Abstract: A method for establishing data transmission between a two devices by performing de-emphasis training is disclosed. While a retry count does not exceed a predetermined threshold: a training pattern with a signal strength is sent from a first device to a second device. If a negative acknowledgement is received from the second device within enough time to determine that the send training pattern was unacceptable to the second device, the retry count is incremented, the signal strength for the training pattern is attenuated and the training pattern is resent.

Abstract: Evaluation of label switched data units is disclosed. In a method, a data unit is received or obtained, and, when the data unit is a label switched data unit, a kind of an encapsulated data unit included in a message body of the data unit is determined by analyzing the message body. The method may be achieved as part of a network interface included on a board in a network testing unit and in a computing device.

Abstract: A startup protocol is provided for use in a communications system having a communications line with a master transceiver at a first end and a slave transceiver at a second end, each transceiver having a noise reduction system, a timing recovery system and at least one equalizer all converging at startup of the system. The operation of the startup protocol is partitioned into stages. The first stage includes the step of converging the equalizer and the timing recovery system of the slave while converging the noise reduction system of the master. Upon completion of the first stage the protocol enters a second stage which includes the step of converging the equalizer and the timing recovery system of the master, converging the noise reduction system of the slave, freezing the timing recovery system of the slave, and resetting the noise reduction system of the master.

Abstract: A system and method of protocol and frame classification in a system for data processing is disclosed, including, analyzing a portion of the, packet or frame according to predetermined tests, and storing characteristics of the packet for use in subsequent processing of the frame. The characteristics are preferably obtained with hardware, which does so quickly and in a uniform time period. The stored characteristics of the packet are then used by the network processing complexes in further processing of the frame. The processor is preconditioned with a starting instruction address or cede entry point and the location of the beginning of the layer 3 header as well as flags for the type of frame.

Abstract: A method for transmitting data signals in full duplex with echo cancellation between a first and a second modem connected by a two-wire channel, wherein a data signal is a function of at least one data symbol in a stream of data symbols generated by a modem comprising: determining echo cancellation coefficients for the first modem; transmitting data signals in full duplex between the two modems using the echo cancellation coefficients to cancel echoes in data signals received by the first modem; providing at least one hiatus in data symbol generation by the second modem while continuing data symbol generation by the first modem at a time at which echo cancellation using the echo cancellation coefficients is effective in canceling echoes in data signals received by the first modem; and updating the first modem echo cancellation coefficients during the at least one second modem hiatus.

Abstract: A mobile station (MS) and method for estimating received signal strength of a radio signal from a neighboring cell in a cellular radio telecommunication network. The MS measures the received signal strength of the radio signal over a plurality of frames, and calculates an average received signal strength. During an idle frame, the MS receives a synchronization channel (SCH) signal, and determines a channel estimate for the SCH using a known extended training sequence. The extended training sequence is then modified with the channel estimate, and the modified extended training sequence is subtracted from the received SCH signal to obtain a residual signal. The MS calculates a residual energy of the residual signal, and subtracts the residual energy from the average received signal strength of the radio signal to obtain an estimated received signal strength of the radio signal from the neighboring cell.

Abstract: An echo cancellation circuit includes delay units at its input unit and output unit in order to adjust the delay caused by a FIFO. The delay times of the delay units are trained using a training signal, such the REVERB signal, that is a system initializing signal. In addition, an upstream pilot tone is used to tune the delay time. The performance of the echo cancellation circuit is optimized according to the device and the method described.

Abstract: Methods and systems for providing and managing training through/over networks to remote multimedia device users are disclosed. Training can be provided through networks to computers and portable hand held devices. Handheld devices can include PDAs, pagers, and wireless phones. Training can be received by a remote trainee through electronic data networks for completion at a wireless device. Methods and systems are also disclosed for managing remote training. Remote training can be tracked and recorded when completed by a remote user of a wireless hand held device. Completed training can be transmitted through an electronic network to course provider servers by a remote hand held device. Remote users authentication and certification of completed training received from a hand held device through an electronic network can be conducted by a training provider's server.

Abstract: A linear/non-linear adaptive filter for transforming an input signal to an output signal. The present invention also includes a novel GSPT LMS algorithm for significantly reducing complexity. The adaptive filter includes a coefficient updater that can execute a Carry-in operation or a Borrow-in operation to adaptively adjust a filtering coefficient according to whether an updating term signal is a Carry-in signal or a Borrow-in signal.

Abstract: Rapid identification and modeling of transmission media channel characteristics of a communications system using a correlation based technique. The technique provides a known training sequence used to generate a known quantity that operates on an observed or measured received signal, which is a function of the training sequence and the channel's impulse response, to give an estimate of the model of the channel. The technique decouples the training sequence from the observed or measured output, leaving the estimated impulse response. The impulse response of the transmission media channel is rapidly computed and processed to set the initial values of filter coefficients, for example, an echo canceller and an equalizer, in the communications system. Once the coefficients are initialized, if needed, a standard technique, such as least mean square (LMS) correlation, can be used to fine-tune the coefficients to converge on or model the transmission media channel's characteristics.

Abstract: The invention provides a system for remotely configuring a plurality of devices to customize a lab network system for testing components and for training operators to use and maintain such systems. The system is configured to remotely access and control such a system via a computer network such as the Internet. Once connected, a user can run testing scenarios on the configured devices remotely from any location that has access to the Internet. In accordance with the invention, an organization's network equipment is integrated with specialized physical switching technologies, and controlled by unique management software. Access to the network equipment may be provided remotely, and granted via a scheduling service. Thus, multiple physical equipment labs can be integrated into one globally, visible resource, enabling one-stop scheduling of lab time without knowing the detailed inventory of a particular network equipment facility.

Abstract: A method and system for routing an externally generated message in a network includes receiving at an ingress port of a network a message from an external network. The message includes Internet protocol (IP) source and destination addresses and message data. The IP source and destination addresses are translated to internal addresses that are non-forwardable in the external network. The message data is routed in the network based on the internal addresses.

Abstract: A modem including an echo canceller adapted to determine locations of far-end echo sources. The echo canceller is adapted to send a signal to turn off network echo suppressors and enter a training mode. A training signal at a predetermined modem training frequency is sent from the modem to the second modem in the link. The return signal is then sampled by the sending modem. Any far-end echoes manifest themselves as sine waves at the modem training frequency, delayed in time. The time difference between the peak of the training signal and the echo signals is used to determine the echo delay.

Abstract: A cancellation system comprises a channel circuit (11) for each noise source, such as echo in a particular cable pair. There are only eighty taps per channel, in two blocks (n_echo_a, f_echo_a). Each block is preceded by a variable delay line comprising blocks of registers cascaded so that a delay value of 0 to 40 clock cycles can be chosen. The delay value is determined by determining an optimum position for each tap block. This is achieved by determining a maximum coefficient sum for a number of windows. Taps from other channels are used during training, so that there is a total of 160 taps for each channel during training to enable the optimum positions to be determined.

Abstract: A method and apparatus for reducing crosstalk in a multi-channel communication system is disclosed. In one embodiment, outgoing signals in a multi-channel environment are manipulated into a transform domain, such as the frequency domain. Thereafter, the signals may be combined and modified based on a weighting variable to create a cancellation signal. Combined processing greatly reduces system complexity and increases processing speed. After processing in the transform domain, the cancellation signal undergoes further processing to return the cancellation signal into the time domain. The cancellation signal may then be combined with received signals to cancel crosstalk or echo. A method and apparatus for crosstalk cancellation in the analog domain and digital domain is also disclosed.

Abstract: A method and apparatus are disclosed for frequency offset estimation and interleaver synchronization, using periodic signature sequences, such as Barker codes. The periodic signature sequence is used for interleaver synchronization or frequency offset estimation or both. The periodic signature sequence is transmitted over a certain number of bins in both the upper and lower sides of the DAB signal. Since the signature sequences are assigned to specific bins known to the receiver, any shift of the correlated peak from the expected location due to frequency offset errors can be estimated by the frequency offset algorithm. If the Barker sequence is placed, for example, in the last column of the DAB interleaver, the location of the Barker sequence upon correlation of the received digital signal identifies the beginning of an interleaver block.

Abstract: A method and apparatus for detecting the location of robbed bits by a digital communications network. A complete echo cancellation circuit also is disclosed employing the robbed bit detection method and apparatus in which the coefficients of the echo cancellation FIR filter are trained simultaneously during the detection of the position of the robbed bit or bits.

Abstract: A method for estimating channel parameters of radio channels of a W-CDMA mobile radio system, for example in accordance with the UMTS standard includes transmitting sequences of known symbols between unknown data symbols by a base station. The channel estimation is carried out by a comparison of the received sequences with the known symbols, and the result of the comparison is integrated over a sequence of known symbols.

Abstract: 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.

Abstract: A method for providing echo cancellation between a first and second communication unit detects an echo condition (200) between first and second communication units. In addition, the method includes detecting whether a decoded near end audio packet contains a suitable level of background noise to be used as a background noise packet. If so, the current near end encoded audio packet is stored (202) in a buffer (26), such as a circular buffer. Previous near end encoded audio packets (42) that are also determined to have a suitable level of background noise based on their decoded corresponding counterparts are also stored in the circular buffer. When an echo condition is detected with respect to a current near end encoded audio packet, the method includes substituting a previous near end encoded audio packet stored in the buffer as the next encoded audio packet for transmission (204).

Abstract: A transmitter produces radio signal bursts in periodic time slots allocated to a time-division multiplexed channel. The radio signal of each burst is made up of digital symbols comprising two training sequences enabling the receiver to estimate demodulation parameters and information symbols which the receiver can estimate by a demodulation applied using the estimated parameters. The two training sequences are placed at the start and the end of the burst so that the receiver uses them to demodulate the received signal in the order of the symbols and demodulate the received signal again in the reverse order of the symbols.

Abstract: A startup protocol is provided for use in a communications system having a communications line with a master transceiver at a first end and a slave transceiver at a second end, each transceiver having a noise reduction system, a timing recovery system and at least one equalizer all converging at startup of the system. The operation of the startup protocol is partitioned into stages. The first stage includes the step of converging the equalizer and the timing recovery system of the slave while converging the noise reduction system of the master. Upon completion of the first stage the protocol enters a second stage which includes the step of converging the equalizer and the timing recovery system of the master, converging the noise reduction system of the slave, freezing the timing recovery system of the slave, and resetting the noise reduction system of the master.

Abstract: An Orthogonal Frequency Division Multiplexing (OFDM) receiver that compensates for FFT window drift by extracting a training symbol from a fast Fourier transformed OFDM signal, and processing the extracted training symbol to derive an FFT window adjustment factor and an associated equalizer tap initialization value. The OFDM receiver controls the position of an FFT window and the initialization of equalizer taps using the FFT adjustment factor and equalizer tap initialization value. The OFDM receiver preferably filters the fast Fourier transformed OFDM signal to remove additive channel noise and increase the likelihood of reliable equalizer tap initialization in a low SNR environment.

Abstract: The process in an xDSL transceiver transfers into a fast retraining sequence when the cause of an error on a telephone circuit is a change from an off hook state to an on hook state of a telephone instrument, a signal indicating an inversion of polarity of a signal on the telephone circuit, a change from an on hook to an off hook and when a handshake waiting time has passed without detecting a predetermined signal on the telephone circuit, or when the predetermined signal is detected within the handshake waiting time. The handshake waiting time can be updated in accordance with a dial pulse width, the maximum number of digits in the dial pulse signal, and the maximum number of pulses in one digit, or depending on whether or not the dial pulse comes from NTT.

Abstract: An echo cancellation circuit includes delay units at its input unit and output unit in order to adjust the delay caused by a FIFO. The delay times of the delay units are trained using a training signal, such the REVERB signal, that is a system initializing signal. In addition, an upstream pilot tone is used to tune the delay time. The performance of the echo cancellation circuit is optimized according to the device and the method described.

Abstract: This invention is generally concerned with the reception of high rate digital data, and more particularly with methods and apparatus for improved channel estimation in high rate digital data communications systems, particularly packet data communications systems.

Abstract: A method of canceling echoes in a telecommunications system wherein an exchange of information takes place between a local subscriber and a subscriber at the remote end of a transmission link and at least one subscriber is assigned an echo canceller, the parameters of which are set as a function of an echo delay time (i). The signs of the signal x(t) transmitted by a subscriber and the signal y(t) received by the subscriber can be determined at equidistant time intervals (Ti) so that sign sequences arise which are stored and compared with one another, and in the event of a direct correspondence or a correspondence as a result of an inversion of the sign sequences of the received signal y(t) and of the transmitted signal x(t) the received signal y(t) is detected as an echo and the echo delay time (i) is calculated.

Abstract: An adaptive DMT modem determines, as part of a startup sequence, subscriber loop conditions. One or more loop condition adaptation operations are then performed to reduce the complexity of the filters employed in the modem, to reduce the power dissipated in the modem, to optimize performance of the modem or to reduce the likelihood of EMI being radiated into the premises of a subscriber.

Abstract: A Voice call Precedence Over Packet Data (VPOPD) technique which would allow a customer of a wireless communication network service provider to choose whether to receive a call during an active packet data session. The VPOPD technique is a method of call processing comprising the steps of setting a feature value to be used in call processing when an associated mobile station has an active packet data session, and determining whether to reject a call termination request for the mobile station when the mobile station has an active packet data session using the feature value. The feature value may be set using a feature code transmitted from the mobile station, or provided by a service provider. If a determination to accept the call termination request is made, the following additional steps are performed: a message is sent to the mobile station to prevent race conditions from occurring, the mobile station is caused to enter a dormant state, and then the mobile is paged.

Abstract: An Orthogonal Frequency Division Multiplexing (OFDM) receiver that compensates for FFT window drift by extracting pilots from a fast Fourier transformed and equalized OFDM signal, and processing the extracted pilots to derive an FFT window adjustment factor and an associated equalizer tap adjustment value. The OFDM receiver simultaneously controls the position of an FFT window and the phase of equalizer taps using the derived FFT adjustment factor and equalizer tap adjustment value.

Abstract: A communication circuitry for providing effective detection of tones in a communication network. The communication circuitry comprises filtration circuitry, summation circuitry, detection circuitry, and interface circuitry. The filtration circuitry is coupled to the summation circuitry and is configured to receive a communication, process the communication to estimate an echo return in the communication, and provide the estimated echo return to the summation circuitry. The summation circuitry is coupled to the detection circuitry and configured to receive the estimated echo return from the filtration circuitry, receive a tone transmission and echo return from the interface circuitry, subtract the estimated echo return from the tone transmission to generate a substantially pure tone, and provide the substantially pure tone to the detection circuitry. The detection circuitry is configured to receive the substantially pure tone and process the substantially pure tone to perform a programmed operation.

Abstract: A technique for training an equalizer of an ADSL Annex C transceiver is provided. The technique defines the points in the transmission sequence at which equalizer training should take place, and what symbols comprising the transmission should be used for training. The technique avoids the effect of strong TCM-ISDN cross-talk noise. The equalizer is trained so as to achieve optimal communication channel performance. During the TEQ training phase, the cyclic prefix is not introduced. The TEQ is trained only on FEXT symbols except the FEXT symbols adjacent to NEXT symbols. In the early phase of FEQ training, the cyclic prefix is not introduced. The FEQ is trained on FEXT symbols only except the FEXT symbols adjacent to NEXT symbols. During a late training phase after the cyclic prefix is introduced, the training of the FEQ is continued by using signals received on all FEXT symbols only.

Abstract: A two-step training method for the estimation filter in the echo cancellation (EC) path of the analog front-end (AFE) circuit for a modem, such as an asymmetric digital subscriber line (ADSL) modem. During the first step, the coefficients of a filter that is preferably equivalent to the combination of the EC path and the receive (RX) path in the AFE circuit are determined with the EC estimation filter held fixed and the transmit (TX) path in the AFE circuit disabled. During the second step, the TX path is enabled and the coefficients of the EC estimation filter are determined using the path equivalent filter generated during the first step. The two-step training method takes into account variations in the operating characteristics of components in the various processing paths in the AFE circuit to converge on satisfactory coefficients for the EC estimation filter within an acceptable number of training symbols.

Abstract: A half-duplex facsimile modem system according to the present invention may exhibit a shorter startup time relative to conventional systems. The modem system exchanges capabilities information concurrently with the transmission of a conventional answer signal, thus obviating the need for performing a separate capabilities exchange procedure. In addition, the modem system is capable of determining a preferred training sequence duration based upon one or more characteristics of the current channel. The preferred training sequence duration is communicated from the answer modem to the calling modem such that the calling modem can format the training sequence in an appropriate manner. The resultant training sequence has a time duration that is variable in response to, e.g., the signal-to-noise ratio of the instant channel. These techniques can result in a significant reduction in the startup latency typically associated with conventional half-duplex facsimile modem systems.

Abstract: A method for fast training of equalizers in a DMT system begins by normalizing the incoming receive signal (&ngr;) via steps (108-116). By normalizing the signal, the convergence rate of the training algorithm becomes relatively independent of channel line length so that long line lengths may converge to optimal equalizer coefficients in short time periods. The method also iteratively adjusts the filter coefficients w over time by using an adaptive gain vector &mgr; that is updated on a component-by-component basis on each iteration via steps (114-146). By allowing each component of the vector &mgr; to iteratively adapt independent of all other components in the vector &mgr; based upon the binary sign bit of both real and imaginary components of frequency domain gradient vectors G, a convergence to optimal equalizer filter coefficients will occur in a short period of time.

Abstract: A system and method for echo cancellation in digital subscriber line (DSL) service using passive devices. The outgoing transmitted signal is attenuated and fed back into the receiver circuit in such a way as to maximize the canceling of the transmitted signal and thus allow the receiver circuit to amplify and process the received signal without interference from the outgoing transmitted signal. The feedback circuit uses only passive elements. The feedback circuit has complex impedance branches. These complex impedance branches parallel the complex impedances of the transformer and transmission line such that any change in the transformer or transmission line impedance is similarly experienced in the feedback circuit. This allows for near total cancellation of the echo signal without the need for costly active circuits.

Abstract: A method and apparatus for efficiently switching cells through a switch fabric are provided. According to one aspect of the present invention, logic for forwarding and filtering multicast data is distributed among various layers of a network device, such as a switch, router, bridge, or the like. Data is received at a first port of an input/output (I/O) card. A multicast group identifier corresponding to the data is determined. The data and the multicast group identifier are then transferred to a switching card which indexes into a first set of correlation data with the multicast group identifier to identify a set of egress forwarding paths that lead to I/O cards having members of the multicast group. The switching card forwards the data to the I/O cards via the set of egress forwarding paths identified. For their part, the I/O cards identify a set of ports associated with the multicast group by indexing into a second set of correlation data and forwarding the data to each of the ports identified.

Abstract: A system and method enable wireless communication from one data processing system to a telephone network. The system and method establish a connection from a local transceiver to a base transceiver using echo cancellation techniques to remove various tones and noise. The system and method enable full duplex communication between the local transceiver and the base transceiver by using forward error correction algorithms to encode and decode messages therebetween, and by using an interleaving algorithm to protect against burst type errors.

Abstract: 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 a sample management buffer to store incoming sample values of a transmitted rate in a buffer and a sample release circuit to release at a slower rate the stored sample values in buffer. An adaptive equalizer with a finite impulse response filter mixes the sample values, and a slicer reconstitutes original data transmitted.

Abstract: In a communications arrangement, a first pulse code modulation (PCM) modem communicates data in the form of PCM words with a second PCM modem through a public switched telephone network (PSTN). The transmitted signal representing the data may be affected by type A and/or type B robbed bit signaling occasioned by the PSTN such that the least significant bits (LSBs) of certain PCM words are “robbed” and substituted with signaling bits. In addition, the transmitted signal is attenuated because of a digital loss imposed by a switch in the PSTN. During training of a PCM modem, any occurrence of type A and/or type B robbed bit signaling is identified, and a signal level conversion table in accordance with the invention is created. Based on this table which takes into account the digital loss, the most likely transmitted PCM word is determined, given a received signal level.

Abstract: A system and method are disclosed that provide for compatibility between different generations of transceivers, such as Gigabit Ethernet transceivers. According to the invention, a novel transceiver is provided that includes a physical layer entity (PHY) comprising a physical coding sublayer (PCS) and a physical medium attachment (PMA) sublayer. In one embodiment, the PHY is designed to switch the PCS encoding/decoding scheme to a legacy-based encoding/decoding scheme in a situation where it is determined that the remote transceiver in communication with the novel transceiver is transmitting data according to a legacy-based scheme.

Abstract: A method and a device are specified for data transmission via an air interface between radio stations in a radio communications system. Data to be transmitted are grouped into message blocks at the transmitting end, the message blocks respectively containing additional symbols of a training sequence. Thereupon, at least two message blocks with different training sequences are simultaneously transmitted on one channel, whereupon the data of the at least two message blocks are detected at the receiving end with knowledge of the at least two training sequences.

Abstract: An improved echo canceler training technique may be employed by a digital server modem in a PCM modem context, such as a V.90 modem system. The disclosed echo canceler training technique establishes the digital impairments within the echo path by transmitting a training signal from a transmitter located at the digital server modem. The echo signal generated in response to the training signal is received by the digital server modem and appropriately analyzed to accurately model the echo path. The echo canceler resident at the server modem is than suitably trained to compensate for the modeled echo path. In the preferred embodiment, the echo canceler training signal is also used during in the context of downstream digital impairment learning by the analog client modem. In the context of the echo canceler training, the server modem does not rely upon any processing or analysis performed by the client modem; the server modem trains its echo canceler without receiving any information from the client modem.

Abstract: The subject invention improves tracking performance of an adaptive equalizing operation while reducing the calculation volume. A frame including a training sequence and a mixed data sequence in which at least one symbol of a whitened sequence is dispersively inserted into a data sequence is generated. The frame is converted into a wireless signal, which is then transmitted. The wireless signal of the frame is received. Tap coefficients of an equalization filter are set by using the training sequence in the frame. During reception of the mixed data sequence, an adaptive operation is performed by using the respective symbols of the whitened sequence in the frame and the tap coefficients of the equalization filter are updated.

Abstract: A startup protocol is provided for use in a communications system having a communications line with a master transceiver at a first end and a slave transceiver at a second end, each transceiver having a noise reduction system, a timing recovery system and at least one equalizer all converging at startup of the system. The operation of the startup protocol is partitioned into stages. The first stage includes the step of converging the equalizer and the timing recovery system of the slave while converging the noise reduction system of the master. Upon completion of the first stage the protocol enters a second stage which includes the step of converging the equalizer and the timing recovery system of the master, converging the noise reduction system of the slave, freezing the timing recovery system of the slave, and resetting the noise reduction system of the master.

Abstract: A system and method for echo cancellation in a communication system having a digital echo canceller and an analog echo canceller for analog reduction of cross coupling echo components in an analog output signal when in analog form before digital processing by the digital echo canceller. An analog cancellation signal is generated which is substantially the same as the acoustic coupling echo component in the analog output signal before digital processing by the digital echo canceller. The analog echo cancellation signal is combined with the analog output signal to reduce the cross coupling echo component before digital processing by the digital echo canceller.

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: A transmitter (20) having means (206, 207) to encode an input signal to form coded data, each element of said coded data having one of at least two discrete signal magnitude levels, the encoding means including in the coded data a periodic training sequence of data (T); and a receiver (30) to receive the coded data and, on the basis of the received training sequence, to adapt a threshold or thresholds to allow the discrete levels to be distinguishable from each other. The training sequence T may comprise a plurality of elements at least one of which, in turn, represents each one of the discrete signal levels. The receiver generates a look-up-table to store the adapted thresholds.

Abstract: Time dispersion of a signal that has been received from a channel is measured by utilizing metrics to determine the energy inside an equalizer window and outside of the equalizer window. In one embodiment, the estimate of the energy outside the window is a difference between residual interference estimates. In another embodiment, the estimate of the energy outside the window is a difference between residual impulse response power estimates.

Abstract: A modem that operates reliably at a symbol rate that corresponds to twice its bandwidth even when it is coupled to a receiving A/D converter that operates under control of a clock is realized by synchronizing the modem's operation to the A/D's clock. The superior operation of this modem advantageously extends to A/D clock frequencies beyond the frequency of twice the modem's bandwidth. To minimize quantization noise, the modem's output is conditioned to minimize intersymbol interference by adjusting the modem's output to the A/D converter's sampling times and slicing levels. When the A/D's clock is higher than twice the bandwidth of the modem's output signal, some intersymbol interference cannot be avoided. In accordance with this invention, the position and value of this interference is computed at the receiver and subtracted from the received signal.