EP0121389A2
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EP
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Apparatus and method for adjusting the receivers of data transmission channels
Assignee: BTG International Ltd
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Filing: 1984-03-26
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Granted: —
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Expires: 2004-03-26
Abstract
Abstract Filters are provided at the outputs of data transmission links to overcome attenuation distortion and phase distortion but such filters tend to increase the noise content of received signals. In the present invention a filter 17 coupled to a linear baseband channel 10 is constrained to be an all pass network, thus avoiding any noise enhancement at its output. The filter 17 is adjusted by means of a channel estimator 19 and an adjustment system 20 to give the channel plus the filter an impulse-response that rises rapidly to its peak, thus simplifying the detection process needed for a satisfactory tolerance to noise. The required response is obtained by finding those roots (zeros) of the z transform of the sampled impulse-response of the channel, which have a modulus greater than some given value which is not less than unity, and adjusting the said filter such that, in the z transform of the sampled impulse-response of the channel and filter, the said roots are replaced by the complex conjugates of their reciprocals, the remaining roots of the channel z-transform being left unchanged.
Inventors
- 👤 Adrian Percy Clark
- 👤 Sau Fat Hau
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-26 12:49
CPC Classifications
H; H04; H04L; H04L25/00; H04L25/02; H04L25/03; H04L25/03006; H04L25/03012; H04L25/03019; H04L25/03057; H04L2025/03433; H04L2025/03439; H04L2025/03445; H04L2025/03471; H04L2025/03484; H04L2025/0349
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
123 words
Apparatus for use in modifying signals received over a data transmission link to make the signals more susceptible of detection, comprising a substantially all pass filter characterised in that the filter has a sampled impulse-response with a z transform with first roots (zeros), and sets of second roots (zeros), the sets of second roots respectively approximating to poles; coinciding with at least most of any roots (zeros) having moduli greater than a predetermined value which is not greater than 1.5 of the z transform of the sampled impulse-response of a predetermined data transmission link, the first roots (zeros) being at values of z which are the complex conjugate reciprocals of those of the poles and there being one first root for each pole,
Claim 2
Dependent Claim
123 words
Apparatus for use in modifying signals received over a data transmission link to make the signals more susceptible of detection, comprising a substantially all pass filter characterised in that the filter has a sampled impulse-response with a z transform with first roots (zeros), and sets of second roots (zeros), the sets of second roots respectively approximating to poles; coinciding with at least most of any roots (zeros) having moduli greater than a predetermined value which is not greater than 1.5 of the z transform of the sampled impulse-response of a predetermined data transmission link, the first roots (zeros) being at values of z which are the complex conjugate reciprocals of those of the poles and there being one first root for each pole,
Claim 3
Independent Claim
143 words
A method of modifying signals received over at data transmission link to make the signals more susceptible of detection, including estimating the sampled impulse-response of a data transmission link, characterised by determining from the estimate respective quantities representative of at least most of any roots (zeros), having a modulus greater than a predetermined value which is not greater than 1.5, of the z transform of the said estimate, and modifying signals received aver the said link by employing a process which has a z transform with first roots (zeros) and sets of second roots (zeros), the sets of second roots respectively approximating to poles coinciding with the roots (zeros) represented by the quantities determined, the first roots (zeros) being at values of z which are the complex conjugate reciprocals of those of the poles, and there bein:g one first root for each pole.
Claim 4
Independent Claim
143 words
A method of modifying signals received over at data transmission link to make the signals more susceptible of detection, including estimating the sampled impulse-response of a data transmission link, characterised by determining from the estimate respective quantities representative of at least most of any roots (zeros), having a modulus greater than a predetermined value which is not greater than 1.5, of the z transform of the said estimate, and modifying signals received aver the said link by employing a process which has a z transform with first roots (zeros) and sets of second roots (zeros), the sets of second roots respectively approximating to poles coinciding with the roots (zeros) represented by the quantities determined, the first roots (zeros) being at values of z which are the complex conjugate reciprocals of those of the poles, and there bein:g one first root for each pole.
Claim 5
Dependent Claim
113 words
Filter forming apparatus characterised in that it is constructed and/or arranged to automatically determine, from an estimate of the sampled impulse-response of a data transmission link, respective quantities representative of roots (z.eros), having a modulus greater than a predetermined walue not greater than 1.5, and to form a filter having a sampled impulse-response with a z transform with first roots (zeros) and sets of second roots (zeros), the sets of second roots appro imating to poles coinciding with the roots (zeros) represented by the quantities determined, the first roots (zeros) being values of z which are the complex conjugate reciprocals of those of the poles, and there being one root for each pole.
Claim 6
Dependent Claim
113 words
Filter forming apparatus characterised in that it is constructed and/or arranged to automatically determine, from an estimate of the sampled impulse-response of a data transmission link, respective quantities representative of roots (z.eros), having a modulus greater than a predetermined walue not greater than 1.5, and to form a filter having a sampled impulse-response with a z transform with first roots (zeros) and sets of second roots (zeros), the sets of second roots appro imating to poles coinciding with the roots (zeros) represented by the quantities determined, the first roots (zeros) being values of z which are the complex conjugate reciprocals of those of the poles, and there being one root for each pole.
Claim 7
Dependent Claim
140 words
Apparatus according to Claim 3 characterised in that the filter forming apparatus determines a quantity which is the negative reciprocal of a first root having a modulus greater than the said predetermined value, from the sampled impulse-response of the data transmission link by taking each sample of the response in reverse sequence starting with the last significant sample, forming, in reversed order, a new sequence of samples by taking each sample in the reversed response in turn and subtracting the product of the previous sample in the new sequence (in reversed order), if any, times a current estimate of the said negative reciprocal, determining a new estimate of the said negative reciprocal by adding to the previous estimate a number proportional to the dividend obtained by dividing the final sample of the new sequence by a correction factor equal to:
Claim 8
Dependent Claim
141 words
from h = 1 to h = g where e h is the m th sample of the new sequence (in the correct, not reversed, ordler), A is the current estimate of the said negative reciprocal, and using the new estimate to repeat the above operation of the reversed impulse-response of the said link until the new estimate of the negative reciprocal is substantially the same as the previous estimate, and then determining the negative reciprocals, in turn, of further roots by, firstly deriving a modified sampled impulse response in which, in effect, roots whose negative reciprocals have been found are cancelled and substituted by roots which are at the complex conjugates of the z values of the said roots, and secondly using the modified response as the sampled impulse-response which is reversed in the procedure for finding the first root.
Claim 9
Dependent Claim
141 words
from h = 1 to h = g where e h is the m th sample of the new sequence (in the correct, not reversed, ordler), A is the current estimate of the said negative reciprocal, and using the new estimate to repeat the above operation of the reversed impulse-response of the said link until the new estimate of the negative reciprocal is substantially the same as the previous estimate, and then determining the negative reciprocals, in turn, of further roots by, firstly deriving a modified sampled impulse response in which, in effect, roots whose negative reciprocals have been found are cancelled and substituted by roots which are at the complex conjugates of the z values of the said roots, and secondly using the modified response as the sampled impulse-response which is reversed in the procedure for finding the first root.
Claim 10
Dependent Claim
67 words
Apparatus according to Claim 4 characterised in that each modified sampled response is obtained by taking, in turn and in the correct order, each sample of the sequence obtained when the final estimate of the negative reciprocal of a root is found and adding to it the product of the previous sample (if any) of the said sequence times the complex conjugate of the said final estimate.
Claim 11
Dependent Claim
49 words
Apparatus for detecting signals received over a data transmission link comprising means for. sampling received signals at regular intervals, a filter or filter forming apparatus, and a detector, characterised in that the filter or filter forming apparatus is as recited in any of Claims 1 or 3 to 5.
Claim 12
Dependent Claim
84 words
Apparatus according to Claim 6 insofar as dependent on Claim 5, characterised in that the detector is a maximum likelihood detector, the filter or filter forming apparatus is connected to the input of the detector and the detector is arranged to employ, as an estimate of the sampled impulse-response of a data transmission link and the said filter, the final said modified sampled impulse-response determined when all roots greater than the predetermined value have been used in forming the said modified sampled impulse- responses.
Claim 13
Dependent Claim
108 words
Apparatus according to Claim 6, insofar as dependent on Claim 5 characterised in that the apparatus employs a non-linear equaliser formed by the said filter or the filter forming apparatus, the said detector, a subtraction circuit, with one input connected to the output of the said filter and output connected to the input of the detector, and a further filter connected between the output of the detector and the other input of the subtraction circuit, the further filter having a sampled impulse-response which depends on the said modified sampled impulse-response determined when all roots greater than the predetermined value have been used in forming the said sampled impulse-response.
Claim 14
Dependent Claim
78 words
Apparatus according to Claim 1 or any of Claims 3 to 8 characterised in that the filter or the filter forming apparatus, and where used the further filter, operate by taking samples of received data, successively delaying the samples by the sampling interval, multiplying each undelayed sample and the delayed samples by respective coefficients, and summing the resultant products, the said coefficients being determined in accordance with the negative complex-conjugate reciprocals and negative reciprocals of the roots found.
Claim 15
Dependent Claim
168 words
Apparatus according to Claim 9 characterised in that the coefficients are found by taking, in turn, each signal of a sequence of signals equal in number to the number of the said coefficients required, the signals of the sequence initially all being zero except the last which is initially one, adding each signal to the product of the previous signal, if any, times the complex-conjugate of one of the negative reciprocals already found to form an intermediate sequence, reversing the order of the intermediate sequence, forming a further sequence by taking each signal in the reversed sequence, in turn, and subtracting the product of the said one negative reciprocal times the previous signal, if any, in the further sequence, repeating the said steps using the negative complex-conjugate reciprocal and negative reciprocal of another root, and using the new sequence generated as the initial sequence for the first step until all roots previously determined have been used, the signals of the final further sequence found being the required coefficients.
Claim 16
Dependent Claim
16 words
Apparatus or method according to any preceding claim characterised in that the predetermined value is 1.3.
Claim 17
Dependent Claim
16 words
Apparatus or method according to any preceding claim characterised in that the predetermined value is unity.
Claim 18
Dependent Claim
45 words
Apparatus according to Claim 1 or any of Claims 3 to 12 characterised in that the filter, or the filter forming apparatus, and if present the further filter, the sampling means and the detector are formed in whole or in part by a programmed computer.
References Cited (Backward Citations)
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