06157679 is referenced by 20 patents and cites 7 patents.

A method is provided of adding an encryption element to the QAM modulation/demodulation process. This is achieved by first forming a sequence of transmit QAM constellation symbols on the basis of the information signal to be modulated/demodulated, which signal is comprised by a corresponding sequence of transmit information values. Each QAM transmit constellation symbol is based on a fixed transmit constellation in a complex plane and is characterized by a real part and an imaginary part, each part including a sign, the sign consisting of plus or minus. On the basis of a fixed algorithm, during signal modulation, one or more of the transmit constellation symbols are altered by, for example, conjugating the sign value of either the real or imaginary parts thereof to form a disguised or encrypted set of symbols. During demodulation, a corresponding "undo" algorithm is employed by the receiver to undo the conjugation/encoding of altered QAM symbols, thus decrypting the signal to arrive at the original sequence of QAM constellation symbols.

Title
Method of adding encryption/encoding element to the modulation/demodulation process
Application Number
8/954348
Publication Number
6157679
Application Date
October 17, 1997
Publication Date
December 5, 2000
Inventor
Christopher L Johnson
Chicago
IL, US
Agent
Jeffrey K Jacobs
George C Pappas
Assignee
Motorola
IL, US
IPC
H04L 27/10
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