Abstract: A method of applying a multidimensional error reduction/correction algorithm on a stream of one dimensional symbols, by converting the stream of one dimensional symbols into a corresponding stream of two dimensional symbols; and, applying the multidimensional error reduction/correction algorithm to the stream of two dimensional symbols. The invention also provides a method of normalizing a metric used by an error reduction/correction algorithm on a stream of symbols wherein the symbols are non-uniformly spaced, by: determining a minimum distance (dmin) between two closest symbols in the stream, for each symbol in the stream, determining a minimum distance (dsym) between each symbol in the stream and each of its adjacent neighboring symbols, and, normalizing the metric used by the error reduction/correction algorithm by the ratio dmin/dsym.

Abstract: Methods of determining systemic impairments in a telecommunications network comprise sending a candidate set of digital symbols from a digital modem to an analog modem. The symbols are affected by systemic impairments in the network. Data information symbols or mapping tables are derived in the analog modem. The data information symbols or mapping tables are then provided to the digital modem. The digital modem may use the data information symbols or mapping tables in a variety of manners, such as for data transmission, spectral shaping, echo cancellation, or adaptation to robbed bit signaling.

Abstract: A method of discovering characteristics of a PCM channel between a first PCM modem and a second PCM modem, comprising the steps of creating a PCM representation of a probing tone ensemble, where the probing tone ensemble comprises one or more tones, transmitting the PCM representation of the probing tone ensemble from the first PCM modem to the second PCM modem, receiving the PCM representation of the probing tone ensemble by the second PCM modem; and, processing the PCM representation of the probing tone ensemble to determine characteristics of the PCM channel.

Abstract: A method of asymmetrical forward error correction for a communication link having two communication directions, comprising a first type of forward error correction method in a first direction of the communication link and a second type of forward error correction method in a second direction of the communication link, where the first and second types of forward error correction methods are different.

Abstract: A method of determining digital channel attenuation; comprising the steps of: receiving a known training sequence of PCM codes, which PCM codes are subjected to the attenuation within the digital channel; quantizing the received known training sequence of PCM codes according to a predetermined thresholding procedure; identifying identical PCM codes created as a result of the thresholding procedure; and, determining the attenuation of the digital channel based upon the identification of identical PCM codes. A method is also disclosed for determining a digital channel PCM code transformation comprising receiving a known training sequence of PCM codes, which PCM codes are subjected to the PCM code transformation within the digital channel, quantizing the received known training sequence of PCM codes according to a predetermined thresholding procedure, and determining the transformation of transmitted codes to those received.

Abstract: A method of compensating for systemic impairments in a telecommunications network is disclosed. The method may involve transmitting a candidate set of digital symbols from a digital model to an analog modem, processing an analog representation of said candidate set of digital symbols in the analog modem, deriving a set of data information symbols from the analog representation of the candidate set of digital symbols, transmitting a representation of the data information symbols from the said analog modem to the digital modem, and using the representation of the data information symbols in digital modem for subsequent transmission of data from the digital modem.

Abstract: A method of applying a multidimensional error reduction/correction algorithm on a stream of one dimensional symbols, by converting the stream of one dimensional symbols into a corresponding stream of two dimensional symbols; and, applying the multidimensional error reduction/correction algorithm to the stream of two dimensional symbols. The inventions provides a method of normalizing a metric used by an error reduction/correction algorithm on a stream of symbols wherein the symbols are non-uniformly spaced, by: determining a minimum distance (dmin) between two closest symbols in the stream, for each symbol in the stream, determining a minimum distance (dsym) between the each symbol in the stream and each of its adjacent neighboring symbols, and, normalizing the metric used by the error reduction/correction algorithm by the ratio dmin/dsym.

Abstract: A method of shaping a transmit spectrum of a PCM modem comprising: selecting a first symbol from a first subset of predetermined symbols; converting said first symbol to its linear value equivalent representation; applying said linear value to a transmit shaping transfer function to obtain a shaping function result; and using said shaping function result to choose a second subset of predetermined symbols for transmission of a second symbol. A method of shaping a transmit spectrum of a PCM modem, comprising: converting a symbol to its linear value equivalent representation; and, applying said linear value to a transmit shaping transfer function to obtain a shaping cost function result, wherein said transmit shaping transfer is expressed in the form of H(z)=(1−a1z−1)/(1−b1z−1) wherein: a1 and b1 are coefficients selected to represent the desired spectral shape.

Abstract: A method of mapping a substring of a bit stream to a symbol selected from a set of symbols, comprising: determining if the numeric value of an n bit substring of the bit stream is below a threshold; selecting the symbol from a first subset of symbols if the numeric value is below the threshold; selecting the symbol from a second subset if the numeric value is equal to or greater than the threshold and the next bit of the bit stream is a 0; and, selecting the symbol from a third subset if the numeric value is equal to or greater than the threshold and the next bit of the bit stream is a 1.

Abstract: A telephone modem which is at least partially powered by electrical power from a telephone line to which it is connected and which is further powered by a local power source, such as power extracted from digital serial data lines to which it is coupled or from a battery source or a combination thereof. Telephone line power is used to operate all analog signal processing, and local power is used to operate the remainder of the modem, including digital signal transmission, reception and manipulation, as well as modem control functions. In a preferred embodiment, optical isolation means provide isolation between differently-powered segments of the modem circuitry. The analog signal processing segment is coupled to the telephone line in a manner which maintains line current requirements and constant a.c. impedance, and regulated power is derived from the intermittent telephone line power source.