| 1. |
- Flordelis, Jose, et al.
(författare)
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Massive MIMO Performance - TDD Versus FDD : What Do Measurements Say?
- 2018
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1536-1276 .- 1558-2248. ; 17:4, s. 2247-2261
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Tidskriftsartikel (refereegranskat)abstract
- Downlink 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.
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| 2. |
- Rusek, Fredrik, et al.
(författare)
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Scaling up MIMO : Opportunities and Challenges with Very Large Arrays
- 2013
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Ingår i: IEEE signal processing magazine (Print). - : IEEE. - 1053-5888 .- 1558-0792. ; 30:1, s. 40-60
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Tidskriftsartikel (refereegranskat)abstract
- Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE) [1]. For example, the LTE standard allows for up to eight antenna ports at the base station. Basically, the more antennas the transmitter/receiver is equipped with, and the more degrees of freedom that the propagation channel can provide, the better the performance in terms of data rate or link reliability. More precisely, on a quasi static channel where a code word spans across only one time and frequency coherence interval, the reliability of a point-to-point MIMO link scales according to Prob(link outage) ` SNR-ntnr where nt and nr are the numbers of transmit and receive antennas, respectively, and signal-to-noise ratio is denoted by SNR. On a channel that varies rapidly as a function of time and frequency, and where circumstances permit coding across many channel coherence intervals, the achievable rate scales as min(nt, nr) log(1 + SNR). The gains in multiuser systems are even more impressive, because such systems offer the possibility to transmit simultaneously to several users and the flexibility to select what users to schedule for reception at any given point in time [2].
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| 3. |
- Gao, Xiang, et al.
(författare)
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Massive MIMO in Real Propagation Environments: Do All Antennas Contribute Equally?
- 2015
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Ingår i: IEEE Transactions on Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0090-6778 .- 1558-0857. ; 63:11, s. 3917-3928
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Tidskriftsartikel (refereegranskat)abstract
- Massive MIMO can greatly increase both spectral and transmit-energy efficiency. This is achieved by allowing the number of antennas and RF chains to grow very large. However, the challenges include high system complexity and hardware energy consumption. Here we investigate the possibilities to reduce the required number of RF chains, by performing antenna selection. While this approach is not a very effective strategy for theoretical independent Rayleigh fading channels, a substantial reduction in the number of RF chains can be achieved for real massive MIMO channels, without significant performance loss. We evaluate antenna selection performance on measured channels at 2.6 GHz, using a linear and a cylindrical array, both having 128 elements. Sum-rate maximization is used as the criterion for antenna selection. A selection scheme based on convex optimization is nearly optimal and used as a benchmark. The achieved sum-rate is compared with that of a very simple scheme that selects the antennas with the highest received power. The power-based scheme gives performance close to the convex optimization scheme, for the measured channels. This observation indicates a potential for significant reductions of massive MIMO implementation complexity, by reducing the number of RF chains and performing antenna selection using simple algorithms.
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| 4. |
- Gao, Xiang, et al.
(författare)
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Multi-Switch for Antenna Selection in Massive MIMO
- 2015
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Ingår i: Proc. 2015 IEEE Global Communications Conference, ISBN: 978-147995952-5. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Massive MIMO has been shown to greatly improve spectral and transmit-energy efficiency. When implementing a massive MIMO system, one challenge is high hardware complexity. A solution is to reduce the number of radio frequency (RF) transceiver chains by performing antenna selection. However, a full RF switch that connects the antennas and RF chains can be highly complex and incurs significant loss in output signal quality, especially when the number of antennas and RF chains are large. We therefore propose a simpler solution - binary switching architecture, which is sub-optimal but provides better signal quality, as compared to the full switching network. To evaluate the proposed technique, we compare the sum-rate capacity when using several different configurations of binary switching with the performance of the full switching. Full MIMO performance obtained without antenna selection is also presented as a reference. The investigations in this paper are all based on measured channel data at 2.6 GHz, using a uniform linear array and a cylindrical array, both having 128 antenna elements. It is found that the proposed binary switching gives very competitive performance that are close to the full switching, for the measured channels. The results indicate a potential to simplify massive MIMO hardware by reducing the number of RF chains, and performing antenna selection with simple binary switching architecture.
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| 5. |
- Larsson, Erik G, et al.
(författare)
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Massive MIMO for Next Generation Wireless Systems
- 2014
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Ingår i: IEEE Communications Magazine. - : Institute of Electrical and Electronics Engineers. - 0163-6804 .- 1558-1896. ; 52:2, s. 186-195
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Tidskriftsartikel (refereegranskat)abstract
- Multi-user MIMO offers big advantages over conventional point-to-point MIMO: it works with cheap single-antenna terminals, a rich scattering environment is not required, and resource allocation is simplified because every active terminal utilizes all of the time-frequency bins. However, multi-user MIMO, as originally envisioned, with roughly equal numbers of service antennas and terminals and frequency-division duplex operation, is not a scalable technology. Massive MIMO (also known as large-scale antenna systems, very large MIMO, hyper MIMO, full-dimension MIMO, and ARGOS) makes a clean break with current practice through the use of a large excess of service antennas over active terminals and time-division duplex operation. Extra antennas help by focusing energy into ever smaller regions of space to bring huge improvements in throughput and radiated energy efficiency. Other benefits of massive MIMO include extensive use of inexpensive low-power components, reduced latency, simplification of the MAC layer, and robustness against intentional jamming. The anticipated throughput depends on the propagation environment providing asymptotically orthogonal channels to the terminals, but so far experiments have not disclosed any limitations in this regard. While massive MIMO renders many traditional research problems irrelevant, it uncovers entirely new problems that urgently need attention: the challenge of making many low-cost low-precision components that work effectively together, acquisition and synchronization for newly joined terminals, the exploitation of extra degrees of freedom provided by the excess of service antennas, reducing internal power consumption to achieve total energy efficiency reductions, and finding new deployment scenarios. This article presents an overview of the massive MIMO concept and contemporary research on the topic.
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| 6. |
- Manoj, B. R., et al.
(författare)
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MOVING OBJECT CLASSIFICATION WITH A SUB-6 GHZ MASSIVE MIMO ARRAY USING REAL DATA
- 2021
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Ingår i: 2021 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP 2021). - : IEEE. - 1520-6149 .- 2379-190X. - 9781728176055 - 9781728176062 ; , s. 8133-8137
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Konferensbidrag (refereegranskat)abstract
- Classification between different activities in an indoor environment using wireless signals is an emerging technology for various applications, including intrusion detection, patient care, and smart home. Researchers have shown different methods to classify activities and their potential benefits by utilizing WiFi signals. In this paper, we analyze classification of moving objects by employing machine learning on real data from a massive multi-input-multi-output (MIMO) system in an indoor environment. We conduct measurements for different activities in both line-of-sight and non line-of-sight scenarios with a massive MIMO testbed operating at 3.7 GHz. We propose algorithms to exploit amplitude and phase-based features classification task. For the considered setup, we benchmark the classification performance and show that we can achieve up to 98% accuracy using real massive MIMO data, even with a small number of experiments. Furthermore, we demonstrate the gain in performance results with a massive MIMO system as compared with that of a limited number of antennas such as in WiFi devices.
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| 7. |
- Manoj, Banugondi Rajashekara, et al.
(författare)
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Sensing and Classification Using Massive MIMO : A Tensor Decomposition-Based Approach
- 2021
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Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 10:12, s. 2649-2653
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Tidskriftsartikel (refereegranskat)abstract
- Wireless-based activity sensing has gained significant attention due to its wide range of applications. We investigate radio-based multi-class classification of human activities using massive multiple-input multiple-output (MIMO) channel measurements in line-of-sight and non line-of-sight scenarios. We propose a tensor decomposition-based algorithm to extract features by exploiting the complex correlation characteristics across time, frequency, and space from channel tensors formed from the measurements, followed by a neural network that learns the relationship between the input features and output target labels. Through evaluations of real measurement data, it is demonstrated that the classification accuracy using a massive MIMO array achieves significantly better results compared to the state-of-the-art even for a smaller experimental data set.
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| 8. |
- Van Der Perre, Liesbet, et al.
(författare)
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RadioWeaves for efficient connectivity : analysis and impact of constraints in actual deployments
- 2019
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Ingår i: Conference record of the Fifty-Third Asilomar Conference on Signals, Systems & Computers. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728143002 - 9781728143019 ; , s. 15-22
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Konferensbidrag (refereegranskat)abstract
- We present a new type of wireless access infrastructure consisting of a fabric of dispersed electronic circuits and antennas that collectively function as a massive, distributed antenna array. We have chosen to name this new wireless infrastructure "RadioWeaves" and anticipate they can be integrated into indoor and outdoor walls, furniture, and other objects, rendering them a natural part of the environment. Technologically, RadioWeaves will deploy distributed arrays to create both favorable propagation and antenna array interaction. The technology leverages on the ideas of large-scale intelligent surfaces and cell-free wireless access. Offering close to the service connectivity and computing, new grades in energy efficiency, reliability, and low latency can be reached. The new concept moreover can be scaled up easily to offer a very high capacity in specific areas demanding so. In this paper we anticipate how two different demanding use cases can be served well by a dedicated RadioWeaves deployment: a crowd scenario and a highly reflective factory environment. A practical approach towards a RadioWeaves prototype, integrating dispersed electronics invisibly in a room environment, is introduced. We outline the many and diverse R&D challenges that need to be addressed to realize the great potential of the RadioWeaves technology.
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| 9. |
- Wyne, Shurjeel, et al.
(författare)
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Outdoor-to-indoor office MIMO measurements, and analysis at 5.2 GHz
- 2008
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 57:3, s. 1374-1386
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Tidskriftsartikel (refereegranskat)abstract
- The outdoor-to-indoor wireless propagation channel is of interest for cellular and wireless local area network applications. This paper presents the measurement results and analysis based on our multiple-input-multiple-output (MIMO) measurement campaign, which is one of the first to characterize the outdoor-to-indoor channel. The measurements were performed at 5.2 GHz, the receiver was placed indoors at 53 different locations in an office building, and the transmitter was placed at three "base station" positions on a nearby rooftop. We report on the root-mean-square (RMS) angular spread, building penetration, and other statistical parameters that characterize the channel. Our analysis is focused on three MIMO channel assumptions often used in stochastic models. 1) It is commonly assumed that the channel matrix can be represented as a sum of a line-of-sight (LOS) contribution and a zero-mean complex Gaussian distribution. Our investigation shows that this model does not adequately represent our measurement data. 2) It is often assumed that the Rician K-factor is equal to the power ratio of the LOS component and the other multipath components (MPCs). We show that this is not the case, and we highlight the difference between the Rician K-factor often associated with LOS channels and a similar power ratio for the estimated LOS MPC. 3) A widespread assumption is that the full correlation matrix of the channel can be decomposed into a Kronecker product of the correlation matrices at the transmit and receive array. Our investigations show that the direction-of-arrival (DOA) spectrum noticeably depends on the direction-of-departure (DOD), therefore, the Kronecker model is not applicable, and models with less-restrictive assumptions on the channel, e.g., the Weichselberger model or the full correlation model, should be used.
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