U.S. patent application number 10/654009 was filed with the patent office on 2004-03-25 for systems and methods for a multi-carrier transceiver with radio frequency interference reduction.
This patent application is currently assigned to AWARE, INC.. Invention is credited to Ramirez-Mireles, Fernando, Tzannes, Marcos C..
Application Number | 20040057508 10/654009 |
Document ID | / |
Family ID | 22783373 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040057508 |
Kind Code |
A1 |
Tzannes, Marcos C. ; et
al. |
March 25, 2004 |
Systems and methods for a multi-carrier transceiver with radio
frequency interference reduction
Abstract
A multi-carrier information transceiver that exhibits robustness
against radio frequency interference (RFI) signals present in the
communications channel. The transceiver includes a RFI mitigation
technique that operates not only during the steady state operation
of the transceiver but also during the training stage of the
transceiver. That requires dynamically modifying the training
signals when the presence of RFI is detected. The modification of
the training signals facilitates the estimation of RFI, improving
the performance of the multi-carrier transceiver.
Inventors: |
Tzannes, Marcos C.; (Orinda,
CA) ; Ramirez-Mireles, Fernando; (Walnut Creek,
CA) |
Correspondence
Address: |
NIXON PEABODY, LLP
401 9TH STREET, NW
SUITE 900
WASINGTON
DC
20004-2128
US
|
Assignee: |
AWARE, INC.
Bedford
MA
|
Family ID: |
22783373 |
Appl. No.: |
10/654009 |
Filed: |
September 4, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10654009 |
Sep 4, 2003 |
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10358246 |
Feb 5, 2003 |
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10358246 |
Feb 5, 2003 |
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09876073 |
Jun 8, 2001 |
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6556623 |
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60210556 |
Jun 9, 2000 |
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Current U.S.
Class: |
375/219 ;
375/260 |
Current CPC
Class: |
H04L 27/2613 20130101;
H04L 5/006 20130101; H04M 3/18 20130101; H04L 5/0044 20130101; H04M
11/062 20130101; H04L 5/003 20130101; H04M 3/2209 20130101; H04L
5/0058 20130101; H04L 27/2601 20130101; H04L 5/0062 20130101 |
Class at
Publication: |
375/219 ;
375/260 |
International
Class: |
H04B 001/38; H04L
005/16 |
Claims
What is claimed is:
1. A multi-carrier modulation transceiver comprising: a tone
manager; and a multi-carrier transmitter that disables one or more
tones during at least one training state based on a received tone
disable message.
2. The transceiver of claim 1, wherein the one or more tones are
disabled to assist in determining impairments in a communications
channel.
3. The transceiver of claim 2, where the impairment is one of radio
frequency interference and communications channel noise.
4. The transceiver of claim 1, wherein the one or more tones can be
disabled during a data communication state.
5. The transceiver of claim 1, further comprising one or more
templates that are used to estimate radio frequency
interference.
6. The transceiver of claim 1, wherein one or more templates model
radio frequency interference and are dynamically chosen for one or
more discrete multi-tone symbols.
7. The transceiver of claim 1, further comprising a symbol
generator and a frequency domain to time domain converter.
Description
RELATED APPLICATION DATA
[0001] This application claims the benefit of U.S. Provisional
Application Serial No. 60/210,556 entitled "Methods to Improve the
Performance of DSL in the Presence of RFI" filed Jun. 9, 2000 and
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to information transceivers. In
particular, this invention relates to multi-carrier information
transceivers with radio frequency interference reduction.
[0004] 2. Description of Related Art
[0005] Multi-carrier communications transceivers allow the
high-speed transmission of information using the twisted-pair
telephone lines that connect individual subscribers to a telephone
central office. Each pair of copper wires provides a communication
channel in which the frequency response attenuates as the frequency
increases. The wires also contain noises of a different nature
produced by a variety of sources. Among these noises are thermal
noises produced by electric devices and cross-talk noises produced
by, for example, other subscribers connected to the same central
office and sharing the same bundle of twisted-pairs.
[0006] The twisting of the twisted-pairs help to reduce the
cross-talk noise by limiting electromagnetic coupling between the
pair of lines that are close together. However, as the frequency of
operation increases, the effect of twisting is limited and the
cross-talk noise increases proportional to frequency.
[0007] In order to provide reliable communications over a channel
with limited bandwidth and frequency-dependent noise, multi-carrier
transceivers apply a "divide and conquer" strategy. In this
strategy, the total bandwidth of the communication channel is
divided into a number of frequency sub-bands. Each sub-band is a
sub-channel in which an information signal is transmitted. The
width of the frequency sub-bands is chosen to be small enough to
allow the distortion introduced by a sub-channel to be modeled by a
simple complex value representing the attenuation and phase shift
of the received signal. Various information signals are transmitted
simultaneously using the various sub-channels. The receiver is able
to separate the information signals in the different frequency
sub-bands by using a bank of band-pass filters each one tuned to
one of the different sub-bands. If these filters are chosen
properly, the noise in each frequency band can be modeled using
only the noise level present in that sub-band, with the noise in
one band having little to no effect in the adjacent sub-bands.
[0008] A primary advantage of a multi-carrier transceiver is that
the transceiver parameters can be optimized for different channel
conditions in order to obtain maximum performance. The optimization
process can be summarized as follow: First, a desired bit error
rate is established. Second, the signal-to-noise ratio available in
every sub-channel is measured. The bit error rate and the
signal-to-noise ratio are then used to determine the maximum bit
transmission rate that the sub-channel can support. Finally, an
optimal set of information signals capable of transmitting this
maximum bit transmission rate is found. By optimizing each
sub-band, the total transmission capacity of the multi-carrier
transceiver for a given error rate is maximized.
[0009] Usually, the noise in the telephone lines also contains
radio frequency interference (RFI) produced by, for example,
electromagnetic coupling of radio frequency signals coming from
radio broadcasting transceivers that operate in the same radio
frequency band as the multi-carrier transceiver. When present, this
RFI can degrade the performance of the multi-carrier transceiver
significantly, making the multi-carrier transceiver operate well
below its optimum performance. The nature of the RFI is different
from the difficulties associated with thermal noise and crosstalk
noise. Optimizing a transceiver to operate in the presence of all
the noises results in transceivers with great complexity, such as
the transceiver disclosed by Sandberg et al. in 1995 entitled
"Overlapped Discrete Multitone Modulation for High Speed Copper
Wire Communications." In practice, RFI mitigation techniques that
minimize the degradation in performance are preferred.
SUMMARY OF THE INVENTION
[0010] For ease of illustration the following terminology will be
used to discuss the operation of an exemplary multi-carrier
transceiver. Specifically, an idle channel is a communications
channel that may contain noise, crosstalk and RF signals in any
portion of the spectrum, but does not contain upstream or
downstream multi-carrier signals. The carriers in the multi-carrier
transceiver will be denoted as tones. A tone is disabled when there
is no energy transmission in that particular tone. A training or
initialization signal, which is typically sent during the training
state, is a multi-carrier transceiver initialization training
signal used to train the transceiver before commencing the
transmission of information. For the multi-carrier transceiver
known as ADSL, these training signals are defined in the
INITIALIZATION section of ITU standards G.992.1 (G.dmt), G.992.2
(G.lite) and the G.994.1 (G.hs), incorporated herein by reference
in their entirety.
[0011] Steady state signals or information signals are the signals
sent by the multi-carrier transceiver when communicating
information data bits. The steady state transmission typically
follows the training state transmission. For the multi-carrier
transceivers known as ADSL, the steady state signals are defined in
the SHOWTIME sections of ITU standards G.992.1 (G.dmt) and the
G.992.2 (G.lite), incorporated herein by reference in their
entirety.
[0012] An RFI band is a group of one or more tones in which a
single RFI is identified. In general, the location of these bands
within the total bandwidth of transmission is not known until the
operation of the multi-carrier transceiver starts; and the tones in
an RFI band may or may not be disabled during the transceiver
operation. However, there are certain restricted RFI bands where
the presence of RFI is highly probable. The location of these
restricted RFI bands can be specified in advance before the
operation of the multi-carrier transceiver starts, and, for
example, the tones in a restricted RFI band permanently disabled
during the operation of the transceiver.
[0013] RFI can, for example, be one of the many performance
limiting factors when a multi-carrier transceiver is deployed in
the field. For the multi-carrier transceiver known as ADSL, tests
that include measuring the performance of ADSL in the presence of
RFI are now being defined in "G.test.bis: Laboratory Set-ups and
procedures to include RFI impairments in the testing of DSL
transceivers" by Nortel Networks.RTM., incorporated herein by
reference in its entirety. These tests, as well as other
industry-standard tests, provide a good reference model in which
the performance RFI mitigation techniques can be measured.
[0014] An exemplary embodiment of the present invention describes a
multi-carrier information transceiver with robustness against radio
frequency interference (RFI) signals present in a communications
channel. The multi-carrier transceiver comprises a radio frequency
interference mitigation technique that operates, for example, not
only during the steady state operation of the transceiver but also
during the training state of the transceiver.
[0015] The transceiver is able to dynamically modify the training
signals when the presence of RFI is detected. For example, the
training signals can be modified by dynamically disabling tones in
the region of the spectrum where the RFI is detected. For example,
this detection can occur during an initialization phase. In this
exemplary embodiment, the receiver sends a message instructing the
transmitter to disable tones in the multi-carrier signals during
certain phases of training and or steady state operation. The
message contains, for example, a field that designates which of the
tone number(s) are to be disabled and during which stages of
training and/or steady state operation they are to be disabled. The
transmitter can also receive this message and, for example, disable
the specified tones during the specified stages of training and or
steady state, for example, during a signal-to-noise ratio
measurement and related calculations, during a training of the
equalizer, or in other types of training or measurement. During the
remaining stages of training and/or steady state, where
instructions are not necessarily specified in the message, the
transmitter does not disable the specified tones, but could send
the standard signals in those tones.
[0016] According, an in accordance with an exemplary embodiment of
this invention, a first aspect of the invention relates to
providing an improved multi-carrier transceiver.
[0017] Aspects of the invention also relate to providing a
multi-carrier information transceiver in which, for example, prior
to the training phase, the presence or absence of RFI in the
communications channel can be established. If, for example, RFI is
detected, the receiver can instruct the transmitter to disable
tones in one or more of the training signals, and during different
stages of the modem training phase. The receiver can also instruct
the transmitter to disable tones in the information signals during
the steady state phase. If no RFI is detected, then, for example,
the transmission of both training and steady state signals can
occur without disabling any tones.
[0018] Aspects of the invention also relate to providing a
multi-carrier information transceiver in which a RFI mitigation
technique takes advantage of the disabled tones in both the
training signals and the steady state signals to better estimate
the RFI.
[0019] These and other features and advantages of this invention
are described in, or are apparent from, the following detailed
description of the embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a block diagram illustrating an exemplary
multi-carrier transceiver according to this invention;
[0021] FIG. 2 is a flowchart illustrating the exemplary operation
of the frequency-domain RFI mitigation device according to this
invention;
[0022] FIG. 3 is a flowchart illustrating an exemplary method of
creating a template according to this invention;
[0023] FIG. 4 shows an example of a set of templates according to
this invention;
[0024] FIG. 5 is a flowchart illustrating an exemplary method of
performing RFI initialization according to this invention;
[0025] FIG. 6 is a flowchart illustrating a method of RFI
mitigation during transceiver training according to this
invention;
[0026] FIG. 7 illustrates an exemplary RFI detection/estimation for
an idle channel with noise and a number of RFI bands according to
this invention;
[0027] FIG. 8 illustrates an exemplary composite RFI estimate
determined using an exemplary method according to this
invention;
[0028] FIG. 9 is a flowchart illustrating an exemplary method of
time-domain windowing according to this invention; and
[0029] FIG. 10 illustrates an exemplary time-domain windowing
operation according to this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] FIG. 1 illustrates an exemplary multi-carrier transceiver
100. Specifically, the transmitter section of one transceiver and
the receiving section of a second transceiver are shown in FIG. 1.
The multi-carrier transceiver 100 comprises a transmitter section
200 and a receiver section 300 interconnected by communications
channel 120 and links 5. The transmitter 200 comprises a clock 210,
a controller 220, a symbol generator 230, a tone manager 240, a
memory 250, a frequency domain to time domain converter 260, a
memory 270, a digital to analog converter 280 and a filter 290
interconnected by link 5. The receiver 300 comprises a filter 310,
an analog to digital converter 320, a memory 330, a time domain RFI
mitigation module 340, a time domain to frequency domain converter
350, a frequency domain RFI mitigation module 360, a memory 370, an
equalizer 380, a memory 390, a symbol decoder 400, a clock 410 and
a controller 420 interconnected by link 5.
[0031] While the exemplary embodiment illustrated in FIG. 1 shows
the transceiver 100 and associated components collocated, it is to
be appreciated that the various components of the transceiver 100
can be located at distant portions of a communications network.
Thus, it should be appreciated that the components of the
transceiver 100 can be combined into one device or separated into a
plurality of devices. Furthermore, it should be appreciated that
for ease of illustration, the various functional components of the
transceiver 100 have been divided as illustrated in FIG. 1.
However, any of the functional components illustrated in FIG. 1 can
be combined or further partitioned without affecting the operation
of the system. As will be appreciated from the following
description, and for reasons of computation efficiency, the
components of the document can be arranged at any location within a
communications network without effecting the operation of the
system. Furthermore, it is to be appreciated that the term module
as used herein includes any hardware and/or software that provide
the functionality as discussed herein. Furthermore, the links 5 can
be a wired or wireless link or any other known or later developed
element(s) that is capable of supplying and communicating data to
and from the connected elements.
[0032] In operation, the transmitter 200 codes input data 105 for
transmission on a communication link 120. The receiver 300 decodes
the data received from the transmitter 200 and outputs the decoded
data as output data 110. In particular, the symbol generator 230
receives a portion of the input data 105, such as a stream of data.
The tone manager 240 determines, with the aid of controller 220,
which tones are enabled or disabled based on, for example, channel
conditions, noise, interference, or the like. The number of
different values a symbol can take will depend on, for example, the
characteristics of the communications channel 120, the desired
robustness of information transmission, or the like. More
specifically, the number of different values a symbol can take
depends on the signal-to-noise ratio available in a particular
sub-channel and the desired bit error probability. When the
controller 220 determines that N bits have been received by symbol
generator 230, the controller 220 instructs the symbol generator
230 to convert the run of received data bits into M symbols
S.sub.1, S.sub.2, . . . , S.sub.M which are stored in the memory,
such as a register 250. The symbols in the register 250 are
assigned to tones in the multi-carrier transceiver. However, if a
tone is disabled, the tone manager 240 does not assign a
symbol.
[0033] For ease of illustration, the transceiver 100 treats the
symbols S.sub.1 as if they were the amplitude of a signal in a
narrow frequency band. It is assumed that the phase deviation of
each signal is zero when the signal enters the communication link
120. Thus, the frequency domain to time domain converter 260
determines, with the aid of controller 220 and clock 210, a
time-domain signal denominated multi-carrier symbol having values
X.sub.i. The X.sub.i signal has its frequency components weighted
by the individual symbols S.sub.1 over the time period represented
by the M samples X.sub.i. The X.sub.i signal values are then stored
in the memory 270. The contents of the memory 270 represent, in
digital form, the next segment of the signal that is to be actually
transmitted over the communication link 120. For the multi-carrier
transceiver known as ADSL, a segment of the final portion of
X.sub.i, denominated a cyclic prefix (CP), is prefixed to the
multi-carrier symbol X.sub.i itself, prior to the D/A conversion.
The actual transmission of the digital signal is accomplished by
clocking the digital values onto communication link 120 after
converting the values to analog voltages using the D/A converter
280. The clock 210 provides the timing pulses for the operation.
The output of the D/A converter 280 is low-pass filtered by the
filter 290 before being placed on the communications link 120.
[0034] The communications link 120 will, in general, both attenuate
and phase shift the signal represented by the X.sub.i. The
communications link 120 will also add noises, such as, thermal
noise, crosstalk and RFI to the signal output by the transmitter
200. At the receiving end of communications link 120, an attempt to
recover each S.sub.1 is made by essentially reversing the
modulation process done by the transmitter 200 and correcting for
losses in the communications link 120.
[0035] Upon receipt of the signal at the receiver 300 from the
transmitter 200, the via the communications link 120, the filter
310 low-pass filters the signal to reduce the effects of
out-of-band noise. Then, with the cooperation of the controller
420, the signals are digitized by A/D converter 320 and shifted, as
X'.sub.i, into the memory 330, such as a register. This is
preferably accomplished with the aid of the clock 410, which can be
synchronized to the clock 210. When M values have been shifted into
the register 330, the contents thereof are processed by the
time-domain RFI mitigation module 340, which multiplies the
received signal composed of CP and X'.sub.i by a window in order to
reduce the sidelobes of the RFI. The output of time-domain RFI
mitigation module 340 is converted, via a time-domain to
frequency-domain converter 350 into a set of frequency-domain
samples. This transformation is the inverse of the transformation
generated by frequency-domain to time-domain converter 260. The
frequency-domain samples at the output of the converter 350 are
processed by the frequency-domain RFI mitigation module 360 to
generate a set of frequency domain symbols Y.sub.i, in which the
RFI component has been mitigated. Then, the equalizer 380 updates
each Y.sub.i for attenuation and phase shifts that may have
resulted from the communication over the communications link 120 to
recover a noisy version S'.sub.i of the original symbols. These
symbols are then stored in the memory, such as a buffer, 390.
Finally, the contents of the memory 390 are decoded by the symbol
decoder 400 and output as the output data stream 110.
[0036] The RFI mitigation modules 340 and 360 attenuate the effects
of the RFI in the communications channel 120, while the tone
manager 240 facilitates the operation of the frequency-domain RFI
mitigation module 360. The exemplary embodiments of the tone
manager 240, the time-domain RFI mitigation module 340 and the
frequency-domain RFI mitigation module are discussed below with
references to FIGS. 2-10. However, those skilled in the art will
readily appreciate that the description given with respect to these
exemplary figures is for illustrative purposes only.
[0037] For the purpose of this discussion, in relation to the
frequency-domain RFI mitigation module 360 and the tone manager
240, the frequency-domain signal values will be represented by bins
in the Fast Fourier Transform (FFT). Each bin is a complex number
representing the amplitude and phase of a tone.
[0038] FIG. 2 is a flowchart illustrating an exemplary method of
operation of the frequency-domain RFI mitigation module 360
according to an embodiment of the invention. In particular, control
begins in step S200 and continues to step S210. In step S210, an
initialization step, a template is created. Next, in step S220, RFI
initialization is performed. Then, in step S230, the RFI is
mitigated during the transceiver training operations. Control then
continues to step S240.
[0039] In step S240, RFI mitigation is performed during the
transceiver steady state operation. Control then continues to step
S250 where the control sequence ends.
[0040] The template creation step S210 can occur, for example,
before the system is run for the first time. Thus, the templates
must be created in advance and, for example, stored in a memory.
Alternatively, the templates can also be created off-line and
pre-stored in a memory.
[0041] FIG. 3 is a flowchart illustrating an exemplary method of
the template creation process according to an embodiment of the
invention. Specifically, control begins in step S300 and continues
to step S310. In step S310, the shape of the time-domain window
which will be used to construct the template is determined. Next,
in step S320, the frequency used to construct the window is
determined. Then, in step S330, a time-domain pass-band window is
determined in accordance with A(t) COS (fT). Control then continues
to step S340.
[0042] In step S340, the frequency-domain representation of the
pass-band window is determined. Next, in step S350, the amplitude
of the pass-band window is normalized resulting in the desired
template. Then, in step S360, the template is stored. Control then
continues to step S370 where the control sequence ends.
[0043] The stored templates can then be used to estimate the RFI
during the mitigation process. In particular, FIG. 4 illustrates an
exemplary set of 10 templates having a size of 31 created according
to an embodiment of the invention. However, in general any number
of templates can be stored based on, for example, the accuracy of
the estimate desired for the RFI.
[0044] FIG. 5 is a flowchart illustrating in greater detail the RFI
initialization step S220 in greater detail. In particular, control
begins in step S500 and continues to step S510. In step S510, the
idle channel is detected. Specifically, the receiver measures the
idle channel, which may contain noise, crosstalk and RFI signals in
any portion of the spectrum, but not upstream or downstream
multi-carrier signals. However, it is to be appreciated that the
channel does not necessarily need to be idle. The channel could
contain, for example, multi-carrier training signals as well as
noises of different nature. Next, in step S520, the RFI bands are
detected. Specifically, using the data obtained from step S510, the
receiver establishes the presence of RFI bands and their locations.
However, it is to be appreciated that in general the detection of
the RFI bands can be accomplished using a variety of criteria, such
as the peak-to-average ratio, or the like. Likewise, more accurate
detection can be accomplished at the expense of more complex
criteria. Control then continues to step S530.
[0045] In step S530, an RFI mask is determined. In particular, a
mask is constructed in which all the values are one, except the
three mask values centered on each RFI bin which are zeroed.
However, in general, the number of values can be altered with the
trade-off being the more values providing better template
estimation at the expense of reducing the number of carriers. Next,
in step S540, the size of templates is determined. Since the RFI
bands can be located near the beginning of the FFT or close to the
end of the FFT, the templates used for those RFI bands may need to
be shortened to conform to the size of the FFT. Then, in step S550,
the filling segments are determined. Based on the positions of the
RFI bins and the lengths of the templates, the filling segments
containing zeros are constructed. Then, the templates are
translated to a particular RFI position with the aid of these
segments. Control then continues to step S560.
[0046] In step S560, the tones located in RFI bands are disabled.
Specifically, the receiver can instruct the transmitter to disable
the tones located in the detected RFI bands. More specifically, the
receiver can send the RFI mask to the tone manager. In an exemplary
embodiment of the invention, the receiver can send a message
instructing the transmitter to disable the tones in the signals
during a certain phase of the training and/or the steady state. The
message can contain a field that designates which tone number(s),
e.g., tone number 77, 78 and 79, are to be disabled and during
which phase(s), e.g., MEDLEY, REVERB1, etc, of training and/or
steady state they are to be disabled. The tone manager would then
receive this message and would disable the specified tones during
the specified phases of training and or steady state, for example,
during a signal-to-noise ratio measurement and related
calculations, during the training of the equalizer, or during other
types of training and/or measurements. During the unspecified
phases of training and/or steady state, the transmitter would not
disable the specified tones but would send the standard signals in
those tones.
[0047] FIG. 6 is a flowchart illustrating RFI mitigation during the
transceiver training procedure according to an exemplary embodiment
of the invention. Specifically, FIG. 6 is outlines the steps of
S230 in greater detail. Control begins in step S600 and continues
to step S610. In step S610, an FFT output vector is determined.
This FFT vector is the frequency-domain representation of a
multi-carrier symbol containing a training signal. Next, in step
S620, the individual RFI estimates are determined. However, in
general, the individual RFI estimate can be determined using a
variety of methods. In the present invention the RFI estimate is
based on a distance measured between a received signal and a
reference signal. The received signal is an individual RFI band in
the FFT output vector and is one of the pre-stored templates scaled
by the bin value at the center of the RFI band. The distance is
measured between the three center bins of the individual RFI band
and the three center bins of each template. The scaled template
that results in minimum distance is then chosen. However, in
general, other forms of reference signals are possible. For
example, it is possible to determine the reference signals using a
pre-defined analytical function. Additionally, it is possible to
select the template using a pre-stored mapping function or some
other selection mechanism. Furthermore, many distance definitions
are possible with the trade off that some are better that others at
the cost of complexity.
[0048] Next, in step S630, a determination is made whether more RFI
bands are present in the FFT output vector. If more RFI bands are
present, control jumps back to step S620. Otherwise control
continues to step S640.
[0049] In step S640, a composite RFI estimate is determined. Then,
using all of the individual RFI estimates, a composite sum is
determined. The composite sum is an RFI estimate of the total RFI
in the FFT output vector determined in step S610. Next, in step
S650, the RFI mitigation operation is performed by subtracting the
composite RFI estimate from the received FFT output signal, thus
mitigating the RFI effects in the training signals. Control then
continues to step S660 where the control sequence ends.
[0050] FIGS. 7 and 8 are examples of the RFI detection/estimation
process. Specifically, FIG. 7 depicts the idle channel with noise
and a number of RFI bands. In particular, the FFT of one frame of
noise at the output of the frequency domain RFI mitigation. Using
this frame of noise, the detection of RFI and the number of RFI
bands can be established. In order to mitigate the RFI, the RFI is
estimated. In particular, FIG. 8 illustrates the composite RFI
estimate determined using the exemplary method of this invention.
The RFI estimate is formed using the strongest individual RFI
components, and it is subtracted from the original received signal
to mitigate the RFI effects.
[0051] The method of FIG. 6 can also apply to the RFI mitigation
during the transceiver steady state procedure according to an
exemplary embodiment of the invention. Specifically, this
corresponds to step S240 in greater detail. In particular, in step
S610 a FFT output vector determined at the output of the time
domain to frequency domain converter is received. This FFT vector
is the frequency-domain representation of a multi-carrier symbol
containing a steady state signal. Next, in step S620, the
individual RFI estimates are determined. Then, in step S630a
determination is made whether an RFI estimate for every RFI band in
the FFT output vector has been determined. If more estimates are
required, control jumps back to step S620. Otherwise, control
continues to step S640.
[0052] In step S640, the composite RFI estimate is determined. All
the individual RFI estimates are used to form a composite sum. The
composite sum is an RFI estimate of the total RFI in the FFT output
vector determined back in step S610. Next, in step S650, the RFI
mitigation operation is performed by subtracting the composite RFI
estimate from the received FFT output signal, thus mitigating the
RFI effects in the steady state signals. Control then continues to
step S660 where the control sequence ends.
[0053] It is to be appreciated that from the above description,
that in this invention the RFI mitigation can operate not only
during the steady state operation of the transceiver but also
during the training state of the transceiver. This requires
dynamically modifying the training signals when the presence of RFI
is detected.
[0054] FIG. 9 is a flowchart illustrating an exemplary operation of
the time-domain RFI mitigation module according to an embodiment of
this invention. In particular, control begins in step S900 and
continues to step S910, In step S910, a signal including both the
multi-carrier symbol X[k] and the cyclic prefix CP[k] is received.
Next, in step S920, CP[k] is retained for use in the windowing
operation. Then, in step S930, the windowing is performed. Control
then continues to step S940.
[0055] In step S940, the FFT of the windowed signal is determined.
Control then continues to step S950 where the control sequence
ends.
[0056] FIG. 10 illustrates an exemplary procedure used to realize
the windowing operation of step S930. Specifically, the windowing
operation is applied to the received signal Z[k] 1000, which
consists of both the received multi-carrier symbol X[k] 1020 and
the complete cyclic prefix CP[k] 1030. The operation can also be
applied to X[k] and part of CP[k], by discarding the initial part
of CP[k]. The example illustrated in FIG. 10 depicts an embodiment
in which the window W[k] 1040 is applied using the complete CP[k].
For example, assume that X[k] has 512 values, that CP[k] has 32
values, that Z[k] has 512+32=544 values and that W[k] has also 544
values. The windowing operation consists of multiplying Z[k] by
W[k], and then folding section 1-A into section 1-B, and folding
section 2-B into section 2-A.
[0057] The result of the windowing operation is denoted U[k] having
512 values. The expression for U[k] in terms of W[k] and Z[k] is: 1
U [ k ] = { W [ 16 + k ] Z [ 16 + k ] + W [ 17 - k ] Z [ 528 + k ]
, for k = 1 , , 16 , Z [ 16 + k ] , for k = 17 , , 496 , W [ 529 -
k ] Z [ 16 + k ] + W [ k - 496 ] Y [ k - 496 ] , for k = 497 , ,
512 ,
[0058] since W[k]=W[545-k], k=1,2, . . . ,32 by definition.
Additionally, 2 U [ k ] = { W [ 16 + k ] Z [ 16 + k ] + ( 1 - W [
16 + k ] ) Z [ 528 + k ] , for k = 1 , , 16 , Z [ 16 + k ] , for k
= 17 , , 496 , ( 1 - W [ k ] ) Z [ 512 + k ] + W [ k ] Z [ k ] ,
for k = 1 , , 16 ,
[0059] since W[k]+W[33-k]=1, k=1,2, . . . ,16 by definition. To
save multiply operations: 3 U [ k ] = { W [ 16 + k ] ( Z [ 16 + k ]
- Z [ 528 + k ] ) + Z [ 528 + k ] , for k = 1 , , 16 , Z [ 16 + k ]
, for k = 17 , , 496 , W [ k ] ( Z [ k ] - Z [ 512 + k ] ) + Z [
512 + k ] , for k = 1 , , 16.
[0060] Notice that in the absence of noise, U[k]=X[((k-16))], i.e.,
U[k], is equal to a cyclically shifted version of X[k].
[0061] As illustrated in FIG. 1, the multicarrier information
transceiver and related components can be implemented either on a
DSL modem, such as an ADSL modem, or separate programmed general
purpose computer having a communication device. However, the
multicarrier information transceiver can also be implemented in a
special purpose computer, a programmed microprocessor or a
microcontroller and peripheral integrated circuit element, an ASIC
or other integrated circuit, a digital signal processor, a
hardwired or electronic logic circuit such as a discrete element
circuit, a programmable logic device, such as a PLD, PLA, FPGA,
PAL, or the like, and associated communications equipment. In
general, any device capable of implementing a finite state machine
that is in turn capable of implementing the flowcharts illustrated
in FIGS. 2-3, 5-6 and 9 can be used to implement the multicarrier
information transceiver according to this invention.
[0062] Furthermore, the disclosed method may be readily implemented
in software using object or object-oriented software development
environments that provide portable source code that can be used on
a variety of computers, work stations, or modem hardware and/or
software platforms. Alternatively, disclosed multicarrier
information transceiver may be implemented partially or fully in
hardware using standard logic circuits or a VLSI design. Other
software or hardware can be used to implement the systems in
accordance with this invention depending on the speed and/or
efficiency requirements of this system, the particular function,
and the particular software and/or hardware systems or
microprocessor or microcomputer systems being utilized. The
multicarrier information transceiver illustrated herein, however,
can be readily implemented in a hardware and/or software using any
known later developed systems or structures, devices and/or
software by those of ordinary skill in the applicable art from the
functional description provided herein and with a general basic
knowledge of the computer and telecommunications arts.
[0063] Moreover, the disclosed methods can be readily implemented
as software executed on a programmed general purpose computer, a
special purpose computer, a microprocessor and associated
communications equipment, a modem, such as a DSL modem, or the
like. In these instances, the methods and systems of this invention
can be implemented as a program embedded in a modem, such as a DSL
modem, or the like. The multicarrier information transceiver can
also be implemented by physically incorporating the system and
method into a software and/or hardware system, such as a hardware
and software system of a multicarrier information transceiver, such
as an ADSL modem, VDSL modem, network interface card, or the
like.
[0064] It is, therefore, apparent that there has been provided in
accordance with the present invention, systems and methods for a
multicarrier information transceiver. While this invention has been
described in conjunction with a number of embodiments, it is
evident that many alternatives, modifications and variations would
be or are apparent to those of ordinary skill in the applicable
art. Accordingly, applicants intend to embrace all such
alternatives, modifications, equivalents and variations that are
within the spirit and the scope of this invention.
* * * * *