| 摘要 |
To avoid spurious energy radiation from a wireline communication resource (42-44) supporting data over voice, such as in xDSL; modems (40, 46) supporting a multi-carrier transmission scheme undertake a line balance assessment (136-138) for each sub-channel carrier within the system. Specifically, an addressed modem (40) measures, for example, the signal to noise ratio of a differential transmission mode and a common transmission mode to provide the balance assessment (138). More particularly, a receive chain in the addressed modem is selectively switched (84) to receive the differential mode as appearing across the terminals of an isolation transformer (66) or the common mode (as seen with respect to ground) from a centre tap (88) in a line-side winding (70) of the isolation transformer (66). Any sub-channel carrier that fails to provide a predetermined level of balance (140) is de-selected (141) by the modem and not used for traffic. Generally, the modems (40, 46) at both ends of the wireline connection (42-44) notify one another of selected sub-channels, while the concept can be employed in a dynamic in-call fashion (152, 158-160).
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