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Analysis of heart rate dynamics by methods derived from nonlinear mathematics : Clinical applicability and prognostic significance
Full text linkAbstractThe traditional methods of analysing heart rate variability based on means and variance are unable to detect subtle but potentially important changes in interbeat heart rate behaviour. This research was designed to evaluate the clinical applicability and prognostic significance of new dynamical methods of analysing heart rate behaviour derived from nonlinear mathematics.The study covered four different patient populations, their controls and one general population of elderly people. The first patient group consisted of 38 patients with coronary artery disease without previous myocardial infarction, the second of 40 coronary artery disease patients with a prior Q-wave myocardial infarction, and the third of 45 patients with a history of ventricular tachyarrhythmia. The fourth group comprised 10 patients with a previous myocardial infarction who had experienced ventricular fibrillation during electrocardiographic recordings. The fifth group comprised a random sample of 347 community-living elderly people invited for a follow-up of 10 years after electrocardiographic recordings.Heart rate variability was analysed by traditional time and frequency domain methods. The new dynamical measures derived from nonlinear dynamics were: 1) approximate entropy, which reflects the complexity of the data, 2) detrended fluctuation analysis, which describes the presence or absence of fractal correlation properties of time series data, and 3) power-law relationship analysis, which demonstrates the distribution of spectral characteristics of RR intervals, but does not reflect the magnitude of spectral power in different spectral bands.Approximate entropy was higher in postinfarction patients (1.17 ± 0.22), but lower in coronary artery disease patients without myocardial infarction (0.93 ± 0.17) than in healthy controls (1.03 ± 014, p The present observations demonstrate that dynamic analysis of heart rate behaviour gives new insight into analysis of heart rate dynamics in various cardiovascular disorders. The breakdown of the normal fractal-like organising principle of heart rate variability is associated with an increased risk of mortality and vulnerability to life-threatening arrhythmias.Academic Dissertation to be presented with the assent of The Faculty of Medicine, University of Oulu, for public discussion in Auditorium 10 of the University hospital of Oulu, on May 15th, 1998, at 12 noon.Abstract
The traditional methods of analysing heart rate variability based on means and variance are unable to detect subtle but potentially important changes in interbeat heart rate behaviour. This research was designed to evaluate the clinical applicability and prognostic significance of new dynamical methods of analysing heart rate behaviour derived from nonlinear mathematics.
The study covered four different patient populations, their controls and one general population of elderly people. The first patient group consisted of 38 patients with coronary artery disease without previous myocardial infarction, the second of 40 coronary artery disease patients with a prior Q-wave myocardial infarction, and the third of 45 patients with a history of ventricular tachyarrhythmia. The fourth group comprised 10 patients with a previous myocardial infarction who had experienced ventricular fibrillation during electrocardiographic recordings. The fifth group comprised a random sample of 347 community-living elderly people invited for a follow-up of 10 years after electrocardiographic recordings.
Heart rate variability was analysed by traditional time and frequency domain methods. The new dynamical measures derived from nonlinear dynamics were: 1) approximate entropy, which reflects the complexity of the data, 2) detrended fluctuation analysis, which describes the presence or absence of fractal correlation properties of time series data, and 3) power-law relationship analysis, which demonstrates the distribution of spectral characteristics of RR intervals, but does not reflect the magnitude of spectral power in different spectral bands.
Approximate entropy was higher in postinfarction patients (1.17 ± 0.22), but lower in coronary artery disease patients without myocardial infarction (0.93 ± 0.17) than in healthy controls (1.03 ± 014, p < 0.01, p < 0.05 respectively). It did not differ between patients with and without ventricular arrhythmia. The short term fractal-like scaling exponent of the detrended fluctuation analysis was higher in coronary artery disease patients without myocardial infarction (1.34 ± 0.15, p < 0.001), but not in postinfarction patients without arrhythmia (1.06 ± 0.13) compared with healthy controls (1.09 ± 0.13). The short term exponent was markedly reduced in patients with life-threatening arrhythmia (0.85 ± 0.25 ventricular tachycardia patients, 0.68 ± 0.18 ventricular fibrillation patients, p < 0.001 for both). The long term power-law slope of the power-law scaling analysis was lower in the ventricular fibrillation group than in postinfarction controls without arrhythmia risk (-1.63 ± 0.24 vs. -1.33 ± 0.23, p < 0.01) and predicted mortality in a general elderly population with an adjusted relative risk of 1.74 (95% CI 1.42–2.13).
The present observations demonstrate that dynamic analysis of heart rate behaviour gives new insight into analysis of heart rate dynamics in various cardiovascular disorders. The breakdown of the normal fractal-like organising principle of heart rate variability is associated with an increased risk of mortality and vulnerability to life-threatening arrhythmias
Carbohydrate-deficient transferrin (CDT) and serum antibodies against acetaldehyde adducts as markers of alcohol abuse
Full text linkAbstractIn the search for more reliable blood markers for excessive alcohol consumption, considerable effort has been devoted to measurements of carbohydrate-deficient transferrin (CDT), which increases in body fluids as a result of prolonged alcohol intake. In the present work, three CDT methods, CDTect (Pharmacia & Upjohn), %CDT radioimmunoassay (%CDT RIA) by Axis (Oslo, Norway), and Axis %CDT turbidimetric immunoassay (%CDT TIA) were examined for their diagnostic performance in cases of alcohol abuse with or without liver disease.The diagnostic performance of CDT as a marker of alcohol abuse correlates positively with alcohol consumption. As compared with g-glutamyltransferase (GGT) and mean corpuscular volume of erythrocytes (MCV), which are conventionally used as laboratory markers of excessive ethanol consumption, CDT (CDTect) has the highest sensitivity (64%) at the specificity level of 100% in heavy drinkers consuming >100 g ethanol/day, but its sensitivity decreases to 34% in cases with an alcohol intake of Patients with alcoholic liver disease (ALD) have significantly higher CDT values than alcoholics with non-liver pathology. However, CDT is primarily increased in cases with an early stage of ALD, so that there is a weak negative correlation between CDT and disease severity, which may prove to be of diagnostic value.Especially in men, CDTect seems to achieve greater sensitivity than %CDT RIA or %CDT TIA for detecting recent alcohol abuse among heavy drinkers, but it does have a significant correlation with serum transferrin, especially in individuals reporting social drinking or no alcohol intake. This should be considered when interpreting the assay results in patients with increased serum transferrin. %CDT methods achieve greater specificity than CDTect when analyzing samples from patients with high serum transferrin concentrations.Acetaldehyde-protein adducts are formed in the body after excessive ethanol intake, and their formation triggers antibody production, which may contribute to some forms of tissue damage seen in alcohol abusers. To obtain more information on the association between serum antibodies against acetaldehyde adducts, ALD and alcohol consumption, assays for antibodies against albumin and haemoglobin adducts were performed.Antibodies of the immunoglobulin (Ig) isotypes A, G, and M against acetaldehyde-adducts are formed in patients with prolonged heavy alcohol consumption. IgA titres in ALD patients are significantly higher than those found in patients with non-alcoholic liver disease, non-drinking controls, or heavy drinkers with no signs of liver disease. Anti-adduct IgG titres, in turn, are increased both in ALD and in heavy drinkers with no signs of liver disease as compared with non-alcoholic liver disease patients or non-drinking controls. It appears that anti-adduct IgA, IgG and IgM titres in ALD patients correlate with the severity of the liver disease. Although this association is a limitation for the usefulness of these antibodies as markers of alcohol abuse, it may serve as a basis for the differential diagnosis of alcohol-induced liver disease.Academic Dissertation to be presented with the assent of the Faculty of Medicine, University of Oulu, for public discussion in the Big Auditorium of the Central Hospital of Southern Ostrobothnia, Seinäjoki, on November 27th, 1998, at 12 noonAbstract
In the search for more reliable blood markers for excessive alcohol consumption, considerable effort has been devoted to measurements of carbohydrate-deficient transferrin (CDT), which increases in body fluids as a result of prolonged alcohol intake. In the present work, three CDT methods, CDTect (Pharmacia & Upjohn), %CDT radioimmunoassay (%CDT RIA) by Axis (Oslo, Norway), and Axis %CDT turbidimetric immunoassay (%CDT TIA) were examined for their diagnostic performance in cases of alcohol abuse with or without liver disease.
The diagnostic performance of CDT as a marker of alcohol abuse correlates positively with alcohol consumption. As compared with g-glutamyltransferase (GGT) and mean corpuscular volume of erythrocytes (MCV), which are conventionally used as laboratory markers of excessive ethanol consumption, CDT (CDTect) has the highest sensitivity (64%) at the specificity level of 100% in heavy drinkers consuming >100 g ethanol/day, but its sensitivity decreases to 34% in cases with an alcohol intake of <100 g/day, which hampers the use of CDT as a community screening method.
Patients with alcoholic liver disease (ALD) have significantly higher CDT values than alcoholics with non-liver pathology. However, CDT is primarily increased in cases with an early stage of ALD, so that there is a weak negative correlation between CDT and disease severity, which may prove to be of diagnostic value.
Especially in men, CDTect seems to achieve greater sensitivity than %CDT RIA or %CDT TIA for detecting recent alcohol abuse among heavy drinkers, but it does have a significant correlation with serum transferrin, especially in individuals reporting social drinking or no alcohol intake. This should be considered when interpreting the assay results in patients with increased serum transferrin. %CDT methods achieve greater specificity than CDTect when analyzing samples from patients with high serum transferrin concentrations.
Acetaldehyde-protein adducts are formed in the body after excessive ethanol intake, and their formation triggers antibody production, which may contribute to some forms of tissue damage seen in alcohol abusers. To obtain more information on the association between serum antibodies against acetaldehyde adducts, ALD and alcohol consumption, assays for antibodies against albumin and haemoglobin adducts were performed.
Antibodies of the immunoglobulin (Ig) isotypes A, G, and M against acetaldehyde-adducts are formed in patients with prolonged heavy alcohol consumption. IgA titres in ALD patients are significantly higher than those found in patients with non-alcoholic liver disease, non-drinking controls, or heavy drinkers with no signs of liver disease. Anti-adduct IgG titres, in turn, are increased both in ALD and in heavy drinkers with no signs of liver disease as compared with non-alcoholic liver disease patients or non-drinking controls. It appears that anti-adduct IgA, IgG and IgM titres in ALD patients correlate with the severity of the liver disease. Although this association is a limitation for the usefulness of these antibodies as markers of alcohol abuse, it may serve as a basis for the differential diagnosis of alcohol-induced liver disease
Self-association, compatibility, and strengthening behavior of liquid crystalline oligomers
Full text linkAbstractSynthetic routes were developed for the preparation of 2-alkoxy-4-hydroxybenzoic acids and 2-alkoxyhydroquinones, and a large-scale synthesis was developed for the preparation of 2-thioalkoxyhydroquinones. The 2-alkoxy-4-hydroxybenzoic acids, which contained alkyl side chains of different length, were used in the synthesis of new main chain liquid crystalline (LC) homo-, random, and block co-oligomers. In addition, oligomers of terephthaloyl chloride and 2-thioalkoxyhydroquinones and oligomers of terephthaloyl chloride and 2-alkoxyhydroquinones were produced.All the oligomers were blended with aliphatic polyamide 11 (PA 11). The effect of alkyl side chain length on the compatibility behavior of the LC oligomers towards the aliphatic polymer was characterized by DSC and FTIR, and the effect of side chain length on the flexural properties of the blends was investigated with a three-point bending test.The miscibility studies showed variable interfacial adhesion between the blended compounds. The strongest adhesion was achieved between PA 11 and the homo-oligomers of 2-alkoxy-4-hydroxybenzoic acids with short or medium long substituents (C₄-C₁₀), but the interactions between PA 11 and the oligomer with long aliphatic side chain (C₁₈) were poor, as were those between PA 11 and the wholly aromatic oligomer of 4-hydroxybenzoic acid. The compatibility between PA 11 and the co-oligomers of 2-alkoxy-4-hydroxybenzoic acids was slightly lower than the compatibility of the corresponding homo-oligomers. DSC and FTIR analyses of the blends of oligomers of terephthaloyl chloride and 2-thioalkoxyhydroquinones and oligomers of terephthaloyl chloride and 2-alkoxyhydroquinones with PA 11 implied that the interactions between the blended compounds were poor.FTIR spectra and viscosity measurements confirmed that all the oligomeric structures could self-associate, with effect on the final mechanical properties of the polyamide. The strength of PA 11 in a three-point bending test was increased by the addition of only 1% of LC oligomers to the matrix. The results also showed that the strengthening ability of the oligomers is directly proportional to the total amount of aliphatic carbons. The best strengthening results were obtained with unsubstituted oligomers, random co-oligomers of 2-alkoxy-4-hydroxybenzoic acids, and homo-oligomer of 2-butoxy-4-hydroxybenzoic acid.DSC investigations of a ternary blend of the oligomer of 2-decanyloxy-4-hydroxybenzoic acid, PA 11, and wholly aromatic commercial LC polymer showed the promising compatibilizing effect of the oligomer.Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Kajaaninsali (Auditorium L 6), on December 19th, 1998, at 12 noon.Abstract
Synthetic routes were developed for the preparation of 2-alkoxy-4-hydroxybenzoic acids and 2-alkoxyhydroquinones, and a large-scale synthesis was developed for the preparation of 2-thioalkoxyhydroquinones. The 2-alkoxy-4-hydroxybenzoic acids, which contained alkyl side chains of different length, were used in the synthesis of new main chain liquid crystalline (LC) homo-, random, and block co-oligomers. In addition, oligomers of terephthaloyl chloride and 2-thioalkoxyhydroquinones and oligomers of terephthaloyl chloride and 2-alkoxyhydroquinones were produced.
All the oligomers were blended with aliphatic polyamide 11 (PA 11). The effect of alkyl side chain length on the compatibility behavior of the LC oligomers towards the aliphatic polymer was characterized by DSC and FTIR, and the effect of side chain length on the flexural properties of the blends was investigated with a three-point bending test.
The miscibility studies showed variable interfacial adhesion between the blended compounds. The strongest adhesion was achieved between PA 11 and the homo-oligomers of 2-alkoxy-4-hydroxybenzoic acids with short or medium long substituents (C₄-C₁₀), but the interactions between PA 11 and the oligomer with long aliphatic side chain (C₁₈) were poor, as were those between PA 11 and the wholly aromatic oligomer of 4-hydroxybenzoic acid. The compatibility between PA 11 and the co-oligomers of 2-alkoxy-4-hydroxybenzoic acids was slightly lower than the compatibility of the corresponding homo-oligomers. DSC and FTIR analyses of the blends of oligomers of terephthaloyl chloride and 2-thioalkoxyhydroquinones and oligomers of terephthaloyl chloride and 2-alkoxyhydroquinones with PA 11 implied that the interactions between the blended compounds were poor.
FTIR spectra and viscosity measurements confirmed that all the oligomeric structures could self-associate, with effect on the final mechanical properties of the polyamide. The strength of PA 11 in a three-point bending test was increased by the addition of only 1% of LC oligomers to the matrix. The results also showed that the strengthening ability of the oligomers is directly proportional to the total amount of aliphatic carbons. The best strengthening results were obtained with unsubstituted oligomers, random co-oligomers of 2-alkoxy-4-hydroxybenzoic acids, and homo-oligomer of 2-butoxy-4-hydroxybenzoic acid.
DSC investigations of a ternary blend of the oligomer of 2-decanyloxy-4-hydroxybenzoic acid, PA 11, and wholly aromatic commercial LC polymer showed the promising compatibilizing effect of the oligomer
On effective irrationality measures for some values of certain hypergeometric functions
Full text linkAbstractThe dissertation consists of three articles in which irrationality measures for some values of certain special cases of the Gauss hypergeometric function are considered in both archimedean and non-archimedean metrics.The first presents a general result and a divisibility criterion for certain products of binomial coefficients upon which the sharpenings of the general result in special cases rely. The paper also provides an improvement concerning th e values of the logarithmic function. The second paper includes two other special cases, the first of which gives irrationality measures for some values of the arctan function, for example, and the second concerns values of the binomial function. All the results of the first two papers are effective, but no computation of the constants for explicit presentation is carried out. This task is fulfilled in the third article for logarithmic and binomial cases. The results of the latter case are applied to some Diophantine equations.Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Kajaaninsali (Auditorium L 6), on May 10th, 1997, at 12 noon.Abstract
The dissertation consists of three articles in which irrationality measures for some values of certain special cases of the Gauss hypergeometric function are considered in both archimedean and non-archimedean metrics.
The first presents a general result and a divisibility criterion for certain products of binomial coefficients upon which the sharpenings of the general result in special cases rely. The paper also provides an improvement concerning th e values of the logarithmic function. The second paper includes two other special cases, the first of which gives irrationality measures for some values of the arctan function, for example, and the second concerns values of the binomial function. All the results of the first two papers are effective, but no computation of the constants for explicit presentation is carried out. This task is fulfilled in the third article for logarithmic and binomial cases. The results of the latter case are applied to some Diophantine equations
From a Strange Wanderer to a Human Being : Finnish Missionary Work among Bushmen and the Image of Bushmen 1950-1985
No full textAbstractMy study is focused on the Finnish missionary workamong Bushmen in eastern Ovambo and Kavango in Namibia and on the image of Bushmen conveyed by it. The encounter of the cultures gave rise to new elements of the Bushman way of life that are partly based on the tradition of the encounter of cultures in the area and on the requirements of the local natural conditions. This helped to give the Bushmen the strength to resist acculturation, and the meeting of cultures brought regular elements, which I have called the borderline culture, to the outskirts of the missionary stations. Increased information reduces uncertainty. This fact began to come to surface in the 1950s in the descriptions of Bushmen by Finnish nurses in Kavango in which the emotions of fear, sympathy and care were present. The pressures for missionary work among the Bushmen towards the end of the 1950s broke the old image of Bushmen. In eastern Ovambo and Kavango, the missionary work among Bushmen which was expanding in the 1960s made the image of Bushmen a more everyday matter in the emerging borderline culture, in which it was typical to associate the image of the Bushman to work and success at work. The missionaries did not yet quite understand the life of the Bushmen, although they were clearly interested in it. They tried to dictate the conditions for the encounter in the 1960s in accordance with the old ideology of missionary work. Thus the 1960s was the era of a Bushman image that was controlled by the preachers who tried to defend the justification and methods of missionary work.The breaking of the language barrier was an important factor on the way to the next change in the image of Bushmen which was seen clearly in the borderline culture which was established in the 1970s. Language meant improved and more profound information and therefore confidential relationships between the missionaries and the Bushmen. The understanding of ethnic cultures improved in general. The new ideals were partly due to the strivings for independence in the area and to more general international pressures in which mission and colonialism were subjected to criticism. The borderline culture had been established, and the life of Bushmen was felt to be part of everyday life. The interest of the missionaries in the Bushmen"s way of life was increased. In the early 80s, the image of the Bushman had become much more diversified and uniform. The Bushman way of life was known quite well, although based on the description of a few missionaries only. As a consequence of the Namibian Civil War, the work of the Finnish missionaries ended in the stations in Ovambo, but the work continued in the form of developmental aid in Kavango. The last image of the Bushmen there was given by the quiet missionaries, the nurses, just like in the early stages in the early 1950s. The concerns over care and everyday nursing were common in their descriptions, but the Bushmen were not any longer strange wanderers in the forest but familiar people in a borderline culture.Esitetään Oulun yliopiston humanistisen tiedekunnan suostumuksella julkisesti tarkastettavaksi Linnanmaan luentosalissa YB210, 17. toukokuuta 1997 klo 12.Abstract
My study is focused on the Finnish missionary workamong Bushmen in eastern Ovambo and Kavango in Namibia and on the image of Bushmen conveyed by it. The encounter of the cultures gave rise to new elements of the Bushman way of life that are partly based on the tradition of the encounter of cultures in the area and on the requirements of the local natural conditions. This helped to give the Bushmen the strength to resist acculturation, and the meeting of cultures brought regular elements, which I have called the borderline culture, to the outskirts of the missionary stations. Increased information reduces uncertainty. This fact began to come to surface in the 1950s in the descriptions of Bushmen by Finnish nurses in Kavango in which the emotions of fear, sympathy and care were present. The pressures for missionary work among the Bushmen towards the end of the 1950s broke the old image of Bushmen. In eastern Ovambo and Kavango, the missionary work among Bushmen which was expanding in the 1960s made the image of Bushmen a more everyday matter in the emerging borderline culture, in which it was typical to associate the image of the Bushman to work and success at work. The missionaries did not yet quite understand the life of the Bushmen, although they were clearly interested in it. They tried to dictate the conditions for the encounter in the 1960s in accordance with the old ideology of missionary work. Thus the 1960s was the era of a Bushman image that was controlled by the preachers who tried to defend the justification and methods of missionary work.
The breaking of the language barrier was an important factor on the way to the next change in the image of Bushmen which was seen clearly in the borderline culture which was established in the 1970s. Language meant improved and more profound information and therefore confidential relationships between the missionaries and the Bushmen. The understanding of ethnic cultures improved in general. The new ideals were partly due to the strivings for independence in the area and to more general international pressures in which mission and colonialism were subjected to criticism. The borderline culture had been established, and the life of Bushmen was felt to be part of everyday life. The interest of the missionaries in the Bushmen"s way of life was increased. In the early 80s, the image of the Bushman had become much more diversified and uniform. The Bushman way of life was known quite well, although based on the description of a few missionaries only. As a consequence of the Namibian Civil War, the work of the Finnish missionaries ended in the stations in Ovambo, but the work continued in the form of developmental aid in Kavango. The last image of the Bushmen there was given by the quiet missionaries, the nurses, just like in the early stages in the early 1950s. The concerns over care and everyday nursing were common in their descriptions, but the Bushmen were not any longer strange wanderers in the forest but familiar people in a borderline culture
Multiuser demodulation for DS-CDMA systems in fading channels
Full text linkAbstractMultiuser demodulation algorithms for centralized receivers of asynchronous direct-sequence (DS) spread-spectrum code-division multiple-access (CDMA) systems in frequency-selective fading channels are studied. Both DS-CDMA systems with short (one symbol interval) and long (several symbol intervals) spreading sequences are considered.Linear multiuser receivers process ideally the complete received data block. The approximation of ideal infinite memory-length (IIR) linear multiuser detectors by finite memory-length (FIR) detectors is studied. It is shown that the FIR detectors can be made near-far resistant under a given ratio between maximum and minimum received power of users by selecting an appropriate memory-length. Numerical examples demonstrate the fact that moderate memory-lengths of the FIR detectors are sufficient to achieve the performance of the ideal IIR detectors even under severe near-far conditions.Multiuser demodulation in relatively fast fading channels is analyzed. The optimal maximum likelihood sequence detection receiver and suboptimal receivers are considered. The parallel interference cancellation (PIC) receiver is demonstrated to achieve better performance in known channels than the decorrelating receiver, but it is observed to be more sensitive to channel coefficient estimation errors than the decorrelator. At high channel loads the PIC receiver suffers from bit error rate (BER) saturation, whereas the decorrelating receiver does not. Choice of channel estimation filters is shown to be crucial if low BER is required. Data-aided channel estimation is shown to be more robust than decision-directed channel estimation, which may suffer from BER saturation caused by hang-ups at high signal-to-noise ratios.Multiuser receivers for dynamic CDMA systems are studied. Algorithms for ideal linear detector computation are derived and their complexity is analyzed. The complexity of the linear detector computation is a cubic function of KL, where K and L are the number of users and multipath components, respectively. Iterative steepest descent, conjugate gradient, and preconditioned conjugate gradient algorithms are proposed to reduce the complexity. The computational requirements for one iteration are a quadratic function of KL. The iterative detectors are also shown to be applicable for parallel implementation. Simulation results demonstrate that a moderate number of iterations yields the performance of the corresponding ideal linear detectors. A quantitative analysis shows that the PIC receivers are significantly simpler to implement than the linear receivers and only moderately more complex than the conventional matched filter bank receiver.Academic Dissertation to be presented with the assent of The Faculty of Technology, University of Oulu, for public discussion in Raahensali (Auditorium L 10), Linnanmaa, on October 17th, 1997, at 12 noon.Abstract
Multiuser demodulation algorithms for centralized receivers of asynchronous direct-sequence (DS) spread-spectrum code-division multiple-access (CDMA) systems in frequency-selective fading channels are studied. Both DS-CDMA systems with short (one symbol interval) and long (several symbol intervals) spreading sequences are considered.
Linear multiuser receivers process ideally the complete received data block. The approximation of ideal infinite memory-length (IIR) linear multiuser detectors by finite memory-length (FIR) detectors is studied. It is shown that the FIR detectors can be made near-far resistant under a given ratio between maximum and minimum received power of users by selecting an appropriate memory-length. Numerical examples demonstrate the fact that moderate memory-lengths of the FIR detectors are sufficient to achieve the performance of the ideal IIR detectors even under severe near-far conditions.
Multiuser demodulation in relatively fast fading channels is analyzed. The optimal maximum likelihood sequence detection receiver and suboptimal receivers are considered. The parallel interference cancellation (PIC) receiver is demonstrated to achieve better performance in known channels than the decorrelating receiver, but it is observed to be more sensitive to channel coefficient estimation errors than the decorrelator. At high channel loads the PIC receiver suffers from bit error rate (BER) saturation, whereas the decorrelating receiver does not. Choice of channel estimation filters is shown to be crucial if low BER is required. Data-aided channel estimation is shown to be more robust than decision-directed channel estimation, which may suffer from BER saturation caused by hang-ups at high signal-to-noise ratios.
Multiuser receivers for dynamic CDMA systems are studied. Algorithms for ideal linear detector computation are derived and their complexity is analyzed. The complexity of the linear detector computation is a cubic function of KL, where K and L are the number of users and multipath components, respectively. Iterative steepest descent, conjugate gradient, and preconditioned conjugate gradient algorithms are proposed to reduce the complexity. The computational requirements for one iteration are a quadratic function of KL. The iterative detectors are also shown to be applicable for parallel implementation. Simulation results demonstrate that a moderate number of iterations yields the performance of the corresponding ideal linear detectors. A quantitative analysis shows that the PIC receivers are significantly simpler to implement than the linear receivers and only moderately more complex than the conventional matched filter bank receiver
Pohjolan taivaan alla
No full textPohjolan jätkä : huviksi, ajanvietteeksi ja opiksi -lehdessä 7.12.1945 julkaistu Kalle Päätalon kirjoitus ”Pohjolan taivaan alla”. Digitoitu Oulun yliopiston Kalle Päätalon lehtikirjoitukset -projektissa.Pohjolan jätkä : huviksi, ajanvietteeksi ja opiksi -lehdessä 7.12.1945 julkaistu Kalle Päätalon kirjoitus ”Pohjolan taivaan alla”. Digitoitu Oulun yliopiston Kalle Päätalon lehtikirjoitukset -projektissa