U.S. patent application number 13/944495 was filed with the patent office on 2014-01-30 for enhanced pilot signal receiver.
This patent application is currently assigned to QUALCOMM Incorporated. Invention is credited to Peter John Black, Qiang Wu, Wanlun Zhao.
Application Number | 20140029705 13/944495 |
Document ID | / |
Family ID | 40160485 |
Filed Date | 2014-01-30 |
United States Patent
Application |
20140029705 |
Kind Code |
A1 |
Wu; Qiang ; et al. |
January 30, 2014 |
ENHANCED PILOT SIGNAL RECEIVER
Abstract
Briefly, in accordance with one embodiment, a method of
adjusting for digital automatic gain control (DAGC) quantization
error in a mobile station is as follows. A first DAGC value is
stored before reception of one or more enhanced pilot signals. A
second DAGC value is computed during reception of the one or more
enhanced pilot signal. The first DAGC value is restored after
reception of the one or more enhanced pilot signals is over. An
advantage associated with this particular embodiment may include
reduction in quantization error for digital automatic gain
control.
Inventors: |
Wu; Qiang; (San Diego,
CA) ; Zhao; Wanlun; (San Diego, CA) ; Black;
Peter John; (San Diego, CA) |
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
40160485 |
Appl. No.: |
13/944495 |
Filed: |
July 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12113903 |
May 1, 2008 |
8514988 |
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13944495 |
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60939035 |
May 18, 2007 |
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60978068 |
Oct 5, 2007 |
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61014706 |
Dec 18, 2007 |
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61038660 |
Mar 21, 2008 |
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61016101 |
Dec 21, 2007 |
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Current U.S.
Class: |
375/345 |
Current CPC
Class: |
H04L 27/2613 20130101;
H04W 16/02 20130101; H03M 1/185 20130101; G01S 19/24 20130101; H04L
5/0048 20130101; H04L 27/261 20130101; H04W 64/00 20130101; H04L
5/0023 20130101; H04W 4/02 20130101 |
Class at
Publication: |
375/345 |
International
Class: |
H04L 27/26 20060101
H04L027/26 |
Claims
1. A method of adjusting for digital automatic gain control (DAGC)
quantization error in a mobile station: storing a first DAGC value
before reception of one or more enhanced pilot signals; computing a
second DAGC value during reception of the one or more enhanced
pilot signal; and restoring the first DAGC value after reception of
the one or more enhanced pilot signals is over.
2. The method of claim 1, wherein, for more than one received
enhanced pilot signals, the enhanced pilot signals are mutually
orthogonal along at least one of the following signal dimensions:
time, frequency, or any combination thereof.
3. The method of claim 2, wherein the one or more enhanced pilot
signals are compatible with at least one of the following signaling
protocols: 1x EV-DO; cdma2000; WiMAX; LTE; or UMB.
4. The method of claim 1, and further comprising: selecting a
portion of an analog-to-digital converted (ADC) value as a DAGC
value for the first and second DAGC values.
5. An article comprising: a storage medium having stored thereon
instructions that if executed direct a mobile station to store a
first DAGC value before reception of one or more enhanced pilot
signals, compute a second DAGC value during reception of the one or
more enhanced pilot signal, and restore the first DAGC value after
reception of the one or more enhanced pilot signals is over.
6. The article of claim 5, wherein, for more than one received
enhanced pilot signals, the enhanced pilot signals are to be
mutually orthogonal along at least one of the following signal
dimensions: time, frequency, or any combination thereof.
7. A mobile station comprising: a computing platform; said
computing platform to store a first DAGC value before reception of
one or more enhanced pilot signals, compute a second DAGC value
during reception of the one or more enhanced pilot signal, and
restore the first DAGC value after reception of the one or more
enhanced pilot signals is over.
8. The mobile of claim 7, wherein, for more than one received
enhanced pilot signals, the enhanced pilot signals are to be
mutually orthogonal along at least one of the following signal
dimensions: time, frequency, or any combination thereof.
9. A mobile station comprising: means for storing a first DAGC
value before reception of one or more enhanced pilot signals; means
for computing a second DAGC value during reception of the one or
more enhanced pilot signal; and means for restoring the first DAGC
value after reception of the one or more enhanced pilot signals is
over.
10. The mobile of claim 9, wherein, for more than one received
enhanced pilot signals, the enhanced pilot signals are mutually
orthogonal along at least one of the following signal dimensions:
time, frequency, or any combination thereof.
Description
RELATED PATENT APPLICATIONS
[0001] This patent application is a divisional that claims priority
to U.S. patent application Ser. No. 12/113,903, entitled "Enhanced
Pilot Signal Receiver," filed on May 1, 2008, which claims the
benefit of: U.S. Provisional Patent Application Ser. No.
60/939,035, filed on May 18, 2007; U.S. Provisional Patent
Application Ser. No. 60/978,068, filed on Oct. 5, 2007; U.S.
Provisional Patent Application Ser. No. 61/014,706, filed on Dec.
18, 2007; U.S. provisional patent application Ser. No. 61/038,660,
filed on Mar. 21, 2008; U.S. Provisional Patent Application Ser.
No. 61/016,101, filed on Dec. 21, 2007; all of the foregoing
assigned to the assignee of currently claimed subject matter and
herein incorporated by reference in their entirety. Furthermore,
the parent application to this divisional application, U.S. patent
application Ser. No. 12/113,903 noted above, was concurrently filed
with U.S. patent application Ser. No. 12/113,900, titled "Enhanced
Pilot Signal", filed on May 1, 2008, by Wu et al. (Attorney Docket
No. 071317); and U.S. patent application Ser. No. 12/113,812,
titled "Position Location for Wireless Communications System",
filed on May 1, 2008, by Attar et al. (attorney docket no. 071421);
both of which are assigned to the assignee of currently claimed
subject matter and incorporated by reference in their entirety.
FIELD
[0002] This disclosure relates to receivers for use in wireless
communications or other systems, such as receivers for enhanced
pilot signals.
BACKGROUND
[0003] Mobile stations or other receivers, such as, for example,
cellular telephones, are beginning to include the ability to gather
information that provides the ability to estimate position of the
mobile station or other receiver. To have this capability, a mobile
device, for example, may receive signals from a satellite
positioning system (SPS), such as, for example, a Global
Positioning System (GPS). Such information, perhaps in conjunction
with other received information, may be employed to estimate
position location. A variety of scenarios in which a mobile station
or receiver may estimate position location are possible.
[0004] However, for a variety of reasons, a mobile station may
encounter difficulties in receiving signals. For example,
difficulties may be experienced if the mobile station is positioned
inside of a building, or in a tunnel, etc. In other circumstances,
a mobile station may not include an SPS receiver. Again, a variety
of scenarios are possible. However, due at least in part to
difficulties related to the ability of a mobile station to receive
signals enabling it to estimate position location, a need exists
for alternate ways for a mobile station or other device to estimate
position location.
SUMMARY
[0005] Briefly, in accordance with one embodiment, a method of
adjusting for digital automatic gain control (DAGC) quantization
error in a mobile station is as follows. A first DAGC value is
stored before reception of one or more enhanced pilot signals. A
second DAGC value is computed during reception of the one or more
enhanced pilot signal. The first DAGC value is restored after
reception of the one or more enhanced pilot signals is over. An
advantage associated with this particular embodiment may include
reduction in quantization error for digital automatic gain
control.
BRIEF DESCRIPTION OF THE FIGURES
[0006] Non-limiting and non-exhaustive embodiments are described
herein with reference to the following figures:
[0007] FIG. 1 is a schematic diagram illustrating an embodiment
employing three time slots reuse scheme for enhanced pilot
signaling;
[0008] FIG. 2 is a schematic diagram of an embodiment of a slot of
a time division multiplexed signal transmission, such as may be
employed in 1xEV-DO, for example, to implement enhanced pilot
signaling;
[0009] FIG. 3 is a schematic diagram illustrating an embodiment
employing nine time slots for enhanced pilot signaling;
[0010] FIG. 4 is a table associated with the embodiment shown in
FIG. 3;
[0011] FIG. 5 is a schematic diagram illustrating an embodiment of
a mobile station; and
[0012] FIG. 6 is a schematic diagram illustrating an embodiment of
a system for processing signals.
DETAILED DESCRIPTION
[0013] In the following detailed description, numerous specific
details are set forth to provide a thorough understanding of
claimed subject matter. However, it will be understood by those
skilled in the art that claimed subject matter may be practiced
without these specific details. In other instances, methods,
apparatuses or systems that would be known by one of ordinary skill
have not been described in detail so as not to obscure claimed
subject matter.
[0014] Reference throughout this specification to one
implementation, an implementation, one embodiment, an embodiment,
or the like may mean that a particular feature, structure, or
characteristic described in connection with a particular
implementation or embodiment may be included in at least one
implementation or embodiment of claimed subject matter. Thus,
appearances of such phrases in various places throughout this
specification are not necessarily intended to refer to the same
implementation or to any one particular implementation described.
Furthermore, it is to be understood that particular features,
structures, or characteristics described may be combined in various
ways in one or more implementations. In general, of course, these
and other issues may vary with the particular context. Therefore,
the particular context of the description or usage of these terms
may provide helpful guidance regarding inferences to be drawn for
that particular context.
[0015] Likewise, the terms, "and", "and/or", and "or" as used
herein may include a variety of meanings that will, again, depend
at least in part upon the context in which these terms are used.
Typically, "and/or", as well as "or" if used to associate a list,
such as A, B or C, is intended to mean A, B, or C, here used in the
exclusive sense, as well as A, B and C. In addition, the term "one
or more" as used herein may be used to describe any feature,
structure, or characteristic in the singular or may be used to
describe some combination of features, structures or
characteristics.
[0016] Some portions of the detailed description which follow are
presented in terms of algorithms or symbolic representations of
operations on data bits or binary digital signals stored within a
computing system memory, such as a computer memory. These
algorithmic descriptions or representations encompass techniques
used by those of ordinary skill in the data processing or similar
arts to convey the substance of their work to others skilled in the
art. An algorithm is here, and generally, considered to be a
self-consistent sequence of operations and/or similar processing
leading to a desired result. The operations and/or processing
involve physical manipulations of physical quantities. Typically,
although not necessarily, these quantities may take the form of
electrical or magnetic signals capable of being stored,
transferred, combined, compared or otherwise manipulated. It has
proven convenient, at times, principally for reasons of common
usage, to refer to these signals as bits, data, values, elements,
symbols, characters, terms, numbers, numerals or the like. It
should be understood, however, that all of these or similar terms
are to be associated with the appropriate physical quantities and
are intended to merely be convenient labels. Unless specifically
stated otherwise, as apparent from the following discussion, it is
appreciated that throughout this specification, discussions
utilizing terms such as "processing", "computing", "calculating",
"determining" or the like refer to the actions or processes of a
computing platform, such as a computer or a similar electronic
computing device, that manipulates or transforms data represented
as physical electronic or magnetic quantities, or other physical
quantities, within the computing platform's memories, registers, or
other information storage, transmission, or display devices.
[0017] As previously indicated, a need exists for ways of
estimating position location for a mobile station or other device.
Although receiving satellite signals, as previously indicated,
provides one approach, other approaches that may either supplement
such signals or be employed instead of such an approach remain
desirable.
[0018] In this context, the term mobile station is meant to refer
to any device having the ability to receive wireless signals and
send wireless signals, which is also capable of being mobile with
respect to position location. A mobile station typically will
receive signals in connection with usage as part of a wireless
communications system. Furthermore, also typically, but not
necessarily, a mobile station may communicate with one or more
cells in a wireless communication system. Typically, such cells may
comprise base stations. Therefore, it may be desirable for
information gathered via base station communications to be utilized
by a mobile station, sometimes referred to as a mobile, in
estimating position location. Likewise, as indicated above, such
information may supplement information available through other
mechanisms, such as via satellite or via a position determining
entity (PDE), for example.
[0019] However, a mobile station in communication with one or more
base stations to gather information may encounter difficulties in
some circumstances due to, for example, interference. For example,
interference may occur between signals transmitted by several base
stations. Thus, in this example, a mobile station may not be able
to adequately communicate with one or more of the base stations,
resulting in an inability or a reduced ability to perform an
accurate position location estimate. This is sometimes referred to
as the "hearability problem" due at least in part to the "near-far
effect". For example, for wireless communications systems, such as
cdma2000 and WCDMA, to provide without limitation only a few
possible examples, downlink pilot signals may be difficult to
detect due at least in part to such interference
[0020] Although claimed subject matter is not limited in scope to
any particular embodiment, in a variety of example embodiments, an
approach to signal communications may be discussed to address at
least in part the issues discussed above. In descriptions of such
example embodiments, aspects of the signaling may relate to the
time domain, the frequency domain or to other aspects of a
particular signal, referred to here as signal dimensions.
Nonetheless, it is intended that claims subject matter not be
limited in scope to signaling in these example domains or signal
dimensions. These examples are merely illustrative. For example, in
other embodiments, instead of time or frequency, other dimensions
of a signal may be involved, such as, for example, phase,
amplitude, spreading code or spreading code sequence, signal energy
or any combinations thereof. In this context, the term signal
dimension is intended to refer to a quantifiable aspect of a signal
that may vary across a variety of signals and that may be used to
categorize or partition signals which vary from one another in this
particular quantifiable aspect. A signal, for example, may occupy
time and frequency domain resources simultaneously. As described in
some of the embodiments below, a scheme may be employed to divide
these resources into orthogonal dimensions: in time domain, in
frequency domain, in fixed time and frequency domain, or code
domain, to provide some examples. Claimed subject matter is not
intended to be limited to the specific example embodiments
discussed. Rather, many other signaling techniques or signaling
approaches that employ other signal dimensions are included within
the scope of claimed subject matter. It is intended that the scope
of claimed subject matter include all such techniques and
approaches.
[0021] In one particular embodiment of a method of transmitting
signals, for example, signal waveforms may be transmitted from at
least two respective sectors of a wireless communications system.
The at least two respective sectors, likewise, may be from at least
two different sets of a superset of sectors. For example, a
superset of sectors, such as illustrated in FIG. 1, as an example,
may be divided into at least two, and as illustrated in FIG. 1, in
some embodiments, more than two sets of sectors. Thus, in this
particular embodiment, the sectors transmitting signals may be from
separate sets of sectors. Likewise, in this particular embodiment,
the signal waveforms transmitted may be at least nearly mutually
orthogonal, at least along a particular signal dimension, such as,
for example, time or frequency, as shall be discussed below in more
detail.
[0022] FIG. 1, for example, illustrates an embodiment in which a
superset of sectors are partitioned or divided into 3 sets, S0, S1,
and S2, although, of course, claimed subject matter is not limited
in scope in this respect. The spatial arrangement of sectors is
illustrated by 110 and the particular time slots in which those
sectors may transmit enhanced pilot signals is illustrated by 120.
As indicated above, this approach could be applied to a variety of
signal dimensions, such as, for example time and/or frequency, to
provide only two out of more than two possible examples. However,
for ease of explanation, we shall illustrate an example embodiment
for the protocol 1xEV-DO, which employs uplink and downlink signal
transmissions in which information is slotted into various time
slots.
[0023] Protocol 1xEV-DO is part of a family of CDMA2000 1x digital
wireless standards. 1xEV-DO is a third generation or "3G" CDMA
standard. There are currently two main versions of 1xEV-DO:
"Release 0" and "Revision A". 1xEV-DO is based on a technology
initially known as "HDR" (High Data Rate) or "HRPD" (High Rate
Packet Data), developed by Qualcomm. The international standard is
known as IS-856.
[0024] FIG. 2 is one possible example embodiment 210 of a time
division multiplexed (TDM) signal that may employ enhanced pilot
signaling, although, of course, claimed subject matter is not
limited in scope to this particular example. Embodiment 210 is
intended to illustrate one enhanced pilot signal slot. In the
1xEVDO downlink, a Pilot Channel is time division multiplexed with
other channels. The Pilot Channel in this example, is designated by
210-250. A 1xEV-DO downlink transmission includes time slots of
length 2048 chips. Groups of 16 slots align with an offset
pseudo-random noise or PN sequence. As illustrated by 210, within a
slot, Pilot, enhanced media access control (MAC) and Traffic or
Control Channels are time division multiplexed. Thus, for an
embodiment of enhanced pilot signaling for a 1xEV-DO downlink, time
slots may be allocated for enhanced pilot signals. Here, FIG. 2
illustrates one possible embodiment of such a slot structure,
although, for course, claimed subject matter is not limited in
scope to this example. Many other possible enhanced pilot signal
configurations or structures are possible and are included within
the scope of claimed subject matter.
[0025] For this embodiment, however, enhanced pilot channels or
signals are transmitted in the data portion of these dedicated
slots, while legacy Pilot and MAC channels are retained for
backward comparability. For this embodiment, the enhanced pilot may
appear as an unintended packet for legacy mobile stations, for
example, that would not have the ability to recognize it. Likewise,
for this embodiment, this slot may be transmitted with a relatively
low "duty cycle", such as around 1% and still provide signaling
benefits. In this way, potential impact on downlink capacity may
not be significant.
[0026] An aspect of embodiments in accordance with claimed subject
matter, such as the embodiment just discussed, relates to so-called
"reuse". This term refers to the concept that signaling resources,
such as frequency bandwidth or signal duration, for example, that
may be available in a particular signaling dimension (or in several
signaling dimensions in some embodiments) may be employed (or
reemployed) by other or different sectors. For example, in the
embodiment described above, dedicated time slots may be partitioned
to correspond, for example, to the sets of sectors illustrated in
FIG. 1. In this example, 3 non-overlapping partitions have been
formed, although claimed subject matter is not limited in scope in
this respect. Any number of groups, referred to here as K or as
reuse factor 1/K may be employed and the sectors are not required
to be non-overlapping. However, regardless of the details of this
particular embodiment, a one-to-one association, by construction,
may exist between the partitions of the dedicated time slots and
the partitions of the sets of sectors of the superset. Sectors of a
particular set may only transmit enhanced pilot signals in its
associated slots. This is referred to as reuse over time, here,
since in this embodiment signaling resources available along the
time signaling dimension have been partitioned to correspond to the
partitioned sets of sectors that together comprise the superset of
sectors.
[0027] One advantage of the approach of this particular embodiment,
as suggested previously, relates to a reduction in signal
transmission interference. In other words, by partitioning sectors
along a signal dimension so that the transmitted signal waveforms
are nearly mutually orthogonal results in pilot signals that are
more easily detected by a mobile station, for example.
[0028] Partitioning of sectors or cells for ease of discussion may
be referred to here as "coloring", although the use "colors" is, of
course, not a necessary feature of claimed subject matter or even
of this particular embodiment. Rather, the term "color" is intended
here to identify partitions or partitioning. Thus, as described in
more detail immediately below, "color" here, which merely
designates a partition, which for a sector, for example, refers to
a 2tuple, rather than the conventional notion of color. For
example, and without limitation, if we let a cell take on a value
from the set {Red, Green, Blue} (abbreviated as {R, G, B}), a
sector may, in this example, take on a value from the set {R, G,
B}x{.alpha., .beta., .gamma.}, where "x" stands for Cartesian
product. Thus, in this example, the "color" of the cell influences
the "color" of the sectors of that cell. Of course, it is
appreciated that claimed subject matter is not necessarily
restricted to partitioning by cells or sectors. For example, in
alternative embodiments, other subdivisions or partitions may be
employed. However, as indicated above, the color of a sector may be
referred to as a 2tuple, for example (R, .alpha.) abbreviated as
R.alpha., the first element, again, coming from the color of the
cell to which the sector belongs. Based at least in part on the
discussion above, it should now be apparent that the reuse factor
for this particular example is K=9 or 1/9.
[0029] An example embodiment 310 is shown in FIG. 3 that differs
from the embodiment shown in FIG. 1. FIG. 3 also illustrates an
example of planned or dedicated coloring. For the particular
embodiment being discussed, transmitted signal waveforms comprise
time division multiplexed (TDM) signal waveforms, as illustrated by
410 in FIG. 4. In planned coloring, colors are assigned in a fixed
or dedicated manner so as to reduce interference among sectors of
the same color in a balanced way, although, of course, claimed
subject matter is not limited in scope to employing such an
approach. Thus, as is illustrated by FIGS. 3 and 4, signals are
transmitted in particular time slots so that potential signal
interference is reduced. As may now be appreciated from the above
discussion, dedicated resource and reuse reduces inter-channel
interference, and thus assists to mitigate the near-far effect and
likewise improve hearability. Therefore, for this particular
embodiment at least, the TDM signal waveforms that are transmitted
in dedicated time slots associated with particular cell sectors
comprise highly detectable pilot (HDP) signals. As shall be
discussed further below, this allows for improved terrestrial
position location estimation accuracy, although, again, claimed
subject matter is not limited in scope in this respect.
[0030] While dedicated or planned coloring provides potential
advantages some of which are discussed above, color assignment to
reduce the interference among sectors of the same color in a
balance a way would involve some amount of effort. If it were
possible to reduce or avoid this effort, it may, in some
situations, provide advantageous. One approach may be to employ
what may be referred to here as time varying coloring, rather than
dedicated coloring. In time varying coloring, the color of various
sectors may change with time. One particular example of time
varying coloring described in more detail below is referred to here
as random coloring. In random coloring, again, the color of various
sectors may change; however, the changes are a pseudo-random. Thus,
in random coloring, the color of a sector varies with time in a
pseudo-random manner, where here, again, with respect to a sector,
the term color refers to a 2tuple, as discussed previously. For
example, assume, as previously, that enhanced pilot signals are
time-multiplexed into 9 time slots to correspond with 9 sets or
groupings of sectors that together form a superset, as previously
discussed.
[0031] As previously described, enhanced pilot channels or signals
may be transmitted and provide the ability for greater accuracy in
making position location estimates of the mobile station if such
signals are received by a mobile station or other receiver.
However, a factor in determining whether improved accuracy will be
realized depends in at least in part on the ability of the mobile
station or other receiver to detect the signals and likewise,
process them in such a manner that provides the desired accuracy.
Therefore, aspects of the configuration of the receiver of the
mobile station or other device may have relevance in connection
with position location estimation by the mobile station.
[0032] Although there are many aspects of receivers, here, a few
specific areas of a configuration of a receiver portion of a mobile
station are considered so that advantages afforded by the use of
enhanced pilot signals will be realized in operation. In this
context, it is desirable to highlight features that may be included
to take advantage of a communications system, for example, in which
enhanced pilot signals are available. However, claimed subject
matter is not limited in scope to particular embodiments.
Therefore, while specific embodiments are discussed to illustrate
various potential feature enhancements, claimed subject matter is
intended to be conceptually much broader than the specifics
associated with the embodiments discussed below.
[0033] One aspect of a receiver of a mobile station to consider in
connection with improved estimates of position location is sources
of receiver quantization error. For example, in an example wireless
communications system, such as one that may employ 1xEV-DO, as
discussed above, wide variations may be observed in received signal
energy, depending at least in part upon whether the DO pilot signal
is being received or an enhanced pilot signal is being received. As
discussed, enhanced pilot signals employ reuse, which has the
potential to reduce signal energy. As simple one example, if K=9 is
the reuse factor, then the signal energy for enhanced pilot signals
may be about an order of magnitude less than that of the DO pilot.
However, to the extent these received signals become quantized,
significant variations in level may result in increased
quantization error due to a relatively large range of possible
signal levels. More specifically, an automatic gain control or AGC
loop is frequently employed to convert a received signal into a
voltage level. Likewise, for processing purposes, the voltage
signal level is converted from an analog signal to a digital
signal. However, as previously suggested, wide variations in the
received signal may contribute to higher levels of quantization
error which may ultimately result in signal quality degradation or
signal accuracy degradation.
[0034] Another aspect to consider is sources of signal
interference. An aspect of employing enhanced pilot signals is to
reduce interference from nearby base stations that may be
transmitting interfering pilot signals. However, other potential
sources of interference likewise exist. Another potential source of
signal interference for example, may result from adjacent channels
other than pilot signals. For example, for 1xEV-DO, bandwidth for a
pilot channel is 1.25 MHz. This bandwidth is sufficiently narrow
that nearby carrier signals transmitting at the same time may have
signal energy at frequencies that overlap with the pilot signal,
potentially resulting in interference. Such interference,
therefore, may affect hearability and, in this respect, is similar
to the near-far effect, discussed previously with respect to
enhanced pilot signals.
[0035] Yet another aspect of a receiver of a mobile station to
consider relates to having adequate time to perform signal
processing. Computing a location position estimate is a relatively
complex computation in terms of the operations to be performed.
With respect to employing enhanced pilot signals, a large number of
signal thresholds are computed due at least in part to the number
of transmitting sectors. It is possible that there may not be
sufficient time available to perform such calculations or
operations for every sector transmitting enhanced pilot signals. If
this is the case, it may be desirable to have a mechanism to limit
the number of enhanced pilots for which signal detection is
performed so that the number of calculations and, as a result, the
amount of time to perform signal processing, is reduced.
[0036] As previously discussed, wide variations in received signal
energy has the potential to affect performance of an AGC loop,
particularly if A/D conversion is also employed. Thus, as
previously indicated errors arising from quantization of an analog
signal may have the potential to affect the quality of a position
location estimate. One possible approach to addressing an issue
such as this may involve a change or upgrade in the base computing
device or platform employed. For example, an increase in the number
of bits used to quantize the signal should reduce quantization
error. However, for a variety of reasons, it may be viewed as
desirable to employ a similar platform to the one employed in
connection with processing pilot signals that have not been
enhanced, such as, for example, the DO pilot signal provided in
compliance with the 1xEV-DO specification, as simply one example.
Advantages of this approach may include reduced cost or reduced
complexity. Increasing the number of bits may increase either or
both. Likewise, it should be desirable to not introduce significant
additional computational complexity even assuming a similar
platform is employed. Again, as suggested previously, increasing
the time to perform signal processing may be undesirable in some
instances at least.
[0037] Assuming, as just indicated, that the platform employed to
process enhanced pilot signals is similar or substantially the same
as the platform, several possible signal processing approaches
remain available to address some of the issues discussed above. As
shall be discussed in more detail below, one option in accordance
with claimed subject matter may include employing a "window" in
which enhanced pilots signals may be received and performing AGC
operations based at least in part on the enhanced pilot signals
received during such a window. Another option, while employing a
similar platform as employed for non-enhanced pilot signals, may
involve the use of separate AGC loops. For example, two AGC loops
may be implemented without significant platform modifications. As
shall become clear from the discussion below, to do this, it is
desirable to be able to execute signal processing operations at
appropriate times with respect to received enhanced pilot
signals.
[0038] Although claimed subject matter is not limited in scope to
this particular embodiment, in one embodiment, a method of reducing
digital AGC quantization error in a mobile station may include the
following. Signal energy from one or more received enhanced pilot
signals may be estimated. A portion of an analog to digital (A/D)
converted signal level value may be selected as a digital AGC value
based at least in part on the foregoing estimate. Likewise, one or
more enhanced pilot signal thresholds may be scaled to at least
approximately to adjust for signal processing applied to reduce
quantization error.
[0039] Signal energy may, for example, be estimated by integrating,
over a period, of time I and Q components of received enhanced
pilot signals. Although claimed subject matter is not limited in
scope in this respect, in one particular embodiment, all six bits
of an output signal of a six-bit A/D converter may not necessarily
be entirely employed in the AGC loop computations. For example,
this may reduce computational complexity, although potentially at
the risk of less precision; however, as described below, for an
embodiment in accordance with claimed subject matter, precision may
be accommodated without resorting to use of all six bits. As an
example, without limitation, in one possible embodiment, four bits
of the A/D converter may be selected to be provided for use in
performing threshold detection.
[0040] In this particular embodiment, for example, an estimate of
signal energy for one or more received enhanced pilot signals is
performed dynamically. Typically, the most significant bits, such
as the four most significant bits, for example, might be provided,
such as in the case of a DO pilot, for example. However, for
enhanced pilot signaling, the received energy should be relatively
low due at least in part to the reuse factor, 1/K. In a situation
such as this, if the most significant bits are provided,
information may be lost that maybe useful, since more information
may be contained in the lesser significant bits. For example, if
the energy of the enhanced pilot signal is relatively low, such as
one the order of 20 dB below regular DO pilot energy. It maybe
desirable to provide the four least significant bits. However, as
alluded to above, since this might be viewed as equivalent to
shifting a binary signal by several places, it may be appropriate
to compensate for changes intended to reduce quantization error,
such as shifting a quantized measurement, through other adjustments
in the computations. For example, one approach may be to
proportionately scale values or thresholds used to determine
whether the level of signal detected is statistically significant.
Although claimed subject matter is not limited in scope in this
respect, signal levels for one or more received enhanced pilot
signals may, for example, be around an order of magnitude less than
signal levels for one or more non-enhanced pilot signals, such as,
for example, the DO pilot signal received in connection with the
1xEV-DO signaling protocol.
[0041] As previously suggested, another possible approach may
involve implementing two AGC loops, one for enhanced pilot signals
and one for non-enhanced pilot signals. This approach has the
advantage that it may be implemented without significant platform
modifications. To do this effectively, however, it is desirable to
be able to execute signal processing operations at appropriate
times with respect to received enhanced pilot signals. For example,
although claimed subject matter is not limited in scope in this
respect, referring to an AGC loop for a mobile station, the energy
of the signal wave front may be accumulated over a number of chips,
such as 40 to 60, as only one potential example, and thereafter,
the loop may update the estimate at regular intervals of chips, if
desired. In contrast, for the AGC loop for the enhanced pilot
signal, such energy may be captured once per enhanced pilot burst,
which for the embodiment previously described, occurs relatively
infrequently, such as about 1% of the time. Therefore, smoothly
switching between AGC loops and doing so at appropriate times is
desirable.
[0042] As previously described, another aspect of potential
performance improvement relates to interference from an adjacent
channel. In general, although other channels other than enhanced
pilot signals may be transmitted over a different carrier, leakage
may occur in overlapping frequencies among the various channels,
potentially affecting performance. More specifically, degradation
may be observed through a lower signal to noise ratio, as one
example. This phenomenon is similar to the near-far problem, and
thus may affect hearability, as previously described. It is noted
likewise, that this effect may not affect all implementations of
enhanced pilot signaling. For example, for OFDM systems, in which
enhanced pilot signaling may be employed, the amount of available
bandwidth is greater, so that interference from adjacent channels
may have a barely measurable impact on performance. In contrast,
however, for time division multiplexed signals, such as in 1xEV-DO,
for example, the allotted bandwidth is 1.25 megahertz, making
signal degradation from interference is more likely.
[0043] Although claimed subject matter is not limited in scope in
this respect, in accordance with one particular embodiment, a notch
filter may be applied to received enhanced pilot signal
transmissions. As previously suggested, the enhanced pilot signal
transmissions from different sets of sectors are mutually
orthogonal at least along a time signal dimension, since they are
TDM signals. In this embodiment, for example, the notch filter may
have a notch at a frequency corresponding to the signal
transmissions for the adjacent potentially interfering channels. It
is noted, of course, that a host of possible implementations are
possible and claimed subject matter is not limited in scope to any
particular one. For example, an FIR or an IRR filter may be
employed.
[0044] Likewise, the filtered signals may be employed to perform
automatic gain control. It is worth observing that a notch filter
may remove interference from adjacent channels, but it likewise may
undesirably increase inter-symbol interference for the enhanced
pilot signals. One possible approach to address this, although
adding complexity, would be to vary the specific application of the
notch filter so that signals are not unnecessarily degraded by its
application if there is little interference attributable to
adjacent channel transmissions. In this particular embodiment,
however, because, again, reduced complexity of signal processing is
desired, instead, filtering is always applied to enhanced pilot
signals before employing automatic gain control. This approach
offers simplicity of implementation without significantly affecting
performance. For sectors providing weak enhanced pilot signals to
the mobile station, interference attributable to adjacent channel
transmissions may be greater than potential inter-symbol
interference that the filter may induce. However, for sectors
providing strong enhanced pilot signals to the mobile station, the
effect of inter-symbol interference from application of filtering
is sufficiently small so as not to significantly degrade
performance.
[0045] As previously suggested, another aspect related to the
receiver configuration for a mobile station involves having
sufficient time to process enhanced pilot signaling that may be
received. As suggested previously, there may not be sufficient time
to process signals from every sector transmitting enhanced pilot
signals. Therefore, an approach is desired to reduce the number of
enhanced pilot signals that a mobile station is to process. If the
mobile station is able to omit processing those signals that are
less likely provide an accurate estimate of position location, this
has the potential to reduce processing time to an acceptable period
of time.
[0046] One particular embodiment in accordance with claimed subject
matter that may permit the mobile station to not process signals
less likely to provide an accurate position location estimate may
involve providing to mobile station with information about the
particular enhanced pilot signaling transmission scheme. For
example, with limitation, in one embodiment, this information may
be loading in memory of the mobile station before the mobile
station is deployed. In another embodiment, perhaps this
information is transmitted to the mobile station. The mobile
station may then use this information to detect enhanced pilot
signals for those sectors of interest while omitting sectors that
are not of interest.
[0047] For example, again, but without limitation, suppose a
particular communication system employs an embodiment of enhanced
pilot signals that includes dedicated "coloring", as previously
described. For ease of discussion, assume this system also employs
time multiplexed signals, although, as previously indicated, many
other approaches may be employed, such as FDM, OFDM, etc. In this
particular embodiment, however, enhanced pilot signals may be
detected for selected time slots corresponding to sectors of
interest to reduce the amount of signal processing and, therefore,
the time to complete the signal processing.
[0048] Of course, alternatively such a system may employ a
non-dedicated scheme, such as a random or time-varying scheme. In
such an embodiment, it may be more complex for the mobile station
to determine those slots to detect and those to omit. However, it
remains possible to reduce the number of enhanced pilot signals to
be processed, as desired. For example, in a non-dedicated scheme
employing random coloring, a pseudo-random process is employed to
make associations between particular sectors and time slots, for
this particular embodiment, for example. If the mobile station has
the particular pseudo-random process and the initial seed, for
example, it may determine the association. Thus, enhanced pilot
signals may be detected based on selected time slots corresponding
to sectors of interest, as before. Of course, a similar approach
may likewise be employed in an embodiment in which the enhanced
pilot signals are FDM signals, for example. Again, by applying the
same pseudo-random process starting with the same seed, for
example, the mobile station is able to determine the selected
frequencies corresponding to selected sectors of interest and check
those frequencies as part of a signal detection process, thereby
reducing processing to perform such computations.
[0049] Similar to non-enhanced pilot signals, enhanced pilot
signals may be encoded using a pseudo-random (PN) sequence. In one
embodiment, for example, so that non-enhanced pilot signals and
enhanced pilot signals are not confused, a frequency inverted PN
sequence, which comprises a complex conjugate, may be employed.
However, this approach to randomizing the enhanced pilot signals
may also be employed as a mechanism to identify those signals to
which signal detection is to be applied. Different signals from
different sectors or base stations will be coded with a different
PN sequence. Thus, by locally generating the PN sequence employed
to encode the signals of interest, for example, a mobile station
may attempt to decode received signals, looking for a match. If
there is a match, the decoded signals may be processed by the
mobile station and the enhanced pilot signals may be employed to
estimate position location for the mobile station. Alternatively,
if there is not a match, then the mobile station may continue to
correlate the PN sequence with received signals until a match
occurs.
[0050] As alluded to previously, in some embodiments, a hybrid
approach to position location may be employed. For example, while
an enhanced pilot signal may be employed as part of a wireless
communications system, it may be supplemented with other
information available via signals received through other mechanism
to determine position location, such as pseudorandom measurements
to space vehicles that may be obtained by processing SPS signals.
Likewise, determining a position location estimate need not be
performed entirely at the mobile unit. It may, for example, include
transmitting location information to an outside entity (e.g., a
position determination entity).
[0051] As previously discussed, enhanced pilot signals may be
provided in many forms, such as time segments, frequency bands, or
time-frequency bins. In any of these latter examples, partitioning
into K groups along one or more signaling dimensions, such as time,
frequency, or time-frequency, for example, may be applied so that
the partitions are orthogonal or nearly so. Likewise, a superset of
sectors may also be partition into K sets or groups. As discussed
previously with reference to a particular embodiment, a one-to-one
association may be established between the orthogonal or nearly
orthogonal partitions and the sector partitions. In such an
embodiment, for a particular set of sectors, an enhanced pilot
signal may be transmitted with the particular window of the
particular one or more signaling dimensions that have been
partitioned. Likewise, as discussed previously with reference to a
particular embodiment, dedicated coloring or time varying coloring,
such as random coloring, may be applied. Therefore, as has been
previously discussed and illustrated with respect to particular
embodiments, enhanced pilot signaling may be applied to OFDM
systems, such as WiMax, LTE, UMB, or other 4G approaches being
developed, for example, by 3GPP or 3GPP2. Of course, again, these
are examples and claimed subject matter is intended to cover more
than OFDM systems as well.
[0052] Therefore, wireless communication or position location
estimation techniques, such as, for example, the embodiments
previously described, may be used for a host of various wireless
communication networks. Without limitation, these may include Code
Division Multiple Access (CDMA) networks, Time Division Multiple
Access (TDMA) networks, Frequency Division Multiple Access (FDMA)
networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA
(SC-FDMA) networks, etc. A CDMA network may implement one or more
radio access technologies (RATs) such as cdma2000, Wideband-CDMA
(W-CDMA), or Universal Terrestrial Radio Access (UTRA), to name
just a few radio technologies. Here, cdma2000 may include
technologies implemented according to IS-95, IS-2000, or IS-856
standards. UTRA may include Wideband-CDMA (W-CDMA) or Low Chip Rate
(LCR). A TDMA network may implement a radio technology such as
Global System for Mobile Communications (GSM). An OFDMA network may
implement a radio technology such as Evolved UTRA (E-UTRA), IEEE
802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM.RTM., etc. UTRA,
E-UTRA, and GSM are part of Universal Mobile Telecommunication
System (UMTS). Long Term Evolution (LTE) is an upcoming release of
UMTS that may use E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are
described in documents that may be obtained from the 3rd Generation
Partnership Project (3GPP). Cdma2000 is described in documents that
may be obtained from the 3rd Generation Partnership Project 2
(3GPP2). 3GPP and 3GPP2 documents are, of course, publicly
available.
[0053] An example implementation of a system for processing signals
is illustrated in FIG. 6. However, this is merely an example of a
system that is capable of acquiring signals by processing according
to a particular example and other systems may be used without
deviating from claimed subject matter. As illustrated in FIG. 6,
according to this particular example, such a system may comprise a
computing platform including a processor 1302, memory 1304, and
correlator 1306. Correlator 1306 may produce correlation functions
or operations for signals provided by a receiver (not shown) to be
processed by processor 1302, either directly or through memory
1304. Correlator 1306 may be implemented in hardware, firmware,
software, or any combination. However, this merely an example of
how a correlator may be implemented and claimed subject matter is
not limited to this particular example.
[0054] Here, however, continuing with this example, memory 1304 may
store instructions which are accessible and executable by processor
1302. Here, processor 1302 in combination with such instructions
may perform a variety of the operations previously described, such
as, for example, without limitation, correlating a PN or other
sequence.
[0055] Turning to FIG. 5, radio transceiver 1406 may modulate a
radio frequency (RF) carrier signal with baseband information, such
as voice or data, or demodulate a modulated RF carrier signal to
obtain baseband information. Antenna 1410 may transmit a modulated
RF carrier or receive a modulated RF carrier, such as via a
wireless communications link.
[0056] Baseband processor 1408 may provide baseband information
from CPU 1402 to transceiver 1406 for transmission over a wireless
communications link. Here, CPU 1402 may obtain such baseband
information from an input device within user interface 1416.
Baseband processor 1408 may also provide baseband information from
transceiver 1406 to CPU 1402 for transmission through an output
device within user interface 1416. User interface 1416 may comprise
a plurality of devices for inputting or outputting user
information, such as voice or data. Such devices may include, for
example, a keyboard, a display screen, a microphone, or a
speaker.
[0057] Here, SPS receiver 1412 may receive and demodulate SPS
transmissions, and provide demodulated information to correlator
1418. Correlator 1418 may apply correlation functions from
information provided by receiver 1412. For a given PN sequence, for
example, correlator 1418 may produce a correlation function which
may, for example, be applied in accordance with defined coherent
and non-coherent integration parameters. Correlator 1418 may also
apply pilot-related correlation functions from information relating
to pilot signals provided by transceiver 1406. Channel decoder 1420
may decode channel symbols received from baseband processor 1408
into underlying source bits. In one example in which channel
symbols comprise convolutionally encoded symbols, such a channel
decoder may comprise a Viterbi decoder. In a second example, in
which channel symbols comprise serial or parallel concatenations of
convolutional codes, channel decoder 1420 may comprise a turbo
decoder.
[0058] Memory 1404 may comprise computer readable media to store
instructions which are executable to perform one or more of
processes or implementations, which have been described or
suggested previously, for example. CPU 1402 may access and execute
such instructions. Through execution of these instructions, CPU
1402 may direct correlator 1418 to perform a variety of signal
processing related tasks. However, these are merely examples of
tasks that may be performed by a CPU in a particular aspect and
claimed subject matter in not limited in these respects. It should
be further understood that these are merely examples of systems for
estimating a position location and claimed subject matter is not
limited in these respects.
[0059] It will, of course, be understood that, although particular
embodiments have just been described, claimed subject matter is not
limited in scope to a particular embodiment or implementation. For
example, one embodiment may be in hardware, such as implemented to
operate on a device or combination of devices, for example, whereas
another embodiment may be in software. Likewise, an embodiment may
be implemented in firmware, or as any combination of hardware,
software, and/or firmware, for example. The methodologies described
herein may be implemented by various means depending upon the
application. For a hardware implementation, the processing units
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, electronic
devices, other electronic units designed to perform the functions
described herein, or a combination thereof. For a firmware and/or
software implementation, the methodologies may be implemented with
modules (e.g., procedures, functions, and so on) that perform the
functions described herein. Any machine readable medium tangibly
embodying instructions may be used in implementing the
methodologies described herein. For example, software codes may be
stored in a memory, for example, a memory of a mobile station, and
executed by a processor, for example a microprocessor. Memory may
be implemented within the processor or external to the processor.
As used herein the term "memory" refers to any type of long term,
short term, volatile, nonvolatile, or other memory and is not to be
limited to any particular type of memory or number of memories, or
type of media upon which memory is stored. Likewise, although
claimed subject matter is not limited in scope in this respect, one
embodiment may comprise one or more articles, such as a storage
medium or storage media. This storage media, such as, one or more
CD-ROMs and/or disks, for example, may have stored thereon
instructions, that if executed by a system, such as a computer
system, computing platform, or other system, for example, may
result in an embodiment of a method in accordance with claimed
subject matter being executed, such as one of the embodiments
previously described, for example. As one potential example, a
computing platform may include one or more processing units or
processors, one or more input/output devices, such as a display, a
keyboard and/or a mouse, and/or one or more memories, such as
static random access memory, dynamic random access memory, flash
memory, and/or a hard drive.
[0060] In the preceding description, various aspects of claimed
subject matter have been described. For purposes of explanation,
specific numbers, systems and/or configurations were set forth to
provide a thorough understanding of claimed subject matter.
However, it should be apparent to one skilled in the art having the
benefit of this disclosure that claimed subject matter may be
practiced without the specific details. In other instances, well
known features were omitted and/or simplified so as not to obscure
claimed subject matter. While certain features have been
illustrated and/or described herein, many modifications,
substitutions, changes and/or equivalents will now occur to those
skilled in the art. It is, therefore, to be understood that the
appended claims are intended to cover all such modifications and/or
changes as fall within the true spirit of claimed subject
matter.
* * * * *