Pulse or digital communications – Repeaters – Testing
Patent
1987-04-13
1988-10-25
Griffin, Robert L.
Pulse or digital communications
Repeaters
Testing
375 43, 375 61, 370 20, H04L 2302
Patent
active
047808845
ABSTRACT:
A bandwidth reduction technique is disclosed for use in digital systems wherein a pair of data signal elements modulate quadrature-related carriers. This modulation, referred to as quadrature amplitude modulation (QAM), phase shift keying (PSK) or amplitude and phase shift keying (APSK), generates a double-sideband signal which is transmitted in a variety of communications systems. In accordance with the present invention, the above-described double-sideband signal is filtered to form either a single sideband or vestigial sideband signal prior to transmission. While this use of a vestigial or single-sideband signal, in lieu of a double-sideband signal, permits the transmission of more information in a given frequency interval, the filtering process contaminates the data signal elements. To recover the data signal elements at the receiver, a pair of received signal elements is formed by extracting the carrier signals. One of these received signal elements is then altered at selected times to recover an associated one of the data signal elements at each selected time. Finally, this associated data signal element at certain ones of the selected times is combined with the other one of the received signal elements at an associated time to form the remaining data signal element.
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American Telephone and Telegraph Company AT&T Bell Laboratories
Chin Stephen
Griffin Robert L.
Padnes David R.
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