Decoding device for performing amplitude-phase demodulation and

Details Decoding device for performing amplitude-phase demodulation and Decoding device for performing amplitude-phase demodulation and

1995-05-04

1996-10-22

Chin, Stephen

Pulse or digital communications

Systems using alternating or pulsating current

Plural channels for transmission of a single pulse train

H04L 512, H04L 2302

Patent

active

055685170

ABSTRACT:
A modulator-demodulator (i.e., modem) permits a personal computer and the like to receive and transmit data in digital format across voice-oriented communications links such as telephone lines. A full-duplex-type modem employs a decoding device decoding the data which are subjected to convolution-encoding operation and amplitude-phase modulation. That data is subjected to amplitude-phase demodulation at first: and then, it is subjected to viterbi decoding by which an error correction is carried out. In the amplitude-phase demodulation, an amplitude-phase plane is employed and is divided into a plurality of areas in accordance with an arrangement of signal-placing points which is used by the amplitude-phase modulation. When receiving the data, a certain receiving point is defined. Then, one of the areas to which the receiving point belongs is determined; and its area information is produced. A plurality of candidate paths are determined by referring to the signal-placing points which are arranged around the area to which the receiving point belongs. A distance between the receiving point and each signal-placing point is computed with respect to each of the candidate paths, thus eventually determining a surviving path whose total distance is the smallest. On the basis of the surviving path, a viterbi decoding is performed to determine low-order bits for decoded data. A random-access memory temporarily stores and retains the area information during a predetermined period of time, so that old area information is currently read out. Based on the old area information, high-order bits for the decoded data are determined in accordance with a predetermined algorithm.

REFERENCES:
patent: 5301209 (1994-04-01), Wei

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