Abstract: A method of analyzing the performance of a modem connection. The method includes connecting a line interface to a communication link carrying signals of a modem connection, between a pair of end modems, collecting signals passing on the communication link, between the end modems, through the line interface, determining quality or transmission characteristics regarding the modem connection, responsive to signals collected through the line interface, and displaying information on the determined characteristics.

Abstract: A method of analyzing the performance of a modem connection. The method includes connecting a line interface to a communication link carrying signals of a modem connection, between a pair of end modems, collecting signals passing on the communication link, between the end modems, through the line interface, determining quality or transmission characteristics regarding the modem connection, responsive to signals collected through the line interface, and displaying information on the determined characteristics.

Abstract: A communication system is disclosed in which information is transmitted using DMT modulation. The communication system includes first logic that is used to measure the response of each of the DMT subchannels and second logic that is used to adapt an equalizer filter associated with each of the DMT channels based on the response measurements. The system further includes third logic that measures the noise variance for each of the DMT subchannels. Using the noise variance measurements, fourth logic is used to assign the number of bits for transmission on each DMT subchannel such that total transmit power is minimized for a fixed data rate. Equations are provided for calculating a near optimal bit load allocation for the DMT subchannels and for calculating the total number of bits to be allocated to the DMT subchannels in a single encoding interval when total transmission power is limited.

Abstract: An apparatus is provided for concatenating Reed-Solomon and trellis encoders. Preferably, the apparatus includes an input for receiving a plurality of information bits. The plurality of information bits are divided or defined to comprise a first portion and a second portion. A Reed-Solomon encoder is disposed to receive the second portion of input bits and generate a first encoded output. A trellis encoder disposed to receive the output of the Reed-Solomon encoder and configured to generate a second encoded output. Finally, a mapper is disposed to receiver the bits output from the trellis encoder as well as the first portion of input bits.

Abstract: A method and apparatus for coding an information signal are provided. In accordance with one aspect of the invention, the method includes the step of encoding all or a portion of the information signal with a first encoder to generate a first set of redundant bits (preferably r.sub.1 bits). The method further includes the step of passing a portion of (and possibly all) the information signal through a structured interleaver to generate an interleaved signal. The method then encodes all or a portion of the interleaved signal with a second encoder to generate a second set of redundant bits (preferably r.sub.2 bits). Finally, the method includes the step of concatenating the information signal, the first set of redundant bits, and the second set of redundant bits to form an encoded output signal. A significant aspect of the present invention is the use of a structured interleaver in the encoder.

Abstract: A improved multilevel encoder and associated method is described. The encoder includes a device (e.g., serial to parallel converter) for presenting a plurality of information bits in parallel format. A symbol selector having a plurality of inputs and an output, the symbol selector being configured to output a symbol that is defined by a signal constellation, whereby the symbol is defined by a magnitude and phase that are uniquely associated with a state of the plurality of inputs. A first encoder has an input and an output, the input of the first encoder being associated with at least one of the outputs of the device and the output being associated with at least one of the inputs of the symbol selector, the first encoder configured by a code defining a four-way set partition of the signal constellation.

Abstract: The problem of error propagation is resolved by using the communications channel to adapt a pre-equalizer of a transmitter, in response to changes in the communications channel. In particular, the pre-equalizer adapts to changes in the communications channel by processing an error signal that is communicated over a reverse channel by a corresponding receiver.

Abstract: A modem that matches itself to a central office codec to which it is connected and incorporates encoding of the data. An echo canceller following the central office codec subtracts an estimate of the echo introduced in the central offices. More particularly, digital data applied to the modem is multi-level encoded and mapped onto a subset of the levels recognized by the central office codec. In an illustrative embodiment, the multi-level encoding encodes the two least significant bits in the binary representation of the levels delivered by the modem. The least significant bit is encoded with a code that is more robust than the code of the next-to-least significant bit, in recognition of the fact that errors in the least significant bit are much more likely. The corresponding echo canceller in the network first estimates the echo and subtracts it from the signal applied to the digital network by the central office. Thereafter, a decoder decodes the received signal in stages.

Abstract: Method and apparatus for efficient encoding of symbols with multilevel encoding, where components of the symbols that are more susceptible to errors are encoded more robustly than components that are less susceptible to error. A non-binary constellation of symbols is handled with a fractional bit rate converter that combines with the multilevel encoder to create an effective and efficient constellation of symbols. Illustratively, digital data is encoded and mapped onto a set of symbols, with the two least significant bits of the symbols being encoded with a multi-level code. The least significant bit is encoded with a code that is more robust than the code of the next-to-least significant bit, in recognition of the fact that errors in the least significant bit are much more likely. The most significant bits are mapped with the aid of a fractional bit rate mapper that optimizes a selected aspect of the symbol constellation, such as average power.