Lund University Publications
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Lund University Lund University Publications2000-01-01T00:00+00:001dailyFully Decentralized Approximate Zero-Forcing Precoding for Massive MIMO Systems
https://lup.lub.lu.se/search/publication/7b005068-2e1a-4b80-8c35-8de59b12da72
Sarajlić, MurisRusek, FredrikRodríguez Sánchez, JesúsLiu, LiangEdfors, Ove2019-06We analyze the downlink of a massive multiuser multiple input, multiple output (MIMO) system where antenna units at the base station are connected in a daisy chain without a central processing unit and only possess local channel knowledge. For this setup, we develop and analyze a linear precoding algorithm for suppressing interuser interference. It is demonstrated that the algorithm is close to zero-forcing precoding in terms of performance for a large number of antennas. Moreover, we show that with careful scheduling of processing across antennas, requirements for interconnection throughput are reduced compared with the fully centralized solution. Favorable tradeoff between performance and interconnection throughput makes the daisy chain a viable candidate topology for real-life implementations of base stations in MIMO systems where the number of antennas is very large.http://lup.lub.lu.se/record/7b005068-2e1a-4b80-8c35-8de59b12da72http://dx.doi.org/10.1109/LWC.2019.2892044scopus:85067928827engIEEE Wireless Communications Letters; 8(3), pp 773-776 (2019)ISSN: 2162-2337Telekommunikationdaisy chaindecentralized processinginterference suppressionMassive MIMOFully Decentralized Approximate Zero-Forcing Precoding for Massive MIMO Systemscontributiontojournal/articleinfo:eu-repo/semantics/articletextGeometry-Based Stochastic Channel Model for High-Speed Railway Communications
https://lup.lub.lu.se/search/publication/8716c3f3-b422-4a27-b066-4ff0e178c3a1
Zhou, LaiLuan, FengyuZhou, ShidongMolisch, Andreas F.Tufvesson, Fredrik2019Reliable wireless communication links are a critical but challenging aspect for high-speed railway (HSR). To develop and analyze such systems, accurate models for the propagation channel are required. The radio channel properties in HSR scenarios are different from those in cellular scenarios not only due to the high velocity, but also due to the special construction elements and the type of surroundings along the train lines. We performed a measurement campaign at a carrier frequency of 2.4 GHz on the Guangzhou-Shenzhen dedicated high-speed train line in China. Motivated by the results from these measurements, we propose the concept of active scatterer region as an improvement for geometry-based stochastic channel models for HSR, to better describe the non-stationary properties of such channels. Further contributions to the total channel impulse response are also studied, including the line-of-sight component and the scattering component from overhead line poles. Each type of component is modeled and fully parameterized based on the measurement results.http://lup.lub.lu.se/record/8716c3f3-b422-4a27-b066-4ff0e178c3a1http://dx.doi.org/10.1109/TVT.2019.2906257scopus:85066628119engIEEE Transactions on Vehicular Technology; 68(5), pp 4353-4366 (2019)ISSN: 0018-9545Teknisk mekanikactive scatterer regionchannel measurementGSCMHigh speed railwaynon-stationaryGeometry-Based Stochastic Channel Model for High-Speed Railway Communicationscontributiontojournal/articleinfo:eu-repo/semantics/articletextCapacity Degradation with Modeling Hardware Impairment in Large Intelligent Surface
https://lup.lub.lu.se/search/publication/a80db21c-5996-4c7d-a7d4-e56444a52b6b
Hu, ShaRusek, FredrikEdfors, Ove2019-02-21In this paper, we consider capacity degradations stemming from potential hardware impairments (HWI) of newly proposed Large Intelligent Surface (LIS) systems. Without HWI, the utility of surface-area (the first-order derivative of the capacity with respect to surface-area) is shown to be proportional to the inverse of it. With HWI, the capacity as well as the utility of surface-area are both degraded, due to a higher effective noise level caused by the HWI. After first modeling the HWI in a general form, we derive the effective noise density and the decrement of utility in closed-forms. With those the impacts of increasing the surface-area can be clearly seen. One interesting but also natural outcome is that both the capacity and utility can be decreased when increasing the surface-area in the cases with severe HWI. The turning points where the capacity and the utility start to decrease with HWI can be evaluated from the derived formulas for them. Further, we also consider distributed implementations of a LIS system by splitting it into multiple small LIS-Units, where the impacts of HWI can be significantly suppressed due to a smaller surface-area of each unit.http://lup.lub.lu.se/record/a80db21c-5996-4c7d-a7d4-e56444a52b6bhttp://dx.doi.org/10.1109/GLOCOM.2018.8647606ISBN: 9781538647271scopus:85063522362engKommunikationssystemCapacity Degradation with Modeling Hardware Impairment in Large Intelligent Surfacecontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextConstant-εr Lens Beamformer for Low-Complexity Millimeter-Wave Hybrid MIMO
https://lup.lub.lu.se/search/publication/12e7a37c-ed7c-4132-a758-9caf557a1f29
Abbasi, Muhammad Ali BabarFusco, Vincent F Tataria, HarshMatthaiou, Michail2019-07It is well established that the utilization of unused millimeter-wave (mmWave) spectrum is inevitable due to unavailability of required bandwidth in the conventional RF band to support the high data demands of 5G. Large antenna arrays with beamforming capabilities are required to compensate for the high path loss at mmWave frequencies. We are at the verge of a massive mmWave radio front-end deployment, and low-complexity low-cost hardware beamforming solutions are required now at this stage than ever before. In this paper, one such solution is demonstrated and analyzed. A high-performance and low-complexity lens-based beamformer consisting of constant dielectric material ( ϵr ) with antenna feeds is presented for multibeam operation. A prototype is developed based on the classical synthesis approach, and in line with the requirements of mmWave hybrid multiuser multiple-input multiple-output (MU-MIMO) systems. A characterization at 28 GHz is performed wherein an uplink signal-to-noise ratio of user terminals is evaluated with the zero-forcing (ZF) baseband signal processing. Radiation performance of a single-source beamformer is measured in an anechoic environment, and end-to-end ergodic sum spectral efficiency performance is estimated based on the measured data. It is shown that the constant- ϵr -based beamformer solution is simple, yet significantly outperforms conventional antenna array beamformers with analog phase shifter networks, making it a promising candidate for future hybrid massive MIMO systems.http://lup.lub.lu.se/record/12e7a37c-ed7c-4132-a758-9caf557a1f29http://dx.doi.org/10.1109/TMTT.2019.2903790scopus:85068460524engIEEE Transactions on Microwave Theory and Techniques; 67(7), pp 2894-2903 (2019)ISSN: 0018-9480TelekommunikationBeamformingLensMillimeter-wavesMIMOMU-MIMOspectral efficiency5GConstant-εr Lens Beamformer for Low-Complexity Millimeter-Wave Hybrid MIMOcontributiontojournal/articleinfo:eu-repo/semantics/articletextFully Decentralized Massive MIMO Detection Based on Recursive Methods
https://lup.lub.lu.se/search/publication/53f03fe8-2d75-4b96-aa10-2500cfa201dc
Sánchez, Jesús RodríguezRusek, FredrikSarajlić, MurisEdfors, OveLiu, Liang2019-01-03Algorithms for Massive MIMO uplink detection typically rely on a centralized approach, by which baseband data from all antennas modules are routed to a central node in order to be processed. In case of Massive MIMO, where hundreds or thousands of antennas are expected in the base-station, this architecture leads to a bottleneck, with critical limitations in terms of interconnection bandwidth requirements. This paper presents a fully decentralized architecture and algorithms for Massive MIMO uplink based on recursive methods, which do not require a central node for the detection process. Through a recursive approach and very low complexity operations, the proposed algorithms provide a sequence of estimates that converge asymptotically to the zero-forcing solution, without the need of specific hardware for matrix inversion. The proposed solution achieves significantly lower interconnection data-rate than other architectures, enabling future scalability.http://lup.lub.lu.se/record/53f03fe8-2d75-4b96-aa10-2500cfa201dchttp://dx.doi.org/10.1109/SiPS.2018.8598321ISBN: 9781538663189scopus:85061402433engSignalbehandlingDecentralizedDetection and zero-forcingGradient DescentMassive MIMORecursive Least SquaresStochastic ApproximationFully Decentralized Massive MIMO Detection Based on Recursive Methodscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextOptimal plasmonic multipole resonances of a sphere in lossy media
https://lup.lub.lu.se/search/publication/74c8677f-cb25-41be-a3a6-4adfe704b6e8
Nordebo, SvenKristensson, GerhardMirmoosa, MohammadTretyakov, Sergei2019Fundamental upper bounds are given for the plasmonic multipole absorption and scattering of a rotationally invariant dielectric sphere embedded in a lossy surrounding medium. A specialized Mie theory is developed for this purpose and when combined with the corresponding generalized optical theorem, an optimization problem is obtained which is explicitly solved by straightforward analysis. In particular, the absorption cross section is a concave quadratic form in the related Mie (scattering) parameters and the convex scattering cross section can be maximized by using a Lagrange multiplier constraining the absorption to be non-negative. For the homogeneous sphere, the Weierstrass preparation theorem is used to establish the existence and the uniqueness of the plasmonic singularities and explicit asymptotic expressions are given for the dipole and the quadrupole. It is shown that the optimal passive material for multipole absorption and scattering of a small homogeneous dielectric sphere embedded in a dispersive medium is given approximately as the complex conjugate and the real part of the corresponding pole positions, respectively. Numerical examples are given to illustrate the theory, including a comparison with the plasmonic dipole and quadrupole resonances obtained in gold, silver, and aluminum nanospheres based on some specific Brendel-Bormann (BB) dielectric models for these metals. Based on these BB models, it is interesting to note that the metal spheres can be tuned to optimal absorption at a particular size at a particular frequency.http://lup.lub.lu.se/record/74c8677f-cb25-41be-a3a6-4adfe704b6e8http://dx.doi.org/10.1103/PhysRevB.99.054301scopus:85061347599engPhysical Review B; 99(5), no 054301 (2019)ISSN: 1550-235XAnnan elektroteknik och elektronikDen kondenserade materiens fysikElectrical propertiesCharge polarizationDielectric propertiesPermittivityOptics and lasersPlasmonicsOptimal plasmonic multipole resonances of a sphere in lossy mediacontributiontojournal/articleinfo:eu-repo/semantics/articletextVertical Gate-All-Around Nanowire GaSb-InAs Core-Shell n-Type Tunnel FETs
https://lup.lub.lu.se/search/publication/66fcfd0e-b1ac-44df-af6a-b2327e9ca8bc
Vasen, T.Ramvall, P.Afzalian, A.Doornbos, G.Holland, M.Thelander, C.Dick, K. A.Wernersson, L. E.Passlack, M.2019-01-17Tunneling Field-Effect Transistors (TFET) are one of the most promising candidates for future low-power CMOS applications including mobile and Internet of Things (IoT) products. A vertical gate-all-around (VGAA) architecture with a core shell (C-S) structure is the leading contender to meet CMOS footprint requirements while simultaneously delivering high current drive for high performance specifications and subthreshold swing below the Boltzmann limit for low power operation. In this work, VGAA nanowire GaSb/InAs C-S TFETs are demonstrated experimentally for the first time with key device properties of subthreshold swing S = 40 mV/dec (Vd = 10 mV) and current drive up to 40 μA/wire (Vd = 0.3 V, diameter d = 50 nm) while dimensions including core diameter d, shell thickness and gate length are scaled towards CMOS requirements. The experimental data in conjunction with TCAD modeling reveal interface trap density requirements to reach industry standard off-current specifications.http://lup.lub.lu.se/record/66fcfd0e-b1ac-44df-af6a-b2327e9ca8bchttp://dx.doi.org/10.1038/s41598-018-36549-zscopus:85060140819engScientific Reports; 9(1), no 202 (2019)ISSN: 2045-2322NanoteknikVertical Gate-All-Around Nanowire GaSb-InAs Core-Shell n-Type Tunnel FETscontributiontojournal/articleinfo:eu-repo/semantics/articletextTrade-off Between Antenna Efficiency and Q-Factor
https://lup.lub.lu.se/search/publication/e0be02a6-b045-4541-af5a-e8ee90b96a71
Gustafsson, MatsCapek, MiloslavSchab, Kurt2019-01-08The trade-off between radiation efficiency and antenna bandwidth, expressed in terms of Q-factor, for small antennas is formulated as a multi-objective optimization problem in current distributions of predefined support. Variants on the problem are constructed to demonstrate the consequences of requiring a self-resonant current as opposed to one tuned by an external reactance. The trade-offs are evaluated for sample problems and the resulting Pareto-optimal sets reveal the relative cost of valuing low radiation Q-factor over high efficiency, the cost in efficiency to require a self-resonant current, the effects of lossy parasitic loading, and other insights. Observations are drawn from the sample problems selected, though the tradeoff evaluation method is valid for studying arbitrary antenna geometries. In the examples considered here, we observe that small increases in Q-factor away from its lower bound allow for dramatic increases in efficiency toward its upper bound.http://lup.lub.lu.se/record/e0be02a6-b045-4541-af5a-e8ee90b96a71http://dx.doi.org/10.1109/TAP.2019.2891448scopus:85059804840engIEEE Transactions on Antennas and Propagation; 67(4), pp 2482-2493 (2019)ISSN: 0018-926XTelekommunikationAntenna theoryAntennasBandwidthConductivityCurrent distributioncurrent distributioneigenvalues and eigenfunctionsMethod of momentsOptimizationoptimization methodsQ-factorradiation efficiencyTrade-off Between Antenna Efficiency and Q-Factorcontributiontojournal/articleinfo:eu-repo/semantics/articletextInAs-oxide interface composition and stability upon thermal oxidation and high-k atomic layer deposition
https://lup.lub.lu.se/search/publication/b3aafe42-6a43-4228-a11c-836a62f3bc98
Troian, AndreaKnutsson, Johan V.McKibbin, Sarah R.Yngman, SofieBabadi, Aein S.Wernersson, Lars ErikMikkelsen, AndersTimm, Rainer2018-12-01Defects at the interface between InAs and a native or high permittivity oxide layer are one of the main challenges for realizing III-V semiconductor based metal oxide semiconductor structures with superior device performance. Here we passivate the InAs(100) substrate by removing the native oxide via annealing in ultra-high vacuum (UHV) under a flux of atomic hydrogen and growing a stoichiometry controlled oxide (thermal oxide) in UHV, prior to atomic layer deposition (ALD) of an Al2O3 high-k layer. The semiconductor-oxide interfacial stoichiometry and surface morphology are investigated by synchrotron based X-ray photoemission spectroscopy, scanning tunneling microscopy, and low energy electron diffraction. After thermal oxide growth, we find a thin non-crystalline layer with a flat surface structure. Importantly, the InAs-oxide interface shows a significantly decreased amount of In3+, As5+, and As0 components, which can be correlated to electrically detrimental defects. Capacitance-voltage measurements confirm a decrease of the interface trap density in gate stacks including the thermal oxide as compared to reference samples. This makes the concept of a thermal oxide layer prior to ALD promising for improving device performance if this thermal oxide layer can be stabilized upon exposure to ambient air.http://lup.lub.lu.se/record/b3aafe42-6a43-4228-a11c-836a62f3bc98http://dx.doi.org/10.1063/1.5054292scopus:85059606297engAIP Advances; 8(12), no 125227 (2018)ISSN: 2158-3226MaterialteknikInAs-oxide interface composition and stability upon thermal oxidation and high-k atomic layer depositioncontributiontojournal/articleinfo:eu-repo/semantics/articletextFacet-selective group-III incorporation in InGaAs template assisted selective epitaxy
https://lup.lub.lu.se/search/publication/876d26d3-61f7-4d47-8975-7cbd6d9efea4
Borg, MattiasGignac, LynneBruley, JohnMalmgren, AndreasSant, SaurabhConvertino, ClarissaRossell, Marta D.Sousa, MarilyneBreslin, ChrisRiel, HeikeMoselund, Kirsten E.Schmid, Heinz2019InGaAs is a potential candidate for Si replacement in upcoming advanced technological nodes because of its excellent electron transport properties and relatively low interface defect density in dielectric gate stacks. Therefore, integrating InGaAs devices with the established Si platforms is highly important. Using template-assisted selective epitaxy (TASE), InGaAs nanowires can be monolithically integrated with high crystal quality, although the mechanisms of group III incorporation in this ternary material have not been thoroughly investigated. Here we present a detailed study of the compositional variations of InGaAs nanostructures epitaxially grown on Si(111) and Silicon-on-insulator substrates by TASE. We present a combination of XRD data and detailed EELS maps and find that the final Ga/In chemical composition depends strongly on both growth parameters and the growth facet type, leading to complex compositional sub-structures throughout the crystals. We can further conclude that the composition is governed by the facet-dependent chemical reaction rates at low temperature and low V/III ratio, while at higher temperature and V/III ratio, the incorporation is transport limited. In this case we see indications that the transport is a competition between Knudsen flow and surface diffusion.http://lup.lub.lu.se/record/876d26d3-61f7-4d47-8975-7cbd6d9efea4http://dx.doi.org/10.1088/1361-6528/aaf547scopus:85059439065engNanotechnology; 30(8), no 084004 (2019)ISSN: 0957-4484NanoteknikFacet-selective group-III incorporation in InGaAs template assisted selective epitaxycontributiontojournal/articleinfo:eu-repo/semantics/articletext