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Sökning: WFRF:(Tufvesson Fredrik)

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  • Alayon Glazunov, Andres, et al. (författare)
  • Mean effective gain of antennas in a wireless channel
  • 2009
  • Ingår i: IET Microwaves, Antennas & Propagation. - Institution of Engineering and Technology. - 1751-8725. ; 3:2, s. 214-227
  • Tidskriftsartikel (refereegranskat)abstract
    • The mean effective gain (MEG) is one of the most important parameters for the characterisation of antennas in wireless channels. An analysis of some fundamental properties of the MEG is provided and corresponding physical interpretations are given. Three points are analysed in detail: (i) closed-form expressions for MEG in a mixed environment with both stochastic and deterministic components are provided, showing that the MEG can be written as a sum of gains for the deterministic and stochastic components, (ii) it is shown that under some assumptions, the propagation channel and the antenna are equivalent in the sense that the impact of the channel cross-polarisation ratio (XPR) and the antenna effective cross-polar discrimination on the MEG are symmetrical, (iii) based on the fact that MEG depends on random variables, such as the XPR and antenna rotations because of user's movements, the average, the minimum and maximum MEG of antennas are defined, respectively. Finally, the maximum effective gain of antennas is derived and shown that it is bounded by 4 pi eta(rad), where eta(rad) is the radiation efficiency of the antenna.
  • Almers, Peter, et al. (författare)
  • Exercises
  • 2005
  • Ingår i: Wireless Communications. - John Wiley & Sons. - 978-0-470-84888-3 - 0-470-84888-X - 13-978-0-470-84887-6 - 0-470-84887-1 ; s. 561-593
  • Bokkapitel (övrigt vetenskapligt)
  • Bengtsson, Erik L, et al. (författare)
  • Transmission schemes for Multiple Antenna Terminals in Real Massive MIMO systems
  • 2016
  • Ingår i: 2016 IEEE Global Communications Conference (GLOBECOM). - IEEE--Institute of Electrical and Electronics Engineers Inc.. - 978-1-5090-1329-6
  • Konferensbidrag (refereegranskat)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.
  • Bourdoux, Andre, et al. (författare)
  • D1.2 MaMi Channel Characteristics: Measurement Results
  • 2015
  • Rapport (övrigt vetenskapligt)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.
  • Dahman, Ghassan, et al. (författare)
  • On the probability of non-shared multipath clusters in cellular networks
  • 2015
  • Ingår i: IEEE Wireless Communications Letters. - IEEE--Institute of Electrical and Electronics Engineers Inc.. - 2162-2345. ; :99
  • Tidskriftsartikel (refereegranskat)abstract
    • In Space Division Multiple Access (SDMA) systems, users are separated based on their positions. The base-station (BS) signals typically reach the users through multipath clusters. The goal of this work is to find the probability that a randomly selected user will receive the signal from the BS via at least one nonshared (by any other user) multipath cluster. This probability, referred to as PSuccess, provides (under some conditions) the limit of the probability that the BS is able to communicate successfully with a randomly selected user using SDMA without causing significant interference to other users. In order to find PSuccess, we first derive a model describing the probability distribution function (pdf) of the non-overlapping area of a set of circles, that have the same radius and are spatially distributed according to a Poisson distribution. Then, the proposed model for this pdf is used to express PSuccess as a function of the user’s intensity and the clusters’ intensity. Simulations, using the COST 2100 model, for outdoor and indoor scenarios, are used to validate the derived expression for PSuccess with a very good agreement, where the maximum error was 0:04.
  • Flordelis, Jose, et al. (författare)
  • Exploiting Antenna Correlation in Measured Massive MIMO Channels
  • 2016
  • Ingår i: 2016 IEEE 27th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC). - IEEE--Institute of Electrical and Electronics Engineers Inc..
  • Konferensbidrag (refereegranskat)abstract
    • We investigate antenna correlation of an $M$-antenna massive multi-antenna (MIMO) setup with the purpose of obtaining a low-rank representation of the instantaneous massive MIMO channel. Low-rank representation bases using short-term and long-term antenna correlation statistics are defined, and their performance is evaluated with data sets obtained from channel measurements in both indoor and outdoor environments at 2.6~GHz. Results indicate that the short-term bases can capture a larger amount of the channel energy compared to the long-term ones, but they have a limited time-span, one coherence time or less. On the other hand, the long-term bases are stable over time-spans of a few seconds. Hence, they can be obtained relatively easily. We also investigate a rank-$p$ vector-scalar LMMSE channel estimator that exploits antenna correlation. Our results show that the investigated estimator can achieve a performance similar to that of full-rank LMMSE at a $(2p+1)/M$ times lower cost. The investigated estimator may be used in conjunction with estimators that exploit correlation in the frequency and time domain or, alternatively, in situations in which these estimators cannot be used, e.g. when pilot separation is larger than the channel coherence bandwidth or time.
  • Flordelis, Jose, et al. (författare)
  • Spatial Separation of Closely-Located Users in Measured Massive MIMO Channels
  • 2016
  • Ingår i: IEEE Transactions on Wireless Communications. - IEEE--Institute of Electrical and Electronics Engineers Inc.. - 1536-1276.
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the ability of massive multiple-inputmultiple-output (MIMO) systems to spatially separate signals sentto users located close to each other in line-of-sight (LOS) prop-agation conditions. The analysis is based on fully-synchronouschannel measurements of 9 single-antenna users conducted inboth indoor and outdoor environments at 2.6 GHz. The users areconfined to a small area and communicate concurrently with a128-antenna base station (BS). We examine the channel conditionnumber, achievable sum rates and number of simultaneouslyserved users in various setups and for various numbers of an-tennas and precoding schemes. Our results indicate that massiveMIMO with 128 antennas and zero forcing (ZF) precoding cansimultaneously serve all 9 users with low transmit power values,and with low sum rate losses relative to optimal dirty-papercoding (DPC). This leads us to conclude that users can be spatiallyseparated with massive MIMO, also in tricky scenarios suchas the one studied here. However, our results do not supportthe use of maximum ratio transmission (MRT) precoding forspatial multiplexing of users in the scenarios considered. Wealso study the physical propagation mechanisms that facilitatespatial separation of users, and the role of antenna polarizationat the BS. Our findings are relevant to the design of future 5Gcommunication systems.
  • Flordelis, Jose, et al. (författare)
  • Spatial Separation of Closely-Spaced Users in Measured Massive Multi-User MIMO Channels
  • 2015
  • Ingår i: 2015 IEEE International Conference on Communications (ICC). - IEEE--Institute of Electrical and Electronics Engineers Inc.. ; s. 1441-1446
  • Konferensbidrag (refereegranskat)abstract
    • Fully-synchronous measurements of a massive multi-user multiple-input multiple-output (MU-MIMO) radio propagation channel are presented. We evaluate the ability of a massive MIMO system to spatially separate users located close to each other in line-of-sight (LOS) propagation conditions. The system consists of a base-station (BS) antenna array equipped with 64 dual-polarized antenna elements (128 ports) arranged in a cylindrical configuration, and eight single-antenna users. The users are confined to a five-meter diameter circle and move randomly at pedestrian speeds. The BS antenna array is located on top of a 20 m tall building and has LOS to the users. We examine user separability by studying singular value spread of the MU-MIMO channel matrix for several subsets of BS antenna array ports, along with sum-rate capacity and achievable sum-rates with both zero-forcing and matched-filtering linear precoders. We also analyze the performance of the user with the lowest rate. Finally, a comparison between the performance offered by the massive MIMO system and that of a conventional MU-MIMO system is provided. To the best of our knowledge, this is the first report of fully-synchronous dynamic measurements of a massive MIMO system. Our investigation shows that even users located close to each other in LOS propagation conditions can be spatially separated in a massive MIMO system.
  • Gao, Xiang, et al. (författare)
  • Channel behavior for very-large MIMO systems - initial characterization
  • 2012
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Wireless communication using very-large multiple-input multiple-output (MIMO) antennas is a new research field, where base stations are equipped with a very large number of antennas as compared to previously considered systems. Unlike the conventional small and compact antenna arrays, the very-large arrays may span many wavelengths in space, thus they can experience large-scale fading over the array. This power variation over the antenna array may be critical to algorithm design and performance evaluations for very-large MIMO systems, and it is thus important that it is included in channel models. Based on channel measurements using a 128-antenna linear array in a semi-urban area, we characterize and model the large-scale fading properties. We focus on cluster-based modeling which can be seen as an extension of the current COST 2100 channel model. In the paper, we report our latest channel behavior modeling progress for very-large MIMO systems.
  • Gao, Xiang, et al. (författare)
  • Extension of the COST 2100 channel model for massive MIMO
  • 2015
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Massive MIMO has been shown, both in theory and through experiments, to offer very promising properties. These include the possibility to decrease output power by at least an order of magnitude while still achieving large gains in spectral efficiency, as compared to today’s access schemes. To efficiently design communication algorithms and evaluate massive MIMO schemes, channel models that capture important massive MIMO channel characteristics are needed. We pursue this by extending a well-known cluster-based MIMO channel model - the COST 2100 model. In the paper, we suggest a model extension for massive MIMO, and we discuss main concepts, parameters and implementation issues. The modeling work is based on measurement data from a measurement campaign in the 2.6 GHz frequency range using a physically-large array with 128 elements.
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