U.S. patent application number 13/286649 was filed with the patent office on 2012-05-03 for system and method for high resolution indoor positioning using a narrowband rf transceiver.
This patent application is currently assigned to DIANI SYSTEMS, INC.. Invention is credited to Gary L. Sugar, Yohannes Tesfai, Chandra Vaidyanathan.
Application Number | 20120106380 13/286649 |
Document ID | / |
Family ID | 45996684 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120106380 |
Kind Code |
A1 |
Vaidyanathan; Chandra ; et
al. |
May 3, 2012 |
SYSTEM AND METHOD FOR HIGH RESOLUTION INDOOR POSITIONING USING A
NARROWBAND RF TRANSCEIVER
Abstract
A sequence of two or more signals representing two or more data
packets is transmitted through a wireless channel using a
transmitter device. The two or more signals are a result of two or
more transmissions that are made sequentially in time at different
center frequencies in order to span a desired bandwidth. At least
one of the two or more signals includes a physical layer preamble.
The sequence of two or more signals is received using a receiver
device. A time of arrival of one or more signals of the received
sequence is calculated using one or more of the received sequence,
the time differences among the two or more transmissions, the
different center frequencies, information from the two or more data
packets, and any carrier phase differences among the two or more
transmissions using the receiver device.
Inventors: |
Vaidyanathan; Chandra;
(Rockville, MD) ; Sugar; Gary L.; (San Francisco,
CA) ; Tesfai; Yohannes; (Silver Spring, MD) |
Assignee: |
DIANI SYSTEMS, INC.
Ijamsville
MD
|
Family ID: |
45996684 |
Appl. No.: |
13/286649 |
Filed: |
November 1, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61409123 |
Nov 2, 2010 |
|
|
|
61421641 |
Dec 10, 2010 |
|
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Current U.S.
Class: |
370/252 |
Current CPC
Class: |
G01S 5/021 20130101;
G01S 5/14 20130101; H04B 1/69 20130101; G01S 1/024 20130101; H04W
64/00 20130101; G01S 5/0226 20130101; G01S 1/20 20130101 |
Class at
Publication: |
370/252 |
International
Class: |
H04W 24/00 20090101
H04W024/00; H04L 12/26 20060101 H04L012/26 |
Claims
1. A system for calculating the time of arrival of a wireless
signal through a wireless channel, comprising: a receiver device
that receives a sequence of two or more signals representing two or
more data packets transmitted through a wireless channel, wherein
the two or more signals are a result of two or more transmissions
that are made sequentially in time at different center frequencies
in order to span a desired bandwidth and wherein at least one of
the two or more signals includes a physical layer preamble, and
calculates a time of arrival of one or more signals in the received
sequence using one or more of the received sequence, the time
differences among the two or more transmissions, the different
center frequencies, information from the two or more data packets,
and any carrier phase differences among the two or more
transmissions.
2. The system of claim 1, wherein said time differences among the
two or more transmissions and said any carrier phase differences
among the two or more transmissions are known to the receiver
device before the received sequence is transmitted.
3. The system of claim 1, wherein a transmission time of each of
the two or more signals is encoded and included in the two or more
data packets before transmission through the wireless channel and
the receiver device determines said time differences among the two
or more transmissions by decoding and subtracting the encoded
transmission times of two or more consecutive data packets of the
two or more data packets.
4. The system of claim 1, wherein transmission time differences
among each of the two or more signals are encoded and included in
the two or more data packets before transmission through the
wireless channel and the receiver device determines said time
differences among the two or more transmissions by decoding the
encoded transmission time differences from the two or more data
packets.
5. The system of claim 1, wherein a carrier phase of each of the
two or more transmitted signals is encoded and included in the two
or more data packets before transmission through the wireless
channel and the receiver device determines said any carrier phase
differences among the two or more transmissions by decoding and
subtracting the encoded carrier phase from the two or more data
packets.
6. The system of claim 1, wherein carrier phase differences among
each of the two or more transmitted signals are encoded and
included in the two or more data packets before transmission
through the wireless channel and the receiver device determines
said any carrier phase differences among the two or more
transmissions by decoding the encoded carrier phase differences
from the two or more data packets.
7. The system of claim 1, wherein the two or more data packets are
different data packets.
8. The system of claim 1, wherein the two or more data packets are
the same data packets.
9. The system of claim 1, wherein the two or more data packets
conform to the IEEE 802.11 (Wi-Fi.TM.) standard.
10. The system of claim 1, wherein the two or more data packets
conform to the Bluetooth.TM. standard.
11. The system of claim 1, wherein the two or more data packets
conform to the Global System for Mobile Communications (GSM)
standard.
12. The system of claim 1, wherein the receiver device calculates
an angle of arrival of one or more signals of the received sequence
by receiving the sequence through two or more antenna paths
simultaneously and using one or more of the received sequence, said
time differences among the two or more transmissions, said any
carrier phase differences among the two or more transmissions,
information from the two or more data packets, and the geometry of
the two or more antennas.
13. The system of claim 1, wherein the receiver device further
calculates a location of the receiver device using the time of
arrival and one or more time of arrivals calculated from one or
more received sequences that are transmitted from one or more
additional locations.
14. The system of claim 13, wherein time division multiple access
(TDMA) is used to differentiate the received sequence and the one
or more additional received sequences at the receiver device.
15. The system of claim 13, wherein orthogonal frequency-division
multiple access (OFDMA) is used to differentiate the received
sequence and the one or more additional received sequences at the
receiver device.
16. The system of claim 13, wherein frequency division multiple
access (FDMA) or code division multiple access (CDMA) is used to
differentiate the received sequence and the one or more additional
received sequences at the receiver device.
17. The system of claim 13, wherein the received sequence and the
one or more received sequences include parametric information that
the receiver device uses to calculate a location of the receiver
device.
18. The system of claim 17, wherein parametric information
comprises one or more of coordinates for the locations of the
devices that transmitted the received sequence and the one or more
received sequences, number, time duration, and center frequencies
of signal transmissions per location beacon for the received
sequence and the one or more received sequences, or nominal start
time for a first location beacon relative to a beacon time for the
received sequence and the one or more received sequences.
19. The system of claim 1, wherein the receiver device further
receives a calibration sequence of two or more calibration signals
before receiving the sequence, which the receiver device uses to
construct a calibration table storing measured changes in group
delay and phase shift over a set of receiver gain settings and/or
RF center frequencies, and later uses the calibration table
contents in time-of-arrival and/or angle-of-arrival
calculations.
20. The system of claim 1, wherein the receiver device further
sends a response sequence of two or more response signals
representing two or more response data packets to a device from
which the sequence was received and embeds in the two or more
response data packets a turn-around-time so that the device
calculates a distance between the receiver device and the device
using the turn-around-time, wherein the turn-around-time comprises
a difference between a first time of the receipt of the first
signal in the sequence at an antenna of the receiver device and a
second time of the beginning of the response sequence's beacon at
an antenna of the receiver device.
21. The system of claim 1, further comprising at least one
additional receiver device that receives the transmitted sequence
and calculates one additional time of arrival for the received
sequence, wherein the time of arrival and the one more additional
time of arrival are used to calculate a location of a device that
transmitted the received sequence.
22. A system for calculating the time of arrival of a wireless
signal through a wireless channel, comprising: a transmitter device
that transmits a sequence of two or more signals representing two
or more data packets through a wireless channel, wherein the two or
more signals are transmitted using two or more transmissions that
are made sequentially in time at different center frequencies in
order to span a desired bandwidth, wherein at least one of the two
or more signals includes a physical layer preamble, wherein a
sequence is received by a receiver device, and wherein a time of
arrival of one or more signals of the received sequence is
calculated by the receiver device using one or more of the received
sequence, the time differences among the two or more transmissions,
the different center frequencies, information from the two or more
data packets, and any carrier phase differences among the two or
more transmissions.
23. A method for calculating the time of arrival of a wireless
signal through a wireless channel, comprising: receiving a sequence
of two or more signals representing two or more data packets
transmitted through a wireless channel using a receiver device,
wherein the two or more signals are a result of two or more
transmissions that are made sequentially in time at different
center frequencies in order to span a desired bandwidth and wherein
at least one of the two or more signals includes a physical layer
preamble, and calculating a time of arrival of one or more signals
in the received sequence using one or more of the received
sequence, the time differences among the two or more transmissions,
the different center frequencies, information from the two or more
data packets, and any carrier phase differences among the two or
more transmissions using the receiver device.
24. A method for calculating the time of arrival of a wireless
signal through a wireless channel, comprising: transmitting a
sequence of two or more signals representing two or more data
packets through a wireless channel using a transmitter device,
wherein the two or more signals are transmitted using two or more
transmissions that are made sequentially in time at different
center frequencies in order to span a desired bandwidth, wherein at
least one of the two or more signals includes a physical layer
preamble, wherein a sequence is received by a receiver device, and
wherein a time of arrival of one or more signals of the received
sequence is calculated by the receiver device using one or more of
the received sequence, the time differences among the two or more
transmissions, the different center frequencies, information from
the two or more data packets, and any carrier phase differences
among the two or more transmissions.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/409,123 filed Nov. 2, 2010 and U.S.
Provisional Patent Application No. 61/421,641 filed Dec. 10, 2010,
which are incorporated by reference herein in their entireties.
INTRODUCTION
[0002] There is a strong market need for an indoor electronic
positioning system that can provide one-meter accuracy or better.
Mobile retail applications for smart phones are perhaps the biggest
revenue driver behind this need, allowing users to find out what is
currently on sale in the aisle of the store they are in, to find
out which items from their shopping list are sold in the aisle they
are walking in, or simply to get information on a nearby product or
display. Other important applications include medical device
location and staff location in hospitals, indoor E911, search and
rescue, route guidance inside large buildings, wireless robots, and
route guidance for the blind.
[0003] State-of-the-art indoor positioning systems for IEEE 802.11
Wi-Fi.TM. devices are generally power-of-arrival (PoA) based, with
accuracies on the order of ten meters at 90% confidence. PoA-based
positioning systems require calibration by physically walking a
measurement device through an area of interest, which is a
time-consuming and expensive process. PoA-based systems are also
known to require a relatively high density of access points (APs)
in order to achieve even ten-meter accuracy. To improve the
PoA-based accuracy from ten to five meters, one can make a strong
argument that the AP density would need to increase by a factor of
four, with additional four-fold density increases for each
additional two-fold accuracy improvement.
[0004] Time-of-flight (ToF) based positioning systems such as GPS
allow devices to estimate their position by measuring the arrival
times of signals transmitted by multiple radio emitters at known
positions, converting the arrival times into distances by dividing
by the speed of propagation, and solving for position using
trigonometry. ToF-based positioning systems generally do not
require calibration and their accuracy is generally not limited by
AP density. The problem with ToF is its accuracy indoors; although
these systems work very well outdoors, they perform notoriously
poorly in indoor environments. The main reason for their poor
performance is multipath-signal reflections off of walls, ceilings,
etc. that smear the arrival time of the over-the-air signals,
making it hard to determine the arrival time of the line-of-site
(LOS) or shortest-distance path. Several companies have attempted
to deploy ToF-based Wi-Fi.TM. location systems indoors as of the
time of this writing, but none at present are known to deliver sub
ten-meter accuracy.
[0005] One well-known way to mitigate the multipath problem is to
use very wideband location signals--hundreds of megahertz wide for
indoor RF applications. The wide signal bandwidth increases the
resolution in the time-domain, allowing receivers to distinguish
the LOS path from other delayed reflected paths (see FIG. 1). The
challenges with using wideband signals are: (1) wideband radios
require leading edge, high-speed components which are expensive to
manufacture, and (2) since spectrum allocation differs from country
to country, it's difficult to standardize a wideband technology
that will work in more than one country and enjoy good economies of
scale. This is one reason why the so-called Ultra-wideband (UWB)
technology that was first introduced in the late 1990's failed to
become standardized. In the U.S., the FCC also placed severe
restrictions on UWB's transmit power to minimize interference, thus
limiting its operating range and hence suitability for many
applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The skilled artisan will understand that the drawings,
described below, are for illustration purposes only. The drawings
are not intended to limit the scope of the present teachings in any
way.
[0007] FIG. 1 is schematic diagram of a time-of-flight (ToF)-based
positioning system, in accordance with various embodiments.
[0008] FIG. 2 is an exemplary plot that shows an impulse response
from an outdoor channel, in accordance with various
embodiments.
[0009] FIG. 3 is an exemplary plot that shows an impulse response
from an indoor channel (e.g., an office environment), in accordance
with various embodiments.
[0010] FIGS. 4-7 are exemplary plots that show the
cross-correlation between a baseband signal x(t) that is sent
through the indoor channel impulse response of FIG. 3 and the
channel output for various signal bandwidths, in accordance with
various embodiments.
[0011] FIG. 8 is an exemplary plot showing a traditional approach
for transmitting a wideband or ultra-wide band signal, in
accordance with various embodiments.
[0012] FIG. 9 is an exemplary plot showing a time/frequency offset
wideband (TF-WB) signaling approach for transmitting a wideband or
ultra-wide band signal, in accordance with various embodiments.
[0013] FIG. 10 is a schematic diagram of the internal architecture
of a TF-WB transmitter, is accordance with various embodiments.
[0014] FIG. 11 is an exemplary plot showing autocorrelation
functions for two different example TF-WB signals, in accordance
with various embodiments.
[0015] FIG. 12 is a schematic diagram of the internal architecture
of a TF-WB receiver, is accordance with various embodiments.
[0016] FIGS. 13-16 are exemplary plots that show correlation vs.
peak-to-peak inter-packet timing jitter amplitude for a TF-WB
waveform consisting of K=23 802.11g OFDM packets, in accordance
with various embodiments.
[0017] FIGS. 17-20 are exemplary plots that show correlation vs.
peak-to-peak carrier phase jitter amplitude for a TF-WB waveform
consisting of K=23 802.11g OFDM packets, in accordance with various
embodiments.
[0018] FIG. 21 is an exemplary plot of TDMA and OFDMA multiplexed
transmissions from multiple clients and APs in an IEEE 802.11-based
TF-WB system, in accordance with various embodiments.
[0019] FIG. 22 is an exemplary plot showing an efficient OFDMA
scheme in which transmissions from multiple Access Points are
time-frequency interleaved in the same OFDM burst, in accordance
with various embodiments.
[0020] FIG. 23 is a schematic diagram of a 3-input TF-WB-capable
receiver, in accordance with various embodiments.
[0021] FIGS. 24-26 are exemplary plots that show Wiener filters for
each of the 3 antenna paths from FIG. 23, in accordance with
various embodiments.
[0022] FIG. 27 is an exemplary flowchart showing a method for
calculating the time of arrival of a wireless signal through a
wireless channel using a receiver device, in accordance with
various embodiments.
[0023] FIG. 28 is a schematic diagram of a system that includes a
receive module and a calculation module that performs a method for
calculating the time of arrival of a wireless signal through a
wireless channel, in accordance with various embodiments.
[0024] FIG. 29 is an exemplary flowchart showing a method for
calculating the time of arrival of a wireless signal through a
wireless channel using a transmitter device, in accordance with
various embodiments.
[0025] FIG. 30 is a schematic diagram of a system that includes a
transmit module that performs a method for calculating the time of
arrival of a wireless signal through a wireless channel, in
accordance with various embodiments.
[0026] Before one or more embodiments of the present teachings are
described in detail, one skilled in the art will appreciate that
the present teachings are not limited in their application to the
details of construction, the arrangements of components, and the
arrangement of steps set forth in the following detailed
description or illustrated in the drawings. Also, it is to be
understood that the phraseology and terminology used herein is for
the purpose of description and should not be regarded as
limiting.
DESCRIPTION OF VARIOUS EMBODIMENTS
[0027] Various embodiments, referred to herein as Time/Frequency
Offset Wideband (TF-WB) signaling, enjoy all of the advantages of
other state-of-the-art wideband or ultra-wideband signaling schemes
without being burdened by the aforementioned challenges. Various
embodiments are first described briefly at a high-level, followed
by a detailed description at the physical and data link layers. To
clarify the terminology, the use of the term "narrowband" in this
discussion refers to signals that have a bandwidth of less than 40
MHz, and the term wideband is reserved for signals that have
bandwidth exceeding 100 MHz. The term "ultra-wideband" is commonly
accepted to mean signal bandwidths in excess of 500 MHz.
[0028] System Overview
[0029] FIG. 1 is schematic diagram of a ToF-based positioning
system 100, in accordance with various embodiments. System 100
includes a mobile Client device 20, a plurality of sensor/emitter
(SE) devices 30 and a Server 40. The Client device 20 is typically
a battery-powered mobile device such as a Smartphone or a laptop
computer containing a wireless communication chipset that complies
with a wireless standard such as IEEE 802.11/Wi-Fi.TM. or
Bluetooth. The SE devices 30, typically the size of a Wi-Fi.TM.
access point (AP), are placed in various known positions in an
indoor environment such as a hospital, retail store or a shopping
mall. The Server 40 is used to control the behavior of the Client
and SEs during the ToA measurements, and to locate the Client based
on ToA measurements received from the SEs.
[0030] The SEs can be configured as sensors, which only receive ToF
location signals from the client, emitters, which only transmit to
the Client, or both. When configured as emitters, each SE
periodically broadcasts TF-WB location beacon signals, allowing
listening Clients to self-locate by measuring the ToA of the beacon
signals received from multiple SEs. This is similar to how GPS is
used today, with satellites being the emitters for GPS. When
configured as sensors, each SE measures the ToA of one or more
TF-WB transmissions received from the Client to estimate its
position.
[0031] All SEs in a network may need to be time synchronized to a
common time base. In emitter mode, this allows the SEs to transmit
their TF-WB location beacons at exactly the same time, using OFDMA
to differentiate their transmissions at the client (the details for
this technique are described in Section entitled "Multiplexing
TF-WB Transmissions From Multiple Devices" below). After
down-converting, digitizing and storing a set of these beacon
transmissions from SEs at known positions, a Client can compute the
ToAs of these signals and estimate its position u=[x y z].sup.T by
solving the equation
u ^ = argmin u min t n = 1 N u - u n - c ( t n - t ) 2 ,
##EQU00001##
where u.sub.n is the known [x y z] position of the nth SE, c is the
speed of light, t.sub.n is the Client's measured ToA of the nth
beacon transmission, and t is the unknown SE beacon transmission
time.
[0032] In sensor mode, the SEs monitor incoming TF-WB transmissions
from the Client, estimate their ToAs and pass the ToA estimates to
the server, which estimates the Client position by solving
u ^ = argmin u min t n = 1 N u - u n - c ( t n - t ) 2 ,
##EQU00002##
where u.sub.n is the known [x y z] position of the nth SE, c is the
speed of light, t.sub.n is the nth SE's ToA estimate (referenced to
the SE's global time base), and t is the unknown transmission time
of the Client's TF-WB location signal.
[0033] In practice, regardless of whether the SEs are configured as
emitters or sensors, the bottleneck in terms of location accuracy
is the accuracy of the time-of-arrival estimates. Since radio
signals travel at the speed of light, a timing error of even a few
nanoseconds (billionths of a second) will exceed the one-meter
positioning error budget.
[0034] FIG. 2 is a plot 200 that shows an impulse response from an
outdoor channel, in accordance with various embodiments. FIG. 3 is
a plot 300 that shows an impulse response from an indoor channel
(e.g., an office environment), in accordance with various
embodiments. The spike at 30 ns in plots 200 and 300 represents the
shortest-distance LOS path between the transmit and receive
antennas. Since light travels at approximately one foot per ns,
this means the antennas in this example are separated by about 30
ft. The outdoor response shows virtually zero energy after the LOS
path. The indoor response shows literally hundreds of closely
spaced reflections after the LOS.
[0035] To estimate the arrival time of a signal sent through this
channel, a commonly used approach is for the transmitter to send a
known signal to the receiver, then for the receiver to correlate
the known signal against what it receives through the channel and
estimate the ToA as the ToA of the earliest correlation peak that
exceeds some appropriate threshold. Mathematically, using x(t) to
represent the complex baseband transmit signal, y(t) the complex
baseband received signal, h(t) the complex channel impulse
response, and z(t) the correlator output, one can write:
y ( t ) = .intg. - .infin. .infin. x ( t - .tau. ) h ( .tau. )
.tau. + v ( t ) ##EQU00003## and ##EQU00003.2## z ( t ) = .intg. -
.infin. .infin. y * ( t ) x ( t - .tau. ) t , ##EQU00003.3##
where v(t) is complex additive white Gaussian noise.
[0036] FIGS. 4-7 are exemplary plots that show the
cross-correlation between a baseband signal x(t) that is sent
through the indoor channel impulse response of FIG. 3 and the
channel output for various signal bandwidths, in accordance with
various embodiments. FIGS. 4-7 show channel impulse responses
(solid lines) and correlator outputs (dashed lines) for transmit
signal bandwidths of 50, 100, 250 and 500 MHz, respectively. In
each case, x(t) is a 1023-bit pseudo-random NRZ sequence filtered
through a root-raised cosine low pass filter. The only difference
among the 4 cases is the symbol rate and hence the RF bandwidth of
x(t).
[0037] FIGS. 4-7 show why accurate ToA estimation indoors needs
very wideband signals. It's because there are so many signal
reflections in the vicinity of the LOS path that the only way to
get the needed time-resolution is to use a very wideband signal.
Without sufficient time resolution, it is too difficult to
differentiate the LOS from other paths.
[0038] Time-Frequency Offset Wideband Signaling--Theory of
Operation
[0039] FIG. 8 is an exemplary plot showing a traditional approach
for transmitting a wideband or ultra-wide band signal, in
accordance with various embodiments. The traditional approach for
transmitting a wideband or ultra-wide band signal is to send one
signal packet that spans the entire transmission bandwidth, B, as
illustrated in FIG. 8. This approach was proposed, for example, in
competing UWB standards.
[0040] FIG. 9 is an exemplary plot showing a time/frequency offset
wideband (TF-WB) signaling approach for transmitting a wideband or
ultra-wide band signal, in accordance with various embodiments.
Instead of sending one broadband packet that spans all frequencies,
TF-WB sends multiple narrowband packets at different times and
frequencies in order to span the same bandwidth, B. It can be shown
that the TF-WB approach provides the same time resolution benefits
as the more traditional techniques as long as it spans the same
amount of bandwidth. Although it generally takes longer to cover
the same amount of spectrum using a sequence of TF-WB transmissions
as it does using a single wideband or UWB transmission, TF-WB
enjoys several important advantages, which are highlighted
below.
[0041] The most important advantage is that its use of narrowband
signals allows TF-WB to be adapted to just about any of today's
popular wireless standards such as Bluetooth, IEEE 802.11 or 3G/4G
cellular, using the same low-cost hardware platforms with at most
only superficial changes to the chipset and software. For example,
to send a TF-WB signal using an IEEE 802.11 Wi-Fi.TM. chipset, one
sends a sequence of 802.11 packets (for example, Probe Request
packets) at different times and frequencies. This makes it possible
to perform high-resolution location on Wi-Fi.TM. smart-phones by
re-using the same Wi-Fi.TM. chipset that is also used for Internet
data communication. If one of the state-of-the-art UWB technologies
was used instead, one would have to burden the smart-phone with the
additional cost, size and battery energy needed to support a new
chipset, antenna, and software needed to implement the new wireless
protocol. As mentioned earlier, traditional UWB radios also cost
more to manufacture and consume more DC current than their
narrowband counterparts.
[0042] Also, as alluded to earlier, another critical advantage is
regulatory. In the U.S., UWB systems are required by the FCC to
transmit no more than -41.3 dBm per MHz of bandwidth. Indoor
Wi-Fi.TM. systems, on the other hand, typically transmit up to 7
dBm per MHz. This gives a TF-WB over Wi-Fi.TM. system a 48 dB or
approximately a thirty-fold range advantage over a UWB system
indoors.
[0043] The basic steps for transmission, reception and ToA
estimation using TF-WB signaling are as follows.
[0044] 1. Transmitter sends a sequence of narrowband signals at
different times and frequencies to the receiver. It is assumed that
the time, frequency, and carrier phase differences among the signal
transmissions are known to the receiver.
[0045] 2. Receiver listens for the transmissions at the known times
and frequencies using its narrowband radio while digitizing and
storing them for post-processing.
[0046] 3. Receiver uses the stored receive signals and the known
time, frequency and carrier phase differences of the transmissions
to obtain a high-resolution estimate of the time-of-arrival of the
received signals at its antenna.
[0047] In a preferred embodiment, the transmitted signals are
waveforms--physical layer representations of binary data packets
that are defined in a wireless standard such as Bluetooth, IEEE
802.11 Wi-Fi.TM. or 3G or 4G cellular.
[0048] FIG. 10 is a schematic diagram of the internal architecture
of a TF-WB transmitter 1000, is accordance with various
embodiments. Samples of the narrowband physical layer complex
baseband waveforms are generated on the fly by MAC and PHY units
1001, and stored in a buffer 1010 until it's time to transmit them.
They are then passed to a complex digital-to-analog converter 1020,
where they are digitized and lowpass filtered. The filtered complex
DAC output is passed to a narrowband analog RF transmitter 1030
where it is I/Q modulated, up-converted 1045 to the appropriate RF
frequency and sent over-the-air through the antenna 1040. The
transmitter's TF-WB Sequencing Logic 1025 controls the timing at
which the narrowband signals are presented to the DAC and directs
the RF transmitter to tune its LO synthesizer to the appropriate
frequencies at the appropriate times.
[0049] A mathematical representation of the TF-WB transmit signal
leaving antenna 1040 is
x ( t ) = Re { k = 1 K x k ( t - .tau. k ) j 2 .pi. ( f c + f k ) t
+ j .phi. k } , ( 1 ) ##EQU00004##
where Re(z) represents the real part of the complex number z, K is
the number of narrowband waveforms transmitted, and x.sub.k (t) is
the complex envelope of the kth narrowband waveform transmitted at
time .tau..sub.k, carrier frequency f.sub.c+f.sub.k and carrier
phase .phi..sub.k. The transmission time .tau..sub.1 of the first
waveform can be assumed to be zero without loss of generality. This
way, the remaining .tau..sub.k can be viewed as time offsets
relative to transmit time of the first waveform.
[0050] FIG. 11 is an exemplary plot showing autocorrelation
functions for two different example TF-WB signals, in accordance
with various embodiments. The autocorrelation functions are
generated according to equation (1) using K=3 and K=15 repetitions,
where each narrowband transmission is a 20 MHz wide IEEE 802.11g
OFDM packet. The same packet is repeated K times at different times
and frequencies. The spacing between the offset frequencies f.sub.k
is 20 MHz. The packet duration is 320 .mu.s, and the timing gap
between transmissions is 100 .mu.s. Note how the time resolution
increases as the number of narrowband signals K, and hence the
bandwidth (which is 20 K MHz) is increased.
[0051] FIG. 12 is a schematic diagram of the internal architecture
of a TF-WB receiver 1200, is accordance with various embodiments.
The received TF-WB signal enters through the antenna 1250, is
down-converted to complex baseband by the narrowband analog RF
receiver 1260, lowpass filtered through a narrowband filter and
digitized via a complex analog-to-digital converter 1270, digitally
allpass filtered and phase shifted to compensate for gain-dependent
group delay and phase shifts 1275, and stored in a buffer 1280
where it awaits processing by the ToA Estimator 1290. The ADC
samples are also routed to PHY demodulator and MAC Rx blocks 1201
and 1202, respectively. The receiver also has TF-WB Sequencing
Logic 1220 to direct the RF Receiver 1260 to tune its LO
synthesizer to the appropriate frequencies at the appropriate
times.
[0052] FIGS. 13-16 are exemplary plots that show correlation vs.
peak-to-peak inter-packet timing jitter amplitude for a TF-WB
waveform consisting of K=23 802.11g OFDM packets, in accordance
with various embodiments. FIGS. 13-16 were generated from
simulations in which the inter-packet spacing between the K
waveforms was shortened or lengthened from its nominal value by a
randomly generated jitter time using a uniform probability
distribution. A different random number was generated for each of
the K-1 inter-packet intervals.
[0053] FIGS. 17-20 are exemplary plots that show correlation vs.
peak-to-peak carrier phase jitter amplitude for a TF-WB waveform
consisting of K=23 802.11g OFDM packets, in accordance with various
embodiments. FIGS. 17-20 were generated from simulations in which
the carrier phase difference between the 1st and the remaining K-1
waveforms was rotated from its nominal value by a randomly
generated jitter value using a uniform probability distribution. A
different random number was generated for each of the K-1 phase
differences.
[0054] FIGS. 13-16 and FIGS. 17-20 show how receiver uncertainty in
the carrier phase and inter-packet timing between narrowband
transmissions affects performance. The figures show the
cross-correlation between an ideal and a distorted 802.11g-based
TF-WB waveform with K=23 narrowband transmission frequencies. The
figures clearly show why it's critical for the receiver to have
accurate knowledge of the values of these parameters. There are
several ways for the receiver to get this information:
[0055] 1. The parameters can be specified in a wireless standard.
For example, the IEEE 802.11 standards committee can release an
updated specification that documents rules for transmitting
802.11-based TF-WB signals. These rules can require all
TF-WB-compatible transmitters to use a fixed inter-packet spacing
of, say, 100 .mu.s+/-0.1 ns, and a carrier phase difference of at
most 3 degrees between any two transmitted packets.
[0056] 2. The transmitter can communicate this information to the
receiver, either by embedding it in each transmitted packet or
using a system configuration message. As an example of the former,
the transmitter could encode and embed each packet's time of
departure on a high-speed clock in a time-stamp field, it could
encode and embed the carrier phase during each packet's
transmission into a phase-stamp field, or it could encode and embed
the inter-packet timing and/or inter-packet carrier phase
differences into time-difference and/or phase-difference fields. An
example of the latter would be for the transmitter to send a
message to the receiver after it joins the network letting the
receiver know that it uses an inter-packet spacing of 100
.mu.s+/-0.1 ns and a carrier phase difference of at most 3 degrees
between any two transmitted packets for all TF-WB
transmissions.
[0057] Depending on how the system is implemented, a standards
specification can document the following additional TF-WB-related
information:
[0058] 1. The receiver may need to know the sequence of
frequencies, the number of transmissions per frequency in order to
properly receive and decode a TF-WB signal. The transmitter can
either embed this information in a TF-WB Information Message that
it sends to the receiver, or can periodically broadcast this
information (if it's an 802.11 AP, in a Beacon message, for
example) so that all receivers can get this information.
[0059] 2. For Clients that perform self-location by measuring the
ToAs of incoming TF-WB transmissions from the SEs, the Client will
need to know the physical location of each of the SEs within
earshot, when to listen for their TF-WB transmissions, the sequence
of frequencies and number of transmissions per frequency, and how
the transmissions from multiple SEs are multiplexed (e.g., using
OFDMA or TDMA is used, if ODMA, which SEs are assigned to which
sub-carriers; if TDMA, which SEs are assign to which timeslots).
For this kind of information, a periodic network broadcast makes
the most sense (for Wi-Fi.TM., perhaps using the Beacon
message).
[0060] 3. For systems in which the SEs locate the Clients by
listening to their transmissions, each client would need:
[0061] a. An assigned time slot in which to send its TF-WB message
(for Wi-Fi.TM., for example, this can be specified as a time
relative to the AP Beacon transmission)
[0062] b. The frequencies, number of transmissions per frequency
and time between transmissions
[0063] c. Information on how to multiplex its transmissions with
other clients. If OFDMA, this would be an assigned set of
sub-carriers, if DSSS, an assigned spreading code.
[0064] For this kind of information, a uni-cast "TF-WB Information"
message exchange to the client from the network seems most
appropriate.
[0065] Returning to the ToA Estimator block 1290 of FIG. 12, the
receiver uses the following high-level steps to estimate the
time-of-arrival of a received TF-WB waveform sequence.
[0066] In step 1, the receiver digitally up-converts the received
narrowband observation waveforms to their known offset frequencies
and sums, yielding a wideband observation waveform.
[0067] In step 2, the receiver synthesizes a narrowband reference
waveform corresponding to each of the received narrowband
observation waveforms using the known (and optionally decoded)
portions of the data packets and the rules prescribed by the
wireless standard.
[0068] In step 3, given the narrowband reference waveforms the
known time, frequency and carrier phase offsets and a
hypothetically selected channel propagation delay, the receiver
defines a model to generate a "wideband model output waveform"--a
most-likely guess for what the wideband observation waveform would
look like given the known information and that prescribed channel
propagation delay.
[0069] In step 4, the receiver uses a one-dimensional search to
find the channel propagation delay that most closely matches the
wideband model output and wideband observation waveforms. The
resulting channel propagation delay from this process is the
estimated time-of-arrival.
[0070] Next, these steps are described again in greater detail and
with more mathematical rigor:
[0071] In step 1, the receiver digitally up-converts the received
narrowband observation waveforms y.sub.k(nT) to their known offset
frequencies f.sub.k, yielding the wideband observation waveform
y ( nT ) = .DELTA. k = 1 K y k ( nT ) j 2 .pi. f k nT .
##EQU00005##
[0072] For each received narrowband observation waveform
y.sub.k(nT), the receiver synthesizes a corresponding narrowband
reference waveform {circumflex over (x)}.sub.k(nT) by encoding and
modulating known portions of the waveform (including the physical
layer preamble and any known data bits) as specified by the
wireless standard. The receiver may optionally chose to demodulate
and decode other unknown portions of the packet and add the decoded
data to the known information that gets encoded and modulated to
generate the narrowband reference waveform {circumflex over
(x)}.sub.k(nT) as well. If the receiver decides not to include the
decoded information in the narrowband reference waveform, it sets
the corresponding portions of that waveform to zero.
[0073] In step 3, given the narrowband reference waveforms
{circumflex over (x)}.sub.k(nT), the known time, frequency and
carrier phase offsets f.sub.k, .tau..sub.k and .phi..sub.k and a
hypothetically selected channel propagation delay .tau..sub.0, the
receiver generates a wideband reference signal defined by
x ^ ( nT , .tau. 0 ) = .DELTA. k = 1 K x ^ k ( nT - .tau. k - .tau.
0 ) j 2 .pi. f k ( nT - .tau. 0 ) + j .phi. k . ##EQU00006##
[0074] It should be noted that with a noise and multipath-free
channel and with the correct choice of .tau..sub.0, the wideband
reference and wideband observation waveforms should be
identical.
[0075] In step 4, the receiver finds the Wiener filter that best
matches the wideband reference signal {circumflex over (x)}(nT,
T.sub.0) generated in the previous step to the wideband observation
signal y(nT), then filters the wideband reference signal through
the Wiener filter. Mathematically speaking, the Wiener filter is
given by
h=h(.tau..sub.0)[R.sub.XX(.tau..sub.0)].sup.-1R.sub.XY(.tau..sub.0),
where R.sub.XY(.tau..sub.0) is the cross correlation vector between
the wideband reference and observation signals, and R.sub.XX
(.tau..sub.0) is the autocorrelation matrix for the wideband
reference signal. Note that each candidate choice for .tau..sub.0
will produce a different Wiener filter h, hence the alternative
notation h(.tau..sub.0) used above.
[0076] It should be noted that with a noise-free channel and with
the correct choice of .tau..sub.0, (a) the Wiener filter output and
the wideband observation waveforms should be identical, and (b) the
frequency response of the channel and the Wiener filter should be
identical over all active RF transmit frequencies.
[0077] In step 5, the receiver iteratively repeats steps 3 and 4
using various choices of .tau..sub.0 to find the candidates
{circumflex over (.tau.)}.sub.0 that minimizes the mean-square
error between the Wiener filter output and the wideband observation
waveform; the value of {circumflex over (.tau.)}.sub.0 that results
from this process is the ToA estimate. This step can be written
mathematically as follows:
.tau. ^ 0 = argmin .tau. 0 n y ( nT ) - x ^ ( nT , .tau. 0 ) * h (
.tau. 0 ) 2 , ##EQU00007##
where the asterisk in the above formula represents the convolution
operator. Any one of a number of well-known single-dimensional
minimization techniques can be used to minimize the number of
iterations needed to find the optimal .tau..sub.0 per the above
formula, including the secant method, Newton's method, quadratic
search, etc.
[0078] Round-Trip Time Measurements
[0079] Another useful application for TF-WB signaling is to use it
to estimate the distance between 2 devices using round-trip-time
(RTT) measurements. Both devices would need to be TF-WB aware for
this scheme to work properly. Using RTT, Device 1 would send a
TF-WB sequence to Device 2, then Device 2 would respond back with
another TF-WB sequence, plus a protocol message containing Device
2's turnaround-time (in fractions of a nanosecond) for the response
sequence. Device 1 can then compute its distance to Device 2 using
the formula
d = .tau. 1 , Rx - .tau. 1 , Tx - .tau. 2 , TAT 2 c ,
##EQU00008##
where .tau..sub.2,TAT is Device 2's measured turn-around-time,
i.e., the time from the beginning of the incoming TF-WB sequence
received from Device 1 at Device 2's antenna to the beginning of
the response packet at Device 2's antenna, (the TAT is reported to
Device 1 by Device 2), .tau..sub.1,Tx is the time at which the
outgoing TF-WB sequence leaves Device 1's antenna, and
.tau..sub.1,Rx is the time at which the incoming TF-WB sequence
arrives at Device 1's antenna, and c is the speed of light.
[0080] Multiplexing TF-WB Transmissions from Multiple Devices
[0081] If TF-WB is deployed in a real-world wireless network, some
sort of multiplexing scheme is needed to differentiate TF-WB
transmissions from multiple devices and to prevent them from
interfering with one another. For Client self-location, for
example, the Client needs to reliably receive transmissions from
multiple SEs without interference. Any of the following well-known
multiplexing methods can be employed for this purpose.
[0082] 1. TDMA--each SE transmits its TF-WB sequence in an assigned
time slot;
[0083] 2. CDMA--each SE transmits its TF-WB sequence at the same
sequence of frequencies and times; spreading codes are used to
differentiate the transmissions at the clients (this is similar to
the approach used to multiplex transmissions from multiple
satellites with GPS); and
[0084] 3. OFDMA--each SE transmits its TF-WB sequence at the same
sequence of frequencies and times; each AP is assigned a unique
mutually exclusive set of OFDM subcarriers to prevent
interference.
[0085] If TF-WB was applied to the IEEE 802.11 Wi-Fi.TM. standard,
OFDMA, TDMA or some combination of both would make the most sense;
TDMA because of its simplicity and effectiveness, OFDMA because of
its efficiency and the fact that Wi-Fi.TM. is mostly an OFDM-based
standard.
[0086] FIG. 21 is an exemplary plot of TDMA and OFDMA multiplexed
transmissions from multiple clients and APs in an IEEE 802.11-based
TF-WB system, in accordance with various embodiments. Each AP in a
multi-AP network is assigned a time slot in which to transmit its
TF-WB sequence that occurs just after the periodic Wi-Fi.TM. Beacon
message. Note that all seven of the APs are assigned to transmit in
the same time slot using OFDMA to prevent interference. TDMA is
only used to prevent the APs from interfering with the Clients and
the Wi-Fi.TM. Beacon in this example--not to prevent the APs from
interfering with each other.
[0087] At the beginning of each time slot, all seven APs transmit
their TF-WB sequences at exactly the same times and frequencies,
allowing a self-locating Client to receive, digitize and store all
seven of the TF-WB transmissions simultaneously. Each AP is
assigned a unique time-frequency interleaving (TFI) code. The TFI
code serves two important purposes: (1) to prevent two or more of
the APs from interfering with each other by transmitting on the
same sub-carrier(s) at the same time(s), (2) to allow each AP to
transmit on all OFDM sub-carriers at some time during each
narrowband OFDM transmission. This is to ensure that there are no
frequency holes in any of the transmitted signals, which is
critical for good channel sounding and ToA/AoA estimation.
[0088] As an example of a TFI code that meets both of these
criteria, suppose that 20 MHz 802.11g OFDM (which has 64
subcarriers) is used for the narrowband transmissions, and that
each transmission contains 50 OFDM symbols. AP #1 can transmit on
subcarriers 1, 8, . . . , 64 during OFDM symbols 1, 8, . . . , 50,
on subcarriers 2, 9, . . . , 58 during OFDM symbols 2, 9, . . . ,
44; on subcarriers 3, 10, . . . , 59 during OFDM symbols 3, 10, . .
. , 45 and so on. AP #2 can transmit on subcarriers 2, 9, . . . ,
58 during OFDM symbols 1, 8, . . . , 50; on subcarriers 2, 9, . . .
, 58 during OFDM symbols 3, 10, . . . , 45; on subcarriers 3, 10, .
. . , 59 during OFDM symbols 4, 11, . . . , 46 and so on,
continuing in this manner until we get to AP #7, which would
transmit on subcarriers 7, 14, . . . , 63 during OFDM symbols 1, 8,
. . . , 50; on subcarriers 1, 8, . . . , 64 during OFDM symbols 2,
9, . . . , 45; on subcarriers 2, 9, . . . , 58 during OFDM symbols
3, 10, . . . , 45, etc.
[0089] By defining the TFI mapping this way, none of the seven APs
transmits on the same sub-carrier at the same time, and all of the
APs visit every sub-carrier multiple times during each narrowband
transmission, so there are no holes.
[0090] FIG. 22 is an exemplary plot showing an efficient OFDMA
scheme in which transmissions from multiple Access Points are
time-frequency interleaved in the same OFDM burst, in accordance
with various embodiments. FIG. 22 shows a simpler example of TFI in
which 3 APs interleave their transmissions within OFDM bursts
spanning 8 sub-carriers in frequency and 10 symbols in
duration.
[0091] Multiplexing is also needed when the location estimate is
performed on the network side in order to prevent TF-WB
transmissions from multiple clients from interfering with other.
This can be achieved in very much the same way as it was for the
APs. Referring again to FIG. 21, each of the Clients in the network
is assigned to transmit in the time slot immediately following the
one assigned to the APs. Assuming there are N Clients for which
periodic locating tracking by the network is enabled, a TFI scheme
similar to the one described for the APs can be used, except it
would be done using modulo N arithmetic on the subcarriers and OFDM
symbols instead of modulo 7.
[0092] Multi-input Receivers and Joint Time/Angle of Arrival
Measurements
[0093] Nearly all IEEE 802.11n-compatible APs and some Clients are
equipped with multi-input receivers, allowing them to receive,
down-convert and digitize signals through up to 4 antenna paths
simultaneously. A multi-input receiver can be leveraged to improve
the accuracy of the ToA estimates in indoor environments. The
improved performance comes from having additional uncorrelated (or
loosely correlated) observations of the ToA through the new antenna
paths.
[0094] If a multi-input receiver is used to receive a TF-WB signal,
that receiver would down-convert, digitize and store each incoming
narrowband transmission through each of its M antenna paths
simultaneously. For ToA estimation, it would compute wideband
observation waveforms and Wiener filters for each antenna path, and
use the following formula to estimate the ToA, which is a
generalization of the formula in Step 5 above for multiple antenna
paths:
.tau. ^ 0 = argmin .tau. 0 m = 1 M n y m ( nT ) - x ^ ( nT , .tau.
0 ) * h m ( .tau. 0 ) 2 .sigma. m 2 ( 2 ) ##EQU00009##
where (nT) and h.sup.(m)(.tau..sub.0) are the wideband observation
waveform and Wiener filters, respectively, and .tau..sub.m.sup.2 is
the average noise power per sample in the mth antenna path. This
can be shown to be a maximum-likelihood estimate for the ToA
.tau..sub.0 given the system model described herein. The estimator
can be described in words as follows: [0095] For each candidate ToA
.tau..sub.0 [0096] For each antenna path m [0097] 1. Compute the
mean-square error (MSE) between the observed and model output
waveforms for that candidate ToA, [0098] 2. Normalize the MSE by
the noise power in that antenna path, [0099] 3. Sum normalized MSEs
for each antenna path. [0100] The ToA estimate {circumflex over
(.tau.)}.sub.0 is the candidate .tau..sub.0 with the lowest summed
MSE.
[0101] It should be noted that the multi-input ToA estimator
described above can be used to enhance the performance of any
single-antenna path ToA estimator--not just one that uses TF-WB
signaling. In other words, for any system that transmits a known
reference waveform {circumflex over (x)}(nT, .tau..sub.0) through a
multipath additive white Gaussian noise channel with propagation
delay .tau..sub.0 and receives through a multi-input receiver
yielding observation waveforms (nT), m=1, . . . , M for each of the
M antenna paths, the approach described above can be shown to
provide the optimum ToA estimate.
[0102] In addition to improving the time-resolution of indoor
time-of-arrival (ToA) measurements, TF-WB can also be used to
improve the accuracy of indoor angle-of-arrival (AoA) measurements
as well. A multi-input receiver is needed for AoA.
[0103] FIG. 23 is a schematic diagram of a 3-input TF-WB-capable
receiver, accordance with various embodiments. The received TF-WB
signals from each antenna path are down-converted 2360, digitized
2365, adjusted for gain dependent group delay and phase shift 2370,
and stored 2375-2377. To estimate the AoA 2301, one first finds the
ToA of the received TF-WB signals using equation (2) above, then
estimates the phase angle of the incoming transmission on each
antenna path by computing the phase angle of Wiener filter at the
tap corresponding to the LOS path. This is illustrated in FIGS.
24-26. FIGS. 24-26 are exemplary plots that show Wiener filters for
each of the 3 antenna paths from FIG. 23, in accordance with
various embodiments.
[0104] Returning to FIG. 23, the three phase angles computed in
this step can then be converted into an AoA estimate 2302 based on
the physical geometry of the antennas. The advantage of using TF-WB
signaling for the AoA measurements is multipath suppression. The
high time resolution allows the Wiener filter to discriminate the
LOS from other paths, so the phase angle we see is the phase of the
signal coming in the direction of the LOS path only--not other
paths. For lower bandwidth signals, the LOS path would be summed
with multipath reflections from other paths, yielding distorted
phase estimates.
[0105] Receiver Calibration
[0106] Most digital receivers use some sort of automatic gain
control (AGC) to adjust their received signal level entering the
analog-to-digital converter (ADC). The gain control circuit is
often implemented as a set of variable gain amplifiers (VGAs) in
series that can be either switched on and off depending on the
value of an input gain control word. When a VGA stage is turned on
vs. off, it can create a carrier phase and/or group delay change.
If the receiver changes its AGC setting to receive the narrowband
transmissions at different frequencies, the phase shifts and group
delay changes will create distortion in the received waveforms.
[0107] Fortunately, these phase and group delay vs. Rx gain
variations don't change much across time and temperature, so they
can be calibrated (i.e., measured at the time of manufacturing),
stored in a table, and compensated for during data digitization and
data storage. This is the purpose of block 1275 in FIG. 12.
[0108] TF-WB Receiver System
[0109] Referring to FIG. 12, a system for calculating the time of
arrival of a wireless signal through a wireless channel includes
receiver device 1200. Receiver device 1200 can include, but is not
limited to, an access point, a smartphone, a laptop computer, or a
wireless smart tag. Receiver device 1200 can include hardware,
software, or a combination of hardware and software.
[0110] Receiver device 1200 receives a sequence of two or more
signals representing two or more data packets transmitted through a
wireless channel. The two or more signals are a result of two or
more transmissions that are made sequentially in time at different
center frequencies in order to span a desired. At least one of the
two or more signals includes a physical layer preamble.
[0111] Receiver device 1200 calculates a time of arrival of one or
more signals of the received sequence using one or more of the
received sequence, the time differences among the two or more
transmissions, the different center frequencies, information from
the two or more data packets, and any carrier phase differences
among the two or more transmissions
[0112] In various embodiments, the time differences among the two
or more transmissions and any carrier phase differences among the
two or more transmissions are known to receiver device 1200 before
the received sequence is transmitted.
[0113] In various embodiments, the transmission time of each of the
two or more signals is encoded and included in the two or more data
packets before transmission through the wireless channel. Receiver
device 1200 determines the time differences among the two or more
transmissions by decoding and subtracting the encoded transmissions
of two or more consecutive data packets of the two or more data
packets.
[0114] In various embodiments, transmission time differences among
each of the two or more signals are encoded and included in the two
or more data packets before transmission through the wireless
channel. Receiver device 1200 determines the time differences among
the two or more transmissions by decoding the encoded transmission
time differences from the two or more data packets.
[0115] In various embodiments, the carrier phase of each of the two
or more transmitted signals is encoded and included in the two or
more data packets before transmission through the wireless channel.
Receiver device 1200 determines any carrier phase differences among
the two or more transmissions by decoding and subtracting the
encoded carrier phase from the two or more data packets.
[0116] In various embodiments, carrier phase differences among each
of the two or more transmitted signals are encoded and included in
the two or more data packets before transmission through the
wireless channel. Receiver device 1200 determines any carrier phase
differences among the two or more transmissions by decoding the
encoded carrier phase differences from the two or more data
packets.
[0117] The two or more data packets are different data packets, for
example. In various embodiments, the two or more data packets are
the same data packets.
[0118] In various embodiments, the two or more data packets conform
to the IEEE 802.11 (Wi-Fi.TM.) standard, the Bluetooth.TM.
standard, or the Global System for Mobile Communications (GSM)
standard.
[0119] In various embodiments, the sequence represents a signal
with a bandwidth that is at least twice as large as the bandwidth
of one or more signals of the sequence.
[0120] In various embodiments, receiver device 1200 calculates an
angle of arrival of one or more signals of the received sequence by
receiving the sequence through two or more antenna paths
simultaneously and using one or more of the received sequence, the
time differences among the two or more transmissions, any carrier
phase differences among the two or more transmissions, information
from the two or more data packets, and the geometry of the two or
more antennas.
[0121] In various embodiments, receiver device 1200 further
calculates a location of receiver device 1200 using the time of
arrival and one or more time of arrivals calculated from one or
more received sequences that are transmitted from one or more
additional locations. In various embodiments, time division
multiple access (TDMA), orthogonal frequency-division multiple
access (OFDMA), frequency division multiple access (FDMA) or code
division multiple access (CDMA) is used to differentiate the
received sequence and the one or more additional received sequences
at the receiver device.
[0122] In various embodiments, the location of receiver device 1200
is calculated periodically and displayed periodically on a floor
map.
[0123] In various embodiments, the received sequence and the one or
more received sequences include parametric information that
receiver device 1200 uses to calculate a location of receiver
device 1200. In various embodiments, the parametric information
includes one or more of coordinates for the locations of the
devices that transmitted the received sequence and the one or more
received sequences, number, time duration, and center frequencies
of signal transmissions per location beacon for the received
sequence and the one or more received sequences, or nominal start
time for a first location beacon relative to a beacon time for the
received sequence and the one or more received sequences.
[0124] In various embodiments, receiver device 1200 further
receives a calibration sequence of two or more calibration signals
before receiving the sequence. Receiver device 1200 uses the
calibration sequence to construct a calibration table storing
measured changes in group delay and phase shift over a set of
receiver gain settings and/or RF center frequencies. Receiver
device 1200 later uses the calibration table contents in its
time-of-arrival and/or angle-of-arrival calculations.
[0125] In various embodiments, receiver device 1200 further sends a
response sequence of two or more response signals representing two
or more response data packets to a device from which the sequence
was received and embeds in the two or more response data packets a
turn-around-time so that the device calculates a distance between
receiver device 1200 and the device using the turn-around-time. The
turn-around-time include a difference between a first time of the
receipt of the first signal in the sequence at an antenna of the
receiver device and a second time of the beginning of the response
sequence's beacon at an antenna of receiver device 1200.
[0126] In various embodiments, at least one additional receiver
device is included in the system that receives the transmitted
sequence and calculates one additional time of arrival for the
received sequence. The time of arrival and the one more additional
time of arrival are used to calculate a location of a device that
transmitted the received sequence.
[0127] TF-WB Receiver Method
[0128] FIG. 27 is an exemplary flowchart showing a method 2700 for
calculating the time of arrival of a wireless signal through a
wireless channel using a receiver device, in accordance with
various embodiments.
[0129] In step 2710 of method 2700, a sequence of two or more
signals representing two or more data packets transmitted through a
wireless channel is received using a receiver device. The two or
more signals are a result of two or more transmissions that are
made sequentially in time at different center frequencies in order
to span a desired. At least one of the two or more signals includes
a physical layer preamble.
[0130] In step 2720, a time of arrival of one or more signals of
the received sequence is calculated using one or more of the
received sequence, the time differences among the two or more
transmissions, the different center frequencies, information from
the two or more data packets, and any carrier phase differences
among the two or more transmissions using the receiver device.
[0131] TF-WB Receiver Computer Program Product
[0132] In various embodiments, a computer program product includes
a tangible computer-readable storage medium whose contents include
a program with instructions being executed on a processor so as to
perform a method for calculating the time of arrival of a wireless
signal through a wireless channel. This method is performed by a
system that includes one or more distinct software modules, for
example.
[0133] FIG. 28 is a schematic diagram of a system 2800 that
includes a receive module 2810 and a calculation module 2820 that
performs a method for calculating the time of arrival of a wireless
signal through a wireless channel, in accordance with various
embodiments.
[0134] Receive module 2810 receives a sequence of two or more
signals representing two or more data packets transmitted through a
wireless channel. The two or more signals are a result of two or
more transmissions that are made sequentially in time at different
center frequencies in order to span a desired. At least one of the
two or more signals includes a physical layer preamble.
[0135] Calculation module 2820 calculates a time of arrival of one
or more signals of the received sequence using one or more of the
received sequence, the time differences among the two or more
transmissions, the different center frequencies, information from
the two or more data packets, and any carrier phase differences
among the two or more transmissions.
[0136] TF-WB Transmitter System
[0137] Referring to FIG. 10, a system for calculating the time of
arrival of a wireless signal through a wireless channel includes
transmitter device 1000. Transmitter device 1000 can include, but
is not limited to, an access point, a smartphone, a laptop computer
or a wireless smart tag. Transmitter device 1000 can include
hardware, software, or a combination of hardware and software.
[0138] Transmitter device 1000 transmits a sequence of two or more
signals representing two or more data packets through a wireless
channel. The two or more signals are transmitted using two or more
transmissions that are made sequentially in time at different
center frequencies in order to span a desired bandwidth. At least
one of the two or more signals includes a physical layer preamble.
The sequence is received by a receiver device. A time of arrival of
one or more signals of the received sequence is calculated by the
receiver device using one or more of the received sequence, the
time differences among the two or more transmissions, the different
center frequencies, information from the two or more data packets,
and any carrier phase differences among the two or more
transmissions.
[0139] TF-WB Transmitter Method
[0140] FIG. 29 is an exemplary flowchart showing a method 2900 for
calculating the time of arrival of a wireless signal through a
wireless channel using a transmitter device, in accordance with
various embodiments.
[0141] In step 2910 of method 2900, a sequence of two or more
signals representing two or more data packets is transmitted
through a wireless channel using a transmitter device. The two or
more signals are transmitted using two or more transmissions that
are made sequentially in time at different center frequencies in
order to span a desired bandwidth. At least one of the two or more
signals includes a physical layer preamble. The sequence is
received by a receiver device. A time of arrival of one or more
signals of the received sequence is calculated by the receiver
device using one or more of the received sequence, the time
differences among the two or more transmissions, the different
center frequencies, information from the two or more data packets,
and any carrier phase differences among the two or more
transmissions.
[0142] TF-WB Transmitter Computer Program Product
[0143] In various embodiments, a computer program product includes
a tangible computer-readable storage medium whose contents include
a program with instructions being executed on a processor so as to
perform a method for calculating the time of arrival of a wireless
signal through a wireless channel. This method is performed by a
system that includes one or more distinct software modules, for
example.
[0144] FIG. 30 is a schematic diagram of a system 3000 that
includes a transmit module 3010 that performs a method for
calculating the time of arrival of a wireless signal through a
wireless channel, in accordance with various embodiments. Transmit
module 3010 transmits a sequence of two or more signals
representing two or more data packets through a wireless channel.
The two or more signals are transmitted using two or more
transmissions that are made sequentially in time at different
center frequencies in order to span a desired bandwidth. At least
one of the two or more signals includes a physical layer preamble.
The sequence is received by a receiver device. A time of arrival of
one or more signals of the received sequence is calculated by the
receiver device using one or more of the received sequence, the
time differences among the two or more transmissions, the different
center frequencies, information from the two or more data packets,
and any carrier phase differences among the two or more
transmissions.
[0145] While the present teachings are described in conjunction
with various embodiments, it is not intended that the present
teachings be limited to such embodiments. On the contrary, the
present teachings encompass various alternatives, modifications,
and equivalents, as will be appreciated by those of skill in the
art.
[0146] Further, in describing various embodiments, the
specification may have presented a method and/or process as a
particular sequence of steps. However, to the extent that the
method or process does not rely on the particular order of steps
set forth herein, the method or process should not be limited to
the particular sequence of steps described. As one of ordinary
skill in the art would appreciate, other sequences of steps may be
possible. Therefore, the particular order of the steps set forth in
the specification should not be construed as limitations on the
claims. In addition, the claims directed to the method and/or
process should not be limited to the performance of their steps in
the order written, and one skilled in the art can readily
appreciate that the sequences may be varied and still remain within
the spirit and scope of the various embodiments.
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