U.S. patent application number 15/257582 was filed with the patent office on 2017-01-05 for system and method for iq imbalance estimation.
The applicant listed for this patent is Entropic Communications LLC. Invention is credited to Na Chen, Michail Tsatsanis.
Application Number | 20170005855 15/257582 |
Document ID | / |
Family ID | 54203921 |
Filed Date | 2017-01-05 |
United States Patent
Application |
20170005855 |
Kind Code |
A1 |
Tsatsanis; Michail ; et
al. |
January 5, 2017 |
System and Method For IQ Imbalance Estimation
Abstract
A system for IQ balance estimation is disclosed and may include
requesting an in-phase and quadrature (IQ) probe comprising tones,
receiving the tones, and calculating an estimate of IQ imbalance
for each received tone. The system may also include requesting an
IQ probe, and calculating an estimate of IQ imbalance for each
received tone by determining an image to tone ratio based on the
received tones. The requesting of the IQ probe, the receiving of
the tones, and the calculating of the image to tone ratio may be
repeated the results of the calculations of the image to tone ratio
may be averaged. Gain, phase, and delay parameters may be
calculated to compensate for the IQ imbalance.
Inventors: |
Tsatsanis; Michail;
(Carlsbad, CA) ; Chen; Na; (Carlsbad, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Entropic Communications LLC |
Carlsbad |
CA |
US |
|
|
Family ID: |
54203921 |
Appl. No.: |
15/257582 |
Filed: |
September 6, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14871290 |
Sep 30, 2015 |
9438464 |
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15257582 |
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14321208 |
Jul 1, 2014 |
9154338 |
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14871290 |
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61981633 |
Apr 18, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 43/12 20130101;
H04L 27/3863 20130101 |
International
Class: |
H04L 27/38 20060101
H04L027/38; H04L 12/26 20060101 H04L012/26 |
Claims
1-21 (canceled)
22. A method, comprising: in a first communication device:
requesting an in-phase and quadrature (IQ) probe from a second
communication device external to the first communication device,
the IQ probe comprising tones; receiving the tones from the second
communication device; and calculating an estimate of IQ imbalance
for each received tone by determining an image to tone ratio based
on the received tones.
23. The method of claim 22, comprising repeating the requesting of
the IQ probe, the receiving of the tones, and the calculating of
the image to tone ratio, and averaging the results of the
calculations of the image to tone ratio.
24. A method, comprising: in a first communication device:
requesting an in-phase and quadrature (IQ) probe from a second
communication device external to the first communication device,
the IQ probe comprising tones; receiving the tones from the second
communication devicee; and calculating an estimate of IQ imbalance
for each received tone.
25. The method of claim 24, comprising calculating gain, phase, and
delay parameters to compensate for the IQ imbalance.
26. The method of claim 25, wherein the IQ imbalance comprises a
receiver IQ imbalance.
27. The method of claim 24, comprising requesting a loopback probe
comprising tones in a loopback circuit including a receiver and
transmitter of the first communication device.
28. The method of claim 27, comprising receiving the tones
transmitted via the loopback probe, and calculating gain, phase,
and delay parameters to compensate for transmitter IQ
imbalance.
29. The method of claim 24, wherein the estimated IQ imbalance
includes a gain imbalance.
30. The method of claim 24, wherein the estimated IQ imbalance
includes a phase imbalance.
31. The method of claim 24, wherein the estimated IQ imbalance
estimate includes a delay imbalance.
32. The method of claim 24, wherein the frequency separation is
selected as being large enough so that transmitter and receiver
images of the tones do not interfere with each other.
33. The method of claim 24, wherein a frequency separation of the
tones comprises 12.5 MHz.
34. The method of claim 24, wherein the first communication device
comprises at least a receiver, and the second communication device,
remotely located from the first communication device, comprises at
least a transmitter.
35. The method of claim 34, wherein the first communication device
comprises a MoCA 2.0 new node (NN) undergoing admission, and the
second communication device comprises a MoCA 2.0 network controller
(NC).
36. The method of claim 34, wherein the first communication device
comprises a MoCA 2.0 existing node (EN), and the second
communication device comprises at least one of a MoCA 2.0 NC or
another MoCA 2.0 EN.
37. A system for communication, the system comprising: a first
communication device comprising a receiver and a transmitter, the
first communication device being operable to: request an in-phase
and quadrature (IQ) probe from a second communication device
external to the first communication device, the IQ probe for
transmitting tones; receive the tones from the second communication
device; and calculate an estimate of IQ imbalance for each received
tone by determining the image to tone ratio based on the received
tones.
38. The system of claim 37, wherein the IQ imbalance comprises an
IQ imbalance associated with the receiver of the first
communication device.
39. The system of claim 37, wherein the first communication device
is operable to request a loopback probe comprising tones in a
loopback circuit including the receiver and transmitter of the
first communication device.
40. The system of claim 39, wherein the first communication device
is operable to receive the tones transmitted via the loopback
probe, and calculate gain, phase, and delay parameters to
compensate for transmitter IQ imbalances.
41. The system of claim 37, wherein the frequency separation is
selected as being large enough so that transmitter and receiver
images of the transmitted tones do not interfere with each
other.
42. The system of claim 37, wherein the request for the IQ probe is
transmitted to the second communication device during admission of
the first communication device to a network.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/981,633 (Atty. Docket No. E110027USP1),
filed Apr. 18, 2014, which is incorporated herein by reference in
its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates generally to communication
systems, In particular, some embodiments provide systems and
methods for estimating IQ imbalance in communications systems.
Background
[0003] Designers of contemporary communications devices face
numerous challenges. Such challenges arise from a continued
increase in the levels of se conductor device integration in
addition to constantly striving to reduce power consumption, size,
and cost, while increasing capabilities. Wired and wireless
communication devices are no exception. In traditional broadcast
systems where one device is broadcasting to many is possible, and
often practical, to design the broadcasting system to more rigorous
specifications. However, in a distributed network or other like
environment, it is not always practical from a commercial
standpoint to design each of the devices in accordance with the
highest standards. Accordingly, in contemporary communication
devices, a low-cost, practical implementation of the physical layer
presents a unique challenge in view of variations associated with
device componentry.
[0004] One such challenge involves the imbalance that typically
occurs between the in-phase (I) and quadrature-phase (Q) branches
when a received radio frequency (RF) signal is down-converted to
baseband. Similarly, at a transmitter, IQ imbalance can be
introduced during frequency up-conversion from baseband to ftF, IQ
imbalance can be the result of "amplitude," "phase," and "delay"
mismatch between the I and Q branches in quadrature heterodyne
communications. Particularly, in typical communication systems, the
gain (amplitude) and phase responses of the I and Q branches can be
different from one another, resulting in signal distortion. The IQ
imbalances can limit the achievable operating signal-to-noise ratio
(SNR) at the receiver, which can adversely impact constellation
sizes and data rates. This imbalance can occur with both heterodyne
receivers as well as with the so-called zero-IF, or
direct-conversion receivers. Although a direct conversion receiver
is preferable for low-cost and power-sensitive applications, it
tends to be more sensitive to IQ imbalance. With IQ imbalances,
translated spectral components from both the desired frequency bin
and the associated "image" frequency bin come into play, although
the former usually dominate.
Summary
[0005] Various embodiments are directed to estimating IQ imbalance
in a communication system are provided, where a first device is
configured to perform a self-characterization. The
self-characterization is performed by requesting an IQ probe from a
second device. The first device receives tones via the IQ probe
with frequency separation such that an image related to one IQ
imbalance is separated from an image related to another IQ
imbalance. The one IQ imbalance may be generated from the
transmitter circuitry and the another IQ imbalance may be generated
from the receiver circuitry. IQ imbalance can be estimated by
calculating tone to image ratio.
[0006] In accordance with one embodiment, a method comprises
requesting an IQ probe for transmitting tones. The method further
comprises receiving the tones with a frequency separation.
Additionally, the method comprises calculating an estimate of the
IQ imbalance for each received tone.
[0007] In accordance with another embodiment, a communication
device comprises a memory configured to store instructions, and a
processor, operatively coupled to the memory and configured to
execute instructions. The instructions cause the processor to
request an IQ probe for transmitting tones. The instructions
further cause the processor to receive the tones with a frequency
separation. Moreover, the instructions cause the processor to
calculate an estimate of the IQ imbalance for each received
tone.
[0008] Other features and aspects of the disclosed method and
apparatus will become apparent from the following detailed
description, taken in conjunction with the accompanying drawings,
which illustrate, by way of example, the features in accordance
with embodiments of the disclosed method and apparatus. The summary
is not intended to limit the scope of the invention, which is
defined solely by the claims attached hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Various embodiments are described in detail with reference
to the following figures. The drawings are provided for purposes of
illustration only and merely depict typical or example embodiments.
These drawings are provided to facilitate the reader's
understanding and shall not be considered limiting of the breadth,
scope, or applicability of the present disclosure. It should be
noted that for clarity and ease of illustration these drawings are
not necessarily made to scale.
[0010] FIG. 1 is a diagram illustrating an example time-domain
model with both transmit and receive included.
[0011] FIG. 2 is a diagram illustrating an example of the effect of
transmit-receive IQ imbalance on a single tone.
[0012] FIG. 3 is a diagram illustrating an example IQ image
frequency separation for estimating IQ imbalance in accordance with
various embodiments.
[0013] FIG. 4 is a diagram illustrating an example IQ image
frequency separation in addition to frequency offset for estimating
IQ imbalance in accordance with various embodiments.
[0014] FIG. 5 is a diagram illustrating an exam IQ image frequency
separation in a mixed network for estimating IQ imbalance in
accordance with various embodiments.
[0015] FIG. 6 is a schematic representation of first and second
devices engaging in IQ imbalance estimation in accordance with
various embodiments.
[0016] FIG. 7 illustrates example operations performed in
accordance with various embodiments for estimating IQ
imbalance.
[0017] FIGS. 8A-8D are example message flow diagrams illustrating
IQ imbalance estimation and calibration in accordance with various
embodiments.
[0018] FIG. 9 is an example of a computing module that can be used
in conjunction with various embodiments.
[0019] The figures are not intended to be exhaustive or to limit
the various embodiments to the precise form disclosed. It should be
understood that embodiments can be practiced with modification and
alteration.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS
[0020] Various embodiments are directed toward systems and methods
for estimating IQ imbalance in a communication system. In
accordance with various embodiments, a device (having a receiver
and a transmitter) is configured to perform a
self-characterization. The device can request that a probe be
transmitted from another device. The receiver of the requesting
device can receive the transmitted probe with a certain amount of
frequency separation calculate an image to tone ratio to estimate
IQ imbalance.
[0021] In various embodiments, the receipt of the transmitted probe
with frequency separation at the requesting device allows for an
image related to one IQ imbalance (fbr example, from the
transmitter circuit)_to be separated from an image related to
another IQ imbalance (for example, from the receiver circuit). In
some embodiments, the frequency separation comprises, for example
10 bins, 20 bins or more. For example, some embodiments may use 64
bins. In general, the number of bins should be large enough so that
the images and tones do not interfere in each computation. An
integer number of frequency bins is preferable for OFDM (Orthogonal
Frequency Division Multiplexing) systems to keep the images
orthogonal to the received tones. Other frequency separations are
also possible, depending on the particular implementation.
[0022] The imbalance estimate can include a gain imbalance, a phase
imbalance or a delay imbalance. Additionally, in various
embodiments, the imbalance estimate includes transmitter IQ
imbalance estimation or receiver IQ imbalance estimation.
[0023] FIG. 1 is a diagram illustrating an example time-domain
model 100 with both transmit and receive included. Referring now to
FIG. 1, for a system to have no EQ imbalance, the effective sine
and cosine waveforms performing up-conversion and down-conversion
need to be orthogonal, i.e., having a 90.degree. phase difference
and the same amplitude. In addition, the time delay and gain that
each branch experiences should be equal. However, because these
waveforms are never exactly orthogonal and the time delay and gain
are never exactly equal, real-world systems will have some form of
IQ imbalance. These IQ imbalances can be modeled as illustrated in
FIG. 1.
[0024] In the absence of transmit-receive (Tx-Rx) frequency offset,
the baseband equivalent model of the output of the transmit
up-conversion imbalance model 102 can be modeled as
p(t)=.mu..sub.txx(t)+v.sub.txx*(t) where .mu..sub.tx=[
cos(.phi..sub.tx)-j.epsilon..sub.tx sin(.phi..sub.tx)] and
v.sub.tx=[.epsilon..sub.tx cos(.phi..sub.tx)-j sin(.phi..sub.tx)]
while the output of the receive down-conversion imbalance model 104
can be modeled as z(t)=.mu..sub.rxy(t)+v.sub.rxy*(t) where
.mu..sub.rx=[ cos(.phi..sub.rx)+j.epsilon..sub.rx
sin(.phi..sub.rx)] and v.sub.rx=[.epsilon..sub.rx
cos(.phi..sub.rx)-j sin(.phi..sub.rx)]. From this, and taking into
account the effect of frequency offset, it can be shown that when
an input b(t) is input into the time-domain imbalance model 100 the
output can be modeled as
b'.sub.rx-tx(t)=.mu..sub.rxC.sub.k.mu..sub.txe.sup.j.alpha..omega.te.sup-
.j.omega.t+.mu..sub.txC.sub.-kv.sub.txe.sup.j.DELTA..omega.te.sup.-j.omega-
..sup.k.sup.t+v.sub.rxC*.sub.k.mu.*.sub.txe.sup.-j.DELTA..omega.te.sup.j.o-
mega..sup.k.sup.t+v.sub.rxC*.sub.-kv*.sub.txe.sup.-j.DELTA..omega.te.sup.j-
.omega..sup.k.sup.t
[0025] The tone frequency components are made up of two signals, a
signal with a gain of .mu..sub.rxC.sub.k.mu..sub.tx shifted upward
by the value of
.DELTA..omega.=.DELTA..omega..sub.tx-.DELTA..omega..sub.rx and a
signal with a gain of v.sub.rxC*.sub.-kv*.sub.tx shifted downward
by the value of
.DELTA..omega.=.DELTA..omega..sub.tx-.DELTA..omega..sub.rx. The
image frequency components are also made up of two signals, a
signal with a gain of .mu..sub.rxC.sub.-kv.sub.tx upward shifted by
the value of
.DELTA..omega.=.DELTA..omega..sub.tx-.DELTA..omega..sub.rx and a
signal with a gain of v.sub.rxC*.sub.k.mu.*.sub.tx downward shifted
by the value of
.DELTA..omega.=.DELTA..omega..sub.tx-.DELTA..omega..sub.rx. These
signals are illustrated in FIG. 2.
[0026] FIG. 2 is a diagram illustrating an example of the effect of
Tx-Rx IQ imbalance on a single tone. Referring now to FIG. 2, when
a signal 200 is transmitted using a system conforming to the
time-domain imbalance model 100 illustrated in FIG. 1, four signals
will be received. As discussed above, a signal 202 with gain of
.mu..sub.rxC.sub.k.mu..sub.tx upward Aw shifted by the value of
.DELTA..omega.=.DELTA..omega..sub.tx-.DELTA..omega..sub.rx and a
signal 204 with gain of v.sub.rxC*.sub.-kv*.sub.tx downward shifted
by the value of
.DELTA..omega.=.DELTA..omega..sub.tx=.DELTA..omega..sub.rx will be
present. Additionally, a signal 206 with gain of
.mu..sub.rxC.sub.-kv.sub.tx upward shifted by the value of
.DELTA..omega.=.DELTA..omega..sub.tx-.DELTA..omega..sub.rx and a
signal 208 with gain of v.sub.rxC*.sub.k.mu.*.sub.tx downward
shifted by the value of
.DELTA..omega.=.DELTA..omega..sub.tx-.DELTA..omega..sub.rx will
also be present.
[0027] The channel gain C.sub.k and the .mu. terms are generally
close to 1. The product of these terms is also generally near 1.
Accordingly, the signal gain is close to 1, but not equal to 1. A
frequency offset, Aw, caused by the IQ imbalance is also
present.
[0028] Certain conventional IQ algorithms use loopback probes with
a small number of tones. IQ imbalance is estimated by the ratio of
the tone to IQ image measured. That is, the Tx and Rx images are
separated or offset in frequency. That is, the Tx synthesizer and
the Rx synthesizer for a device are offset by, e.g., 12.5 MHz so
that the Tx and Rx images can be separated.
[0029] In a conventional loopback system the channel gain, C.sub.k,
will generally be close enough to 1 to be treated as equal to 1.
Accordingly, a conventional loopback system with input b(t) can be
modeled as:
b rx - tx ' ( t ) = .mu. rx .mu. tx j.DELTA..omega. t j.omega. k t
+ .mu. rx v tx j.DELTA..omega. t - j.omega. k t + v rx .mu. tx * -
j.DELTA..omega. t - j.omega. k t + v rx v tx * - j.DELTA..omega. t
j.omega. k t . ##EQU00001##
The gain, phase and delay IQ imbalance can be calculated using
these parameters.
[0030] However, conventional loopback systems suffer the drawback
of requiring the transmitter and receiver of a device to tune to
different frequencies at the same time to support the
aforementioned frequency offset. That is, two or more programmable
synthesizers (which include Phase Locked Loops and Voltage
Controlled Oscillators) are required in a device. This can lead to
significant cost increases. In general, a radio tunes to a single
channel at a time and is typically designed with a single
synthesizer. The cost of the second synthesizer is incurred solely
for the purpose of providing the loopback-with-frequency offset
capability required by these conventional IQ imbalance calibration
techniques. Other approaches like manual tuning can also be cost
prohibitive when mass producing devices, such as radios made on
silicon.
[0031] Accordingly, various embodiments are provided for estimating
IQ imbalance by requesting a probe from a remote device. Thus, a
loopback system need not be implemented on a device, and the need
for multiple phase-locked loops is negated. Instead, an Rx node may
shift its Rx synthesizer by some specified amount (as will be
described in greater detail below) in order to achieve the
aforementioned frequency separation. It is contemplated herein that
various embodiments can be used to determine the gain, phase, and
delay IQ imbalance caused by real-world systems,
[0032] Various IQ tuning probes are contemplated for use in
accordance with various embodiments. A first probe, which can be
referred to as an RxIQ50 probe, may comprise a remote transmitter
to receiver probe that is a Multimedia over Coax Alliance (MoCA)
Standard 1.0-defined Type II probe. This probe is utilized for
calibration of the receive path IQ of the device under
self-calibration. This first probe is preceded by an error vector
magnitude (EVM) probe for the purposes of obtaining automatic gain
control (AGC), frequency offset, and channel signal-to-noise ratio
(SNR) estimates. Receiver configuration with the correct
gain/frequency offset etc. is a consideration for the practical
implementation of this technique, and the use of EVM probes is one
way of achieving correct receiver configuration.
[0033] After the receive path IQ imbalance has been calibrated, a
second probe, which can be referred to as a TxIQ50 probe is used to
calibrate the IQ imbalance of the transmit path of the device under
self-calibration. This probe may be a loopback probe with no
frequency offset. This probe is preceded by the RxIQ50 probe (and
receive path IQ calibration) as the lack of dual synthesizers may
cause Tx images and Rx images to appear at the same frequency. This
probe is also preceded by RF calibration to ensure unity gain
through the low-power loopback path.
[0034] In some communications standards, systems may be configured
to utilize different communication channel bandwidths. For example,
in the MoCA standard, systems can use either 50 MHz or 100 MHz
channel bandwidth. In this case, the IQ calibration procedure may
have to be repeated independently for the 50 MHz configuration and
the 100 MHz configuration.
[0035] After the 50 MHz configuration has been IQ calibrated, a
third probe, which can be referred to as an RxIQ100 probe, may
again be a remote transmitter to receiver probe preceded by an EVM
probe for the purposes of obtaining AGC, frequency offset, and
channel signal-to-noise ratio estimates. This third probe is also
preceded by calibration to ensure unity gain through the low-power
loopback path. A fourth probe, which can be referred to as a
TxIQ100 probe, can be a low-power loopback probe preceded by the
RxIQ 100 probe as again, the lack of dual synthesizers in certain
scenarios may cause Tx images and Rx images to appear at the same
frequency.
[0036] FIG. 3 illustrates an example of frequency separation for
separating the image related to a first IQ imbalance (e.g., Tx IQ
image) from an image related to another IQ imbalance (e.g., Rx IQ
image). During admission of a new node to a network, e.g., a MoCA
network, the new node may request an IQ probe with e.g., two or
four tones located in the [-25, 0] MHz band. In this example, two
tones 300 are transmitted. It should be noted that if the new node
is the first node to be admitted to the network, a Network
Controller (NC) may repeat IQ estimation as described herein, as
this may be the NC's first opportunity to calibrate its IQ. When
tones 300 are transmitted from a remote/far node (e.g., the
transmitter of another radio device), the tones 300 are
up-converted from baseband for modulating a higher frequency
carrier signal, f.sub.c, for transmission. This results in tones
302, here Tx IQ images 304 are generated at the respective
symmetric frequencies.
[0037] At a receiver of the requesting device (the device
requesting transmission of the IQ probe), a shift of for example,
25 MHz is programmed at the Rx synthesizer as illustrated in FIG.
3. That is, and for example, tones 302 and Tx IQ images 304 are
down-converted back to baseband plus 25 MHz, resulting in tones 306
and Tx IQ images 308. As a result, tones 302 and Tx IQ images 304
are down-converted to 25 MHz above baseband, and Rx IQ images 310
images are separated in frequency from Tx IQ images 308.
[0038] It should be noted that restriction of the tones in [-25, 0]
MHz can be relaxed to [-50, +25] MHz of the transmitter band (or
[-25, +50] MHz of the receiver band) as long as the frequencies are
chosen judiciously, so that the Tx and Rx IQ images do not
interfere with each other. Furthermore, if interference does exist
in certain areas of the frequency band (e.g., as may be the case in
Advanced Television Systems Committee (ATSC) or Global System for
Mobile Communications (GSM)), the IQ probe tone frequencies can be
chosen to avoid the interference.
[0039] In accordance with another embodiment, small frequency
offset between a transmitter and a receiver due to crystal
variations can be accounted for. That is, during admission of a new
node to a network, e.g., a MoCA network, the new node may request
an IQ probe with e.g., two or four tones located in the [-25, 0]
MHz band. In this example, as illustrated in FIG. 4, two tones 400
are transmitted. It should be noted that if the new node is the
first node to be admitted to the network, a network controller (NC)
may repeat IQ estimation as described herein, as this may be the
NC's first opportunity to calibrate its IQ. When tones 400 are
transmitted from a remote/far node (e.g., the transmitter of
another radio device), the tones 400 are up-converted from baseband
for modulating a higher frequency carrier signal, f.sub.c, for
transmission. This results in tones 402, where Tx IQ images 404 are
generated at the respective symmetric frequencies.
[0040] At a receiver of the requesting device (the device
requesting transmission of the IQ probe), a shift of, e g., 25 MHz,
is programmed at the Rx synthesizer as illustrated in FIG. 4. That
is, and for example, tones 402 and 404 are down-converted back to
baseband plus 25 MHz. As a result, tones 402 and 404 are
down-converted to 25 MHz above baseband, resulting in tones 406 and
408, with and Rx IQ images 410 images being separated in frequency
from Tx IQ images 408.
[0041] As illustrated in FIG. 4, the transmitted tones are still
identical to the tones and images at mirror frequencies. A receiver
mixer, however, may have a frequency offset to the transmitter
frequency (in addition to the "bulk" 25 MHz separation) due to
natural variation between the crystal of the transmitter and the
crystal of the receiver. Accordingly, the tones and TX IQ images
412 and 414 will be shifted (to the right in FIG. 4) compared to
the previous non-offset scenario. Therefore Rx EQ images 416
generated in this example are shifted in a direction opposite to Rx
IQ images 414 (to the left in FIG. 4).
[0042] The shifting of transmitted tones and Tx IQ images are
inconsequential with respect to IQ imbalance estimation, while Rx
IQ images 416 remain at the mirror frequencies of received tones
412. Hence, there is the additional consideration that the received
tones 412 (and Rx IQ images 416) may have shifted out of the Fast
Fourier Transform (HT) grid. This can introduce two issues, both of
which stem from the associated FFT leakage. That is, the phase of
each tone (or the nearest bin to the tone) is not constant in
successive orthogonal frequency division multiplexing (OFDM)
symbols. Therefore, any coherent averaging done to improve SNR is
no longer possible. Additionally, leakage from the tone may mask a
weak image signal.
[0043] To address the above-noted issues, the image to tone ratio
is used for averaging, where the phase of the tone and the image
should cancel out. Additionally, windowing may be utilized to
account for the aforementioned leakage issue. That is, a window
length may be chosen such that a null is located at an image point.
Hence, the image may be positioned at a null of leakage sidelobes,
thereby reducing interference. It should be noted that other
methods of addressing frequency offset may be utilized in
accordance with other embodiments, such as by increasing
tone-to-image distance.
[0044] In particular, and assuming an expected tone at frequency
bin k, that tone may be received at a frequency between two bins
(more precisely at frequency
2 .pi. ( k + .delta. ) N F S ##EQU00002##
where N=512 is the size of the FFT (for MoCA 2.0), R.sub.S=100 MHz
is the sampling rate (for MoCA 2.0), and 0<.delta.<0.5 is a
fractional bin frequency offset due to frequency offset between the
transmitter and the receiver. Accordingly, the received signal
is
x ( n ) = A j ( 2 .pi. ( k + .delta. ) n N + .theta. ) + .alpha. A
- j ( 2 .pi. ( k + .delta. ) n N + .theta. ) , 0 .ltoreq. n
.ltoreq. N - 1 ( 1 ) ##EQU00003##
where the second term is due to IQ imbalance and
.alpha.=pe.sup.j.phi. is the IQ imbalance coefficient to be
estimated.
[0045] Assuming that the frequency offset .delta. is known, the
following frequency offset correction operation may be applied,
x ~ ( n ) = x ( n ) A - j ( 2 .pi..delta. n N + .theta. ) = A j ( 2
.pi. kn N + .theta. ) + .alpha. A - j ( 2 .pi. ( k + 2 .delta. ) n
N + .theta. ) . ( 2 ) ##EQU00004##
This operation centers the tone back on the grid but pushes the
image to a frequency offset of 2.delta..
[0046] Taking the FFT of the signal of (2) the following is
obtained at bin k,
X ( k ) = n = 0 N - 1 x ~ ( n ) - j 2 .pi. kn N = NA - j.theta. +
.alpha. A - j.theta. n = 0 N - 1 - j ( 2 .pi. ( 2 k + 2 .delta. ) n
N ) . ( 3 ) ##EQU00005##
The first term in (3) is the FFT of the tone (which now is on grid)
and the second term is the leakage onto the tone bin from the
image. This is a second order effect and may be ignored here,
arriving at X(k).apprxeq.N (4).
[0047] The FFT at bin -k is
X ( - k ) = n = 0 N - 1 x ~ ( n ) j 2 .pi. kn N = A - j.theta. n =
0 N - 1 j 2 .pi.2 kn N + .alpha. A - j.theta. n = 0 N - 1 - j ( 2
.pi. ( 2 .delta. ) n N ) . ( 5 ) ##EQU00006##
The first term in is identically equal to zero (i.e., no leakage
from the tone, since the tone in on grid) and the second term in
the FFT of the image. However, since the image is off grid, it is
multiplied by the summation of exponentials constituting the sine
function,
[0048] thereby arriving at X(-k)=.alpha.Ae.sup.-j.theta.D (6) with
a distortion factor,
D = n = 0 N - 1 - j ( 2 .pi. ( 2 .delta. ) n N ) . ( 7 )
##EQU00007##
[0049] The ratio of (4) and (7) results in
X ( - k ) X * ( k ) = .alpha. D . ( 8 ) ##EQU00008##
[0050] Hence, the IQ imbalance coefficient a can be estimated by
utilizing the image to tone ratio and compensating for the
distortion factor D.
[0051] In accordance with some embodiments, it may be preferable to
compensate for 0<2 .delta.<0.5 in this manner. However, for
fractional bin delays larger than that (half a bin), various
embodiments may start from the -k+1 bin to compensate for the
smaller 1-2 .delta. fractional offset.
[0052] In a mixed MoCA network, calibration should be performed for
both the 100 MHz and the 50 MHz IQ. That is, and when admitting (a
new node) to a MoCA 2.0 NC, the above IQ algorithm is repeated
using the MoCA 1.x receive configuration (i.e., with 50 MHz
baseband filters engaged). FIG. 5 illustrates the resulting
tones/signals and images in this case (e.g., transmitted tones 500,
up-converted tones 502 and Tx IQ images 504, down-converted tones
506 and Tx IQ images 508 and Rx IQ images 510). When admitting to a
MoCA 1.x NC, FIG. 6 remains applicable, but transmitted tones 500
are sent per a request for a Type II probe.
[0053] Referring to FIG. 6, various embodiments operate generally
as follows. A first device 600 may include a transmitter 602 and a
receiver 604. As described above, the effective sine and cosine
waveforms performing up-conversion and down-conversion are never
exactly orthogonal, nor are e time delay and gain. Accordingly,
real-world systems will have some form of IQ imbalance. In
accordance with various embodiments receiver 604 of first device
600 can request that an IQ probe be sent from other device, such as
second, remote device 606, in particular, transmitter 608 of second
device 606.
[0054] FIG. 7 illustrates example operations performed in
accordance with various embodiments for estimating (and
compensating for) IQ imbalance. It should be noted that when a MoCA
2.0 New Node (NN) receives a valid Beacon, the NN examines whether
the NC is a MoCA 1.x or MoCA 2.0 node. If the NC is a MoCA 2.0
node, the NN performs 100 MHz IQ calibration during admission.
[0055] At operation 700, an IQ probe is requested for transmitting
tones. The IQ probe may be an RxIQ100 probe. It should be noted
that during admission and prior to requesting an IQ probe, an NN
requests multiple Error Vector Magnitude (EVM) probes, e.g., EVM100
probes. Upon receipt of the EVM probes, AGC, frequency offset
(i.e., receiver mixer offset) and channel SNR are estimated. At
operation 702, the tones sent in response to the IQ probe request
are received with a frequency separation. The frequency separation
may be set at 12.5 MHz (64 bins) or 25 MHz, for example. As
described above, a first device may request the IQ probe from a
second, remote device. Accordingly, a receiver of the first device
is tuned in accordance with the frequency separation. At operation
704, the image to tone ratio based on the received tones are
calculated.
[0056] It should be noted that operations 700-704 may be repeated
for accuracy. That is, the first device may repeatedly request IQ
probes, receive tones, and calculate the image to tone ratio in
order to obtain an IQ imbalance sampling/sample set. At operation
706, I, Q, and D parameters are calculated for Rx EQ imbalance
compensation. At operation 708, the first device (i.e., hardware)
is configured for Rx IQ imbalance compensation. As described above,
the receiver of the first device requests and receives tones
transmitted by a transmitter of a second, remote device.
Accordingly, the IQ imbalance estimated is relevant to the receiver
of the first device.
[0057] in order to estimate Tx IQ imbalance, a loopback circuit may
be formed with the receiver and the transmitter of the first
device. As described previously, conventional systems and methods
may rely on such a loopback configuration in order to
self-characterize IQ imbalance. Accordingly, to estimate Tx IQ
imbalance, various embodiments may rely on conventional loopback
estimation. One system and method of IQ imbalance estimation using
loopback is disclosed in U.S. Patent Publication No. 2009/0325516
to Saeid Safavi, entitled "System and Method for IQ imbalance
Estimation Using Loopback With Frequency Offset," and assigned to
the assignee of the present disclosure, which is incorporated
herein by reference in its entirety.
[0058] Referring back to FIG. 7, a loopback probe is requested at
operation 710. That is, the receiver of the first device may
request a loopback probe from the transmitter of the first device.
At operation 712, the loopback probe tones are received. Similar to
Rx IQ estimation described above, operations 710 and 712 may be
repeated for accuracy. That is, upon requesting a plurality of
loopback probes, and receiving a plurality of loopback probe tones,
the results may be averaged. At operation 714, the I, Q, and D
parameters for Tx IQ imbalance compensation. At operation 716, the
first device is further configured for Tx IQ imbalance
compensation.
[0059] It should be noted that once admission has been completed,
the NN, if a MoCA 2.0 node, performs 50 MHz IQ calibration using a
receiver-determined IQ probe during a link maintenance operation
(LMO), as well as a loopback probe during LMO. 50 MHz IQ
calibration is substantially similar to that described above, which
is for 100 MHz IQ calibration.
[0060] That is, multiple EVM50 probes can be requested for
estimating AGC, frequency offset, and channel SNR, while an RxIQ50
probe with desired tones is requested, and received with a 12.5 MHz
frequency separation, and the image to tone ratio may be
calculated. In some embodiments repeated IQ probe requests can be
made, effectuating repeated receipt of multiple tones with the
frequency separation . Image to tone ratio can be calculated for
each receipt of the tones with frequency separation, and the
results can be averaged. I, Q, and D parameters for Rx IQ imbalance
compensation can be calculated, and the first device hardware can
be configured accordingly. A loopback probe can be requested,
effectuating the transmission of tones in order to estimate 50 MHz
Tx IQ imbalance. Again, in some embodiments, this can be repeated
to obtain an average result, after which I, Q, and D parameters can
be calculated for 50 MHz Tx IQ imbalance compensation, where the
first device can be configured to compensate for the 50 MHz Tx IQ
imbalance.
[0061] If the NC is a MoCA 1.x NC, the NN performs 50 MHz IQ
calibration during admission following the procedure defined in the
MoCA 1.1 specification. When detecting a handoff/failover from MoCA
1.x NC to a MoCA 2.0 NC, each MoCA 2.0 node performs 100 MHz IQ
calibration using a receiver-determined probe during LMO (for Rx EQ
imbalance) and a loopback probe during LMO (for Tx IQ imbalance).
In a mixed mode network, if 100 MHz IQ calibration has not yet been
performed, a node may derive the 100 MHz IQ calibration parameters
from the 50 MHz IQ calibration parameters and vice versa.
[0062] FIG. 8A is an example message flow diagram 800 illustrating
the message flow between a MoCA 2.0 NN 802 and a MoCA 2.0 NC 804
during admission of the MoCA 2.0 NN in accordance with various
embodiments. When a MoCA 2.0 NN is admitted by a MoCA 2.0 NC, the
M0CA 2.0 NN performs 100 MHz IQ calibration in a "Begin Node
Admission State" using "Probe Transmission Requests" (PTR) and
"Receiver-Determined Probe" (RDP) Requests in "Admission Control
Frame" (ACF) slots.
[0063] MoCA 2.0 NN 802 sends a PTR to MoCA 2.0 NC 804 to request
ACE slots for, e.g., four EVM Probe transmissions. MoCA 20.0 NC 804
transmits an EVM probe four times. Upon receipt of the EVM100
probes, the MoCA 2.0 NN 802 estimates AGC, frequency offset and
channel SNR. MoCA 2.0 NN 802 sends a PTR to MoCA 2.0 NC 804 to
request ACF slots for, e.g., five, RDP requests and twenty RDP
transmissions. At this point, the I, Q, and D parameters can be
calculated to compensate for 100 MHz Rx IQ imbalance. Once MoCA 2.0
NC 804 schedules the ACF slot for the loopback probe transmission,
MoCA 2.0 NN 802 sends a TxIQ100 probe. MoCA 2.0 NN 802 MAY request
up to, e.g., three, loopback probes. Thereafter, I, Q, and D
parameters for 100 MHz Tx IQ imbalance compensation can be
calculated. Once MoCA 2.0 NN 802 finishes all the TxIQ100 probe
transmissions, it sends a PTR with zero elements to inform MoCA 2.0
NC 804 that it has no more PTRs.
[0064] If MoCA 2.0 NN 802 is the second MoCA 2.0 node in the
network, MoCA 2.0 NC 804 performs 100 MHz EQ calibration for itself
after MoCA 2.0 NN 802 finishes its 100 MHz IQ calibration (as
alluded to above). Otherwise, MoCA 2.0 NC 804 may optionally choose
to perform 100 MHz IQ calibration. FIG. 8B illustrates an example
message flow diagram 806 for 100 MHz IQ calibration of MoCA 2.0 NC
804 (which is similar to that for 100 MHz IQ calibration for MoCA
2.0 NN 802). That is, the message flow substantially mirror that of
FIG. 8A, except that MoCA 2.0 NC 804 is the entity requesting
probes, receiving probe transmissions, calculating I, Q, and D
parameters, and configuring its hardware for 100 MHz IQ
calibration/compensation.
[0065] As described previously, once MoCA 2.0 NN 802 finishes
admission with a MoCA 2.0 NC, e.g., MoCA 2.0 NC 804, (and becomes
an existing node (EN)) it performs 50 MHz IQ calibration by
requesting ail RDP LMO followed by a loopback probe LMO. In the RDP
LMO, the MoCA 2.0 EN 802 may choose any other MoCA 2.0 node as the
probe-transmitting node, although it is preferable that MoCA 2.0 EN
802 choses a node that has the best 100 MHz unicast bitloading
associated with it.
[0066] FIG. 8C illustrates an example message flow diagram 808
illustrating messages exchanged between MoCA 2.0 EN 802 and MoCA
2.0 NC/EN 804. Once MoCA 2.0 NC 804 changes the LINK_STATE_II to
Receiver-Determined Probe State from Steady State, MoCA 2.0 EN 802
transmits a RDP request to specify the key parameters used to
create the RxIQ50 probes. The tone location of RXIQ 50 probes can
be derived from the measurements of EVM100 Probes transmitted
during admission. After receiving, e.g., eight, RxIQ50 probes, the
MoCA 2.0 EN 802 may request additional RxIQ50 probe transmissions.
Generally, MoCA 2.0 EN 802 receives three sets of eight RxIQ50
probes. If the RDP LMO is not completed successfully, e.g., it is
aborted due to node admission or timeout, MoCA 2.0 EN 802 can
request another RDP LMO when the link state is back to Steady
State. After the RDP LMO is completed successfully, MoCA 2.0 EN 802
requests a loopback probe transmission for the TxIQ50 probe. The
duration of each loopback probe is TC TIME_SLOTs (i.e., the
duration of Type C probes in MoCA 1.1). MoCA 2.0 EN 802 may request
multiple additional loopback probes.
[0067] It should be noted that when a MoCA 2.0 NN is admitted by a
MoCA 1.x NC, the moCA 2.0 NN follows the MoCA 1.x node admission
procedure specified in the MoCA 1.1 specification for IQ50
tuning.
[0068] FIG. 8D illustrates an example message flow diagram 810
between MoCA 2.0 NN 802 and MoCA 2.0 NC 804 when a MoCA 2.0 EN
becomes the NC after a handoff or failover from a MoCA 1.x NC. Each
MoCA 2.0 node (including the NC) performs 100 MHz IQ calibration by
requesting a RDP LMO and a loopback probe LMO. The RDP LMO and the
loopback probe LMO may be requested after the node finishes its
first regular LMO after handoff/failover.
[0069] Again, a MoCA 2.0 node may choose any other MoCA 2.0 node as
the probe-transmitting node, although it is preferable that the
MoCA 2.0 node chooses another MoCA 2.0 node that has the best 100
MHz unicast bitloading to it. As illustrated in FIG. 8D, once MoCA
2.0 NC 804 changes the LINK_STATE_II to Receiver-Determined Probe
State from Steady State, the MoCA 2.0 EN 802 transmits a RDP
Request to request four EVM100 probes. The EMV100 Probe is
specified using the EVM Probe request element. After receiving the
EVM100 probes from MoCA 2.0 NC 804, MoCA 2.0 EN 802 transmits
another RDP request to request four 2-tone RxIQ100 probes. MoCA 2.0
EN 802 repeats the RDP request and RDPs for all 5 2-tone RxIQ 100
probes. If the RDP LMO is not completed successfully, e.g., aborted
due to node admission or timeout, MoCA 2.0 EN 802 may request
another RDP LMO after the link state returns to Steady State. After
the RDP LMO is completed successfully, MoCA 2.0 EN 802 requests a
loopback probe transmission for the TxIQ100 probe. The
request/transmission process may be repeated multiple times.
[0070] When a MoCA 2.0 NC admits the first MoCA 1.x node to the
network, it follows the MoCA 1.x node admission procedure specified
in the MoCA 1.1 specification for IQ50 tuning.
[0071] MoCA 1.xType II (also referred to as MoCA 1.x RX IQ) probe
packets may include two tones located at sufficient frequency
spacing with sufficient SNR. The locations of the two tones (SC1
and SC2) are defined in the MoCA 1.x specification as follows.
RXIQ100 calibration shall be performed via five RDPs, where each
RDP consists of two tones. The receiver will have 10 image to tone
ratios computed (5.times.2 tones) at the end of this process. The
two tones shall be picked similarly to MOCA 1.x Type II probe tone
locations that is based on high SNR. Five IQ segments indicative of
RxIQ 100 transmit tone locations may be provided by an RF systems
group for tone selection of RXIQ 100.
[0072] The first step in transmit tone selection is determining the
bins with the highest SNR that are within the bands defined per the
aforementioned five IQ segments. New Node Type I (EVM) Probe during
node admission stage may be used for this purpose. The EVM probe
data can consist of 16 bits pseudo floating number and is converted
to SNR. Once the EVM data is converted to SNR in, e.g., log2
format, the bin with highest SNR can be selected. The receiving
node's LO frequency may be shifted (to achieve frequency
separation) by +12.5 MHz (64 bins). Accordingly, the tone and image
locations for the receiving node can be computed. It should be
noted the amount of frequency separation implemented in accordance
with various embodiments can vary. It should be noted that a bin
shifting algorithm may be utilized to account for large frequency
offsets that would cause tones to shift into neighbor bins. The
highest frequency offset in terms of Hz can be computed as 1600
MHz*200 ppm=320 KHz which will cause the tone to shift by 2 bins.
Time domain frequency offset estimation status can be converted to
Hz as well. In accordance with one embodiment the bins of the tones
and images (e.g., a total of 4) can be set to 1 on the Rx
bitloading table of the receiving node, while all the other bins
may be set to 0. Tone selection for MoCA 2.0 TX IQ probes can be
based on, e.g., a proprietary selection algorithm.
[0073] Regarding the computation (averaged) of image to tone ratio,
in one example, TX tone locations are picked at bins 420 and 495,
while the frequency separation between the nodes is 150 ppm (in the
case of a MoCA 1.x Type II probe). Upon successful acquisition of a
MoCA I .x RX IQ probe; the Rx IQ probe data is saved to the shared
memory using direct memory access. This data may include 160 32-bit
fields (2 tones*2 images*40 symbols). A similar operation may be
performed for MoCA 2.0 Rx IQ probes, but repeated five times for a
total of 10 image to tone ratios that are computed from each RDP.
After the accumulation of image to tone ratios, RX IQ coefficients
can be computed.
[0074] As used herein, the term module might describe a given unit
of functionality that can be performed in accordance with one or
more embodiments of the present application. As used herein, a
module might be implemented utilizing any form of hardware,
software, or a combination thereof. For example, one or more
processors, controllers, ASICs, PLAs, PALs, CPLDs, FPGAs, logical
components, software routines or other mechanisms might be
implemented to make up a module. In some implementations, the
various modules described herein might be implemented as discrete
modules or the functions and features described can be shared in
part or in total among one or more modules. In other words, as
would be apparent to one of ordinary skill in the art after reading
this description, the various features and functionality described
herein may be implemented in any given application and can be
implemented in one or more separate or shared modules in various
combinations and permutations. Even though various features or
elements of functionality may be individually described or claimed
as separate modules, one of ordinary skill in the art will
understand that these features and functionality can be shared
among one or more common software and hardware elements, and such
description shall not require or imply that separate hardware or
software components are used to implement such features or
functionality.
[0075] Where components or modules of the application are
implemented in whole or in part using software, in one embodiment,
these software elements can be implemented to operate with a
computing or processing module capable of carrying out the
functionality described with respect thereto. One such example
computing module is shown in FIG. 9. Various embodiments are
described in terms of this example-computing module 900. After
reading this description, it will become apparent to a person
skilled in the relevant art how to implement the application using
other computing modules or architectures.
[0076] Referring now to FIG. 9, corn pitting module 900 may
represent, for example, computing or processing capabilities found
within a desktop, laptop, notebook, and tablet computers; hand-held
computing devices (tablets, PDA's, smart phones, cell phones,
palmtops, etc.); workstations or other devices with displays;
servers; set top boxes, smart TVs or other networked home
appliances; or any other type of special-purpose or general-purpose
computing devices as may be desirable or appropriate for a given
application or environment. Computing module 900 might also
represent computing capabilities embedded within or otherwise
available to a given device. For example, a computing module might
be found in other electronic devices such as, for example
navigation systems, portable computing devices, and other
electronic devices that might include some form of processing
capability.
[0077] Computing module 900 might include, for example, one or more
processors, controllers, control modules, or other processing
devices, such as a processor 904. Processor 904 might be
implemented using a general-purpose or special-purpose processing
engine such as, for example, a microprocessor, controller, or other
control logic. In the illustrated example, processor 904 is
connected to a bus 902, although any communication medium can he
used to facilitate interaction with other components of computing
module 900 or to communicate externally.
[0078] Computing module 900 might also include one or more memory
modules, simply referred to herein as main memory 908. For example,
preferably random access memory (RAM) or other dynamic memory,
might be used for storing information and instructions to be
executed by processor 904. Main memory 908 might also be used for
storing temporaly variables or other intermediate information
during execution o of instructions to be executed by processor
1004. Computing module 900 might likewise include a read only
memory ("ROM") or other static storage device coupled to bus 902
for storing static information and instructions for processor
904.
[0079] Computing module 900 might also include one or more various
forms of information storage mechanism 910, which might include,
for example, a media drive 912 and a storage unit interface 920.
The media drive 912 might include a drive or other mechanism to
support fixed or removable storage media 914. For example, a hard
disk drive, a solid state drive, a magnetic tape drive, an optical
disk drive, a CD or DVD drive (R or RW), or other removable or
fixed media drive might be provided. Accordingly, storage media 914
might include, for example, a hard disk, an integrated circuit
assembly, magnetic tape, cartridge, optical disk, a CD or DVD, or
other fixed or removable medium that is read by, written to or
accessed by media drive 912. As these examples illustrate, the
storage media 914 can include a computer usable storage medium
having stored therein computer software or data.
[0080] In alternative embodiments, information storage mechanism
910 might include other similar instrumentalities for allowing
computer programs or other instructions or data to be loaded into
computing module 900. Such instrumentalities might include, for
example, a fixed or removable storage unit 922 and an interface
920. Examples of such storage units 922 and interfaces 920 can
include a program cartridge and cartridge interface, a removable
memory (for example, a flash memory or other removable memory
module) and memory slot, a PCMCIA slot and card, and other fixed or
removable storage units 922 and interfaces 920 that allow software
and data to be transferred from the storage unit 922 to computing
module 900.
[0081] Computing module 900 might also include a communications
interface 924. Communications interface 924 might be used to allow
software and data to be transferred between computing module 900
and external devices. Examples of communications interface 924
might include a modem or softmodem, a network interface (such as an
Ethernet, network interface card, WiMedia, IEEE 802.XX or other
interface), a communications port (such as for example, a USB port,
IR port, RS232 port Bluetooth.RTM. interface, or other port), or
other communications interface. Software and data transferred via
communications interface 924 might typically be carried on signals,
which can be electronic, electromagnetic (which includes optical)
or other signals capable of being exchanged by a given
communications interface 924. These signals might be provided to
communications interface 924 via a channel 928. This channel 928
might carry signals and might be implemented using a wired or
wireless communication medium. Some examples of a channel might
include a phone line, a cellular link, an RF link, an optical link,
a network interface, a local or wide area network, and other wired
or wireless communications channels.
[0082] While various embodiments of the disclosed method and
apparatus have been described above, it should be understood that
they have been presented by way of example only, and not of
limitation. Likewise, the various diagrams may depict an example
architectural or other configuration for the disclosed method and
apparatus, which is done to aid in understanding the features and
functionality that can be included in the disclosed method and
apparatus. The disclosed method and apparatus is not restricted to
the illustrated example architectures or configurations, but the
desired features can be implemented using a variety of alternative
architectures and configurations. Indeed, it will be apparent to
one of skill in the art how alternative functional, logical or
physical partitioning and configurations can be implemented to
implement the desired features of the disclosed method and
apparatus. Also, a multitude of different constituent module names
other than those depicted herein can be applied to the various
partitions. Additionally, with regard to flow diagrams, operational
descriptions and method claims, the order in which the steps are
presented herein shall not mandate that various embodiments be
implemented to perform the recited functionality in the same order
unless the context dictates otherwise.
[0083] Although the disclosed method and apparatus is described
above in terms of various exemplary embodiments and
implementations, it should be understood that the various features,
aspects and functionality described in one or more of the
individual embodiments are not limited in their applicability to
the particular embodiment with which they are described, but
instead can be applied, alone or in various combinations, to one or
more of the other embodiments of the disclosed method and
apparatus, whether or not such embodiments are described and
whether or not such features are presented as being a part of a
described embodiment. Thus, the breadth and scope of the claimed
invention should not be limited by any of the above-described
exemplary embodiments.
[0084] Terms and phrases used in this document, and variations
thereof, unless otherwise expressly stated, should be construed as
open ended as opposed to limiting. As examples of the foregoing:
the term "including" should be read as meaning "including, without
limitation" or the like; the term "example" is used to provide
exemplary instances of the item in discussion, not an exhaustive or
limiting list thereof; the terms "a" "an" should be read as meaning
"at least one" "one or more" or the like; and adjectives such as
"conventional," "traditional," "normal," "standard," "known" and
terms of similar meaning should not be construed as limiting the
item described to a given time period or to an item available as of
a given time,but instead should be read to encompass conventional,
traditional, normal, or standard technologies that may be available
or known now or at any time in the future. Likewise, where this
document refers to technologies that would be apparent or known to
one of ordinary skill in the art, such technologies encompass those
apparent or known to the skilled artisan now or at any time in the
future
[0085] A group of items linked with the conjunction "and" should
not be read as requiring that each and every one of those items be
present in the grouping, but rather should be read as "and/or"
unless expressly stated otherwise. Similarly, a group of items
linked with the conjunction "or" should not be read as requiring
mutual exclusivity among that group, but rather should also be read
as "and/or" unless expressly stated otherwise. Furthermore,
although items, elements or components of the disclosed method and
apparatus may be described or claimed in the singular, the plural
is contemplated to be within the scope thereof unless limitation to
the singular is explicitly stated.
[0086] The presence of broadening words and phrases such as "one or
more," "at least," "but not limited to" or other like phrases in
some instances shall not be read to mean that the narrower case is
intended or required in instances where such broadening phrases may
be absent. The use of the term "module" does not imply that the
components or functionality described or claimed as part of the
module are all configured in a common package. Indeed, any or all
of the various components of a module, whether control logic or
other components, can be combined in a single package or separately
maintained and can further be distributed in multiple groupings or
packages or across multiple locations.
[0087] Additionally, the various embodiments set forth herein are
described in terms of exemplary block diagrams, flow charts and
other illustrations. As will become apparent to one of ordinary
skill in the art after reading this document, the illustrated
embodiments and their various alternatives can be implemented
without confinement to the illustrated examples. For example, block
diagrams and their accompanying description should not be construed
as mandating a particular architecture or configuration.
* * * * *