Hong C Jiang

US Patent:

61920886, Feb 20, 2001

Filed:

Mar 31, 1998

Appl. No.:

9/052455

Inventors:

Ahmad K. Aman - Fairfax VA
Cecil William Farrow - Highlands Borough NJ
Hong Jiang - Montclair NJ
Agesino Primatic - Frenchtown NJ
Charles Albert Webb - Rumson Borough NJ

Assignee:

Lucent Technologies Inc. - Murray Hill NJ

International Classification:

H04L 2714
H04L 2716
H04L 2722

US Classification:

375326

Abstract:

A digital carrier recovery system includes at least two modes of operation, namely, an acquisition mode and a tracking mode. The bandwidth of the carrier recovery loop filter is different for the acquisition mode and the tracking mode. In the acquisition mode, the digital phase-locked loop seeks and locks to the long term frequency offset of the received carrier signal. In the tracking mode, the digital phase-locked loop tracks the instantaneous variations in the carrier phase. Switching between the acquisition mode and the tracking mode is realized digitally, and includes programmable hysteresis, resulting in optimal performance in the presence of signals having high levels of phase noise (jitter). More specifically, the carrier recovery loop filter "locks" to the pilot signal of an incoming signal, e. g. , a vestigial side band (VSB) video signal, by employing a so-called digital vector tracking phase-locked loop that demodulates the VSB signal.

US Patent:

61342769, Oct 17, 2000

Filed:

Mar 31, 1998

Appl. No.:

9/052454

Inventors:

Ahmad K. Aman - Fairfax VA
Cecil William Farrow - Highlands Borough NJ
Hong Jiang - Montclair NJ
Agesino Primatic - Frenchtown NJ
Charles Albert Webb - Rumson Borough NJ

Assignee:

Lucent Technologies Inc. - Murray Hill NJ

International Classification:

H04L 2714

US Classification:

375326

Abstract:

A digital timing recovery system advantageously employs both demodulated I-phase and Q-phase components to more accurately locate the synchronization signal of an incoming VSB signal. The Q-phase component is advantageously employed to detect the phase error. The use of the Q-phase component provides a more accurate measure of the phase error and results in a larger (wider) acquisition range for timing frequency offset. More specifically, the timing recovery system of this invention performs symbol clock recovery based on the VSB signal segment synchronization (sync) signal and generates a pulse density modulated (PDM) phase difference signal that controls a voltage controlled crystal oscillator (VCXO) in the phase-locked loop. This is realized, in one embodiment of the invention, by correlating received sync segment data with the known sync signal pattern and searching for "peaks" in the correlation values that are periodic at the known sync segment data rate. Once the sync pattern is found, the correlation values for adjacent samples are advantageously employed to generate the necessary feedback control signal value for the VCXO.