Adaptive allocation for variable bandwidth multicarrier communication

Abstract

Data is distributed among the channels of an asynchronous data subscriber loop (ADSL) communications system in accordance with an adaptive algorithm which from time to time measures the signal to noise ratio of the various channels and finds a margin for each channel dependent on achievement (where possible) of a given bit error rate and a desired data transmission rate. The margin distribution is achieved by augmenting the constellation signal to noise ratio to enhance computational efficiency and allow redetermination of bit allocation tables during transmission as necessary. Pairs of bit allocation tables are maintained at the transmitter and receiver and one table of each pair at the transmitter and receiver is updated while the other pair is in use for controlling communication.

1 . A transmitter in a multicarrier modulation system, comprising: 
 a first bit allocation table specifying a first allocation of bits to subchannels used during current communication with a receiver; and    a second bit allocation table specifying a different allocation of bits to subchannels than the first bit allocation table,    wherein the transmitter stores the second bit allocation table for use during subsequent communication with the receiver.    
     
     
         2 . The transmitter of  claim 1  wherein the second bit allocation table produces a different transmission bit rate than the first bit allocation table.  
     
     
         3 . A receiver in a multicarrier modulation system, comprising: 
 a first bit allocation table specifying a first allocation of bits to subchannels used during current communication with a transmitter over a communication channel; and    a second bit allocation table specifying a different allocation of bits to subchannels than the first bit allocation table,    wherein the receiver stores the second bit allocation table for use during subsequent communication with the transmitter.    
     
     
         4 . The receiver of  claim 3  wherein the second bit allocation table produces a different transmission bit rate than the first bit allocation table.  
     
     
         5 . A multicarrier transmission system, comprising: 
 a plurality of communication units in communication with each other over a communications channel having a plurality of subchannels, each communication unit storing a first bit allocation table that specifies a first allocation of bits to the subchannels for use during current communication with each other communication unit over the communication channel; and    a second bit allocation table, stored by each of the communication units, specifying a different allocation of bits to subchannels than the first bit allocation tables, for use during subsequent communication between the communication units.    
     
     
         6 . The multicarrier transmission system of  claim 5  wherein one of the communication units comprises a switch unit that switches from the first bit allocation table stored by that communication unit to the second bit allocation table stored by that communication unit for allocating bits to the subchannels.