US5001747A
Expired / Lapsed
US
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Frequency offset estimator for data modem
Assignee: Racal Data Communications Inc
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Filing: 1990-01-22
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Granted: 1991-03-19
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Expires: 2010-01-22
Abstract
Abstract A method for estimating an amount of phase roll on a transmission channel. A signal of known frequency is transmitted over the channel by a near end modem. An average noise autocorrelation matrix is subtracted from an average signal plus noise autocorrelation matrix, both as received by a near end modem. The eigenvector of the resulting matrix is computed. The complex root of a quadratic with coefficients equal to the eigenvector elements is computed to solve for a difference between the frequency of the transmitted signal and the echoed receive signal to determine the phase roll.
Inventors
- 👤 Thomas A. Sexton
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 22:22
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/20; H04B3/23; H04B3/238; H04B3/232
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
116 words
A method for estimating a phase roll on a communication channel, comprising the steps of: measuring a noise correlation on said communication channel; transmitting a known signal having a predetermined frequency w o over said channel; measuring an average signal plus noise correlation echoed as a result of said transmitting of said known signal; forming a noise autocorrelation matrix B and a signal plus noise autocorrelation matrix D; subtracting B from D to form a difference matrix F; calculating an eigenvector C associated with a zero eigenvalue of F; solving for a root of said eigenvector C; and computing a phase roll by finding a difference between an angle of said root and said predetermined frequency.
Claim 2
Independent Claim
116 words
A method for estimating a phase roll on a communication channel, comprising the steps of: measuring a noise correlation on said communication channel; transmitting a known signal having a predetermined frequency w o over said channel; measuring an average signal plus noise correlation echoed as a result of said transmitting of said known signal; forming a noise autocorrelation matrix B and a signal plus noise autocorrelation matrix D; subtracting B from D to form a difference matrix F; calculating an eigenvector C associated with a zero eigenvalue of F; solving for a root of said eigenvector C; and computing a phase roll by finding a difference between an angle of said root and said predetermined frequency.
Claim 3
Dependent Claim
20 words
The method of claim 1, further comprising the step of canceling a near end echo prior to the other steps.
Claim 4
Dependent Claim
14 words
The method of claim 1, wherein all computations are carried out using complex numbers.
Claim 5
Dependent Claim
14 words
The method of claim 1, wherein all computations are carried out using real numbers.
Claim 6
Dependent Claim
25 words
The method of claim 1, wherein said B and D matrices are formed from samples taken at sample times n=-2, -1, 0, 1 and 2.
Claim 7
Dependent Claim
50 words
The method of claim 5, wherein said solving step is carried out by forming the quadratic equation: 0=c(0)+c(1)z+c(2)z.sup.2 where z is a variable and the values c(0), c(1) and c(2) are taken from the C vector: ##EQU5## and wherein said root is a root z 1 of said quadratic equation.
Claim 8
Dependent Claim
22 words
The method of claim 5 wherein said B matrix takes the form: ##EQU6## and wherein said D matrix takes the form ##EQU7##
Claim 9
Dependent Claim
24 words
The method of claim 6, wherein said computing step comprises computing a phase roll frequency w z as: w.sub.z =TAN.sup.-1 ( Im(z.sub.1) / Re(z.sub.1)).
Claim 10
Dependent Claim
20 words
The method of claim 8, further comprising the step of computing said phase roll w roll as: w.sub.roll =w.sub.z -w.sub.o.
Claim 11
Independent Claim
133 words
An apparatus for computing a phase roll frequency of a channel, comprising in combination: transmitting means for selectively transmitting a known signal having a predetermined frequency w o over said channel; measuring means for measuring an average noise correlation and an average signal plus noise correlation echoed as a result of said transmitting of said known signal; means for forming a noise autocorrelation matrix B and a signal plus noise autocorrelation matrix D; subtracting means for subtracting B from D to form a difference matrix F; calculating means for calculating an eigenvector C associated with a zero eigenvalue of F; solving means for solving for a root of said eigenvector C; and computing means for computing a phase roll by finding a difference between an angle of said root and said predetermined frequency.
Claim 12
Independent Claim
133 words
An apparatus for computing a phase roll frequency of a channel, comprising in combination: transmitting means for selectively transmitting a known signal having a predetermined frequency w o over said channel; measuring means for measuring an average noise correlation and an average signal plus noise correlation echoed as a result of said transmitting of said known signal; means for forming a noise autocorrelation matrix B and a signal plus noise autocorrelation matrix D; subtracting means for subtracting B from D to form a difference matrix F; calculating means for calculating an eigenvector C associated with a zero eigenvalue of F; solving means for solving for a root of said eigenvector C; and computing means for computing a phase roll by finding a difference between an angle of said root and said predetermined frequency.
Claim 13
Dependent Claim
14 words
The method of claim 10, further comprising means for canceling a near end echo.
Claim 14
Dependent Claim
16 words
The apparatus of claim 10, further comprising memory means for storing said B and D matrices.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-03-18 | 1994-09-17 | 1995-03-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-03-18 | 1998-09-17 | 1999-03-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-03-18 | 2002-09-17 | 2003-03-19 | $7700.00 | Window Closed / Lapsed |