US20100098149A1 - Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback - Google Patents

Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback Download PDF

Info

Publication number
US20100098149A1
US20100098149A1 US12/640,838 US64083809A US2010098149A1 US 20100098149 A1 US20100098149 A1 US 20100098149A1 US 64083809 A US64083809 A US 64083809A US 2010098149 A1 US2010098149 A1 US 2010098149A1
Authority
US
United States
Prior art keywords
subchannel
frequency domain
domain equalizer
intersymbol interference
constellation point
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US12/640,838
Inventor
Richard W. Gross
Yan Yang
Mei Yong
Stuart Sandberg
Arnon Friedmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Aware Inc
Original Assignee
Aware Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Aware Inc filed Critical Aware Inc
Priority to US12/640,838 priority Critical patent/US20100098149A1/en
Publication of US20100098149A1 publication Critical patent/US20100098149A1/en
Priority to US12/783,796 priority patent/US20100296570A1/en
Assigned to DLI LENDING AGENT, LLC reassignment DLI LENDING AGENT, LLC SECURITY INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: TQ DELTA, LLC
Assigned to ALTER DOMUS (US) LLC reassignment ALTER DOMUS (US) LLC AMENDED AND RESTATED INTELLECTUAL PROPERTY SECURITY AGREEMENT Assignors: TQ DELTA LLC
Abandoned legal-status Critical Current

Links

Images

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/02Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006Arrangements for removing intersymbol interference
    • H04L25/03012Arrangements for removing intersymbol interference operating in the time domain
    • H04L25/03019Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/02Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006Arrangements for removing intersymbol interference
    • H04L25/03159Arrangements for removing intersymbol interference operating in the frequency domain
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/02Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006Arrangements for removing intersymbol interference
    • H04L2025/0335Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375Passband transmission
    • H04L2025/03414Multicarrier
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/02Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006Arrangements for removing intersymbol interference
    • H04L2025/03433Arrangements for removing intersymbol interference characterised by equaliser structure
    • H04L2025/03439Fixed structures
    • H04L2025/03522Frequency domain

Definitions

  • the systems and methods of this invention generally relate to communication systems.
  • the systems and methods of this invention relate to equalization using decision feedback.
  • a transmission channel is partitioned into a multitude of sub-channels, each with its own associated carrier.
  • multicarrier modulation known as discrete multitone (DMT) transmission, or orthogonal frequency division multiplexing (OFDM)
  • DMT discrete multitone
  • OFDM orthogonal frequency division multiplexing
  • the generation and modulation of the sub-channels is accomplished digitally, using an orthogonal transformation on each of a sequence of blocks, i.e., frames, of the data stream.
  • a receiver performs the inverse transformation on segments of the sampled waveform to demodulate the data.
  • DMT used as the signaling standard for asymmetric digital subscriber lines (ADSL)
  • the transforms used for demodulation and modulation are the Discrete Fourier Transform (DFT) and its inverse, respectively.
  • DFT Discrete Fourier Transform
  • DWMT discrete wavelet multitone
  • a discrete wavelet transform and its inverse are employed as discussed in M.
  • M. A. Tzannes et al “The DWMT: A Multicarrier Transceiver for ADSL Using M-Band Wavelets,” ANSI Standard Committee T1E1.4 contribution 93-067, March 1993, M. A. Tzannes, “System Design Issues for the DWMT Transceiver,” ANSI Standard Committee T1E1.4 contribution 93-100, April 1993 and M.
  • A. Tzannes et al “DMT Systems, DWMT Systems and Digital Filter Banks,” Proc. ICC 1994, all of which are incorporated herein by reference in their entirety.
  • a communication path having a fixed bandwidth is divided into a number of sub-bands having different frequencies.
  • the width of the sub-bands is chosen to be small enough to allow the distortion in each sub-band to be modeled by a single attenuation and phase shift for the band.
  • the volume of data sent in each band may be optimized by choosing a symbol set having the maximum number of symbols consistent with the available signal to noise ratio of the channel. By using each sub-band at its maximum capacity, the amount of data that can be transmitted in the communication path is maximized.
  • FFT Fast Fourier Transforms
  • the time domain signal to be sent on the communication path is obtained by selecting a QAM point on each sub-carrier and then adding the modulation carriers to form the signal to be placed in the communication path.
  • This operation is normally carried out by transforming the vector of M symbols via the inverse Fourier transform to generate N, where N represents the size of the transform, time domain values that are sent in sequence on the communication path.
  • N represents the size of the transform
  • the N time domain values are accumulated and transformed via a Fourier transform to recover the original M symbols after equalization of the transformed data to correct for the attenuation and phase shifts that may have occurred in the channels.
  • ISI intersymbol interference
  • the time domain equalizer works to shorten the overall length of the impulse response but usually does not remove all of the ISI.
  • the symbol decoded by the subscriber will include interference from other symbols in other sub-bands and/or earlier or later symbols transmitted in the subscriber's sub-band. This type of interference is further aggravated by the high side lobes in the sub-bands provided by the Fourier transform. Further information regarding multicarrier transmission systems can be obtained from U.S. Pat. No. 5,636,246 entitled “Multicarrier Transmission System,” incorporated herein by reference in its entirety.
  • the receiver transform output is a replica of the modulating data, due to the orthogonality (Nyquist) properties of the particular transform used.
  • the practical channels can contain severe intersubchannel and interframe interference. That is, the receiver transform output for sub-channel m 1 and frame i 1 has a contribution not only from s i 1 m 1 but also from s m i for ⁇ m,i ⁇ m 1 ,i 1 ⁇ , where s i m denotes the symbol transmitted in sub-channel m for frame i.
  • ISI intersymbol interference
  • the receiver transform outputs can also have contributions from independent background noise, which, also for sake of clarity, will be disregarded for this discussion.
  • Multicarrier systems typically employ equalization to compensate for the effects of ISI. Such equalization is typically done in the time-domain and in the frequency-domain. For time-domain equalization (TDQ), an adaptive filter is trained then applied to the sequence of samples at the receiver, before the sequence is passed to the receiver transform. For frequency-domain equalization (FDQ), processing is employed on the receiver transform outputs.
  • TDQ time-domain equalization
  • FDQ frequency-domain equalization
  • S m 1 i 1 denote the actual transmitted symbol, and let denote the FDQ output for subchannel m 1 and frame i 1 .
  • the desired net effect of TDQ and FDQ is for to be equal to S m 1 i 1 , plus a very small contribution from ISI.
  • the receiver can make a decision about the value for s m 1 i 1 by quantizing to the nearest constellation point. This decision will be denoted by d i 1 m 1 .
  • each FDQ is implemented as a single-tap complex multiply, applied to the associated sub-channel output.
  • aspects of the invention relate to reducing intersymbol interference.
  • Additional aspects of the invention relate to reducing intersymbol interference through the use of feedback.
  • Additional aspects of the invention relate to reducing intersymbol interference through the use of feedback in a multicarrier environment.
  • aspects of the invention further relate to combining multiple FFT outputs as well as decision feedback to create an estimate of a transmitted QAM symbol.
  • aspects of the invention additionally relate to using a multi-tap frequency domain equalizer with decision feedback to minimize intersymbol interference in a multicarrier modulation communication system.
  • FIG. 1 is a functional block diagram illustrating the equalizer portion of a conventional receiver
  • FIG. 2 is a functional block diagram illustrating a portion of a receiver according to this invention.
  • FIG. 3 is a flowchart illustrating an exemplary method for mitigating intersymbol interference according to this invention.
  • FIG. 4 is a plot illustrating the exemplary benefits achieved in SINR using the systems and methods of this invention.
  • the systems and methods of this invention can generally be applied to any type of communication system including wireless communication systems, such as wireless LANs, power line communications, or any other system or combination of systems that use multicarrier communication or any other form of modulation in which it is desired to reduce intersymbol interference.
  • wireless communication systems such as wireless LANs, power line communications, or any other system or combination of systems that use multicarrier communication or any other form of modulation in which it is desired to reduce intersymbol interference.
  • the various components of the communication system can be located at distant portions of a distributed network, such as a telecommunications network and/or the Internet, or within a dedicated intersymbol interference reduction module.
  • a distributed network such as a telecommunications network and/or the Internet
  • the components of the communication system can be combined into one or more devices or collocated on a particular node of a distributed network, such as a telecommunications network.
  • the components of the communication system can be arranged at any location within a distributed network without affecting the operation of the system.
  • the various links connecting the elements can be wired or wireless links, or a combination thereof, or any other known or later developed element(s) that is capable of supplying and/or communicating data to and from the connected elements.
  • the term module as used herein can refer to any known or later developed hardware, software, or combination of hardware and software that is capable of performing the functionality associated with that element.
  • FIG. 1 illustrates a portion of conventional receiver 10 .
  • the receiver 10 comprises a time domain equalizer 100 , a fast Fourier transform module 110 , a frequency domain equalizer 120 and a constellation decoder 130 .
  • a plurality of received samples 140 are received at the time-domain equalizer 100 .
  • the time-domain equalizer 100 applies adaptive filtering to the sequence of samples and passes the sequence to the fast Fourier transform module 110 .
  • the fast Fourier transform module 110 outputs a complex output f m for each tone m in the set of total tones M in each frame.
  • the frequency domain equalizer 120 then performs a single-tap complex multiply to each associated sub-channel resulting in the received point R m 160 .
  • the constellation decoder 130 determines the constellation point ⁇ circumflex over (D) ⁇ m closest to the received point R m for each tone.
  • ⁇ m i represent the transform output for subchannel m, in frame i.
  • the FDQ combiner output for the subchannel, frame pair is:
  • A(m 1 ) is a set containing ordered pairs ⁇ m, j ⁇ of indices corresponding to the particular subchannel, frame pairs for which the receiver transform outputs are used in the FDQ combiner, for subchannel m 1 .
  • the second element j of the ordered pair is an offset relative to frame i 1 .
  • the ⁇ j m (m 1 ) are the corresponding FDQ combiner weights.
  • the above equation will be referred to as a multi-tap FDQ (MFDQ) in what follows. Note that if A(m 1 ) consists of the single element ⁇ m 1 , 0 ⁇ , the above equation reduces to the application of a single-tap FDQ.
  • B(m 1 ) is a set containing ordered pairs ⁇ m, j ⁇ of indices corresponding to the particular subchannel, frame pairs for which decisions are used in the FDQ combiner for subchannel m 1 .
  • the ⁇ j m are the corresponding combiner weights.
  • the sets B(m) must be constructed in an ordered fashion. That is, B(m 1 ) should contain no ordered pair ⁇ m, j ⁇ for which is determined before , in which case the decision feedback term d i 1 +j m would not be available.
  • the method defined by Eq. (2) will be referred to as multi-tap FDQ with decision feedback (MFDQ-DF).
  • the settings for ⁇ j m (m 1 ) and ⁇ j m (m 1 ) can be trained during an initialization interval in which the transmitter sends a signal modulated with a symbol sequence s i m known to the receiver. Specifically, fix i 1 at an arbitrary value and for subchannel m 1 , let ⁇ be a vector constructed from the weights ⁇ j m (m 1 ) and ⁇ j m (m 1 ), and let be the vector having the corresponding observation elements ⁇ i 1 +j m . In this construction, ⁇ m, j ⁇ varies over B(m 1 ) and A(m 1 ), for the feedback and non-feedback portions, respectively.
  • the complex output of the FFT for tone m is given by f m
  • the complex output of the multi-tap frequency domain equalization with decision feedback (MFDQ-DF) is R m
  • ⁇ circumflex over (D) ⁇ m is the constellation point closest to the received point R m .
  • N and L are variables that determine the number of forward and feedback combiner taps that are being used in the system.
  • the subscript i has been removed, and the subscript m moved to the subscript location.
  • the R m is determined in increasing order such that the feedback values will always be available. Converting from Eq.
  • the multi-tap and decision feedback equalizer 180 is illustrated with two taps for A and one tap for B. However, it is to be appreciated that this can be adjusted based, for example on the particular application and/or accuracy needed.
  • FIG. 2 illustrates graphically how feedback is used in the multi-tap and decision feedback equalizer 180 .
  • FIG. 2 comprises one or more received samples 140 , a time-domain equalizer 100 , an FFT module 110 , a plurality of complex outputs 150 , a multi-tap decision feedback equalizer 180 , a plurality of determined received points 160 corresponding to a respective tone, a constellation decoder 130 and plurality of output constellation points 170 that were determined to be closest to the received point 160 .
  • the operation of the equalizer 180 in FIG. 2 is comparable to that of the equalizer illustrated in FIG. 1 , with the exception of constellation points 170 being fed back to aid in determining the R m for another tone.
  • ⁇ circumflex over (D) ⁇ 2 190 is fed back to tone 3 and ⁇ circumflex over (D) ⁇ M ⁇ 1 200 is fed back to tone N.
  • ⁇ circumflex over (D) ⁇ can be fed back to any one or more other tones to aid in determining the received point R m .
  • the system can begin with the determination of ⁇ circumflex over (D) ⁇ M and proceed “backwards” an until ⁇ circumflex over (D) ⁇ 1 is determined.
  • the system can jump around between tones with the only limitation being R M is dependent on decisions made on earlier tones.
  • any ⁇ circumflex over (D) ⁇ can be used as feedback alone or in combination, with other ⁇ circumflex over (D) ⁇ 's and, as discussed above, can be either forward looking or backward looking, or a combination thereof, for feedback terms.
  • FIG. 3 illustrates an exemplary method of determining intersymbol interference reduced output samples.
  • control begins in step S 100 and continues to step S 110 .
  • step S 110 one or more samples are received.
  • step S 120 time-domain equalization is performed on the one or more received samples.
  • step S 130 the complex outputs are determined for each tone through the use of a transform, such as a fast Fourier transform, discrete wavelet transform, or like.
  • a transform such as a fast Fourier transform, discrete wavelet transform, or like.
  • step S 140 for each tone m in the set of total tones M in each frame, step S 142 determines the received point and in step S 144 the received point R m is constellation decoded to output the constellation point closest to the received point R m . Control then continues to step S 150 .
  • step S 150 the intersymbol interference compensated output samples are output. Control then continues to step S 160 where the control sequence ends.
  • FIG. 4 illustrates the exemplary advantages of using decision feedback in frequency domain equalization.
  • FIG. 4 illustrates the SINR verse subchannel outputs for various FDQ schemes over 9 kft. of 26 AWG wire. In particular, these tests were conducted over a multicarrier ADSL system upstream length. Subsequent to each TDQ training session, the FDQ was trained in a least squares fashion using the ADSL medley signal for each of the FDQ schemes discussed above, and the resulting SINR profiles plotted. As illustrated in FIG. 4 , the SINR verse subchannel is illustrated (note subchannel 16 was not used).
  • A(m 1 ) comprises the 5 ordered pans ⁇ m, 0 ⁇ with m 1 ⁇ 2 ⁇ m ⁇ m 1 +2.
  • A(m 1 ) comprises the two ordered pairs ⁇ m 1 , 0 ⁇ and ⁇ m 1 +1, 0 ⁇ , and B(m 1 ) contains only the single pair ⁇ m 1 +1, 0 ⁇ .
  • A(m 1 ) comprises the two ordered pairs ⁇ m 1 , 0) and ⁇ m 1 ⁇ 1, 0 ⁇
  • B(m 1 ) contains only the single pair ⁇ m 1 ⁇ 1, 0 ⁇ . Modest improvement is noted as the single-tap FDQ is expanded to 5 MFDQ taps.
  • a normal 1-tap FDQ, or an MFDQ, depending on A(m) can be used for the uppermost subchannel in the “3-tap MFDQ-FB+” scheme, and the lowermost subchannel in the “3-tap MFDQ-FB ⁇ ” scheme.
  • intersymbol interference reduction system can be implemented on a telecommunications device, such a modem, a DSL modem, an ADSL modem, a multicarrier transceiver, a VDSL modem, or the like, or on a separate programmed general purpose computer having a communications device.
  • the systems and methods of this invention can also be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit element, and ASIC or other integrated circuit, a digital signal processor, a hard-wired electronic or logic circuit such as discrete element circuit, a programmable logic device such as PLD, PLA, FPGA, PAL, modem, receiver, or the like.
  • any device capable of implementing a state machine that is in turn capable of implementing the flowchart illustrated herein can be used to implement the various intersymbol interference reduction methods according to this invention.
  • the disclosed methods 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 computer or workstation hardware platforms.
  • the disclosed intersymbol interference reduction system may be implemented partially or fully in hardware using standard logic circuits or VLSI design. Whether software or hardware is used to implement the systems in accordance with this invention is dependent on the speed and/or efficiency requirements of the system, the particular function, and the particular software or hardware systems or microprocessor or microcomputer systems being utilized.
  • intersymbol interference reduction systems and methods illustrated herein can be readily implemented in hardware and/or software using any known or 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.
  • the disclosed methods may be readily implemented in software executed on programmed general purpose computer, a special purpose computer, a microprocessor, or the like.
  • the systems and methods of this invention can be implemented as program embedded on personal computer such as JAVA® or CGI script, as a resource residing on a server or graphics workstation, as a routine embedded in a dedicated intersymbol interference reduction system, or the like.
  • the intersymbol interference reduction system can also be implemented by physically incorporating the system and method into a software and/or hardware system, such as the hardware and software systems of a communications transceiver.

Abstract

Through the use of feedback in determining frequency domain equalization, interference can be reduced. Specifically, the determined constellation point closest to the determined received point can be fed back to aid in determining one or more other closest constellation points.

Description

    RELATED APPLICATION DATA
  • This application claims the benefit of and priority under 35 U.S.C. §119(e) to U.S. Patent Application Ser. No. 60/309,631, filed Aug. 2, 2001, entitled “Multicarrier Modulation Method Using Multi-Tap Frequency-Domain Equalization and Decision Feedback,” which is incorporated herein by reference in its entirety.
  • BACKGROUND OF THE INVENTION
  • 1. Field of the Invention
  • The systems and methods of this invention generally relate to communication systems. In particular, the systems and methods of this invention relate to equalization using decision feedback.
  • 2. Description of Related Art
  • In multicarrier modulation, a transmission channel is partitioned into a multitude of sub-channels, each with its own associated carrier. In implementations of multicarrier modulation known as discrete multitone (DMT) transmission, or orthogonal frequency division multiplexing (OFDM), the generation and modulation of the sub-channels is accomplished digitally, using an orthogonal transformation on each of a sequence of blocks, i.e., frames, of the data stream. A receiver performs the inverse transformation on segments of the sampled waveform to demodulate the data. In the implementation of DMT used as the signaling standard for asymmetric digital subscriber lines (ADSL), the transforms used for demodulation and modulation are the Discrete Fourier Transform (DFT) and its inverse, respectively. Further information regarding the asymmetric digital subscriber line standard can be found in the article Asymmetric Digital Subscriber Line (ADSL) Metallic Interface, ANSI T1E1.4/94-007R8, 1994, incorporated herein by reference in its entirety.
  • In another implementation, referred to as discrete wavelet multitone (DWMT) transmission, a discrete wavelet transform and its inverse are employed as discussed in M. A. Tzannes et al, “The DWMT: A Multicarrier Transceiver for ADSL Using M-Band Wavelets,” ANSI Standard Committee T1E1.4 contribution 93-067, March 1993, M. A. Tzannes, “System Design Issues for the DWMT Transceiver,” ANSI Standard Committee T1E1.4 contribution 93-100, April 1993 and M. A. Tzannes et al, “DMT Systems, DWMT Systems and Digital Filter Banks,” Proc. ICC 1994, all of which are incorporated herein by reference in their entirety.
  • Thus, in a multicarrier system, a communication path having a fixed bandwidth is divided into a number of sub-bands having different frequencies. The width of the sub-bands is chosen to be small enough to allow the distortion in each sub-band to be modeled by a single attenuation and phase shift for the band. If the noise level in each band is known, the volume of data sent in each band may be optimized by choosing a symbol set having the maximum number of symbols consistent with the available signal to noise ratio of the channel. By using each sub-band at its maximum capacity, the amount of data that can be transmitted in the communication path is maximized.
  • In practice, such systems are implemented by banks of digital filters which make use of Fast Fourier Transforms (FFT). In the case in which a single data stream is to be transmitted over the communication path is broken into M sub-bands, during each communication cycle, the portion of the data stream to be transmitted is converted to M QAM symbols chosen to match the capacity of the various channels.
  • The time domain signal to be sent on the communication path is obtained by selecting a QAM point on each sub-carrier and then adding the modulation carriers to form the signal to be placed in the communication path. This operation is normally carried out by transforming the vector of M symbols via the inverse Fourier transform to generate N, where N represents the size of the transform, time domain values that are sent in sequence on the communication path. At the other end of the communication path, the N time domain values are accumulated and transformed via a Fourier transform to recover the original M symbols after equalization of the transformed data to correct for the attenuation and phase shifts that may have occurred in the channels.
  • One type of problem encountered in transmission systems is intersymbol interference (ISI). When the time domain values are transmitted, the values are spread over time by the impulse response of the system. Often, a guard band is included to prevent previous frames from interfering with subsequent frames, but these guard bands are often too small to be sufficient on their own. Also, values from within the same frame can interfere with each other to cause ISI, sometimes referred to as intersubchannel interference. The time domain equalizer works to shorten the overall length of the impulse response but usually does not remove all of the ISI.
  • Therefore, the symbol decoded by the subscriber will include interference from other symbols in other sub-bands and/or earlier or later symbols transmitted in the subscriber's sub-band. This type of interference is further aggravated by the high side lobes in the sub-bands provided by the Fourier transform. Further information regarding multicarrier transmission systems can be obtained from U.S. Pat. No. 5,636,246 entitled “Multicarrier Transmission System,” incorporated herein by reference in its entirety.
  • SUMMARY OF THE INVENTION
  • For an ideal transmission channel, the receiver transform output is a replica of the modulating data, due to the orthogonality (Nyquist) properties of the particular transform used. However, without compensation, as discussed above, the practical channels can contain severe intersubchannel and interframe interference. That is, the receiver transform output for sub-channel m1 and frame i1 has a contribution not only from si 1 m 1 but also from sm i for {m,i}≠{m1,i1}, where si m denotes the symbol transmitted in sub-channel m for frame i. For sake of clarity, in the following disclosure a distinction between intersubchannel and interframe interference will not be made, but rather the combination of the two referred to as intersymbol interference (ISI). However, it is to be appreciated that the receiver transform outputs can also have contributions from independent background noise, which, also for sake of clarity, will be disregarded for this discussion.
  • Multicarrier systems typically employ equalization to compensate for the effects of ISI. Such equalization is typically done in the time-domain and in the frequency-domain. For time-domain equalization (TDQ), an adaptive filter is trained then applied to the sequence of samples at the receiver, before the sequence is passed to the receiver transform. For frequency-domain equalization (FDQ), processing is employed on the receiver transform outputs.
  • Let Sm 1 i 1 denote the actual transmitted symbol, and let
    Figure US20100098149A1-20100422-P00001
    denote the FDQ output for subchannel m1 and frame i1. The desired net effect of TDQ and FDQ is for
    Figure US20100098149A1-20100422-P00002
    to be equal to Sm 1 i 1 , plus a very small contribution from ISI. The receiver can make a decision about the value for sm 1 i 1 by quantizing
    Figure US20100098149A1-20100422-P00003
    to the nearest constellation point. This decision will be denoted by di 1 m 1 .
  • Typically, the time-domain equalizer is relied on to perform the bulk of the ISI mitigation, with the frequency domain equalization being used only to perform a phase and amplitude correction for the channel/TDQ combination at the given sub-channel center frequency. In these schemes, each FDQ is implemented as a single-tap complex multiply, applied to the associated sub-channel output.
  • However, as discussed in U.S. Pat. No. 5,636,246, additional ISI suppression can be obtained by allowing each FDQ to have multiple taps, and combining the receiver transform outputs for several neighboring sub-channel, frame pairs. However, a further reduction in ISI can be achieved by incorporating feedback from one or more neighboring sub-channel, frame pairs in the frequency-domain equalizer combiner.
  • Accordingly, aspects of the invention relate to reducing intersymbol interference.
  • Additional aspects of the invention relate to reducing intersymbol interference through the use of feedback.
  • Additional aspects of the invention relate to reducing intersymbol interference through the use of feedback in a multicarrier environment.
  • Aspects of the invention further relate to combining multiple FFT outputs as well as decision feedback to create an estimate of a transmitted QAM symbol.
  • Aspects of the invention additionally relate to using a multi-tap frequency domain equalizer with decision feedback to minimize intersymbol interference in a multicarrier modulation communication system.
  • 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
  • The embodiments of the invention will be described in detailed, with reference to the following figures, wherein:
  • FIG. 1 is a functional block diagram illustrating the equalizer portion of a conventional receiver;
  • FIG. 2 is a functional block diagram illustrating a portion of a receiver according to this invention;
  • FIG. 3 is a flowchart illustrating an exemplary method for mitigating intersymbol interference according to this invention; and
  • FIG. 4 is a plot illustrating the exemplary benefits achieved in SINR using the systems and methods of this invention.
  • DETAILED DESCRIPTION OF THE INVENTION
  • The exemplary systems and methods of this invention will be described in relation to digital subscriber line communications, and more particularly to multicarrier modulation communications. However, to avoid unnecessarily obscuring the present invention, the following description omits well-known structures and devices that may be shown in block diagram form or otherwise summarized. For the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It should be appreciated however that the present invention may be practiced in a variety of ways beyond the specific details. For example, the systems and methods of this invention can generally be applied to any type of communication system including wireless communication systems, such as wireless LANs, power line communications, or any other system or combination of systems that use multicarrier communication or any other form of modulation in which it is desired to reduce intersymbol interference.
  • Furthermore, while the exemplary embodiments illustrated herein show the various components of the communication system collocated, it is to be appreciated that the various components of the system can be located at distant portions of a distributed network, such as a telecommunications network and/or the Internet, or within a dedicated intersymbol interference reduction module. Thus, it should be appreciated that the components of the communication system can be combined into one or more devices or collocated on a particular node of a distributed network, such as a telecommunications network. As will be appreciated from the following description, and for reasons of computational efficiency, the components of the communication system can be arranged at any location within a distributed network without affecting the operation of the system.
  • Furthermore, it should be appreciated that the various links connecting the elements can be wired or wireless links, or a combination thereof, or any other known or later developed element(s) that is capable of supplying and/or communicating data to and from the connected elements. Additionally, the term module as used herein can refer to any known or later developed hardware, software, or combination of hardware and software that is capable of performing the functionality associated with that element.
  • FIG. 1 illustrates a portion of conventional receiver 10. In particular, the receiver 10 comprises a time domain equalizer 100, a fast Fourier transform module 110, a frequency domain equalizer 120 and a constellation decoder 130. As previously discussed, a plurality of received samples 140 are received at the time-domain equalizer 100. The time-domain equalizer 100 applies adaptive filtering to the sequence of samples and passes the sequence to the fast Fourier transform module 110. The fast Fourier transform module 110 outputs a complex output fm for each tone m in the set of total tones M in each frame. The frequency domain equalizer 120 then performs a single-tap complex multiply to each associated sub-channel resulting in the received point R m 160. The constellation decoder 130 then determines the constellation point {circumflex over (D)}m closest to the received point Rm for each tone.
  • In U.S. Pat. No. 5,636,246, it was noted that additional ISI suppression could be obtained by allowing each frequency domain equalizer to have multiple taps and combining the receiver transform outputs for several neighboring sub-channel frame pairs.
  • Let θm i, represent the transform output for subchannel m, in frame i. For the method, discussed in U.S. Pat. No. 5,636,246, the FDQ combiner output for the subchannel, frame pair is:
  • = { m , j } A ( m 1 ) λ j m ( m 1 ) θ i 1 + j m ( 1 )
  • In this expression, A(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which the receiver transform outputs are used in the FDQ combiner, for subchannel m1. The second element j of the ordered pair is an offset relative to frame i1. The λj m(m1) are the corresponding FDQ combiner weights. The above equation will be referred to as a multi-tap FDQ (MFDQ) in what follows. Note that if A(m1) consists of the single element {m1, 0}, the above equation reduces to the application of a single-tap FDQ.
  • For the present invention, further improvement can be obtained by incorporating a feedback decision term in the FDQ combiner. The expression for the new combiner is obtained by expanding the equation above, and is rewritten as:
  • ( 2 )
  • In Eq. 2, B(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which decisions are used in the FDQ combiner for subchannel m1. The γj m are the corresponding combiner weights. Note that the sets B(m) must be constructed in an ordered fashion. That is, B(m1) should contain no ordered pair {m, j} for which
    Figure US20100098149A1-20100422-P00004
    is determined before
    Figure US20100098149A1-20100422-P00005
    , in which case the decision feedback term di 1 +j m would not be available. The method defined by Eq. (2) will be referred to as multi-tap FDQ with decision feedback (MFDQ-DF).
  • The settings for λj m(m1) and γj m(m1) can be trained during an initialization interval in which the transmitter sends a signal modulated with a symbol sequence si m known to the receiver. Specifically, fix i1 at an arbitrary value and for subchannel m1, let ω be a vector constructed from the weights λj m(m1) and γj m(m1), and let
    Figure US20100098149A1-20100422-P00006
    be the vector having the corresponding observation elements θi 1 +j m. In this construction, {m, j} varies over B(m1) and A(m1), for the feedback and non-feedback portions, respectively. Note that since the Si 1 +j m are known apriori, they are substituted for the di 1 +j m. A goal for training ω is to minimize the square of error e=si 1 m 1 −ω
    Figure US20100098149A1-20100422-P00006
    , in the average, over several frames i1. This yields the standard least-squares (LS) solution ω=Σ−1 ρ, where Σ is the sample covariance matrix for
    Figure US20100098149A1-20100422-P00006
    , and ρ is the sample correlation vector, for Sm 1 i 1 and
    Figure US20100098149A1-20100422-P00006
    .
  • By way of simple example Eq. 2 can be rewritten as:
  • R m = k = 0 N - 1 A m , k f m - k + k = 1 L B m , k D ^ m - k ( 3 )
  • where the complex output of the FFT for tone m is given by fm, the complex output of the multi-tap frequency domain equalization with decision feedback (MFDQ-DF) is Rm, and {circumflex over (D)}m is the constellation point closest to the received point Rm. Note that N and L are variables that determine the number of forward and feedback combiner taps that are being used in the system. Also, note that, for this example, there is no dependence across frames so the subscript i has been removed, and the subscript m moved to the subscript location. For this simple case, the Rm is determined in increasing order such that the feedback values will always be available. Converting from Eq. 2, γ is equivalent B, d is equivalent to {circumflex over (D)}, λ is equivalent to A and θ is equivalent to f. For this particular simple example, the multi-tap and decision feedback equalizer 180 is illustrated with two taps for A and one tap for B. However, it is to be appreciated that this can be adjusted based, for example on the particular application and/or accuracy needed.
  • Specifically, FIG. 2 illustrates graphically how feedback is used in the multi-tap and decision feedback equalizer 180. In particular, FIG. 2 comprises one or more received samples 140, a time-domain equalizer 100, an FFT module 110, a plurality of complex outputs 150, a multi-tap decision feedback equalizer 180, a plurality of determined received points 160 corresponding to a respective tone, a constellation decoder 130 and plurality of output constellation points 170 that were determined to be closest to the received point 160. The operation of the equalizer 180 in FIG. 2 is comparable to that of the equalizer illustrated in FIG. 1, with the exception of constellation points 170 being fed back to aid in determining the Rm for another tone. In this simple particular example, {circumflex over (D)}2 190 is fed back to tone 3 and {circumflex over (D)}M−1 200 is fed back to tone N. It is to be appreciated that, in general, {circumflex over (D)} can be fed back to any one or more other tones to aid in determining the received point Rm. For example, the system can begin with the determination of {circumflex over (D)}M and proceed “backwards” an until {circumflex over (D)}1 is determined. Alternatively, the system can jump around between tones with the only limitation being RM is dependent on decisions made on earlier tones.
  • Additionally, it is to be appreciated that any {circumflex over (D)} can be used as feedback alone or in combination, with other {circumflex over (D)}'s and, as discussed above, can be either forward looking or backward looking, or a combination thereof, for feedback terms.
  • FIG. 3 illustrates an exemplary method of determining intersymbol interference reduced output samples. In particular, control begins in step S100 and continues to step S110. In step S110, one or more samples are received. Next, in step S120, time-domain equalization is performed on the one or more received samples. Then, in step S130, the complex outputs are determined for each tone through the use of a transform, such as a fast Fourier transform, discrete wavelet transform, or like. Control then continues to step S140.
  • In step S140, for each tone m in the set of total tones M in each frame, step S142 determines the received point and in step S144 the received point Rm is constellation decoded to output the constellation point closest to the received point Rm. Control then continues to step S150.
  • In step S150, the intersymbol interference compensated output samples are output. Control then continues to step S160 where the control sequence ends.
  • FIG. 4 illustrates the exemplary advantages of using decision feedback in frequency domain equalization. In particular, FIG. 4 illustrates the SINR verse subchannel outputs for various FDQ schemes over 9 kft. of 26 AWG wire. In particular, these tests were conducted over a multicarrier ADSL system upstream length. Subsequent to each TDQ training session, the FDQ was trained in a least squares fashion using the ADSL medley signal for each of the FDQ schemes discussed above, and the resulting SINR profiles plotted. As illustrated in FIG. 4, the SINR verse subchannel is illustrated (note subchannel 16 was not used).
  • For the curve labeled “5-tap MFDQ”, A(m1) comprises the 5 ordered pans {m, 0} with m1−2≦m≦m1+2. For the curve labeled “3-tap MFDQ-FB+”, A(m1) comprises the two ordered pairs {m1, 0} and {m1+1, 0}, and B(m1) contains only the single pair {m1+1, 0}. For the curve labeled “3-tap MFDQ-FB−”, A(m1) comprises the two ordered pairs {m1, 0) and {m1−1, 0}, and B(m1) contains only the single pair {m1−1, 0}. Modest improvement is noted as the single-tap FDQ is expanded to 5 MFDQ taps.
  • However, large additional improvement is noted when either of the MFDQ-DF schemes are used. To adhere to the causality requirements for the B(m), a normal 1-tap FDQ, or an MFDQ, depending on A(m), can be used for the uppermost subchannel in the “3-tap MFDQ-FB+” scheme, and the lowermost subchannel in the “3-tap MFDQ-FB−” scheme.
  • The above-described intersymbol interference reduction system can be implemented on a telecommunications device, such a modem, a DSL modem, an ADSL modem, a multicarrier transceiver, a VDSL modem, or the like, or on a separate programmed general purpose computer having a communications device. However, the systems and methods of this invention can also be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit element, and ASIC or other integrated circuit, a digital signal processor, a hard-wired electronic or logic circuit such as discrete element circuit, a programmable logic device such as PLD, PLA, FPGA, PAL, modem, receiver, or the like. In general, any device capable of implementing a state machine that is in turn capable of implementing the flowchart illustrated herein can be used to implement the various intersymbol interference reduction methods according to this invention.
  • Furthermore, the disclosed methods 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 computer or workstation hardware platforms. Alternatively, the disclosed intersymbol interference reduction system may be implemented partially or fully in hardware using standard logic circuits or VLSI design. Whether software or hardware is used to implement the systems in accordance with this invention is dependent on the speed and/or efficiency requirements of the system, the particular function, and the particular software or hardware systems or microprocessor or microcomputer systems being utilized. The intersymbol interference reduction systems and methods illustrated herein however can be readily implemented in hardware and/or software using any known or 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.
  • Moreover, the disclosed methods may be readily implemented in software executed on programmed general purpose computer, a special purpose computer, a microprocessor, or the like. In these instances, the systems and methods of this invention can be implemented as program embedded on personal computer such as JAVA® or CGI script, as a resource residing on a server or graphics workstation, as a routine embedded in a dedicated intersymbol interference reduction system, or the like. The intersymbol interference reduction system can also be implemented by physically incorporating the system and method into a software and/or hardware system, such as the hardware and software systems of a communications transceiver.
  • It is, therefore, apparent that there has been provided, in accordance with the present invention, systems and methods for intersymbol interference reduction. 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 arts. Accordingly, it is intended to embrace all such alternatives, modifications, equivalents and variations that are within the spirit and scope of this invention.

Claims (24)

1. An intersymbol interference reduction system comprising:
a frequency domain equalizer; and
a constellation decoder, the frequency domain equalizer determining at least one received point based at least on at least one previously determined constellation point.
2. The system of claim 1, wherein the at least one previously determined constellation point is feedback which can be one or more of forward looking feedback and backward looking feedback.
3. The system of claim 1, wherein a plurality of decisions about the value of sm 1 i 1 obtained by quantizing
Figure US20100098149A1-20100422-P00007
to the nearest constellation point are used in determining the at least one received point.
4. The system of claim 1, wherein a sub-channel output for the frequency domain equalizer for a subchannel m1 and frame i1 are determined in accordance with:
= { m , j } A ( m 1 ) λ j m ( m 1 ) θ i 1 + j m + { m , j } B ( m 1 ) γ j m ( m 1 ) d i 1 + j m
where A(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which the receiver transform outputs are used in the frequency domain equalizer, for subchannel m1, B(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which decisions are used in the frequency domain equalizer for subchannel m1, λj m(m1) are the corresponding frequency domain equalizer weights, θm i represents the transform output for subchannel m, in frame i, γj m is the corresponding combiner weights and di 1 m 1 is a value for sm 1 i 1 determined by quantizing
Figure US20100098149A1-20100422-P00008
to the nearest constellation point.
5. The system of claim 1, wherein the intersymbol interference reduction system is used to reduce intersymbol interference in a multicarrier communication environment.
6. The system of claim 1, wherein the intersymbol interference reduction system is incorporated into a transceiver.
7. A method for reducing intersymbol interference reduction comprising:
determining at least one constellation point; and
determining at least one received point based at least on at least one previously determined constellation point.
8. The method of claim 7, wherein the at least one previously determined constellation point is feedback which can be one or more of forward looking feedback and backward looking feedback.
9. The method of claim 7, wherein a plurality of decisions about the value of sm 1 i 1 obtained by quantizing
Figure US20100098149A1-20100422-P00009
to the nearest constellation point are used in determining the at least one received point.
10. The method of claim 7, wherein a sub-channel output for the frequency domain equalizer for a subchannel m1 and frame i1 are determined in accordance with:
= { m , j } A ( m 1 ) λ j m ( m 1 ) θ i 1 + j m { m , j } B ( m 1 ) γ j m ( m 1 ) d i 1 + j m
where A(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which the receiver transform outputs are used in the frequency domain equalizer, for subchannel m1, B(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which decisions are used in the frequency domain equalizer for subchannel m1, λj m(m1) are the corresponding frequency domain equalizer weights, θm i represents the transform output for subchannel m, in frame i, γj m is the corresponding combiner weights and di 1 m 1 is a value for sm 1 i i determined by quantizing
Figure US20100098149A1-20100422-P00010
to the nearest constellation point.
11. The method of claim 7, wherein the intersymbol interference reduction method is used to reduce intersymbol interference in a multicarrier communication environment.
12. The method of claim 7, wherein the intersymbol interference reduction method is incorporated into a transceiver.
13. An intersymbol interference reduction system comprising:
means for determining at least one constellation point; and
means for determining at least one received point based at least on at least one previously determined constellation point.
14. The system of claim 13, wherein the at least one previously determined constellation point is feedback which can be one or more of forward looking feedback and backward looking feedback.
15. The system of claim 13, wherein a plurality of decisions about the value of sm 1 i 1 obtained by quantizing
Figure US20100098149A1-20100422-P00011
to the nearest constellation point are used in determining the at least one received point.
16. The system of claim 13, wherein a sub-channel output for the frequency domain equalizer for a subchannel m1 and frame 1 1 are determined in accordance with:
= { m , j } A ( m 1 ) λ j m ( m 1 ) θ i 1 + j m { m , j } B ( m 1 ) γ j m ( m 1 ) d i 1 + j m
where A(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which the receiver transform outputs are used in the frequency domain equalizer, for subchannel m1, B(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which decisions are used in the frequency domain equalizer for subchannel m1, λj m(m1) are the corresponding frequency domain equalizer weights, θm i represents the transform output for subchannel m, in frame i, γj m is the corresponding combiner weights and di 1 m 1 is a value for sm 1 i 1 determined by quantizing
Figure US20100098149A1-20100422-P00012
to the nearest constellation point.
17. The system of claim 13, wherein the intersymbol interference reduction method is used to reduce intersymbol interference in a multicarrier communication environment.
18. The system of claim 13, wherein the intersymbol interference reduction method is incorporated into a transceiver.
19. An information storage media comprising information for reducing intersymbol interference reduction comprising:
information that determines at least one constellation point; and
information that determines at least one received point based at least on at least one previously determined constellation point.
20. The media of claim 19, wherein the at least one previously determined constellation point is feedback which can be one or more of forward looking feedback and backward looking feedback.
21. The media of claim 19, wherein a plurality of decisions about the value of sm 1 i 1 obtained by quantizing
Figure US20100098149A1-20100422-P00013
to the nearest constellation point are used in determining the at least one received point.
22. The media of claim 19, wherein a sub-channel output for the frequency domain equalizer for a subchannel m1 and frame i1 are determined in accordance with:
= { m , j } A ( m 1 ) λ j m ( m 1 ) θ i 1 + j m { m , j } B ( m 1 ) γ j m ( m 1 ) d i 1 + j m
where A(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which the receiver transform outputs are used in the frequency domain equalizer, for subchannel m1, B(m1) is a set containing ordered pairs {m, j} of indices corresponding to the particular subchannel, frame pairs for which decisions are used in the frequency domain equalizer for subchannel m1, λj m(m1) are the corresponding frequency domain equalizer weights, θm i represents the transform output for subchannel m, in frame i, γj m is the corresponding combiner weights and di 1 m 1 is a value for sm 1 i 1 determined by quantizing
Figure US20100098149A1-20100422-P00014
to the nearest constellation point.
23. The media of claim 19, wherein the intersymbol interference reduction method is used to reduce intersymbol interference in a multicarrier communication environment.
24. The media of claim 19, wherein the intersymbol interference reduction method is incorporated into a transceiver.
US12/640,838 2001-08-02 2009-12-17 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback Abandoned US20100098149A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US12/640,838 US20100098149A1 (en) 2001-08-02 2009-12-17 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US12/783,796 US20100296570A1 (en) 2001-08-02 2010-05-20 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US30963101P 2001-08-02 2001-08-02
US10/211,425 US6760373B2 (en) 2001-08-02 2002-08-02 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US10/834,193 US20040202259A1 (en) 2001-08-02 2004-04-29 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US11/964,409 US7656976B2 (en) 2001-08-02 2007-12-26 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US12/640,838 US20100098149A1 (en) 2001-08-02 2009-12-17 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback

Related Parent Applications (1)

Application Number Title Priority Date Filing Date
US11/964,409 Continuation US7656976B2 (en) 2001-08-02 2007-12-26 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US12/783,796 Continuation US20100296570A1 (en) 2001-08-02 2010-05-20 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback

Publications (1)

Publication Number Publication Date
US20100098149A1 true US20100098149A1 (en) 2010-04-22

Family

ID=23199004

Family Applications (5)

Application Number Title Priority Date Filing Date
US10/211,425 Expired - Lifetime US6760373B2 (en) 2001-08-02 2002-08-02 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US10/834,193 Abandoned US20040202259A1 (en) 2001-08-02 2004-04-29 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US11/964,409 Expired - Lifetime US7656976B2 (en) 2001-08-02 2007-12-26 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US12/640,838 Abandoned US20100098149A1 (en) 2001-08-02 2009-12-17 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US12/783,796 Pending US20100296570A1 (en) 2001-08-02 2010-05-20 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback

Family Applications Before (3)

Application Number Title Priority Date Filing Date
US10/211,425 Expired - Lifetime US6760373B2 (en) 2001-08-02 2002-08-02 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US10/834,193 Abandoned US20040202259A1 (en) 2001-08-02 2004-04-29 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US11/964,409 Expired - Lifetime US7656976B2 (en) 2001-08-02 2007-12-26 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback

Family Applications After (1)

Application Number Title Priority Date Filing Date
US12/783,796 Pending US20100296570A1 (en) 2001-08-02 2010-05-20 Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback

Country Status (3)

Country Link
US (5) US6760373B2 (en)
AU (1) AU2002326489A1 (en)
WO (1) WO2003012990A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070211812A1 (en) * 2002-08-01 2007-09-13 Aware, Inc. Multi-tap frequency domain equalization with decision feedback and trellis decoding
US20100296570A1 (en) * 2001-08-02 2010-11-25 Aware, Inc. Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback

Families Citing this family (29)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5955992A (en) * 1998-02-12 1999-09-21 Shattil; Steve J. Frequency-shifted feedback cavity used as a phased array antenna controller and carrier interference multiple access spread-spectrum transmitter
US7430257B1 (en) 1998-02-12 2008-09-30 Lot 41 Acquisition Foundation, Llc Multicarrier sub-layer for direct sequence channel and multiple-access coding
US8670390B2 (en) 2000-11-22 2014-03-11 Genghiscomm Holdings, LLC Cooperative beam-forming in wireless networks
US9893774B2 (en) 2001-04-26 2018-02-13 Genghiscomm Holdings, LLC Cloud radio access network
US10425135B2 (en) 2001-04-26 2019-09-24 Genghiscomm Holdings, LLC Coordinated multipoint systems
US9819449B2 (en) 2002-05-14 2017-11-14 Genghiscomm Holdings, LLC Cooperative subspace demultiplexing in content delivery networks
US10931338B2 (en) 2001-04-26 2021-02-23 Genghiscomm Holdings, LLC Coordinated multipoint systems
US10355720B2 (en) 2001-04-26 2019-07-16 Genghiscomm Holdings, LLC Distributed software-defined radio
US20030187528A1 (en) * 2002-04-02 2003-10-02 Ke-Chiang Chu Efficient implementation of audio special effects
US10644916B1 (en) 2002-05-14 2020-05-05 Genghiscomm Holdings, LLC Spreading and precoding in OFDM
US10200227B2 (en) 2002-05-14 2019-02-05 Genghiscomm Holdings, LLC Pre-coding in multi-user MIMO
US9628231B2 (en) 2002-05-14 2017-04-18 Genghiscomm Holdings, LLC Spreading and precoding in OFDM
US10142082B1 (en) 2002-05-14 2018-11-27 Genghiscomm Holdings, LLC Pre-coding in OFDM
JP4136517B2 (en) * 2002-07-31 2008-08-20 株式会社日立製作所 Mobile terminal
WO2004019505A2 (en) * 2002-08-21 2004-03-04 Enikia Llc Method and system for modifying modulation of power line communications signals for maximizing data throughput rate
US7260144B2 (en) * 2003-12-12 2007-08-21 Texas Instruments Incorporated Architecture for per tone equalizer with reduced complexity for DMT-based xDSL modems
US11184037B1 (en) 2004-08-02 2021-11-23 Genghiscomm Holdings, LLC Demodulating and decoding carrier interferometry signals
US11552737B1 (en) 2004-08-02 2023-01-10 Genghiscomm Holdings, LLC Cooperative MIMO
US11431386B1 (en) 2004-08-02 2022-08-30 Genghiscomm Holdings, LLC Transmit pre-coding
US8009752B2 (en) * 2004-10-01 2011-08-30 Qualcomm Incorporated Multi-carrier incremental redundancy for packet-based wireless communications
US7693225B2 (en) * 2005-07-21 2010-04-06 Realtek Semiconductor Corp. Inter-symbol and inter-carrier interference canceller for multi-carrier modulation receivers
US7711059B2 (en) * 2005-09-08 2010-05-04 Realtek Semiconductor Corp. Low noise inter-symbol and inter-carrier interference cancellation for multi-carrier modulation receivers
EP2123077B1 (en) * 2007-01-16 2015-11-18 Koninklijke Philips N.V. Communicating between devices with directional antennas
US10243773B1 (en) 2017-06-30 2019-03-26 Genghiscomm Holdings, LLC Efficient peak-to-average-power reduction for OFDM and MIMO-OFDM
US10637705B1 (en) 2017-05-25 2020-04-28 Genghiscomm Holdings, LLC Peak-to-average-power reduction for OFDM multiple access
US11917604B2 (en) 2019-01-25 2024-02-27 Tybalt, Llc Orthogonal multiple access and non-orthogonal multiple access
US11343823B2 (en) 2020-08-16 2022-05-24 Tybalt, Llc Orthogonal multiple access and non-orthogonal multiple access
CN113454964A (en) 2019-01-25 2021-09-28 珍吉斯科姆控股有限责任公司 Orthogonal and non-orthogonal multiple access
WO2020242898A1 (en) 2019-05-26 2020-12-03 Genghiscomm Holdings, LLC Non-orthogonal multiple access

Citations (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4679227A (en) * 1985-05-20 1987-07-07 Telebit Corporation Ensemble modem structure for imperfect transmission media
US5048054A (en) * 1989-05-12 1991-09-10 Codex Corporation Line probing modem
US5206886A (en) * 1990-04-16 1993-04-27 Telebit Corporation Method and apparatus for correcting for clock and carrier frequency offset, and phase jitter in mulicarrier modems
US5285474A (en) * 1992-06-12 1994-02-08 The Board Of Trustees Of The Leland Stanford, Junior University Method for equalizing a multicarrier signal in a multicarrier communication system
US5636246A (en) * 1994-11-16 1997-06-03 Aware, Inc. Multicarrier transmission system
US6012161A (en) * 1997-11-26 2000-01-04 At&T Corp. System and method for joint coding and decision feedback equalization
US6226322B1 (en) * 1998-03-30 2001-05-01 Texas Instruments Incorporated Analog receive equalizer for digital-subscriber-line communications system
US6295326B1 (en) * 1999-03-08 2001-09-25 Bandspeed, Inc. Kalman filter based equalization for digital multicarrier communications systems
US6356586B1 (en) * 1999-09-03 2002-03-12 Lucent Technologies, Inc. Methods and apparatus for parallel decision-feedback decoding in a communication system
US6389062B1 (en) * 1997-09-17 2002-05-14 Texas Instruments Incorporated Adaptive frequency domain equalizer circuits, systems, and methods for discrete multitone based digital subscriber line modem
US6400781B1 (en) * 1997-10-27 2002-06-04 Alcatel Multiband detector
US6456654B1 (en) * 1998-12-22 2002-09-24 Nortel Networks Limited Frame alignment and time domain equalization for communications systems using multicarrier modulation
US20030063663A1 (en) * 2001-10-01 2003-04-03 Bryant Paul Henry Multistage equalizer that corrects for linear and nonlinear distortion in a digitally-modulated signal
US6661837B1 (en) * 1999-03-08 2003-12-09 International Business Machines Corporation Modems, methods, and computer program products for selecting an optimum data rate using error signals representing the difference between the output of an equalizer and the output of a slicer or detector
US20040096008A1 (en) * 2002-08-01 2004-05-20 Aware, Inc. Multi-tap frequency domain equalization with decision feedback and trellis decoding
US6760373B2 (en) * 2001-08-02 2004-07-06 Aware, Inc. Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US6847693B1 (en) * 2000-05-16 2005-01-25 3Com Corporation Method and device providing data derived timing recovery for multicarrier communications
US7042367B2 (en) * 2002-02-04 2006-05-09 Halliburton Energy Services Very high data rate telemetry system for use in a wellbore
US7058141B1 (en) * 2000-06-02 2006-06-06 Nec Usa, Inc. MLSE decoding of PRS type inter-bin interference in receiver-end windowed DMT system

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5872817A (en) 1997-07-02 1999-02-16 Lucent Technologies Inc. Joint viterbi decoder and decision feedback equalizer

Patent Citations (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4731816A (en) * 1985-05-20 1988-03-15 Telebit Corporation Ensemble modem structure for imperfect transmission media
US4679227A (en) * 1985-05-20 1987-07-07 Telebit Corporation Ensemble modem structure for imperfect transmission media
US5048054A (en) * 1989-05-12 1991-09-10 Codex Corporation Line probing modem
US5206886A (en) * 1990-04-16 1993-04-27 Telebit Corporation Method and apparatus for correcting for clock and carrier frequency offset, and phase jitter in mulicarrier modems
US5285474A (en) * 1992-06-12 1994-02-08 The Board Of Trustees Of The Leland Stanford, Junior University Method for equalizing a multicarrier signal in a multicarrier communication system
US5636246A (en) * 1994-11-16 1997-06-03 Aware, Inc. Multicarrier transmission system
US6389062B1 (en) * 1997-09-17 2002-05-14 Texas Instruments Incorporated Adaptive frequency domain equalizer circuits, systems, and methods for discrete multitone based digital subscriber line modem
US6400781B1 (en) * 1997-10-27 2002-06-04 Alcatel Multiband detector
US6012161A (en) * 1997-11-26 2000-01-04 At&T Corp. System and method for joint coding and decision feedback equalization
US6226322B1 (en) * 1998-03-30 2001-05-01 Texas Instruments Incorporated Analog receive equalizer for digital-subscriber-line communications system
US6456654B1 (en) * 1998-12-22 2002-09-24 Nortel Networks Limited Frame alignment and time domain equalization for communications systems using multicarrier modulation
US6295326B1 (en) * 1999-03-08 2001-09-25 Bandspeed, Inc. Kalman filter based equalization for digital multicarrier communications systems
US6661837B1 (en) * 1999-03-08 2003-12-09 International Business Machines Corporation Modems, methods, and computer program products for selecting an optimum data rate using error signals representing the difference between the output of an equalizer and the output of a slicer or detector
US6356586B1 (en) * 1999-09-03 2002-03-12 Lucent Technologies, Inc. Methods and apparatus for parallel decision-feedback decoding in a communication system
US6847693B1 (en) * 2000-05-16 2005-01-25 3Com Corporation Method and device providing data derived timing recovery for multicarrier communications
US7058141B1 (en) * 2000-06-02 2006-06-06 Nec Usa, Inc. MLSE decoding of PRS type inter-bin interference in receiver-end windowed DMT system
US6760373B2 (en) * 2001-08-02 2004-07-06 Aware, Inc. Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US20040202259A1 (en) * 2001-08-02 2004-10-14 Aware, Inc. Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US7656976B2 (en) * 2001-08-02 2010-02-02 Aware, Inc. Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US20100296570A1 (en) * 2001-08-02 2010-11-25 Aware, Inc. Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US20030063663A1 (en) * 2001-10-01 2003-04-03 Bryant Paul Henry Multistage equalizer that corrects for linear and nonlinear distortion in a digitally-modulated signal
US7042367B2 (en) * 2002-02-04 2006-05-09 Halliburton Energy Services Very high data rate telemetry system for use in a wellbore
US20040096008A1 (en) * 2002-08-01 2004-05-20 Aware, Inc. Multi-tap frequency domain equalization with decision feedback and trellis decoding
US20070211812A1 (en) * 2002-08-01 2007-09-13 Aware, Inc. Multi-tap frequency domain equalization with decision feedback and trellis decoding
US20100293442A1 (en) * 2002-08-01 2010-11-18 Aware, In. Multi-tap frequency domain equalization with decision feedback and trellis decoding
US20100299582A1 (en) * 2002-08-01 2010-11-25 Aware, In. Multi-tap frequency domain equalization with decision feedback and trellis decoding

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100296570A1 (en) * 2001-08-02 2010-11-25 Aware, Inc. Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US20070211812A1 (en) * 2002-08-01 2007-09-13 Aware, Inc. Multi-tap frequency domain equalization with decision feedback and trellis decoding
US20100293442A1 (en) * 2002-08-01 2010-11-18 Aware, In. Multi-tap frequency domain equalization with decision feedback and trellis decoding
US20100299582A1 (en) * 2002-08-01 2010-11-25 Aware, In. Multi-tap frequency domain equalization with decision feedback and trellis decoding

Also Published As

Publication number Publication date
US20030067865A1 (en) 2003-04-10
WO2003012990A1 (en) 2003-02-13
WO2003012990A8 (en) 2004-01-29
US20040202259A1 (en) 2004-10-14
AU2002326489A1 (en) 2003-02-17
US7656976B2 (en) 2010-02-02
US20080101452A1 (en) 2008-05-01
US20100296570A1 (en) 2010-11-25
US6760373B2 (en) 2004-07-06

Similar Documents

Publication Publication Date Title
US7656976B2 (en) Systems and methods for multicarrier modulation using multi-tap frequency-domain equalizer and decision feedback
US6526105B1 (en) Time domain equalization for discrete multi-tone systems
US6608864B1 (en) Method and apparatus for fault recovery in a decision feedback equalizer
US7561627B2 (en) Method and system for channel equalization and crosstalk estimation in a multicarrier data transmission system
US7020212B1 (en) Method and system for a multiple dimensional adaptive frequency domain noise canceler for DMT transceivers
JP4834269B2 (en) How to process data received from a communication channel in a finite precision arithmetic application
US7936851B2 (en) Channel equalization
US7916801B2 (en) Time-domain equalization for discrete multi-tone systems
US6563841B1 (en) Per-bin adaptive equalization in windowed DMT-type modem receiver
JP2000307481A (en) Receiver for discrete multitone modulated signal having window function
US20050276340A1 (en) Method and system for determining symbol boundary timing in a multicarrier data transmission system
US8290033B2 (en) Systems and methods for performing combined equalization in communication systems
US20050276339A1 (en) Training sequence for symbol boundary detection in a multicarrier data transmission system
US6512789B1 (en) Partial equalization for digital communication systems
US7561626B2 (en) Method and system for channel estimation in a data transmission system
US20100293442A1 (en) Multi-tap frequency domain equalization with decision feedback and trellis decoding
US20030043894A1 (en) Time domain equalizer for DMT modulation
US7953163B2 (en) Block linear equalization in a multicarrier communication system
US7697619B2 (en) Training sequence for channel estimation in a data transmission system
EP1206093B1 (en) Frequency-domain equalisation
US20030210742A1 (en) Methods and system for equalizing data
US20030152156A1 (en) Multicarrier receiver
Skowronek et al. A novel computationally efficient time-domain equalizer for ADSL/VDSL system
Helms A simple RLS-POCS solution for reduced complexity ADSL impulse shortening

Legal Events

Date Code Title Description
STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION

AS Assignment

Owner name: DLI LENDING AGENT, LLC, CALIFORNIA

Free format text: SECURITY INTEREST;ASSIGNOR:TQ DELTA, LLC;REEL/FRAME:047212/0551

Effective date: 20181005

AS Assignment

Owner name: ALTER DOMUS (US) LLC, ILLINOIS

Free format text: AMENDED AND RESTATED INTELLECTUAL PROPERTY SECURITY AGREEMENT;ASSIGNOR:TQ DELTA LLC;REEL/FRAME:054898/0850

Effective date: 20201231