Abstract: 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.

Abstract: 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.

Abstract: The invention features the drawbridge assembly and its applications in optical switches, optical crossconnects, optical add/drop multiplexers and variable optical attenuators. In optical switches and optical crossconnects, an array of the drawbridge assemblies can be used to redirect the multiple input lights to multiple outputs. In add/drop multiplexers, the drawbridge assemblies can select the light channels to be added and dropped. In the attenuator embodiment, a vertical mirror is inserted into two fibers, the first one as the input and the second one as output. The drawbridge assembly controls the position of the vertical mirror for blocking a certain portion of the light and enabling the attenuation. The continuous change of the mirror position results in variable attenuation. A series of VOA form a multi-channel VOA system on a single substrate.

Abstract: 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.

Abstract: 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.

Abstract: An improved two-point equalizer training technique for use with V.90 modem systems utilizes a number of scaling parameters to enable the compensation of robbed bit signaling (RBS) effects in a manner that is decoupled from the compensation of analog impairments in the data communication channel. The preferred technique employs six scaling parameters corresponding to the six RBS phases typically associated with practical V.90 systems. One of the scaling parameters is fixed at a value of one to simplify the computational load associated with the adaptive training algorithms. The decision error is utilized to adaptively adjust the equalizer filter taps and the scaling parameters. The techniques of the present invention may be used to initially train the equalizer resident at the analog client modem and/or to initially train the echo canceler resident at the digital server modem.

Abstract: 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.

Abstract: 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.

Abstract: 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 (“RFT”) or Fast FT (“RFFT”), or an RDS, for each transmitted sample.

Abstract: An improved multiple modulus conversion (MMC) procedure is provided that employs an alternate scheme for obtaining the MMC outputs in response to a binary input of a number of bits. The alternate MMC procedure utilizes short-word division operations such that a practical digital processor may efficiently perform the required binary divisions. An exemplary short-word division process partitions the original long-word binary input into a plurality of short binary words, each having an equal number of bits. Individual short words or a combination of two short words are then divided by the appropriate modulus in a systematic manner to obtain the quotient and remainder associated with the particular division operation. The short-word divisions technique may be employed throughout the entire MMC procedure to suitably obtain the output values associated with each modulus.

Abstract: 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.

Abstract: 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.

Abstract: A multiuser receiver for use in additive white Gaussian noise, multiple-access communication channels. The receiver includes an interference estimator which estimates multiple-access interference signals using a variable weighting provided by a soft decision processor. The interference estimator may receive signals from matched-filter/sample-and-hold circuits, decorrelator circuits, or sliding-window-decorrelator circuits. The soft decision processor is provided having a soft-decision nonlinearity characteristic, which may correspond to a multilevel quantizer characteristic, a dead-zone nonlinearity characteristic, or a linear clipper characteristic.