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US5280489A
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Time-varying Viterbi detector for control of error event length
Assignee: International Business Machines Corp
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Filing: 1992-04-15
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Granted: 1994-01-18
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Expires: 2012-04-15
Abstract
Abstract A method and apparatus for detecting spectral null sequences of a spectrally-constrained code on a noisy communications channel. From a Viterbi detector with a trellis structure comprising a plurality of states and edges, predetermined ones of the states and edges in the trellis structure are deleted at preselected times modulo N, such as times φ modulo N and/or at intermediate times m modulo N, where m=φ, thereby to create a time-varying trellis structure for limiting the maximum length of dominant error events. The deleted edges are generally those edges which would have entered or emanated from the deleted states if they were not deleted. The trellis structure may be a so-called systolic structure, in which case the spectral null sequences are preferably DC-free or Nyquist free.
Inventors
- 👤 Lyle J. Fredrickson
- 👤 Razmik Karabed
- 👤 James W. Rae
- 👤 Paul H. Siegel
- 👤 Hemant K. Thapar
- 👤 Roger W. Wood
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 11:07
CPC Classifications
H; H03; H03M; H03M13/00; H03M13/31
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
129 words
A method for detecting spectral null sequences of a spectrally-constrained code, comprising the steps of: using an encoder, generating the spectral null sequences from digital electrical signals representing unencoded input data; transmitting the sequences from the encoder to a partial response channel subject to noise; and transmitting the sequences from the channel to a Viterbi detector with a trellis structure with a plurality of states and edges from which predetermined ones of said states and edges in the trellis structure are absent in the preselected time-dependent pattern to create a time-varying trellis structure for limiting the maximum length of dominant error events in said sequences; at least some of the absent states and edges corresponding to a lowest and a highest charge value occurring at preselected times modulo N.
Claim 2
Independent Claim
129 words
A method for detecting spectral null sequences of a spectrally-constrained code, comprising the steps of: using an encoder, generating the spectral null sequences from digital electrical signals representing unencoded input data; transmitting the sequences from the encoder to a partial response channel subject to noise; and transmitting the sequences from the channel to a Viterbi detector with a trellis structure with a plurality of states and edges from which predetermined ones of said states and edges in the trellis structure are absent in the preselected time-dependent pattern to create a time-varying trellis structure for limiting the maximum length of dominant error events in said sequences; at least some of the absent states and edges corresponding to a lowest and a highest charge value occurring at preselected times modulo N.
Claim 3
Dependent Claim
48 words
The method of claim 1, wherein the trellis structure comprises a plurality of stages, the number of which determines the periodicity of the trellis structure, and wherein at least some of the absent states and edges are absent from the first and last stages of the trellis structure.
Claim 4
Dependent Claim
34 words
The method of claim 2, wherein said stages include at least one stage between said first and last stages from which are also absent predetermined other states together with edges entering or emanating therefrom.
Claim 5
Dependent Claim
10 words
The method of claim 1, wherein the sequences are DC-free.
Claim 6
Dependent Claim
10 words
The method of claim 1, wherein the sequences are Nyquist-free.
Claim 7
Dependent Claim
15 words
The method of claim 1, wherein the code is a rate 16/20 balanced spectrally-constrained code.
Claim 8
Dependent Claim
15 words
The method of claim 1, wherein the code is a rate 8/10 adjacent/nonadjacent spectrally-constrained code.
Claim 9
Dependent Claim
19 words
The method of claim 1, wherein the code is a rate 12/15 spectrally-constrained code having a spectral density null.
Claim 10
Dependent Claim
21 words
The method of claim 1, wherein the code is a rate 15B/10Q quarternary balanced spectral code having a spectral density null.
Claim 11
Dependent Claim
17 words
The method of claim 1, wherein the code is a rate 8B/6Q optimal adjacent/nonadjacent quaternary spectrally-constrained code.
Claim 12
Independent Claim
114 words
A method for detecting spectral null sequences of a spectrally-constrained code from data samples in the form of digital electrical signals generated at the output of a noisy communications channel, comprising the steps of: providing a Viterbi detector that tracks the spectral content of said sequences of electrical signals with a trellis structure having N stages, each comprising a plurality of states and edges; and deleting states corresponding to a lowest and a highest charge value and also all edges entering or emanating from the deleted states from the trellis structure at preselected times modulo N to create a time-varying trellis structure for limiting the maximum length of dominant error events in said sequences.
Claim 13
Independent Claim
114 words
A method for detecting spectral null sequences of a spectrally-constrained code from data samples in the form of digital electrical signals generated at the output of a noisy communications channel, comprising the steps of: providing a Viterbi detector that tracks the spectral content of said sequences of electrical signals with a trellis structure having N stages, each comprising a plurality of states and edges; and deleting states corresponding to a lowest and a highest charge value and also all edges entering or emanating from the deleted states from the trellis structure at preselected times modulo N to create a time-varying trellis structure for limiting the maximum length of dominant error events in said sequences.
Claim 14
Dependent Claim
25 words
The method of claim 11, wherein the trellis structure form which the states and edges are deleted during the deleting step is a systolic structure.
Claim 15
Independent Claim
107 words
An apparatus for detecting spectral null sequences of a spectrally-constrained code generated from unencoded input data, comprising: a finite state machine for generating the spectral null sequences from the input data; a Viterbi detector for tracing spectral content of said sequences with a trellis structure having N stages, each comprising plurality of states and edges; and means for deleting from the trellis structure states corresponding to a lowest and highest charge value and edges corresponding to those entering or emanating from the deleted states at preselected times modulo N to create a time-varying trellis structure for limiting the maximum length of dominant error events in said sequences.
Claim 16
Independent Claim
107 words
An apparatus for detecting spectral null sequences of a spectrally-constrained code generated from unencoded input data, comprising: a finite state machine for generating the spectral null sequences from the input data; a Viterbi detector for tracing spectral content of said sequences with a trellis structure having N stages, each comprising plurality of states and edges; and means for deleting from the trellis structure states corresponding to a lowest and highest charge value and edges corresponding to those entering or emanating from the deleted states at preselected times modulo N to create a time-varying trellis structure for limiting the maximum length of dominant error events in said sequences.
Claim 17
Independent Claim
138 words
An apparatus for detecting spectral null sequences of a spectrally constrained code from data samples generated at the output of a noisy communications channel, comprising a Viterbi detector having a trellis structure comprising a plurality of states and edges; and means for removing predetermined ones of said states and edges in a preselected time-dependent pattern to limit the maximum length of dominant error events, said means including a plurality of add-compare-select (ACS) units, one for each said state, each unit having as inputs at least one survivor metric that corresponds to an edge terminating at a predetermined one of said states and is output by a preceding one of the ACS units, each ACS unit also having a control input and an override input for selectively deleting selectable ones of said survivor metrics and hence their corresponding edges.
Claim 18
Independent Claim
138 words
An apparatus for detecting spectral null sequences of a spectrally constrained code from data samples generated at the output of a noisy communications channel, comprising a Viterbi detector having a trellis structure comprising a plurality of states and edges; and means for removing predetermined ones of said states and edges in a preselected time-dependent pattern to limit the maximum length of dominant error events, said means including a plurality of add-compare-select (ACS) units, one for each said state, each unit having as inputs at least one survivor metric that corresponds to an edge terminating at a predetermined one of said states and is output by a preceding one of the ACS units, each ACS unit also having a control input and an override input for selectively deleting selectable ones of said survivor metrics and hence their corresponding edges.
Claim 19
Dependent Claim
80 words
The apparatus of claim 14, including means for providing a branch metric input for each survivor metric that is input to a particular one of the ACS units, each branch metric being a prespecified function of each data sample; mean for adding the branch metric and corresponding metric inputs to provide a plurality of sums; and means for selecting as the survivor metric the smallest one of the sums in a subset determined by the control input and override input.
Claim 20
Dependent Claim
29 words
The apparatus of claim 14, wherein said control input and override input effect the selective deletion of the selectable ones of the survivor metrics at preselected times modulo N.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1997-01-17 | 1997-07-19 | 1998-01-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2001-01-17 | 2001-07-19 | 2002-01-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2005-01-17 | 2005-07-19 | 2006-01-18 | $7700.00 | Window Closed / Lapsed |