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Performance Bounds for Very Large Multiuser MIMO Systems
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The last ten years have seen significant advances of multiuser MIMO (MU-MIMO) in wireless communication. MU-MIMO is now being introduced in several new generation wireless standards (e.g.,LTE-Advanced, 802.16m). The number of users is increasing with more and more applications. At the same time, high transmission data rate and communication reliability are required. Furthermore, there is a growing concern about green communication which relates to the effects of  the radiation emitted from wireless devices onthe human body. Therefore, the future MU-MIMO systems have to satisfy three main requirements: i) serving many autonomous users in the same time-frequency resource, ii) having high data rate and communication reliability, and iii) less energy consumption/radiation. These are seemingly contradictory requirements since the more users are served, the more interference the systems will suffer, or the more data rate is transmitted, the more power is required. MU-MIMO with very large antenna arrays seems to meet above demands and hence, it can be considered as a promising technology for next generation wireless systems. With very large antenna arrays (we mean arrays comprising say a hundred of antennas), the channel vectors are nearly-orthogonal and hence, multiuser interference can be significantly reduced. As a result, many users can be simultaneously served with high data rate. In particular, with coherent processing, transmit power can be reduced dramatically owing to array gain. In this thesis, we focus on the performance bounds of MU-MIMO with very large antenna arrays. We study the fundamental limits on the system performance when using large antenna arrays under practical constraints such as low complexity processing, imperfect channel state information, intercell interference, and finite-dimensional channels.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 23 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1562
National Category
Communication Systems Signal Processing Telecommunications
Identifiers
URN: urn:nbn:se:liu:diva-85240ISBN: 978-91-7519-729-6 (print)OAI: oai:DiVA.org:liu-85240DiVA: diva2:567398
Presentation
2012-12-14, Systemet, Hus B, Campus Valla, Linköping University, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2012-11-21 Created: 2012-11-12 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Energy and Spectral Efficiency of Very Large Multiuser MIMO Systems
Open this publication in new window or tab >>Energy and Spectral Efficiency of Very Large Multiuser MIMO Systems
2013 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 4, 1436-1449 p.Article in journal (Refereed) Published
Abstract [en]

A multiplicity of autonomous terminals simultaneously transmits data streams to a compact array of antennas. The array uses imperfect channel-state information derived from transmitted pilots to extract the individual data streams. The power radiated by the terminals can be made inversely proportional to the square-root of the number of base station antennas with no reduction in performance. In contrast if perfect channel-state information were available the power could be made inversely proportional to the number of antennas. Lower capacity bounds for maximum-ratio combining (MRC), zero-forcing (ZF) and minimum mean-square error (MMSE) detection are derived. An MRC receiver normally performs worse than ZF and MMSE. However as power levels are reduced, the cross-talk introduced by the inferior maximum-ratio receiver eventually falls below the noise level and this simple receiver becomes a viable option. The tradeoff between the energy efficiency (as measured in bits/J) and spectral efficiency (as measured in bits/channel use/terminal) is quantified for a channel model that includes small-scale fading but not large-scale fading. It is shown that the use of moderately large antenna arrays can improve the spectral and energy efficiency with orders of magnitude compared to a single-antenna system.

National Category
Communication Systems Signal Processing
Identifiers
urn:nbn:se:liu:diva-85224 (URN)10.1109/TCOMM.2013.020413.110848 (DOI)000318998100022 ()
Available from: 2012-11-12 Created: 2012-11-12 Last updated: 2017-12-07
2. The Multicell Multiuser MIMO Uplink with Very Large Antenna Arrays and a Finite-Dimensional Channel
Open this publication in new window or tab >>The Multicell Multiuser MIMO Uplink with Very Large Antenna Arrays and a Finite-Dimensional Channel
2013 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 6, 2350-2361 p.Article in journal (Refereed) Published
Abstract [en]

We consider multicell multiuser MIMO systems with a very large number of antennas at the base station (BS). We assume that the channel is estimated by using uplink training. We further consider a physical channel model where the angular domain is separated into a finite number of distinct directions. We analyze the so-called pilot contamination effect discovered in previous work, and show that this effect persists under the finite-dimensional channel model that we consider. In particular, we consider a uniform array at the BS. For this scenario, we show that when the number of BS antennas goes to infinity, the system performance under a finite-dimensional channel model with P angular bins is the same as the performance under an uncorrelated channel model with P antennas. We further derive a lower bound on the achievable rate of uplink data transmission with a linear detector at theBS. We then specialize this lower bound to the cases of maximum-ratio combining (MRC) and zero-forcing (ZF) receivers, for a finite and an infinite number of BS antennas. Numerical results corroborate our analysis and show a comparison between the performances of MRC and ZF in terms of sum-rate.

Keyword
Finite-dimensional channel, multicell mutiuser MIMO, pilot contamination, very large MIMO systems
National Category
Communication Systems Signal Processing
Identifiers
urn:nbn:se:liu:diva-85223 (URN)10.1109/TCOMM.2013.032713.120408 (DOI)000321219100023 ()
Available from: 2013-04-04 Created: 2012-11-12 Last updated: 2017-12-06Bibliographically approved
3. EVD-based Channel Estimations for Multicell Multiuser MIMO with Very Large Antenna Arrays
Open this publication in new window or tab >>EVD-based Channel Estimations for Multicell Multiuser MIMO with Very Large Antenna Arrays
2012 (English)In: Proceedings of the IEEE International Conference on Acoustics, Speed and Signal Processing (ICASSP), IEEE , 2012, 3249-3252 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper considers multicell multiuser MIMO systems with verylarge antenna arrays at the base station. We propose an eigenvalue-decomposition-based approach to channel estimation, that estimates the channel blindly from the received data. The approach exploits the asymptotic orthogonality of the channel vectors in very large MIMO systems. We show that the channel to each user can be estimated from the covariance matrix of the received signals, up to a remaining scalar multiplicative ambiguity. A short training sequence is required to resolve this ambiguity. Furthermore, to improve the performance of our approach, we combine it with the iterative least-square with projection (ILSP) algorithm. Numerical results verify the effectiveness of our channel estimation approach.

Place, publisher, year, edition, pages
IEEE, 2012
Series
Acoustics, Speech and Signal Processing (ICASSP), ISSN 1520-6149
National Category
Communication Systems
Identifiers
urn:nbn:se:liu:diva-74084 (URN)10.1109/ICASSP.2012.6288608 (DOI)000312381403081 ()978-1-4673-0045-2 (ISBN)978-1-4673-0044-5 (ISBN)
Conference
IEEE International Conference on Acoustics, Speed and Signal Processing (ICASSP, March 25-30, Kyoto, Japan
Available from: 2012-01-18 Created: 2012-01-18 Last updated: 2016-08-31Bibliographically approved

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Ngo, Hien Quoc

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