Title: Wireless local area network with geo-location capability
Abstract: A system of the present invention is operative for locating a wireless mobile device in communication with a wireless local area network (WLAN) that includes a plurality of cells defining a wireless local area network each having an access point base station. The access point base stations communicate with wireless mobile devices using wireless communication signals as typically spread spectrum communication signals. A processor is operatively connected to each of the access point base stations and operative to process communication signals transmitted from a mobile device and determine which signals are first-to-arrive signals based on a common timing signal and conduct differentiation of the first-to-arrive signals to locate the mobile device.
Patent Number: 6,987,744 Issued on 01/17/2006 to Harrington, et al.
| Inventors:
|
Harrington; Timothy C. (Los Gatos, CA);
Boyd; Robert W. (Rogersville, TN);
Belcher; Donald K. (Rogersville, TN);
Wisherd; David (Sunnyvale, CA)
|
| Assignee:
|
Wherenet CORP (Santa Clara, CA)
|
| Appl. No.:
|
997282 |
| Filed:
|
November 29, 2001 |
| Current U.S. Class: |
370/328; 370/338; 370/355; 342/450; 342/457 |
| Current Intern'l Class: |
H04Q 7/21.6 (20060101); H04Q 7/24 (20060101) |
| Field of Search: |
370/235,328,252,338,386,394,416,418
342/51,57,450,457,451
|
References Cited [Referenced By]
U.S. Patent Documents
| 5393965 | Feb., 1995 | Bravman et al.
| |
| 5418812 | May., 1995 | Reyes et al.
| |
| 5528621 | Jun., 1996 | Heiman et al.
| |
| 5536930 | Jul., 1996 | Barkan et al.
| |
| 5646389 | Jul., 1997 | Bravman et al.
| |
| 5768140 | Jun., 1998 | Swartz et al.
| |
| 5768531 | Jun., 1998 | Lin.
| |
| 5802101 | Sep., 1998 | Maruyama.
| |
| 5812589 | Sep., 1998 | Sealander et al.
| |
| 5850187 | Dec., 1998 | Carrender et al.
| |
| 5920287 | Jul., 1999 | Belcher et al.
| |
| 5923702 | Jul., 1999 | Brenner et al.
| |
| 5995046 | Nov., 1999 | Belcher et al.
| |
| 6031863 | Feb., 2000 | Jusa et al.
| |
| 6121926 | Sep., 2000 | Belcher et al.
| |
| 6127976 | Oct., 2000 | Boyd et al.
| |
| 6128549 | Oct., 2000 | Swartz et al.
| |
| 6236365 | May., 2001 | LeBlanc et al.
| |
| 6268723 | Jul., 2001 | Hash et al.
| |
| Foreign Patent Documents |
| 1 050 793 | Nov., 2000 | EP.
| |
| 99/37047 | Jul., 1999 | WO.
| |
Primary Examiner: Qureshi; Afsar
Attorney, Agent or Firm: Allen, Dyer, Doppelt, Milbrath & Gilchrist, P.A.
Parent Case Text
RELATED APPLICATION
This application is based upon prior filed copending provisional application
Ser. No. 60/250,720 filed Dec. 1, 2000, and prior filed copending provisional application
Ser. No. 60/257,014 filed Dec. 20, 2000.
Claims
What is claimed is:
1. A system for locating a wireless station in communication with a wireless
local area network comprising:
a plurality of cells defining a wireless local area network (WLAN) and each having
an access point base station and adapted for communicating with wireless mobile
devices using wireless communications signals; and
a processor operatively connected to each of said access point base stations
and operative to process communications signals transmitted from a mobile device
and determining which signals are first-to-arrive signals based on a common timing
signal and conducting differentiation of the first-to-arrive signals to locate
the mobile device.
2. A system according to claim 1, wherein said common timing signal comprises
a wireless timing signal broadcast to each of said access point base stations.
3. A system according to claim 2, wherein a mobile station located at a known
location is operative for generating the common timing signal.
4. A system according to claim 2, wherein an access point base station is operative
for generating the common timing signal.
5. A system according to claim 1, and further comprising a common bus operatively
connected to each of said access point base stations through which a common timing
signal is provided to each access point base station.
6. A system according to claim 1, wherein any communications signals transmitted
from mobile devices further comprise a location pulse appended to the wireless
communications signal.
7. A system according to claim 6, wherein said location pulse is appended to
a rising edge of the wireless communications signal transmitted from the mobile device.
8. A system according to claim 6, wherein said location pulse is appended to
the falling edge of the wireless communications signal transmitted from the mobile device.
9. A system according to claim 1, and further comprising a network interconnecting
each of said access point base stations and a server.
10. A system according to claim 9, wherein said network comprises an ethernet
local area network.
11. A system according to claim 1, wherein said wireless communications signals
comprise spread spectrum communications signals.
12. A system for locating a wireless station in communication with a wireless
local area network comprising:
a plurality of cells defining a wireless local area network (WLAN) and each having
an access point base station and adapted for communicating with wireless mobile
devices using wireless spread spectrum communications signals, each base station
further comprising edge detection circuitry time for detecting the leading edge
of a communications signal transmitted from a mobile device; and
a processor operatively connected to each of said access point base stations
and operative to process the detected leading edge of received communications signals
and determining first-to-arrive signals based on a common timing signal and conducting
differentiation of the first-to-arrive signals to locate the mobile station.
13. A system according to claim 12, wherein said common timing signal comprises
a wireless timing signal broadcast to the edge detection circuitry of each of said
access point base stations.
14. A system according to claim 12, wherein a mobile device located at a known
location is operative for generating the common timing signal.
15. A system according to claim 12, wherein an access point base station at a
known location is operative for generating the common timing signal.
16. A system according to claim 12, and further comprising a common bus operatively
connected to each of said access point base stations and edge detection circuitry
through which a common timing signal is provided.
17. A system according to claim 12, and further comprising a network interconnecting
each of said access point base stations and a server.
18. A system according to claim 17, wherein said network comprises an ethernet
local area network.
19. A system for locating a wireless station in communication with a wireless
local area network comprising:
a plurality of cells defining a wireless local area network (WLAN) and each having
an access point base station and adapted for communicating with wireless mobile
devices contained within a cell using wideband spread spectrum communications signals; and
a correlator operative with each of said access point base stations and time
referenced with a common timing signal for receiving a portion of a wideband spread
spectrum communications signal received from a mobile device for determining first-to-arrive
signals and conducting differentiation of the first-to-arrive signals to locate
the mobile device.
20. A system according to claim 19, wherein said correlator comprises a spread
spectrum matched filter.
21. A system according to claim 19, wherein said common timing signal comprises
a wireless timing signal broadcast to each of said access point base stations.
22. A system according to claim 19, wherein a mobile station located at a known
location is operative for generating the common timing signal.
23. A system according to claim 19, wherein an access point base station at a
known location is operative for generating the common timing signal.
24. A system according to claim 19, and further comprising a common bus operatively
connected to each of said access point base stations through which a common timing
signal is provided.
25. A system according to claim 19, and further comprising a network interconnecting
each of said access point base stations and said server.
26. A system according to claim 25, wherein said network comprises an ethernet
local area network.
27. A system for locating a wireless station in communication with a wireless
local area network comprising:
a plurality of cells defining a wireless local area network (WLAN) and each having
an access point base station time;
at least one wireless mobile station for communicating with said access point
base stations and each comprising a wireless local area network (WLAN) transmitter
for transmitting a wireless communication signal to base stations and a location
transmitter for appending a spread spectrum location pulse onto one of a rising
or falling edge of the wireless communication signal; and
a processor operatively connected to each of said access point base stations
and operative to receive and process the appended location pulse from a mobile
station and determining which signals are first-to-arrive signals based on a common
timing signal and conducting differentiation of the first-to-arrive signals to
locate the mobile station.
28. A system according to claim 27, and further comprising a radio frequency
(RF) switch operatively connected to said WLAN transmitter and said location transmitter
for allowing transmission through a common antenna.
29. A system according to claim 28, and further comprising a signal detect circuit
operatively connected to said WLAN transmitter and said location transmitter for
triggering said location transmitter and said RF switch.
30. A system according to claim 27, wherein each base station further comprises
a location receiver for receiving the location pulse.
31. A system according to claim 27, wherein said common timing signal comprises
a wireless timing signal broadcast to each of said access point base stations.
32. A system according to claim 27, wherein a mobile station located at a known
location is operative for generating the common timing signal.
33. A system according to claim 27, wherein an access point base station at a
known location is operative for generating the common timing signal.
34. A system according to claim 27, and further comprising a common bus operatively
connected to each of said access point base stations through which a common timing
signal is provided.
35. A system according to claim 27, and further comprising a network interconnecting
each of said access point base stations and said server.
36. A system according to claim 35, wherein said network comprises an ethernet
local area network.
Description
FIELD OF THE INVENTION
This invention relates to the field of wireless local area networks (WLAN),
and more particularly, this invention relates to a wireless local area network
that provides mobile device location.
BACKGROUND OF THE INVENTION
Wireless local area networks are becoming more commonplace as the use of
portable computers, such as "laptop," "notebook," and "pen" computers become increasingly
common in office environments and other locations. In most conventional wireless
local area networks, a number of access point base stations form a cellular network
for communicating with wireless mobile stations or other mobile devices. Each access
point base station is typically connected to a network server, such as part of
an ethernet or other network infrastructure. Any messages transmitted as wireless
communication signals are first transmitted to an access point base station instead
of transmitted along wireless stations. This type of centralized wireless communication
using cells provides control over communications along existing wireless mobile
devices. Typically, the wireless communication signals are a spread spectrum communications
signal, for example, a direct sequence spread spectrum signal, or a frequency hopping
spread spectrum signal.
Although wireless local area networks are becoming more commonplace in offices
and similar environments, most wireless local area networks do not provide the
capability of determining the location of a wireless mobile device operating in
the wireless LAN environment. Although some wireless LAN systems provide for signal
strength analysis of spread spectrum signals to determine location, none of them
provide an accurate means of determining the location of a mobile device operative
within the wireless infrastructure defined by access point base stations.
SUMMARY OF THE INVENTION
The present invention advantageously provides a system for locating a wireless
station in communication with a wireless local area network. The system typically
includes a network server, such as an ethernet network server, that is operative
with an ethernet local area network. A plurality of cells define a wireless local
area network (WLAN), each having an access point base station and typically operatively
connected to the server. Each access point base station communicates with wireless
mobile devices using wireless communication signals, such as spread spectrum communication
signals. A processor is operatively connected to each of the access point base
stations and operative to process communication signals transmitted from a mobile
device. The processor determines which signals are first-to-arrive signals based
on a common timing signal and conducts differentiation of the first-to-arrive signals
to locate a mobile device.
In one aspect of the present invention, the common timing signal comprises a
wireless
timing signal broadcast to each of the access point base stations. This wireless
timing signal could also be broadcast from a mobile device located at a known location
or from an access point base station. A common bus could be operatively connected
to each of the access point base stations to which a common timing signal is provided.
The common bus could be part of the LAN infrastructure connected to the network
server, such as an ethernet local area network.
The wireless communication signal transmitted from the mobile devices could include
a location pulse appended to the wireless communication signal. The location pulse
could be appended to one of the rising edge or falling edge of the wireless communication
signal transmitted from a mobile device. This location pulse is typically a spread
spectrum signal of short duration, i.e., a pulse.
In yet another aspect of the present invention, each base station could include
edge detection circuitry for detecting the leading edge of a communication signal
transmitted from a mobile device. This detected leading edge is processed and the
first-to-arrive signals are determined based on a common timing signal. A processor
conducts differentiation of the first-to-arrive signals to locate the mobile device.
In yet another aspect of the present invention, a correlator is time referenced
with the common timing signal and operative with each of the access point base
stations and receives a portion of a wideband spread spectrum communication signal
received from a mobile device to determine first-to-arrive signals and conduct
differentiation of first-to-arrive signals to locate the mobile device. This correlator
could include a spread spectrum matched filter and associated processing circuitry.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the present invention will become
apparent from the detailed description of the invention which follows, when considered
in light of the accompanying drawings in which:
FIG. 1 is an overall system diagram of the location determination system of
the present invention.
FIG. 2 is a graph showing the appending of a location pulse to a wireless communication signal.
FIG. 3 is a block diagram showing an access point base station having a wireless
local area network (WLAN) receiver that receives a wireless communications signal
and location receiver that receives a location pulse.
FIGS. 4A and 4B are block diagrams showing a mobile device having a wireless
local area network (WLAN) transmitter for transmitting a wireless communications
signal and location transmitter that transmits a location pulse that will be appended
to the wireless communications signal through a radio frequency switch, and use
of a signal detect circuit (FIG. 4B).
FIGS. 5A and 5B are block diagrams showing an access point base station having
an edge detector circuit.
FIG. 6 illustrates another block diagram of an access point base station with
an operatively connected correlator that could be a spread spectrum matched filter
for wideband spread spectrum communications signals.
FIG. 7 is a high level block diagram of one example of the circuit architecture
that can be used for a location receiver.
FIG. 8 is another high level block diagram of one example of the circuit architecture
that can be used for a correlation-based, RF signal processor in accordance with
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described more fully hereinafter with reference
to the accompanying drawings, in which preferred embodiments of the invention are
shown. This invention may, however, be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein. Rather, these
embodiments are provided so that this disclosure will be thorough and complete,
and will fully convey the scope of the invention to those skilled in the art. Like
numbers refer to like elements throughout.
The present invention advantageously provides a system for locating a wireless
mobile device, or mobile station (MS) as hereinafter referred, operating in communication
with a wireless local area network (WLAN). Much of the technology and detection
capability as associated with the system and method of the present invention can
use the circuitry and algorithms described in commonly assigned U.S. Pat. Nos.
5,920,287; 5,995,046; 6,121,926; and 6,127,976, the disclosures which are hereby
incorporated by reference in their entirety.
FIG. 1 illustrates a high level block diagram of the system
20 of the
present invention and showing a network server
22 that is part of an ethernet
local area network
24. A plurality of access point base stations
26
each define a cell (shown as
27a,
26b,
27c)
as part of a wireless local area network
30 that communicates with wireless
mobile stations (MS) using wireless communication signals that, in a preferred
embodiment, are spread spectrum wireless communication signals. A processor
32
is operatively connected to each of the access point base stations and operative
to process communication signals transmitted from a mobile station and determine
which signals are first-to-arrive signals based on a common timing signal. The
processor conducts differentiation of the first-to-arrive signals to locate the
mobile station. The processor function could also be incorporated with each access
point base station by incorporating a processor
32a at each access
point base station
26. A common timing signal can be applied to each access
point base station (and to processor
32 and
32a) and could
be provided by a wireless timing signal broadcast to each of the access point base
stations, such as by a mobile station (MS) located at a known location
34
or an access point base station that provides the common timing signal. In yet
another aspect of the present invention, a common timing signal can be supplied
through a common bus, such as part of the ethernet structure.
FIG. 3 illustrates one type of access point base station
26 having a
wireless local area network (WLAN) receiver
36 for receiving communications
signals and a location receiver
38, operatively connected to the processor
32,
32a for determining which signals are first-to-arrive signals
and conducting differentiation of the first-to-arrive signals to locate the mobile
station. The receivers
36,
38 can operate from the same antenna
40.
As shown in FIG. 2, a wireless local area network communications signal
42
is transmitted from a mobile station (MS) and includes a spread spectrum location
pulse
44 appended to the wireless communication signal. This location pulse
44 is a short duration (typically less than one millisecond) spread spectrum
transmission as a location pulse that is distinct and different from the wireless
local area network communications signal. As shown in FIG. 2, the location pulse
44 can be appended to the falling edge of the wireless communications signal
or appended to the beginning or rising edge of the communications signal.
As shown in FIG. 4A, each mobile station (MS) preferably includes a wireless
local
area network (WLAN) transmitter
46 for transmitting a communications signal,
such as a spread spectrum communications signal, having appropriate data that is
part of the mobile station transmission, including verification data and message
data. A location transmitter
48 for generating the location pulse
44
can be part of the mobile station (MS) and connect to a radio frequency (RF) switch
50 that forwards the communications signal
42 and pulse
44
to an antenna
52. A controller
54 can be operatively connected to
the wireless local area network transmitter
46 and location transmitter
48 to operate the radio frequency switch
50 for determining proper
transmission and appending of location pulse onto the communications signal, using
synchronizing techniques known to those skilled in the art. It is also possible
that a signal detect circuit
56 (FIG. 4B) can be connected to the location
transmitter
48 and wireless local area network transmitter
46 for
detecting a transmission from the wireless local area network transmitter and operatively
signal the radio frequency switch
50 and location transmitter
48
for proper operation. Various synchronizing concepts can be applied.
The type of location pulse
44 that is transmitted by the location transmitter
48 can vary, but typically comprises a direct sequence spread spectrum pulse,
although a frequency hopping, chirp or other spread spectrum signal can also used.
The pulse is a short duration wideband spread spectrum pulse of RF energy that
can be about 100 millisecond duration. A repetition rate could vary with applications
from tens of seconds to several hours, more or less as desired by those skilled
in the art. Further details of the type of pulse are set forth in the incorporated
by reference patents.
For purposes of description, the type of location circuits, algorithm, and associated
functions that can be used with the present invention, such as the processor functions
and location receiver and location transmitter, are set forth in the incorporated
by reference patents. For purposes of description, FIGS. 7 and 8 describe representative
examples of circuit architectures that can be used for the location receiver and processor.
FIG. 7 diagrammatically illustrates one type of circuitry configuration of a
respective location receiver (or "reader") architecture for "reading" location
pulses or associated signals, "blink" as sometimes referred, such as emitted from
a mobile station. An antenna
210 senses appended transmission bursts or
other signals from a respective mobile station. The antenna, which is preferably
omnidirectional and circularly polarized, is coupled to a power amplifier
212,
whose output is filtered by a bandpass filter
214. Respective I and Q channels
of the bandpass filtered signal are processed in associated circuits corresponding
to that coupled downstream of filter
214. To simplify the drawing only a
single channel is shown.
A respective bandpass filtered I/Q channel is applied to a first input
221
of a down-converting mixer
223. Mixer
223 has a second input
225
coupled to receive the output of a phase-locked local IF oscillator
227.
IF oscillator
227 is driven by a highly stable reference frequency signal
(e.g., 175 MHz) coupled over a (75 ohm) communication cable
231 from a control
processor. The reference frequency applied to phase-locked oscillator
227
is coupled through an LC filter
233 and limited via limiter
235.
The IF output of mixer
223, which may be on the order of 70 MHz, is coupled
to a controlled equalizer
236, the output of which is applied through a
controlled current amplifier
237 and applied to communication cable
231
to a communication signal processor, which could be associated processor
32,
32a.
The communication cable
231 also supplies DC power for the various components
of the location receiver by way of an RF choke
241 to a voltage regulator
242, which supplies the requisite DC voltage for powering an oscillator,
power amplifier and analog-to-digital units of the receiver.
The amplitude of the (175 MHZ) reference frequency supplied by the communications
control processor to the phase locked local oscillator
227 implies the length
of any communication cable
231 between the processor and the receiver. This
magnitude information can be used as control inputs to equalizer
236 and
current amplifier
237, so as to set gain and/or a desired value of equalization,
that may be required to accommodate any length of a communication cable. For this
purpose, the magnitude of the reference frequency may be detected by a simple diode
detector
245 and applied to respective inputs of a set of gain and equalization
comparators shown at
247. The outputs of comparators are quantized to set
the gain and/or equalization parameters.
FIG. 8 diagrammatically illustrates the architecture of a correlation-based,
RF signal processor as part of processor
32 and/or
32a to
which the output of a respective RF/IF conversion circuit of FIG. 7 can be coupled
for processing the output and determining location. The correlation-based RF signal
processor correlates spread spectrum signals detected by its associated receiver
with successively delayed or offset in time (by a fraction of a chip) spread spectrum
reference signal patterns, and determines which spread spectrum signal received
by the receiver is the first-to-arrive corresponding to a "blink" or location pulse
from the location transmitter as part of the communications signal that has traveled
over the closest observable path between the mobile station and the location receiver.
Because each receiver can be expected to receive multiple signals from the
mobile station, due to multipath effects caused by the signal transmitted by the
mobile station being reflected off various objects/surfaces between the mobile
station and the receiver, the correlation scheme ensures identification of the
first observable transmission, which is the only signal containing valid timing
information from which a true determination can be made of the distance from the
tag to the receiver.
For this purpose, as shown in FIG. 8, the RF processor employs a front end, multi-channel
digitizer
300, such as a quadrature IF-baseband down-converter for each
of an N number of receivers. The quadrature baseband signals are digitized by associated
analog-to-digital converters (ADCs)
272I and
272Q. Digitizing (sampling)
the outputs at baseband serves to minimize the sampling rate required for an individual
channel, while also allowing a matched filter section
305, to which the
respective channels (reader outputs) of the digitizer
300 are coupled to
be implemented as a single, dedicated functionality ASIC, that is readily cascadable
with other identical components to maximize performance and minimize cost.
This provides an advantage over bandpass filtering schemes, which require either
higher sampling rates or more expensive ADCs that are capable of directly sampling
very high IF frequencies and large bandwidths. Implementing a bandpass filtering
approach typically requires a second ASIC to provide an interface between the ADCs
and the correlators. In addition, baseband sampling requires only half the sampling
rate per channel of bandpass filtering schemes.
The matched filter section
305 may contain a plurality of matched filter
banks
307, each of which is comprised of a set of parallel correlators,
such as described in the above identified, incorporated by reference '926 patent.
A PN spreading code generator could produce a PN spreading code (identical to that
produced by the PN spreading sequence generator of the location transmitter). The
PN spreading code produced by PN code generator is supplied to a first correlator
unit and a series of delay units, outputs of which are coupled to respective ones
of the remaining correlators. Each delay unit provides a delay equivalent to one-half
a chip. Further details of the parallel correlation are found in the incorporated
by reference '926 patent.
As a non-limiting example, the matched filter correlators may be sized and clocked
to provide on the order of 4×10
6 correlations per epoch. By continuously
correlating all possible phases of the PN spreading code with an incoming signal,
the correlation processing architecture effectively functions as a matched filter,
continuously looking for a match between the reference spreading code sequence
and the contents of the incoming signal. Each correlation output port
328
is compared with a prescribed threshold that is adaptively established by a set
of 'on-demand' or 'as needed' digital processing units
340-
1,
340-
2,
. . . ,
340-K. One of the correlator outputs
328 has a summation
value exceeding the threshold, which delayed version of the PN spreading sequence
is effectively aligned (to within half a chip time) with the incoming signal.
This signal is applied to a switching matrix
330, which is operative
to couple a 'snapshot' of the data on the selected channel to a selected digital
signal processing unit
340-
i of the set of digital signal processing
units
340. The mobile station can 'blink' or transmit location pulses randomly,
and can be statistically quantified, and thus, the number of potential simultaneous
signals over a processor revisit time could determine the number of such 'on-demand'
digital signal processors required. A processor would scan the raw data supplied
to the matched filter and the initial time tag. The raw data is scanned at fractions
of a chip rate using a separate matched filter as a co-processor to produce an
auto-correlation in both the forward (in time) and backwards (in time) directions
around the initial detection output for both the earliest (first observable path)
detection and other buried signals. The output of the digital processor is the
first path detection time, threshold information, and the amount of energy in the
signal produced at each receiver's input, which is supplied to and processed by
the time-of-arrival-based multi-lateration processor section
400.
Processor section
400 uses a standard multi-lateration algorithm
that relies upon time-of-arrival inputs from at least three detectors to compute
the location of the object. The algorithm may be one which uses a weighted average
of the received signals. In addition to using the first observable signals to determine
object location, the processor also can read any data read out of a mobile station's
memory and superimposed on the transmission. Object position and parameter data
can be downloaded to a data base where object information is maintained. Any data
stored in a mobile station memory may be augmented by altimetry data supplied from
a relatively inexpensive, commercially available altimeter circuit. Further details
of such circuit are found in the incorporated by reference '926 patent.
It is also possible to use an enhanced circuit as shown in the incorporated by
reference '926 patent to reduce multipath effects, by using dual antenna and providing
spatial diversity-based mitigation of multipath signals. In such systems, the antennas
of each location receiver at a base station are spaced apart from one another by
a distance that is sufficient to minimize destructive multipath interference at
both antennas simultaneously, and also ensure that the antennas are close enough
to one another so as to not significantly affect the calculation of the location
of the object by the downstream multi-lateration processor.
The multi-lateration algorithm executed by the processor is modified to include
a front end subroutine that selects the earlier-to-arrive outputs of each of the
detector pairs as the value to be employed in the multi-lateration algorithm. A
plurality of auxiliary 'phased array' signal processing paths can be coupled to
the antenna set (e.g., pair), in addition to the paths containing the directly
connected receivers and their associated first arrival detector units that feed
the triangulation processor. Each respective auxiliary phased array path is configured
to sum the energy received from the two antennas in a prescribed phase relationship,
with the energy sum being coupled to associated units that feed a processor as
a triangulation processor.
The purpose of a phased array modification is to address the situation in a multipath
environment where a relatively 'early' signal may be canceled by an equal and opposite
signal arriving from a different direction. It is also possible to take advantage
of an array factor of a plurality of antennas to provide a reasonable probability
of effectively ignoring the destructively interfering energy. A phased array provides
each site with the ability to differentiate between received signals, by using
the 'pattern' or spatial distribution of gain to receive one incoming signal and
ignore the other.
The multi-lateration algorithm executed by the processor could include a front
end subroutine that selects the earliest-to-arrive output of its input signal processing
paths and those from each of the signal processing paths as the value to be employed
in the multi-lateration algorithm (for that receiver site). The number of elements
and paths, and the gain and the phase shift values (weighting coefficients) may
vary depending upon the application.
It is also possible to partition and distribute the processing load by using a
distributed data processing architecture as described in the incorporated by reference
U.S. Pat. No. 6,127,976 . This architecture can be configured to distribute the
workload over a plurality of interconnected information handling and processing
subsystems. Distributing the processing load enables fault tolerance through dynamic reallocation.
The front end processing subsystem can be partitioned into a plurality of detection
processors, so that data processing operations are distributed among sets of detection
processors. The partitioned detection processors are coupled in turn through distributed
association processors to multiple location processors. For maximum mobile station
detection capability, each receiver is preferably equipped with a low cost omnidirectional
antenna, that provides hemispherical coverage within the monitored environment.
A detection processor filters received energy to determine the earliest time-of-arrival
energy received for a transmission, and thereby minimize multi-path effects on
the eventually determined location of a mobile device. The detection processor
demodulates and time stamps all received energy that is correlated to known spreading
codes of the transmission, so as to associate a received locatoin pulse with only
one mobile station. It then assembles this information into a message packet and
transmits the packet as a detection report over a communication framework to one
of the partitioned set of association processors, and then de-allocates the detection report.
A detection processor to association control processor flow control mechanism
equitably
distributes the computational load among the available association processors,
while assuring that all receptions of a single location pulse transmission, whether
they come from one or multiple detection processors, are directed to the same association processor.
The flow control mechanism uses an information and processing load distribution
algorithm, to determine which of the association processors is to receive the message,
and queues the message on a prescribed protocol coupling socket connecting the
detection processor to the destination association processor. To select a destination
association processor, the information and processing load distribution algorithm
may include a prime number-based hashing operation to ensure a very uniform distribution
of packets among association processors. In addition, to provide relatively even
partitioning in the case of widely varying transmission rates, the hashing algorithm
may use a sequence number contained in each transmission.
Each association processor can organize its received message packets by identification
(ID) and time-of-arrival (TOA), and stores them as association reports. The association
processor compresses the data within the association report, transmits that information
over an association communication process of the communication framework to one
of a plurality of distributed location processors, and then de-allocates the association report.
In order to deliver all association reports that have been generated for an individual
mobile station (or device) to a single destination location processor, the association
communication process of the communication framework may employ the same information
and processing load distribution algorithm executed by the detection communication
process of the communication framework. Each location processor determines the
geographical location of a mobile station using the time-of-arrival measurement
information originally sourced from the detection processors. The specific algorithm
employed for location determination matches the number of arrival time measurements
with whatever a priori information is available.
To locate a mobile station, a location processor may employ all available diversity
information associated with the mobile station of interest, including, but not
limited to the mobile station ID, any data contained in the transmission and metrics
indicating confidence it these values. It then forwards a location report containing
this information over a location communication process to an asset management data
base. A location estimate may be derived from the measured time-of-arrival information
in a received association report packet, using a differential time-of-arrival algorithm,
such as a hyperbolic geometry-based function.
It is also possible to use a wireless local area network (WLAN) spread spectrum
waveform to perform the geo-location function of the present invention. The assumption
is that the wireless communication signal, as a spread spectrum signal, has a high
signal-to-noise ratio with reasonable power levels. The leading edge of this communication
signal can be detected to a high accuracy and this information used with the algorithms
as described before to provide relative time of arrival information for subsequent
processing. FIG. 5A shows edge detector circuitry
60 as part of an access
point base station
26 having the wireless local area network (WLAN) receiver
36. It is also possible to have a timing signal from a known location or
unknown location as shown in FIG. 5B. Other component locations would have to be
known, of course. For example, some wireless local area network (WLAN) transmitters
have known locations to enable the use of the algorithm when an access point base
station or mobile station location is known.
It is also known that the communications signal as a spread spectrum communications
signal can have sufficient bandwidth to provide useful time accuracy. For example,
a 50 MHz bandwidth could provide approximately 5 nanoseconds of timing accuracy
that is about 5 feet of accuracy using much of the technology and teachings described
before. It is possible to use a correlator
62 operative as a functional
spread spectrum matched filter to enable a higher quality estimate with integration
over many chips of the spread spectrum transmission (FIG. 6). It is possible to
use a matched filter that spans multiple symbols and improve accuracy by collecting
more energy in the filter prior to leading edge detection.
Many modifications and other embodiments of the invention will come to the mind
of one skilled in the art having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it is to be understood
that the invention is not to be limited to the specific embodiments disclosed,
and that the modifications and embodiments are intended to be included within the
scope of the dependent claims.
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