| 1. |
- Björnson, Emil, et al.
(författare)
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Schur-convexity of the Symbol Error Rate in Correlated MIMO Systems with Precoding and Space-time Coding
- 2008
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Ingår i: Proceedings of the twentieth Nordic Conference on Radio Science and Communications.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper analyzes the symbol error rate (SER) of spatially correlated multiple-input multiple-output (MIMO) systems with linear precoding, space-time block codes, and long-term statistical channel state information at the transmitter. Majorization theory and the notion of Schur-convexity is used to show how the SER depends on the signal-to-noise ratio (SNR), on the transmit and receive correlation, and on the choice of precoder. Depending on these conditions, the Chernoff bound on the SER is shown to be Schur- convex (i.e., increasing with the amount of correlation) with respect to the receive correlation, while it is Schur-convex at high SNR and Schur-concave (i.e., decreasing with increasing amount of correlation) at low SNR with respect to the transmit correlation. These properties are inherited by the exact SER, as shown analytically and illustrated numerically.
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| 2. |
- Björsell, Niclas, 1964-, et al.
(författare)
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Improved estimate of parametric models for analogue to digital converters by using weighted integral nonlinearity data
- 2010
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Ingår i: 17th Symposium IMEKO TC4 - Measurement of Electrical Quantities, 15th International Workshop on ADC Modelling and Testing, and 3rd Symposium IMEKO TC19 - Environmental Measurements. - 9781617823381 ; , s. 597-600, s. 597-600
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Konferensbidrag (refereegranskat)abstract
- Error modelling has played a major role in generating post-corrections of analogue to digital converters (ADC). Benefits by using parametric models for post-correction are that they requires less memory and that they are easier to identify for arbitrary signals. However, the parameters are estimated in two steps; firstly, the integral nonlinearity (INL) is estimated and secondly, the model parameters. In this paper we propose a method to improve the performance in the second step, by utilizing information about the statistical properties of the first step.
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| 3. |
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| 4. |
- Medawar, Samer, et al.
(författare)
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ADC Characterization By Dynamic Integral Nonlinearity
- 2008
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Ingår i: 13th Workshop on ADC Modelling and Testing. - 9788890314933 ; , s. 1037-1042
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Konferensbidrag (refereegranskat)abstract
- Wide band characterization of analog-digital converter integral nonlinearity (INL) based on parametric modeling and least-squares parameter fit is performed. In particular, the variations in the INL due to the frequency of theADC stimuli are modeled. The INL is divided into two main entities describing the static and dynamic behavior of theADC, respectively. The static component is modeled by a high code component (HCF) of piecewise linear segmentscentered around zero. A static low code (LCF) polynomial inherent to the INL data is added to the segments to complete the static part of the model. The INL dynamic part is modeled by an LCF polynomial. Method implementationis considered and is applied to 12-bit ADC data at 210 MSPS.
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| 5. |
- Medawar, Samer, et al.
(författare)
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Approximate Maximum Likelihood Estimation of Rician K-Factor and Investigation of Urban Wireless Measurements
- 2013
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 12:6, s. 2545-2555
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Tidskriftsartikel (refereegranskat)abstract
- We consider the problem of estimating the K-factor of a Rician fading wireless channel based on observations of the envelope only, i.e., without phase-information. An approximate Rician power density function (pdf) is introduced to overcome the complexity of the exact pdf. A closed-form maximum-likelihood estimator is derived based on this approximate Rician pdf, while a maximum-likelihood estimator based on the exact Rician pdf appears to be infeasible. An improved estimator is also proposed that features less bias and less variance than the first estimator. The performance of the latter estimator is compared to moment-based estimators that were previously proposed in the literature and is found to have superior performance to closed-form moment estimators, especially for low sample numbers and/or large K-values. The estimator is applied to real wireless macro-cell urban-area measurements. The results show generally low K-factors (below 3dB), with occasional higher values in particular circumstances.
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| 6. |
- Medawar, Samer, et al.
(författare)
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Dynamic Calibration of Undersampled Pipelined ADCs by Frequency Domain Filtering
- 2013
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662. ; 62:7, s. 1882-1891
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Tidskriftsartikel (refereegranskat)abstract
- Integral nonlinearity (INL) is used for the post-correction of pipelineanalog-digital converters (ADC)s. An input-frequency-dependentINL model is developed for the compensation. The model consistsof a static term that is dependent on the ADC output code and adynamic term that has an additional dependence on the input signalfrequency. The INL model is subtracted from thedigital output for post-correction. The static compensationis implemented with a look-up-table (LUT). The dynamic calibration isperformed by a bank of frequency domain filters using an overlap-add structure.Two ADCs of the same type (Analog Devices AD9430) are compensated in the first three Nyquist bands.The performance improvements in terms of spurious-free dynamic range(SFDR) and intermodulation distortion (IMD) are investigated. Using the proposed method, improvements up to 17 dB are reported in favorable scenarios.
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| 7. |
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| 8. |
- Medawar, Samer, et al.
(författare)
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Dynamic Characterization of Analog-Digital-Converters Non-Linearities
- 2007
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Ingår i: <em>Proceedings Mosharaka International Conference on Wireless Communications and Mobile Computing</em>.
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Konferensbidrag (refereegranskat)abstract
- A characterization of a state of the art pipeline ADC is presented. Measurements are performed on a wide set of frequencies. The integral non linearity (INL) is modeled by high code and low code components, HCF and LCF. The HCF component is to be deprived of any dynamic behavior, and varies piecewise linearly in certain intervals. Hence, the LCF represents the dynamic behavior that should varies the frequency of the test signal. Employement of the method presented in [1] on measured data is performed and complemented with modifications stimulated by the behavior of measured data.
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| 9. |
- Medawar, Samer, et al.
(författare)
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Input-Dependent Integral Nonlinearity Modeling for Pipelined Analog-Digital Converters
- 2010
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - : IEEE. - 0018-9456 .- 1557-9662. ; 59:10, s. 2609-2620
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Tidskriftsartikel (refereegranskat)abstract
- Integral nonlinearity (INL) for pipelined analog-digital converters (ADCs) operating at RF is measured and characterized. A parametric model for the INL of pipelined ADCs is proposed, and the corresponding least-squares problem is formulated and solved. The INL is modeled both with respect to the converter output code and the frequency stimuli, which is dynamic modeling. The INL model contains a static and a dynamic part. The former comprises two 1-D terms in ADC code that are a sequence of zero-centered linear segments and a polynomial term. The 2-D dynamic part consists of a set of polynomials whose parameters are dependent on the ADC input stimuli. The INL modeling methodology is applied to simulated and experimental data from a 12-bit commercial ADC running at 210 mega samples per second. It is demonstrated that the developed methodology is an efficient way to capture the INL of nowadays ADCs running at RF, and it is believed that the methodology is powerful for INL-based ADC postcorrection in wideband applications.
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| 10. |
- Medawar, Samer, et al.
(författare)
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Model order determination and segmentation of analog-digital converters integral non linearity
- 2010
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Ingår i: 2010 IEEE International Instrumentation and Measurement Technology Conference, I2MTC 2010. - IEEE, 345 E 47TH ST, NEW YORK, NY 10017 USA : IEEE. - 9781424428328 ; , s. 36-41, s. 36-41
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Konferensbidrag (refereegranskat)abstract
- Analog-digital converter (ADC) integral nonlinearity (INL) modeling is investigated. The model is comprised of two entities: a low code frequency (LCF) component modeled by an L-order polynomial, and a static high code frequency component (HCF), modeled by P linear disjoint segments centered around zero. Both model components are functions of the ADC output code k. A methodical way of estimating the LCF polynomial order L and the set of segments (number of and their borders), is suggested. The method computes the polynomial order L and the set of segments (number and borders) that minimizes the root mean square (RMS) distance between the INL data and its model. The method is applied to measured INL sequences of a 12-bit Analog Devices pipeline ADC (AD9430).
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