Method and apparatus for selecting an optimal swapping technique in discrete multi-tone system

A method for performing gain-swapping in a discrete multi-tone (DMT) system having multiple sub-channels, gain factor constraints, and a maximum mean square error (MSEmax) and a minimum mean square error (MSEmin), wherein the gain factor constraints have a maximum gain factor constraint (Gcm) and a minimum gain factor constraint (Gcn), gmax denotes the gain of the sub-channel respecting MSEmax, gmin denotes the gain of the channel respecting MSEmin, said method comprising the steps of:

• obtaining an eleventh gain margin value (Gmv11) by subtracting gmax from Gcm,
• and obtaining a twelfth gain margin value (Gmv12) by subtracting Gcn from gmin;
• obtaining a tenth parameter (P10) by subtracting MSEmin from MSEmax;
• obtaining the value MIN of the smallest one of the group consisting of Gmv11, Gmv12 and (0.5*P10);
• and
• adding gain in amount of MIN to the sub-channel having MSEmax and subtracting gain in amount of MIN from the sub-channel having MSEmin.

A swapping technique selector for selecting an optimal swapping technique from a group consisting of a bit-swapping and a gain-swapping techniques in a discrete multi-tone (DMT) system having multiple sub-channels, gain factor constraints, and a threshold index value (T) and a maximum mean square error (MSEmax) and a minimum mean square error (MSEmin), the swapping technique selector comprising:

• a performance improvement pre-calculator for determining a first index value (I) and a second index value (J) based on MSEmax, MSEmin and said gain factor constraints according to a predetermined manner, I denoting range of improvement when adopting the gain-swapping as the optimal swapping technique, and J denoting range of improvement when adopting a combination of the gain-swapping and the bit-swapping as the optimal swapping technique;
• a threshold comparator, connected to the performance improvement pre-calculator, for determining whether the larger one of I and J is larger than T;
• a performance improvement comparator, connected to the threshold comparator, for selectively determining whether I is equal to or larger than J;
• and
• a swapping technique selection device, connected to the performance improvement comparator, for selecting either the gain-swapping or the combination of gain-swapping and bit-swapping as the optimal swapping technique.