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AIS demodulator for unknown carrier phase and baud alignment

Patent image
NSA

A method of demodulating an AIS signal by receiving the signal, sampling the signal, estimating the carrier frequency, estimating the complex conjugate of the carrier frequency contribution to each sample, multiplying each sample by the complex conjugate and calling the results a base-banded sampled signal (BBSS), correlating the BBSS with known preambles, identifying a maximum magnitude of the BBSS/preamble correlation and its location and the associated preamble, computing a complex inner product of the preamble with a segment of the BBSS, estimating the carrier phase as an argument function of the eighth step result, estimating a complex conjugate of the carrier phase contribution to the BBSS, multiplying each fifth step result starting at the location of the maximum magnitude of the BBSS/preamble correlation by the tenth step result, and demodulating the results starting at that location.

Inventors: 
Smith, David C.
Patent Number: 
Technical domain: 
Communications
FIle Date: 
2011-02-24
Grant Date: 
2014-03-04
Grant time: 
1,104 days
Grant time percentile rank: 
20
Claim count percentile rank: 
5
Citations percentile rank: 
1
'Cited by' percentile rank: 
1
Assignee: 
US DIRECTOR THE NAT SECURITY A