Patent US4881049A successfully refreshed from Google Patents.
US4881049A
Expired / Lapsed
US
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QAM modulator/demodulator
Assignee: NEC Corp
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Filing: 1988-04-04
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Granted: 1989-11-14
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Expires: 2008-04-04
Abstract
Abstract A digital signal transmission system adopting a quadrature amplitude modulation and demodulation principle and feasible for large capacity data transmission in which a number of levels are used. Each of a modulating and a demodulating device of the system is constructed to shift the phase difference between two carrier waves by a suitable angle of Δθ radian from π/2 radian. The tuning phase in the demodulating device is limited to one so as to allow a bit error rate characteristic to remain constant.
Inventors
- 👤 Manabu Yagi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 14:32
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/32; H04L27/34; H04L27/38; H04L27/3818; H04L27/3827; H04L27/36; H04L27/362
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
112 words
A digital signal transmission system comprising: a modulating device for effecting substantially quadrature amplitude modulation and including a phase shifter which applies phase shift processing to a carrier wave so as to produce two carrier waves which are different in phase from each other; and a demodulating device for producing a demodulated signal from a received modulated signal by quadramplitude demodulation and including a phase shifter for applying phase shift processing to a recovered carrier wave so as to produce two recovered carrier waves which are different in phase from each other; said phase shifters each effecting a phase shift of (π/2-Δθ) radian or (π/2+Δθ) radian where Δθis a predetermined phase angle.
Claim 2
Dependent Claim
112 words
A digital signal transmission system comprising: a modulating device for effecting substantially quadrature amplitude modulation and including a phase shifter which applies phase shift processing to a carrier wave so as to produce two carrier waves which are different in phase from each other; and a demodulating device for producing a demodulated signal from a received modulated signal by quadramplitude demodulation and including a phase shifter for applying phase shift processing to a recovered carrier wave so as to produce two recovered carrier waves which are different in phase from each other; said phase shifters each effecting a phase shift of (π/2-Δθ) radian or (π/2+Δθ) radian where Δθis a predetermined phase angle.
Claim 3
Dependent Claim
26 words
A digital signal transmission system as claimed in claim 1, in which when the number of levels used is 64, Δθ is greater than π/28 radian.
Claim 4
Dependent Claim
25 words
A digital signal transmission as claimed in claim 1, in which when the number of levels used is 256, Δθ is greater than π/60 radian.
Claim 5
Dependent Claim
66 words
A digital signal transmission system comprising at least a modulating device for effecting substantially quadrature amplitude modulation and including a phase shifter which applies phase shift processing to a carrier wave so as to produce two carrier waves which are different in phase from each other, said phase shifter effecting a phase shift of (π/2-Δθ) radian or (π/2+Δθ) radian where Δθ is a predetermined phase angle.
Claim 6
Dependent Claim
66 words
A digital signal transmission system comprising at least a modulating device for effecting substantially quadrature amplitude modulation and including a phase shifter which applies phase shift processing to a carrier wave so as to produce two carrier waves which are different in phase from each other, said phase shifter effecting a phase shift of (π/2-Δθ) radian or (π/2+Δθ) radian where Δθ is a predetermined phase angle.
Claim 7
Dependent Claim
26 words
A digital signal transmission system as claimed in claim 4, in which when the number of levels used is 64, Δθ is greater than π/28 radian.
Claim 8
Dependent Claim
26 words
A digital signal transmission system as claimed in claim 4, in which when the number of levels used is 256, Δθ is greater than π/60 radian.
Claim 9
Dependent Claim
69 words
A digital signal transmission system comprising: means for generating a first carrier wave; means for phase-shifting the first carrier wave by (π/2+Δθ) radian or (π/2-Δθ) radian where Δθ is a predetermined phase angle, thereby providing a second carrier wave; and means for modulating the first and second carrier waves in response to first and second signals, respectively and combining them to provide a substantially quadrature amplitude modulated carrier wave.
Claim 10
Dependent Claim
69 words
A digital signal transmission system comprising: means for generating a first carrier wave; means for phase-shifting the first carrier wave by (π/2+Δθ) radian or (π/2-Δθ) radian where Δθ is a predetermined phase angle, thereby providing a second carrier wave; and means for modulating the first and second carrier waves in response to first and second signals, respectively and combining them to provide a substantially quadrature amplitude modulated carrier wave.
Claim 11
Dependent Claim
129 words
A digital signal transmission system comprising: means for generating a first carrier wave; means for shifting the first carrier wave by (π/2+Δθ) radian or (π/2-Δθ) radian where Δθ is a predetermined phase angle, thereby providing a second carrier wave; means for modulating the first and second carrier waves in response to first and second signals, respectively and combining them to provide a substantially quadrature amplitude modulated carrier wave; means for recovering a third carrier wave from the modulated carrier wave; means for phase-shifting the third carrier wave by (π/2+Δθ) radian or (π/2-Δθ) radian where Δθis said predetermined phase angle, thereby providing a fourth carrier wave; and means for detecting the modulated carrier wave in response to the third and fourth carrier waves, thereby providing the first and second signals.
Claim 12
Dependent Claim
129 words
A digital signal transmission system comprising: means for generating a first carrier wave; means for shifting the first carrier wave by (π/2+Δθ) radian or (π/2-Δθ) radian where Δθ is a predetermined phase angle, thereby providing a second carrier wave; means for modulating the first and second carrier waves in response to first and second signals, respectively and combining them to provide a substantially quadrature amplitude modulated carrier wave; means for recovering a third carrier wave from the modulated carrier wave; means for phase-shifting the third carrier wave by (π/2+Δθ) radian or (π/2-Δθ) radian where Δθis said predetermined phase angle, thereby providing a fourth carrier wave; and means for detecting the modulated carrier wave in response to the third and fourth carrier waves, thereby providing the first and second signals.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-11-13 | 1993-05-15 | 1993-11-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-11-13 | 1997-05-15 | 1997-11-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-11-13 | 2001-05-15 | 2001-11-14 | $7700.00 | Window Closed / Lapsed |