102 results about "Time domain equalizer" patented technology

A system and method for broadband communications over power lines has a low-voltage transformer for the house connection unit and / or the electricity distribution inside the house. The system method allow for several parallel asynchronous data communications in different sub-channels with individual transmit power in each sub-channel. Sub-channel separation uses pass-band filters with high stop-band attenuation. High data rate in each sub-channel is achieved through the use of discrete wavelet multi-tone modulation. Coarse synchronization in each sub-channel and the optimization of the coefficients of the time-domain equalizer are carried out using a training sequence.

A novel time-domain equalizer (TEQ) is provided for the receiver of a Discrete Multi-tone (DMT) system to shorten the length of the effective channel impulse response. The TEQ is based on a variant of the conventional decision-feedback equalizer (DFE) structure along with a training method for the TEQ settings. By using this DFE-based TEQ for DMT systems, the data symbols transmitted through the effective shortened channel would be more reliable.

A system and a method are proposed for broadband communications over power lines comprising the area of the low-voltage transformer to the house connection unit and / or the electricity distribution inside the house. The new method allows for several parallel asynchronous data communications in different sub-channels with individual transmit power in each sub-channel. Sub-channel separation uses pass-band filters with high stop-band attenuation. High data rate in each sub-channel is achieved through the use of discrete wavelet multi-tone modulation. Coarse synchronization in each sub-channel and the optimization of the coefficients of the time-domain equalizer are carried out using a training sequence.

A DTV receiver includes a tuner, a demodulator, a known sequence detector, and a frequency domain equalizer. The tuner initially receives a broadcast signal including valid data in which a known data sequence is periodically repeated. The demodulator demodulates the broadcast signal, and the known sequence detector detects the known data sequence from the demodulated signal. The frequency domain equalizer compensates channel distortion of the demodulated broadcast signal in a frequency domain using the detected known data sequence. In addition, the DTV receiver may further include a time domain equalizer which compensates channel distortion of the time domain signal, or a noise canceller which removes a predicted noise from the time domain signal.

An apparatus for receiving a discrete multi-tone signal over a communications channel having an impulse response h(n), energy of the impulse response being substantially concentrated in a first band of samples, the apparatus including: a receiver for receiving the discrete multi-tone signal; and a T coefficient finite impulse response time-domain equalizer included in the receiver, the time-domain equalizer having an output additive noise signal, the T coefficients of the time-domain equalizer being provided such that: (a) energy of an effective impulse response heff(n) of at least the communications channel combined with the time-domain equalizer is substantially concentrated in a second band of V+1 samples, whereby the second band of samples is shorter than the first band of samples; and (b) a variance in a frequency spectrum of the output additive noise signal of the time-domain equalizer is controlled.

A method and apparatus for efficient filter structure for an enhanced operation of an ADSL-DMT modem on a subscriber loop with an environment consisting of ISDN interference. The method performs equalization of the channel by impulse response shortening and at the same time rejecting interference signals exhibiting cyclostationary properties. The method and apparatus for reducing the crosstalk involves a frequency-shifted versions of the received signal being filtered through frequency-shifted adaptive filters in the appropriate branches, and providing a joint time domain equalizer / crosstalk canceller to perform equalization of the channel and crosstalk cancellation in one instance and a separate crosstalk canceller to cancel crosstalk plus a time domain equalizer to equalize the channel. Downsampling the signal outputs of both the combined crosstalk equalizer and the frequency-shifted adaptive filters to reduce sampling rate; and subtracting the outputs of the combined crosstalk equalizer and the frequency-shifted adaptive filters to remove the cyclostationary interferer.

An algorithm for computing an efficient, reduced complexity, windowed optimal linear time domain equalizer for a dispersive channel comprises the steps of determining a window of maximum energy in the impulse response of length equal to or less than a number of cyclic prefix samples associated with a received digital data signal, computing the corresponding inside and outside matrices, performing an inverse Cholesky decomposition of the inside matrix, creating a resultant matrix as the product of the outer and the upper and lower square root inner matrix, followed by Householder reduction and QL transformation to thereby compute the time domain equalizer as the linear transformation of the eigenvector corresponding to the smallest eigenvalue at the receiver. The smallest eigenvalue is determined using the aforementioned orthogonal transformations without determining all the eigenvalues efficiently but without the loss accuracy associated with iterative methods like the conventional power method. The algorithm may be most conveniently implemented, for example, in the form of a thirty-two bit digital signal processor at a data receiver.

An update mechanism and approach are provided for configuring a communications receiver. According to the approach, a time domain equalizer and a frequency domain equalizer in a communications receiver are dynamically updated based upon performance data that indicates the performance of a communications channel from which the communications receiver receives data. This approach accounts for changes in the communications channel attributable to changes in the transmission medium or changes in interference sources.

Error contributions in a DMT system where a received DMT-signal is effected by intersymbol interference, intercarrier interference and additive noise are minimized. Intersymbol interference average power, intercarrier interference average power, and additive noise average power are calculated. A cost function is determined by adding the intersymbol interference average power, the intercarrier interference average power, and the additive noise average power. A constraint is introduced which avoids a trivial solution where a time domain equalizer (TEQ) vector is equal to zero. The cost function is minimized by optimizing the TEQ vector.

A method for estimating a phase response for an upstream area in a channel is based on an extrapolation and, following forcible distortion of an amplitude response, coefficients of a time domain equalizer and coefficients of a channel target circuit are determined using a minimum MSE algorithm. When the cost function of a minimum MES is determined, the square of the coefficients of the time domain equalizer are included for determining the cost function in order to reduce the probability that the coefficients of the time domain equalizer diverge. A channel-shortening effect of the time domain equalizer is improved to reduce inter-symbol interference (ISI) and inter-channel interference (ICI). As a result, a signal to noise ratio (SNR) of a communication system is improved.

Provided is a block Time Domain Equalizer (TDE) for a Time Reversal-Space Time Block Codes (TR-STBC) system. The block TDE comprises a block equalizer which generates an output based on an equalizer tap weight with respect to two consecutively received blocks, an equalizer tap weight updating unit which generates an error vector based on the output and the equalizer tap weight and updates the equalizer tap weight using the error vector, and a signal processing unit which processes the output into a digital signal wherein zero padding is eliminated from the output.

An algorithm for computing an efficient, reduced complexity, windowed optimal linear time domain equalizer for a dispersive channel comprises the steps of determining a window of maximum energy in the impulse response of length equal to or less than a number of cyclic prefix samples associated with a received digital data signal, computing the corresponding inside and outside matrices, performing an inverse Cholesky decomposition of the inside matrix, creating a resultant matrix as the product of the outer and the upper and lower square root inner matrix, followed by Householder reduction and QL transformation to thereby compute the time domain equalizer as the linear transformation of the eigenvector corresponding to the smallest eigenvalue at the receiver. The smallest eigenvalue is determined using the aforementioned orthogonal transformations without determining all the eigenvalues efficiently but without the loss accuracy associated with iterative methods like the conventional power method. The algorithm may be most conveniently implemented, for example, in the form of a thirty-two bit digital signal processor at a data receiver.

A channel decoder employs a hybrid frequency-time domain equalizer for effectively combining a frequency domain equalizer with a time domain equalizer to achieve superior static and dynamic multi-path performance compared to conventional decision feedback equalizers. A frequency domain equalizer structure is included within the forward path of a time domain, decision feedback equalizer, with both the frequency domain and time domain portions employing a common error vector. Updates to the taps (frequency bins) may be adapted individually, or fully within the frequency domain without altering the feedback filter. Improved performance, including performance for noisy channels with deep notches, is achieved, and the frequency domain equalizer portion is relieved from equalizing minimum phase zeros of the channel.

A method for deriving coefficients for a time domain equalizer function (24) as implemented by a digital signal processor (35) in a DSL modem (20) is disclosed. A transmitting modem (10), such as at a central office, issues a pseudo-random training sequence that is received by the receiving modem (20). Correlation matrices are derived by the digital signal processor (35), from which sets of eigenvalues and eigenvectors are derived. A flatness constraint on the frequency response of the time domain equalizer is established, and included with a flatness scaling factor (λ) into a minimization cost function. One or more values of the flatness scaling factor (λ), preferably between minimum and maximum eigenvalues, are evaluated in the cost function, to derive the optimum filter for the time-domain equalizer. The flatness constraint ensures that the time-domain equalizer is not subject to near null conditions and large variations in its frequency response.

A method and system for enhancing reach-performance of a multi-carrier VDSL System estimates loop length, estimates maximum available bandwidth that can be utilized at that particular loop length, optimally selects an FFT size and sampling rate, and decides whether to apply a time domain equalization to its receiver and if so, selects a cyclic extension size. To minimize the implementation complexity, the sampling frequencies at receiver and transmitter are lowered to match the actual usable bandwidth. The FFT / IFFT sizes in the implementation are also required to set appropriately accordingly.

The present invention provides a method for initialization and stepsize control of a time-domain equalizer (TEQ) in a receiver of a multi-carrier communication system to upgrade the performance of adaptive TEQ algorithms. As to TEQ initialization, the Time-domain Window Mask method generates a modified channel impulse response (CIR) by performing a locate maximum energy algorithm and then applies a time-domain window mask to adjust the modified CIR to obtain an initial value of a target impulse response. Then, a dividing operation is performed on the frequency-domain initial target impulse response and the modified CIR to determine an initial value of the frequency-domain TEQ impulse response. The Head-tail Equalizing method also performs the locate maximum energy algorithm, and the remaining points other than the consecutive points with maximum energy are combined and padded zero to the last few points to generate a modified CIR. The reciprocal of the frequency-domain modified CIR is determined to be an initial value of the frequency-domain TEQ impulse response. The initial value of the frequency-domain target impulse response is determined by multiplying the determined frequency-domain. TEQ impulse response with the frequency-domain of the CIR. The stepsize control method configures the stepsize coefficient as a time-varying coefficient during the whole adapting TEQ algorithm. It is smaller value at an early stage to prevent from divergence and becomes larger at a late adapting stage to prevent from slow convergence.

An apparatus for noise mitigation in a multi-carrier communication system includes a filter to receive a signal from an analog front end, a time-domain equalizer (TEQ) coupled with the filter, a fast Fourier transform (FFT) module, a frequency-domain equalizer (FEQ) coupled with the FFT module, a slicer to serve as a decision device, and a controller to calculate a power of signal at at least one of an input of the filter, an input of the TEQ, an output of the TEQ, an output of the FFT module, an output of the FEQ or an output of the slicer and compare at least one of the power of the at least one signal with a respective threshold so as to determine whether impulse noise occurs, wherein the controller is configured to disable adaptation of system parameters in at least one of the FEQ, a phase-lock loop (PLL) or a digital echo canceller (DEC) when impulse noise is detected.

An OFDM system generates a channel estimate in the time domain for use in either a frequency domain equalizer or in a time domain equalizer. Preferably channel estimation is accomplished in the time domain using a locally generated reference signal. The channel estimator generates an initial estimate from a cross correlation between the time domain reference signal and an input signal input to the receiver and generates at least one successive channel estimate. Preferably the successive channel estimate is determined by vector addition (or subtraction) to the initial channel estimate. The at least one successive channel estimate reduces the minimum mean square error of the estimate with respect to a received signal.

The related time-domain adaptive equalizer with overlay structure overlays the backward part of forward feedback filter to the some taps of feedback filter on time domain to eliminate the strong multi-path signal. This invention improves equalizer performance to anti strong multi-path signal as well as its convergence speed.

Channel equalizer of VSB modulation system in a digital TV receiver, including a frequency domain equalizer for equalizing a received signal to remove a distorted component from the received signal, a noise removing part for removing noise from the equalized signal, a time domain equalizer for equalizing a signal from the frequency domain equalizer or the noise removing part to remove a distorted component from the signal, and an error providing part for estimating an error required for renewal of a coefficient at the time domain equalizer by using a signal from the time domain equalizer or the noise removing part, and feeding the error back to the time domain equalizer.

The present invention provides for a method and system to implement time-domain equalizer (TEQ) training to shorten the channel impulse response of twisted copper lines for DMT-based VDSL systems. The coefficients of TEQ are trained when training signal has cyclic extension (CE), such as specified in current VDSL standard and proposed for VDSL2. The invention effects frame alignment and removal of CE to effectively permit implementation of TEQ training for VDSL where the training signal has cyclic extension. The advantage of this new invent is that Intersymbol interference (ISI) can be reduced in the current VDSL systems and FFT (Fast Fourier Transform) can be applied in place of presently used DFT (Direct Fourier Transform) for TEQ training. Use of the present invention in effectively implementing TEQ training in systems having cyclic extension results in reduced complexity, power saving, reduced memory requirements in terms of code space, and cost savings

The 60 GHz channel between the transmitter and receiver can have AWGN characteristics allowing a Time Domain Equalizer (TDE) to be used at the receiver instead of a Frequency Domain Equalizer (FDE). The complexity of performing matrix inversion on a received signal is reduced when directional antennas are used in a 60 GHz system. Incorporating the TDE in place of the FDE saves almost an order of magnitude in power dissipation. For portable units, such a savings is beneficial since the battery life can be extended. The signal quality of wireless channel is based on the characteristics of the received signal to switch the equalization operation from a system performing FDE to TDE and vice versa. The receiver adapts to the received signal to reduce the power dissipation of the system.

A system, device, and method for time-domain equalizer training uses a two-pass auto-regressive moving average model. A communication channel is first modeled using p1 poles and q1 zeros to form a first shortened channel impulse response having a first approximation H1(z)=B1(z) / 1+A1(z), wherein q1, is greater than a predetermined cyclic prefix length. A time-mirrored image of the first shortened channel impulse response is then formed, and the resulting time-mirrored image of the first shortened channel impulse response is modeled using p2 poles and q2 zeros to form a second shortened channel impulse response having a second approximation H2(z)=B2(z) / 1+A2(z), wherein q2 is less than or equal to the predetermined cyclic prefix length. The time-domain equalizer coefficients are determined by combining A1(z) and A2(1 / z) with an appropriate amount of delay.

The related time-domain adaptive equalizer with virtual center improves the capacity anti channel Doppler effect. Unlike to prior art, though also locating in TIR, this virtual center does not match to the main path signal with strongest amplitude while keeps initial parameters same as other taps in some range. This invention needs no switch between main and auxiliary paths, and can stabilize tap coefficient on dynamic channel.

A novel structure for the TEQ in a DMT system receiver to shorten the length of the effective channel impulse response is provided. A time-domain equalizer, based on the decision-feedback filter structure, along with a training method is disclosed. In accordance with the DFE-based TEQ in the DMT system, the data symbols that transmitted through the effective shortened channel would be more reliable.

A method and apparatus for efficient filter structure for an enhanced operation of an ADSL-DMT modem on a subscriber loop with an environment consisting of ISDN interference. The method performs equalization of the channel by impulse response shortening and at the same time rejecting interference signals exhibiting cyclostationary properties. The method and apparatus for reducing the crosstalk involves a frequency-shifted versions of the received signal being filtered through frequency-shifted adaptive filters in the appropriate branches, and providing a joint time domain equalizer / crosstalk canceller to perform equalization of the channel and crosstalk cancellation in one instance and a separate crosstalk canceller to cancel crosstalk plus a time domain equalizer to equalize the channel. Downsampling the signal outputs of both the combined crosstalk equalizer and the frequency-shifted adaptive filters to reduce sampling rate; and subtracting the outputs of the combined crosstalk equalizer and the frequency-shifted adaptive filters to remove the cyclostationary interferer.

A system for processing radio frequency (RF) signals includes a searcher and a plurality of Cluster Path Processor (CPPs). The searcher detects a maximum signal energy level and position of at least one of a plurality of individual distinct path signals in a signal cluster of a first information signal, wherein at least a portion of the plurality of individual distinct path signals is received within a duration of a corresponding delay spread. The sampling position is used as a starting sampling location by the plurality of CPPs, including a first information signal CPP and a second information signal CPP. Fine sampling positions of the plurality of CPPs are based upon channel energy estimates for the plurality of individual distinct path signals. CPP outputs are employed to produce channel estimates, which are themselves used in subsequent equalization operations. Sampling positions may change over time in order to satisfy alignment criteria.

A method for forming a non-iterative time-domain equalizer (TEQ) and apparatus corresponding thereto. A channel response H(z) is followed by a TEQ response A(z) and a residual output B(z) is chosen so that its degree is less than a cyclic prefix. An error signal is formed so that E(z)=H(z)A(z)−B(z). With a unit input, the error signal is set to zero and B(z)=H(z)A(z). Each signal is expressed as a polynomial, having varying degrees, and a having corresponding coefficients. Once expanded, the coefficients of similar degree can be equated on both sides of the equation. The error signal can then be determined in terms of coefficients corresponding to the TEQ and the residual signal. The coefficients of the channel response can be derived from the channel training estimates. The error signal is minimized and the result is solved for in terms of the desired TEQ coefficients.

Various systems and methods are described for performing fractionally spaced time domain equalization (TEQ). One embodiment is a method implemented in a communication system for training a fractionally spaced time domain equalizer (TEQ). The method comprises performing an initialization phase, averaging a received signal in the system to reduce effects of noise in a channel, determining a channel estimate, and aligning an ideal reference signal with the received signal. The method further comprises updating a target response filter according to a non-integer multiple of a base sampling rate, determining an adaptation error based on useful information both inside and outside a Nyquist band of the TEQ, and updating the TEQ according to the adaptation error.

Techniques are disclosed related to calibrating and operating a multiple input multiple output (MIMO) radio system. In some embodiments, a dual mode calibration may be employed to calibrate a remote transmitter (RT). During a first, Sparse Full System Calibration (SFSC) mode, the RT may be physically connected to the MIMO radio system. In some embodiments, first and second equalizers may be derived for each of the RT and a local transmitter (LT), respectively. During a subsequent, Real-time Calibration (RTC) mode, the RT may be located remotely from the MIMO radio system, and the RT may be configured to communicate with the MIMO radio system over the air via an antenna. In the RTC mode, third equalizers may be derived for the LT. The RT may then be calibrated based on an equalizer that is derived from each of the first, second, and third equalizers. As one non-limiting example, the techniques described herein may enable real-time calibration for the RT even while the RT is located remotely from the MIMO radio system. In different embodiments, the calibration may be achieved by deriving either fractionally spaced frequency domain equalizers, or time domain equalizers.