The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 15, 1993
Filed:
Dec. 21, 1990
Joseph R Burns, Pennington, NJ (US);
Mikros Systems Corp., Princeton, NJ (US);
Abstract
A multiple tone signal is demodulated and synchronization is obtained by precisely locating frame boundaries in order to ensure reliable communication in the presence of anomalies such as Doppler shift, multipath propagation, and additive electronic noise. One such signal, TADIL-A or Link-11, employs multiple tone audio waveforms that are used to modulate RF carriers for the transmission of digital data. Initially, the signal is frequency divided and classified to determine if the incoming frame is a preamble, data or noise. For preamble frames, a digital filter is used to extract the 605 Hz tone in the time domain, and the resulting real-valued signal is passed through a first Hilbert transform to generate the corresponding imaginary complex-valued signal. Unfiltered data frames are passed through a second Hilbert transform and the output is multiplied by the complex conjugate of the stored Doppler reference signal to produce a Link-11 Signal stripped of Doppler. As a result of the demodulation process, the entire waveform now includes frequencies separated by an integer multiple of 110 Hz. Therefore, the composite waveform has a period of 9.09 milliseconds. The composite waveform partially repeats itself at least once in each 13.33 msec frame interval. Using this property, it is possible to determine the location at which the composite signal becomes discontinuous and thereby locate the synchronization frame boundaries.