Differential quadrature phase shift keying encoder for subcarrier systems
First Claim
1. An apparatus, comprisingat least one encoder for encoding a pair of synchronous binary input data streams S0 (t), S1 (t), into a pair of encoded binary data streams d0 (t), d1 (t), each said input data stream having a single bit period T between successive data bits;
- said encoder further including a first time delay circuit for delaying d0 (t) by a period T to produce a first time-delayed encoded signal d0 (t-T);
a second time delay circuit for delaying d1 (t) by a period T to produce a second time-delayed encoded signal d1 (t-T); and
a logic circuit for producing encoded signals d0 (t) and d1 (t) from S0 (t), S1 (t), d0 (t-T), and d1 (t-T) according to the logical relationships;
space="preserve" listing-type="equation">d.sub.0 (t)=S.sub.0 (t) S.sub.1 (t) d.sub.0 (t-T)+S.sub.0 (t) S.sub.1 (t) d.sub.1 (t-T)+S.sub.0 (t) S.sub.1 (t) d.sub.0 (t-T)
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">d.sub.1 (t)=S.sub.0 (t) S.sub.1 (t) d.sub.1 (t-T)+S.sub.0 (t) S.sub.1 (t) d.sub.0 (t-T)+S.sub.0 (t) S.sub.1 (t) d.sub.1 (t-T).at least one QPSK modulator for modulating with the encoded signals d0 and d1 the phase φ
(t) of at least one carrier signal having a frequency f and an amplitude A, said modulated carrier signal being given by
space="preserve" listing-type="equation">x(t)=A cos(2π
ft+φ
(t));
wherein said phase φ
(t) is determined by the logical values of said encoded binary data streams d0 (t) and d1 (t), and said encoder encodes d0 (t) and d1 (t) to satisfy the relationships
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}>
0 for S.sub.0 (t)=1,
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}<
0 for S.sub.0 (t)=0,
space="preserve" listing-type="equation">cos{Δ
φ
+45°
}>
0 for S.sub.1 (t)=1,
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">cos{Δ
φ
+45°
}<
0 for S.sub.1 (t)=0where Δ
φ
=φ
(t)-φ
(t).
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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 S0 (t) and S1 (t) are encoded into a pair of encoded binary data streams d0 (t) and d1 (t) which QPSK modulate the phase φ(t) of a carrier signal. An encoder features time delay circuits for delaying d0 (t) and d1 (t) by a period T to produce d0 (t-T) and d1 (t-T) respectively. A logic circuit produces d0 (t) and d1 (t) from S0 (t), S1 (t), d0 (t-T) and d1 (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 d0 (t), a second mixer for mixing the quadrature subcarrier with d1 (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 S0 (t) and S1 (t) from the detected subcarrier signal.
118 Citations
37 Claims
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1. An apparatus, comprising
at least one encoder for encoding a pair of synchronous binary input data streams S0 (t), S1 (t), into a pair of encoded binary data streams d0 (t), d1 (t), each said input data stream having a single bit period T between successive data bits; -
said encoder further including a first time delay circuit for delaying d0 (t) by a period T to produce a first time-delayed encoded signal d0 (t-T); a second time delay circuit for delaying d1 (t) by a period T to produce a second time-delayed encoded signal d1 (t-T); and a logic circuit for producing encoded signals d0 (t) and d1 (t) from S0 (t), S1 (t), d0 (t-T), and d1 (t-T) according to the logical relationships;
space="preserve" listing-type="equation">d.sub.0 (t)=S.sub.0 (t) S.sub.1 (t) d.sub.0 (t-T)+S.sub.0 (t) S.sub.1 (t) d.sub.1 (t-T)+S.sub.0 (t) S.sub.1 (t) d.sub.0 (t-T)
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">d.sub.1 (t)=S.sub.0 (t) S.sub.1 (t) d.sub.1 (t-T)+S.sub.0 (t) S.sub.1 (t) d.sub.0 (t-T)+S.sub.0 (t) S.sub.1 (t) d.sub.1 (t-T).at least one QPSK modulator for modulating with the encoded signals d0 and d1 the phase φ
(t) of at least one carrier signal having a frequency f and an amplitude A, said modulated carrier signal being given by
space="preserve" listing-type="equation">x(t)=A cos(2π
ft+φ
(t));wherein said phase φ
(t) is determined by the logical values of said encoded binary data streams d0 (t) and d1 (t), and said encoder encodes d0 (t) and d1 (t) to satisfy the relationships
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}>
0 for S.sub.0 (t)=1,
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}<
0 for S.sub.0 (t)=0,
space="preserve" listing-type="equation">cos{Δ
φ
+45°
}>
0 for S.sub.1 (t)=1,
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">cos{Δ
φ
+45°
}<
0 for S.sub.1 (t)=0where Δ
φ
=φ
(t)-φ
(t). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
-
-
13. An apparatus, comprising
an encoder for encoding a pair of synchronous binary input data streams Sm,0 (t), Sm,1 (t) associated with said subcarrier at fm, each said input data stream having a single bit period T between successive data bits, into a pair of encoded binary data streams dm,0 (t), dm,1 (t); -
said encoder further including a first time delay circuit for delaying dm,0 (t) by a period T to produce a first time-delayed encoded signal dm,0 (t-T); a second time delay circuit for delaying dm,1 (t) by a period T to produce a second time-delayed encoded signal dm,1 (t-T); and said each said encoder further including means to enable dm,0 (t) and dm,1 (t) to satisfy the logical relationships ##EQU8## a plurality of microwave subcarrier QPSK modulators each associated with a microwave subcarrier signal for modulating with the encoded binary data streams dm,0 (t), dm,1 (t) the phase φ
m (t) of the associated microwave subcarrier having a frequency fm and an amplitude Am, where m is the index number of the microwave subcarrier, each said modulated subcarrier signal being given by
space="preserve" listing-type="equation">x.sub.m (t)=A.sub.m cos(2π
f.sub.m t+φ
(t));wherein said phase φ
(t) is determined by the logical values of said encoded binary data streams dm,0 (t) and dm,1 (t), and said encoder encodes dm,0 (t) and dm,1 (t) to satisfy the relationships
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}>
0 for S.sub.m,0 (t)=1,
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}<
0 for S.sub.m,0 (t)=0,
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}>
0 for S.sub.m,1 (t)=1,
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}<
0 for S.sub.m,1 (t)=0where Δ
φ
m =φ
m (t)-φ
m (t). - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
-
-
21. An apparatus for transferring digital data across an optical data link, comprising
an encoder for encoding a first input data signal S0 and a second input data signal S1 into a first encoded signal d0 and second encoded signal d1, said first and second input data signals being synchronous with each other and having the same single bit time period T between successive data bits; -
said encoder further includes a first time delay circuit for delaying d0 by a period T to produce a first time-delayed encoded signal d'"'"'0 ; a second time delay circuit for delaying d1 by a period T to produce a second time-delayed encoded signal d'"'"'1 ; and a logic circuit for producing encoded signals d0 and d1 from S0, S1, d'"'"'0 and d'"'"'1 according to the boolean expressions;
space="preserve" listing-type="equation">d.sub.0 =S.sub.0 S.sub.1 d'"'"'.sub.0 +S.sub.0 S.sub.1 d'"'"'.sub.1 +S.sub.0 S.sub.1 d'"'"'.sub.1 +S.sub.0 S.sub.1 d'"'"'.sub.0
space="preserve" listing-type="equation">and,
space="preserve" listing-type="equation">d.sub.1 =S.sub.0 S.sub.1 d'"'"'.sub.1 +S.sub.0 S.sub.1 d'"'"'.sub.0 +S.sub.0 S.sub.1 d'"'"'.sub.0 +S.sub.0 S.sub.1 d'"'"'.sub.1 ;at least one subcarrier modulator for simultaneously modulating an associated subcarrier with said first and second encoded signals to produce a modulated subcarrier signal that contains two bits of information for each symbol period, said symbol period equal to said bit period T of each said input data signals S0 and S1 ; an optical modulator for modulating at least one said modulated subcarrier signal on an optical carrier signal; an optical detector for detecting at least one said subcarrier from said optical carrier signal to provide a detected subcarrier signal; and a demodulator for demodulating said first input data signal from said detected subcarrier signal. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. An apparatus for receiving digital data from an optical data link, comprising
an optical detector for detecting at least one subcarrier from a subcarrier modulated optical carrier signal to provide a detected subcarrier signal; - and
a demodulator for demodulating a first data signal and a second data signal from said detected subcarrier signal, said demodulator comprising (a) a phase delay network for delaying the phase of said detected subcarrier by a predetermined phase delay and providing a phase-delayed detected subcarrier; (b) a phase advance network for advancing the phase of said detected subcarrier by a predetermined phase advance and providing a phase-advanced detected subcarrier, said predetermined phase delay and said predetermined phase advance each being selected such that the resulting phase difference between said phase-delayed detected subcarrier and said phase-advanced detected subcarrier is substantially 90°
;(c) a time delay circuit for delaying said detected subcarrier by said single bit time period T to provide a time-delayed detected subcarrier; (d) a first demodulation mixer for mixing said phase-delayed detected subcarrier with said time-delayed detected subcarrier; and (e) a second demodulation mixer for mixing said phase-advanced detected subcarrier with said time-delayed detected subcarrier. - View Dependent Claims (32)
- and
-
33. A method of modulating a carrier signal with digital information, comprising the steps of
encoding a pair of synchronous binary input data streams S0, S1, into a pair of encoded binary data streams d0, d1, each said input stream having a single bit period between T between successive data bits; -
delaying d0 by a period T to produce a first time-delayed encoded signal d'"'"'0 ; delaying d1 by a period T to produce a second time-delayed encoded signal d'"'"'1 ; and producing encoded signals d0 and d1 from S0, S1, d'"'"'0 and d'"'"'1 according to the boolean expressions;
space="preserve" listing-type="equation">d.sub.0 =S.sub.0 S.sub.1 d'"'"'.sub.0 +S.sub.0 S.sub.1 d'"'"'.sub.1 +S.sub.0 S.sub.1 d'"'"'.sub.1 +S.sub.0 S.sub.1 d'"'"'.sub.0
space="preserve" listing-type="equation">and,
space="preserve" listing-type="equation">d.sub.1 =S.sub.0 S.sub.1 d'"'"'.sub.1 +S.sub.0 S.sub.1 d'"'"'.sub.0 +S.sub.0 S.sub.1 d'"'"'.sub.0 +S.sub.0 S.sub.1 d'"'"'.sub.1 ;modulating the phase φ
(t) of at least one carrier signal having a frequency f and an amplitude A, said modulated carrier signal being given by
space="preserve" listing-type="equation">x(t)=A cos(2π
ft+φ
(t)wherein said phase φ
(t) is determined by the logical values of said encoded binary data streams d0 (t) and d1 (t) and said encoder encodes d0 (t) and d1 (t) to satisfy the relationships
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}>
0 for S.sub.0 (t)=1,
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}<
0 for S.sub.0 (t)=0,
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}>
0 for S.sub.1 (t)=1,
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">cos{Δ
φ
-45°
}<
0 for S.sub.1 (t)=0;where Δ
φ
=φ
(t)-φ
(t). - View Dependent Claims (34, 35, 36, 37)
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Specification