Bit Loading

The amount of bits that can be carried per channel depends upon the SNR at that particular frequency, lower SNR levels may need more power to transmit data and since each frequency is subject to an overall power limit, those frequencies are able to carry less bits than a channel with a better SNR.

• 　　The better the SNR at that frequencies in the sub-channel range, then the more bits that can be allocated to that particular carrier bin.

• 　　If the signal is good then 15 bits (maximum) can be allocated to that tone.

• 　　If the SNR is weak/weaker at a particular frequency range, then not as many bits can be carried by the tone.

• 　　Each 3dB of SNR equates to 1 bit (of data),

A minimum of 2 bits per bin is needed for the tone to be usable for ADSL1 (6dB)

ADSL2 and ADSL 2+ support single bit tones (3dB).

If there s insufficient SNR in the channel, then the carrier bin is marked by the router as unusable