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  • Resultat 1-10 av 67
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  • Alayon Glasunov, Andrés, et al. (författare)
  • Experimental characterization of the propagation channel along a very large virtual array in a reverberation chamber
  • 2014
  • Ingår i: Progress in Electromagnetics Research B. - 1937-6472. ; :59, s. 205-217
  • Tidskriftsartikel (refereegranskat)abstract
    • We show that the combined use of radio frequency absorbers and directive antennas can produce significant changes of the radio propagation channel properties along the positions of a virtual array inside a reverberation chamber. A multidimensional characterization of the channel was performed at 40 antenna positions with spacing of 0:233? at 1 GHz. The average power, the Ricean K-factor, the coherence bandwidth, the r.m.s. delay spread, the mean delay, the beamforming power angle spectrum and array antenna correlation have been studied for different arrangements in the reverberation chamber. The analysis shows that the joint average over time and frequency channel behavior is, as expected, rather homogeneous along the very large array. However, individual realizations of the channel present a pronounced selective behavior in space, time and frequency with parameters varying along the positions of the virtual array suggesting that a heterogeneous behavior of the radio channels can be emulated in reverberation chambers. An important application of the presented study comprises testing of antenna array designs and algorithms in multipath environments. Further development may lead to Over The Air testing of Multiple Input Multiple Output antenna systems of various sizes, i.e., from small to very large arrays.
  • Amin, Shoaib, et al. (författare)
  • Behavioral Modeling and Linearization of Crosstalk and Memory Effects in RF MIMO Transmitters
  • 2014
  • Ingår i: Ieee Transactions on Microwave Theory and Techniques. - 0018-9480. ; 62:4, s. 810-823
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper proposes three novel models for behavioral modeling and digital pre-distortion (DPD) of nonlinear 2 x 2 multiple-input multiple-output (MIMO) transmitters in the presence of crosstalk. The proposed models are extensions of the single-input single-output generalized memory polynomial model. Three types of crosstalk effects were studied and characterized as linear, nonlinear, and nonlinear & linear crosstalk. A comparative study was performed with previously published models for the linearization of crosstalk in a nonlinear 2 x 2 MIMO transmitter. The experiments indicate that, depending on the type of crosstalk, the selection of the correct model in the transmitter is necessary for behavioral modeling and sufficient DPD performance. The effects of coherent and partially noncoherent signal generation on the performance of DPD were also studied. For crosstalk levels of 30 dB, the difference in the normalized mean square error and adjacent channel power ratio was found to be 3-4 dB between coherent and partially noncoherent signal generation.
  • Amin, Shoaib, et al. (författare)
  • Characterization of concurrent dual-band power amplifiers using a dual two-tone excitation signal
  • 2015
  • Ingår i: IEEE Transactions on Instrumentation and Measurement. - IEEE. - 0018-9456. ; 64:10, s. 2781-2791
  • Tidskriftsartikel (refereegranskat)abstract
    • A method to characterize the memory effects in a nonlinear concurrent dual-band transmitter is presented. It is an extension of the conventional two tone test for power amplifiers to concurrent dual band transmitters. The output signal of a concurrent dual-band transmitter is affected not only by intermodulation products but also by cross-modulation products. In one frequency band, the transmitter is excited by a two tone signal which frequency separation is swept. In the second band the transmitter is concurrently excited by an other two tone signal with slightly wider frequency separation. The frequency difference of the two signals is fixed during the frequency sweep. The two tone test is made at different power levels. The upper and lower third-order inter- and cross-modulation products are measured. The asymmetry between the upper and lower third-order inter- and cross-modulation products are measures of the transmitter's memory effects. The measurement results show that the memory effects are more dominant in the third-order intermodulation products than in the cross modulation products. An error analysis and system calibration was performed and measurement results for two different devices are presented.
  • Amin, Shoaib, 1985-, et al. (författare)
  • Noise Impact on the Identification of DigitalPredistorter Parameters in the Indirect LearningArchitecture
  • 2012
  • Ingår i: 2012 Swedish Communication Technologies Workshop (Swe-CTW). - IEEE conference proceedings. - 978-1-4673-4763-1 ; s. 36-39
  • Konferensbidrag (refereegranskat)abstract
    • The indirect learning architecture (ILA) is the mostused methodology for the identification of Digital Pre-distorter(DPD) functions for nonlinear systems, particularly for highpower amplifiers. The ILA principle works in black box modelingrelying on the inversion of input and output signals of thenonlinear system, such that the inverse is estimated. This paperpresents the impact of disturbances, such as noise in the DPDidentification. Experiments were performed with a state-of-artDoherty power amplifier intended for base station operationin current telecommunication wireless networks. As expected,a degradation in the performance of the DPD (measured innormalized mean square error (NMSE)) is found in our experiments.However, adjacent channel power ratio (ACPR) canbe a misleading figure of merit showing improvement in theperformance for wrongly estimated DPD functions.
  • Bjorsell, Niclas, et al. (författare)
  • Measuring Volterra kernels of analog to digital converters using a stepped three-tone scan
  • 2006
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Volterra theory can be used to mathematically model nonlinear dynamic components such as analog-to-digital converter (ADC). This paper describes how frequency domain Volterra kernels of an ADC are determined from measurements. The elements of Volterra theory are given and practical issues are considered, such as methods for signal conditioning, finding the appropriate test signals scenario and suitable sampling frequency. The results show that for the used pipeline ADC, the frequency dependence is significantly stronger for second order difference products than for sum products and the linear frequency dependence was not as pronounced as that of the second order Volterra kernel.
  • Bjorsell, Niclas, et al. (författare)
  • Post-correction of under-sampled analog to digital converters
  • 2007
  • Ingår i: 2007 IEEE INSTRUMENTATION & MEASUREMENT TECHNOLOGY CONFERENCE. - 978-1-4244-0588-6 ; s. 58-62
  • Konferensbidrag (refereegranskat)abstract
    • Applications with wide bandwidth and high center frequencies force the analog to digital converter (ADC) to be active in a working range with less dynamic performance in relation to lower frequency bands. However using under-sampling techniques in combination with post-correction methods enable a combination of high sampling rate, wide bandwidth and low distortion. In this paper the employed dynamic post-correction is a combination of look-up tables and model based correction. The results are mainly based on measurements on a 12-bit 210 MSPS ADC. The improvement in total harmonic distortion and spurious free dynamic range are acceptable over a wide frequency range and it is robust to variations in amplitude.
  • Björsell, Niclas, et al. (författare)
  • A Statistical Evaluation of ADC Histogram Tests with Arbitrary Stimuli Signal
  • 2005
  • Ingår i: ADDA 2005. ; s. 259-264
  • Konferensbidrag (refereegranskat)abstract
    • Histogram tests are a commonly used method for characterizing analogue to digital converters. However, different stimuli signals can be used in the histogram test. An overview of common input stimuli for the test is presented. Previous works have analysed the statistical properties of the resulting histograms for different stimuli signals, separately. In this paper, generally applicable results for asymptotically unbiased minimum variance estimator and Cramer-Rao lower bound are derived, irrespective of used input stimuli. Where available, the general expression is compared and found in accordance with signal-specific expressions.
  • Björsell, Niclas, et al. (författare)
  • Achievable ADC Performance by Post-Correction Utilizing Dynamic Modeling of the Integral Nonlinearity
  • 2008
  • Ingår i: EURASIP Journal on Advances in Signal Processing. - 1110-8657. ; s. 497187-1-497187-10
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a need for a universal dynamic model of analog-to-digital converters (ADC’s) aimed for postcorrection. However, it is complicated to fully describe the properties of an ADC by a single model. An alternative is to split up the ADC model in different components, where each component has unique properties. In this paper, a model based on three components is used, and a performance analysis for each component is presented. Each component can be postcorrected individually and by the method that best suits the application. The purpose of postcorrection of an ADC is to improve the performance. Hence, for each component, expressions for the potential improvement have been developed. The measures of performance are total harmonic distortion (THD) and signal to noise and distortion (SINAD), and to some extent spurious-free dynamic range (SFDR).
  • Björsell, Niclas, et al. (författare)
  • Analog-to-Digital Converters for High-Speed Applications
  • 2005
  • Ingår i: GigaHz 2005. ; s. 151-154
  • Konferensbidrag (refereegranskat)abstract
    • There is a rapid development of the performance of state-of-the-art analog to digital converters (ADC). Resolution and sampling rate are increasing continuously. Sampling rates in the high intermediate frequency (IF) range with sufficient dynamic range for communication applications were introduced about the turn of the millennium. Post-correction methods enable fast ADCs with modest linearity, and thereby weak dynamic performance, for high-speed applications.A post-correction procedure involves a characterization of the ADC non-linearity and then utilizing this information by processing the ADC output samples to remove the distortion. ADC characterization is usually performed by estimating ADC characteristics from measurements. Consequently, successful characterizations require both developed test methods and high performance test-beds.Characterization and testing ADCs are interesting in many different aspects. Not only that a proper characterization can be used for error compensation, testing is a major factor of cost for manufacturers, and shortening of the test cycle implies large savings. Testing ADCs is complicated, time consuming and demands high-performance instrumentation.
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