| 41. |
- Svensson, Arne, 1955, et al.
(författare)
-
Performance Evaluation of Differential and Discriminator Detection of Continuous Phase Modulation
- 1986
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 35:3, s. 106-117
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Tidskriftsartikel (refereegranskat)abstract
- Recently, bandwidth efficient constant-amplitude digital modulation schemes have also been shown to be power efficient when coherent detection is used. Partial-response continuous phase modulation (CPM) schemes are within this class. In some applications noncoherent detection is preferred. The performance of CPM systems is analyzed for differential and discriminator detection. An additive white Gaussian channel is assumed. The detectors make symbol-by-symbol decisions. The considered schemes are M-ary with an arbitrary modulation index and pulse shaping over several symbol intervals. The performance is analyzed by means of error probability expressions. The IF filter for the detectors is optimized within a special class of filters to give good performance. The differential detector is also analyzed on a Rayleigh fading channel. The fading is assumed to be slow. The IF filter is also optimized on this channel. Simulated error probabilities for discriminator detection with a Viterbi detector are also presented both for the Gaussian and the Rayleigh fading channel. The discriminator detector making symbol-by-symbol decisions is simulated on the Rayleigh fading channel. It is shown that partial-response CPM schemes with good performance can also be obtained with noncoherent detectors.
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| 42. |
- Svensson, Arne, 1955, et al.
(författare)
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Performance of AMF Receivers for CPM
- 1984
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Ingår i: Proceedings IEEE Global Telecommunications Conference, Atlanta, Georgia. ; , s. 32.4.1-32.4.7
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Konferensbidrag (refereegranskat)
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| 43. |
- Svensson, Arne, 1955, et al.
(författare)
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Performance of Generalised AMF Receivers for Continuous Phase Modulation
- 1985
-
Ingår i: IEE Proceedings-F, Communications, Radar and Signal Processing. ; 132:7, s. 541-547
-
Tidskriftsartikel (refereegranskat)abstract
- Partial-response continuous phase modulation (CPM) signals can in many cases yield power spectra with narrow mainlobe and also low sidelobes. The optimum receiver for these signals is sometimes complex. In the paper the idea of using a smaller signal set in the receiver than used by the transmitter is considered. This is done by means of using a generalised average matched filter (AMF) receiver. Only coherent detection of signals transmitted over an additive white Gaussian noise channel is considered. The multiple-symbol AMF receiver can be implemented with fewer filters than the optimum receiver. These receivers are analysed for various partial-response CPM signals. The analysis is done under the assumption of error-free filter and phase updating. A Euclidean distance for mismatched signal sets is used to give the symbol error probability for large signal/noise ratios conditioned on error-free updating. Under the above assumptions, it is shown that the multiple-symbol AMF receiver performs equally well as the optimum receiver for schemes with low modulation indices and also for large modulation indices for some schemes. This is the case both for binary and quarternary schemes. A simple updatiing method is also simulated.
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| 44. |
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| 45. |
- Svensson, Arne, 1955, et al.
(författare)
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Serial MSK-Type Detection of Partial Response Continuous Phase Modulation
- 1985
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 33:1, s. 44-52
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Tidskriftsartikel (refereegranskat)abstract
- Partial response continuous phase modulation (CPM) schemes have a high spectrum utilization and also a high immunity to nonlinear distortion, since they have a constant envelope. Schemes with high power efficiency can also be designed when they are coherently detected with a Viterbi detector. These schemes are sometimes complex, however. In this paper two minimum-shift-keyed (MSK)type receivers are studied. The MSK-type receiver can be implemented as a serial receiver and as a parallel receiver. Both receivers are useful for binary modulation schemes with modulation indexh = 1/2. Only coherent detection of signals transmitted over an additive white Gaussian noise channel is considered. The serial receiver can be implemented with only two filters and simple decision logic. The decisions are made serially in one decision eye pattern. Two types of receiver filters are considered. Error probability results are presented for the receiver, both with and without phase and timing errors present in the receiver. It is shown that, assuming perfect phase and time synchronization, the serial and parallel receivers have equal performances. The advantages of the serial receiver over the parallel receiver are the same for partial response continuous phase modulation as for classical MSK; i.e., both in implementation aspects and in the reduced sensitivity to phase errors.
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| 46. |
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| 47. |
- Svensson, Erik
(författare)
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Costs, benefits and constraints in the evolution of avian reproductive tactics: a study on the blue tit
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this study I have investigated the various factors influencing reproductive tactics among breeding blue tits (Parus caeruleus). The study was carried out in a nestbox-breeding population of marked individuals at the Revinge Area, outside Lund, southern Sweden. I have especially investigated the energetic, physiological and temporal factors influencing the reproductive decisions. This included use of various physiological methods such as metabolic measurements of energy expenditure, measurements of immunocompetence using ELISA:s and sexing of nestlings using quantification of DNA-contents using flow cytometry. Three themes were explored: 1/Reproductive effort and costs of reproduction, 2/sex allocation and 3/reproductive timing in a seasonal environment.
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| 48. |
- Svensson, Erik, et al.
(författare)
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Energetic stress, immunosuppression and the costs of an antibody response
- 1998
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Ingår i: Functional Ecology. - : Wiley. - 1365-2435 .- 0269-8463. ; 12:6, s. 912-919
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Tidskriftsartikel (refereegranskat)abstract
- 1. Recently, there has been much interest in physiological trade-offs between parasite resistance and fitness-related traits such as secondary sexual characters or reproductive effort. More specifically it has been suggested that (i) energetically costly activities may suppress the immune system and (ii) that this immunosuppression is caused by costly immune defences competing with other bodily demands for scarce resources, e.g. energy. 2. The possibility was investigated of an energetically based trade-off between humoral (antibody-based) immunocompetence and other costly activities, by immunizing Blue Tits, Parus caeruleus, with novel antigens (proteins) thereby inducing antibody responses, and performing two experiments. In experiment i, one group of birds was subjected to cold stress, thereby increasing their daily energy expenditure and the effect on immune responsiveness was investigated. In experiment 2, the basal metabolic rate (BMR) of immunized birds was measured to investigate the energetic costs of mounting the antibody responses. 3. In experiment I, birds subject to increased energy turnover had significantly lower antibody responses, consistent with the hypothesis that environmental stress could suppress immunocompetence. However, in experiment 2 the energetic costs of these antibody responses were found to be low and at most 8-13% of BMR, indicating that adaptive resource allocation of energy was an unlikely explanation for the lowered immune responsiveness in the cold stress treatment (experiment 1). 4. It is concluded that our data provide some support to the idea that there may be a trade-off between immunocompetence and energetically costly activities such as thermoregulation, reproduction or mate attraction, although this trade-off may not necessarily be based on energy or nutrient limitation (i.e. resource allocation models). Two non-energetic explanations are briefly discussed, one adaptive and one non-adaptive, that could explain the immunosuppression in our study as well as in other behavioural and ecological contexts.
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| 49. |
- Svensson, Erik, et al.
(författare)
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Mate quality affects offspring sex ratio in blue tits
- 1996
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - : The Royal Society. - 0962-8452. ; 263:1368, s. 357-361
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Tidskriftsartikel (refereegranskat)abstract
- Questions concerning the occurrence of adaptive sex ratio manipulation have a long research tradition in evolutionary biology, but evidence from birds is scarce. It has been suggested that birds are unable to adaptively determine the sex of their young because of the constraints of their sex determination systems. Here we report results from a study of variation in offspring sex ratio in the blue tit, Parus caeruleus, a small passerine bird. Our data suggest that females are able to manipulate their primary sex ratios away from the equal sex ratio predicted from simple chromosomal segregation at meiosis. Contrary to the situation in some other birds, offspring sex ratio variation in this species was not influenced by timing of breeding or brood size. We show that females mated to males with high survival prospects bias the hatching sex ratio of their broods in favour of sons. Although it has previously been proposed that females should produce an excess of sons when mated to high-quality males, our data provide the first evidence that the phenotypic quality of fathers contributes to the sex ratio variation in a natural population.
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| 50. |
- Svensson, Erik
(författare)
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Pharmacodynamic effects of antibiotics on growing and nongrowing bacteria
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this thesis was to study antibiotic effects on nongrowing baCteria and to study the development of resistance in Staphylococcus epidermidis, a bacterium which is often found in biofilm infections. The antibiotic effect on biofilm infections is generally weak, which probably is due to decreased growth rate of the bacteria. The effects of antibiotics on growing and nongrowing bacteria were studied with pharmacodynamic parameters. One of these parameters is postantibiotic effect (PAE). The conventional PAE measurement is performed with viable count. Viable counting is very laborious, which is why other methods have been used. However, the results may differ from those obtained with the viable count method for determining PAE. In this study effective regrowth time (ERT) and control-related effective regrowth time (CERT) were shown to be independent of the method used for bacterial quantification. With CERT and PAE it possible to study antibiotic effects on nongrowing and growing bacteria.CERT and PAE of amikacin, ciprofloxacin, and imipenem were investigated on growing and nongrowing Escherichia coli and Pseudonumas aeruginosa. All drugs had long CERT and PAE on growing bacteria. Arnikacin and ciprofloxacin, but not imipenem had long CERT and PAE on nongrowing bacteria.Amikacin, imipenem, ofloxacin, rifampicin, and vancomycin induced CERT and PAE on growing S. epidermidis, and imipenem combination with amikacin or vancomycin had a synergistic CERT and PAE in these cultures. Only rifampicin or antibiotic combinations containing rifampicin were effective against nongrowing S. epidermidis. There was no synergistic CERT or PAE on nongrowing bacteria.Selection and regrowth of highly rifampicin resistant S. epidermidis, which was present at a frequency of 10·7 in the initial inoculum, were seen when the bacteria were in~ubated with rifampicin at a high inoculum. Rifampicin combined with high concentrations of amikacin or ofloxacin prevents selection and regrowth of rifampicin resistant bacteria.
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