Telegraphy – Systems – Line-clearing and circuit maintenance
Patent
1975-04-04
1976-04-27
Heyman, John S.
Telegraphy
Systems
Line-clearing and circuit maintenance
328155, 340147SY, 340207P, H04L 700
Patent
active
039536742
ABSTRACT:
Simultaneous phase lock and synchronization acquisition of an L format biphase input signal having a pseudorandom sequence are obtained with a delay lock loop including a feedback shift register for deriving a first non-return to zero (NRZ) output signal having the same pseudorandom sequence as the input signal. An output of the shift register is compared with the input signal to derive a phase indicating binary error signal that is fed to a digital filter for deriving a binary output signal to control the transition times of a clock signal derived from a voltage controlled clock source. The digital filter is activated and the shift register is advanced in response to the clock signal. The input signal is converted into a second NRZ signal that has the same information content as the input signal. The first and second NRZ signals are compared to derive a further signal indicative of an estimate of the correlation function between the input signal and the output signal of the shift register. To provide an estimate of the pseudorandom input signal, the feedback shift register is loaded with bits of the second NRZ until the correlation value achieves a predetermined value. The synchronizer stays in a search mode until the correlation value achieves a predetermined value after a complete frame of the input signal has been received. Thereafter, the system is switched into a verify mode, during which tests are performed to determine if the system should revert back to the search mode or go into a lock mode. In response to K consecutive good frames wherein the correlation value achieves the predetermined value the system is activated into the lock mode; in response to L consecutive bad frames the system reverts back to the search mode. The system stays in the lock mode until M consecutive bad frames are received.
REFERENCES:
patent: 3271688 (1966-09-01), Gschwind et al.
patent: 3591720 (1971-07-01), Othmer
patent: 3629503 (1971-12-01), Rempert
patent: 3683345 (1972-08-01), Faulkes et al.
patent: 3889186 (1975-06-01), Larson
IEEE Transactions on Communication Tech., Vol. Com. 13, No. 4, Dec. 1965, "Acquisition of Pseudonoise Signals by Sequential Estimation", by Ward.
Fletcher James C. Administrator of the National Aeronautics and Space
Pardoe Carroll T.
Grafel Gary F.
Heyman John S.
Manning John R.
Sandler Ronald F.
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