Yigang Fan

US Patent:

6744836, Jun 1, 2004

Filed:

May 8, 2001

Appl. No.:

09/850080

Inventors:

Yigang Fan - Germantown MD
Prakash Chakravarthi - Germantown MD

Assignee:

Comsat Corporation - Clarksburg MD

International Classification:

H04L 704

US Classification:

375362, 375341, 370509

Abstract:

The present invention relates to burst mode digital communication systems where data transmission is preceded by a preamble for acquisition of carrier and clock synchronization using maximum likelihood (ML) principle. The preamble is sampled and the set of samples obtained is processed using the optimization algorithms of the present invention to provide the ML timing estimate. The optimization algorithms in the present invention consist of three parts. The first part deals with isolating the desired optimal estimate from non-optimal extremes satisfying the same necessary condition, and provides the initial conditions for activating the binary search schemes. The second part performs the binary search for the optimal timing estimate that guarantees the convergence. On the basis of the obtained iterative sequence, the last part constructs a more rapidly convergent sequence to obtain the ML symbol timing estimate. Using the obtained symbol timing estimate, the ML carrier phase estimate can be computed explicitly, and synchronization performed.

US Patent:

6560303, May 6, 2003

Filed:

Oct 26, 2000

Appl. No.:

09/695980

Inventors:

Yigang Fan - Germantown MD
Prakash Chakravarthi - Germantown MD

Assignee:

Comsat Corporation - Clarksburg MD

International Classification:

H04L 700

US Classification:

375365, 370514, 370509

Abstract:

The present invention provides a method to achieve frame synchronization from a received data sequence before the carrier phase and frequency offset recovery for any MPSK modulated signals on the basis of maximum likelihood theory. Two overhead configurations are considered in developing the frame synchronization algorithms. One overhead configuration consists of a unique word followed by a preamble, and the other consists of unique word only. For the first overhead, the frame synchronization can be decoupled from carrier recovery because the preamble following the unique word is a known sequence pattern. In this case, the maximum-likelihood frame synchronization rule is simply a complex correlation. In second overhead, the unique word is immediately followed by random traffic data and thus the coupling effects are generated between frame synchronization and carrier recovery. These coupling effects are not dominant, however, and may be neglected in actual practice.