Abstract: An echo cancellation scheme for DMT MDSL digital subscriber loop telecommunications data transfer is disclosed. The echoed data stream frame is aligned with the incoming data stream frame. The time domain equalizer trims the lengths of both the DSL channel and echo channel within the length of the cyclic prefix, so that the time domain convolution for synthesizing the echo is accomplished within the FFT process, enabling the echo to be subtracted in the frequency domain.

Abstract: An echo canceller apparatus consists of a frame aligner circuit and an echo canceller. The frame aligner circuit forcibly generates a data slip of a receive input signal by a recursive buffer of a FIFO when a slip between timings of receive and transmit clocks is accumulated. A data slip detection circuit outputs its detection of the data slip to an adaptation correction section of the echo canceller. In the adaptation correction section, when the data slip of the receive input signal is detected depending on the output of the data slip detection circuit, a correction operation is performed so that a delay by N taps is increased in an impulse response of an H-register, thereby canceling an echo.

Abstract: A digital transmission system comprising a receiver, the receiver including a receiver input stage and a digital memory for storing a sequence of binary symbols of sample values, formed in the receiver input stage, of a signal distorted by a transmission channel, and an equalizer for forming a sequence of binary estimates from the sample values by an impulse response of a substitute system describing the transmission channel, the impulse response being determined by first correlations of coefficients of a known training sequence with the sample values of a part of the known training sequence extended by at least one binary symbol.

Abstract: In a method for establishing a data communication connection in a data channel utilizing PAM signals, a transmitter transmits a training sequence, formed of predetermined symbols, a predetermined number of times. The data channel is monitored in order to detect a predetermined signal, samples are taken and amplification is adjusted in such a way that the signal, settle at a predetermined level. In order that the method can be applied in a data channel with previously unknown properties, when the transmitter starts repeating the training sequence, samples taken from the data channel are buffered to form a sample sequence. A channel pulse response estimate is calculated by convoluting the buffered samples with a predetermined symbol sequence.

Abstract: An echo canceler for calculating an echo impulse response during a training sequence, wherein a sequence of data samples is selected such that a full rank data correlation matrix comprised of such data samples is diagonal at the Nth iteration. The echo canceler estimates the echo impulse response based on such data samples and an echo generated during the training sequence using a normalized least means square algorithm, wherein the length of the data sequence to sound the echo channel is N. This normalized LMS algorithm, wherein the data sequence is specifically selected, converges toward an echo impulse response much faster than standard LMS algorithms, while having a computational complexity comparable to that of the standard LMS algorithm.

Abstract: A full-duplex modem having improved transmission speeds over voice grade telephone circuits that extends the concepts of asymmetric transmission to include echo cancellation techniques. The preferred modem has a high speed forward channel and an overlapping low speed back channel and is capable of transmitting or receiving over either of the channels, depending on the relative data rates. A narrow band echo canceler substantially cancels all or part of reflected transmit signals. Because the echo cancellation technique employed is narrow band, there is a significant reduction in the complexity and computational requirements for the modem.

Abstract: A multi-channel transcoder with rate adapter converts the data rate of GSM and PSTN network data in a multi-channel network. A transcoder having echo-cancellation features uses the robust voice activity detection functions of the GSM transcoder functions to enhance the accuracy of echo-cancellation of near-end signals. A method for decoding a GSM signal in which the transmission of the audio data over the network is commenced prior to the completing of the decoding process. A transcoder unit having rate adaption and echo-cancellation with improved decoding is implemented in a single DSP and processes multiple traffic channels simultaneously.

Abstract: A far-end modem transmits a "pilot tone" during the time that a near-end modem is training its echo canceler. Correspondingly, the near-end modem is modified to notch, or filter, out this pilot tone from the received signal. The filtered received signal is then used by the near-end modem to train its echo canceler.

Abstract: A fast response gain tracker operates to adjust the magnitude of an echo cancellation signal. The latter signal is developed from an echo canceler. The fast response gain tracker provides an adjusted echo cancellation signal that is subtracted from an echo-corrupted received signal to provide an echo-canceled signal. In particular, the fast response gain tracker correlates the echo-canceled signal with the echo cancellation signal from the echo canceler. If the gain of the gain tracker is correct the echo is canceled and there is zero correlation between the echo-canceled signal and the echo cancellation signal. However, if the echo level changes then a residual echo component appears in the echo-canceled signal, which now becomes correlated with the echo cancellation signal. In response, the magnitude of the gain tracker automatically adjusts the gain of the echo cancellation signal to match the change in echo level and thereby subsequently eliminates the residual echo.

Abstract: A processor of a cellular modem monitors for the presence of a residual echo signal during a full-duplex portion of a training sequence. In particular, the processor monitors an equalizer error signal during a full-duplex training phase that follows the half-duplex training phase for the echo canceler. If the processor detects a level of the error signal greater than a predefined threshold, the processor presumes the increase in the error signal is due to the presence of a residual echo signal and performs a predefined adjustment of the taps of the corresponding echo canceler of the cellular modem.

Abstract: An apparatus and method are provided for a data communications device, such as a modem (100,101), software modem, or facsimile machine, to detect and discriminate various amplitude modulated signals, such as an ANS signal of the ITU V.25 protocol and an ANSam signal of the ITU V.8 protocol. The apparatus and method embodiments first determine the presence of a first frequency component in a received signal, such as the 2100 Hz component of ANS and ANSam signals (205). The received signal is then demodulated (215) and low pass filtered (220), followed by removing any resulting direct current component (225) to form an inclusive signal. A second frequency component, such as the frequency of the 15 Hz amplitude modulating component of an ANSam signal, is removed from the inclusive signal (235), and its resulting magnitude is determined, as a filtered signal magnitude (240). The filtered signal magnitude is subtracted from the magnitude of the inclusive signal (230) to form a discrimination value (245).

Abstract: An echo canceler is disclosed having a voice detector. When the voice detector detects the absence of input signals, the echo canceler is trained. In the training mode, the echo canceler receives an impulse signal from an impulse generator, as input through a switching device. When the input of the echo canceler is the impulse signal, a switch is turned off, a signal on a receiving line is stored in a tap coefficient memory, and the impulse signal on a transmitting line is stored in a transmission signal memory. Using the signals stored in the two memories, a convolution operation is performed by a convolution arithmetic unit. The data of the tap coefficient memory directly before the end of training are used for the tap coefficients after the training period.