surface is made.
BRIEF SUMMARY OF THE INVENTION
[0004] In accordance with an embodiment of the present invention, a
mobile communication device includes, in part, a first wireless
receiver adapted to determine, as it travels along a path, a
multitude of positions of the mobile communication device using
signals received from a primary positioning source, a second
wireless receiver adapted to receive signals from one or more
ambient wireless sources as the mobile communication device travels
along the path, and a module adapted to use the multitude of
determined positions of the mobile communication device and the
received ambient wireless signals to estimate positions of the
ambient sources.
[0005] In one embodiment, the mobile communication device includes
an internal memory or database operative to store estimated
positions and corresponding time references of the signals of the
one or more ambient sources. In another embodiment, the mobile
communication device includes a transceiver that accesses and
stores or retrieves estimated positions of the one or more ambient
sources and their corresponding time references in an external
memory or database. In one embodiment, the primary positioning
source includes satellite based communication sources. In one
embodiment, an ambient source includes digital television, digital
radio transmission, or cellular based stations.
[0006] In one embodiment, the mobile communication devices is
further adapted to estimate differential distances to the ambient
sources and apply a trilateration technique to the estimated
differential distances to estimate distances to the ambient sources
and to determine the position of the mobile communication device.
In one embodiment, the positions of the ambient sources are
estimated using markers carried by signals transmitted by the
ambient sources. In one embodiment, the positions of the ambient
sources are estimated using one or more fields disposed in the
frames transmitted by the ambient sources.
[0007] In accordance with one embodiment of the present invention,
an external database is accessible to a multitude of communication
devices and is adapted to store estimated positions of a number of
ambient sources as well as corresponding times of markers
transmitted by the ambient sources. The external database is
further adapted to receive and store updates to the estimated
positions as the estimates are generated. The external database is
further adapted to supply estimates of the positions of the ambient
sources as well as corresponding times of markers transmitted by
the ambient sources to any another communication device that can
gain access to the database. Such access enables a mobile device
that has no access to a primary positioning signal to estimate its
position using data stored in the external database.
[0008] A method of estimating positions of a number of ambient
wireless sources, in accordance with one embodiment of the present
invention, includes in part, determining a multitude of positions
of a mobile communication device using signals received from one or
more primary positioning sources as the mobile communication device
travels along a path, receiving signals from one or more ambient
wireless sources as the mobile communication device travels along
the path, and estimating positions of the ambient sources using the
determined plurality of positions and the received ambient wireless
signals.
[0009] In one embodiment, estimated positions and corresponding
time references of the one or more ambient sources are stored in an
internal memory or database.
[0010] In one embodiment, the primary positioning source includes
satellite based communication sources. In one embodiment, ambient
sources include digital television, digital radio transmission, or
cellular based stations.
[0011] In one embodiment, the estimated differential distances to
the ambient sources are applied to a trilateration technique to
generate estimates of distances to the ambient sources. In one
embodiment, the positions of the ambient sources are estimated
using markers carried by signals transmitted by the ambient
sources. In one embodiment, the positions of the ambient sources
are estimated using one or more fields disposed in the frames
transmitted by the ambient sources. The estimated positions of the
ambient sources are used to estimate the position of the mobile
communication device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a wireless receiver in communication with a
primary positioning system, an ambient signal source, and internal
an external databases, in accordance with one embodiment of the
present invention.
[0013] FIG. 2 shows a number of frames transmitted by an ambient
source and received by the receiver at a number of locations.
[0014] FIG. 3A shows an exemplary DTV signal received by a DTV
receiver in frequency domain and used to locate positions in
accordance with one embodiment of the present invention.
[0015] FIG. 3B shows the signal of FIG. 3A transformed into time
domain and used to locate positions in accordance with one
embodiment of the present invention.
[0016] FIG. 4 shows a wireless receiver in communication with an
ambient signal source and a databases, in accordance with one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] In accordance with embodiments of the present invention, the
position of a receiver traveling along a path is estimated using
signals transmitted from digital radio or TV broadcasts, such as
those conforming with DVB-T, DVB-H, ISDB-T, CMMB, MediaFLO, ATSC,
DAB standards, signals transmitted from cellular phone systems,
such as GSM, 3G, CDMA, W-CDMA, LTE, WiFi, WiMax, or the like, as
well as any other sources of such signals that are synchronized to
stable time bases and either do not know or do not broadcast their
precise locations. All such signals are collectively referred to
herein as ambient signals. Sources generating ambient signals are
referred to as ambient sources. The positions estimated using
ambient sources may be enhanced using signals transmitted from
primary positioning systems such as the satellite based systems
(e.g., GNSS, GPS). Signals transmitted by a satellite based system
are collectively referred to as primary positioning signals.
Sources generating primary positioning signals are referred to as
primary positioning sources.
[0018] The following description of the exemplary embodiments of
the present invention is provided with reference to an ambient
signal transmitted from a DTV system and a primary positioning
signal transmitted from a GNSS system. It is understood however
that any other source of ambient signals and any other source of
primary positioning signals may be used by embodiments of the
present invention.
[0019] In accordance with embodiments of the present invention, a
receiver establishes the positions of some or all of ambient
sources whose signals are received by the receiver. The receiver
subsequently uses positions of ambient sources (also referred to
herein as ambient beacons or beacons) when the primary positioning
system(s) becomes unavailable or is otherwise impaired. The
positions of ambient beacons may be uploaded to a database or
otherwise made accessible to other receivers within the range of
the same ambient beacons to establish the receivers' positions
without any need for the primary signals.
[0020] A receiver system (alternatively referred to herein as
receiver), in accordance with one embodiment of the present
invention, includes, in part, a receiver and a network-accessible
database which exchanges information with the receiver. The
receiver has access to the database through one or more wireless or
wireline networks. The receiver is adapted to concurrently receive
primary positioning signals as well as ambient signals. Such a
receiver performs the following operations in accordance with
embodiments of the present invention.
[0021] Using the primary positioning signal (e.g. the GNSS
signals), the receiver establishes data corresponding to the
receiver's positions and the associated times that the receiver was
present in each such position (due, for example, to the natural
motion of the receiver).
[0022] Concurrently, since the receiver is also receiving ambient
signals at each such position, the receiver also establishes time
reference for each received ambient signal. Using this information,
and as described further below, the receiver establishes the
positions and corresponding time references associated with the
ambient sources. The positions and corresponding time references of
the ambient sources are uploaded to a database via one or more
wireless or wireline networks or otherwise made available to other
receiver systems. The positions and time references for the ambient
sources may also be downloaded from the database or otherwise
communicated to and used by a receiver which does not have access
to a primary positioning source. Therefore, such a receiver despite
not having access to primary positioning signals, is enabled in
accordance with embodiments of the present invention, to estimate
its position using only the ambient sources whose signals can be
received by the receiver.
[0023] In the following description as well as in the Figures the
following indexing convention is used. A quantity such as distance
D, or receiver location LR, is typically indexed using two indices
i and j, e.g. D.sub.ij or LR.sub.ij. The first index i identifies
the ambient source related to the quantity, and the second index j
identifies the position of the receiver to the ambient source. For
example, D.sub.12 refers to the distance from ambient source 1 to
the receiver position 2.
[0024] FIG. 1 shows a receiver 100 that includes a primary
positioning receiver 102 as well as an ambient signal receiver 104.
Primary positioning receiver 102, that may be a GNSS receiver,
enables receiver 100 to estimate its positions and obtain the
associated times that the receiver is present in each such position
as is travels along the path 140 using the GNSS signals received
from GNSS system 250. It is assumed herein that the estimated
positions and the associated times obtained from the primary
positioning receiver correspond substantially to the actual values
of such positions and times. In one embodiment, receiver 100 has a
database 106 that stores the positions and time values obtained
using the primary positioning receiver 102 disposed in receiver
100. In another embodiment, receiver 100 includes a transceiver 108
enabling receiver 100 to store the position and time values
obtained using the primary positioning receiver 102 in an external
database 170 via network 160. Access to database 170 may be
provided from network 160 using the Internet. Receiver 100 may
operate in a number of different modes as described further
below.
Ambient Source Localization
[0025] In this mode of operation, receiver 100 receives signals
from both primary positioning sources as well as ambient sources.
Receiver 100 uses the signals transmitted from the primary
positioning source 250 to establish its position along a multitude
of points while traversing path 140. Since receiver 100 is also in
the range of one or more ambient sources, such as ambient source 1,
as receiver 100 traverses along path 140, it receives from ambient
source 1 signal AS.sub.1i at location LR.sub.1i, at time TR.sub.1i,
where i is an integer varying from 1 to N. Receiver 100 then uses
the position data obtained from the primary positioning source to
determine the position of ambient source 1, as described further
below. Receiver 100 uses the same technique to determine the
position of any other source of ambient signals. It is understood
that the signals from the primary positioning source and the
ambient source need not be received simultaneously so long as
receiver 100 has a time base which is relatively stable over short
time intervals (such as a few seconds), as is widely available in
consumer products today.
[0026] To determine the position of ambient sources, the ambient
sources are assumed to transmit their signals with markers
MM.sub.1i (e.g., frame boundaries or any characteristics that occur
in known locations within the frame) whose time intervals are known
in advance in a predictable manner, as is the case with frame
boundaries in many transmission protocols. FIG. 2 shows a number of
frames transmitted by ambient source 1 as received by receiver 100.
To determine the position of ambient source 1, receiver 100 is
adapted to perform the following operations.
[0027] Referring to FIG. 2, frame boundary MM.sub.11 of signal
AS.sub.11 transmitted by ambient source 1 is shown as being
received by receiver 100 at time TR.sub.11. Receiver 100 associates
time TR.sub.11 with position L.sub.11. Time TR.sub.12' is the
expected reception time of frame boundary MM.sub.12 if receiver 100
were to remain stationary at position L.sub.11. Likewise, receiver
100 associates time TR.sub.1i at which signal AS.sub.1i is received
with position L.sub.1i, where index i identifies the position of
the receiver. But since receiver 100 is assumed to be moving, it
receives frame MM.sub.12 at time TR.sub.12 at position LR.sub.12.
The difference between times TR.sub.12 and TR.sub.12', i.e.,
(TR.sub.12-TR.sub.12') is shown in FIG. 2 as DT.sub.12. The product
of DT.sub.12 and the speed of light in air represents the
difference between D.sub.12 and D.sub.11, designated herein as
DD.sub.121. In general, for differential distance DD.sub.ijk, index
i corresponds to the ambient source, and indices j and k correspond
to positions of the receiver. It is understood that frames
MM.sub.11, MM.sub.11+1 . . . are not actually received at position
LR.sub.12 and are only shown to indicate their relative expected
reception times by receiver 100 at that location. Frames that are
not received by receiver 100 and are only included to aid in
understanding embodiments of the present invention are shown using
diagonally hashed lines.
[0028] In a similar manner, for ambient source 1, the difference
between D.sub.1j and D.sub.1k may be calculated to determine the
differential distances DD.sub.1jk. These differential distances and
their associated locations LR.sub.1j and LR.sub.1k are subsequently
used by well-known trilateration techniques to establish an
estimate of the position (LT.sub.1) of ambient source 1. It is
understood that with more data points, estimated position LT.sub.1
may be improved through filtering and other known noise reduction
techniques. In a similar manner, the position LTi of any number of
ambient sources may be obtained.
[0029] One example of an ambient source suitable for use in
accordance with embodiments of the present invention is the GSM
system in conformity with which a cellular base station transmits
frames of data in regular, precisely-timed intervals. The frame
boundaries of GSM signals may be used as markers. Another example
is the DTV broadcast system in conformity with which digital data
is broadcast in frames which are frequently synchronized to a
system clock to implement what is commonly referred to as
single-frequency networks (SFN). Broadcast towers of an SFN system
covering a region transmit data in a synchronous fashion. The
absolute time TTAi of transmission of the markers MMij can also be
determined.
[0030] Once the position LT, of an ambient source i is estimated by
a receiver, as described above, the receiver may store the position
information in either or both databases 106 and 170, depending, for
example, on their availability. Such information includes, among
other things, the identity of the ambient source i, the position
LTi of ambient source i, the absolute time TTAi associated with its
marker MMij, time of upload of the data, confidence level, and any
other statistics of the estimated data and ambient source, such as
average offset of the ambient source.
Use of Ambient Sources to Establish Position
[0031] In this mode of operation, receiver 100 detects and
identifies ambient sources that are in its vicinity and whose
signals are received by receiver 100. Receiver 100 retrieves the
associated data and statistics for such ambient sources from its
own database 106 or an external database 170, depending on their
availability. The reception of signals from the ambient sources
need not be simultaneous as long as receiver 100 maintains a time
base which is relatively stable over short time intervals, as is
widely available in mobile devices. With this information retrieved
from such a database, receiver 100 may extract the difference in
distances among the different ambient sources it is receiving
signals from, and using the knowledge of their positions,
trilaterates to determine the position of receiver 100, even in the
absence of a GNSS signal or an accurate time estimate. FIG. 4 shows
a receiver 100 that estimates its position using signals received
only from ambient source 300 and external database 170.
Assisted Location
[0032] In this mode of operation, receiver 100 uses the information
it retrieves from its own database 106 or an external database 170
about one or more ambient sources to compute the positions of such
sources and further to improve the accuracy or the acquisition time
of the signals received from the primary positioning source.
Accordingly, in this mode the ambient sources are treated as
additional primary sources. This information is delivered to a
standard positioning engine which trilaterates the position of
receiver 100. For example, relatively few base stations may be
within the range of receiver 100. In such cases, the receiver may
supplement the data received from the primary positioning source
with data retrieved from internal database 106 or external database
170 to enable the positioning engine to improve the accuracy of the
estimated position of the receiver.
Database Functions
[0033] In addition to receiving and storing the position, absolute
transmission time of the markers, upload time and confidence
(certainty) estimates from the receiver and subsequently permitting
retrieval of this information, the database may also track
information such as the relative stability of each ambient source
over time (e.g. offsets or drifts). It may compute a more accurate
estimate of the ambient source information using an ensemble of
information obtained from a large number of receivers about these
ambient sources.
Enhancements
[0034] The receiver may be enhanced to obtain more accurate
estimates of the time of arrival of markers MMi. FIG. 3A shows a
DTV signal received by a DTV receiver in the frequency domain. FIG.
3B shows the signal of FIG. 3A transformed into time domain in
accordance with an embodiment of the present invention. The DTV
receiver uses OFDM modulation and pilot tones PTi or training
sequences, as defined by the DTV standards, to demodulate the DTV
signal. The pilot tones PTi in the frequency domain may be used by
the receiver to obtain a time-domain estimate of the channel
impulse response 225 (shown in FIG. 3B) using an inverse FFT.
[0035] Referring to FIG. 3B, because of channel impairments such as
multipath, the receiver may receive the ambient signal in a direct
path at time P1 as well as echoes at P2 and P3. The receiver may
use the pilot tones PTi, or training sequences commonly available
in wireless transmission standards, to estimate the channel and
extract P1 from the total signal, thereby obtaining a more accurate
estimate for precise first time of arrival of markers MMij.
[0036] The DTV receiver system may be optimized for the purpose of
location estimation, as described further below. The receiver may
perform averaging, filtering and other noise-reduction techniques
on the pilot tones PTi or training sequences to reduce the
effective bandwidth of the receiver and thereby significantly
increase its sensitivity. In the DTV standard, this involves
averaging over the continuous and scattered pilot tones to sense
transmission towers that are much farther than conventional TV
reception ranges.
[0037] In a CMMB system, the signals present at the beginning of
each frame includes two consecutive known symbols which can be used
to obtain very long-distance, accurate estimates of differential
distance among transmission towers. Furthermore, the receiver may
switch frequencies and receive other DTV channels to obtain
relative distance information at other frequencies to improve the
estimation of the relative distance. This has the benefit of
providing the system with a diverse range of signal sources, some
of which may be stronger and more easily received.
[0038] The databases uses in accordance with embodiments of the
present invention provide a number of other advantages, as
described further below. A multitude of receivers may share access
to the same external database, thereby building up a shared source
of information regarding ambient sources. This allows users to
benefit from collective knowledge of the positions of ambient
sources without determining them independently. It also allows the
accuracy and validity of the shared database to be checked and
improved by data from a large number of users.
[0039] The sharing and further improvements of such a database
enables receivers which do not have a built-in primary positioning
receiver to determine their positions using other ambient source
signals that they can receive to determine their positions
accurately. The database can also be used to obtain statistical
information concerning the positions of users of such a shared
database and system at any given time. This information can be
extremely valuable for the purposes of marketing, planning, or
emergency services.
[0040] Furthermore, the timing and position information about
ambient sources which are not adequately stable may be stored and
updated in the shared database when the database is updated by a
sufficient number of users. So long as the timing information about
the less stable sources is updated with sufficient frequency to
keep the accumulated timing error within bounds acceptable to a
particular application, users within range of such less stable
sources can use them as ambient signal sources for positioning
purposes.
[0041] The above embodiments of the present invention are
illustrative and not limiting. Various alternatives and equivalents
are possible. The invention is not limited by the type or the
number of primary positioning systems. The invention is not limited
by the type or the number ambient sources. The invention is not
limited by the rate used to transfer the data. The invention is not
limited by the type of integrated circuit in which the present
disclosure may be disposed. Nor is the disclosure limited to any
specific type of process technology, e.g., CMOS, Bipolar, or
[0042] BICMOS that may be used to manufacture the present
disclosure. Other additions, subtractions or modifications are
obvious in view of the present disclosure and are intended to fall
within the scope of the appended claims.
* * * * *