Cryptography – Communication system using cryptography – Wireless communication
Patent
1994-03-10
1996-01-30
Cain, David C.
Cryptography
Communication system using cryptography
Wireless communication
342189, 342132, 367125, 375208, 375209, H04K 110
Patent
active
054886627
ABSTRACT:
A transmitter (12) broadcasts a PN encoded message (16). A receiver (14) includes a SAW correlator (38) configured to autocorrelate with the PN sequence used in the broadcast signal. A preamble of the message (16) conveys two successive bits (18) that are each encoded with the PN sequence. After the correlator (38) has been preloaded with the PN sequence from the first bit (18), its non-correlation output exhibits reduced amplitude time sidelobes. A timing comparison circuit (60) compares a correlation signal (46) with a timing threshold (72). The timing threshold (72) is established at a very low level to minimize the influence of multipath. False triggering on noise is prevented by disabling the timing comparison circuit (60) until after the first bit (18). At this point in time the correlator (38) has been preloaded with its PN sequence, is again being loaded with its PN sequence, and outputs reduced amplitude time sidelobes.
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Anderson Neal R.
Fox Thomas M.
Heeren Julius A.
Cain David C.
Motorola Inc.
Nehr Jeffrey D.
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