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On Multiantenna Cellular Communications: From Theory to Practice
KTH, School of Electrical Engineering (EES), Information Science and Engineering.ORCID iD: 0000-0002-5526-9213
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Today, wireless communications are an essential part of our everyday life. Both the number of users and their demands for wireless data have increasedtremendously during the last decade. Multiantenna communicationsis a promising solution to meet this ever-growing traffic demands. However, impairments that exist in most practical communication networks may substantially limit the performance of a multiantenna system. The characterizationof such a performance loss and how to minimize that are still largelyopen problems. The present thesis addresses this important research gap. Inparticular, we focus on three major impairments of a multiantenna cellularnetwork: impairment in the channel state information (CSI), interference andimpairment in the transceiver hardware components.To fully realize the benefits of multiantenna communications, the users need to acquire a certain level of information about their propagation environment; that is, their corresponding CSI. In practice, the CSI is not known bythe users and should be acquired by allocating part of the network resourcesfor pilot transmission. This problem is mainly important in the systems with a large number of antennas, as in general the required network resources for CSI acquisition scales with the number of transmitting antennas. Theproblem of CSI acquisition in a single-cell multiuser multiple-input multipleoutput(MIMO) system is addressed in this thesis. A linear spatial precodingand combining scheme for pilot transmission is proposed. This scheme requiresless number of network resources for channel estimation compared tothe conventional schemes. The gains of the proposed scheme are characterized by finding an upper-bound and a lower-bound on the channel estimation error.Moreover, as an ultimate performance metric, an achievable sum-rate ofthe network is formulated and analyzed numerically.Due to the broadcast nature of the wireless channels, the performanceof the users in a network is intertwined; the desired signal of one user mayinterfere other users. Hence, the interference is another major impairment inwireless communication systems. In this thesis, the practical challenges of aninterference management technique, namely MIMO interference alignment isinvestigated by implementation on a multiuser MIMO testbed. Then, in thecontext of interference alignment, the problem of optimal power allocation forpilot and data transmission is studied and verified by the measurements.The impairment in the hardware components of the transceivers, that is, any deviation of the components from their ideal behavior, degrades the performance of a communication system. In particular, the impact of nonlineartransmitter power amplifiers (PA)s is investigated in this thesis. First, consideringa memoryless third-order polynomial model for the PAs, a model forthe transmitted nonlinear distortion signal from a multiantenna transmitter isproposed and validated by measurements. This model implies that the spatialdirection of the transmitted distortion is dependent on the spatial directionof the desired signal. Then, this model is extended for a general arbitrary order polynomial model. Exploiting the developed distortion model, the energyefficiency of a multiantenna system operating at millimeter wave frequenciesis studied.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. , p. 43
Series
TRITA-EE, ISSN 1653-5146 ; 050
National Category
Signal Processing
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-207623ISBN: 978-91-7729-435-1 (print)OAI: oai:DiVA.org:kth-207623DiVA, id: diva2:1097523
Public defence
2017-06-09, Kollegiesalen, Brinellvägen 8, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20170523

Available from: 2017-05-24 Created: 2017-05-22 Last updated: 2017-05-24Bibliographically approved
List of papers
1. Pilot Precoding and Combining in Multiuser MIMO Networks
Open this publication in new window or tab >>Pilot Precoding and Combining in Multiuser MIMO Networks
Show others...
2017 (English)In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. June, no 6Article in journal (Refereed) Published
Abstract [en]

Although the benefits of precoding and combining data signals are widely recognized, the potential of these techniques for pilot transmission is not fully understood. This is particularly relevant for multiuser multiple-input multiple-output(MU-MIMO) cellular systems using millimeter-wave (mmWave)communications, where multiple antennas have to be used both at the transmitter and the receiver to overcome the severe path loss.In this paper, we characterize the gains of pilot precoding and combining in terms of channel estimation quality and achievable data rate. Specifically, we consider three uplink pilot transmission scenarios in a mmWave MU-MIMO cellular system: 1) non-precoded and uncombined, 2) precoded but uncombined, and3) precoded and combined. We show that a simple precoder that utilizes only the second-order statistics of the channel reduces the variance of the channel estimation error by a factor that is proportional to the number of user equipment (UE) antennas.We also show that using a linear combiner design based on the second-order statistics of the channel significantly reduces multiuser interference and provides the possibility of reusing some pilots. Specifically, in the large antenna regime, pilot preceding and combining help to accommodate a large number ofUEs in one cell, significantly improve channel estimation quality, boost the signal-to-noise ratio of the UEs located close to the cell edges, alleviate pilot contamination, and address the imbalanced coverage of pilot and data signals.

Place, publisher, year, edition, pages
IEEE Press, 2017
Keywords
multiuser MIMO, multiple antenna UEs, channel estimation, millimeter-wave, transceiver design
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-207619 (URN)10.1109/JSAC.2017.2699398 (DOI)000404242600017 ()2-s2.0-85021270765 (Scopus ID)
Projects
Ericsson Research's HARALD project
Note

QC 20170523

Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2017-07-11Bibliographically approved
2. Test-Bed Implementation of Iterative Interference Alignment and Power Control for Wireless MIMO Interference Networks
Open this publication in new window or tab >>Test-Bed Implementation of Iterative Interference Alignment and Power Control for Wireless MIMO Interference Networks
2014 (English)In: 2014 IEEE 15th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE , 2014, p. 239-243Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents for the first time the testbed implementation of an iterative interference alignment and power control algorithm for downlink transmission in a multiple-input multiple-output (MIMO) cellular network. The network is composed of three cells where within each cell one base station (BS) communicates with one mobile station (MS). Each terminal is equipped with two antennas. All the BSs transmit at the same time and the same frequency band. Transmitter beamforming vectors and receiver filtering vectors are computed according to the interference alignment concept, and power control is performed to guarantee successful communication of each BS-MS pair at a desired fixed rate. The indoor measurements performed on an universal software radio peripheral (USRP) based test-bed, show that the power can be reduced by at least 4 dB, 90% of the time, while at the same time reducing the bit-error-rate (BER).

Place, publisher, year, edition, pages
IEEE, 2014
Series
IEEE International Workshop on Signal Processing Advances in Wireless Communications, ISSN 2325-3789
Keywords
Interference alignment, power control, test-bed implementation, MIMO, 5G
National Category
Telecommunications Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-160802 (URN)10.1109/SPAWC.2014.6941514 (DOI)000348859000049 ()2-s2.0-84932641798 (Scopus ID)978-1-4799-4903-8 (ISBN)
Conference
IEEE 15th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), JUN 22-25, 2014, Toronto, Canada
Note

QC 20150227

Available from: 2015-02-27 Created: 2015-02-27 Last updated: 2017-05-23Bibliographically approved
3. Optimal Power Allocation for Pilot-Assisted Interference Alignment in MIMO Interference Networks: Test-bed Results
Open this publication in new window or tab >>Optimal Power Allocation for Pilot-Assisted Interference Alignment in MIMO Interference Networks: Test-bed Results
2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This paper addresses channel training and data communication over multi-input multi-input (MIMO) interference networks. We consider a pilot-assisted interference alignment scheme in which part of radio resources are allocated to channel training and the remaining resources are used for data transmission. A more accurate channel estimation can be obtained by increasing pilot transmission power. Since each transmitter has limited energy budget, this implies that less power is available for data transmission. Clearly, there is a trade off between the allocated power for channel training and the one for data communication. In order to investigate this trade off, first we compute an achievable sum-rate, and next we find the optimum power allocation to pilot transmission and data transmission. Finally, we verify these theoretical results with experimental measurements on USRP-based test-bed.

Place, publisher, year, edition, pages
IEEE, 2015
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-182424 (URN)10.1109/ICDSP.2015.7251941 (DOI)000380506600123 ()2-s2.0-84961368506 (Scopus ID)
Conference
Digital Signal Processing (DSP), 2015 IEEE International Conference on
Note

QC 20160226

Available from: 2016-02-18 Created: 2016-02-18 Last updated: 2017-05-23Bibliographically approved
4. Correlation of distortion noise between the branches of MIMO transmit antennas
Open this publication in new window or tab >>Correlation of distortion noise between the branches of MIMO transmit antennas
2012 (English)In: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on, IEEE , 2012, p. 2079-2084Conference paper, Published paper (Refereed)
Abstract [en]

Despite the tremendous research effort spent on MIMO systems - very few papers address the impact of hardware imperfections. In this paper we analyze the distortion noise of the transmitter branches of a MIMO transmitter. In particular we analyze the cross-correlation of the distortion noises for the case that the transmitted signals are correlated. This case arises when there is just a single stream being transmitted with beamforming or in the case of multiple streams and linear precoding. We analyze the problem in two ways: using analytical derivations and using measurements on our testbed. In the analytical case we assume a transmitter impaired by a 3rd order non-linearity. For this scenario we find that the absolute correlation coefficient of the distortion noises is given by the absolute value of the correlation coefficients of the input signals to the power of three, while the phase is the same as that of the input signal. Our measurements also show good agreement between measurements and analytical results. It seems to suggest that the distortion noises can be regarded as practically independent whenever there are two or more modulation streams being transmitted (spatial multiplexing). In a single-stream scenario, the distortion noise will tend to have the same spatial distribution as the desired signal.

Place, publisher, year, edition, pages
IEEE, 2012
Series
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, ISSN 2166-9570
Keywords
Bussgang theorem, distortion, EVM, MIMO, phase noise, polynomial model of amplifiers, power amplifiers
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-107753 (URN)10.1109/PIMRC.2012.6362697 (DOI)000312809400354 ()2-s2.0-84872005254 (Scopus ID)9781467325691 (ISBN)
Conference
2012 IEEE 23rd International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2012; Sydney, NSW; 9 September 2012 through 12 September 2012
Note

QC 20130118

Available from: 2012-12-17 Created: 2012-12-17 Last updated: 2017-05-23Bibliographically approved
5. On the Energy Efficiency of MIMO Hybrid Beamforming for Millimeter Wave Systems with Nonlinear Power Amplifiers
Open this publication in new window or tab >>On the Energy Efficiency of MIMO Hybrid Beamforming for Millimeter Wave Systems with Nonlinear Power Amplifiers
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Multiple-input multiple-output (MIMO) millimeter wave (mmWave) systems are a promising candidate to support extremely high data rate services in future wireless communication networks. However, operating at high frequencies and employing a large number of radio frequency (RF) hardware components make MIMO mmWave systems vulnerable to hardware impairments. In particular, nonlinear power amplifiers (PAs) employed at the transmitter distort the signal when operated close to their saturation regions due to energy efficiency considerations. In this paper, we study the performance of a MIMO mmWave hybrid beamforming scheme in the presence of nonlinear PAs. First, distortion signal we develop a statistical model for the transmitted signal in such systems and show that the spatial distortion signal is shaped by the beamforming filter. This suggests thateven in the large antenna regime, where narrow beams can begenerated and steered toward the receiver, the impact of thenonlinear PAs should not be ignored. Then, by employing arealistic power consumption model for the PAs, we investigate thetrade-off between spectral and energy efficiency in such systems.For the special case, when the number of transmit RF-chains isone, closed forms for the achievable spectral efficiency as wellas the system energy efficiency is derived. Our results show thatwhen using hybrid beamforming, increasing the transmit powerlevel when the number of transmit antennas grows large can becounter-effective in terms of spectral and energy efficiency. Onthe other hand, with a moderate number of transmit antennas,increasing the transmit power up to a certain threshold isbeneficial for the spectral and energy efficiency of the system.

Keywords
millimeter wave systems, hybrid beamforming, power amplifier, energy efficiency, spectral efficiency
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-207743 (URN)
Projects
HARALD
Note

QC 20170523

Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-05-23Bibliographically approved

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Citation style
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Output format
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