Optimised bit allocation adapted for VDSL

A method for providing bit loading computation in a multi-carrier communication system, using a plurality of simultaneous different carriers, where the carriers are tones, the method comprising:

• measuring the signal to noise ratios for the carriers;
• and
• determining based on the signal to noise ratios a related number of bits to be loaded or allocated to a respective carrier,
• wherein said determining comprises:
• providing a sliding window having a frequency width comprising a predetermined number of the carriers,
• moving the sliding window over a frequency spectrum of the carriers through a plurality of positions of the window with respect to the carrier frequencies, the movement being such that after each movement at least one new carrier is positioned in the window, said at least one new carrier is in a current position next to a carrier that was previously positioned in the current position;
• when the window contains the predetermined number of the carriers and there is at least one further carrier to be positioned in the window as a new carrier for bit loading, the movement of the window being made such that on positioning the new carrier into the window at one of its frequency borders, a carrier already in the window at other frequency border leaves the window;
• for each position of the window determining bit allocation for a respective at least one carrier from the predetermined number of the carriers within the window;,
• in the event that a predetermined average power spectrum density threshold of the carriers over the window for the current window position is exceeded, selecting at least one carrier within the window for power spectrum density reduction at expense of at least one bit.