H - Electricity – 04 – L
Patent
H - Electricity
04
L
340/205
H04L 25/49 (2006.01) H04L 7/02 (2006.01)
Patent
CA 1296792
ABSTRACT OF THE DISCLOSURE In a receiver for a loop interface circuit of a digital data transmission system, comprising: sampling means for sampling a received four-level substantially randomized digital signal, and multilevel decision or slicing means for comparing samples of such received signal selectively with a plurality of thresholds to extract its four symbols, timing recovery means determines a sampling instant as a function of a precursor sample and a main pulse sample one baud apart, according to the timing function: f(t) = (1/r)h(t) - h(t-T) where 1/T is the baud rate, h(t) and h(t-T) denote the main pulse sample and precursor sample , respectively, r is the ratio between the main pulse sample and the precursor pulse sample, and t is the sampling instant. The timing recovery means includes a timing estimator responsive to baud rate samples (xn and an) of the received signal before and after slicing, respectively, for deriving a precursor estimate (zn) of the difference between the actual sampling instant and a desired sampling instant with reference to the ratio between the main sample pulse and said precursor sample one baud earlier, and means for generating a baud rate clock signal variable in dependence upon said estimate (Zn), the index n denoting the current baud interval. The sampling means is responsive to said baud rate clock to vary said 33 sampling instant. The timing estimator derives said precursor timing estimate zn in accordance with the expression:- zn = (-1)m.(an-1xn - anxn-1) where m represents the magnitude bit of the 2B1Q symbol (m = 1 for magnitude 1, m = 0 for magnitude 3). The slicer may have three thresholds adaptable according to the magnitude of the main cursor. 34
580828
Adams Thomas
Nortel Networks Limited
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