Patent ID: 6134273
Filing Date: 2000-10-17
Classification: H04L

Abstract:
In a discrete multitone (DMT) digital subscriber loop (DSL) data communications system wherein subchannel bit coding constellation size is selected based on number of bits assigned to a respective subchannel, and a bit loading algorithm is employed to adaptively assign different numbers of bits to different subchannels according to determined subchannel signal-to-noise ratios, a method for data communication comprising:defining a generic I, Q component, n-bit constellation bit-mapping table, having smaller constellations usable for subchannel lower bit number assignments nested within bigger constellations usable for subchannel larger bit number assignments;defining respective gain correction factors g.sub.n corresponding to the size constellation to be used for each subchannel bit number assignment;at the transmitter side, mapping bits of transmission data to subchannels according to table look-up of I, Q components using the generic mapping table;before transmitting, after mapping table look-up, scaling the obtained I, Q components for each subchannel by multiplying by the gain correction factor g.sub.n corresponding to the number of bits assigned to that subchannel;defining a generic I, Q component, constellation bit-demapping table, having smaller constellations usable for subchannel lower bit number assignments nested within bigger constellations usable for subchannel larger bit number assignments;defining respective gain correction factors 1/g.sub.n corresponding to size constellation to be used for each subchannel bit number assignment;at the receiver side, descaling the received I, Q components for each subchannel by multiplying by the gain correction factor 1/g.sub.n corresponding to the number of bits assigned to that subchannel; anddemapping bits of received data from subchannels after descaling, according to table look-up of I, Q components using the generic demapping table.