Abstract: A method includes generating a two-dimensionally filtered pilot tone based on a plurality of received pilot tones received using a first subcarrier of each of a plurality of received OFDM symbols and a plurality of data symbols received using a second subcarrier of each of the plurality of received OFDM symbols. The plurality of OFDM symbols is received sequentially over a plurality of OFDM symbol times. The method may include generating inverse channel coefficients based on the two-dimensionally filtered pilot tone. The method may include applying the inverse channel coefficients to a subsequently received OFDM symbol to recover data encoded in the subsequently received OFDM symbol. Generating the two-dimensionally filtered pilot tone may use at least one least-mean-squares filter.

Abstract: A method includes generating a two-dimensionally filtered pilot tone based on a plurality of received pilot tones received using a first subcarrier of each of a plurality of received OFDM symbols and a plurality of data symbols received using a second subcarrier of each of the plurality of received OFDM symbols. The plurality of OFDM symbols is received sequentially over a plurality of OFDM symbol times. The method may include generating inverse channel coefficients based on the two-dimensionally filtered pilot tone. The method may include applying the inverse channel coefficients to a subsequently received OFDM symbol to recover data encoded in the subsequently received OFDM symbol. Generating the two-dimensionally filtered pilot tone may use at least one least-mean-squares filter.

Abstract: An apparatus includes a plurality of delay elements, a plurality of multipliers and an accumulator to form a biquad stage; and a precision logic circuit. The biquad stage includes feedback paths; at least one feedback path has an adjustable bit precision; and the precision logic is adapted to regulate the bit precision of the feedback path(s) based at least in part on at least one parameter that is associated with the biquad stage.

Abstract: An apparatus includes a plurality of delay elements, a plurality of multipliers and an accumulator to form a biquad stage; and a precision logic circuit. The biquad stage includes feedback paths; at least one feedback path has an adjustable bit precision; and the precision logic is adapted to regulate the bit precision of the feedback path(s) based at least in part on at least one parameter that is associated with the biquad stage.

Abstract: We describe and claim a video system and method for automatic size and position adjustment according to the incoming stream. A detection module detects a size and a position of video including an aspect ratio of video on at least one channel of at least one video input source. An execution module adjusts a scale mode responsive to the detection of the size and position or aspect ratio of the video. Once the aspect ratio has been detected and the scale mode adjusted responsive to the detection, video is provided to the display of a display device. The detection and execution modules crop unintentional vertical blanking interval (VBI) lines from upconverted video signals. An on screen display includes a selection for active management that provides for automatic detection of size and position information, or a manual control mode for selection by the user.

Abstract: Method and apparatus for shifting of a lowpass signal to a higher frequency and for precompensating distortion caused by a digital to analog converter (DAC). Higher frequency signals are generated by filtering the output of the DAC so that at least one of the replicas generated by the DAC is the signal of interest. In this manner, the higher frequency signals for wireless transmitters, or for other applications, may be generated more easily. Moreover, compensation for distortion caused by the DAC is performed by a precompensator which modifies for distortion, not at the baseband signal, but at a passband frequency.

Abstract: Method and apparatus for shifting of a lowpass signal to a higher frequency and for precompensating distortion caused by a digital to analog converter (DAC). Higher frequency signals are generated by filtering the output of the DAC so that at least one of the replicas generated by the DAC is the signal of interest. In this manner, the higher frequency signals for wireless transmitters, or for other applications, may be generated more easily. Moreover, compensation for distortion caused by the DAC is performed by a precompensator which modifies for distortion, not at the baseband signal, but at a passband frequency.

Abstract: An apparatus and method for transmitting envelope modulated data signals on a Radio Frequency (RF) carrier system, which produces high error performance through remodulation of the data signals onto an RF carrier are provided. The apparatus includes a transmit chain where, the data signal is input to a mixer to create upper and lower sidebands of the data signal. A low pass filter removes the upper sideband and passes the lower sideband to a frequency modulation (FM) modulator which modulates an RF carrier with the lower sideband. The apparatus also includes a receiver chain that has an FM receiver which receives the FM RF carrier signal transmitted by the transmit chain and recovers the lower sideband, which is then input to a multiplier to again generate upper and lower sideband signals. A bandpass filter removes the lower sideband and passes the upper sideband as a received envelope modulated data signal.

Abstract: An interpolating bandpass filter for packet-data receiver synchronization comprises a single delay line that delays the passband-sampled data from the analog-to-digital converter, and a convolving structure that uses the delay line to implement a L-times oversampling bandpass filter. A separate accumulator accumulates a fractional phase difference that represents the frequency offset between the remote transmitter's frequency and the receiver's sampling frequency. The integer portion of the accumulator is used to determine the number of samples to delay the input of the filter, while the fractional portion is used to choose two coefficient sets closest to the desired delay and to interpolate between these two filter sets.

Abstract: Method and apparatus for shifting of a lowpass signal to a higher frequency and for precompensating distortion caused by a digital to analog converter (DAC). Higher frequency signals are generated by filtering the output of the DAC so that at least one of the replicas generated by the DAC is the signal of interest. In this manner, the higher frequency signals for wireless transmitters, or for other applications, may be generated more easily. Moreover, compensation for distortion caused by the DAC is performed by a precompensator which modifies for distortion, not at the baseband signal, but at a passband frequency.

Abstract: A method and apparatus for estimating the frequency of a periodic signal and for canceling the interference in a modem signal. Power line noise may interfere with electronic signals. Since power lines may be either 50 Hz or 60 Hz, depending on the country, frequency estimation of the periodic power line noise is necessary. Modem signals are received and autocorrelated in order to identify the periodic characteristics of the signal over time. Once the frequency is identified, the power line noise is modeled based on creating a circular buffer. Initially, the circular buffer is composed of scaled samples of one cycle of the fundamental frequency of the power line noise. Thereafter, samples are received, scaled, and combined with previous buffer values in order to update the buffer. In this manner, the buffer models the power line noise, so that the power line noise may be removed from the system.

Abstract: A signal for exception processing is provided. The signal includes a first sequence of PCM codewords. Each PCM codeword in the sequence has a magnitude corresponding to a maximum point within an active constellation. The signal further includes a timing mark following the first sequence. In addition, a client device is provided. The client device includes a receiver and a detector coupled to the receiver. The receiver is coupled to an analog subscriber loop and has a decision feedback equalizer. The receiver provides a decision corresponding to data sent by a digital data source. The detector monitors the decision of the receiver to determine when an exception has been requested by the digital data source. Further, a method of requesting a change in a mode of operation of a client device when the client device is operating in a data mode is provided. The data mode includes receiving signal points selected from an active constellation and deciding which points have been received to thereby recover data.

Abstract: Apparatus and methods of compensating for distortions introduced in communication signals received over a telephone network. An adaptive linear equalizer (LE) pre-filter is used for filtering incoming sampled communication signals received via the telephone network transmission medium. An adaptive decision feedback equalizer (DFE) is used in conjunction with the LE to provide error filtering as a hybrid equalizer system to determine which of a plurality of communication states of the sampled communication signals as an accurate estimate of the originally transmitted signals over the transmission medium, responsive to the filtered communication signals from the LE. An error signal is generated relative to the difference between the determined states of the decision mechanism of the DFE and the filtered communication signals from the LE.

Abstract: The present invention provides a method of generating a signal that may be used to determine the characteristic response of a communication channel that utilizes the public Digital Telephone Network (DTN). The channel includes the DTN, which may have Network Digital Attenuators (NDA) and/or Robbed Bit Signalling (RBS), and a Digital-to-Analog Converter (DAC), (also known as a codec), as well as the analog characteristics of the local loop, typically a twisted pair of copper wires. The present invention provides a method and apparatus to determine the optimal sampling instant of the received data stream. The present invention provides a probing signal that is well-suited for use in determining the channel's response to a known sequence of PCM codes used as data symbols. This is especially useful in so-called PCM modulation schemes that utilize the DTN, where knowledge of network and DAC distortion predicates the selection of available PCM codes used to represent data.

Abstract: A method of detecting the presence of signal impairments that introduce distortion in one or more time slots of a communication link by comparing a received training sequence of signal points with hypothetical received signal points, where the hypothetical points are predistorted versions of the training sequence, and are based on the known, predetermined training sequence of signal points. A detection matrix is formed where one dimension of the matrix corresponds to a time slot within a frame, preferably six time slots to a frame, and the other dimension corresponds to a particular impairment, or combination of impairments. The individual signal impairments are generally one or more of the following: robbed bit signaling where the robbed bit is replaced with a logic `0`; robbed bit signaling where the robbed bit is replaced with a logic `1`; robbed bit signaling where the robbed bit is replaced with a logic `1/2`; 3 dB digital attenuator; 6 dB digital attenuator.

Abstract: Decision-based timing information extraction from a baud-rate sampled digital transmission system. Samples are interpolated from a data sample stream to obtain samples shifted forward and backward in time. A timing metric is applied to the forward and backward shifted sample stream to create forward and backward timing metric values. A timing recovery metric is applied to the forward and backward timing metric values, and is used as a phase feedback term to recover timing information. The method and system yield a very fast, data-driven convergence for baud-rate timing, and does not rely on any specific data sequence. The method and system are used in digital communication devices such as digital modems.

Abstract: Abbreviated subsystem retraining in a local modem including an information processor having a plurality of subsystems configurable with the information processor for data communications over a first transmission medium, e.g., an analog local loop of a public telephone network. The local modem subsystems are configured with the information processor in accordance with at least one operating characteristic of the first transmission medium, such as the echo characteristics or the like. A remote modem for data communications over a second transmission medium, e.g., a digital telephone network (DTN) is coupled to the first transmission medium for providing an exchange of information between the local modem and the remote modem. The local modem is operable in a retraining mode, responsive to the at least one operating characteristic of the first transmission medium, e.g., echo divergence, observed by the information processor during the exchange of information between the local modem and said remote modem.

Abstract: The present invention provides a method of generating a signal that may be used to determine the characteristic response of a communication channel that utilizes the public Digital Telephone Network (DTN). The channel includes the DTN, which may have Network Digital Attenuators (NDA) and/or Robbed Bit Signalling (RBS), and a Digital-to-Analog Converter (DAC), (also known as a codec), as well as the analog characteristics of the local loop, typically a twisted pair of copper wires. The present invention provides a method and apparatus to determine the optimal sampling instant of the received data stream. The present invention provides a probing signal that is well-suited for use in determining the channel's response to a known sequence of PCM codes used as data symbols. This is especially useful in so-called PCM modulation schemes that utilize the DTN, where knowledge of network and DAC distortion predicates the selection of available PCM codes used to represent data.

Abstract: The present invention provides a method of generating a signal that may be used to determine the characteristic response of a communication channel that utilizes the public Digital Telephone Network (DTN). The channel includes the DTN, which may have Network Digital Attenuators (NDA) and/or Robbed Bit Signalling (RBS), and a Digital-to-Analog Converter (DAC), (also known as a codec), as well as the analog characteristics of the local loop, typically a twisted pair of copper wires. The present invention provides a method and apparatus to determine the optimal sampling instant of the received data stream. The present invention provides a probing signal that is well-suited for use in determining the channel's response to a known sequence of PCM codes used as data symbols. This is especially useful in so-called PCM modulation schemes that utilize the DTN, where knowledge of network and DAC distortion predicates the selection of available PCM codes used to represent data.

Abstract: A method and apparatus for estimating the frequency of a periodic signal and for canceling the interference in a modem signal. Power line noise may interfere with electronic signals. Since power lines may be either 50 Hz or 60 Hz, depending on the country, frequency estimation of the periodic power line noise is necessary. Modem signals are received and autocorrelated in order to identify the periodic characteristics of the signal over time. Once the frequency is identified, the power line noise is modeled based on creating a circular buffer. Initially, the circular buffer is composed of scaled samples of one cycle of the fundamental frequency of the power line noise. Thereafter, samples are received, scaled, and combined with previous buffer values in order to update the buffer. In this manner, the buffer models the power line noise, so that the power line noise may be removed from the system.