Pulse or digital communications – Repeaters – Testing
Patent
1994-10-18
1996-09-24
Gregory, Bernarr E.
Pulse or digital communications
Repeaters
Testing
375205, 375206, 380 34, 370 18, H04B 169, H04B 1707, H04J 1302, H04J 1304
Patent
active
055598285
ABSTRACT:
The disclosed spread spectrum system has the reference transmitted on one phase (basis vector) of a .pi./2-offset QPSK signal, and the spread data signal transmitted on another phase (basis vector). The two received phases are combined to recover the baseband signal. Such a transmission system is tolerant to multipath dispersion since all delay paths carry an appropriately delayed reference and signal path induced dispersion on the spread data signal is also present on the reference. If one of the two signals is delayed by a predetermined time interval and a corresponding delay is present in each of two cross-coupled signal processing paths following a conventional I-Q demodulator, the resulting two phase quadrature baseband signals may be combined to form a replica of the original baseband signal. The resultant asynchronous demodulation eliminates the usual requirement for carrier lock at the receiver and is therefore tolerant to Doppler shifts and other frequency errors. Both the asynchronous and synchronous (coherent demodulation) embodiments offer multiple use of the same center frequency through a novel "delay division" multiplexing concept.
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Armstrong John T.
Richert John D.
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