Abstract: A system and method for frequency-selective demodulation is presented. An input signal is received that is modulated by frequency shift keying (FSK) and encodes data at a first and second frequency. The input signal is supplied to a plurality of estimators that include a first estimator configured to detect a first signal at the first frequency, a second estimator configured to detect a second signal at the second frequency, a third estimator configured to detect a third signal at a third frequency, and a fourth estimator configured to detect a fourth signal at a fourth frequency. An output is generated indicating receipt of the data encoded at the first frequency or the second frequency based upon outputs of the first estimator, the second estimator, the third estimator, and the fourth estimator.

Abstract: A system and method for frequency-selective demodulation is presented. An input signal is received that is modulated by frequency shift keying (FSK) and encodes data at a first and second frequency. The input signal is supplied to a plurality of estimators that include a first estimator configured to detect a first signal at the first frequency, a second estimator configured to detect a second signal at the second frequency, a third estimator configured to detect a third signal at a third frequency, and a fourth estimator configured to detect a fourth signal at a fourth frequency. An output is generated indicating receipt of the data encoded at the first frequency or the second frequency based upon outputs of the first estimator, the second estimator, the third estimator, and the fourth estimator.

Abstract: A decision feedback equalizer is operated by making first symbol decisions from an output of the decision feedback equalizer such that the first symbol decisions are characterized by a relatively long processing delay, by making second symbol decisions from the output of the decision feedback equalizer such that the second symbol decisions are characterized by a relatively short processing delay, and by determining tap weights for the decision feedback equalizer based on the first and second symbol decisions. The first symbol decisions may be derived from the output of a long traceback trellis decoder. The second symbol decisions may be derived either from the output of a short traceback trellis decoder or from shorter delay outputs of the long traceback trellis decoder.

Abstract: An output of an equalizer is decoded to produce first decoded data having a first accuracy. The output of the equalizer is further decoded to produce second decoded data having a second accuracy, and the second accuracy is greater than the first accuracy. Tap weights for the equalizer are calculated using the first and second decoded data. The calculated tap weights are applied to the taps of the equalizer.

Abstract: An impulse response is estimated for a channel by estimating an intermediate impulse response of the channel. The intermediate impulse response comprises at least one multipath spike and one or more non-deterministic noise components at locations throughout the channel Then, a threshold function is applied to the estimated intermediate impulse response across at least a portion of the channel in order to provide an estimated final impulse response of the channel. The threshold function has the effect of nulling the noise components of the channel having values less than the threshold function at the location within the channel of the respective noise component, and the threshold function is characterized by a level that varies across the portion of the channel from a minimum value to a maximum value in a manner determined by the location of the at least one multipath spike within the channel.

Abstract: Input data segments of received symbols are continuously stored in a decision feedback equalizer buffer at a symbol rate S. Output data sections of received symbols are supplied from the decision feedback equalizer buffer at an output rate of nS such that void times separate the output data sections, and n>1. The received symbols supplied by the decision feedback equalizer buffer are equalized in a decision feedback equalizer to provide equalized symbols; and the equalized symbols are decoded by a decoder to provide decoded symbols. Adjustments for the decision feedback equalizer are calculated during the void times such that the adjustments are calculated based on both the received symbols supplied by the decision feedback equalizer buffer and the decoded symbols. The adjustments are applied to the decision feedback equalizer.

Abstract: An equalizer system includes an equalizer, first and second decoders, and a tap weight controller. The equalizer equalizes a received signal to provide an equalizer output. The first decoder is characterized by a first parallel output, and the first decoder decodes the equalizer output to provide first symbol decisions having a first accuracy. The second decoder is characterized by a second parallel output, the second decoder receives the first parallel output and decodes the equalizer output to provide second symbol decisions having a second accuracy, the first accuracy is greater than the second accuracy, and the second decoder applies the second parallel output to the equalizer. The tap weight controller determines tap weights based on the first symbol decisions and supplies the tap weights to the equalizer.

Abstract: A channel impulse response is determined from a cross-correlation of a received training sequence and a stored version of the transmitted training sequence. The channel impulse response is iteratively cleansed of noise caused by the finiteness of the cross-correlation. Initial values of the tap weights for the taps of an equalizer such as a decision feedback equalizer may be determined based on the cleansed channel impulse response.

Abstract: An impulse response of a channel is estimated by correlating a received signal with a stored vector. The received signal contains a training sequence having a length Ltr, the stored vector has a length Lsv, Ltr/n=Lsv, and n is greater than two. The signal is received by a device. The vector is determined based on the training sequence and an ideal channel. The ideal channel is an idealized form of a channel through which the device receives the signal. A plurality of correlations may be performed where each correlation provides a substantially noise-free estimate of the impulse response of a different portion of the channel. The correlations are combined to provide an estimate of the impulse response of the channel.

Abstract: An impulse response is estimated for a channel by estimating an intermediate impulse response of the channel. The intermediate impulse response comprises at least one multipath spike and one or more non-deterministic noise components at locations throughout the channel. Then, a threshold function is applied to the estimated intermediate impulse response across at least a portion of the channel in order to provide an estimated final impulse response of the channel. The threshold function has the effect of nulling the noise components of the channel having values less than the threshold function at the location within the channel of the respective noise component, and the threshold function is characterized by a level that varies across the portion of the channel from a minimum value to a maximum value in a manner determined by the location of the at least one multipath spike within the channel.

Abstract: A channel impulse response for a channel is determined by determining an initial channel impulse response estimate based upon a stored training sequence and a received signal, by thresholding the initial channel impulse response estimate, by estimating a noise variance for the channel based upon the stored training sequence, the thresholded initial channel impulse response estimate, and the received signal, by determining an inverse of a covariance matrix based on the estimated noise variance and the thresholded initial channel impulse response estimate, by updating the channel impulse response based on the inverse covariance matrix, the stored training sequence, and the received signal, and by thresholding the updated channel impulse response estimate.

Abstract: The tap weights of an equalizer are initialized in response to a received relatively short training sequence, and new tap weights for the equalizer are thereafter successively calculated in response to relatively long sequences of received symbols and corresponding sequences of decoded symbols. These new tap weights are successively applied to the equalizer.

Abstract: An impulse response of a channel is estimated by cross-correlating a known training signal with a received training signal to produce a cross-correlation vector. The cross-correlation vector is characterized by a known noise component resulting from the finiteness of the correlation. A correction vector is estimated based on the known training signal, where the correction vector is related to the noise component. Truncated representations of the correction vector are iteratively subtracted from the cross-correlation vector in order to produce a succession of cross-correlation outputs of increased accuracy. When the cross-correlation output is sufficiently accurate, it may be used to determine the weights to be given to the taps of an equalizer.

Abstract: A channel impulse response for a channel is determined by determining an initial channel impulse response estimate based upon a stored training sequence and a received signal, by thresholding the initial channel impulse response estimate, by estimating a noise variance for the channel based upon the stored training sequence, the thresholded initial channel impulse response estimate, and the received signal, by determining an inverse of a covariance matrix based on the estimated noise variance and the thresholded initial channel impulse response estimate, by updating the channel impulse response based on the inverse covariance matrix, the stored training sequence, and the received signal, and by thresholding the updated channel impulse response estimate.

Abstract: The tap weights of an equalizer are initialized in response to a received relatively short training sequence, and new tap weights for the equalizer are thereafter successively calculated in response to relatively long sequences of received symbols and corresponding sequences of decoded symbols. These new tap weights are successively applied to the equalizer.

Abstract: An impulse response of a channel is estimated by correlating a received signal with a stored vector. The received signal contains a training sequence having a length Ltr, the stored vector has a length Lsv, Ltr/n=Lsv, and n is greater than two. The signal is received by a device. The vector is determined based on the training sequence and an ideal channel. The ideal channel is an idealized form of a channel through which the device receives the signal. A plurality of correlations may be performed where each correlation provides a substantially noise-free estimate of the impulse response of a different portion of the channel. The correlations are combined to provide an estimate of the impulse response of the channel.

Abstract: An impulse response is estimated for a channel by estimating an intermediate impulse response of the channel. The intermediate impulse response comprises at least one multipath spike and one or more non-deterministic noise components at locations throughout the channel. Then, a threshold function is applied to the estimated intermediate impulse response across at least a portion of the channel in order to provide an estimated final impulse response of the channel. The threshold function has the effect of nulling the noise components of the channel having values less than the threshold function at the location within the channel of the respective noise component, and the threshold function is characterized by a level that varies across the portion of the channel from a minimum value to a maximum value in a manner determined by the location of the at least one multipath spike within the channel.

Abstract: An impulse response of a channel is estimated by cross-correlating a known training signal with a received training signal to produce a cross-correlation vector. The cross-correlation vector is characterized by a known noise component resulting from the finiteness of the correlation. A correction vector is estimated based on the known training signal, where the correction vector is related to the noise component. Truncated representations of the correction vector are iteratively subtracted from the cross-correlation vector in order to produce a succession of cross-correlation outputs of increased accuracy. When the cross-correlation output is sufficiently accurate, it may be used to determine the weights to be given to the taps of an equalizer.