Constellation adjustment based on detected encoding and encoding conversion for modem connections

摘要

A first transceiver transmits a set of test levels to a second transceiver through a communication channel with one or more types of companding laws. The second transceiver determines line encoding with, and conversion between, the companding laws present in the communication channel based on the received set of test signals. The set of test levels are signals having levels determined based on the difference between the normalized amplitude, vertex, or energy curves for the types of companding laws, with or without accounting for other sources of network distortion. Additional distortion from line characteristics, such as robbed-bit signaling (RBS) and/or line impairment, may be detected based on changes in encoding sample levels of transmitted test signals that are reconstructed by the second transceiver. The second transceiver may then transmit information to the first transceiver about the companding laws and other sources of distortion present in the network. The second transceiver employs a method of constellation adjustment to correct for distortion resulting from line encoding, encoding conversion, RBS and other line impairments. For a given, detected encoding conversion during the training phase, two constellations are employed, one for the first transceiver and one for the second transceiver. For constellation adjustment, each transceiver first detects encoding, encoding conversion, RBS, and other line impairments using a set of PCM test levels during their respective training phases. The second transceiver then adjusts its transmit constellation for communication with the first transceiver based on the detected encoding, encoding conversion, RBS, and other line impairments.