428 results about "Adaptive equalizer" patented technology

A DTV signal has a plural-data-segment frame header including complementary first and second ghost-cancellation reference signals differentially delayed by the duration of two NTSC horizontal scan lines. A receiver for such DTV signal has an adaptive equalizer for baseband symbol code with kernel weights calculated by a computer operative on the equalizer response after comb filtering. The comb filter combines the equalizer response as differentially delayed by the duration of two NTSC horizontal scan lines to cancel artifacts of co-channel NTSC interference in the comb filtered equalizer response supplied to the computer. This reduces the undesirable influence of such artifacts on equalization to reduce intersymbol interference.

In accordance with the teachings described herein, systems and methods are provided for a precision adaptive equalizer. A variable gain equalizer may be used to apply a variable gain to an input signal to generate an equalized output signal. A phase and pattern detector circuit may be coupled in a feedback loop with the variable gain equalizer. The phase and pattern detector circuit may be used to identify a high frequency data pattern in the equalized output signal and compare the high frequency data pattern with a clock signal to detect a high frequency phase error. The phase and pattern detector circuit may be further operable to generate an automatic gain control signal as a function of the high frequency phase error, the automatic gain control signal being fed back to the variable gain equalizer to control the variable gain applied to the input signal.

A communication system and method for extending coverage of a base transceiver station. The communication system includes processing circuitry that receives a communication signal over a wireless channel. The received communication signal is processed through an adaptable equalizer to reduce noise, distortion, interference, and frequency errors. In another aspect of the invention, a frequency of a reference signal in the communication system is adjusted to compensate for frequency errors between the communication system and the source of the communication signal. The equalized and frequency adjusted communication signal is then retransmitted into an extended coverage area. Wireless coverage is thereby provided between a base transceiver station and a mobile device in the extended coverage area.

Adaptive equalization methods and adaptive equalizers used with precoded systems dominated by intersymbol interference (ISI) monitor the output of a DFE and compare it to a reference for updating a precoder in response to the comparison. To accomplish this, an adaptive equalizer includes a feed forward equalizer receiving a signal from a communication channel, the feed forward equalizer equalizing variations in pre-cursor intersymbol interference resulting from changes in characteristics of the channel and providing an output signal to an error correction decoder, a decision circuit, coupled to the feed forward equalizer, for generating error vectors in response to the output signal of the feed forward equalizer and a decision feedback equalizer, coupled to the decision circuit, the decision feedback equalizer monitoring the pre-cursor intersymbol interference of the channel, determining when the transmitter coefficients to the precoder warrant updating, and generating a signal indicating that an update to the transmitter coefficients to the precoder is warranted. The adaptive equalizer farther includes a comparison circuit, the comparison circuit receiving an output from the decision feedback equalizer and comparing the output from the decision feedback equalizer to a reference, the comparison circuit generating the signal indicating that an update to the transmitter coefficients to the precoder is warranted in response to the comparison.

A linear compensation system of a digital TV relay or other apparatus preferably includes a transmitting unit configured to modulate a data to an intermediate frequency (IF) signal, up convert the IF signal to an RF signal, and amplify the RF signal to a predetermined level using a high power amplifier (HPA). The system also includes a linear compensation unit to preferably directly vary a step size of an adaptive equalizer according to whether a signal-to-noise ratio (SNR) or an error vector magnitude (EVM) for an output signal of the HPA satisfies an advanced television systems committee (ATSC) or other standard. The linear compensation unit is thus configured to output an improved linear compensation coefficient to a modulator of the transmitting unit.

A training circuit for training a tap coefficient of an adaptive equalizer that performs error calculations in a training process and updating of the tap coefficient in a time area and thereby makes the tap coefficient converge stably in a short time.

There is provided an apparatus and method for initializing a tap coefficient of an adaptive equalizer constituting a read path for a storage medium, where the apparatus includes an FIR filter, a Viterbi decoder, a level error detector, and a tap coefficient updater, the FIR filter receives a first signal stream and outputs the first signal stream in the form of a second signal stream, the Viterbi decoder corrects a bit error of the second signal stream, the level error detector detects a level error between the second signal stream and a third signal stream that is an ideal output signal corresponding to the second signal stream, the tap coefficient updater selects a tap coefficient minimizing the level error and provides the selected tap coefficient as a tap coefficient of the FIR filter, the tap coefficient minimizing the level error is determined as an initial value in a system initialization mode, and the determined initial value is used as an initial value of the tap coefficient of the FIR filter in a normal operation mode.

A radio receiver (100) has an equalizer (500) that operates in the time domain to remove residual interference that is not removed by an IF filter (200) operating in the frequency domain that is caused by an adjacent interfering FM station. The equalizer (500) includes a modified constant modulus algorithm (CMA) to generate a tap update signal from the output of the equalizer (500). The equalizer (500) uses the modified CMA to reduce an amplitude fluctuation of the received signal caused by the adjacent interfering station. The CMA is modified to use an infinite impulse response (IIR) filter (540) to generate the tap update. The IIR filter (540) also speeds up a convergence of the modified CMA to provide better performance.

A method for an adaptive equalization apparatus in a multiple-link hopping radio system includes hopping among a plurality of radio links to receive variable-length bursts of radio signals on the plurality of radio links and equalizing amplitude and phase variations of a slow channel for each radio link from a received burst on the radio link. Further, the method includes storing the estimated tap coefficients pertinent to each radio link and using the tap weights of the current burst of the radio link to reliably pre-compensate the channel amplitude and phase distortion of a next received burst on the radio link.

An adaptive equalizer system for use in a serial communication link uses timing information generated by a phase detector of a clock and data recovery circuit of the serial communication link and a frequency pattern of the recovered data to determine whether the data received over the serial communication link is over-equalized or under-equalized. The equalizer strength of the adaptive equalizer system is adjusted based on such determination.

A method and apparatus for data communication in an oil well environment, wherein the method comprises detecting an acoustic signal transmitted along an acoustic channel, the acoustic signal being distorted from transmission through the acoustic channel, generating a transmitted data signal in response to the acoustic signal, inputting the transmitted data signal to an adaptive equalizer and adaptively equalizing the transmitted data signal to produce an equalized data signal related to the transmitted data signal by a mathematical function. The detecting step may include positioning an acoustic receiver in a communication unit along the acoustic channel. The communication unit may be positioned downhole and the adaptive equalizer may be positioned remotely relative to the communication unit or may be placed in the communication unit. The adaptive equalizer may be a frequency domain filter, a neural net adaptive equalizer or a nonlinear recurrent neural net equalizer. The acoustic signal may comprise a plurality of discrete transmissions which may be a training sequence for training the adaptive equalizer and may comprise a first discrete transmission transmitted repeatedly.The method of data communication in an oil well environment may comprise the steps of transmitting an acoustic signal from a first location along an acoustic channel, detecting the acoustic signal at a second location along the acoustic channel, generating a transmitted data signal in response to the acoustic signal, inputting the transmitted data signal to an adaptive equalizer and adaptively equalizing the transmitted data signal to produce an equalized data signal related to the transmitted data signal by a mathematical function. The transmitting step may further comprise positioning an acoustic transmitter in a first communication unit along the acoustic channel downhole or elsewhere. The method may further comprise acquiring data, generating an original data signal in response to the acquired data and inputting the original data signal to the acoustic transmitter. The acoustic signal may comprise a series of acoustic training signals for training the adaptive equalizer. The acoustic training signals may be transmitted at a predetermined time. A stored training signal may include a series of stored training data signals corresponding to the series of acoustic training signals. At least a portion of the stored training signals may be cross-correlated to the transmitted data signal. The acoustic signal may comprise a notification signal for notifying the adaptive equalizer of a training session.

An RF transmitter (10) includes a nonlinear predistorter (24). The nonlinear predistorter (24) is implemented using adaptive equalizers (30′, 30″). A feedback signal (20) is developed by downconverting an RF communication signal (16). The feedback signal (20) is used in driving tap coefficients (34) for the adaptive equalizers (30′, 30″). The adaptive equalizers (30′, 30″) filter higher-ordered basis function signals (47′, 47″) generated from an excursion signal 13. The excursion signal 13 exhibits the same phase as a baseline communication signal (12) but has a magnitude that is reduced by a nonlinear threshold (100) when the baseline communication signal (12) exceeds the nonlinear threshold (100) and has a magnitude of zero at other times. The tap coefficients (34) may be formed from proto-coefficients (168) in response to the magnitude of the corresponding portion of the signal being filtered in the adaptive equalizers (30′, 30″).

A receiver for an optical transmission system, has a polarization diverse and phase diverse coherent optical receiver, and a digital adaptive equalizer for compensating for distortions in the optical signal introduced by the optical path. The entire field of the optical signal is mapped including phase and polarization information, to enable more complete compensation for impairments such as chromatic dispersion and PMD. Furthermore, it can also reduce the problems which have so far held back coherent optical detection from widespread implementation, such as polarization alignment and phase tracking. This can be applied to upgrade existing installed transmission routes to increase capacity without the expense of replacing the old fiber.

An equalization circuit is disclosed that enables high data rate transmission over high loss communications channels. Also disclosed is a set of functional blocks and update criteria that allow for the equalization function to be adapted for a large variety of different communications channels. A fully continuous adaptive equalizer is used in conjunction with a Decision Feedback Equalizer to fully equalize a wide range of communications channels. Interoperability and Bit Error Rate performance are optimized through compensation of pre-cursor inter-symbol interference, which is performed adaptively in the receiver as opposed to the transmitter.

In a QAM demodulator including an adaptive equalizer, a method of carrier tracking comprising the following steps is disclosed: (A) sampling a QAM signal received from a transmission channel; (B) recovering a symbol clock function from the sampled QAM signal; (C) applying the sampled QAM signal to the adaptive equalizer in order to obtain a QAM equalized signal in a Blind Equalization (BE) mode; (D) using a slicer to locate a nearest plant point for the QAM Blind equalized signal for each recovered symbol clock; (E) using a complex conjugate multiplier to obtain an instantaneous inphase component and an instantaneous quadrature component of a phase angle error signal; (F) using a linear phase detector to obtain an instantaneous phase angle error for each symbol clock; (G) averaging the instantaneous phase angle error signal by using a carrier loop filter; (H) using a complex multiplier to insert an inverse of the averaged phase angle error signal into the QAM Blind equalized signal to compensate for the carrier phase angle error; and (I) repeating the steps (D-H) to close a carrier frequency loop.

Initial values of the tap weights for the taps of a linear equalizer are determined based on a channel impulse response of a channel so that the values corresponding to the weights of the equalizer taps achieve optimum initialization of the equalizer. These values are determined through use of a nested summation where the number of summations is dependent upon the number of multi-paths characterizing the channel.

In a waveform equalizer for a communication apparatus, a magnetic recording apparatus, or an optical recording/reproducing apparatus, a feed-forward filter (FFF) is provided and, at a subsequent stage, a decision feedback equalizer (DFE) or a fixed delay tree search/decision feedback equalizer (FDTS/DFE) employing FDTS for a determination unit is provided. Partial response (PR) is performed on only a first portion of inter-symbol interference (ISI) of a waveform equalized by the FFF and equalization that does not consider subsequent response (i.e., trailing-edge ISI) is performed. A feed-back filter (FBF) generates a response for the trailing-edge ISI and the DFE structure subtracts the generated response from a response provided by the FFF so that a result becomes a partial response.

Adaptive equalizers for a communication channel and corresponding methods of equalizing are described. The adaptive equalizer includes: a fixed pre-filter configured to be coupled to a received signal and provide a pre-filter signal; an adaptive filter coupled to and configured to compensate the pre-filter signal for changes in phase and amplitude; and an interference remover coupled to the adaptive filter and configured to reduce interference in the received signal.

A network receiver is configured for receiving a modulated carrier signal representing a data frame from a network transmitter via a network medium, the receiver includes an adaptive equalizer with a finite impulse response filter for filtering the received signal. The filter utilizes a plurality filter coefficients. A cache stores a plurality of sets of coefficients for use by the filter and the equalizer selects a set of coefficients for receiving the data frame.