Lund University Publications
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Lund University Lund University Publications2000-01-01T00:00+00:001dailyDecentralized Massive MIMO Systems : Is There Anything to be Discussed?
https://lup.lub.lu.se/search/publication/e1ca883c-f64f-46bb-b68f-9e8dc38f1589
Sanchez, Jesus RodriguezVidal Alegria, JuanRusek, Fredrik2019Algorithms for Massive MIMO uplink detection are typically based on a centralized approach, by which baseband data from all antenna modules need to be routed to a central node for further processing. In the case of Massive MIMO, where hundreds or thousands of antennas are expected in the base-station, such architecture requires high interconnection bandwidth between antennas and the central node. Recently, decentralized architectures have been proposed to maintain low interconnection bandwidth, where channel-state-information (CSI) is obtained locally in each antenna node and not shared. Further, Massive MIMO performance is sensitive to CSI quality. However, in the literature, ideal CSI is typically assumed in decentralized systems, which is not only far from reality but also limits the generality of the analysis.This paper proposes a decentralized (a term that will be defined in the main body of the paper) architecture with the following main features: (i) the channel matrix is not made available at any single node, (ii) there is no inter-communication among antennas, (iii) the architecture used during the payload data phase, is reused to provide a certain statistic to a processing node, (iv) A non-standard channel estimation problem based on said statistic arises, (v) a matrix inversion is needed (in case of zero-forcing) at said processing node.A hefty share of the paper is devoted to (iv).http://lup.lub.lu.se/record/e1ca883c-f64f-46bb-b68f-9e8dc38f1589http://dx.doi.org/10.1109/ISIT.2019.8849465ISBN: 9781538692912scopus:85073149812engKommunikationssystemdecentralizeddetectionMAPMassive MIMOMLMMSEwishartzero-forcingDecentralized Massive MIMO Systems : Is There Anything to be Discussed?contributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextCapacity 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/conferencePapertextSpatial Separation of Closely-Located Users in Measured Massive MIMO Channels
https://lup.lub.lu.se/search/publication/82e55a25-787f-4b58-b8e5-724b47fe8725
Flordelis, JoseRusek, FredrikGao, XiangDahman, GhassanEdfors, OveTufvesson, Fredrik2018-07-08We investigate the ability of Massive multiple-input multiple-output (MIMO) systems to spatially separate up to eighteen users located close to one another in line-of-sight (LOS) propagation conditions, in both indoor and outdoor environments. For that, we use fully-synchronous measured channels at 2.6 GHz of single-antenna users moving within a small area and concurrently communicating with a base station (BS) equipped with a compact 128-port array. To quantify the degree of spatial user separability, we use three scalar metrics, namely, the achievable sum-rates, the condition number of the channel matrix, and the angle to interference factor. Our results show that Massive MIMO with zero-forcing (ZF) or regularized ZF (RZF) can spatially separate nine, even eighteen, concurrent users at practical SNR values even in the challenging case of dominant LOS propagation. In particular, signal-to-noise ratio losses relative to ideal (non-interfering and equally strong) channels can be reduced dramatically compared with standard multiuser MIMO systems, which typically have the same number of users as BS antennas. Our findings suggest that with RZF or ZF the ratio of BS antennas to number of served users should be at least three to four, to harvest most of the available spatial gains that the environment can offer. Although orthogonality and array gains complement each other, for the suggested ratios of antennas to users, the main contribution to improving system performance, measured in sum-rates, comes from the orthogonality gain.http://lup.lub.lu.se/record/82e55a25-787f-4b58-b8e5-724b47fe8725http://dx.doi.org/10.1109/ACCESS.2018.2854307scopus:85049797888engIEEE Access; 6, pp 40253-40266 (2018)ISSN: 2169-3536KommunikationssystemChannel measurementsMassive MIMOspatial separationSpatial Separation of Closely-Located Users in Measured Massive MIMO Channelscontributiontojournal/articleinfo:eu-repo/semantics/articletextMassive MIMO Performance - TDD Versus FDD : What Do Measurements Say?
https://lup.lub.lu.se/search/publication/58cd02bd-dd1d-4b3f-bf92-fe276feb54be
Flordelis, JoseRusek, FredrikTufvesson, FredrikLarsson, Erik G.Edfors, Ove2018-04Downlink beamforming in Massive MIMO either relies on uplink pilot measurements--exploiting reciprocity and time-division duplexing (TDD) operation, or on the use of a predetermined grid of beams with user equipments reporting their preferred beams, mostly in frequency-division duplexing (FDD) operation. Massive MIMO in its originally conceived form uses the first strategy, with uplink pilots, whereas there is currently significant commercial interest in the second, grid-of- beams. It has been analytically shown that with isotropic scattering (independent Rayleigh fading) the first approach outperforms the second. Nevertheless, there remains controversy regarding their relative performance in practical channels. In this contribution, the performances of these two strategies are compared using measured channel data at 2.6 GHz.http://lup.lub.lu.se/record/58cd02bd-dd1d-4b3f-bf92-fe276feb54behttp://dx.doi.org/10.1109/TWC.2018.2790912scopus:85041185733engIEEE Transactions on Wireless Communications; 17(4), pp 2247-2261 (2018)ISSN: 1536-1276Kommunikationssystemchannel measurementsFDDMassive MIMOperformanceTDDMassive MIMO Performance - TDD Versus FDD : What Do Measurements Say?contributiontojournal/articleinfo:eu-repo/semantics/articletextMultiuser Bandwidth Minimization with Individual Rate Requirements for Non-Orthogonal Multiple Access
https://lup.lub.lu.se/search/publication/49829fea-c95d-4ec5-bd64-4775cb198a8d
Rusek, FredrikChitti, KrishnaChaitanya, Tumula2017-06-04Non-Orthogonal Multiple Access (NOMA) for a multi-user single- input single-output (SISO) setup is studied in the power and the frequency domains simultaneously. The problem of sum-bandwidth minimization under perfect channel state information is solved for various combinations of rate requirements and user pairings. In this process, an iterative Tabu-search based algorithm is applied to avoid an exhaustive search over all possible user pairing combinations. It is assumed that each constituent user of the pair has a required quality of service and a flat power spectrum. Further, for each user pair, the NOMA operating region is defined by dividing the allocated bandwidth into two non-overlapping Orthogonal Multiple Access (OMA) sub-bands and an overlapping NOMA sub-band. Such an assumption achieves a greater capacity region when compared to the conventional power domain only NOMA. Also for most of the rate requirements, only one of the OMA sub-bands is active in addition to the NOMA sub-band. This simplifies the NOMA user rate expressions and power allocation process. To verify the performance gain, NOMA is compared to an OMA technique.http://lup.lub.lu.se/record/49829fea-c95d-4ec5-bd64-4775cb198a8dhttp://dx.doi.org/10.1109/VTCSpring.2017.8108686ISBN: 978-1-5090-5932-4 ISBN: 978-1-5090-5933-1scopus:85040592539engKommunikationssystemMultiuser Bandwidth Minimization with Individual Rate Requirements for Non-Orthogonal Multiple Accesscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextThe Potential of Using Large Antenna Arrays on Intelligent Surfaces
https://lup.lub.lu.se/search/publication/61d4e6ec-7895-43b4-9ba5-6b83e16704f2
Hu, ShaRusek, FredrikEdfors, Ove2017-11-16In this paper, we consider capacities of single-antenna terminals communicating to large antenna arrays that are deployed on surfaces. That is, the entire surface is used as an intelligent receiving antenna array. Under the condition that the surface area is sufficiently large, the received signal after matched-filtering (MF) can be well approximated by an intersymbol interference (ISI) channel where channel taps are closely related to a sinc function. Based on such an approximation, we have derived the capacities for both one-dimensional (terminals on a line) and high dimensional (terminals on a plane or in a cube) terminal-deployments. In particular, we analyze the normalized capacity $\bar{\mathcal{C}}$, measured in nats/s/Hz/m$^2$, under the constraint that the transmit power per m$^2$, $\bar{P}$, is fixed. We show that when the user-density increases, the limit of $\bar{\mathcal{C}}$, achieved as the wavelength $\lambda$ approaches 0, is $\bar{P}/(2N_0)$ nats/s/Hz/m$^2$, where $N_0$ is the spatial power spectral density (PSD) of noise. In addition, we also show that the number of signal dimensions is $2/\lambda$ per meter deployed surface for the one-dimensional case, and $\pi/\lambda^2$ per m$^2$ deployed surface for two and three dimensional terminal-deployments.http://lup.lub.lu.se/record/61d4e6ec-7895-43b4-9ba5-6b83e16704f2http://dx.doi.org/10.1109/VTCSpring.2017.8108330ISBN: 978-1-5090-5932-4 scopus:85040542986engKommunikationssystemThe Potential of Using Large Antenna Arrays on Intelligent Surfacescontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextA Simulation Framework for Multiple-Antenna Terminals in 5G Massive MIMO Systems
https://lup.lub.lu.se/search/publication/8f74d937-6bd6-4962-8010-8ad221184dbb
Bengtsson, Erik L.Rusek, FredrikMalkowsky, SteffenTufvesson, FredrikKarlsson, Peter C.Edfors, Ove2017-11-18The 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&#x2019;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.http://lup.lub.lu.se/record/8f74d937-6bd6-4962-8010-8ad221184dbbhttp://dx.doi.org/10.1109/ACCESS.2017.2775210scopus:85035793841engIEEE Access; 5, pp 26819-26831 (2017)ISSN: 2169-3536Kommunikationssystem5GAntenna measurementschannel modelChannel modelsDirective antennasDiversitymassive MIMOMIMONRpilot signalReceiving antennasSRSterminal antennatransmission schemeTransmitting antennasA Simulation Framework for Multiple-Antenna Terminals in 5G Massive MIMO Systemscontributiontojournal/articleinfo:eu-repo/semantics/articletextBeyond Massive-MIMO : The Potential of Data-Transmission with Large Intelligent Surfaces
https://lup.lub.lu.se/search/publication/552776ea-89af-4ec4-953d-a0d9716117ad
Hu, ShaRusek, FredrikEdfors, Ove2018-05-15In this paper, we consider the potential of data-transmission in a system with a massive number of radiating and sensing elements, thought of as a contiguous surface of electromagnetically active material. We refer to this as a Large Intelligent Surface (LIS). The "LIS" is a newly proposed concept, which conceptually goes beyond contemporary massive MIMO technology, and arises from our vision of a future where man-made structures are electronically active with integrated electronics and wireless communication making the entire environment "intelligent". Firstly, we consider capacities of single-antenna autonomous terminals communicating to the LIS where the entire surface is used as a receiving antenna-array in a perfect line-of-sight (LOS) propagation environment. Under the condition that the surface-area is sufficiently large, the received signal after a matched-filtering (MF) operation can be closely approximated by a sinc-function-like intersymbol interference (ISI) channel. Secondly, we analyze a normalized capacity measured per unit-surface, for a fixed transmit power per volume-unit with different terminal-deployments. As terminal-density increases, the limit of the normalized capacity [nats/s/Hz/volume-unit] achieved when wavelength <formula><tex>$\lambda$</tex></formula> approaches zero is equal to half of the transmit power per volume-unit divided by noise spatial power spectral density (PSD). Thirdly, we show that the number of independent signal dimensions that can be harvested per meter deployed surface is <formula><tex>$2/\lambda$</tex></formula> for one-dimensional terminal-deployment, and <formula><tex>$\pi/\lambda^{2}$</tex></formula> per square meter for two and three dimensional terminal-deployments. Lastly, we consider implementations of the LIS in the form of a grid of conventional antenna-elements, and show that the sampling lattice that minimizes the surface-area and simultaneously obtains one independent signal dimension for every spent antenna is the hexagonal lattice.http://lup.lub.lu.se/record/552776ea-89af-4ec4-953d-a0d9716117adhttp://dx.doi.org/10.1109/TSP.2018.2816577scopus:85044028460engIEEE Transactions on Signal Processing; 66(10), pp 2746-2758 (2018)ISSN: 1053-587XKommunikationssystem2D samplingHankel transformhexagonal latticeindependent signal dimensionintersymbol interference (ISI)Large intelligent surface (LIS)LatticesLensesline-of-sight (LOS)massive multiinput multi-output (MIMO)MIMO communicationnormalized capacityReceiving antennasSurface treatmentSurface wavesBeyond Massive-MIMO : The Potential of Data-Transmission with Large Intelligent Surfacescontributiontojournal/articleinfo:eu-repo/semantics/articletextBeyond Massive MIMO: The Potential of Positioning with Large Intelligent Surfaces
https://lup.lub.lu.se/search/publication/2b8a8240-0f1a-4ef2-8828-46b70b2627f8
Hu, ShaRusek, FredrikEdfors, Ove2018-04-01We consider the potential for positioning with a system where antenna arrays are deployed as a large intelligent surface (LIS), which is a newly proposed concept beyond massive multi-input multi-output (MIMO) where future man-made structures are electronically active with integrated electronics and wireless communication making the entire environment "intelligent". In a first step, we derive Fisher-information matrix (FIM) and Cramer-Rao lower bound (CRLB) in closed-form for positioning a terminal located perpendicular to the center of the LIS, whose location we refer to as being on the central perpendicular line (CPL) of the LIS. For a terminal that is not on the CPL, closed-form expressions of the FIM and CRLB seem out of reach, and we alternatively find approximations which are shown to be accurate. Under mild conditions, we show that the CRLB for all three Cartesian dimensions ($x$, $y$ and $z$) decreases quadratically in the surface-area of the LIS, except for a terminal exactly on the CPL where the CRLB for the $z$-dimension (distance from the LIS) decreases linearly in the same. In a second step, we analyze the CRLB for positioning when there is an unknown phase $\varphi$ presented in the analog circuits of the LIS. We then show that the CRLBs are dramatically {\color{red}degraded} for all three dimensions but decrease in the third-order of the surface-area. Moreover, with an infinitely large LIS the CRLB for the $z$-dimension with an unknown $\varphi$ is 6 dB higher than the case without phase uncertainty, and the CRLB for estimating $\varphi$ converges to a constant that is independent of the wavelength $\lambda$. At last, we extensively discuss the impact of centralized and distributed deployments of LIS, and show that a distributed deployment of LIS can enlarge the coverage for positioning and improve the overall performance.http://lup.lub.lu.se/record/2b8a8240-0f1a-4ef2-8828-46b70b2627f8http://dx.doi.org/10.1109/TSP.2018.2795547scopus:85040932814engIEEE Transactions on Signal Processing; 66(7), pp 1761-1774 (2018)ISSN: 1053-587XKommunikationssystemBeyond Massive MIMO: The Potential of Positioning with Large Intelligent Surfacescontributiontojournal/articleinfo:eu-repo/semantics/articletextImproving the Performance of OTDOA based Positioning in NB-IoT Systems
https://lup.lub.lu.se/search/publication/8240e864-8fee-4917-ab43-75c59bff90e9
Hu, ShaBerg, AxelLi, XuhongRusek, Fredrik2018In this paper, we consider positioning with observed-time-difference-of-arrival (OTDOA) for a device deployed in long-term-evolution (LTE) based narrow-band Internet-of-things (NB-IoT) systems. We propose an iterative expectation- maximization based successive interference cancellation (EM-SIC) algorithm to jointly consider estimations of residual frequency- offset (FO), fading-channel taps and time-of- arrival (ToA) of the first arrival-path for each of the detected cells. In order to design a low complexity ToA detector and also due to the limits of low-cost analog circuits, we assume an NB-IoT device working at a low-sampling rate such as 1.92 MHz or lower. The proposed EM-SIC algorithm comprises two stages to detect ToA, based on which OTDOA can be calculated. In a first stage, after running the EM-SIC block a predefined number of iterations, a coarse ToA is estimated for each of the detected cells. Then in a second stage, to improve the ToA resolution, a low-pass filter is utilized to interpolate the correlations of time-domain PRS signal evaluated at a low sampling-rate to a high sampling-rate such as 30.72 MHz. To keep low-complexity, only the correlations inside a small search window centered at the coarse ToA estimates are upsampled. Then, the refined ToAs are estimated based on upsampled correlations. If at least three cells are detected, with OTDOA and the locations of detected cell sites, the position of the NB-IoT device can be estimated. We show through numerical simulations that, the proposed EM-SIC based ToA detector is robust against impairments introduced by inter-cell interference, fading-channel and residual FO. Thus significant signal-to-noise (SNR) gains are obtained over traditional ToA detectors that do not consider these impairments when positioning a device.http://lup.lub.lu.se/record/8240e864-8fee-4917-ab43-75c59bff90e9http://dx.doi.org/10.1109/GLOCOM.2017.8254510scopus:85046373371engKommunikationssystemImproving the Performance of OTDOA based Positioning in NB-IoT Systemscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextCramer-Rao Lower Bounds for Positioning with Large Intelligent Surfaces
https://lup.lub.lu.se/search/publication/22d6df59-efbe-41df-8f42-31835607d73c
Hu, ShaRusek, FredrikEdfors, Ove2018-02-12We consider the potential for positioning with a system where antenna arrays are deployed as a large intelligent surface (LIS). We derive Fisher-informations and Cram\'{e}r-Rao lower bounds (CRLB) in closed-form for terminals along the central perpendicular line (CPL) of the LIS for all three Cartesian dimensions. For terminals at positions other than the CPL, closed-form expressions for the Fisher-informations and CRLBs seem out of reach, and we alternatively provide approximations (in closed-form) which are shown to be very accurate. We also show that under mild conditions, the CRLBs in general decrease quadratically in the surface-area for both the x and y dimensions. For the z-dimension (distance from the LIS), the CRLB decreases linearly in the surface-area when terminals are along the CPL. However, when terminals move away from the CPL, the CRLB is dramatically increased and then also decreases quadratically in the surface-area. We also extensively discuss the impact of different deployments (centralized and distributed) of the LIS.http://lup.lub.lu.se/record/22d6df59-efbe-41df-8f42-31835607d73chttp://dx.doi.org/10.1109/VTCFall.2017.8288263scopus:85045284667engKommunikationssystemCramer-Rao Lower Bounds for Positioning with Large Intelligent Surfacescontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextTransmission schemes for Multiple Antenna Terminals in Real Massive MIMO systems
https://lup.lub.lu.se/search/publication/6daa2654-3111-448d-be8b-30f0ee3bc2f3
Bengtsson, Erik Lkarlsson, Peter C.Tufvesson, FredrikVieira, JoaoMalkowsky, SteffenLiu, LiangRusek, FredrikEdfors, Ove2016-12-13In 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&#126;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.http://lup.lub.lu.se/record/6daa2654-3111-448d-be8b-30f0ee3bc2f3http://dx.doi.org/10.1109/GLOCOM.2016.7842355ISBN: 978-1-5090-1328-9 ISBN: 978-1-5090-1329-6 scopus:85015444185engKommunikationssystemTransmission schemes for Multiple Antenna Terminals in Real Massive MIMO systemscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextA Soft-Output MIMO Detector with Achievable Information Rate based Partial Marginalization
https://lup.lub.lu.se/search/publication/4a1a9cd3-578e-44c8-b184-55bb1afc0caa
Hu, ShaRusek, Fredrik2017-03-15In this paper, we propose a soft-output detector for multiple-input multiple-output (MIMO) channels that utilizes achievable information rate (AIR) based partial marginalization (PM). The proposed AIR based PM (AIR-PM) detector has superior performance compared to previously proposed PM designs and other soft-output detectors such as K-best, while at the same time yielding lower computational complexity, a detection latency that is independent of the number of transmit layers, and straightforward inclusion of soft input information. Using a tree representation of the MIMO signal, the key property of the AIRPM is that the connections among all child layers are broken. Therefore, least-square (LS) estimates used for marginalization are obtained independently and in parallel, which have better quality than the zero-forcing decision feedback (ZF-DF) estimates used in previous PM designs. Such a property of the AIRPM detector is designed via a mismatched detection model that maximizes the AIR. Furthermore, we show that the chain rule holds for the AIR calculation, which facilitates an information theoretic characterization of the AIR-PM detector.http://lup.lub.lu.se/record/4a1a9cd3-578e-44c8-b184-55bb1afc0caahttp://dx.doi.org/10.1109/TSP.2016.2641393scopus:85014949602wos:000395423500019engIEEE Transactions on Signal Processing; 65(6), pp 1622-1627 (2017)ISSN: 1053-587XSignalbehandlingA Soft-Output MIMO Detector with Achievable Information Rate based Partial Marginalizationcontributiontojournal/articleinfo:eu-repo/semantics/articletextComparison of two channel shortening approaches for MIMO-ISI channels
https://lup.lub.lu.se/search/publication/aad27d72-b2dd-45be-839f-902328cd4cfe
Hu, ShaRusek, FredrikAl-Dhahir, Naofal2016-09-12We consider a multiple-input multiple-output (MIMO) channel with inter-symbol interference (ISI) where signal detection is highly complex due to the large signal state-space dimensionality. A common strategy is to apply a front-end filter (FEF) to eliminate the ISI dimension (i.e. full ISI equalization). This FEF is then followed by a frequency non-selective MIMO detector. However, another, much less researched, strategy is to apply an FEF that eliminates the MIMO dimension and results in a set of parallel ISI channels followed by a bank of parallel single-input single-output (SISO) detectors. Which of the two strategies is better in a Shannon capacity sense? In this paper, we show that the answer to this question depends on system parameters such as SNR, number of antennas, ISI duration, and spatial correlation properties.http://lup.lub.lu.se/record/aad27d72-b2dd-45be-839f-902328cd4cfehttp://dx.doi.org/10.1109/WCNC.2016.7564884ISBN: 978-1-4673-9814-5ISBN: 978-1-4673-9815-2scopus:84989919673engTelekommunikationComparison of two channel shortening approaches for MIMO-ISI channelscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextExploiting antenna correlation in measured massive MIMO channels
https://lup.lub.lu.se/search/publication/68f66d39-8a88-4351-a8be-8480a10c1365
Flordelis, JoseHu, ShaRusek, FredrikEdfors, OveDahman, GhassanGao, XiangTufvesson, Fredrik2016-12-21We investigate antenna correlation of an M-antenna massive multiple-input multiple-output (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. Our 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 timespan, 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 domains 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.application/pdfhttp://lup.lub.lu.se/record/68f66d39-8a88-4351-a8be-8480a10c1365http://dx.doi.org/10.1109/PIMRC.2016.7794664ISBN: 9781509032549http://lup.lub.lu.se/search/ws/files/11792298/paper.pdfscopus:85010032081enginfo:eu-repo/semantics/openAccessTelekommunikationExploiting antenna correlation in measured massive MIMO channelscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextOn the Design of Reduced State Demodulators with Interference Cancellation for Iterative Receivers
https://lup.lub.lu.se/search/publication/7b5c1a1f-79d4-4555-851a-100f5a3f2b0d
Hu, ShaRusek, Fredrik2015-09We consider the problem of designing demodulators for channels with memory that use reduced-size trellis descriptions for the received signal. We assume an overall iterative receiver, and for the parts of the signal not covered by the trellis description, we use interference cancellation based on the soft information provided by the outer decoder. In order to reach a trellis description, a linear filter is applied as front-end to compress the signal structure into a small trellis. This process requires three parameters to be designed: (i) the front-end filter, (ii) the feedback filter through which the interference cancellation is done, and (iii) a target response which specifies the trellis. While (i) and (ii) can be found in closed form, a numerical search is required for (iii). The numerical search is, however, very efficient and stable. Demodulators of this form have been studied before under the name channel shortening (CS), but the interplay between CS and interference cancellation has not been adequately addressed in the literature.http://lup.lub.lu.se/record/7448311http://dx.doi.org/10.1109/PIMRC.2015.7343440scopus:84958044523engElektroteknik och elektronikOn the Design of Reduced State Demodulators with Interference Cancellation for Iterative Receiverscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextA Low-complexity Channel Shortening Receiver with Diversity Support for Evolved 2G Devices
https://lup.lub.lu.se/search/publication/6c675ec1-9da6-4896-b351-074cfcfe6cf8
Hu, ShaKröll, HaraldHuang, QiutingRusek, Fredrik2016-05The second generation (2G) cellular networks are the current workhorse for machine-to-machine (M2M) communications. Diversity in 2G devices can be present both in form of multiple receive branches and blind repetitions. In presence of diversity, intersymbol interference (ISI) equalization and co-channel interference (CCI) suppression are usually very complex. In this paper, we consider the improvements for 2G devices with receive diversity. We derive a low-complexity receiver based on a channel shortening filter, which allows to sum up all diversity branches to a single stream after filtering while keeping the full diversity gain. The summed up stream is subsequently processed by a single stream Max-log-MAP (MLM) equalizer. The channel shortening filter is designed to maximize the mutual information lower bound (MILB) with the Ungerboeck detection model. Its filter coefficients can be obtained mainly by means of discrete-Fourier transforms (DFTs). Compared with the state-of-art homomorphic (HOM) filtering based channel shortener which cooperates with a delayed-decision feedback MLM (DDF-MLM) equalizer, the proposed MILB channel shortener has superior performance. Moreover, the equalization complexity, in terms of real-valued multiplications, is decreased by a factor that equals the number of diversity branches.http://lup.lub.lu.se/record/6c675ec1-9da6-4896-b351-074cfcfe6cf8http://dx.doi.org/10.1109/ICC.2016.7511498scopus:84981335378engTelekommunikationA Low-complexity Channel Shortening Receiver with Diversity Support for Evolved 2G Devicescontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextReciprocity Calibration for Massive MIMO: Proposal, Modeling and Validation
https://lup.lub.lu.se/search/publication/7f9779c0-1634-4c58-928f-efe16178911a
Vieira, JoaoRusek, FredrikEdfors, OveMalkowsky, SteffenLiu, LiangTufvesson, Fredrik2017-03-17This paper presents a mutual coupling based calibration method for time-division-duplex massive MIMO systems, which enables downlink precoding based on uplink channel estimates. The entire calibration procedure is carried out solely at the base station (BS) side by sounding all BS antenna pairs. An Expectation-Maximization (EM) algorithm is derived, which processes the measured channels in order to estimate calibration coefficients. The EM algorithm outperforms current state-of-the-art narrow-band calibration schemes in a mean squared error (MSE) and sum-rate capacity sense. Like its predecessors, the EM algorithm is general in the sense that it is not only suitable to calibrate a co-located massive MIMO BS, but also very suitable for calibrating multiple BSs in distributed MIMO systems. The proposed method is validated with experimental evidence obtained from a massive MIMO testbed. In addition, we address the estimated narrow-band calibration coefficients as a stochastic process across frequency, and study the subspace of this process based on measurement data. With the insights of this study, we propose an estimator which exploits the structure of the process in order to reduce the calibration error across frequency. A model for the calibration error is also proposed based on the asymptotic properties of the estimator, and is validated with measurement results.application/pdfhttp://lup.lub.lu.se/record/7f9779c0-1634-4c58-928f-efe16178911ahttp://dx.doi.org/10.1109/TWC.2017.2674659http://lup.lub.lu.se/search/ws/files/25556784/FINAL_VERSION.pdfscopus:85027885273wos:000401083800024enginfo:eu-repo/semantics/openAccessIEEE Transactions on Wireless Communications; 16(5), pp 3042-3056 (2017)ISSN: 1536-1276TelekommunikationMassive MIMOreciprocity calibrationmutual couplingexpectation maximizationvalidationReciprocity Calibration for Massive MIMO: Proposal, Modeling and Validationcontributiontojournal/articleinfo:eu-repo/semantics/articletextAn information theoretic characterization of channel shortening receivers
https://lup.lub.lu.se/search/publication/82de250a-db85-430b-8b25-60366169a36a
Rusek, FredrikEdfors, Ove2016-04-01Optimal data detection of data transmitted over a linear channel can always be implemented through the Viterbi algorithm (VA). However, in many cases of interest the memory of the channel prohibits direct application of the VA. A popular and conceptually simple method in this case, studied since the early 1970s, is to first filter the received signal in order to shorten the memory of the channel, and then to apply a VA that operates with the shorter memory. We shall refer to this general concept as a channel shortening (CS) receiver. Although studied for almost four decades, an information theoretic understanding of what such a simple receiver solution is actually doing is not available. In this paper, we show that an optimized CS receiver has a direct correspondance to the chain rule of mutual information. Furthermore, we show that the tools for analyzing the ensuing achievable rates from an optimized CS receiver are precisely the same as those used for analyzing the achievable rates of a minimum mean-square-error (MMSE) receiver.http://lup.lub.lu.se/record/82de250a-db85-430b-8b25-60366169a36ahttp://dx.doi.org/10.1109/TCOMM.2016.2536664scopus:84964355109wos:000375032400011engIEEE Transactions on Communications; 64(4), pp 1490-1502 (2016)ISSN: 0090-6778Elektroteknik och elektronikChannel shortening detectionMismatched mutual informationMismatched receiversReceiver designReduced complexity detectionAn information theoretic characterization of channel shortening receiverscontributiontojournal/articleinfo:eu-repo/semantics/articletextLower bounds on the information rate of intersymbol interference channels based on the Ungerboeck observation model
https://lup.lub.lu.se/search/publication/e049b5be-b089-4e9a-9e8d-d0ec79e34d20
Rusek, FredrikFertonani, Dario2009We consider the problem of lower bounding the information rate of intersymbol interference channels via Monte Carlo algorithms.
We adopt a novel approach based on the Ungerboeck observation model, unlike the existing ones that are all based on the Forney model.
The two approaches, yet equivalent in the case of full-complexity detection, lead to different results in the case of reduced-complexity detection, which is the only viable option when the channel memory is large.
In particular, the proposed approach significantly outperforms the existing ones at low-to-medium values of the signal-to-noise ratio.http://lup.lub.lu.se/record/1277678wos:000280141401042scopus:70449476546engElektroteknik och elektronikIntersymbol InterferenceShannon CapacityLower bounds on the information rate of intersymbol interference channels based on the Ungerboeck observation modelcontributiontoconference/paperinfo:eu-repo/semantics/conferenceObjecttextReciprocity calibration methods for Massive MIMO based on antenna coupling
https://lup.lub.lu.se/search/publication/ac41dfe7-32bf-4458-931d-9a4368d5e66f
Vieira, JoaoRusek, FredrikTufvesson, Fredrik2014In this paper we consider time-division-duplex (TDD) reciprocity calibration of a massive MIMO system. The calibration of a massive MIMO system can be done entirely at the base station (BS) side by sounding the BS antennas one-by-one while receiving with the other BS antennas. With an M antenna BS, this generates M(M - 1) signals that can be used for calibration purposes. In this paper we study several least-squares (LS) based estimators, differing in the number of received signals that are being used. We compare the performance of the estimators, and we conclude that is possible to accurately calibrate an entire BS antenna array using the mutual coupling
between antennas as the main propagation mechanism.application/pdfhttp://lup.lub.lu.se/record/4857515http://lup.lub.lu.se/search/ws/files/6137947/4857516.pdfscopus:84949923280enginfo:eu-repo/semantics/openAccessElektroteknik och elektronikMassive MIMOTDD reciprocityantenna calibrationestimationReciprocity calibration methods for Massive MIMO based on antenna couplingcontributiontoconference/paperinfo:eu-repo/semantics/conferenceObjecttextA first encounter with faster-than-Nyquist signaling on the MIMO channel
https://lup.lub.lu.se/search/publication/bd2bee8d-f6c0-4329-ac9d-5cc1c37be5d5
Rusek, Fredrik2007In this paper we investigate MIMO systems where faster-than-Nyquist (FTN) signaling is used as modulation. On the AWGN channel, the main characteristic of FTN is the so called Mazo limit; it is possible to signal considerably faster than conventional without loss in minimum Euclidean distance. We show that MIMO-FTN systems inherit this property from the AWGN-FTN systems. Moreover, not only does it exist a Mazo limit in MIMO, but it occurs at exactly the same signaling rate as for the AWGN channel. We also discuss information rates of MIMO-FTN systems.http://lup.lub.lu.se/record/643466http://dx.doi.org/10.1109/WCNC.2007.207wos:000252337102020scopus:36348962882engElektroteknik och elektronikfaster-than-Nyquist signalingMIMO-FTN systemsMIMO channelMazo limitAWGN channelAWGN-FTN systemsA first encounter with faster-than-Nyquist signaling on the MIMO channelcontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextSpatial Separation of Closely-Spaced Users in Measured Massive Multi-User MIMO Channels
https://lup.lub.lu.se/search/publication/c2853508-a976-4cb8-b25d-1f37ad514e86
Flordelis, JoseGao, XiangDahman, GhassanRusek, FredrikEdfors, OveTufvesson, Fredrik2015Fully-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.application/pdfhttp://lup.lub.lu.se/record/5154187http://lup.lub.lu.se/search/ws/files/5990411/5154208.pdfscopus:84953717299enginfo:eu-repo/semantics/openAccessElektroteknik och elektronikmulti-user multiple-input multiple-output systemsMU-MIMOmassive MIMOlarge-scale MIMOMIMO channel measurementsspatial separationsingular value spreadsum-rate capacitysum-ratelinear precoderSpatial Separation of Closely-Spaced Users in Measured Massive Multi-User MIMO Channelscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextOn information rates for faster than Nyquist signaling
https://lup.lub.lu.se/search/publication/ddc5e077-b3bd-4ffb-bf76-3d86a365562c
Rusek, FredrikAnderson, John B2006In this paper we consider the information rates of faster than Nyquist (FTN) signaling schemes. We consider binary, quaternary and octal schemes that use root raised cosine pulses. Lower and upper bounds to the information rates are given. The main result is that the lower bounds are often above the information rates for standard Nyquist signaling schemes. This implies that FTN must be superior to Nyquist signaling in some cases. Test results for one coding scheme are given; these show that high throughput communication based on FTN is indeed practical.application/pdfhttp://lup.lub.lu.se/record/643391http://dx.doi.org/10.1109/GLOCOM.2006.52http://lup.lub.lu.se/search/ws/files/5943219/695070.pdfscopus:50949111787enginfo:eu-repo/semantics/openAccessElektroteknik och elektronikChannel capacityInformation ratesFaster than Nyquist signalingOn information rates for faster than Nyquist signalingcontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextA low-complex peak-to-average power reduction scheme for OFDM based massive MIMO systems
https://lup.lub.lu.se/search/publication/eb4cd13c-a0cb-4fcf-a86d-ae33a4c40b56
Prabhu, HemanthEdfors, OveRodrigues, JoachimLiu, LiangRusek, Fredrik2014An Orthogonal Frequency-Division Multiplexing (OFDM) based multi-user massive Multiple-Input Multiple-Output (MIMO) system is considered. The problem of high Peak-to-Average Ratio (PAR) in OFDM based systems is well known and the large number of antennas (RF-chains) at the Base Station (BS) in massive MIMO systems aggravates this further, since large numbers of these Power Amplifiers (PAs) are used. High PAR necessitates linear PAs, which have a high hardware cost and are typically power inefficient. In this paper we propose a low-complex approach to tackle the issue. The idea is to deliberately clip signals sent to one set of antennas, while compensating for this by transmitting correction signals on a set of reserved antennas (antenna-reservation). A reduction of 4 dB in PAR is achieved by reserving 25% of antennas, with only a 15% complexity overhead.application/pdfhttp://lup.lub.lu.se/record/4332152http://lup.lub.lu.se/search/ws/files/5684734/5364201.pdfwos:000346443500029scopus:84906732304enginfo:eu-repo/semantics/openAccessElektroteknik och elektronikpre-codingMassive MIMOPAR awareA low-complex peak-to-average power reduction scheme for OFDM based massive MIMO systemscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextOn decision depths for partial response codes
https://lup.lub.lu.se/search/publication/8f4b881d-db62-4aa7-94ba-2f097ab09b12
Rusek, FredrikAnderson, John B2005The decision depth for finite and infinite partial response signaling (PRS) schemes is investigated. New measures are proposed that take into account error event multiplicity. We conclude that small to moderate decoder decision depths achieve performance near MLSE even for near catastrophic codes. Under some constraints, the decision depth should be an increasing function of the signal to noise ratioapplication/postscripthttp://lup.lub.lu.se/record/615443http://dx.doi.org/10.1109/ICC.2005.1494420ISBN: 0-7803-8938-7http://lup.lub.lu.se/search/ws/files/5613637/637424.pswos:000231726400111scopus:24344499871enginfo:eu-repo/semantics/openAccessElektroteknik och elektronikerror event multiplicitydecoder decision depthsnear catastrophic codespartial response codesinfinite partial response signalingtrellis codesOn decision depths for partial response codescontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextHigh Order Modulation in Faster-than-Nyquist Signaling Communication Systems
https://lup.lub.lu.se/search/publication/88f74d29-6144-4897-a1ec-5b92d2d27b98
Yu, JungpilPark, JoosungRusek, FredrikKudryashov, BorisBocharova, Irina2014http://lup.lub.lu.se/record/4647444wos:000353345400198scopus:84919459025engElektroteknik och elektronikHigh Order Modulation in Faster-than-Nyquist Signaling Communication Systemscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextMutual Information of IID complex Gaussian signals on block Rayleigh-faded channels
https://lup.lub.lu.se/search/publication/470ddda1-2402-45c6-8a70-9e4c29478e0c
Rusek, FredrikLozano, AngelJindal, Nihar2010We present a method to compute, quickly and efficiently, the mutual information achieved by an IID (independent identically distributed) complex Gaussian input
on a block Rayleigh-faded channel. The method accommodates both scalar and MIMO (multiple-input multiple-output) settings.
Operationally, the mutual information thus computed represents the highest spectral efficiency that can be attained using standard Gaussian codebooks.
Examples are provided that
illustrate the loss in spectral efficiency caused by fast fading and how that loss is amplified by the use of multiple transmit antennas.
These examples are further enriched by comparisons with the channel capacity under perfect channel-state information at the receiver, and with the spectral
efficiency attained by pilot-based transmission.http://lup.lub.lu.se/record/1527943http://dx.doi.org/10.1109/ISIT.2010.5513329ISBN: 978-1-4244-6960-4wos:000287512700061scopus:77955701511engElektroteknik och elektronikwireless communicationsMIMOmutual informationNon coherentGaussian signalingMutual Information of IID complex Gaussian signals on block Rayleigh-faded channelscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextApproximative Matrix Inverse Computations for Very-large MIMO and Applications to Linear Pre-coding Systems
https://lup.lub.lu.se/search/publication/8fe68d84-fc23-4970-89ae-0bae28eef268
Prabhu, HemanthRodrigues, JoachimEdfors, OveRusek, Fredrik2013In very-large multiple-input multiple-output (MIMO) systems, the BS (base station) is equipped with very large number of antennas as compared to previously considered systems. There are various advantages of increasing the number of antennas, and some schemes would require handling large
matrices for joint processing (pre-coding) at the base station. The dirty paper coding (DPC) is an optimal pre-coding scheme and has a very high complexity. However with increasing number of BS antennas linear pre-coding performance tends
to that of the optimal DPC. Although linear pre-coding is less complex than DPC, there is a need to compute pseudo inverses of large matrices. In this paper we present a low complexity approximation of down-link Zero Forcing linear pre-coding for very-large multi-user MIMO systems. Approximation using a Neumann series expansion is opted for inversion of matrices over traditional exact computations, by making use of special properties of the matrices, thereby reducing the cost of hardware. With this approximation of linear pre-coding,
we can significantly reduce the computational complexity for large enough systems, i.e., where we have enough BS antenna elements. For the investigated case of 8 users, we obtain 90% of the full ZF sum rate, with lower computational complexity, when the number of BS antennas per user is about 20 or more.application/pdfhttp://lup.lub.lu.se/record/3288141http://lup.lub.lu.se/search/ws/files/5498921/5364198.pdfwos:000326048102137scopus:84881564216enginfo:eu-repo/semantics/openAccessElektroteknik och elektroniklinear precodingmassive mimomatrix inverse approximationApproximative Matrix Inverse Computations for Very-large MIMO and Applications to Linear Pre-coding Systemscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextLinear pre-coding performance in measured very-large MIMO channels
https://lup.lub.lu.se/search/publication/88f20b8a-3aa5-4e76-a9c2-9a8fa7bca97c
Gao, XiangEdfors, OveRusek, FredrikTufvesson, Fredrik2011Wireless 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. In theory, as the number of antennas increases, propagation properties that were random before start to become deterministic. Theoretical investigations with independent identically distributed (i.i.d.)\ complex Gaussian (Rayleigh fading) channels and unlimited number of antennas have been done, but in practice we need to know what benefits we can get from very large, but limited, number of antenna elements in realistic propagation environments. In this study we evaluate properties of measured residential-area channels, where the base station is equipped with 128 antenna ports. An important property to consider is the orthogonality between channels to different users, since this property tells us how advanced multi-user MIMO (MU-MIMO) pre-coding schemes we need in the downlink. We show that orthogonality improves with increasing number of antennas, but for two single-antenna users there is very little improvement beyond 20 antennas. We also evaluate sum-rate performance for two linear pre-coding schemes, zero-forcing (ZF) and minimum mean squared-error (MMSE), as a function of the number of base station antennas. Already at 20 base station antennas these linear pre-coding schemes reach 98\% of the optimal dirty-paper coding (DPC) capacity for the measured channels.application/pdfhttp://lup.lub.lu.se/record/2199294http://lup.lub.lu.se/search/ws/files/5499580/2541120.pdfwos:000298891500479scopus:83755161752enginfo:eu-repo/semantics/openAccessElektroteknik och elektronikLinear pre-coding performance in measured very-large MIMO channelscontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextLarge antenna array and propagation environment interaction
https://lup.lub.lu.se/search/publication/8728cebb-8b80-4de9-b5ed-5a1c599e9dc9
Gao, XiangZhu, MeifangRusek, FredrikTufvesson, FredrikEdfors, Ove2014In conventional MIMO, propagation conditions are often considered wide-sense stationary over the entire antenna array. In massive MIMO systems, where arrays can span over large physical dimensions, the situation is quite different. For instance, significant variations in signal strength, due to shadowing, can be experienced across a large array. These effects vary with propagation environment in which the array is placed, and influence achievable sum-rates. We characterize these variations for several measured propagation scenarios in the 2.6 GHz frequency range and illustrate how power variations and correlation properties change along the array.application/pdfhttp://lup.lub.lu.se/record/5114759http://dx.doi.org/10.1109/ACSSC.2014.7094530ISBN: 978-147998297-4http://lup.lub.lu.se/search/ws/files/5499730/5114788.pdfscopus:84940532768enginfo:eu-repo/semantics/openAccessElektroteknik och elektronikmassive MIMOchannel measurementsspatial correlationKronecker modelToeplitz structuresum-rateLarge antenna array and propagation environment interactioncontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextA Comparison of Ungerboeck and Forney Models for Reduced-Complexity ISI Equalization
https://lup.lub.lu.se/search/publication/b3ad9da5-c5ee-4dac-b4b1-2254b0226ca1
Rusek, FredrikLoncar, MajaPrlja, Adnan2007This paper investigates the performance of reduced-state
trellis-based intersymbol interference equalizers, which are based
on the so-called Ungerboeck and Forney observation models.
Although the two models are equivalent when an optimum equalizer
is employed, their performances differ significantly when using
reduced-complexity methods. It is demonstrated that practical
equalizers operating on the Forney model outperform those
operating on the Ungerboeck model for high signal-to-noise ratios
(SNRs), while the situation is reversed for low SNR levels. A
novel reduced-complexity equalization strategy that improves on
previous Ungerboeck-based equalizers is proposed.application/pdfhttp://lup.lub.lu.se/record/1048951http://dx.doi.org/10.1109/GLOCOM.2007.275ISBN: 978-1-4244-1043-9http://lup.lub.lu.se/search/ws/files/4822294/1048953.pdfwos:000257505701079scopus:39349118061enginfo:eu-repo/semantics/openAccesspp 1431-1436 (2007)ISSN: 1930-529XElektroteknik och elektronikA Comparison of Ungerboeck and Forney Models for Reduced-Complexity ISI Equalizationcontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextScaling up MIMO: opportunities and challenges with very large arrays
https://lup.lub.lu.se/search/publication/a897be1f-e44f-466d-bbdc-ed11cc9cb14d
Rusek, FredrikPersson, DanielLau, Buon KiongLarsson, Erik G.Marzetta, Thomas L.Edfors, OveTufvesson, Fredrik2013application/pdfhttp://lup.lub.lu.se/record/2174140http://dx.doi.org/10.1109/MSP.2011.2178495http://lup.lub.lu.se/search/ws/files/4313105/5323005.pdfwos:000315349700006scopus:85032752174enginfo:eu-repo/semantics/openAccessIEEE Signal Processing Magazine; 30(1), pp 40-60 (2013)ISSN: 1053-5888Elektroteknik och elektronikScaling up MIMO: opportunities and challenges with very large arrayscontributiontojournal/articleinfo:eu-repo/semantics/articletextModulation Formats and Waveforms for 5G Networks: Who Will Be the Heir of OFDM? [An overview of alternative modulation schemes for improved spectral efficiency]
https://lup.lub.lu.se/search/publication/704de9b1-600d-4a65-8910-1fd2f24a07a4
Banelli, PaoloBuzzi, StefanoColavolpe, GiulioModenini, AndreaRusek, FredrikUgolini, Alessandro2014http://lup.lub.lu.se/record/4960550http://dx.doi.org/10.1109/MSP.2014.2337391wos:000346043700012scopus:85032751906engIEEE Signal Processing Magazine; 31(6), pp 80-93 (2014)ISSN: 1053-5888Elektroteknik och elektronikModulation Formats and Waveforms for 5G Networks: Who Will Be the Heir of OFDM? [An overview of alternative modulation schemes for improved spectral efficiency]contributiontojournal/articleinfo:eu-repo/semantics/articletextPhysical Layer Security for Massive MIMO: An Overview on Passive Eavesdropping and Active Attacks
https://lup.lub.lu.se/search/publication/226ab1aa-bc4e-4e73-a9e0-78c7f1c0e327
Kapetanovic, DzevdanZheng, GanRusek, Fredrik2015This article discusses opportunities and challenges of physical layer security integration in MaMIMO systems. Specifically, we first show that MaMIMO itself is robust against passive eavesdropping attacks. We then review a pilot contamination scheme that actively attacks the channel estimation process. This pilot contamination attack not only dramatically reduces the achievable secrecy capacity but is also difficult to detect. We proceed by reviewing some methods from literature that detect active attacks on MaMIMO. The last part of the article surveys the open research problems that we believe are the most important to address in the future and give a few promising directions of research to solve them.http://lup.lub.lu.se/record/7605082wos:000356157000004scopus:84933037312engIEEE Communications Magazine; 53(6), pp 21-27 (2015)ISSN: 0163-6804Elektroteknik och elektronikPhysical Layer Security for Massive MIMO: An Overview on Passive Eavesdropping and Active Attackscontributiontojournal/articleinfo:eu-repo/semantics/articletextChannel Shortening for Nonlinear Satellite Channels
https://lup.lub.lu.se/search/publication/4c4efaca-8a18-43ec-aa32-77acc0e49a77
Colavolpe, GiulioModenini, AndreaRusek, Fredrik2012We design of an efficient channel shortener for nonlinear satellite channels. When the memory of the channel is too large to be taken into account by a full complexity detector, excellent performance can be achieved by properly filtering the received signal followed by a reduced-state detector. This letter derives closed-form expressions for the front-end filter and the target response of the reduced-state detector.http://lup.lub.lu.se/record/3366230http://dx.doi.org/10.1109/LCOMM.2012.102612.121929wos:000312564200005scopus:84871280188engIEEE Communications Letters; 16(12), pp 1929-1932 (2012)ISSN: 1089-7798Elektroteknik och elektronikNonlinear satellite channelschannel shorteninginformation rateintersymbol interferencereceiver optimizationChannel Shortening for Nonlinear Satellite Channelscontributiontojournal/articleinfo:eu-repo/semantics/articletextMeasured propagation characteristics for very-large MIMO at 2.6 GHz
https://lup.lub.lu.se/search/publication/351f1fde-abe4-4327-8a00-7a8f076a8563
Gao, XiangTufvesson, FredrikEdfors, OveRusek, Fredrik2012application/pdfhttp://lup.lub.lu.se/record/3288101http://lup.lub.lu.se/search/ws/files/3368853/3288127.pdfwos:000320768400054scopus:84876261871enginfo:eu-repo/semantics/openAccesspp 295-299 (2012)ISSN: 1058-6393Elektroteknik och elektronikMeasured propagation characteristics for very-large MIMO at 2.6 GHzcontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertextFaster-Than-Nyquist Signaling
https://lup.lub.lu.se/search/publication/992a1db9-7f85-416d-9b13-8fbdd45f188f
Anderson, John BRusek, FredrikÖwall, Viktor2013In this paper, we survey Faster-than-Nyquist (FTN) signaling, an extension of ordinary linear modulation in which the usual data bearing pulses are simply sent faster, and consequently are no longer orthogonal. Far from a disadvantage, this innovation can transmit up to twice the bits as ordinary modulation at the same bit energy, spectrum, and error rate. The method is directly applicable to orthogonal frequency division multiplex (OFDM) and quadrature amplitude modulation (QAM) signaling. Performance results for a number of practical systems are presented. FTN signaling raises a number of basic issues in communication theory and practice. The Shannon capacity of the signals is considerably higher.http://lup.lub.lu.se/record/3954769http://dx.doi.org/10.1109/JPROC.2012.2233451wos:000322143400003scopus:84880778754engProceedings of the IEEE; 101(8), pp 1817-1830 (2013)ISSN: 0018-9219Elektroteknik och elektronikBandwidth-Eﬃcient CodingConstrained CapacitiesCoded ModulationFaster than Nyquist (FTN)Intersymbol Interference (ISI)Faster-Than-Nyquist Signalingcontributiontojournal/articleinfo:eu-repo/semantics/articletextNon-binary and linear precoded faster-than-Nyquist signaling
https://lup.lub.lu.se/search/publication/3270d435-15a0-45aa-a163-5e5771b12203
Rusek, FredrikAnderson, John B2008Faster than Nyquist (FTN) signaling is an important method of
narrowband coding. The concept is extended here to non
binary signal constellations; these are much more bandwidth efficient
than binary ones. A powerful method of finding the minimum distance for binary and non binary FTN is
presented. Precoding FTN transmissions with short linear
filters proves to be an effective way to gain distance. A
Shannon limit to bit error rate is derived that applies for FTN. Tests of an M-algorithm receiver are performed and compared to this limit.application/pdfhttp://lup.lub.lu.se/record/1046258http://dx.doi.org/10.1109/TCOMM.2008.060075http://lup.lub.lu.se/search/ws/files/3195917/1738048.pdfwos:000255869900016scopus:44949113435enginfo:eu-repo/semantics/openAccessIEEE Transactions on Communications; 56(5), pp 808-817 (2008)ISSN: 0090-6778Elektroteknik och elektronikMazo limitFaster Than NyquistBandwidth efficient codingCoded modulationNon-binary and linear precoded faster-than-Nyquist signalingcontributiontojournal/articleinfo:eu-repo/semantics/articletextMassive MIMO performance evaluation based on measured propagation data
https://lup.lub.lu.se/search/publication/237c181b-16ec-49bd-883a-9dbfcf401339
Gao, XiangEdfors, OveRusek, FredrikTufvesson, Fredrik2015Massive MIMO, also known as very-large MIMO or large-scale antenna systems, is a new technique that potentially can offer large network capacities in multi-user scenarios. With a massive MIMO system, we consider the case where a base station equipped with a large number of antenna elements simultaneously serves multiple single-antenna users in the same time-frequency resource. So far, investigations are mostly based on theoretical channels with independent and identically distributed (i.i.d.) complex Gaussian coefficients, i.e., i.i.d. Rayleigh channels. Here, we investigate how massive MIMO performs in channels measured in real propagation environments. Channel measurements were performed at 2.6 GHz using a virtual uniform linear array (ULA) which has a physically large aperture, and a practical uniform cylindrical array (UCA) which is more compact in size, both having 128 antenna ports. Based on measurement data, we illustrate channel behavior of massive MIMO in three representative propagation conditions, and evaluate the corresponding performance. The investigation shows that the measured channels, for both array types, allow us to achieve performance close to that in i.i.d. Rayleigh channels. It is concluded that in real propagation environments we have characteristics that can allow for efﬁcient use of massive MIMO, i.e., the theoretical advantages of this new technology can also be harvested in real channels.application/pdfhttp://lup.lub.lu.se/record/5218941http://dx.doi.org/10.1109/TWC.2015.2414413http://lup.lub.lu.se/search/ws/files/3145420/5323121.pdfwos:000357805200030scopus:84937134074enginfo:eu-repo/semantics/openAccessIEEE Transactions on Wireless Communications; 14(7), pp 3899-3911 (2015)ISSN: 1536-1276Elektroteknik och elektroniksingular value spreadangular power spectrachannel capacityvery-large MIMOMassive MIMOchannel measurementsmulti-user MIMO5GMassive MIMO performance evaluation based on measured propagation datacontributiontojournal/articleinfo:eu-repo/semantics/articletextMulticarrier faster-than-Nyquist transceivers: hardware architecture and performance analysis
https://lup.lub.lu.se/search/publication/86a801b1-356d-4585-aa32-b17408a97be1
Dasalukunte, DeepakRusek, FredrikÖwall, Viktor2011This paper evaluates the hardware aspects of multicarrier faster-than-Nyquist (FTN) signaling transceivers. The choice of time-frequency spacing of the symbols in an FTN system for improved bandwidth efficiency is targeted towards efficient hardware implementation. This work proposes a hardware architecture for the realization of iterative decoding of FTN multicarrier modulated signals. Compatibility with existing systems
has been considered for smooth switching between the faster-than-Nyquist and orthogonal signaling schemes. One such being the use of FFTs for multicarrier modulation. The performance of the fixed point model is very close to that of the floating point representation. The impact of system parameters such as number of projection points, time-frequency spacing, finite wordlengths and their design trade-offs for reduced complexity
iterative decoders in FTN systems have been investigated. The FTN decoder has been designed and synthesized in both 65nm CMOS and FPGA. From the hardware resource usage numbers it can be concluded that FTN signaling can be used to achieve higher bandwidth efficiency with acceptable complexity overhead.http://lup.lub.lu.se/record/1699314http://dx.doi.org/10.1109/TCSI.2010.2089549wos:000289159700017scopus:79953291790engIEEE Transactions on Circuits and Systems Part 1: Regular Papers; 58(4), pp 827-838 (2011)ISSN: 1549-8328Elektroteknik och elektronikMulticarrier faster-than-Nyquist transceivers: hardware architecture and performance analysiscontributiontojournal/articleinfo:eu-repo/semantics/articletextHardware Efficient Approximative Matrix Inversion for Linear Pre-Coding in Massive MIMO
https://lup.lub.lu.se/search/publication/e7dc60f9-6b5a-49ed-bd10-228c88baa113
Prabhu, HemanthEdfors, OveRodrigues, JoachimLiu, LiangRusek, Fredrik2014This paper describes a hardware efficient linear pre-coder for Massive MIMO Base Stations (BSs) comprising a very large number of antennas, say, in the order of 100s, serving multiple users simultaneously. To avoid hardware demanding direct matrix inversions required for the Zero-Forcing (ZF) pre-coder, we use low complexity Neumann series based approximations. Furthermore, we propose a method to speed-up the convergence of the Neumann series by using tri-diagonal pre-condition matrices, which lowers the complexity even further. As a proof of concept a flexible VLSI architecture is presented with an implementation supporting matrix inversion of sizes up-to 16 × 16. In 65 nm CMOS, a throughput of 0.5M matrix inversions per sec is achieved at clock frequency of 420 MHz with a 104K gate count.application/pdfhttp://lup.lub.lu.se/record/4248962http://lup.lub.lu.se/search/ws/files/2068506/5364185.pdfwos:000346488600427scopus:84907389998enginfo:eu-repo/semantics/openAccesspp 1700-1703 (2014)ISSN: 0271-4310ISSN: 2158-1525Elektroteknik och elektronikMassive MIMOPre-coderHardware Efficient Approximative Matrix Inversion for Linear Pre-Coding in Massive MIMOcontributiontobookanthology/conferenceinfo:eu-repo/semantics/conferencePapertext