Multiplex communications – Wide area network – Packet switching
Patent
1994-02-25
1995-07-04
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
375261, 375269, H04J 1100
Patent
active
054307112
ABSTRACT:
A group modulator provided a plurality of digitally modulated signals with frequency division multiplex, having a time division multiplexer (11) for multiplexing a plurality of input data (#l through #n). A mapping circuit (12) provides an I-channel signal and a Q-channel signal according to a pattern of the multiplexed signal and the modulation system. A pulse shaping circuit (13) restricts bandwidth of the I-channel signal and the Q-channel signal. A frequency shift circuit (14) shifts frequency of the I-channel signal and the Q-channel signal by the frequency defined by the carrier control signal (i) for each input data. An accumulator (21,22) accumulates each of the I-channel signal and the Q-channel signal of the output of the frequency shift circuit (14) during a predetermined period (T). A D/A converter (31, 32) converts the output of the accumulator from digital form to analog form. A low pass filter (41, 42) is provided at the output of the D/A converter. A quadrature modulator (5) modulates carrier frequency (f.sub.c) with quadrature modulation according to the I-channel signal and the Q-channel signal at the output of the low pass filter. A multiplicity control (6) controls multiplicity in the time division multiplexer (11) according to an external multiplicity signal.
REFERENCES:
patent: 4780884 (1988-10-01), Karabinis
patent: 5237586 (1993-08-01), Bottomley
"A FH Modulator with Sampling Period Conversion Technique", Yamada et al., Proceedings of the 1992 IEICE Spring Conference, Mar. 24-27, 1992, pp. 2-359.
Shibato Tadashi
Yamada Yoshifumi
Nippon Telegraph & Telephone Corporation
Olms Douglas W.
Ton Dang
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