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  • Resultat 1-10 av 79
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  • Alayón Glazunov, 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 0:233λ 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.
  • Alayon Glazunov, Andres, et al. (författare)
  • Impact of Scattering Within a Multipath Simulator Antenna Array on the Ricean Fading Distribution Parameters in OTA Testing
  • 2014
  • Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 62:6, s. 3257-3269
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we investigate the unwanted scattering that exists within the multipath simulator (MPS) array antennas employed in over the air (OTA) testing of mobile terminals. The impact of scattering is evaluated in terms of the measurement uncertainty of the average received power and the Ricean K-factor. The maximum ratio combining diversity is investigated for a generic device under test comprising two half-wavelength dipole antennas. We provide closed-form expressions for the uncertainties of the average received power and the Ricean K-factor for a uniform circular array of MPS antennas and a 2-D uniformly distributed angle-of-arrival spectrum. We also derive the maximum number of MPS antennas and the minimum ring radius of the MPS system as a function of the separation between the most distant antenna elements if the device under test employs a uniform linear array. As a result, we provide design guidelines for MPS array in terms of the number antennas, the radius of the MPS array and the wavelength of the carrier frequency.
  • Alizadeh Khameneh, Mohammad Amin, et al. (författare)
  • A new Block-Structure Modeling Technique for RF Power Amplifiers in a 2x2 MIMO System
  • 2017
  • Ingår i: 13th International Conference on Advanced Technologies, Systems and Services in Telecommunications (TELSIKS). - IEEE. - 978-1-5386-1800-4 ; s. 224-227
  • Konferensbidrag (refereegranskat)abstract
    • A new block-structure behavioral model is proposed for radio frequency power amplifiers in a 2x2 multiple-input multiple-output system including input cross-talk. The proposed model forms kernels of blocks of different nonlinear order that correspond to the significant frequency response of measured frequency domain Volterra kernels. The model can therefore well describe the input-output relationships of the nonlinear dynamic behavior of PAs. The proposed model outperforms conventional models in terms of model errors.
  • Amin, Shoaib, et al. (författare)
  • 2D Extended envelope memory polynomial model for concurrent dual-band RF transmitters
  • 2017
  • Ingår i: International journal of microwave and wireless technologies. - 1759-0795. ; 9:8, s. 1619-1627
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper presents a 2D extended envelope memory polynomial (2D-EEMP) model for concurrent dual-band radio frequency (RF) power amplifiers (PAs). The model is derived based on the physical knowledge of a dual-band RF PA. The derived model contains cross-modulation terms not included in previously published models; these terms are found to be of importance for both behavioral modeling and digital pre-distortion (DPD). The performance of the derived model is evaluated both as the behavioral model and DPD, and the performance is compared with state-of-the-art2D-DPD and dual-band generalized memory polynomial (DB-GMP) models. Experimental result shows that the proposed model resulted in normalized mean square error (NMSE) of -51.7/-51.6dB and adjacent channel error power ratio (ACEPR) of -63.1/-63.4 dB, for channel 1/2, whereas the 2D-DPD resulted in the largest model error and DB-GMP resulted in model parameters that are 3 times more than those resulted with the proposed model with the same performance. As pre-distorter, the proposed model resulted in adjacent channel power ratio (ACPR) of -55.8/ -54.6 dB for channel 1/2 and is 7-10 dB lower than those resulted with the 2D-DPD model and2-4 dB lower compared to the DB-GMP model.
  • Amin, Shoaib, 1985-, 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$,times,$ 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 $,times,$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 ${-}{hbox{30}}$ 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, 1985-, et al. (författare)
  • Characterization and modeling of RF amplifiers with multiple input signals
  • 2016
  • Konferensbidrag (refereegranskat)abstract
    • A characterization technique for RF PAs excited with multiple signals is presented. The technique can be used for characterization of memory effects in IM/CM products. The extracted information can in return be of use for modifying behavioral models to better capture memory in IM/CM products.
  • 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 Press. - 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)
  • Concurrent dual-band power amplifier model modification using dual two-tone test
  • 2016
  • Ingår i: 46th Europena Microwave Conference (EUMC) 2016. - 978-2-87487-043-9 - 978-1-5090-1514-6 ; s. 186-189
  • Konferensbidrag (refereegranskat)abstract
    • A dual two-tone technique for the characterization of memory effects in concurrent dual-band transmitters is revisited to modify a 2D-DPD model for the linearization of concurrent dual-band transmitters. By taking into account the individual nonlinear memory effects of the self- and cross-kernels, a new2D modified digital pre-distortion (2D-MDPD) model is proposed,which not only supersedes the linearization performance but also reduces the computational complexity compared to the 2DDPDmodel in terms of a number of floating point operations(FLOPs). Experimental results show an improvement of 1.7 dBin normalized mean square error (NMSE) and a 58% reduction in the number of FLOPs.
  • Amin, Shoaib, et al. (författare)
  • Digital Predistortion of Single and Concurrent Dual BandRadio Frequency GaN Amplifiers with Strong NonlinearMemory Effects
  • 2017
  • Ingår i: IEEE transactions on microwave theory and techniques. - IEEE Press. - 0018-9480. ; 65:7, s. 2453-2464
  • Tidskriftsartikel (refereegranskat)abstract
    • Electrical anomalies due to trapping effects in gallium nitride (GaN) power amplifiers (PAs) give rise to long-term or strong memory effects. We propose novel models based on infinite impulse response fixed pole expansion techniques for the behavioral modeling and digital predistortion of single-input single-output (SISO) and concurrent dual-band GaN PAs. Experimental results show that the proposed models outperform the corresponding finite impulse response (FIR) models by up to 17 dB for the same number of model parameters. For the linearization of a SISO GaN PA, the proposed models give adjacent channel power ratios (ACPRs) that are 7-17 dB lower than the FIR models. For the concurrent dual-band case, the proposed models give ACPRs that are 9-14 dB lower than the FIR models.
  • 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.
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