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- Host-Madsen, A., et al.
(författare)
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The effect of sampling and quantization on frequency estimation
- 1998
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Ingår i: 1998 IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP. ; , s. 2217-2220
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Konferensbidrag (refereegranskat)abstract
- The effect of sampling and quantization on frequency estimation for a single sinusoid is investigated. The Cramer-Rao bound for 1 bit quantization is derived, and compared with the limit of infinite quantization. It is found that 1 bit quantization gives a slightly worse performance, however, with a dramatic increase of variance at certain frequencies. This can be avoided by using 4 times oversampling. The effect of sampling when using non-ideal antialiasing lowpass filters is therefore investigated. Cramer-Rao lower bounds are derived, and the optimal filters and sampling frequencies are found. Finally, fast estimators for 1 bit sampling, in particular correlation based estimators, are derived. The paper concludes with simulation results for 4 times oversampled 1 bit quantization
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- Händel, Peter, 1962-, et al.
(författare)
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On frequency estimation from oversampled quantized observations
- 1999
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Ingår i: Acoustics, Speech, and Signal Processing, 1999. Proceedings., 1999 IEEE International Conference on. ; , s. 1549-1552
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Konferensbidrag (refereegranskat)abstract
- The effect of sampling and quantization on frequency estimation for a single sinusoid is investigated. Asymptotic Cramer-Rao bounds (CRB) for 1-bit quantization and for non-ideal filters are derived, which are simpler to calculate than the exact CRB while still relatively accurate. It is further investigated how many bits should be used in quantization to avoid the problems of 1-bit quantization, and it turns out that 3-4 bits are enough. Finally, oversampled 1-bit quantization is investigated. It is determined how much the signal should be oversampled, and in addition Sigma; Delta; modulators are investigated
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- Händel, Peter, 1962-, et al.
(författare)
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Particle velocity and size estimation from two channel laser anemometry measurements
- 1997
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Ingår i: Acoustics, Speech, and Signal Processing, 1997. ICASSP-97., 1997 IEEE International Conference on. ; , s. 3529-3532
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Konferensbidrag (refereegranskat)abstract
- A mathematical treatment of particle size and velocity estimation from two channel laser anemometry measurements is considered. Cramer-Rao bounds for the general case are derived, and the corresponding maximum likelihood estimator is analyzed through computer simulations. Low complexity correlation based estimators are derived and their performance is characterized. The results predicted by theory are illustrated by some numerical examples
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- Jorgensen, F S, et al.
(författare)
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MULTISCAN--a Scandinavian multicenter second trimester obstetric ultrasound and serum screening study
- 1999
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Ingår i: Acta Obstetricia et Gynecologica Scandinavica. - 1600-0412. ; 78:6, s. 501-510
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Tidskriftsartikel (refereegranskat)abstract
- AIM: To study the detection rates of second trimester ultrasound screening for neural tube defects (NTD), abdominal wall defects (AWD) and Down's syndrome (DS) in low risk populations at tertiary centers, and to compare the ultrasound screening detection rates with those that were obtainable by biochemical serum screening (double test: alpha-fetoprotein/human chorion gonadotrophin/age test). STUDY DESIGN: Prospective multicenter study with a three year inclusion period: 1/1/1989-31/12/1991. SUBJECTS: 27,844 low-risk women at 18-34 years of age who had a second trimester ultrasound screening examination. Of these, 10,264 also had a serum test. METHODS: An ultrasound malformation scan and a serum test were carried out at 17-19 weeks of gestation. Risk calculations regarding DS were based on alpha-fetoprotein, human chorion gonadotrophin and maternal age; performed retrospectively for the first two years. RESULTS: In total 73 cases were identified in the study population: NTD (n=34), AWD (n=7) and DS (n=32). The detection rates, (%, with 95% confidence interval) for ultrasound screening were: NTD: 79.4 (62.1-91.3); AWD: 85.7 (42.1-99.6); DS: 6.3 (0.8-20.8). In the subgroup of women who had both tests, the detection rates for ultrasound screening vs double test were: NTD: 62.5 (24.5-91.5) vs 75.0 (34.9-96.8); AWD: 66.7 (9.4-99.2) vs 100 (29.2-100.0); DS: 7.7 (0.2-36.0) vs 46.2 (19.2-74.9). The false positive rates (%) for ultrasound screening vs double test were: NTD: 0.01/3.3; AWD: 0.01/3.3; DS: 0.1/4.0. CONCLUSION: Second trimester ultrasound screening in a low risk population gave a low detection rate for fetal DS (6.3%) and an acceptable detection rate for NTD (79.4%) and AWD (85.7%). In the subgroup of women who had both tests, serum screening performed better than ultrasound as applied in the present study, especially regarding DS.
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