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1.
  • Chen, Jingjing, 1982, et al. (author)
  • Does LO Noise Floor Limit Performance in Multi-Gigabit Millimeter-Wave Communication?
  • 2017
  • In: IEEE Microwave and Wireless Components Letters. - 1558-1764 .- 1531-1309. ; 27:8, s. 769-771
  • Journal article (peer-reviewed)abstract
    • Extremely high data rate communication can potentially be achieved by combining high-order modulations and wide bandwidths at millimeter-wave (mm-wave) frequencies. However, it has been challenging to practically implement this combination, even if the SNR of the system appears to be sufficiently high. An explanation from a recent theoretical study is that the practical data rates in mm-wave systems are limited by the local oscillator (LO) white phase noise. In this letter, we present an experimental investigation on whether the white noise floor of frequency multiplied LO sources is a major noise contribution to wideband signals. Hardware measurements are performed using multi-gigabit 64 quadrature amplitude modulation (QAM) signals. The measured results show that the transmitter performance degrades as the LO noise floor increases. Hence, the LO noise floor is identified to be one primary limitation for achieving the highest possible data rate in wideband mm-wave systems.
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2.
  • Chen, Jingjing, 1982, et al. (author)
  • Influence of White LO Noise on Wideband Communication
  • 2018
  • In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 66:7, s. 3349-3359
  • Journal article (peer-reviewed)abstract
    • Applying a spectrally efficient modulation to a wideband signal provides an extremely high data rate potential in millimeter-wave communication. In reality, wideband systems, as reported in open literature, typically suffer from insufficient signal-to-noise ratio (SNR) and thus are not able to support high-order modulation. In a recent experimental study, we have identified that a high noise floor from frequency-multiplied local oscillator (LO) sources is a major data rate limitation in wideband systems. In this paper, we present a detailed study with a mathematical model to describe the influence of the LO noise on a communication signal through frequency conversion. Followed by experimental investigations using multigigabit 64-quadrature amplitude modulation signals, measurements are performed at frequency up- and down-conversions. Both cases show SNR degradation on the frequency-converted signals as the corresponding LO noise floor increases. We provide experimental proof that the nature of the LO noise floor is white, with nearly the same amount of phase and amplitude noises. Various ways to reduce the white LO noise floor through the new hardware design are discussed providing design requirements and considerations.
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3.
  • Erlinge, D., et al. (author)
  • Bivalirudin versus Heparin Monotherapy in Myocardial Infarction
  • 2017
  • In: New England Journal of Medicine. - : Massachusetts Medical Society. - 0028-4793 .- 1533-4406. ; 377:12, s. 1132-1142
  • Journal article (peer-reviewed)abstract
    • Background The comparative efficacy of various anticoagulation strategies has not been clearly established in patients with acute myocardial infarction who are undergoing percutaneous coronary intervention (PCI) according to current practice, which includes the use of radial-artery access for PCI and administration of potent P2Y12 inhibitors without the planned use of glycoprotein IIb/IIIa inhibitors. Methods In this multicenter, randomized, registry-based, open-label clinical trial, we enrolled patients with either ST-segment elevation myocardial infarction (STEMI) or non-STEMI (NSTEMI) who were undergoing PCI and receiving treatment with a potent P2Y12 inhibitor (ticagrelor, prasugrel, or cangrelor) without the planned use of glycoprotein IIb/IIIa inhibitors. The patients were randomly assigned to receive bivalirudin or heparin during PCI, which was performed predominantly with the use of radial-artery access. The primary end point was a composite of death from any cause, myocardial infarction, or major bleeding during 180 days of follow-up. Results A total of 6006 patients (3005 with STEMI and 3001 with NSTEMI) were enrolled in the trial. At 180 days, a primary end-point event had occurred in 12.3% of the patients (369 of 3004) in the bivalirudin group and in 12.8% (383 of 3002) in the heparin group (hazard ratio, 0.96; 95% confidence interval [CI], 0.83 to 1.10; P=0.54). The results were consistent between patients with STEMI and those with NSTEMI and across other major subgroups. Myocardial infarction occurred in 2.0% of the patients in the bivalirudin group and in 2.4% in the heparin group (hazard ratio, 0.84; 95% CI, 0.60 to 1.19; P=0.33), major bleeding in 8.6% and 8.6%, respectively (hazard ratio, 1.00; 95% CI, 0.84 to 1.19; P=0.98), definite stent thrombosis in 0.4% and 0.7%, respectively (hazard ratio, 0.54; 95% CI, 0.27 to 1.10; P=0.09), and death in 2.9% and 2.8%, respectively (hazard ratio, 1.05; 95% CI, 0.78 to 1.41; P=0.76). Conclusions Among patients undergoing PCI for myocardial infarction, the rate of the composite of death from any cause, myocardial infarction, or major bleeding was not lower among those who received bivalirudin than among those who received heparin monotherapy. (Funded by the Swedish Heart-Lung Foundation and others; VALIDATE-SWEDEHEART ClinicalTrialsRegister.eu number, 2012-005260-10 ; ClinicalTrials.gov number, NCT02311231 .).
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5.
  • Farjana, Sadia, 1983, et al. (author)
  • Realizing a 140 GHz Gap Waveguide–Based Array Antenna by Low-Cost Injection Molding and Micromachining
  • 2021
  • In: Journal of Infrared, Millimeter and Terahertz Waves. - : Springer. - 1866-6892 .- 1866-6906. ; 42:8, s. 893-914
  • Journal article (peer-reviewed)abstract
    • This paper presents a novel micromachining process to fabricate a 140 GHz planar antenna based on gap waveguide technology to be used in the next-generation backhauling links. The 140 GHz planar array antenna consists of three layers, all of which have been fabricated using polymer-based microfabrication and injection molding. The 140 GHz antenna has the potential to be used as an element in a bigger 3D array in a line-of-sight (LOS) multiple input multiple output (MIMO) configuration to boost the network capacity. In this work, we focus on the fabrication of a single antenna array element based on gap waveguide technology. Depending on the complexity of each antenna layer’s design, three different micromachining techniques, SU8 fabrication, polydimethylsiloxane (PDMS) molding, and injection molding of the polymer (OSTEMER), together with gold (Au) coating, have been utilized to fabricate a single 140 GHz planar array antenna. The input reflection coefficient was measured to be below − 11 dB over a 14% bandwidth from 132 to 152 GHz, and the antenna gain was measured to be 31 dBi at 140 GHz, both of which are in good agreement with the simulations. © 2021, The Author(s).
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7.
  • Meyer, E., et al. (author)
  • The state of the art in beyond 5G distributed massive multiple-input multiple-output communication system solutions
  • 2022
  • In: Open Research Europe. - : F1000 Research Ltd. - 2732-5121. ; 2
  • Research review (peer-reviewed)abstract
    • Beyond fifth generation (5G) communication systems aim towards data rates in the tera bits per second range, with improved and flexible coverage options, introducing many new technological challenges in the fields of network architecture, signal pro- cessing, and radio frequency front-ends. One option is to move towards cell-free, or distributed massive Multiple-Input Multiple-Output (MIMO) network architectures and highly integrated front-end solutions. This paper presents an outlook on be- yond 5G distributed massive MIMO communication systems, the signal processing, characterisation and simulation challenges, and an overview of the state of the art in millimetre wave antennas and electronics.
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8.
  • Naylor, Andrew Stuart, 1977, et al. (author)
  • Voluntary running rescues adult hippocampal neurogenesis after irradiation of the young mouse brain.
  • 2008
  • In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 1091-6490. ; 105:38, s. 14632-7
  • Journal article (peer-reviewed)abstract
    • Cranial radiation therapy is commonly used in the treatment of childhood cancers. It is associated with cognitive impairments tentatively linked to the hippocampus, a neurogenic region of the brain important in memory function and learning. Hippocampal neurogenesis is positively regulated by voluntary exercise, which is also known to improve hippocampal-dependent cognitive functions. In this work, we irradiated the brains of C57/BL6 mice on postnatal day 9 and evaluated both the acute effects of irradiation and the effects of voluntary running on hippocampal neurogenesis and behavior 3 months after irradiation. Voluntary running significantly restored precursor cell and neurogenesis levels after a clinically relevant, moderate dose of irradiation. We also found that irradiation perturbed the structural integration of immature neurons in the hippocampus and that this was reversed by voluntary exercise. Furthermore, irradiation-induced behavior alterations observed in the open-field test were ameliorated. Together, these results clearly demonstrate the usefulness of physical exercise for functional and structural recovery from radiation-induced injury to the juvenile brain, and they suggest that exercise should be evaluated in rehabilitation therapy of childhood cancer survivors.
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9.
  • Patel, Riyaz S., et al. (author)
  • Subsequent Event Risk in Individuals With Established Coronary Heart Disease : Design and Rationale of the GENIUS-CHD Consortium
  • 2019
  • In: Circulation. - 2574-8300. ; 12:4
  • Journal article (peer-reviewed)abstract
    • BACKGROUND: The Genetics of Subsequent Coronary Heart Disease (GENIUS-CHD) consortium was established to facilitate discovery and validation of genetic variants and biomarkers for risk of subsequent CHD events, in individuals with established CHD.METHODS: The consortium currently includes 57 studies from 18 countries, recruiting 185 614 participants with either acute coronary syndrome, stable CHD, or a mixture of both at baseline. All studies collected biological samples and followed-up study participants prospectively for subsequent events.RESULTS: Enrollment into the individual studies took place between 1985 to present day with a duration of follow-up ranging from 9 months to 15 years. Within each study, participants with CHD are predominantly of self-reported European descent (38%-100%), mostly male (44%-91%) with mean ages at recruitment ranging from 40 to 75 years. Initial feasibility analyses, using a federated analysis approach, yielded expected associations between age (hazard ratio, 1.15; 95% CI, 1.14-1.16) per 5-year increase, male sex (hazard ratio, 1.17; 95% CI, 1.13-1.21) and smoking (hazard ratio, 1.43; 95% CI, 1.35-1.51) with risk of subsequent CHD death or myocardial infarction and differing associations with other individual and composite cardiovascular endpoints.CONCLUSIONS: GENIUS-CHD is a global collaboration seeking to elucidate genetic and nongenetic determinants of subsequent event risk in individuals with established CHD, to improve residual risk prediction and identify novel drug targets for secondary prevention. Initial analyses demonstrate the feasibility and reliability of a federated analysis approach. The consortium now plans to initiate and test novel hypotheses as well as supporting replication and validation analyses for other investigators.
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10.
  • Svensson, Nina, 1988-, et al. (author)
  • Ride the future – strategisk satsning : fem studier med fokus på autonoma bussar i städer
  • 2022
  • Reports (other academic/artistic)abstract
    • Fem noga utvalda förstudier har initierats av VTI som en del i den strategiska satsningen ”Ride the future” kopplad till framtidens mobilitetslösningar. Förstudiernas titel är följande: ▪ Databearbetning och visualisering av mobila luftkvalitetsmätningar. ▪ SUMO och Unreal Engine för co-simulering. ▪ Exploring spatio-temporal accessibility in Lambohov: a pre-study. ▪ Vägytans betydelse för vibrationer och komfort i långsamma fordon. ▪ Infrastrukturbehov vid busshållplatser. Föreliggande pm innehåller en kort beskrivning av studierna och den mer utförliga redovisningen återfinns i bilagan.
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12.
  • Zhu, Changlian, 1964, et al. (author)
  • X chromosome-linked inhibitor of apoptosis protein reduces oxidative stress after cerebral irradiation or hypoxia-ischemia through up-regulation of mitochondrial antioxidants.
  • 2007
  • In: The European journal of neuroscience. - : Wiley. - 1460-9568 .- 0953-816X. ; 26:12, s. 3402-10
  • Journal article (peer-reviewed)abstract
    • We demonstrate that X chromosome-linked inhibitor of apoptosis protein (XIAP) counteracts oxidative stress in two essentially different disease-related models of brain injury, hypoxia-ischemia and irradiation, as judged by lower expression of nitrotyrosine (5-fold) and 4-hydroxy-2-nonenal (10-fold) in XIAP-overexpressing compared with wild-type mice. XIAP overexpression induced up-regulation of at least three antioxidants residing in mitochondria, superoxide dismutase 2, thioredoxin 2 and lysine oxoglutarate reductase. Cytochrome c release from mitochondria was reduced in XIAP-overexpressing mice. Hence, in addition to blocking caspases, XIAP can regulate reactive oxygen species in the brain, at least partly through up-regulation of mitochondrial antioxidants. XIAP-induced prevention of oxidative stress was not secondary to tissue protection because although XIAP overexpression provides tissue protection after hypoxia-ischemia, it does not prevent tissue loss after irradiation. This is a previously unknown role of XIAP and may provide the basis for development of novel protective strategies for both acute and chronic neurodegenerative diseases, where oxidative stress is an integral component of the injury mechanisms involved.
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13.
  • Afsar Doost, Sepideh, 1983, et al. (author)
  • Digital Predistortion Using a Vector Switched Model
  • 2012
  • In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 60:4, s. 1166-1174
  • Journal article (peer-reviewed)abstract
    • Abstract—A switched behavioral model considering memory effects with special focus on ”difficult” amplifier architectures is proposed in this paper. The proposed model is shown to be very simple and linearly identifiable. A digital predistorter based on the proposed model is implemented for a 100–W, 2.6 GHz Doherty power amplifier that has been considered difficult in other reports, and it is shown that the proposed model can succesfully linearize the amplifier. In particular, the proposed model and the digital predistorter is shown to outperform other state-of-the-art models and digital predistorers in terms of computational complexity for a given desired accuracy.
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14.
  • Agrell, Erik, 1965, et al. (author)
  • Closest point search in lattices
  • 2002
  • In: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 48:8, s. 2201-2214
  • Journal article (peer-reviewed)abstract
    • In this semitutorial paper, a comprehensive survey of closest point search methods for lattices without a regular structure is presented. The existing search strategies are described in a unified framework, and differences between them are elucidated. An efficient closest point search algorithm, based on the Schnorr-Euchner variation of the Pohst method, is implemented. Given an arbitrary point x is an element of R-m and a generator matrix for a lattice A, the algorithm computes the point of A that is closest to x. The algorithm is shown to be substantially faster than other known methods, by means of a theoretical comparison with the Kannan algorithm and an experimental comparison with the Pohst algorithm and its variants, such as the recent Viterbo-Boutros decoder. Modifications of the algorithm are developed to solve a number of related search problems for lattices, such as finding a shortest vector, determining the kissing number, computing the Voronoi-relevant vectors, and finding. a Korkine-Zolotareff reduced basis.
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17.
  • Agrell, Erik, 1965, et al. (author)
  • Optimization of lattices for quantization
  • 1998
  • In: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 44:5, s. 1814-1828
  • Journal article (peer-reviewed)abstract
    • A training algorithm for the design of lattices for vector quantization is presented. The algorithm uses a steepest descent method to adjust a generator matrix, in the search for a lattice whose Voronoi regions have minimal normalized second moment. The numerical elements of the found generator matrices are interpreted and translated into exact values. Experiments show that the algorithm is stable, in the sense that several independent runs reach equivalent lattices. The obtained lattices reach as low second moments as the best previously reported lattices, or even lower. Specifically, we report lattices in nine and ten dimensions with normalized second moments of 0.0716 and 0.0708, respectively, and nonlattice tessellations in seven and nine dimensions with 0.0727 and 0.0711, which improves on previously known values. The new nine- and ten-dimensional lattices suggest that Conway and Sloane's (1993) conjecture on the duality between the optimal lattices for packing and quantization might be false. A discussion of the application of lattices in vector quantizer design for various sources, uniform and nonuniform, is included.
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18.
  • Amani, Navid, 1985, et al. (author)
  • Array Configuration Effect on the Spatial Correlation of MU-MIMO Channels in NLoS Environments
  • 2020
  • In: 14th European Conference on Antennas and Propagation, EuCAP 2020. ; 2020:March
  • Conference paper (peer-reviewed)abstract
    • In this paper, three different base-station antenna (BSA) configurations are compared in terms of inter-user spatial correlation in a two dimensional (2D) non-line-of-sight (NLoS) environment. The three configurations are: (i) a regular uniform linear array (ULA); (ii) a periodic sparse array; and (iii) an aperiodic sparse array. Electromagnetic modeling of the NLoS channel is proposed where scatterers are considered as resonant dipoles confined in clusters of scatterers (CoSs). While the probability of facing highly correlated user-equipments (UEs) in a multi-user multiple-input multiple-output (MU-MIMO) system is decreasing as the richness of mutipath increases, the sparsity (increased inter-element spacing) is seen to be capable of reducing this probability as well. This is due to the larger spatial variations experienced by the sparse array. Moreover, the results show that further improvement can be achieved by deploying an aperiodic distribution of antenna elements into the sparse antenna aperture.
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19.
  • Amani, Navid, 1985, et al. (author)
  • Sparse Array Synthesis Including Mutual Coupling for MU-MIMO Average Capacity Maximization
  • 2022
  • In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 70:8, s. 6617-6626
  • Journal article (peer-reviewed)abstract
    • A hybrid optimization algorithm including mutual coupling (MC) is proposed to synthesize an irregular sparse array (ISA) for average capacity maximization in a multi-user multiple-input multiple-output (MU-MIMO) system. The hybrid approach is composed of two phases to sub-optimally determine the location of a fixed number of omni-directional thin dipole antennas in an arbitrary sparse aperture via a diagonal antenna selection matrix. In Phase I, the problem is relaxed to a convex optimization by ignoring the MC and weakening the constraints. The output of Phase I is accounted as a reliable initial guess for the genetic algorithm (GA) in Phase II, which incorporates the MC effects through the coupling matrix and avoids the convex relaxation technique. The proposed approach outperforms the conventional GA with a random initial population, while it avoids trying several starting positions. Meanwhile, the undesirable appearance of grating lobes, due to the under-sampling, and the degrading MC effects are suppressed by aperiodicity. It is observed that, doubling the conventional inter-element spacing (half-wavelength) and finding the location of eight dipoles in a sparse aperture by the proposed method improves the average capacity by 3.27-11.9% when the number of users varies from two to eight and the signal-to-noise ratio (SNR) is 30dB.
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20.
  • Banar, Jafar, 1991, et al. (author)
  • Effect of Phase-Noise on the Distributed Massive MIMO Networks
  • 2022
  • In: 2022 52nd European Microwave Conference, EuMC 2022. ; , s. 700-703
  • Conference paper (peer-reviewed)abstract
    • We study the effect of phase noise on the achievable spectral efficiency (SE) of a distributed massive multi-input multiple-output (DM-MIMO) network. We obtain a closed-form expression for this network considering the phase noise, independent Rayleigh fading channel, and minimum mean square error (MMSE) channel estimation. In this network, Access points (APs) under the time-division duplex (TDD) operation estimate the channels via the uplink training phase and transmit the downlink data. The equations and simulation results present the effect of phase noise introduced by oscillators in APs. Results show the impact of phase noise at APs on the achievable SE. Consequently, we observe that in the DM-MIMO network, with increasing the number of UEs, PN causes some degradation in the SE. On the other hand, with increasing the variance of the PN, the SE decreases. Through simulations, we verify our analytical results and closed-form equations.
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21.
  • Bao, Husileng, 1991, et al. (author)
  • Automatic Distributed MIMO Testbed for beyond 5G Communication Experiments
  • 2021
  • In: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. ; 2021-June, s. 697-700
  • Conference paper (peer-reviewed)abstract
    • This paper demonstrates an automated testbed suitable for beyond-5G distributed MIMO experiments, where bandwidth, number of transmitters and precoding methods are flexible and configured through a central unit. This is based on an all-digital radio-over-fiber approach to communication through 12 fully coherent, low-complexity remote radio transmitters. An automated robot receiver is implemented to facilitate efficient communication data collection in realistic environments. Using the proposed system, co-located and distributed MIMO communication antenna configurations are compared in a real in-door environment. The results show that distributed MIMO provides more significantly more uniform power distribution and better overall MIMO capacity compared to co-located MIMO.
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22.
  • Baykal, Gokce Elif, et al. (author)
  • Teaching Design of Technologies for Collaborative Interaction in Physical, Digital, and Hybrid Spaces
  • 2023
  • In: Interaction Design and Architecture(s). - 2283-2998 .- 1826-9745. ; :58, s. 53-71
  • Journal article (peer-reviewed)abstract
    • There is an increasing awareness of the importance of considering and mediating human collaboration in the design of technology. There are several research approaches focused on this, such as e.g., computer supported cooperative work (CSCW) and computer supported cooperative learning (CSCL), however, less attention has been given to developing educational materials for the role that technology play in mediating human collaboration in human -computer interaction (HCI) in physical, digital and hybrid spaces, why hands-on teaching activities are insufficient. In this paper, we present an emergent pedagogical framework on teaching for collaborative interaction in HCI, consisting of a collection of eleven pedagogical patterns. The paper is based on results from applying a modified pedagogical design pattern approach in the iterative development of an open educational resource containing teaching patterns, and from pilot testing of patterns with students. Preliminary results from pilot testing indicate that teachers experience an increased capacity to teach design of technologies that mediate human collaborative interaction in relevant and innovative ways. As part of "Design Education for Hybrid Environments" special issue, we hope this emerging pedagogical framework can provide teachers with inspiration to sensitize their students and make them better prepared to become responsible designers of technologies for collaborative interaction and contribute crafting next-generation physical, digital and hybrid spaces.
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23.
  • Behravan, Ali, 1971, et al. (author)
  • A model for bandpass nonlinearities based on Harmonic measurements
  • 2003
  • In: Proceedings of the IEEE Radio and Wireless conference, Boston, MA, USA, AUG 10-13. - 0780378296 ; , s. 409-412
  • Conference paper (peer-reviewed)abstract
    • This paper presents a model for a bandpass nonlinearity which is based on measurements on several harmonies of the output. The model has a quadrature structure, with a memoryless nonlinearity and a filter in each branch. structure can describe AM/AM as well as AM/PM conversions. The parameters of the nonlinearity and the filter are jointly optimized to fit the measurements. Analytic expressions for the parameters of the model is found by means of the MMSE optimization. The method is applied to find a model for a 60GHz solid-state power amplifier based on a set of measurements on different harmonics of the output.
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26.
  • Behravan, Ali, 1971, et al. (author)
  • Baseband compensation techniques for bandpass nonlinearities
  • 2003
  • In: Proceedings of the IEEE Vehicular technology conference fall 2003, Orlando, Florida, USA, OCT 06-09. ; , s. 279-283
  • Conference paper (peer-reviewed)abstract
    • In this paper we present and compare several methods of compensating the nonlinearity of the RF front-end of a wireless system. Two baseband compensation techniques, namely predistortion and postdistortion (equalization) of the baseband signal are discussed and the problems associated with each one is addressed. Furthermore a combination of a predistorter and a nonlinear equalizer and also predistortion of oversampled baseband signal are analyzed. It will be shown that under realistic conditions with a frequently saturated amplifier and ISI channel, the latter two methods are able to compensate the nonlinearity up to a good extent, while the first two methods can only operate under certain assumptions for channel conditions and nonlinearity type.
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28.
  • Behravan, Ali, 1971, et al. (author)
  • Harmonic-based model for bandpass nonlinearity and its application to RF predistorter design
  • 2003
  • In: Proceedings of the 15th international conference on wireless communications, Calgary, Canada.
  • Conference paper (peer-reviewed)abstract
    • Due to their large bandwidth of operation, RF predistorters are suitable for linearizing amplifier nonlinearity in high speed wireless applications. Unlike baseband linearization techniques, RF predistorters generate overtones which contribute to the first zone output of the bandpass high power amplifier. This paper presents a model for a bandpass nonlinearity that is based on measurements on several harmonics of the output. The model matches different harmonics of the output signal fairly well. The model is then used to design an RF predistorter. The advantage of the method compared to a design based on first zone of the output, is that the predistorter minimizes the total distortion power instead of reducing one specific intermodulation product.
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29.
  • Behravan, Ali, 1971, et al. (author)
  • PAPR and other measures for OFDM systems with nonlinearity
  • 2002
  • In: Proc of the 5th International Symposium on Wireless Personal Multimedia Communications, OCT 27-30, Honolulu, Hawaii. ; , s. 149-153
  • Conference paper (peer-reviewed)abstract
    • In this paper, we discuss the effects of nonlinearity on the performance in transmission of OFDM signals. Furthermore, we study measures related to nonlinearities, such as PAPR (Peak-to-Average-Power-Ratio), with respect to their ability to correctly predict the effect of a nonlinearity in an OFDM system. We also propose new measures for signal distortion in nonlinear systems. The performance of the measures are studied using several examples.
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32.
  • Behravan, Ali, 1971, et al. (author)
  • Tone reservation to reduce the envelope fluctuations of multicarrier signals
  • 2009
  • In: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 8:5, s. 2417-2423
  • Journal article (peer-reviewed)abstract
    • Abstract—In this paper we propose a method for reducing nonlinearity distortion by limiting the envelope fluctuations of an OFDM signal. The method is based on tone reservation, and the free tones are assigned in a way to limit the variations of the instantaneous power of the time domain signal. The problem is shown to be convex, and by adding an equality constraint, zero constellation error is guaranteed. We present an iterative solution for this problem, and show that the globally optimal point can be approached by only a few iterations. Both in-band and out-of-band distortions are reduced at the expense of a small increase in bandwidth of the signal. The corrected signal is less sensitive to nonlinearities, and therefore the distortion is reduced for all input backoff values.
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33.
  • Bergman, Becky, 1970, et al. (author)
  • Reflections on an Integrated Content and Language Project-Based Design of a Technical Communication Course for Electrical Engineering Students.
  • 2013
  • In: Journal of Academic Writing. - 2225-8973. ; 3:1, s. 1-14
  • Journal article (peer-reviewed)abstract
    • Effective ways of teaching technical communication skills to engineering students have been much discussed. This article reflects on one setting, a first year course in Technical Communication at a university in Sweden, where electrical engineering teachers, language and communication teachers and student counsellors work in close, team-based cooperation using a project model which requires the students to analyse, implement and communicate technical problems. The paper discusses the change in this course - from an EAP course primarily prioritizing language training which ran parallel with a project course - to one unified ICL course. The progression is described through the changes in the organization of the course, and the article focuses on one learning activity: interdisciplinary tutorials on project reports. Through a pilot study where these sessions were video recorded and mapped, we conclude that the presence of different roles became an asset for the range of what the students see as relevant for their project report. In particular, the technical report genre was critically analysed, including problematic areas such as textual sequencing and display of technical problems; data visualisation and commentary; and referencing.
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34.
  • Brihuega, Alberto, et al. (author)
  • Digital Predistortion for Multiuser Hybrid MIMO at mmWaves
  • 2020
  • In: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 68, s. 3603-3618
  • Journal article (peer-reviewed)abstract
    • Efficient mitigation of power amplifier (PA) nonlinear distortion in multi-user hybrid precoding based broadband mmWave systems is an open research problem. In this article, we carry out detailed signal and distortion modeling in broadband multi-user hybrid MIMO systems, with a bank of nonlinear PAs in each subarray, while also take the inevitable crosstalk between the antenna/PA branches into account. Building on the derived models, we adopt and describe an efficient closed-loop (CL) digital predistortion (DPD) solution that utilizes only a single-input DPD unit per transmit chain or subarray, despite crosstalk, providing thus substantial complexity-benefit compared to the state-of-the art multi-dimensional DPD solutions. We show that under spatially correlated multipath propagation, each single-input DPD unit can provide linearization towards every intended user, or more generally, towards all spatial directions where coherent propagation is taking place, and that the adopted CL DPD system is robust against crosstalk. Extensive numerical results building on practical measurement-based mmWave PA models are provided, demonstrating and verifying the excellent linearization performance of the overall DPD system in different evaluation scenarios.
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35.
  • Brihuega, Alberto, et al. (author)
  • Linearizing Active Antenna Arrays: Digital Predistortion Method and Measurements
  • 2019
  • In: 2019 IEEE MTT-S International Microwave Conference on Hardware and Systems for 5G and Beyond, IMC-5G 2019.
  • Conference paper (peer-reviewed)abstract
    • In this paper, we provide a novel framework for efficient digital predistortion (DPD) based linearization of active antenna arrays with multiple and mutually different nonlinear power amplifiers. The proposed method builds on the use of a combined feedback signal essentially characterizing the observable nonlinear distortion at the receiving end. The proposed method is validated with extensive over-the-air RF measurements on a 64-element active antenna array transmitter operating at 28 GHz carrier frequency and transmitting a 200 MHz wide 5G New Radio (NR) waveform. The obtained results demonstrate the excellent linearization capabilities of the proposed solution, which allows for a very efficient implementation in practical systems.
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36.
  • Brihuega, Alberto, et al. (author)
  • On the Power and Beam Dependency of Load Modulation in mmWave Active Antenna Arrays
  • 2020
  • In: 2020 50TH EUROPEAN MICROWAVE CONFERENCE (EUMC). - 2325-0305.
  • Conference paper (peer-reviewed)abstract
    • Linearization of active antenna arrays is gaining increasing interest due to their wide applicability in 5G New Radio (NR) networks. As direct access to the output ports of the power amplifiers (PAs) in highly integrated millimeter-wave (mmW) active arrays is difficult, different over-the-air (OTA) digital predistortion (DPD) solutions have been recently proposed. Large majority of such solutions build on the assumption that the nonlinear behaviors of the parallel PA units are independent of the beam direction. However, in this paper, we show through comprehensive OTA measurements on a commercial 64-element active array operating at 28 GHz, that the nonlinear distortion characteristics and the involved load modulation phenomenon largely depend on the beam direction as well as on the considered transmit power, and also that the beam-dependence increases with increasing transmit power. The findings of the measurements are also connected to the state-of-the-art PA models, paving the way towards the development of more efficient DPD solutions and the associated parameter learning methods for mmW active antenna array transmitters.
  •  
37.
  • Brihuega, Alberto, et al. (author)
  • Piecewise Digital Predistortion for mmWave Active Antenna Arrays: Algorithms and Measurements
  • 2020
  • In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 68:9, s. 4000-4017
  • Journal article (peer-reviewed)abstract
    • In this article, we describe a novel framework for digital predistortion (DPD)-based linearization of strongly nonlinear millimeter-wave active antenna arrays. Specifically, we formulate a piecewise (PW) closed-loop (CL) DPD solution and low-complexity gradient-adaptive parameter learning algorithms, together with a region partitioning method, which can efficiently handle deep compression of the PA units. The impact of beamsteering on the DPD performance is studied, showing strong beam-dependence, thus necessitating frequent updating of the DPD. In order to facilitate fast adaptation, an inexpensive, noniterative, pruning algorithm is introduced, which allows us to significantly reduce the number of model coefficients. The proposed methods are validated with extensive over-the-air RF measurements on a 64-element active antenna array transmitter operating at 28-GHz carrier frequency and transmitting a 400-MHz 5G new radio (NR) standard-compliant orthogonal frequency-division multiplexing waveform. The obtained results demonstrate the excellent linearization capabilities of the proposed solution, conforming to the new 5G NR requirements for frequency range 2 (FR2) in terms of both in-band waveform quality and out-of-band emissions. The proposed PW-CL DPD is shown to outperform the state-of-the-art PW DPD based on the indirect learning architecture, as well as the classical single-polynomial-based DPD solutions in terms of linearization performance and computational complexity by a clear margin.
  •  
38.
  • Buisman, Koen, 1978, et al. (author)
  • Designing and characterizing MATE, the Chalmers mm-wave MIMO testbed
  • 2018
  • In: IET Conference Publications. - : Institution of Engineering and Technology. ; 2018:CP741
  • Conference paper (peer-reviewed)abstract
    • In this paper, we report on the design and characterization of MATE, the mm-wave testbed at the Chalmers University of Technology. We elaborate around design choices of various parts of the testbed, baseband hardware, required software and RF frontend. We also perform a thorough characterization of the testbed, in terms of I/Q imbalance, stability, frequency offset, DC offsets, and ADC/DAC clock rate offset. The study shows that the utilized design techniques for baseband and RF frontend hardware are feasible, and also that many hardware imperfections are possible to accurately characterize, for subsequent calibration and digital compensation.
  •  
39.
  • Buisman, Koen, 1978, et al. (author)
  • Estimation of Obtainable Data-rates in an Over-The-Air mm-wave MIMO Testbed
  • 2024
  • In: 18th European Conference on Antennas and Propagation, EuCAP 2024.
  • Conference paper (peer-reviewed)abstract
    • In the era of 5G and the forthcoming 6G technology, the demand for advanced communication systems has surged, driving the need for innovative testbeds. These testbeds are vital for the rapid development of hardware and algorithms. Estimation of the capacity potential of mm-wave transceiver arrays is essential to maximise performance. Moreover, an efficient and effective estimation method is indispensable to ensure swift iterations during the development process. Such rapid experimentation is essential for identifying and addressing potential bottlenecks. Here we demonstrate a method based on cross correlation to estimate data-rates in a mm-wave testbed using Over-The-Air measurements only. The method is tested using the Chalmers mm-wave testbed MATE at 29.4 GHz.
  •  
40.
  • Buisman, Koen, 1978, et al. (author)
  • MIMO mmWave Over-the-air Testbed Calibration using Symmetries and Experimental Verification
  • 2022
  • In: 2022 16th European Conference on Antennas and Propagation, EuCAP 2022.
  • Conference paper (peer-reviewed)abstract
    • Calibration and validation of mm-wave transceiver arrays with respect to phase and amplitude of all elements is an essential part of production testing. Also afterwards during operation it may be necessary to update calibration coefficients. Here we present an algorithm based on channel symmetries, derive mathematically its expression, experimentally verify its results with respect to amplitude in a mm-wave testbed and compare the results to an extract model.
  •  
41.
  • Buisman, Koen, 1978, et al. (author)
  • Towards Complex Over-The-Air Calibration of a MIMO mmWave Testbed
  • 2023
  • In: 17th European Conference on Antennas and Propagation, EuCAP 2023. ; , s. 1-5
  • Conference paper (peer-reviewed)abstract
    • Calibration of mm-wave transceiver arrays with respect to phase and amplitude of signals on all its antenna elements is essential for proper operation. Moreover, during operation it may be necessary to update such calibration coefficients. Here we present an algorithm based on channel symmetries to calibrate both transmitter and receiver amplitude and phase in a mm-wave testbed using Over-The-Air measurements only. The algorithm is tested using the Chalmers mm-wave testbed MATE at 29 GHz.
  •  
42.
  • Callebaut, Gilles, et al. (author)
  • 6G Radio Testbeds: Requirements, Trends, and Approaches
  • 2024
  • In: IEEE Microwave Magazine. - 1527-3342 .- 1557-9581. ; 25:4, s. 14-31
  • Journal article (peer-reviewed)abstract
    • The proof of the pudding lies in eating, and that is why 6G testbeds are essential in the progress toward the next generation of wireless networks. Theoretical research toward 6G wireless networks proposes advanced technologies to serve new applications and drastically improve energy performance. Testbeds are indispensable to validate these new technologies under more realistic conditions. This article clarifies the requirements for 6G radio testbeds, reveals trends, and introduces approaches toward their development.
  •  
43.
  • Cao, Haiying, 1982, et al. (author)
  • Comparison of bandwidth reduction schemes in dynamic load modulation power amplifier architectures
  • 2011
  • In: IEEE Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits (INMMIC), 2011. - 9781457706509 ; , s. 1-4
  • Conference paper (peer-reviewed)abstract
    • This paper compares bandwidth reduction schemes for baseband control signals used in high efficiency power amplifier (PA) architectures, such as envelope tracking and dynamic load modulation (DLM). The baseband control signal used in such architectures usually has 3–4 times wider bandwidth than the modulated radio frequency (RF) signal. Such a wideband signal brings challenges for practical hardware design. In this paper, two bandwidth reduction schemes originally used in envelope tracking are applied on a DLM PA. The performance of both schemes are investigated by simulation. The results show that the bandwidth of the baseband control signal can be effectively reduced from 12.5 MHz to 4 MHz, while at the same time, maintaining a 49% average power-added and acceptable linearity.
  •  
44.
  • Cao, Haiying, 1982, et al. (author)
  • Compensation of Transmitter Distortion Using a Nonlinear Modeling Approach
  • 2008
  • In: International Workshop on Integrated Nonlinear Microwave and Millimetre-wave Circuits 2008. - 9781424426461 ; , s. 131-134
  • Conference paper (peer-reviewed)abstract
    • In this paper, a nonlinear modeling approach is used to demonstrate a joint compensation scheme for the linear and nonlinear distortions in the I/Q modulator and the power amplifier. Based on this nonlinear model, a digital pre-compensator is constructed. The effects of these two mostdominant nonlinear components in a modern transmitter cantherefore be digitally pre-compensated in a single step. The results are verified by experiments, and the proposed approach shows promising performance.
  •  
45.
  • Cao, Haiying, 1982, et al. (author)
  • Digital Predistortion for Dual-Input Doherty Amplifiers
  • 2012
  • In: RWW 2012 - Proceedings. 2012 IEEE Topical Conference on Power Amplifiers for Wireless and Radio Applications, PAWR 2012. Santa Clara, CA, 15-18 January 2012. - 9781457711541 ; , s. 45-48
  • Conference paper (peer-reviewed)abstract
    • This paper presents a digital predistortion techniquefor dual-input Doherty power amplifiers. The proposedtechnique utilizes both RF inputs of the main and peakamplifiers in the digital predistorter. The effectiveness ofthe resulting dual-input predistorter is evaluated on a twowayDoherty amplifier operating at 2.14 GHz with 53.5 dBmpeak output power. The experimental results demonstratethat the dual-input approach outperforms the conventionalsingle-input predistortion technique by ∼3 dB in terms ofadjacent channel leakage ratio.
  •  
46.
  • Cao, Haiying, 1982, et al. (author)
  • Digital Predistortion for High Efficiency Power Amplifier Architectures Using a Dual-input Modeling Approach
  • 2012
  • In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 60:2, s. 361-369
  • Journal article (peer-reviewed)abstract
    • In this paper, a novel model is proposed for dual-input highefficiency power amplifier (PA) architectures, such as envelope tracking (ET) and varactor-based dynamic load modulation (DLM). Compared to the traditional single-input modeling approach, the proposed model incorporates the baseband supply voltage/load control as an input. This advantage makes the new approach capable to achieve maximized average power-added efficiency (PAE) and minimizedoutput distortion simultaneously. Furthermore, the new approach has shown to be robust towards time misalignment between the RF input and baseband supply voltage/load control signals, and it can be applied with a reduced-bandwidth baseband supply voltage/load control.Experiments have been performed in a varactor-based DLM PAarchitecture to evaluate the new modeling approach. The results show that it can achieve 9 dB and 7 dB better performance than the traditional approaches in terms of adjacent channel leakage ratio and normalized mean square error, respectively. At the same time, the average PAE is maximized. Similar results have been achieved with the proposed model even when reduced-bandwidth baseband loadcontrol signal is used or time misalignment between the RF and baseband load control input signals exists. Although the new approach is only tested with DLM architecture in this paper, it is very general and can be applied to ET architectures as well.
  •  
47.
  • Cao, Haiying, 1982, et al. (author)
  • Dual-Input Nonlinear Modeling for I/Q Modulator Distortion Compensation
  • 2009
  • In: 2009 IEEE Radio and Wireless Symposium, RWS 2009; San Diego, CA; United States; 18 January 2008 through 22 January 2008. - 9781424426997 ; , s. 39-42
  • Conference paper (peer-reviewed)abstract
    • This paper focuses on modeling and compensation of both linear and nonlinear distortions in RF I/Q modulators using a dual-input Volterra series-based modeling approach. Moreover, dual-input memory polynomial and dual-input dynamic deviation reduction-based Volterra series models are proposed. The proposed models are evaluated by digital pre-compensation of a high performance I/Q modulator with a wideband input signal. The results show that the proposed dual-input models efficiently compensate for distortion in the I/Q modulator and may therefore greatly improve performance in modern communication systems.
  •  
48.
  • Cao, Haiying, 1982, et al. (author)
  • I/Q Imbalance Compensation Using a Nonlinear Modeling Approach
  • 2009
  • In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 57:3, s. 513-518
  • Journal article (peer-reviewed)abstract
    • In-phase/quadrature (I/Q) imbalance is one of the main sources of distortion in RF modulators. In this paper, a dual-input nonlinear model based on a real-valued Volterra series is proposed for compensation of the nonlinear frequency-dependent I/Q imbalance. First, different sources of distortion are identified from experimental measurements, then a dual-input nonlinear I/Q imbalance model is developed. Further, the inverse model is used for I/Q imbalance compensation. Finally, the performance of the I/Q imbalance compensator is evaluated with both simulations and experiments. In comparison with previously published results, the proposed I/Q imbalance compensator shows significantly improved performance. Thus, we prove that a complete nonlinear I/Q imbalance compensation can minimize the effects of the RF modulator in high-performance digital communication systems.
  •  
49.
  • Cao, Haiying, 1982, et al. (author)
  • Identification of Distortions in a RF Measurement System
  • 2008
  • In: GHz Symposium 2008.
  • Conference paper (other academic/artistic)abstract
    • Distortions in a RF measurement system can adversely impact the characteristics of the measured signal. In this paper, signal processing techniques are used to identify the sources for distortions. Promising measurement results are shown.
  •  
50.
  • Cao, Haiying, 1982, et al. (author)
  • Linearization of Efficiency-Optimized Dynamic Load Modulation Transmitter Architectures
  • 2010
  • In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 58:4, s. 873-881
  • Journal article (peer-reviewed)abstract
    • In this paper, a detailed linearization procedure for dynamic load modulation (DLM) transmitter architectures is proposed for the first time. Compared with the conventional single-input/single-output digital predistortion (DPD) approach used with traditional power amplifiers (PAs), the proposed linearization scheme is based on a regular memory DPD in combination with an efficiency-optimized static one-to-two mapping inverse model, which constructs the predistorted input signals to the DLM transmitter. The time-alignment issue, which is very important to this dual-input architecture, is also considered. The proposed technique is demonstrated by a 1-GHz 10-W LDMOS PA that employs a varactor-based tunable matching network. A normalized mean square error of $-{hbox {35 dB}}$, and adjacent channel leakage ratio of $-hbox{43 dBc}$ is achieved, with an average power-added efficiency of 53% for a single-carrier WCDMA signal with 7-dB peak-to-average ratio. Finally, it is shown that the time-alignment sensitivity is relaxed when the proposed linearization scheme is used. This means that the overall complexity of the transmitter implementation can be reduced.
  •  
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