METHOD AND APPARATUS FOR CLOCK TIMING RECOVERY IN chi DSL, PARTICULARLY VDSL MODEMS

摘要

Method and modem for fast timing recovery of transmitted data between a master chi DSL modem and a slave chi DSL modem, over a noisy, high loss, high distortion wiring. Transmitted QAM symbols are received and sampled (10) at the slave modem. The sampled data is split into in-phase (I) and quadrature (Q) channels (11, 12), each of which is filtered by matched filter (13, 14). The filtered I and Q outputs are sampled at twice the symbol rate and the lower and upper band edge components are extracted by modulating each of the sampled sequence of I and Q outputs with two discrete time sequences: cos(0.5 pi n) = ...,1,0,-1,0,... and sin(0.5 pi n) = ...,0,1,0,-1,... Each of the resulting products is filtered with a first order low-pass filter (26, 27) and re-sampled again at the symbol rate. The Bit Error Rate is computed (28), and the slave modem switches from blind timing recovery mode, to data directed timing recovery mode, after the Bit Error Rate has sufficiently decreased.