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VOCAL has developed and patented a variety of industry-critical technologies. This list identifies several of the patents which have already issued and/or published. As always, please search for all relevant patents to find any VOCAL patents which may apply.

Direct Connect Modem Deriving Power From Telephone Line

A telephone modem which is at least partially powered by electrical power from a telephone 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 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 the line current requirements and constant a.c. impedance, and regulated power is derived from the intermittent telephone line power source. In a further specific embodiment, charge pump circuitry is employed to extract both positive and negative inverted power from the digital serial data line for use as local power.

Patent No 5,086,454 – Issued February 4, 1992

Maximal Bit Packing Method

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; selected the symbol from a first subset of symbols if the numeric value is below the threshold; selecting the symbol from a second subset is the numeric value is equal 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.

Patent No 6,067,034 – Issued May 23, 2000

Variable Spectral Shaping Method For PCM Modems

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. 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 function is expressed in the form of H(z) =
((1-a1z-1)/(1-b1z-1))*((1-a2z-1)/(1-b2z-1)) wherein: a1, a2, b1 and b2 are coefficients selected to represent the desired spectral shape.

Patent No 6,222,890 B1 – Issued April 24, 2001

Trellis Encoding Technique For PCM Modems

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 ration dmin/dysm.

Patent No 6,301,683 B1 – Issued October 9, 2001

Adaptation to Digital Network Impairments By PCM Modems

A method of compensating for systemic impairments in a telecommunications network is disclosed. The method may involved
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 said analog modem to the digital modem for subsequent transmission of data from the digital modem. The method may also include the preceding steps of sending digital symbols from the digital modem to the analog modem, converting the digital symbols into
analog signals in the telephone network, processing the analog signals in the analog modem, and training a receiver of the analog modem to recognize changes in the analog signals that correspond to known changes in digital symbols transmitted by the digital modem.

Patent No 6,327,301 B1 – Issued December 4, 2001

Method For Determining Attenuation in a Digital PCM Channel

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. A method is also disclosed for improved echo cancellation in a communications network having an analog and a digital modem, comprising saving codes transmitted from the digital modem to the analog modem for echo cancellation, transforming, by a mapping table, codes transmitted from
said digital modem to codes received by the analog modem, and, using the received codes as a reference signal for cancellation of echo. A method of improved spectral shaping using a transmit shaping transfer function in a communications network having an analog and a digital modem, comprising, transforming, by a mapping table, codes transmitted from the digital modem to codes received by the analog modem, using the received codes for transformation to their linear value equivalent representations, and, applying the linear value representations to the transmit shaping transfer function.

Patent No 6,480,549 B1 – Issued November 12, 2002

Method Of Improving Echo Canceller Training In Modems

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. The invention also comprises a method of improving echo canceller training of a modem comprising generating an echo canceller training reference signal modifying the echo canceller training reference signal sending the modified echo canceller training reference signal into a channel, receiving an echo of the modified echo canceller training signal; and, processing the echo canceller training reference signal and the received echo of the modified echo canceller
training reference signal.

Patent No 6,633,604 B1 – Issued October 14, 2003

Compensating For Impairments In A Telecommunications Network

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.

Patent No 6,643,270 B1 – Issued November 4, 2003

Turbo-Like Codes For QAM Modulation and XDSL Systems

A transmitter produces a modulated signal with forward error correction from an information bit stream in a QAM transmitter. The transmitter produces parity bit streams that correspond to an inputted information bit stream using firs and second concatenated coders interconnected by an interleaver. Subsets of the first and second parity bit streams are selected in accordance with a puncturing pattern. A variety of novel puncturing patterns providing various coding rates for various constellations are disclosed. The transmitter combines the selected subsets of said first and second parity bit streams with said information bit stream. A QAM symbol is produced by mapping a first
subset of the combined bit streams to an I dimension and mapping a second subset of the combined bit streams to a Q dimension. The QAM
symbol stream is modulated to produce a modulated signal that is transmitted over a communication link. A complementary receiver is also
disclosed. The puncturing pattern used in the transmitter may be adapted based on a performance metric determined in the receiver.

Publication No 2002/0051501 A1 – Published May 2, 2002

Asymetrical Forward Error Correction In A Communications System

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 the communication link, where the first and second types of forward error correction methods are different.

Publication No 2003/0152158 A1 – Published August 14, 2003

Multi-Dimension Constellations With Low Receiver Extraction Requirements

A non-separable symbol constellation may comprise constituent constellations having separable I and Q. Such a non-separable
constellation may be decoded with the efficiency of a separable constellation by decoding for each of the constituent constellations
individually. In a transmitter, transmit data may be mapped to symbols by selecting s constituent constellation and I and Q values for a symbol to be transmitted. In a receiver, decoders may decode for each constituent individually.

Publication No 2002/0131524 A1 – Published September 19, 2002

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