| 1. |
- Ahnström, Ulrika, et al.
(författare)
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Detection and direction-finding of spread spectrum signals using correlation and narrowband interference rejection
- 2003
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Ingår i: Nordic Matlab Conference 2003.
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Konferensbidrag (refereegranskat)abstract
- An algorithm for correlation-based detection of direct sequence spread spectrum signals with direction finding, including direction-filtering and narrow-band interference rejection, is implemented and evaluated in MATLAB. An analog noise-free signal is generated and sampled by a test-bed system. Numerical simulations are run based on data corrupted by mutually uncorrelated white Gaussian noise sequences, and also with recorded noise from two spatially separated HF radio receivers. The simulations and measurements show promising results for detection and direction-finding of covert wideband signals in low SNR and in presence of narrowband interferers. Direction filtering is shown to improve the results.
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| 2. |
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| 3. |
- Andersson, Tomas, et al.
(författare)
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Frequency estimation utilizing the Hadamard transform
- 2001
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Ingår i: 2001 IEEE WORKSHOP ON STATISTICAL SIGNAL PROCESSING PROCEEDINGS. - NEW YORK : IEEE. - 0780370112 ; , s. 409-412
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Konferensbidrag (refereegranskat)abstract
- Fast analog to digital conversion with only one bit per sample does not only make high sampling rates possible but also reduces the required hardware complexity. For short data buffers or block lengths, it has been shown that tone frequency estimators can be implemented by a simple table look-up. In this paper we present an analysis of such tables using the Hadamard transform. As an outcome of the analysis, we propose a class of nonlinear estimators of low complexity. Their performance is evaluated using numerical simulations. Comparisons are made with the proper Cramer-Rao bound and with the table look-up approach.
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| 4. |
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| 5. |
- Andersson, Tomas, et al.
(författare)
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Multiple-tone estimation by IEEE standard 1057 and the expectation-maximization algorithm
- 2003
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Ingår i: IMTC/O3: PROCEEDINGS OF THE 20TH IEEE INSTRUMENTATION AND MEASUREMENT TECHNOLOGY CONFERENCE. ; , s. 739-742
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Konferensbidrag (refereegranskat)abstract
- The aim of this work is to present an efficient algorithm for multiple-tone parameter estimation. The algorithm is inspired by the expectation-maximization algorithm, and it utilizes the IEEE standard 1057 for single tone parameter estimation. In the derivation of the algorithm it is assumed that the number of tones are known and that the frequencies are well separated The algorithm is evaluated using data consisting of multiple real-valued tones. The performance of the frequency estimator is studied and compared with the asymptotic Cramer-Rao bound (CRB). It is shown that the algorithm produces statistically efficient frequency estimates at high signal to noise ratios, that is the variance of the estimates reaches the CRB. Finally, it is shown that the algorithm can produce efficient estimates independent of the number of tones in the input signal.
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| 6. |
- Andersson, Tomas, et al.
(författare)
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Standardized sine-wave fitting algorithms, extensions and applications
- 2003
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Ingår i: Northern Light Workshop on Sensors, Signals and Systems, Björkliden, Sverige, April 7-9, 2003.
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Konferensbidrag (refereegranskat)abstract
- The objective of this paper is to present the statistical properties of the IEEE-STD-1057/IEEE-STD-1241 sine-wave fitting algorithms. The proper Cramér-Rao bound is derived for both the three-parameter and four-parameter algorithms. Further, we investigate the residual, and derive its statistical properties, in both the three- and four-parameter fitting case. In a practical setup were the frequency is almost known, we derive an analytical expression for the mean of the residual. By analysis we compare the two methods and state in which case one should use one over the other. Finally, we present some numerical evaluations confirming our analytical findings.
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| 7. |
- Andersson, Tomas, et al.
(författare)
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Toward a Standardized Multi-Sinewave Fit Algorithm
- 2004
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Ingår i: 9th European Workshop on ADC Modelling and Testing. - 9781634391849 ; , s. 337-342
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Konferensbidrag (refereegranskat)abstract
- Multi-sinewave test methods require algorithms for multiple-tone parameter estimation.There exist a vast amount of publications on the topic [1]. This paper presents a generalization ofthe IEEE four-parameter sinewave fit algorithm suitable to handle data comprising multiple sinewaves.The proposed method directly estimates the 3p + 1 parameters of a p-tone model. The algorithmis analyzed numerically with emphasize on its convergence properties and statistical efficiency. Theinitialization of the algorithm is of major importance and an attempt to formulate a proper initializationprocedure is presented.
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| 8. |
- Bergenheim, Jon, et al.
(författare)
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Ekosläckning
- 2002
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Patent (populärvet., debatt m.m.)abstract
- The present invention relates to a cancellation of echoes in telecommunications systems, more specifically it relates to adaptive alignment of a linear filter (500) used for echo cancellation. According to the invention, it is continuously determined, by means of control logic (520), if a reflection replica delay included in an echo replica signal (110), which delay is provided by a signal buffer (510), should be attempted to be increased or not. Similarly, it is continuously determined if the reflection replica delay should be attempted to be decreased or not. In this way it is possible to provide a delay of the reflection replica which corresponds to the pure delay of a corresponding reflection included in an echo signal (120) received over an echo path. The invention is advantageous since the filter (500) will continuously and quickly adapt to changes in the echo path delay by continuously increasing or decreasing, in an incremental and smooth manner, a present replica delay.
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| 9. |
- Björsell, Niclas, et al.
(författare)
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Benefits with Truncated Gaussian Noise in ADC Histogram Tests
- 2004
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Ingår i: 9th IMEKO Workshop on ADC Modeling and Testing, IWADC 2004, Held Together with the 13th IMEKO TC4 Symposium on Measurements for Research and Industrial Applications. - : IMEKO-International Measurement Federation Secretariat. - 9781634391856 ; , s. 787-792
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Konferensbidrag (refereegranskat)abstract
- One method to characterize ADCs is to use a histogram, where Gaussian noise may be used as stimulus signal. However, a Gaussian noise signal that excites all transition levels also generates input values outside working range of the ADC. Modern signal generators can generate arbitrary signals. Hence, excluding undesired values outside the ADC full scale can minimize test sequences. Truncating the signal to the working range gives further advantages, which are explored in this paper. The statistical properties is theoretically evaluated and compared. It is shown that accuracy increases for a fixed sample length and that variation over transition levels decrease.
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| 10. |
- Falk, Johan, et al.
(författare)
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Direction Finding for Electronic Warfare Systems Using the Phase of the Cross Spectral Density
- 2002
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Ingår i: RadioVetenskap och Kommunikation (RVK). ; , s. 264-268
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Konferensbidrag (refereegranskat)abstract
- In modern electronic warfare systems there is a need for direction-finding of transmitters using waveforms for military stealth communication. In this paper, a correlation-based method is investigated utilizing the phase of the cross spectral density to estimate the time-difference-of-arrival from a two-channel digital receiver. A least squares method is reviewed, and its performance is investigated by theoretical analysisand by Monte-Carlo simulations. Proper Cramér-Raobounds are derived. It is shown that the method is statistically efficient for flat spectrum signals. The method is found to be a promising method for use against military communication in an electronic warfare direction-finding system.
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