S5N8950

G.dmt ADSL Transceiver for CO and CPE

CONFIDENTIAL

Preliminary Information ( Rev 1.2 )

samples are fixed by the sync recovery algorithm using a known synchronization symbol. The TEQ is a

filter that adaptively alters the channel so that the impulse response is reduced to the length of the cyclic

prefix which will be removed prior to FFT. The FEQ is a one tap complex adaptive filter for each sub-

channel, which adjusts the gains and phases of the received signals. The equalizers are adaptively updated

due to the transmission channel environment.

In FDM-based DMT modulation, the frequency band, 0 to 1.104 MHz, is divided into 256 equi-spaced

sub-channels, of which 26 KHz (#6) to 134 KHz (#31) is allocated for the upstream, and 142 KHz (#33)

to 1.100 MHz (#255) for the downstream. The Nyquist rate, therefore, should be 2.208 MHz (276kHz).

DMT inherently transmits an optimized time-variable spectrum. This spectrum is adjusted according to

the desired data rate and the transmission characteristics (transfer function and noise spectrum) on each

and every sub-channel. For this, CO and CPE transmit 128.4 KHz wide tone downstream and upstream

respectively to each other during initialization. They measure the quality of each of these received tones

and then decided whether a tone has sufficient quality to be used for further transmission and, if so, how

much data this tone should carry relative to the other tones that are used. They inform the bit lo9ading

result to each other.