| 1. |
- Afsar Doost, Sepideh, 1983, et al.
(författare)
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Digital Predistortion Using a Vector Switched Model
- 2012
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 60:4, s. 1166-1174
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Agrell, Erik, 1965, et al.
(författare)
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Closest point search in lattices
- 2002
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 48:8, s. 2201-2214
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Agrell, Erik, 1965, et al.
(författare)
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Optimization of lattices for quantization
- 1998
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 44:5, s. 1814-1828
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Amani, Navid, 1985, et al.
(författare)
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Array Configuration Effect on the Spatial Correlation of MU-MIMO Channels in NLoS Environments
- 2020
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Ingår i: 14th European Conference on Antennas and Propagation, EuCAP 2020. ; 2020:March
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Konferensbidrag (refereegranskat)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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| 5. |
- Amani, Navid, 1985, et al.
(författare)
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Sparse Array Synthesis Including Mutual Coupling for MU-MIMO Average Capacity Maximization
- 2022
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 70:8, s. 6617-6626
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Banar, Jafar, 1991, et al.
(författare)
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Effect of Phase-Noise on the Distributed Massive MIMO Networks
- 2022
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Ingår i: 2022 52nd European Microwave Conference, EuMC 2022. ; , s. 700-703
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Konferensbidrag (refereegranskat)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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| 7. |
- Bao, Husileng, 1991, et al.
(författare)
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Automatic Distributed MIMO Testbed for beyond 5G Communication Experiments
- 2021
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. ; 2021-June, s. 697-700
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Konferensbidrag (refereegranskat)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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| 8. |
- Behravan, Ali, 1971, et al.
(författare)
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A model for bandpass nonlinearities based on Harmonic measurements
- 2003
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Ingår i: Proceedings of the IEEE Radio and Wireless conference, Boston, MA, USA, AUG 10-13. - 0780378296 ; , s. 409-412
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Konferensbidrag (refereegranskat)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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| 10. |
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