QPSK Direct Regenerator with a Frequency Tripler and a Quadrupler

This paper describes a regenerator for quadriphase phase shift keying (QPSK) signals at the carrier frequency, which is called a "direct regenerator." The direct regenerator proposed here is realized using a tripler and a quadrupler. This regenerator is characterized by the symbols
m
,
n
and
s
, which denote the intermediate combiner amplitude ratio, the final combiner amplitude ratio and the limiter dynamic range, respectively. Complete regeneration is obtained at
m = n = 1
and
s = \infty
. Even if this condition is not satisfied, sufficient regenerative performance for practical use is preserved, when
0.8 < m < 1.25, 0.7 < n < 1.4
and
s > 5
dB. To verify the operation principle, an experiment was carried out for 1.7 GHz QPSK signals transmitted at 40 Mbits/s. It is shown that this regenerator has satisfactory decision and reshaping capability in dynamic operation. Using this direct regenerator, decision and reshaping of the QPSK signals can be made without detection. Thus, a repeater can be simplified, compared to a conventional repeater composed of a detector, a baseband regenerator and a modulator.