US Patent 7933318 Carrier re-activation in case of signal to noise ratio improvement

The present invention relates to a first transceiver unit, acting as a receiver unit, and to a second transceiver unit, acting as a transmitter unit. The first transceiver unit measures the signal to noise ratio for each tone, and determine whether a tone shall be shut off, thereby reducing interference on neighboring lines and power consumption. If so, the first transceiver unit keeps on measuring the noise level over that tone. If the ratio of the initially measured signal level to the newly measured noise level exceeds a pre-determined threshold, then the first transceiver unit requests the second transceiver unit to re-activate that tone. A new initialization sequence is transmitted over that tone for initializing the frequency domain equalizer, for measuring the signal to noise ratio, and finally for agreeing on a bit loading.