US6891792B1
Expired / Lapsed
US
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Method for estimating time and frequency offset in an OFDM system
Assignee: AT&T Intellectual Property II LP
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Filing: 1999-05-14
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Granted: 2005-05-10
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Expires: 2019-05-14
Abstract
Abstract The synchronization technique invention uses inherent characteristics of the frequency domain representation of the data symbols. By computing a differential-in-frequency function across a large number of OFDM tones, robust estimates of time and frequency offset can be easily obtained. The technique also allows the system designer to directly trade performance in the presence of channel impairments against signal processing complexity. Analysis and simulation have shown good performance in the presence of noise and channel delay dispersion, impairments that are the harshest in a wireless environment. Prior techniques for OFDM synchronization have focussed on the time domain representation of the signal. Those that have recognized the translation of time and frequency offset to the frequency domain have not considered the systematic modification of the signal by the offsets.
Inventors
- 👤 Leonard Joseph Cimini, Jr.
- 👤 Bruce Edwin McNair
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 10:21
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/26; H04L27/2601; H04L27/2647; H04L27/2655; H04L27/2657; H04L27/2662; H04L27/2668; H04L27/2673; H04L27/2676; H04L27/2679
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
75 words
A receiver system including a front-end stage that develops a plurality of individually modulated carriers, and a following stage, characterized in that: said front-end stage receives an incoming signal, develops an offset measure-by developing signals related to said incoming signals and employing a plurality of modulated carriers created from a transformation into frequency domain of said signals related to said incoming signals, which offset measure participates in creating said signals related to said incoming signals.
Claim 2
Dependent Claim
75 words
A receiver system including a front-end stage that develops a plurality of individually modulated carriers, and a following stage, characterized in that: said front-end stage receives an incoming signal, develops an offset measure-by developing signals related to said incoming signals and employing a plurality of modulated carriers created from a transformation into frequency domain of said signals related to said incoming signals, which offset measure participates in creating said signals related to said incoming signals.
Claim 3
Dependent Claim
45 words
The system of claim 1 , where said offset measure is a timing offset, and said processing operates on a plurality of pairs of said modulated carriers from said plurality of modulated carriers, taking account of frequency separation between carriers within each of said pairs.
Claim 4
Dependent Claim
18 words
The system of claim 2 , where the individually modulated transmission carriers are Orthogonal Frequency Division Multiplexed carriers.
Claim 5
Dependent Claim
28 words
The system of claim 2 where said processing on said plurality of pairs develops a set of results, and develops said timing offset from the set of results.
Claim 6
Dependent Claim
22 words
The system of claim 4 , where carriers of a pair in said pairs are adjacent to each other in the frequency.
Claim 7
Dependent Claim
27 words
The system of claim 4 , where carriers of a pair in said pairs are equally spaced in the frequency domain, but not adjacent to each other.
Claim 8
Dependent Claim
21 words
The system of claim 6 where the processor, in computing the timing offset, computes differences in phase between said received carriers.
Claim 9
Dependent Claim
22 words
The system of claim 4 , where carriers of a pair in said pairs are not equally spaced in the frequency domain.
Claim 10
Dependent Claim
30 words
The system of claim 4 where said timing offset between any pair of modulated carriers is developed by raising the complex representation of the modulated carriers to an integer power.
Claim 11
Dependent Claim
26 words
The system of claim 9 where the carriers are modulated by an N-level phase modulation scheme, and the carriers are raised to the N th power.
Claim 12
Dependent Claim
22 words
The system of claim 10 where the modulation is Quadrature Phase Shift Keying and the carriers are raised to the fourth power.
Claim 13
Dependent Claim
25 words
The system of claim 1 where said offset measure is a frequency offset that is developed by computing phases of said plurality of modulated carriers.
Claim 14
Dependent Claim
31 words
The system of claim 1 where the plurality of modulated carries are used in combination to determine said offset measure with the contribution of each carrier weighted according to its accuracy.
Claim 15
Dependent Claim
19 words
The system of claim 13 where the accuracy of each carrier's contribution is determined based on the carrier's amplitude.
Claim 16
Dependent Claim
59 words
The system of claim 14 where, for each carrier, the carrier's amplitude and phase, represented by a complex number in a Cartesian coordinate system, is summed with the other carriers' complex representation to yield a composite vector, representing the composite amplitude and phase; said processor further employing the phase of this composite vector to create a frequency synchronization signal.
Claim 17
Dependent Claim
27 words
The system of claim 15 where the carriers' modulating data signals are known by the receivers and can be used to determine the precise transmitter carriers' phases.
Claim 18
Dependent Claim
36 words
The system of claim 15 where the carriers' modulating data signals are not known by the receivers but can be estimated by attempting to demodulate the carriers and then used to estimate the transmit carriers' phases.
Claim 19
Dependent Claim
34 words
The system of claim 15 where the carriers' modulating data signals are not known by the receivers but where the effect of the modulation can be removed from the carriers without demodulating the carriers.
Claim 20
Dependent Claim
30 words
The system of claim 18 where the means to remove the carriers' data modulation is by raising the complex representation of the carrier amplitude and phase to an integer power.
Claim 21
Dependent Claim
39 words
The system of claim 19 where the modulation of the carriers is by N level phase modulation and the data modulation is removed by raising the complex representation of the carrier amplitude and phase to the N th power.
Claim 22
Dependent Claim
35 words
The system of claim 20 where the modulation is a Quadrature Phase Shift Keying and the data modulation is removed by raising the complex representation of the carrier amplitude and phase to the fourth power.
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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) | 2008-05-09 | 2008-11-08 | 2009-05-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2012-05-09 | 2012-11-08 | 2013-05-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2016-05-09 | 2016-11-08 | 2017-05-10 | $7700.00 | Window Closed / Lapsed |