Differential quadrature phase shift keying encoder for subcarrie

Details Differential quadrature phase shift keying encoder for subcarrie Differential quadrature phase shift keying encoder for subcarrie

1991-01-02

1993-06-22

Kuntz, Curtis

Pulse or digital communications

Repeaters

Testing

345 84, 345 67, 359279, 332103, 329304, H04L 2718

Patent

active

052221032

ABSTRACT:
This invention features a differential QPSK digital communications apparatus and method, suitable for optical communications systems, where a pair of synchronous binary input data streams S.sub.0 (t) and S.sub.1 (t) are encoded into a pair of encoded binary data streams d.sub.0 (t) and d.sub.1 (t) which QPSK modulate the phase .phi.(t) of a carrier signal. An encoder features time delay circuits for delaying d.sub.0 (t) and d.sub.1 (t) by a period T to produce d.sub.0 (t-T) and d.sub.1 (t-T) respectively. A logic circuit produces d.sub.0 (t) and d.sub.1 (t) from S.sub.0 (t), S.sub.1 (t), d.sub.0 (t-T) and d.sub.1 (t-T) according to logical relationships. A microwave subcarrier is modulated by a microwave QPSK subcarrier modulator. The microwave QPSK subcarrier modulator includes an in-phase and quadrature subcarrier signal source, a mixer for mixing the in-phase subcarrier with d.sub.0 (t), a second mixer for mixing the quadrature subcarrier with d.sub.1 (t), and a combiner circuit for combining the two mixer outputs to produce a QPSK modulated microwave subcarrier signal. An optical modulator modulates the QPSK modulated microwave subcarrier signal onto an optical carrier signal, an optical detector detects the modulated subcarrier from the optical carrier signal to produce a detected subcarrier signal, and a QPSK demodulator recovers S.sub.0 (t) and S.sub.1 (t) from the detected subcarrier signal.

REFERENCES:
patent: 3875400 (1975-04-01), Pao et al.
patent: 4285062 (1981-08-01), Yoshida et al.

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