Conexant Systems, Inc.

Silicon Laboratories Inc.

Zhenyu Zhou

Xuming Zhang

Sverrir Olafsson

Yuanjie Chen

Jason Brent

Thomas C Liau

A technique for identifying the encoding law utilized by a central office codec may be implemented in a receive modem. The encoding law, which is typically dictated by the country in which the central office is located, is employed to generate a plurality of transmission levels during an initialization period associated with the modem system. The receive modem analyzes a number of these transmission levels to determine whether the levels have certain characteristics associated with the particular encoding law followed by the central office codec. When the receive modem detects the codec type, it may transmit a suitable identifier back to the transmit modem.

Method and apparatus for identifying the encoding type of a central office codec

An initialization procedure for a digital modem system treats the presence of ADPCM as if it were a digital impairment such that the modem system can utilize effective compensation techniques to address the ADPCM. The modem system initially determines whether the current communication channel is a fully digital channel. Next, the modem system determines whether the channel includes any ADPCM elements. If ADPCM is detected, then a digital impairment learning routine is performed to obtain the ADPCM compression characteristics and data rate. The digital impairment learning routine may use a single probing sequence to obtain the ADPCM characteristics while identifying any concurrent digital impairments such as RBS, digital pads, and encoding law conversions. Once the digital channel is characterized, the modem system may condition its transmitters and receivers in an appropriate manner to obtain an increased data rate.

Method and apparatus for detecting and determining characteristics of a digital channel in a data communication system

The present invention relates to multiple modulus conversion (MMC) techniques for mapping data in a pulse code modulation (PCM) modem system. In accordance with the present invention, signal point constellations are arranged to receive the output indices generated by the MMC procedure such that the probability of transmission of higher power codewords is relatively low compared to the probability of transmission of lower power codewords, while maintaining the same or larger minimum distance between signal points. In addition, the present invention provides techniques for obtaining the probability of occurrence for each constellation or signal point associated with a given data communication session and for determining the theoretical average transmit power associated with a given set of signal point constellations and MMC parameters. In addition, the present invention provides a method for estimating a reasonable upper bound for the average transmit power associated with a given set of signal point constellations and MMC parameters. The present invention is also capable of transmitting the codewords defined by an MMC procedure in a specific order that may be optimized in accordance with a particular cost function associated with the modem system.

Method and apparatus for implementing enhanced multiple modulus conversion techniques in a signal point mapping context

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.

Method and apparatus for training an echo canceler in a PCM modem context

A method and apparatus for controlling and shaping the spectrum of transmitted signal samples having predetermined frequency characteristics and allowable transmit signal levels. A running measure of unwanted components is measured and, for each block of the transmitted samples, an objective function based on the previously calculated running measure is computed. Depending upon the measurements, redundancy is determined and selected for each block of the transmitted samples. Accordingly, at least one redundant sample may be added or, the sign of the sample modified, at structured or randomized locations within the block to optimize the objective function.

System for controlling and shaping the spectrum and redundancy of signal-point limited transmission

A method and apparatus for performing spectral shaping transmitted samples with a set of predetermined frequency characteristics and a predetermined set of allowable transmitted signal levels are disclosed. The method first calculates, for each of the transmitted samples, a running measure of unwanted components upto the current sample. It then computes, for each block of the transmitted samples, an objective function based on the running measure previously calculated. It then selects, for each block of the transmitted samples, at least one redundant sample to be added or at least one transmitted sample to be modified, at structured or randomized location within the block to optimize the objective function. The location of the dependent sample can further be fixed, scrambled (pseudo random) or randomized. The method of computing can be any one of the following: a Running Filter Sum, a Running Fourier Transform (&ldquo;RFT&rdquo;) or Fast FT (&ldquo;RFFT&rdquo;), or an RDS, for each transmitted sample.

Method and apparatus for spectral shaping in signal-point limited transmission systems

Method and apparatus for implementing enhanced multiple modulus

Methods and apparatus are disclosed for shaping and controlling the spectrum of transmitted samples with a set of predetermined frequency characteristics and a predetermined set of allowable transmitted signal levels are disclosed. In particular, methods of minimizing the energy of the signal at unwanted frequencies are described. For each of the transmitted samples, the system computes a running measure of unwanted components. It then computes, for each block (or 'data frame') of the transmitted samples, an objective function, for example, a running filter sum based upon a biquad filter function. It then selects, for each block or spectral shaping frame of transmitted samples, a sign combination from a sign-combination subset such that the objective function is optimized.

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Irvine, CA, United States of America

Zhenyu Zhou