| 1. |
- Alegria, Juan Vidal, et al.
(author)
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Decentralized equalizer construction for large intelligent surfaces
- 2019
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In: 2019 IEEE 90th Vehicular Technology Conference, VTC 2019 Fall - Proceedings. - 1550-2252. - 9781728112206 ; 2019-September
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Conference paper (peer-reviewed)abstract
- In this paper we present fully decentralized methods for calculating an approximate zero- forzing (ZF) equalizer in a large intelligent surface (LIS). A LIS is intended for wireless communication and facilitates unprecedented MU- MIMO performance, far superior to that of Massive MIMO. Antenna modules in the grid connect to their neighbors to exchange messages of information needed for interference cancellation in a fully- decentralized fashion, making the system scalable. By a careful design of how the messages are routed, we show that the proposed method is able to cancel inter-user interference sufficiently well without any centralized coordination, opening the door for the realization of this type of structures.
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| 2. |
- Bengtsson, Erik L, et al.
(author)
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A Case Study on the Influence of Multiple Users on the Effective Channel in a Massive MIMO System
- 2019
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In: IEEE Wireless Communications Letters. - 2162-2337. ; , s. 1-6
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Journal article (peer-reviewed)abstract
- We investigate the importance of weak clusters when modeling a wireless massive MIMO channel. We do this by studying the influence of densely spaced terminals and the number of base-station antennas for a zero-forcing precoded massive MIMO system. In particular, we focus on the influence on the correlation and imbalance between the signals at the terminal antennas, the effective channel-gain, the eigenvalue distributions and the number of clusters.The study is based on measured radio-channels from terminal prototypes with integrated antennas connected to a massive MIMO testbed.We further evaluate the advantage of using block-diagonalized zero-forcing compared to conventional zero-forcing in a massive MIMO system. Unexpectedly, terminals with low antenna envelope correlation coefficient may benefit significantly from block-diagonal zero-forcing in a massive MIMO system.The main conclusion is that weaker clusters are important when modeling multi-user scenarios.
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| 3. |
- Bengtsson, Erik L., et al.
(author)
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A Simulation Framework for Multiple-Antenna Terminals in 5G Massive MIMO Systems
- 2017
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In: IEEE Access. - 2169-3536. ; 5, s. 26819-26831
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Journal article (peer-reviewed)abstract
- The recent interest in massive MIMO has spurred intensive work on massive MIMO channel modeling in contemporary literature. However, current models fail to take the characteristics of terminal antennas into account. There is no massive MIMO channel model available that can be used for evaluation of the influence of different antenna characteristics at the terminal side. In this paper, we provide a simulation framework that fills this gap. We evaluate the framework with antennas integrated into Sony Xperia handsets operating at 3.7 GHz as this spectrum is identified for the 5G new radio standard by 3GPP. The simulation results are compared with measured terminal performance when communicating with the Lund University’s massive MIMO testbed under the same loading conditions. Expressions are derived for comparison of the gain obtained from different diversity schemes computed from measured far-field antenna patterns. We conclude that the simulation framework yields results close to the measured ones and that the framework can be used for antenna evaluation for terminals in a practical precoded massive MIMO system.
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| 4. |
- Bengtsson, Erik L., et al.
(author)
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Analysis of Transmission Schemes for Dual-Antenna Terminals in Massive MIMO Systems
- 2018
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In: 2018 25th International Conference on Telecommunications, ICT 2018. - 9781538623213 ; , s. 76-82
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Conference paper (peer-reviewed)abstract
- The overall system performance of massive MIMO is improved by equipping user terminals with multiple antennas. In this paper, we investigate transceiver designs for the case of a single downlink stream and in particular, we study the uplink pilot design. Moreover, we study the consequences of channel estimation errors at the base-station, and to what extent a dual-antenna terminal can get access to relevant channel statistics for optimization of the pilot signal. Gain expressions for comparison of different designs are derived. We verify the analytic results based on antennas integrated into Sony-Xperia handsets measured with the Lund University massive MIMO testbed. The measurements are performed at frequencies <6GHz since this part of the spectrum is a candidate for NR standard according to 3GPP.
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| 5. |
- Bengtsson, Erik L, et al.
(author)
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Transmission schemes for Multiple Antenna Terminals in Real Massive MIMO systems
- 2016
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In: 2016 IEEE Global Communications Conference (GLOBECOM). - 9781509013289 - 9781509013296
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Conference paper (peer-reviewed)abstract
- In massive MIMO performance evaluations it is often assumed that the terminal has a single antenna. The combination of multiple antennas in a terminal and massive MIMO precoding at the base station side can further improve overall system performance. We present measurement results for multi antenna terminals operating in different transmission schemes and how they perform under varying loading conditions. Gain expressions are derived that enable easy comparison between the transmission schemes. The evaluation is performed on realistic antennas integrated into Sony Xperia handsets tuned to 3.7~GHz and operated together with the Lund University massive MIMO (LuMaMi) test bed. It is concluded that the approach used in today's mobile systems, where up link and down link are addressed independently, will not provide the best performance. The performance can be improved by the selection of transmission schemes optimized for massive MIMO.
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| 6. |
- Bengtsson, Erik, et al.
(author)
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UE Antenna Properties and Their Influence on Massive MIMO System Performance
- 2015
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In: 2015 9th European Conference on Antennas and Propagation, EuCAP 2015. - 9788890701856
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Conference paper (peer-reviewed)abstract
- The use of large-scale antenna arrays can bring substantial improvements both in energy and spectral efficiency. This paper presents an initial study of user equipment (UE) antenna performance based on prototypes for a massive MIMO test bed. Most publications in the massive MIMO area have assumed isotropic or dipole antenna behavior at the UE side. It is, however, of greatest interest to evaluate the impact of realistic antenna implementations and user loading on such systems. Antennas are integrated into realistic UE form factors. Simulations are carried out to evaluate system performance using the UE antenna behavior measured in a Satimo StarGate 64. Comparisons are made with ideal isotropic un-correlated antennas. The presented UEs are designed for the 3.7 GHz band used by the LuMaMi massive MIMO test bed at Lund University.
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| 7. |
- Bourdoux, Andre, et al.
(author)
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D1.2 MaMi Channel Characteristics: Measurement Results
- 2015
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Reports (other academic/artistic)abstract
- This deliverable presents channel measurement results for the scenariosOpen exhibition and Crowded auditiorium. The measurement procedureand equipment are described. Massive MIMO (MaMi) channel characteristicsand key parameters are extracted and used in an extended COST 2100channel model for MaMi. The initial validation performed shows that themodel is capable of reproducing the statistics in terms of temporal behaviorof the user separability, singular value spread, capacity and sum-rate anddirectional characteristics. The model can be used for system and link levelMaMi simulations.
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| 8. |
- Chung, Min Keun, et al.
(author)
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Phase Noise Compensation for OFDM Systems Exploiting Coherence Bandwidth
- 2019
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In: 20th International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2019. - 9781538665282 ; 2019-July
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Conference paper (peer-reviewed)abstract
- Millimeter-wave (mmWave) systems must overcome severe phase noise impairment to exploit its full advantage (e.g. high data rate). However, the estimation of phase noise combined with wireless channel requires not only high-computational complexity, but also does not guarantee a stable solution. In this paper, the fact that the coherence bandwidth of a mmWave system is much larger than those of conventional systems is exploited to acquire the knowledge regarding phase noise by linear estimator. The channel coefficients are assumed to be piecewise-constant over Ncb successive subcarriers within coherence bandwidth. Utilizing the coherence structure, we propose a new algorithm for phase noise compensation on orthogonal frequency division multiplexing (OFDM) systems. Numerical results with phase noise generated as a Wiener process demonstrate that the proposed algorithm can provide improved performance even in severe phase noise environments.
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| 9. |
- Chung, Min Keun, et al.
(author)
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Robust timing synchronization for full duplex communications : Design and implementation
- 2018
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In: 2017 IEEE Global Conference on Signal and Information Processing, GlobalSIP 2017 - Proceedings. - 9781509059904 ; 2018-January, s. 883-887
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Conference paper (peer-reviewed)abstract
- This paper presents a robust timing synchronization method for full duplex orthogonal frequency division multiplexing (OFDM) systems based on Long Term Evolution (LTE). The proposed method contains two essential steps: 1) time alignment between the desired signal and self-interference 2) normalized synchronization peak (NSP) index switching. The time alignment is to make the difference in arrival times of the desired signal and the self-interference signal within cyclic prefix (CP) duration of an OFDM symbol, exploiting a time advance, thereby adopting low-complexity, frequency domain self-interference cancellation and decoding. In the second step, to improve the probability of successful time synchronization, a Zadoff-Chu sequence with a different root index is used for the primary synchronization signal at each node. To validate the proposed method with experimental evidence, we implement a full duplex physical layer (PHY) on an FPGA-based software-defined radio (SDR) platform. It is shown that our full duplex OFDM synchronizer is flexible and robust, in a real-world wireless channel, compared to existing synchronization method.
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| 10. |
- Diaz, Isael, et al.
(author)
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A 350μW Sign-Bit architecture for multi-parameter estimation during OFDM acquisition in 65nm CMOS
- 2015
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In: 2015 IEEE International Symposium on Circuits and Systems (ISCAS). - 9781479983919
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Conference paper (peer-reviewed)abstract
- Correct estimation of symbol timing, Carrier Frequency Offset (CFO), and Signal-to-Noise Ratio (SNR) is crucial in Orthogonal Frequency Division Multiplexing (OFDM) communication. Typically, high estimation accuracy is desired, but often comes with increased complexity. Which has a direct repercussion in energy consumption. In this article, an architecture based on Sign-Bit estimation with low complexity, and hence low power dissipation, is presented. The architecture, is capable of estimating the afore-mentioned parameters in virtually any OFDM standard. The proof of concept has been fabricated in 65 nm CMOS technology with low-power high-VT cells. Measurements performed with supply voltage of 1.2V. resulted in a power dissipation of 350 μW, 6 times smaller to that of an equivalent 8-bit architecture, and the lowest power density reported in literature.
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