US4462108A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Modem signal acquisition technique
Assignee: Northrop Grumman Space and Mission Systems Corp
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Filing: 1982-08-02
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Granted: 1984-07-24
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Expires: 2002-08-02
Abstract
Abstract Apparatus, and a related method, for fast carrier acquisition in a modem. The apparatus includes circuitry to speed carrier acquisition by the determination of which of two alternate phasors is being received during a baud synchronization period of a signal preamble before data transmission. Another aspect of the invention involves the use of a complex matched filter for the determination of the start of an equalizer training sequence in the signal preamble. The output of the matched filter exhibits a deep null at the start of the training sequence, since the beginning of the sequence bears an inverse relationship to the end of the preceeding baud synchronization period.
Inventors
- 👤 Chauncey S. Miller
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 07:02
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/32; H04L27/34; H04L27/38; H04L7/00; H04L7/04; H04L7/041; H04L7/046
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
214 words
For use in a receiving-end modem, apparatus for fast carrier acquisition, comprising: means for determining which of two alternate phasors is currently being received at the modem during a baud synchronization period; means for computing a phase error signal from the actual angle of the phasor being received and the expected angle of the phasor being received; and a phase-lock loop for computing, from the phase error signal, sine and cosine values for use in demodulating the carrier; and wherein said means for determining which of the phasors is being received includes an arctangent circuit, for providing a signal indicative of the actual angle of the phasor being received; a delay circuit for providing a signal indicative of the actual angle of the phasor received one baud interval earlier; means for subtracting the signals indicative of the phase angle and delayed phase angle to obtain a phase angle difference signal; means for subtracting one from the other of the phase angle difference signal and a signal indicative of a fixed angle, to obtain a second difference signal indicative of which of the two alternate phasors is currently being received; and means for generating from the second difference signal a signal indicative of the phase angle of a corresponding one of the two alternate phasors.
Claim 2
Dependent Claim
214 words
For use in a receiving-end modem, apparatus for fast carrier acquisition, comprising: means for determining which of two alternate phasors is currently being received at the modem during a baud synchronization period; means for computing a phase error signal from the actual angle of the phasor being received and the expected angle of the phasor being received; and a phase-lock loop for computing, from the phase error signal, sine and cosine values for use in demodulating the carrier; and wherein said means for determining which of the phasors is being received includes an arctangent circuit, for providing a signal indicative of the actual angle of the phasor being received; a delay circuit for providing a signal indicative of the actual angle of the phasor received one baud interval earlier; means for subtracting the signals indicative of the phase angle and delayed phase angle to obtain a phase angle difference signal; means for subtracting one from the other of the phase angle difference signal and a signal indicative of a fixed angle, to obtain a second difference signal indicative of which of the two alternate phasors is currently being received; and means for generating from the second difference signal a signal indicative of the phase angle of a corresponding one of the two alternate phasors.
Claim 3
Dependent Claim
70 words
Apparatus as set forth in claim 1, wherein: the two alternate phasors have angles of 180 degrees and 315 degrees; the phase angle difference has one of the two possible values of approximately 135 degrees and approximately 225 degrees; and the fixed angle is 180 degrees, whereby said means for generating yields a result corresponding to approximately +45 degrees or approximately -45 degrees, depending on which phasor is being received.
Claim 4
Dependent Claim
30 words
Apparatus as set forth in claim 1, wherein said phase-lock loop includes a predictor circuit to compensate for time delays in the modem, and thereby stabilize operation of the apparatus.
Claim 5
Dependent Claim
199 words
For use in a receiving-end modem, a method for fast carrier acquisition, comprising the steps of: determining which of two alternate phasors is currently being received at the modem during a baud synchronization period; computing a phase error signal from the actual angle of the phasor being received and the expected angle of the phasor being received; and deriving from the phase error signal, sine and cosine values for use in demodulating the carrier; and wherein said determining step includes generating in a arctangent circuit an angle signal indicative of the actual angle of the phasor being received; delaying the signal generated in said generating step, to provide a delayed angle signal indicative of the actual phasor angle received one baud interval earlier; subtracting the angle signal from the delayed angle signal to provide a phase angle difference signal; subtracting one from the other of the phase angle difference signal and a signal indicative of a fixed angle, to obtain a second difference signal indicative of which of the two alternate phasors is currently being received; and generating from the second difference signal a signal indicative of the phase angle of a corresponding one of the two alternate phasors.
Claim 6
Dependent Claim
199 words
For use in a receiving-end modem, a method for fast carrier acquisition, comprising the steps of: determining which of two alternate phasors is currently being received at the modem during a baud synchronization period; computing a phase error signal from the actual angle of the phasor being received and the expected angle of the phasor being received; and deriving from the phase error signal, sine and cosine values for use in demodulating the carrier; and wherein said determining step includes generating in a arctangent circuit an angle signal indicative of the actual angle of the phasor being received; delaying the signal generated in said generating step, to provide a delayed angle signal indicative of the actual phasor angle received one baud interval earlier; subtracting the angle signal from the delayed angle signal to provide a phase angle difference signal; subtracting one from the other of the phase angle difference signal and a signal indicative of a fixed angle, to obtain a second difference signal indicative of which of the two alternate phasors is currently being received; and generating from the second difference signal a signal indicative of the phase angle of a corresponding one of the two alternate phasors.
Claim 7
Dependent Claim
76 words
A method as set forth in claim 4, wherein: the two alternate phasors have angles of 180 degrees and 315 degrees; the phase angle difference has one of the two possible values of approximately 135 degrees and approximately 225 degrees; and the fixed angle is 180 degrees, whereby said step of generating from the second difference signal yields a result corresponding to approximately +45 degrees or approximately -45 degrees, depending on which phasor is being received.
Claim 8
Dependent Claim
32 words
A method as set forth in claim 4, wherein said step of deriving sine and cosine values is performed in a phase-lock loop and includes compensating for time delays in the modem.
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) | 1987-07-24 | 1988-01-23 | 1988-07-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-07-24 | 1992-01-23 | 1992-07-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-07-24 | 1996-01-23 | 1996-07-24 | $7700.00 | Window Closed / Lapsed |