U.S. patent application number 15/162018 was filed with the patent office on 2016-09-15 for position location using phase-adjusted transmitters.
The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Fuyun Ling, Krishna Kiran Mukkavilli, Gordon Kent Walker.
Application Number | 20160270022 15/162018 |
Document ID | / |
Family ID | 37684349 |
Filed Date | 2016-09-15 |
United States Patent
Application |
20160270022 |
Kind Code |
A1 |
Ling; Fuyun ; et
al. |
September 15, 2016 |
POSITION LOCATION USING PHASE-ADJUSTED TRANSMITTERS
Abstract
Systems and methods are provided for determining position
location information in a wireless network. In one embodiment,
timing offset information is communicated between multiple
transmitters and one or more receivers. Such information enables
accurate position or location determinations to be made that
account for timing differences throughout the network. In another
embodiment, transmitter phase adjustments are made that advance or
delay transmissions from the transmitters to account for potential
timing differences at receivers. In yet another embodiment,
combinations of timing offset communications and/or transmitter
phase adjustments can be employed in the wireless network to
facilitate position location determinations.
Inventors: |
Ling; Fuyun; (San Diego,
CA) ; Walker; Gordon Kent; (Poway, CA) ;
Mukkavilli; Krishna Kiran; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Family ID: |
37684349 |
Appl. No.: |
15/162018 |
Filed: |
May 23, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11326868 |
Jan 5, 2006 |
9354297 |
|
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15162018 |
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60721505 |
Sep 27, 2005 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 64/00 20130101;
G01S 1/024 20130101; G01S 5/0226 20130101; G01S 5/021 20130101;
G01S 5/14 20130101 |
International
Class: |
H04W 64/00 20060101
H04W064/00; G01S 1/02 20060101 G01S001/02; G01S 5/02 20060101
G01S005/02; G01S 5/14 20060101 G01S005/14 |
Claims
1. A system in a wireless network, comprising: at least three base
stations, wherein: each of the base stations are configured to
determine a time difference between a future transmission time of
the base stations and a common clock in the wireless network; at
least one of the base stations is further configured to regulate an
effective channel delay spread, as perceived by at least one
receiver, by advancing or delaying transmission timing of future
transmission of the at least one base station relative to the
common clock; and each of the base stations are further configured
to regulate cyclically shifting a signal based on a determined time
difference, wherein the signal is cyclically shifted according to a
cyclic convolution; and each of the base stations are further
configured to transmit the cyclically shifted signal to the at
least one receiver at the future transmission time, wherein a
position of the at least one receiver is determined based at least
on a linear convolution of a channel with the transmitted signal,
from the at least three base stations, that is processed as the
cyclic convolution based on the delay spread of the channel being
less than a cyclic prefix employed by the signal.
2. The system of claim 1, wherein each of the base stations are
further configured to generate at least two timing offsets denoted
as d.sub.a and d.sub.b.
3. The system of claim 2, wherein each of the base stations are
further configured to determine a first parameter .tau.'.sub.a that
is an actual delay perceived by a line of sight propagation
component based on a distance between a first base station A and
the at least one receiver, and determining a second parameter
.tau.'.sub.b that is an actual delay that is perceived by a line of
sight component from a second base station B to the at least one
receiver.
4. The system of claim 3, wherein at least a first and second base
station of the base stations are further configured to process
additional delays d.sub.a and d.sub.b at the first and second base
stations based on a delay spread .tau.'.sub.b-.tau.'.sub.a
exceeding a cyclic prefix.
5. The system of claim 4, wherein the receiver is configured to
process the following equation:
y(n)=h.sub.a(n)*x.sub.a(n-d.sub.a)+h.sub.b(n)*x.sub.b(n-d.sub.b)+w(n),
where y(n) represents a signal received at the receiver, h.sub.a(n)
and x.sub.a(n) are a channel and a signal with respect to the first
base station A, * represents a linear convolution operation, w(n)
is noise added at the receiver.
6. The system of claim 5, wherein the receiver is further
configured to process the following equation:
y(n)=h.sub.a(n-d.sub.a)*x(n)+h.sub.b(n-d.sub.b)*x(n)+w(n), where a
perceived channel delay spread is given by
(.tau.'.sub.a-d.sub.b)-(.tau.'.sub.a-d.sub.a) and controlled by
introducing timing offsets at the first base station A.
7. The system of claim 5, wherein the receiver is further
configured to determine a cyclic convolution based on an effective
delay spread being less than a cyclic prefix as in the following
equations:
y(n)=h.sub.a(n)x.sub.a(n-d.sub.a)+h.sub.b(n)x.sub.b(n-d.sub.b)+w(n),
or
y(n)=h.sub.a(n-d.sub.a)x.sub.a(n)+h.sub.b(n-d.sub.b)x.sub.b(n)+w(n)
where denotes circular convolution.
8. The system of claim 7, wherein at least one base station of the
base stations is further configured to delay transmissions from
transmitters thereby meeting length requirements of cyclic
prefix.
9. The system of claim 7, wherein at least one base station of the
base stations is further configured to employ a long cyclic prefix
to enable an estimation of delay from weak transmitters that are
far away.
10. The system of claim 9, further comprising means for undoing an
effect of physical delays by a cyclic shift of a positioning
signal, where x.sub.a,p(n) is an intended positioning signal from
the first base station A with timing delay d.sub.a, and a
transmitter sends a cyclically shifted version given by
x.sub.a,p(n+d.sub.a).
11. The system of claim 10, further comprising processing the
following equation:
y(n)=h.sub.a(n)x.sub.a,p(n)+h.sub.b(n)x.sub.b,p(n)+w(n).
12. The system of claim 1, wherein timing information is available
offline.
13. The system of claim 12, wherein pseudo ranges are measured.
14. The system of claim 13, wherein each of the base stations are
further configured to receive the pseudo ranges.
15. A method in a wireless network, comprising: determining, by
each of at least three base stations, a time difference between a
future transmission time of the base stations and a common clock in
the wireless network; regulating, by at least one base station of
the base stations, an effective channel delay spread, as perceived
by at least one receiver, by advancing or delaying transmission
timing of future transmission of the at least one of the base
stations relative to the common clock; regulating cyclically
shifting, by each of the base stations, a signal based on a
determined time difference, wherein the signal is cyclically
shifted according to a cyclic convolution; and transmitting the
cyclically shifted signal, by each of the base stations, to the at
least one receiver at the future transmission time, wherein a
position of the at least one receiver is determined based at least
on a linear convolution of a channel with the transmitted signal,
from the at least three base stations, that is processed as the
cyclic convolution based on the delay spread of the channel being
less than a cyclic prefix employed by the signal.
16. The method of claim 15, further comprising: generating, by each
of the base stations, at least two timing offsets denoted as
d.sub.a and d.sub.b.
17. The method of claim 16, further comprising: determining, by
each of the base stations, a first parameter .tau.'.sub.a that that
is an actual delay perceived by a line of sight propagation
component based on a distance between a first base station A and
the at least one receiver; and determining, by each of the base
stations, a second parameter .tau.'.sub.b that is an actual delay
that is perceived by a line of sight component from a second base
station B to the at least one receiver.
18. The method of claim 17, further comprising: processing
additional delays d.sub.a and d.sub.b at the first and second base
stations based on a delay spread .tau.'.sub.b-.tau.'.sub.a
exceeding a cyclic prefix.
19. The method of claim 18, further comprising: processing the
following equation:
y(n)=h.sub.a(n)*x.sub.a(n-d.sub.a)+h.sub.b(n)*x.sub.b(n-d.sub.b-
)+w(n), where y(n) represents a signal received at the receiver,
h.sub.a(n) and x.sub.a(n) are a channel and a signal with respect
to the first base station A, * represents a linear convolution
operation, w(n) is noise added at the receiver.
20. The method of claim 19, further comprising: processing the
following equation:
y(n)=h.sub.a(n-d.sub.a)*x(n)+h.sub.b(n-d.sub.b)*x(n) +w(n), where a
perceived channel delay spread is given by
(.tau.'.sub.b-d.sub.b)-(.tau.'.sub.a-d.sub.a) and controlled by
introducing timing offsets at the first base station A.
21. The method of claim 19, further comprising: determining a
cyclic convolution based on an effective delay spread being less
than a cyclic prefix as in the following equations:
y(n)=h.sub.a(n)x.sub.a(n-d.sub.a)+h.sub.b(n)x.sub.b(n-d.sub.b)+w(n),
or
y(n)=h.sub.a(n-d.sub.a)x.sub.a(n)+h.sub.b(n-d.sub.b)x.sub.b(n)+w(n)
where denotes circular convolution.
22. The method of claim 21, further comprising: delaying
transmissions from transmitters thereby meeting length requirements
of cyclic prefix.
23. The method of claim 21 further comprising: employing a long
cyclic prefix to enable an estimation of delay from weak
transmitters that are far away.
24. The method of claim 23, further comprising: undoing an effect
of physical delays by a cyclic shift of a positioning signal, where
x.sub.a,pp(n) is an intended positioning signal from the first base
station A with timing delay d.sub.a, and a transmitter sends a
cyclically shifted version given by x.sub.a,p(n+d.sub.a).
25. The method of claim 24, further comprising: processing the
following equation:
y(n)=h.sub.a(n)x.sub.a,p(n)+h.sub.b(n)x.sub.b,p(n)+w(n).
26. The method of claim 15, wherein timing information is available
offline.
27. The method of claim 26, further comprising: measuring pseudo
ranges.
28. The method of claim 27, further comprising: receiving, by each
of the base stations, the pseudo ranges.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of co-pending,
commonly assigned, U.S. patent application Ser. No. 11/326,868
entitled "POSITION LOCATION USING PHASE-ADJUSTED TRANSMITTERS,"
filed Jan. 5, 2006, which claims priority to U.S. provisional
application Ser. No. 60/721,505 entitled "POSITION LOCATION USING
TRANSMITTERS WITH TIMING OFFSET" filed Sep. 27, 2005, and assigned
to the assignee hereof and each of which priority is hereby claimed
and the disclosures of which are hereby expressly incorporated by
reference herein. The present application is related to commonly
assigned U.S. patent applications Ser. No. 11/327,536 entitled
"POSITION LOCATION USING TRANSMITTERS WITH TIMING OFFSET" filed
Jan. 5, 2006, and Ser. No. 11/327,535 "POSITION LOCATION USING
TRANSMITTERS WITH TIMING OFFSET AND PHASE ADJUSTMENT" filed Jan. 5,
2006, the disclosures of which are hereby expressly incorporated by
reference herein.
FIELD
[0002] The subject technology relates generally to communications
systems and methods, and more particularly to systems and methods
that determine position locations in accordance with wireless
networks by employing timing offsets or transmitter phase
adjustment techniques within the networks.
BACKGROUND
[0003] One technology that has dominated wireless systems is Code
Division Multiple Access (CDMA) digital wireless technology. In
addition to CDMA, an air interface specification defines FLO
(Forward Link Only) technology that has been developed by an
industry-led group of wireless providers. In general, FLO has
leveraged the most advantageous features of wireless technologies
available and used the latest advances in coding and system design
to consistently achieve the highest-quality performance. One goal
is for FLO to be a globally adopted standard.
[0004] The FLO technology was designed in one case for a mobile
multimedia environment and exhibits performance characteristics
suited ideally for use on cellular handsets. It uses the latest
advances in coding and interleaving to achieve the highest-quality
reception at all times, both for real-time content streaming and
other data services. FLO technology can provide robust mobile
performance and high capacity without compromising power
consumption. The technology also reduces the network cost of
delivering multimedia content by dramatically decreasing the number
of transmitters needed to be deployed. In addition, FLO
technology-based multimedia multicasting complements wireless
operators' cellular network data and voice services, delivering
content to the same cellular handsets used on 3G networks.
[0005] The FLO wireless system has been designed to broadcast real
time audio and video signals, apart from non-real time services to
mobile users. The respective FLO transmission is carried out using
tall and high power transmitters to ensure wide coverage in a given
geographical area. Further, it is common to deploy 3-4 transmitters
in most markets to ensure that the FLO signal reaches a significant
portion of the population in a given market. Because of FLO
transmitter coverage, it is possible to determine position
locations based on triangulation techniques, for example.
Traditional position location techniques make use of satellite
based GPS signals for range measurements. However, the problem with
satellite based signals is the lack of availability of the signal
in indoor environments, for example, where line of sight to the
satellites is not available. Conversely, FLO networks are often
designed to achieve indoor coverage, and so the respective
waveforms can provide positioning information to devices while
located indoors.
SUMMARY
[0006] The following presents a simplified summary of various
embodiments in order to provide a basic understanding of some
aspects of the embodiments. This summary is not an extensive
overview. It is not intended to identify key/critical elements or
to delineate the scope of the embodiments disclosed herein. Its
sole purpose is to present some concepts in a simplified form as a
prelude to the more detailed description that is presented
later.
[0007] Systems and methods are provided for determining position or
location information across wireless networks and in lieu of (or in
connection with) conventional Global Positioning System (GPS)
techniques. In one embodiment, position location in a broadcast
network is determined using multiple transmitters that account for
timing differences between transmitters. Many position location
algorithms assume that transmitters emanating signals used for
range measurements are aligned in time using a common central clock
such as GPS, for example. However, it is of some advantage in
certain broadcast systems to advance/delay transmissions from some
of the transmitters with respect to the central clock to facilitate
signal reception and quality throughout the network. In such cases,
position location algorithms make use of timing offset information
of the transmitters to result in more accurate range measurements
over conventional position location components. Thus, in some
embodiments, overhead parameter information (e.g., timing offset
information) can be transmitted as well as the use of this
additional information at the receiver to result in accurate range
measurements.
[0008] In another embodiment, signal transmission timing can be
advanced or delayed at the respective transmitters to alleviate the
need to account for timing offsets at the receiver. By adjusting
the timing of transmitted signals at the transmitters, accurate
position information can be determined at the respective receivers
while mitigating timing offset calculations since timing mismatches
from a centralized clock have already been accounted for at the
transmitters. As can be appreciated, some systems can include
combinations of timing offsets that are communicated to the
receivers and/or timing adjustments at the transmitters to
facilitate accurate position location determinations.
[0009] To the accomplishment of the foregoing and related ends,
certain illustrative embodiments are described herein in connection
with the following description and the annexed drawings. These
aspects are indicative of various ways in which the embodiments may
be practiced, all of which are intended to be covered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic block diagram illustrating a wireless
network positioning system.
[0011] FIG. 2 is an example system that employs timing offset
information for position location determinations.
[0012] FIG. 3 illustrates example techniques for transmitting
timing offset information.
[0013] FIG. 4 illustrates an example system for adjusting timing
information in a wireless positioning system.
[0014] FIG. 5 is a diagram illustrating example network layers for
a wireless positioning system.
[0015] FIG. 6 is a diagram illustrating an example data structure
and signal for a wireless positioning system.
[0016] FIG. 7 illustrates an example timing process for a wireless
positioning system.
[0017] FIG. 8 is a diagram illustrating an example user device for
a wireless system.
[0018] FIG. 9 is a diagram illustrating an example base station for
a wireless system.
[0019] FIG. 10 is a diagram illustrating an example transceiver for
a wireless system.
DETAILED DESCRIPTION
[0020] Systems and methods are provided for determining position
location information in a wireless network. In one embodiment,
timing offset information is communicated between multiple
transmitters and one or more receivers. Such information enables
accurate position or location determinations to be made that
account for timing differences throughout the network. In another
embodiment, transmitter phase adjustments are made that advance or
delay transmissions from the transmitters to account for potential
timing difference between the transmitters and the common clock. In
this manner, position location determinations can be made without
further timing adjustment at the receivers. In yet another aspect,
combinations of timing offset communications and/or transmitter
phase adjustments can be employed in the wireless network to
facilitate position location computations or determinations.
[0021] It is noted that timing offset can be considered a mismatch
in timing between a transmitter clock and a common clock source
which leads to synchronization symbols at the transmitter being
transmitted at an offset compared to the common clock
synchronization signals. For example, in the case of Forward Link
Only (FLO) signals, the superframe boundary at the transmitter is
generally expected to be synchronized to a 1 PPS signal from a GPS.
However, due to timing mismatch or sometimes intentionally for
network optimization purposes, the superframe boundary may actually
be earlier or delayed with respect to the 1 PPS signal from the
GPS. This is referred to as timing offset at the transmitter.
[0022] With phase adjustments at the transmitter, the transmitter
waveform is essentially modified to regulate the propagation delay
perceived by the receiver, irrespective of timing offsets at the
transmitter. In this case, even though the transmitter's clock (and
hence transmission) may be precisely synchronized with the common
clock source, it is possible that the transmitter waveform is
modified to result in skewed propagation delay measurements at the
receiver. For example, in the case of FLO employing OFDM signaling,
the superframe boundary could be synchronized with the 1 PPS signal
from GPS. However, the transmitter could adjust the transmission
phase by employing a cyclic shift of the OFDM symbol buffer. The
cyclic prefix for the OFDM symbol can be formed based on the
cyclically shifted OFDM symbol. With such a signal modification,
the delay perceived by the receiver changes with the transmission
phase chosen (or equivalently the amount of cyclic shift on the
OFDM symbol). This is referred to as phase adjustment at the
transmitter.
[0023] As used in this application, the terms "component,"
"network," "system," and the like are intended to refer to a
computer-related entity, either hardware, a combination of hardware
and software, software, or software in execution. For example, a
component may be, but is not limited to being, a process running on
a processor, a processor, an object, an executable, a thread of
execution, a program, and/or a computer. By way of illustration,
both an application running on a communications device and the
device can be a component. One or more components may reside within
a process and/or thread of execution and a component may be
localized on one computer and/or distributed between two or more
computers. Also, these components can execute from various computer
readable media having various data structures stored thereon. The
components may communicate over local and/or remote processes such
as in accordance with a signal having one or more data packets
(e.g., data from one component interacting with another component
in a local system, distributed system, and/or across a wired or
wireless network such as the Internet).
[0024] FIG. 1 illustrates a wireless network positioning system
100. The system 100 includes one or more transmitters 110 that
communicate across a wireless network to one or more receivers 120.
The receivers 120 can include substantially any type of
communicating device such as a cell phone, computer, personal
assistant, hand held or laptop devices, and so forth. The system
100 employs one or more position location components 130 to
facilitate determining a position or location for the receivers
120. In general, timing synchronization information between the
transmitters 110 and the receivers 120 may need to be adjusted in
various embodiments described herein to facilitate accurate
position location determinations at the receivers. In one case,
timing offset components 140 can be communicated between
transmitter 110 and receiver 120 to indicate timing differences or
adjustments in the wireless network to be accounted for in a
position location determination component or algorithm. Another
case employs phase adjustment components 150 at the transmitters
110 to advance or delay signals that have the effect of
compensating for timing mismatches or differences that may occur in
the system 100. In other embodiments, various combinations of
timing offset components 140 and/or phase adjustment components 150
can be employed concurrently to facilitate position location
determinations in the wireless network positioning system 100. As
illustrated, one or more pilot symbols 154 can be provided for
delay measurement.
[0025] Generally, conventional position location techniques make
use of satellite based GPS signals for range measurements. However,
one problem with satellite based signals is the lack of
availability of the signal such as with indoor environments where
line of sight to the satellites is not available. On the other
hand, the high power nature of Forward Link Only (FLO) transmission
facilitates that the FLO waveform is available in indoor
environments where the GPS signal is not available. Hence, there is
an alternative to position location based on measurements made from
FLO signals when the FLO signal from multiple transmitters is
available. In the following description, it may be assumed that a
FLO receiver is able to access signals from at least three
different FLO transmitters (other configurations possible), which
may or may not be transmitting the same information content.
[0026] The FLO network is generally deployed for Single Frequency
Network (SFN) mode of operation where the transmitters are
synchronized to a common clock source. The clock source, for
example, could be derived from a 1PPS signal from the GPS, for
example. The FLO waveform is based on Orthogonal Frequency Division
Multiplexing (OFDM) signaling and can be designed under the
assumption that delay spread of a channel would be less than about
135 us, for example. When multiple transmitters 110 are visible to
a receiver 120, the delay spread perceived by the receiver is a
function of the relative position of the receiver from various
transmitters. In some cases, it is possible that the receiver 120
is close to one of the transmitters 110 and far from one other
transmitter thus resulting in a large delay spread. If the
resulting delay spread exceeds the design specification of 135 us
(or other reference), it can incur significant penalty on system
performance. However, it is possible to control the delay spread
perceived by the receiver 120 at various points in the network by
delaying or advancing a super-frame boundary with respect to a
synchronization pulse from the central clock. Hence, in an
optimized FLO network deployment, it can also be realistic to
assume that there is a fixed timing offset between different
transmitters 110.
[0027] In a SFN deployment of a FLO network, the transmitters 110
are likely to be tuned to operate a fixed timing offset with
respect to a central clock (and hence each other) to optimize the
delay spread seen at the receiver 120 and hence the system
performance. The relative timing offsets at the transmitter can
adversely affect range measurements for position location if not
accounted for. However, in mobile-based position location and
network-based position location, it is possible to account for
transmitter timing offset by modifying the range calculations. This
can include having the FLO network provide the transmitter timing
offset information to the receiver 120 in a mobile-based position
location system, adjusting transmitting timing and phase signals,
or a combination of timing offsets with signal adjustments.
[0028] FIG. 2 illustrates an example system 200 that employs timing
offsets for position determinations. In this example, transmitters
A, B and C at 210 can be three different FLO transmitters carrying
FLO signals that are within the range of reception of a receiver
220 at a given point in time. Further, let d.sub.a, d.sub.b and
d.sub.c refer to a timing offset 230 of the respective transmitters
with respect to a common clock source 240. Here, positive offset
refers to advancing the transmission with respect to the central
clock 240 while a negative offset would refer to delaying
transmission with respect to the central clock. It can be assumed
that a receiver clock is synchronized to the common clock source
240 in phase and frequency.
[0029] The FLO air interface specification which is commonly
available allows for each transmitter 210 to insert symbols (known
as positioning pilot channel) unique to the transmitter. These
symbols can be designed to allow the receiver 220 to estimate the
propagation delay from each of the transmitters 210. The
positioning pilot channel is essentially a set of pilot tones
specific to each transmitter, designed with high processing gain so
that a channel with long delay spread as well as weak energy can
still be detected at the receiver 220. In the case of line of sight
propagation without significant scattering from the transmitter 210
to the receiver 220, the channel estimate obtained via the
positioning pilot generally comprises of a single path. The
distance of the receiver 220 from the transmitter 210 is determined
based on the location of the channel path in the channel
estimate.
[0030] In the system example 200, let .tau..sub.a be the location
of the single path (or the first arriving path in the case of
multi-path) in the channel estimate based on positioning pilot
channel from transmitter A. Similarly, let .tau..sub.b and
.tau..sub.c be the delay of the first arriving path in the channel
estimate from the transmitters B and C respectively. If the clocks
at the three transmitters 210, as well as the receiver 220, were
synchronized in frequency as well as phase, then the distance of
the receiver from the transmitters is calculated as the velocity of
light (c) multiplied by the propagation delay measured via the
channel estimate. However, in the presence of timing offsets at the
transmitters 210, the measured delays at the receiver 220 should be
corrected by timing offset 230 between the transmitter and the
receiver. Hence, the distance of the receiver from the transmitter
A is given by:
[0031] S.sub.a=(d.sub.a+.tau..sub.a).times.c, where c is the
velocity of light.
[0032] Similarly, S.sub.b=(d.sub.b+.tau..sub.b).times.c and
S.sub.c=(d.sub.c+.tau..sub.c).times.c. When the relative distance
of the receiver 220 from three known locations is determined (in
this case, the known locations are the FLO transmitters), the
location of the receiver can be obtained by the well known method
of triangulation. The method of triangulation is essentially
determining the single point of intersection for circles drawn
around the three transmitters A, B and C with radii S.sub.a,
S.sub.b and S.sub.c respectively. Hence it is clear that in the
case of relative timing offsets at the transmitters 210, it is
useful for the receiver 220 to be aware of the timing offset values
230 to determine position or location accurately.
[0033] FIG. 3 illustrates example methods for communicating timing
information 300. As can be appreciated, there are several possible
techniques for transmitting timing offset information 300 to a
receiver. It is noted that it is sufficient for the receiver to be
aware of the timing offset of each of the transmitters with respect
to a common central clock such as the GPS clock or other common
clock.
[0034] At 310, one possible transmission mechanism is for the
transmitters to broadcast the information about the timing offset
using overhead symbols. For instance, in the FLO system, the timing
information from all the transmitters in a given local area can be
contained in the local area OIS field (Overhead Information
Symbols) which is specific to a given local area but changes across
different local areas in a given wide area. One advantage of such
an approach is that the transmitter timing information is
localized. It is noted that it may not offer an advantage to a
receiver to receive timing offset information about a transmitter
from which it cannot receive the positioning pilot channel. On the
other side, the local OIS field may be more susceptible to
interference at the edge of coverage than the positioning pilot
channel. As a result, the receiver may be able to decode the
positioning pilot channel successfully while unable to get the
timing information from the local OIS channel. One variant of this
approach would be to include the timing information in the wide
area OIS which would remove the edge of coverage issues at the cost
of broadcasting the transmitter timing information over a much
wider geographical area (and hence useful bandwidth).
[0035] At 320, another possible technique to transmit timing
information is to embed the transmitter timing information in the
positioning pilot channel (PPC). In this case, the receiver can
first estimate the channel from a given transmitter using the PPC
from the transmitter and then decode the timing information
embedded in the PPC. The processing gain of the PPC may have to be
increased sufficiently in this case to facilitate that the
detection probability of the PPC is not affected in the presence of
additional information embedded in the symbols.
[0036] At 330, a third possible technique to transmit timing
information is to broadcast an almanac of the transmitters as a
non-real time MLC (MediaFLO Logical Channel) periodically and
facilitate that the receivers decode this particular information
MLC. At 340, another attractive technique mitigates the timing
offset information at the transmitter by modifying the transmitter
waveform for the PPC symbols by taking the timing offsets into
consideration as discussed below with respect to FIG. 4.
[0037] FIG. 4 illustrates an example system 400 for adjusting
timing information in a wireless positioning system. In this
example, two transmitters A and B are shown at 410. A signal from
the transmitters 410 can be advanced or delayed at 420 to account
for possible timing differences in the system. Thus, a receiver 430
may be able to determine position locations without having to
determine offsets from a centralized clock as described above. The
concept of advancing or delaying the transmitter timing at 420 is
introduced in the FLO system so as to regulate the effective
channel delay spread as perceived by the receiver 430. In one case,
in an OFDM system, the linear convolution of the channel with the
transmitted signal can be treated as a cyclic convolution if the
delay spread of the channel is less than the cyclic prefix employed
by the OFDM signal.
[0038] In this example, consider transmitters A and B at 410 with
timing offsets d.sub.a and d.sub.b. Let .tau..sub.a be actual delay
that would be perceived by a line of sight propagation component
based on the distance between the transmitter A and the receiver
430. Similarly, let .tau..sup.b be the actual delay that would be
perceived by a line of sight component from the transmitter B to
the receiver 430. Note that additional delays d.sub.a and d.sub.b
are introduced at the transmitters when the delay spread
.tau..sub.b-.tau..sub.a exceeds the cyclic prefix (assuming one
line of sight component from each of the transmitters). With delays
d.sub.a and d.sub.b at the transmitters, the signal received at the
receiver is given by:
y(n)=h.sub.a(n)*x.sub.a(n-d.sub.a)+h.sub.b(n)*x.sub.b(n-d.sub.b)+w(n),
Equation 1
[0039] Where h.sub.a(n) and x.sub.a(n) are the channel and the
signal with respect to the transmitter A, * represents the linear
convolution operation and w(n) is the noise added at the receiver.
In the case of traffic channel in a wide area network, x.sub.a(n)
and x.sup.b(n) are generally the same (say x(n)).
[0040] Using the properties of linear convolution the above
equation can be written as,
y(n)=h.sub.a(n-d.sub.a)*x(n)+h.sub.b(n-d.sub.b)*x(n)+w(n) Equation
2
[0041] So that the perceived channel delay spread is now given by
(.tau.'.sub.b-d.sub.b)-(.tau.'.sub.a-d.sub.a) and can be controlled
by introducing timing offsets at the transmitter. When the
effective delay spread is less than the cyclic prefix, the received
signal in Equation 1 can be written as the cyclic convolution
instead of a linear convolution. Thus:
y(n)=h.sub.a(n)x.sub.a(n-d.sub.a)+h.sub.b(n)x.sub.b(n-d.sub.b)+w(n),
Equation 3
or equivalently,
y(n)=h.sub.a(n-d.sub.a)x.sub.a(n)+h.sub.b(n-d.sub.b)x.sub.b(n)+w(n)
Equation 4
[0042] where denotes circular convolution. If the cyclic prefix is
long enough, then the operation of delaying the signal x.sub.a(n)
by d.sub.a in Equation 1 to result in Equation 3 can be
accomplished by circular rotation of x.sub.a(n) by d.sub.a in
Equation 3.
[0043] Based on the above cases, the following is proposed for the
pilot positioning channel with respect to regular traffic channels.
During the regular traffic channel, the cyclic prefix employed is
typically short (512 chips in the case of FLO) and hence, the
cyclic shift technique discussed in Equation 3 cannot be employed
to regulate the effective delay spread of the channel. Therefore,
the transmissions from the respective transmitters will be
physically delayed (transmitters A and B by d.sub.a and d.sub.b in
this example) to meet the cyclic prefix requirements. On the other
hand, for the positioning pilot channel, a long cyclic prefix (of
the order of 2500 chips in FLO, where chips refer to bits encoded
into data packets) may be employed so as to enable the estimation
of delay from weak transmitters that are far away. Further, the
delays d.sub.a and d.sub.b introduced by the transmitters for the
traffic channel affect the delay observations made in the
positioning pilot channel, thus requiring this overhead information
at the receiver as discussed previously.
[0044] Given the availability of a long cyclic prefix for the pilot
positioning channel, the transmitter can undo the effect of the
actual physical delays d.sub.a and d.sub.b by a cyclic shift of the
positioning signal. If x.sub.a,p(n) is the intended positioning
signal from the transmitter A with timing delay d.sub.a, then the
transmitter can send out a cyclically shifted version given by
x.sub.a,p(n+d.sub.a). Similarly, cyclically shift the signal from
the transmitter B. Due to the presence of long cyclic prefix,
Equation 3 is still valid and hence:
y(n)=h.sub.a(n)x.sub.a,p(n)+h.sub.b(n)x.sub.b,p(n)+w(n), Equation
5
[0045] thus alleviating the need to send out the transmitter delay
information to the receiver. This technique can be used to account
for the transmitter timing offsets resulting from delays introduced
as part of network planning as well as other timing delays that may
arise due to filters, cables and such other components, for
example.
[0046] Relating to another embodiment, the above discussion may
assume that the range measurements are being calculated at the
mobile receiver. However, it is possible that the calculations are
performed in the network where the timing information is available
offline. In this case, the receiver can measure pseudo ranges
S'.sub.a, S'.sub.b and S'.sub.c, where for instance,
S'.sub.a=.tau..sub.a.times.c, without taking the transmitter timing
offset into account. The receiver would relay the pseudo range
S'.sub.a to the network and the further corrections by the timing
offsets can be easily carried out at the network since the entire
almanac can be made available at the network.
[0047] The above discussion assumed that the receiver clock is
closely synchronized to the common clock and a mismatch between the
common clock and the transmitter clock exists due to timing offset
or phase adjustment at the transmitter. However, note that this can
be considered a special case and the receiver clock need not be
synchronized to the common clock. When the receiver clock is not
synchronized to the common clock, the delay measurements from the
respective transmitters can also include a common bias term, which
is the amount of mismatch between the common clock and the receiver
clock. The common bias is now another unknown that needs to be
computed in addition to the spatial co-ordinates of the receiver.
The unknowns in the spatial co-ordinates as well as the clock bias
can all be solved for with the help of measurements from additional
transmitters. In particular, it suffices to have measurements from
e.g., four different transmitters (with the timing offset
information available with respect to the common clock source and
assuming that the receiver is on the surface of the earth), to
solve for both the spatial co-ordinates as well as the common clock
bias at the receiver. In the absence of the common clock bias at
the receiver (i.e., receiver clock is synchronized to the common
clock), it suffices to have delay measurements from e.g., three
different transmitters.
[0048] FIG. 5 illustrates example network layers 500 for a wireless
positioning system.
[0049] A Forward Link Only (FLO) air interface protocol reference
model is shown in FIG. 5. Generally, the FLO air interface
specification covers protocols and services corresponding to OSI6
having Layers 1 (physical layer) and Layer 2 (Data Link layer). The
Data Link layer is further subdivided into two sub-layers, namely,
Medium Access (MAC) sub-layer, and Stream sub-layer. Upper Layers
can include compression of multimedia content, access control to
multimedia, along with content and formatting of control
information.
[0050] The FLO air interface specification typically does not
specify the upper layers to allow for design flexibility in support
of various applications and services. These layers are shown to
provide context. The Stream Layer includes multiplexes up to three
upper layer flows into one logical channel, binding of upper layer
packets to streams for each logical channel, and provides
packetization and residual error handling functions. Features of
the Medium Access Control (MAC) Layer includes controls access to
the physical layer, performs the mapping between logical channels
and physical channels, multiplexes logical channels for
transmission over the physical channel, de-multiplexes logical
channels at the mobile device, and/or enforces Quality of Service
(QOS) requirements. Features of Physical Layer include providing
channel structure for the forward link, and defining frequency,
modulation, and encoding requirements.
[0051] In general, FLO technology utilizes Orthogonal Frequency
Division Multiplexing (OFDM), which is also utilized by Digital
Audio Broadcasting (DAB), Terrestrial Digital Video Broadcasting
(DVB-T), and Terrestrial Integrated Services Digital Broadcasting
(ISDB-T). Generally, OFDM technology can achieve high spectral
efficiency while effectively meeting mobility requirements in a
large cell SFN. Also, OFDM can handle long delays from multiple
transmitters with a suitable length of cyclic prefix; a guard
interval added to the front of the symbol (which is a copy of the
last portion of the data symbol) to facilitate orthogonality and
mitigate inter-carrier interference. As long as the length of this
interval is greater than the maximum channel delay, reflections of
previous symbols are removed and the orthogonality is
preserved.
[0052] Proceeding to FIG. 6, a FLO physical layer 600 is
illustrated. The FLO physical layer uses a 4K mode (yielding a
transform size of 4096 sub-carriers), providing superior mobile
performance compared to an 8K mode, while retaining a sufficiently
long guard interval that is useful in fairly large SFN cells. Rapid
channel acquisition can be achieved through an optimized pilot and
interleaver structure design. The interleaving schemes incorporated
in the FLO air interface facilitate time diversity. The pilot
structure and interleaver designs optimize channel utilization
without annoying the user with long acquisition times. Generally,
FLO transmitted signals are organized into super frames as
illustrated at 600. Each super frame is comprised of four frames of
data, including TDM pilots (Time Division Multiplexed), Overhead
Information Symbols (OIS) and frames containing wide-area and
local-area data. The TDM pilots are provided to allow for rapid
acquisition of the OIS. The OIS describes the location of the data
for each media service in the super frame.
[0053] Typically, each super frame consists of 200 OFDM symbols per
MHz of allocated bandwidth (1200 symbols for 6 MHz), and each
symbol contains 7 interlaces of active sub-carriers. Each interlace
is uniformly distributed in frequency, so that it achieves the full
frequency diversity within the available bandwidth. These
interlaces are assigned to logical channels that vary in terms of
duration and number of actual interlaces used. This provides
flexibility in the time diversity achieved by any given data
source. Lower data rate channels can be assigned fewer interlaces
to improve time diversity, while higher data rate channels utilize
more interlaces to minimize the radio's on-time and reduce power
consumption.
[0054] The acquisition time for both low and high data rate
channels is generally the same. Thus, frequency and time diversity
can be maintained without compromising acquisition time. Most
often, FLO logical channels are used to carry real-time (live
streaming) content at variable rates to obtain statistical
multiplexing gains possible with variable rate codecs (Compressor
and Decompressor in one). Each logical channel can have different
coding rates and modulation to support various reliability and
quality of service requirements for different applications. The FLO
multiplexing scheme enables device receivers to demodulate the
content of the single logical channel it is interested in to
minimize power consumption. Mobile devices can demodulate multiple
logical channels concurrently to enable video and associated audio
to be sent on different channels.
[0055] Error correction and coding techniques can also be employed.
Generally, FLO incorporates a turbo inner code and a Reed Solomon
(RS) outer code. Typically, the turbo code packet contains a Cyclic
Redundancy Check (CRC). The RS code need not be calculated for data
that is correctly received, which, under favorable signal
conditions, results in additional power savings. Another aspect is
that the FLO air interface is designed to support frequency
bandwidths of 5, 6, 7, and 8 MHz. A highly desirable service
offering can be achieved with a single Radio Frequency channel.
[0056] FIG. 7 illustrates a position and location process 700 for
wireless systems. While, for purposes of simplicity of explanation,
the methodology is shown and described as a series or number of
acts, it is to be understood and appreciated that the processes
described herein are not limited by the order of acts, as some acts
may occur in different orders and/or concurrently with other acts
from that shown and described herein. For example, those skilled in
the art will understand and appreciate that a methodology could
alternatively be represented as a series of interrelated states or
events, such as in a state diagram. Moreover, not all illustrated
acts may be required to implement a methodology in accordance with
the subject methodologies disclosed herein.
[0057] Proceeding to 710, various timing corrections are
determined. This can include performing calculations to determine
timing differences between transmitters, receivers, and/or a
centralized clock source. Such differences can be employed to
determine timing offsets that may be employed at receivers to
correct for differences with a clock or such calculations can be
used to determine how much to advance or delay transmitter
broadcasts in order to account for timing differences. Test devices
can be employed to monitor for potential system changes, where
feedback is received from such devices to facilitate determining
offsets or transmitter signal adjustments. At 720 one or more time
offsets are transmitted as part of a data packet to indicate how
potential receiver should adjust position or location calculations.
Alternatively, signals can be advance or delayed at 730 to account
for timing differences in the wireless network and in reference to
a centralized clock. As can be appreciated, both approaches at 720
and 730 can be applied concurrently. For instance, it may be
advantageous to transmit constant time offsets at 720 and utilize
an adjustable signal advance or delay at 730 if environmental or
electrical conditions change. These changes can be monitored and
closed loop mechanisms can be employed to automatically adjust
system transmissions or timing. In another aspect, an advance or
delay in transmit timing may be applied as a constant and time
offsets computed and transmitted dynamically at 720 to account for
potential detected changes.
[0058] At 740, corrected or adjusted signals and/or time offsets
are received. As noted above, time offsets may be received,
adjusted signals with respect to a clock may be received, or
combinations of time offsets and adjusted signals may be received.
At 750, time offsets and/or phase adjusted signals are utilized to
determine a position at a receiver or receivers. Such information
can be employed to automatically compute position location
information that accounts for differences that may occur between
clocks and reference sources. For instance, time offsets or phase
adjusted signals can be received indoors to determine position of a
receiver.
[0059] FIG. 8 is an illustration of a user device 800 that is
employed in a wireless communication environment, in accordance
with one or more aspects set forth herein. User device 800
comprises a receiver 802 that receives a signal from, for instance,
a receive antenna (not shown), and performs typical actions thereon
(e.g., filters, amplifies, down converts, etc.) the received signal
and digitizes the conditioned signal to obtain samples. Receiver
802 can be a non-linear receiver, such as a maximum likelihood
(ML)-MMSE receiver or the like. A demodulator 804 can demodulate
and provide received pilot symbols to a processor 806 for channel
estimation. A FLO channel component 810 is provided to process FLO
signals as previously described. This can include digital stream
processing and/or positioning location calculations among other
processes. Processor 806 can be a processor dedicated to analyzing
information received by receiver 802 and/or generating information
for transmission by a transmitter 816, a processor that controls
one or more components of user device 800, and/or a processor that
both analyzes information received by receiver 802, generates
information for transmission by transmitter 816, and controls one
or more components of user device 800.
[0060] User device 800 can additionally comprise memory 808 that is
operatively coupled to processor 806 and that stores information
related to calculated ranks for user device 800, a rank calculation
protocol, lookup table(s) comprising information related thereto,
and any other suitable information for supporting list-sphere
decoding to calculate rank in a non-linear receiver in a wireless
communication system as described herein. Memory 808 can
additionally store protocols associated rank calculation, matrix
generation, etc., such that user device 800 can employ stored
protocols and/or algorithms to achieve rank determination in a
non-linear receiver as described herein.
[0061] It will be appreciated that the data store (e.g., memories)
components described herein can be either volatile memory or
nonvolatile memory, or can include both volatile and nonvolatile
memory. By way of illustration, and not limitation, nonvolatile
memory can include read only memory (ROM), programmable ROM (PROM),
electrically programmable ROM (EPROM), electrically erasable ROM
(EEPROM), or flash memory. Volatile memory can include random
access memory (RAM), which acts as external cache memory. By way of
illustration and not limitation, RAM is available in many forms
such as synchronous RAM (SRAM), dynamic RAM (DRAM), synchronous
DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM
(ESDRAM), Synchlink DRAM (SLDRAM), and direct Rambus RAM (DRRAM).
The memory 808 of the subject systems and methods is intended to
comprise, without being limited to, these and any other suitable
types of memory. User device 800 further comprises a background
monitor 814 for processing FLO data, a symbol modulator 814 and a
transmitter 816 that transmits the modulated signal.
[0062] FIG. 9 is an illustrates an example system 900 that
comprises a base station 902 with a receiver 910 that receives
signal(s) from one or more user devices 904 through a plurality of
receive antennas 906, and a transmitter 924 that transmits to the
one or more user devices 904 through a transmit antenna 908.
Receiver 910 can receive information from receive antennas 906 and
is operatively associated with a demodulator 912 that demodulates
received information. Demodulated symbols are analyzed by a
processor 914 that is similar to the processor described above with
regard to FIG. 8, and which is coupled to a memory 916 that stores
information related to user ranks, lookup tables related thereto,
and/or any other suitable information related to performing the
various actions and functions set forth herein. Processor 914 is
further coupled to a FLO channel 918 component that facilitates
processing FLO information associated with one or more respective
user devices 904.
[0063] A modulator 922 can multiplex a signal for transmission by a
transmitter 924 through transmit antenna 908 to user devices 904.
FLO channel component 918 can append information to a signal
related to an updated data stream for a given transmission stream
for communication with a user device 904, which can be transmitted
to user device 904 to provide an indication that a new optimum
channel has been identified and acknowledged. In this manner, base
station 902 can interact with a user device 904 that provides FLO
information and employs a decoding protocol in conjunction with a
non-linear receiver, such as an ML-MIMO receiver, and so forth.
[0064] FIG. 10 shows an exemplary wireless communication system
1000. The wireless communication system 1000 depicts one base
station and one terminal for sake of brevity. However, it is to be
appreciated that the system can include more than one base station
and/or more than one terminal, wherein additional base stations
and/or terminals can be substantially similar or different for the
exemplary base station and terminal described below.
[0065] Referring now to FIG. 10, on a downlink, at access point
1005, a transmit (TX) data processor 1010 receives, formats, codes,
interleaves, and modulates (or symbol maps) traffic data and
provides modulation symbols ("data symbols"). A symbol modulator
1015 receives and processes the data symbols and pilot symbols and
provides a stream of symbols. A symbol modulator 1020 multiplexes
data and pilot symbols and provides them to a transmitter unit
(TMTR) 1020. Each transmit symbol may be a data symbol, a pilot
symbol, or a signal value of zero. The pilot symbols may be sent
continuously in each symbol period. The pilot symbols can be
frequency division multiplexed (FDM), orthogonal frequency division
multiplexed (OFDM), time division multiplexed (TDM), frequency
division multiplexed (FDM), or code division multiplexed (CDM).
[0066] TMTR 1020 receives and converts the stream of symbols into
one or more analog signals and further conditions (e.g., amplifies,
filters, and frequency up converts) the analog signals to generate
a downlink signal suitable for transmission over the wireless
channel. The downlink signal is then transmitted through an antenna
1025 to the terminals. At terminal 1030, an antenna 1035 receives
the downlink signal and provides a received signal to a receiver
unit (RCVR) 1040. Receiver unit 1040 conditions (e.g., filters,
amplifies, and frequency down converts) the received signal and
digitizes the conditioned signal to obtain samples. A symbol
demodulator 1045 demodulates and provides received pilot symbols to
a processor 1050 for channel estimation. Symbol demodulator 1045
further receives a frequency response estimate for the downlink
from processor 1050, performs data demodulation on the received
data symbols to obtain data symbol estimates (which are estimates
of the transmitted data symbols), and provides the data symbol
estimates to an RX data processor 1055, which demodulates (i.e.,
symbol de-maps), de-interleaves, and decodes the data symbol
estimates to recover the transmitted traffic data. The processing
by symbol demodulator 1045 and RX data processor 1055 is
complementary to the processing by symbol modulator 1015 and TX
data processor 1010, respectively, at access point 1005.
[0067] On the uplink, a TX data processor 1060 processes traffic
data and provides data symbols. A symbol modulator 1065 receives
and multiplexes the data symbols with pilot symbols, performs
modulation, and provides a stream of symbols. A transmitter unit
1070 then receives and processes the stream of symbols to generate
an uplink signal, which is transmitted by the antenna 1035 to the
access point 1005.
[0068] At access point 1005, the uplink signal from terminal 1030
is received by the antenna 1025 and processed by a receiver unit
1075 to obtain samples. A symbol demodulator 1080 then processes
the samples and provides received pilot symbols and data symbol
estimates for the uplink. An RX data processor 1085 processes the
data symbol estimates to recover the traffic data transmitted by
terminal 1030. A processor 1090 performs channel estimation for
each active terminal transmitting on the uplink. Multiple terminals
may transmit pilot concurrently on the uplink on their respective
assigned sets of pilot subbands, where the pilot subband sets may
be interlaced.
[0069] Processors 1090 and 1050 direct (e.g., control, coordinate,
manage, etc.) operation at access point 1005 and terminal 1030,
respectively. Respective processors 1090 and 1050 can be associated
with memory units (not shown) that store program codes and data.
Processors 1090 and 1050 can also perform computations to derive
frequency and impulse response estimates for the uplink and
downlink, respectively.
[0070] For a multiple-access system (e.g., FDMA, OFDMA, CDMA, TDMA,
etc.), multiple terminals can transmit concurrently on the uplink.
For such a system, the pilot subbands may be shared among different
terminals. The channel estimation techniques may be used in cases
where the pilot subbands for each terminal span the entire
operating band (possibly except for the band edges). Such a pilot
subband structure would be desirable to obtain frequency diversity
for each terminal. The techniques described herein may be
implemented by various means. For example, these techniques may be
implemented in hardware, software, or a combination thereof. For a
hardware implementation, the processing units used for channel
estimation may be implemented within one or more application
specific integrated circuits (ASICs), digital signal processors
(DSPs), digital signal processing devices (DSPDs), programmable
logic devices (PLDs), field programmable gate arrays (FPGAs),
processors, controllers, micro-controllers, microprocessors, other
electronic units designed to perform the functions described
herein, or a combination thereof With software, implementation can
be through modules (e.g., procedures, functions, and so on) that
perform the functions described herein. The software codes may be
stored in memory unit and executed by the processors 1090 and
1050.
[0071] For a software implementation, the techniques described
herein may be implemented with modules (e.g., procedures,
functions, and so on) that perform the functions described herein.
The software codes may be stored in memory units and executed by
processors. The memory unit may be implemented within the processor
or external to the processor, in which case it can be
communicatively coupled to the processor via various means as is
known in the art.
[0072] What has been described above includes exemplary
embodiments. It is, of course, not possible to describe every
conceivable combination of components or methodologies for purposes
of describing the embodiments, but one of ordinary skill in the art
may recognize that many further combinations and permutations are
possible. Accordingly, these embodiments are intended to embrace
all such alterations, modifications and variations that fall within
the spirit and scope of the appended claims. Furthermore, to the
extent that the term "includes" is used in either the detailed
description or the claims, such term is intended to be inclusive in
a manner similar to the term "comprising" as "comprising" is
interpreted when employed as a transitional word in a claim.
* * * * *