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Showing papers by "Codex Corporation published in 1984"


Journal ArticleDOI
TL;DR: This paper attempts to present a comprehensive tutorial survey of the development of efficient modulation techniques for bandlimited channels, such as telephone channels, with principal emphasis on coded modulation techniques, in which there is an explosion of current interest.
Abstract: This paper attempts to present a comprehensive tutorial survey of the development of efficient modulation techniques for bandlimited channels, such as telephone channels. After a history of advances in commercial high-speed modems and a discussion of theoretical limits, it reviews efforts to optimize two-dimensional signal constellations and presents further elaborations of uncoded modulation. Its principal emphasis, however, is on coded modulation techniques, in which there is an explosion of current interest, both for research and for practical application. Both block-coded and trellis-coded modulation are covered, in a common framework. A few new techniques are presented.

770 citations


Patent
08 Mar 1984
TL;DR: In this paper, the quality of the channel is monitored, a communication rate is selected based on the channel quality, the desire for an increased rate is indicated, and the increased rate can be implemented by the modem when the remote device concurs.
Abstract: In a modem that transmits signals to and receives signals from a remote device at a multiplicity of communication rates, the quality of the channel is monitored, a communication rate is selected based on the channel quality, the desire for an increased rate is indicated, and the increased rate is implemented by the modem when the remote device concurs.

167 citations


Journal ArticleDOI
Lee-Fang Wei1
TL;DR: Design rules and procedures for 180° rotationally invariant convolutional codes with expanded signal space having 90, 180, and 270° phase ambiguities are extended and a new class of codes described as "generalized feedback" is also considered.
Abstract: This is the second paper on rotationally invariant convolutional channel coding with expanded signal space. Signal space with 90, 180, and 270° phase ambiguities is generally preferred to signal space with only 180° phase ambiguity. In this paper, design rules and procedures for 180° rotationally invariant convolutional codes in the previous paper are extended to rotationally invariant codes with expanded signal space having 90, 180, and 270° phase ambiguities. As in the previous paper, we illustrate these rules and procedures by designing simple codes with coding gain of 4 dB. Nonlinear convolutional codes result from these design rules and procedures. These simple nonlinear convolutional codes are being considered as international standards on voiceband modems at rate greater than or equal to 9.6 kbits/s. Codes with higher coding gain can be obtained using the same rules and procedures. Both feedforward and feedback codes are considered. In addition, a new class of codes described as "generalized feedback" is also considered.

129 citations


Journal ArticleDOI
Lee-Fang Wei1
TL;DR: Design rules and procedures for 180° rotationally invariant codes are presented and extended to codes which are transparent to 90, 180, and 270° signal element rotations.
Abstract: Convolutional channel coding with expanded signal space improves error performance of synchronous data links without sacrificing data rate or requiring more bandwidth. Due to the phase ambiguity(ies) in the expanded signal space, it is desirable to design the code' to be transparent to signal element rotations. In this paper, design rules and procedures for 180° rotationally invariant codes are presented. In a companion paper, we extend these rules and procedures to codes which are transparent to 90, 180, and 270° signal element rotations. We illustrate these rules and procedures by designing simple codes that achieve coding gain of 3-4 dB. These are the codes of practical interest. Codes with higher coding gain can be obtained using the same rules and procedures. Both feedforward and feedback codes are considered.

119 citations


Patent
16 Apr 1984
TL;DR: In this article, a block of digital data bits is sent over a band-limited channel using a plurality of modulation signal points drawn from a two-dimensional constellation of available signals.
Abstract: A block of digital data bits is sent over a band-limited channel using a plurality of modulation signal points drawn from a two-dimensional constellation of available signals. The constellation comprises a plurality of inner signals, and a plurality of outer signals located farther from the origin than the inner signals. One bit of the block of digital data determines whether any of the plurality of signal points will be drawn from the outer signals. If an outer signal will be drawn, at least one other bit of the block of digital data determines which of the plurality of signal points will be an outer signal point.

65 citations


Patent
28 Dec 1984
TL;DR: In this paper, a receiver for use in deciding which signal points were sent from a transmitter based on corresponding noise affected signals received over a channel, the transmitter including an encoder which encodes a stream of information symbols into the signal points, the signal affected signals carrying information about a particular sequence of possible states occupied in a succession of time intervals by a finite state process.
Abstract: A receiver for use in deciding which signal points were sent from a transmitter based on corresponding noise affected signals received over a channel, the transmitter including an encoder which encodes a stream of information symbols into the signal points, the noise affected signals carrying information about a particular sequence of possible states occupied in a succession of time intervals by a finite state process. The receiver includes feedback circuitry for generating a plurality of different modified versions of each received signal, and a decoder for deciding which signal points were sent, given the received signals, based on estimating the particular sequence of states, and using at least two different modified versions.

48 citations


Patent
06 Feb 1984
TL;DR: In this paper, the authors propose an approach for sending bits of information over a band-limited channel by modulating a carrier in accordance with a sequence of signal points drawn from a constellation of available signal points, in which the apparatus includes circuitry for accumulating groups of the information bits for encoding into the signal points.
Abstract: Apparatus for sending bits of information over a band-limited channel by modulating a carrier in accordance with a sequence of signal points drawn from a constellation of available signal points, in which the apparatus includes circuitry for accumulating groups of the information bits for encoding into the signal points, different groups having different numbers of information bits from a primary data source, and an encoder for encoding at least the bits of each said group into at least one signal point drawn from the constellation, the encoder being arranged to draw different available signal points with different probabilities.

43 citations


Patent
23 Apr 1984
TL;DR: In this article, a data communication network over which data handling devices can transmit and receive packets among themselves having a bus, a number of sub-networks (each having interfaces for connecting devices connected to each sub-network), a concentrator for connecting each interface to the bus, each concentrator having a transceiver for transmitting, to the buses and to devices connected in each subnetwork, packets originating from devices within a subnetwork (transmitted packets), and for receiving from the bus packets originating in other sub-nets (received packets), collision avoidance circuitry for monitoring transmission attempts
Abstract: A data communication network over which data handling devices can transmit and receive packets among themselves having a bus, a number of subnetworks (each having interfaces for connecting a number of devices to each subnetwork), a concentrator for connecting each interface to the bus, each concentrator having a transceiver for transmitting, to the bus and to devices connected to each subnetwork, packets originating from devices within a subnetwork (transmitted packets), and for receiving from the bus packets originating from other subnetworks (received packets), collision avoidance circuitry for monitoring transmission attempts by devices connected to the subnetwork, for detecting competing transmission attempts that would create a collision on the subnetwork, and, upon such detection, permitting a selected attempt to enter the subnetwork, while preventing other attempts from entering it, collision detection circuitry for monitoring the bus and preventing all attempted transmissions from entering the bus whenever a packet from another subnetwork is present on the bus. In another aspect the interface means and the concentrator means include a network interface unit and a further interface unit.

24 citations


Proceedings ArticleDOI
01 Mar 1984
TL;DR: The root LPC system has closed form analysis and formant like synthesis structure and by using quadratic coefficient quantization and section repeat its data rate can be lower than 1Kbps and its quality can be continuously improved.
Abstract: The root LPC system has closed form analysis and formant like synthesis structure. By using quadratic coefficient quantization and section repeat its data rate can be lower than 1Kbps. By including representative residual signal of variable repetition rate its quality can be continuously improved. A special purpose NMOS-LSI chip was built to implement the synthesis function.