621results about "Demodulator for amplitude-modulated oscillations" patented technology

An apparatus and method for adaptive broadcast transmission. A broadcast transmission can be received. Insufficiency of a broadcast channel quality can be determined. A negative acknowledgement signal can be sent on a common uplink channel in response to determining the broadcast channel quality is insufficient. The negative acknowledgement signal can be received on the common uplink channel at another location, the negative acknowledgement signal indicating broadcast channel quality is insufficient. The broadcast channel quality can be adjusted in response to receiving the negative acknowledgement signal.

This invention describes a wireless system comprising a plurality of transmitters and receivers, wherein each transmitter has between 1 and n antennas and each receiver has between 1 and m antennas wherein one of said transmitter is arranged to transmit to one of the receivers, said one transmitter is controlled in dependence on at least one of at least one parameter of said transmitters, at least one parameter of said receiver, and at least one parameter of a wireless environment between said transmitter and said receiver.

A method is provided for an equalization strategy for compensating channel distortions in a dual-polarization optical transport system wherein the received signal includes a complex signal of a first transmitted polarization component and a complex signal of a second transmitted polarization component. In a first step, a blind self-recovery mode used a blind adaptation algorithm in calculating and modifying multiple complex equalizer transfer function coefficients to enable recovery of only the complex signal of the first transmitted polarization component. By recovering only a single polarization component in the first step the degenerate case of recovering only a single transmitted signal at both polarization component outputs of an equalizer is prevented. In a second step, equalization is performed in a training mode for calculating and modifying the multiple complex equalizer transfer function coefficients to enable recovery of the complex signals of the first and second transmitted polarization components. In a third step, equalization is performed in a data directed mode for continuing to calculate and modify the multiple complex equalizer transfer function coefficients to ensure continued recovery of the complex signals of the first and second transmitted polarization components. The method is suited for a digital signal processing implementation in a coherent receiver when a modulation scheme used on a transmitted signal is quadriphase-shift keying (QPSK). In other embodiments, the method can be used with modulation schemes such as binary PSK, M-ary PSK where M>4, or Quadrature Amplitude Modulation (QAM).

A beam formation circuit and an apparatus and a method of receiving radio frequency signals making use of a smart antenna are described in which the amount of computation tasks required for the weight calculation is significantly reduced. In realizing the directivity of the smart antenna, the output signals corresponding to a plurality of sub-carriers are weighted with a common antenna weight for each of the antenna elements.

A Fiber-wireless uplink consists of a wireless channel followed by a radio-over-fiber (ROF) link. Typically, nonlinear distortion of the ROF link is the major concern when the radio frequency is only a few GHz. This especially severe in the uplink, because of the multipath fading of the wireless channel. A Hammerstein type decision feedback equalizer is described for the fiber wireless uplink, that compensates for nonlinear distortion of the ROF link as well as linear dispersion of the wireless channel. Since the linear and nonlinear parts of the receiver are separated, tracking the fast changing wireless channel is virtually independent of compensating for the relatively static nonlinearity. Analytical results show that the receiver provides excellent compensation with notably less complexity.

A digital signal demodulator digitizes an OFDM signal at a sampling frequency from a sampling oscillator to produce a digital OFDM signal. The digital OFDM signal is converted into I and Q components using a carrier frequency from a carrier oscillator. The IQ components are transformed into digital complex symbols, and pilot signals are extracted from the complex symbols. A processor calculates an inter-symbol difference of phase differences between pilot signals to control the sampling oscillator to correct the sampling frequency; calculates an inter-symbol difference for one of the pilot signals to control the carrier oscillator to correct the carrier frequency; and calculates a phase angle for one of the subcarriers at a frequency in the middle of the plurality of subcarriers for the OFDM signal to control the carrier oscillator to correct the carrier frequency phase.

A receiver circuit has an equalizer that equalizes a received signal propagating through a transmission medium; a data detection circuit that detects an analog output signal of the equalizer at a data sample timing and outputs a digital signal; an intersymbol interference detection circuit that detects an intersymbol interference level from the analog output signal of the equalizer at the data sample timing and from the digital signal of the data detection circuit; and an equalization characteristic control unit that controls the characteristic of the equalizer to minimize the detected intersymbol interference level. The receiver circuit further has a data sample timing control unit in which the data sample timing is controlled to a sample timing at which the difference between the amplitude of the analog output waveform of the equalizer with respect to an impulse and the amplitude of an ideal impulse response waveform is minimal.

A data reception apparatus and method for generating and transmitting feedback information in a multi-antenna system using grouped antennas, and a data transmission apparatus and method for transmitting a data stream of a user according to a transmission mode selected depending on the feedback information is disclosed. The reception apparatus generates feedback information depending on maximum channel quality information, an antenna group index associated with the maximum channel quality information, rank information, and remaining channel quality information associated with the rank information, and transmits the feedback information to the transmission apparatus. The transmission apparatus selects one of a multi-user mode and a single-user mode as a transmission mode depending on the feedback information and transmits a data stream of a user via multiple antenna groups or one antenna group, according to the selected transmission mode.

A radio communications receiver which detects radio signals and recovers data representative of the radio signals in a presence of contemporaneously detected interfering signals, the radio communications receiver having a detector that detects said radio signals and generates digital base band signals representative of the radio signals, a matrix former that forms a correlation matrix having rows and columns from the base band signals, and a data processor that generates a factor matrix of the correlation matrix, the factor matrix having rows and columns, and recovers data from the factor matrix. The data processor generates the factor matrix by calculating first elements of the factor matrix from the correlation matrix using a factorization algorithm in accordance with a pre-determined structure of the factor matrix, and forming second elements of the factor matrix by selectively copying first elements in accordance with the pre-determined structure.

The method is for estimating the fading coefficients of a plurality of transmission channels on which signals to be sent, generated as a function of a sequence of symbols, are transmitted according to a particular modulation, e.g. AM-PSK modulation. The fading coefficients are estimated by using estimations of the transmitted symbols obtained in advance, thus obtaining DC components of the received signal by coherent demodulation locked to the phases of the transmitted AM-PSK signals, and processing these DC components. The method may not require the choice of a stochastic distribution model of the channel fading, thus it remains efficient even when the channel characteristics vary significantly. Moreover, the method works correctly even if the received stream is disturbed by inter-symbolic interference (ISI) and / or by multi-path fading.

In an Orthogonal Frequency Division Multiplexing communication system, a user equipment reports channel quality information that is sufficient to construct a fading profile of a frequency bandwidth and that does not consuming the overhead resulting from the reporting of CQI for every sub-band of the frequency bandwidth. In the communication system, the frequency bandwidth may be represented by multiple sub-band levels, wherein each sub-band level comprises a division of the frequency bandwidth into a number of sub-bands different from the number of sub-bands of the other sub-band levels. The user equipment measures a channel quality associated with each sub-band of a sub-band level of the multiple sub-band levels, selects a sub-band of the sub-band level based on the measured channel qualities, and reports channel quality information associated with the selected sub-band to a radio access network.

An iterative method (400) and apparatus (200) for a receiver for reducing interference in a desired signal in a GSM communication system uses a finite-impulse-response filter combined with alternate quadrature component output selection for alternate linear equalization are disclosed The method includes inputting a burst of data of a received waveform including interference, training an alternate linear output filter with a midamble of known quadrature phase, providing an estimate of the desired signal by operating on the received waveform with the finite-impulse-response filter, generating log likelihood ratio estimates for a plurality of bits in the burst of data, selecting bits from the burst of data base upon a predetermined condition, and re-training the alternate linear output filter to provide a second improved estimate of the desired signal.

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 system comprises a wireless device that communicates across a spectrum having a plurality of sub-channels. The wireless device comprises a plurality of antennas through which the wireless device communicates with another wireless device, wherein each antenna communicates with the other wireless device via an associated communication pathway. The wireless device further comprises sub-channel power analysis logic coupled to the antennas and adapted to determine which communication pathway has the highest communication quality on a sub-channel by sub-channel basis. The wireless device still further comprises diversity selection logic coupled to the sub-channel power analysis logic and adapted to determine a weighting vector for an associated antenna based on the communication quality, wherein the weighting vector specifies a relative transmission power for each sub-channel for the associated antenna.

A method and system thereof for determining feedback for iterative channel estimation based on the summation of soft output decisions or Bit Error Rate (BER) derived from the output of an equalizer. The channel impulse response initially obtained according to a training sequence is used to estimate the received signal, and output hard values. The BER of the training sequence is calculated and judged, and if the BER is too high, the channel is estimated again according to the feedback until the BER satisfies a predetermined value. If the BER is still unsatisfactory after a predetermined number of trials, the channel is assumed to be an authentic bad channel, thus terminating the feedback procedure. If the equalizer is capable of outputting soft output decision, the summation of soft outputs is used instead of BER to determine whether feedback is appropriate.

A Signal Conditioning Filter (SCF) and a Signal Integrity Unit (SIU) address the coupled problem of equalization and noise filtering in order to improve signal fidelity for decoding. Specifically, a received signal can be filtered in a manner to optimize the signal fidelity even in the presence of both significant (large magnitudes of) ISI and noise. The present invention can provide an adaptive method that continuously monitors a signal fidelity measure. Monitoring the fidelity of a multilevel signal can be performed by external means such as by the SIU. A received signal y(t) can be “conditioned” by application of a filter with an electronically adjustable impulse response g(t). A resulting output z(t) can then be interrogated to characterize the quality of the conditioned signal. This fidelity measure q(t) can be used to adjust the filter response to maximize the fidelity measure of the conditioned signal.

The invention relates to a method and a system for estimating a symbol time error in a broadband transmission system, comprising: determination a timing error signal of an input-signal of a discrete Fourier-transformation block (5) in a data symbol stream on the basis of intersymbol correlation using a predetermined period in each received symbol, selecting as a predetermined period a number of samples of different useful data parts of a symbol, determining the time error value (ε) based on the intersymbol interference of the selected samples of the different parts of said symbol.

A method to efficiently deal with FEXT crosstalk in wireline communication system via MIMO equalization is presented. A MIMO-DFE based receiver architecture is developed to demonstrate the advantage over the traditional receiver design. A MIMO structure for systems with TH precoding is also developed for 10GBASE-T application. The proposed architecture overcomes the limitation of the traditional schemes and achieves a better SNR performance and lower receiver complexity. The proposed method relies on the fact that FEXT inherently contains information about the symbols transmitted from the three far end transmitters and it can be viewed as a signal rather than noise. Therefore, MIMO techniques are applied to turn FEXT into a benefit for the receiver design.

Techniques are disclosed that efficiently obtain channel crosstalk estimates in DSL systems and other communication systems that may include unsynchronized channels. For example, a method includes obtaining a first set of estimated measures of crosstalk for a first portion of a plurality of communication channels over which data signals are to be transmitted from a transmitter to a plurality of receivers, and interpolating a second set of estimated measures of crosstalk for a second portion of the plurality of communication channels based on the first set of estimated measures of crosstalk. The first portion of the plurality of communication channels may be a subset of the plurality of communication channels and the second portion of the plurality of communication channels is a remainder of the plurality of communication channels. Each estimated measure of crosstalk may relate to at least one tone associated with at least one of the plurality of communication channels.

The present invention relates to improved multiple access communications. In one form, the invention relates to an improved signal processing method and apparatus for an iterative method of determining the reception of a signal in a multi user packet based wireless OFDM (Orthogonal Frequency Division Multiplexing) communication system. In other forms the present invention provides recursive filtering for joint iterative decoding in a variety of systems and functions such as linear multiple access channel decoders, iterative equalisation, iterative joint channel estimation and detection / decoding, iterative space-time processing, iterative multi user interference cancellation and iterative demodulation. In one particular form the present invention provides an iterative decoding circuit for a wireless multiuser communications receiver comprising a first signal processing means for receiving at least one received signal, said first signal processing means comprising at least two linear iterative filters such that the first linear iterative filter provides an estimate of a selected received signal to an estimated signal output and a second linear iterative filter provides estimates of at least one other received signal, delayed by one iteration cycle, to an input of said first linear iterative filter, a second signal processing means for receiving the estimated signal output of the first linear iterative filter and providing a further received signal estimate to the input of the first signal processing means in a succeeding iteration cycle of the decoding circuit.

In a wireless system including a wireless communication channel, a method for estimating a signal quality of a received signal includes the steps of receiving a signal from the wireless communication channel, the received signal including at least one field that is modulated and encoded in a substantially fixed manner, and generating at least one reference field based, at least in part, on the at least one field and on a channel estimation signal. The channel estimation signal is representative of at least one characteristic of the wireless communication channel. The method further includes the step of generating a signal quality estimate as a function of the at least one field in the received signal and the generated at least one reference field.

Operational data is utilized to determine the FEXT interference induced by one line into the other DSL line. FEXT interference can be calculated using the NEXT interference measured between the two lines at the upstream ends of the loops and the downstream channel transfer function of one of the loops. Because the NEXT and transfer function constitute a linear time-invariant system, as does the FEXT interference between the lines, the NEXT interference and line transfer function can be multiplied (if in linear format) or added (if in logarithmic format) to approximate the FEXT interference between the lines. The collection of data, calculations and other functions performed in these techniques may be performed by a system controller, such as a DSL optimizer. An Xlog(u,n) quantity is a decibel-magnitude representation of the insertion-loss equivalent of FEXT transfer functions and is defined as the ratio of (1) a line u's source power into a matched load of 100 Ohms when no binder is present to (2) the power at the output of the subject line when line u is excited with the same source and the binder is present. Xlin(u,n) is the linear equivalent of Xlog(u,n). The Xlog(u,n) and Xlin(u,n) quantities may be represented in specific formats that assist in their use in DSL and other systems. When defined as a line's insertion loss, Xlin (or equivalently Xlog) does not include the effect of any transmit filter.

An OFDM receiver receives an OFDM signal transmitted from an OFDM transmitter by using a sub-carrier. The OFDM receiver includes a channel estimator configured to obtain a channel estimated value of each multi-path based on OFDM signals received through a plurality of multi-paths; a transmission signal estimated value calculator configured to calculate a transmission signal estimated value as an estimated value of the OFDM signal; and an inter-carrier interference compensator configured to extract a multi-path not becoming a form to contain a signal component only of a target symbol in an FFT window based on the transmission signal estimated value and the channel estimated value of each multi-path, and to compensate for inter-carrier interference in the OFDM signal based on signal components corresponding to all sub-carriers of the multi-paths.

A super-regenerative receiver uses controlled Q-quenching and may limit the resonant tank circuit amplitude by loading the tank circuit as soon as regenerative oscillation is detected. An amplitude detector is coupled to the regenerative amplifier and controls a Q loading circuit coupled to the tank circuit of the regenerative amplifier. The amplitude detector turns on the Q loading circuit which then stops the regenerative amplifier from oscillating, and the Q-loading remains on for a brief time to insure that the regenerative amplifier has stopped oscillating. After the brief time, the Q loading circuit is turned off and the regenerative amplifier goes into oscillation again. This cycle repeats controllably over and over, resulting in a lower self-induced noise floor and improved received signal sensitivity. The super-regenerative receiver may be used in the very low frequency (VLF), low frequency (LF), medium frequency (MF), high frequency (HF), very high frequency (VHF) and super high frequency (SHF) ranges to receive continuous wave (CW), amplitude modulated (AM) and frequency modulated (FM) radio signals.

A novel method and apparatus is disclosed, that embeds with, or otherwise makes available to an adaptive equalizer, suitable for use in IEEE 10G-LRM standard compliant receivers, digital logic that monitors some of the Layer 1 and preferably some of the Layer 2 processing that typically occurs after the equalization step during decoding and processing of the record data stream. From this additional logic information, the equalizer is able to make a much more accurate prediction of equalizer convergence by counting processing errors and prove convergence by calculation of BER. The novel method and apparatus are applicable to ASIC embodiments and the complexity of the logic information obtained can be programmably scaled back or enhanced as appropriate in light of the particular communication environment.

Systems and methods for analyzing the jitter content of an oversampled digital communication signal are disclosed. Advantageously, the communication signal can correspond to an arbitrary data sequence, rather than only to a repeating test sequence. For example, the systems and methods can be embodied in test equipment and in simulation equipment as design tools and / or validation tools. The systems and methods disclosed advantageously facilitate the decomposition and quantification of the main jitter components (random and deterministic), as well as its various subcomponents (periodic jitter, data-dependent jitter, inter-symbol interference, device-state-dependent jitter, other bounded uncorrelated jitter, and data-dependent-random jitter).

The method is for estimating the fading coefficients of a plurality of transmission channels on which signals to be sent, generated as a function of a sequence of symbols, are transmitted according to a particular modulation, e.g. AM-PSK modulation. The fading coefficients are estimated by using estimations of the transmitted symbols obtained in advance, thus obtaining DC components of the received signal by coherent demodulation locked to the phases of the transmitted AM-PSK signals, and processing these DC components. The method may not require the choice of a stochastic distribution model of the channel fading, thus it remains efficient even when the channel characteristics vary significantly. Moreover, the method works correctly even if the received stream is disturbed by inter-symbolic interference (ISI) and / or by multi-path fading.

Methods and apparatus for implementing a wireless communication transceiver having receive path performance diversity. The transceiver implements a plurality of signal paths that can be configured as space diversity receive paths. Each of the plurality of signal paths includes a distinct RF filter. Each RF filter can be configured to provide a distinct frequency response, and in particular, a distinct jammer rejection profile. One of the RF filters can be configured to provide substantially no in-band jammer rejection. Each additional distinct RF filter can be configured to reject at least one distinct in-band jammer frequency or band of frequencies. A diversity receiver coherently combines the path performance diverse signals from each filter output. A transmitter can time division duplex transmit communications over at least a subset of the signal paths and their associated RF filters.